第十一章植物的生殖生理 Chapter 1l Plant re In their life cycle, plants enter juvenile vegetative phase after germination and then transition to an adult vegetative phase before producing reproductive structures. The juvenile phase is the time of life characterized by differences in appearance from the adult in which the plant lacks the ability to respond to flower-inducing stimuli. During its development, plant shoots progresses from a juvenile to an adult phase of vegetative growth and from a reproductively incompetent to a reproductively competent state. The acquisition of competence, which is the first development stage plants have to pass through for floral evocation, enables plants to sense and respond to signals that induce flowering. The next stage that a competent vegetative bud goes through is determination. Environmental signals can induce a state of floral determination in competent plants. A bud is said to be determined if it progresses to the next developmental age(flowering) even after being removed from its normal context. The two major signals for inducing light (photoperiod) and temperature(cold treatment). In this chapter, we will examine juvenility, vernalization, photoperiodism, and floral organ morphogenes 植物在其生长周期中经历了种子萌发,幼年期,成年期,以及生殖器官的发生等阶段。幼年期的 植株与成年期的形态不同,且对成花诱导无应答。随着不断生长,植株从幼年期转变为成年期,从无 生殖能力转变为性成熟状态。生殖能力的获得是成花诱导的第一步,之后植株便可以感知并应答诱导 开花的信号。接下来是花芽的出现,这对成花诱导起决定性作用。外界信号可促使发育完全的植株进 入成花决定状态。当花芽生长到即将开花的阶段时,其分化命运已被决定,即使从正常生长环境中被 移除,结果也不会改变。诱导开花的两个主要信号是光(光周期)和温度(低温)。本章将对幼年期 春化作用,光周期现象,以及花器官的形成展开研究 111 Juvenility(幼年期) The character and timing of the juvenile-to-adult transition vary widely between species. In annual plants, this transition occurs soon after germination and usually involves relatively minor me hanges, whereas in trees and other perennial woody plants it occurs after months or years and can major changes in shoot architecture 植株从幼年期转变到成年期的特点及时机因种类而异。对于一年生植物,这种转变发生在种子萌 发后的较短时间内,且伴随着较小的形态变化:然而对于树木以及大部分木本植物而言,这种转变发 生在种子萌发后的几个月甚至几年后,且在植株建成过程中发生较大的形态变化。 In the juvenile phase, a young seedling plant displays one or more distinctive characteristics of both a morphological and physiological nature. These distinguish a juvenile plant from an adult. There are numerous substantive phenotypic traits associated with juvenility, but they vary considerably among pecies. Commonly the leaves on young plants are of a different shape than those on mature parts and may be simple rather than compound. Juvenile leaves may also have a special type of cuticle and be arranged with a distinct phyllotaxy. The juvenile plant also exhibit different physiological features such as higher rates of photosynthesis, respiration, and growth. 幼年期的植株在形态及生理方面均有显著特征,与成年期植株明显不同。植株在幼年期拥有众多 表型特征,但均存在较大的种间差异。一般而言,幼苗的叶片与成熟植物的叶片有着不同的形状且前 者更为简单。幼叶有着特殊类型的表皮以及独特的叶序。与成年植株相较,幼年植株也展现出不同的 生理特征,如较高的光合速率,呼吸速率及生长速率等。 When a plant is juvenile, it puts on juvenile growth. When a plant is sufficiently old and large, it goes through phase change and develops adult characteristics. These characteristics will manifest themselves on the newest growth. Therefore, the outside and higher portion of a mature tree is the most adult. The lower and older portion of the plant retains their juvenile characteristics. There can be a transition region between
第十一章 植物的生殖生理 Chapter 11 Plant reproductive physiology In their life cycle，plants enter juvenile vegetative phase after germination and then transition to an adult vegetative phase before producing reproductive structures. The juvenile phase is the time of life characterized by differences in appearance from the adult in which the plant lacks the ability to respond to flower-inducing stimuli. During its development, plant shoots progresses from a juvenile to an adult phase of vegetative growth and from a reproductively incompetent to a reproductively competent state. The acquisition of competence, which is the first development stage plants have to pass through for floral evocation, enables plants to sense and respond to signals that induce flowering. The next stage that a competent vegetative bud goes through is determination. Environmental signals can induce a state of floral determination in competent plants. A bud is said to be determined if it progresses to the next developmental stage (flowering) even after being removed from its normal context. The two major signals for inducing flowering are light (photoperiod) and temperature (cold treatment). In this chapter, we will examine juvenility, vernalization, photoperiodism, and floral organ morphogenesis. 植物在其生长周期中经历了种子萌发，幼年期，成年期，以及生殖器官的发生等阶段。幼年期的 植株与成年期的形态不同，且对成花诱导无应答。随着不断生长，植株从幼年期转变为成年期，从无 生殖能力转变为性成熟状态。生殖能力的获得是成花诱导的第一步，之后植株便可以感知并应答诱导 开花的信号。接下来是花芽的出现，这对成花诱导起决定性作用。外界信号可促使发育完全的植株进 入成花决定状态。当花芽生长到即将开花的阶段时，其分化命运已被决定，即使从正常生长环境中被 移除，结果也不会改变。诱导开花的两个主要信号是光（光周期）和温度（低温）。本章将对幼年期， 春化作用，光周期现象，以及花器官的形成展开研究。 11.1 Juvenility（幼年期） The character and timing of the juvenile-to-adult transition vary widely between species. In annual plants, this transition occurs soon after germination and usually involves relatively minor morphological changes, whereas in trees and other perennial woody plants it occurs after months or years and can involve major changes in shoot architecture. 植株从幼年期转变到成年期的特点及时机因种类而异。对于一年生植物，这种转变发生在种子萌 发后的较短时间内，且伴随着较小的形态变化；然而对于树木以及大部分木本植物而言，这种转变发 生在种子萌发后的几个月甚至几年后，且在植株建成过程中发生较大的形态变化。 In the juvenile phase, a young seedling plant displays one or more distinctive characteristics of both a morphological and physiological nature. These distinguish a juvenile plant from an adult. There are numerous substantive phenotypic traits associated with juvenility, but they vary considerably among species.Commonly, the leaves on young plants are of a different shape than those on mature parts and may be simple rather than compound. Juvenile leaves may also have a special type of cuticle and be arranged with a distinct phyllotaxy. The juvenile plant also exhibit different physiological features such as higher rates of photosynthesis，respiration，and growth. 幼年期的植株在形态及生理方面均有显著特征，与成年期植株明显不同。植株在幼年期拥有众多 表型特征，但均存在较大的种间差异。一般而言，幼苗的叶片与成熟植物的叶片有着不同的形状且前 者更为简单。幼叶有着特殊类型的表皮以及独特的叶序。与成年植株相较，幼年植株也展现出不同的 生理特征，如较高的光合速率，呼吸速率及生长速率等。 When a plant is juvenile, it puts on juvenile growth. When a plant is sufficiently old and large, it goes through phase change and develops adult characteristics. These characteristics will manifest themselves on the newest growth. Therefore, the outside and higher portion of a mature tree is the most adult. The lower and older portion of the plant retains their juvenile characteristics. There can be a transition region between
the juvenile and adult portion of the plant. Leaf drop or abscission in deciduous plant occurs mainly in the adult parts of a tree, juvenile parts of the tree usually hold their senescence leaves throughout the winter 幼年期的植株按这一时期所特有的生长规律进行生长,转入成年期后,逐步发展出成熟植物的特 点,这些特点表明植株处于一个新的生长期。因此,一棵成熟树木的顶端是其最成熟的部位,基部仍 然保留着幼年期的特点,中部则为过渡型。到了冬季,落叶植物处于成年期的叶片脱落而幼年期的叶 片仍存于树上。 112 Vernalization春化作用 112. Definition of vernalization春化作用的概念 Vernalizaiton refers specifically to the promotion of flowering in an imbibed seed or a growing plant by a period of low temperature. Vernalization occurs most commonly in winter annuals and biennials. Plants differ considerably in the age at which they become sensitive to vernalization. Winter annuals, such as the winter forms of cereals, which are sown in the fall and flower in the following summer, have the capacity to perceive a vermalizaiton treatment as an imbibed seed. Other plants, including most biennials, which grow as rosettes in the first season, bolt and flower in the following summer, must advance through the juvenile stage into an adult stage before they have the capacity to perceive a venalizaiton treatment. 春化作用特指用一段时间的低温诱导吸胀的种子或生长中的植物开花的过程,主要发生于冬性 年生植物及一些二年生植物上。不同植物在不同的生长期感知春化作用。冬性一年生植物,如冬小麦, 在头一年秋季播种,第二年夏季开花,其在种子吸胀萌动时就可感知春化作用。其他大部分二年生植 物,在第一年只长莲座状的叶丛,第二年夏季抽薹开花,它们必须从幼年期转化为成年期才能感知春 化作用。 The range of temperatures effective and duration of exposure in vemaliation varies widely depending on the species. In general, vermalizaiton can occur at temperatures ranging from just below freezing to about The effect of cold is proportional to the duration of the cold treatment until the response is saturated he response usually requires several weeks of exposure to low temperature, but the precise duration varies widely with species and variety. For instance, Lunaria biennis L. requires nine week, Secale cereale L. (winter rye)requires six week. In contrast, vernalization time can be as short as 6-8 days for R sativus Chinese jumbo radish Scarlet 有效温度及低温持续时间 春化作用的有效温度和低温持续时间的范围取决于植物种类。一般而言,0-14°C下可发生春化, 大多数种类植物的最适温度介于1~7°之间。 在春化过程结束前,低温效应与低温持续时间成比例关系。春化时通常需要将植物低温处理几周, 但具体持续时间随植物种类而定。例如,缎花(银扇草)需要9周,冬黑麦需要6周,而萝卜短至6~8 日 1123 Devernalization(脱春化作用) The reversal of vernalization by environmental conditions is referred to as'devernalozation'. The period between the completion of a vernalization treatment and flower initiation can be divided into two phases. Phase I is a period immediately after vernaliation when vernalization can be lost as a result of Il is that period after phase I when flower induction is stable and reversed(是否应该为 irreversible?) 由外界条件变化引起的春化作用的逆转称为脱春化作用。从春化过程结束到开始开花前的这段时 间可被分为两个阶段。第一阶段紧随春化作用的结束,这个阶段中春化作用会被诸如高温、低辐照、 短日照等条件消除。第二阶段在第一阶段之后,此时成花诱导是稳定且不可逆转的
the juvenile and adult portion of the plant. Leaf drop or abscission in deciduous plant occurs mainly in the adult parts of a tree, juvenile parts of the tree usually hold their senescence leaves throughout the winter. 幼年期的植株按这一时期所特有的生长规律进行生长，转入成年期后，逐步发展出成熟植物的特 点，这些特点表明植株处于一个新的生长期。因此，一棵成熟树木的顶端是其最成熟的部位，基部仍 然保留着幼年期的特点，中部则为过渡型。到了冬季，落叶植物处于成年期的叶片脱落而幼年期的叶 片仍存于树上。 11.2 Vernalization 春化作用 11.2.1 Definition of vernalization 春化作用的概念 Vernalizaiton refers specifically to the promotion of flowering in an imbibed seed or a growing plant by a period of low temperature. Vernalization occurs most commonly in winter annuals and biennials. Plants differ considerably in the age at which they become sensitive to vernalization. Winter annuals, such as the winter forms of cereals, which are sown in the fall and flower in the following summer, have the capacity to perceive a vernalizaiton treatment as an imbibed seed. Other plants, including most biennials, which grow as rosettes in the first season, bolt and flower in the following summer, must advance through the juvenile stage into an adult stage before they have the capacity to perceive a vernalizaiton treatment. 春化作用特指用一段时间的低温诱导吸胀的种子或生长中的植物开花的过程，主要发生于冬性一 年生植物及一些二年生植物上。不同植物在不同的生长期感知春化作用。冬性一年生植物，如冬小麦， 在头一年秋季播种，第二年夏季开花，其在种子吸胀萌动时就可感知春化作用。其他大部分二年生植 物，在第一年只长莲座状的叶丛，第二年夏季抽薹开花，它们必须从幼年期转化为成年期才能感知春 化作用。 11.2.2 Effective temperature and required duration of exposure The range of temperatures effective and duration of exposure in vernaliation varies widely depending on the species. In general, vernalizaiton can occur at temperatures ranging from just below freezing to about 14°C, there is an optimal temperature usually between about 1 and 7°C for most species. The effect of cold is proportional to the duration of the cold treatment until the response is saturated. The response usually requires several weeks of exposure to low temperature, but the precise duration varies widely with species and variety. For instance, Lunaria biennis L. requires nine week, Secale cereale L. (winter rye) requires six week. In contrast, vernalization time can be as short as 6-8 days for R. sativus ‘Chinese Jumbo Radish Scarlet’. 有效温度及低温持续时间 春化作用的有效温度和低温持续时间的范围取决于植物种类。一般而言， 0~14°C下可发生春化， 大多数种类植物的最适温度介于1~7°C之间。 在春化过程结束前，低温效应与低温持续时间成比例关系。春化时通常需要将植物低温处理几周， 但具体持续时间随植物种类而定。例如，缎花（银扇草）需要9周，冬黑麦需要6周，而萝卜短至6~8 日。 11.2.3 Devernalization（脱春化作用） The reversal of vernalizarion by environmental conditions is referred to as ‘devernalozation’. The period between the completion of a vernalization treatment and flower initiation can be divided into two phases. Phase I is a period immediately after vernaliation when vernalization can be lost as a result of exposure to devernalizing conditions, such as high temperature, low irradiance, and/or SD conditions. Phase II is that period after phase I when flower induction is stable and reversed（是否应该为irreversible？）. 由外界条件变化引起的春化作用的逆转称为脱春化作用。从春化过程结束到开始开花前的这段时 间可被分为两个阶段。第一阶段紧随春化作用的结束，这个阶段中春化作用会被诸如高温、低辐照、 短日照等条件消除。第二阶段在第一阶段之后，此时成花诱导是稳定且不可逆转的
112.4 Perception of vernalization(春化作用的感知) The site of perception of vernalization is the shoot apical meristem. Studies conducted where different portions of the plant were cooled relative to the rest of the plant indicate that the shoot apical meristem is solely capable of perception 感知春化刺激的部位是茎尖端分生组织。有研究通过低温处理植物的不同部位来探究其对其他部 位的影响,结果表明:唯有茎尖端分生组织具有感知低温刺激的能力。 112.5 The nature of the vernalization stimulus(春化刺激的本质) When a vernalized Hyoscyamus plant is grafted to an unvernalized plant, both will flower under long days. Experiments such as this suggested the existence of transmissible verbalization stimulus, which called'vernalin', but attempts to isolate vernalin have never been successful. No conclusive picture has so far emerged 将已春化的天仙子叶片嫁接到未春化植物的砧木上,一段时间后,两者均会开花。类似的实验证 明春化过程中形成一种可传导的剌激物质,这种物质称为春化素,目前还未能将其从植物体中分离出 来。因此,对于春化素至今仍没有定论 112.6 Molecular aspects of vernalization(春化作用的分子机理) Recent studies have revealed some of the molecular mechanisms involving downregu protein FLOWERING LOCUS C(FLC), which would otherwise prevent flowering, through epigenetic modification. This hypothesis was first generated from the studies on Arabidopsis. The key epigenetic hanges accompanying vernalization in this species is the trimethylation of lysine 27(K27me3)in histone 13 that repress FLC. The H3K27me3 modification is responsible for the epigenetic downregulation of FLC. The absence of the repressor protein FLC following vemalization then activates the expression of two other genes, FLOWERING LOCUS T (FT)and SUPPRESSOR OF OVER EXPRESSION OF CONSTANS (SOC1), and the activity of their gene products triggers the genes that control flower development. It has DNA methyltion. The cold treatment results in demethyltion of the promoter regions and subsequent actiation of a gene or genes critical for initiating reproductive developmen 近期的研究通过表观遗传修饰的方法揭示了开花阻抑蛋白 FLOWERING LOCUS C(FLC)的下调 机理,该理论是在对拟南芥的研究中首次被发现的。研究表明,伴随着拟南芥的春化而产生的关键性 遗传改变是H3上K27的三甲基化,这导致了FLC被抑制,即H3K27me3与FCL的下调直接相关。 春化时阻抑蛋白FCL的减少激活了另外两个基因 FLOWERING LOCUS T(FT)和 SUPPRESSOR OF OⅤ ER EXPRESSION OF CONSTANS(SOC1)的表达,其基因产物进而触发了开花控制基因的活化 另外,拟南芥及其他植物的春化反应也受DNA甲基化/去甲基化的调节。由低温处理而导致的基因增 强子区的去甲基化以及随后引发的一系列其他基因的活化对植物生殖生长的启动十分重要。 13 Photoperiodism光周期现象 113.1 Definition of photoperiodism(光周期现象的概念) Photoperiod is the duration of daily period of light and dark. In most latitudes there are seasonal changes in the length of the photoperiod, photoperiodism is the developmental responses of plants to the relative lengths of the light and dark periods, Plant responses controlled by photoperiodism are numerous, dormancy. Photoperiodism is primarily associated with longer-lived species that survive for at least a single growing season. Development of such species can often depend on photoperiod to synchronize flowering to ensure that flowering occurs at a specific time of year in order to allow successful seed set and maturation along with cross-pollination. 光周期是指一昼夜的光暗交替。地球上大多数纬度地区存在昼夜长短的季节性变化,光周期现象
11.2.4 Perception of vernalization（春化作用的感知） The site of perception of vernalization is the shoot apical meristem. Studies conducted where different portions of the plant were cooled relative to the rest of the plant indicate that the shoot apical meristem is solely capable of perception. 感知春化刺激的部位是茎尖端分生组织。有研究通过低温处理植物的不同部位来探究其对其他部 位的影响，结果表明：唯有茎尖端分生组织具有感知低温刺激的能力。 11.2.5 The nature of the vernalization stimulus（春化刺激的本质） When a vernalized Hyoscyamus plant is grafted to an unvernalized plant, both will flower under long days. Experiments such as this suggested the existence of transmissible verbalization stimulus, which is called ‘vernalin’, but attempts to isolate vernalin have never been successful. No conclusive picture has so far emerged. 将已春化的天仙子叶片嫁接到未春化植物的砧木上，一段时间后，两者均会开花。类似的实验证 明春化过程中形成一种可传导的刺激物质，这种物质称为春化素，目前还未能将其从植物体中分离出 来。因此，对于春化素至今仍没有定论。 11.2.6 Molecular aspects of vernalization（春化作用的分子机理） Recent studies have revealed some of the molecular mechanisms involving downregulation of the protein FLOWERING LOCUS C (FLC), which would otherwise prevent flowering, through epigenetic modification. This hypothesis was first generated from the studies on Arabidopsis. The key epigenetic changes accompanying vernalization in this species is the trimethylation of lysine 27 (K27me3) in histone H3 that repress FLC. The H3K27me3 modification is responsible for the epigenetic downregulation of FLC. The absence of the repressor protein FLC following vernalization then activates the expression of two other genes, FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVER EXPRESSION OF CONSTANS (SOC1), and the activity of their gene products triggers the genes that control flower development. It has also been proposed that vernalization responses, in Arabidopsis and other plants, is mediated by changes in DNA methyltion. The cold treatment results in demethyltion of the promoter regions and subsequent actiation of a gene or genes critical for initiating reproductive development. 近期的研究通过表观遗传修饰的方法揭示了开花阻抑蛋白 FLOWERING LOCUS C (FLC)的下调 机理，该理论是在对拟南芥的研究中首次被发现的。研究表明，伴随着拟南芥的春化而产生的关键性 遗传改变是 H3 上 K27 的三甲基化，这导致了 FLC 被抑制，即 H3K27me3 与 FCL 的下调直接相关。 春化时阻抑蛋白 FCL 的减少激活了另外两个基因 FLOWERING LOCUS T (FT) 和 SUPPRESSOR OF OVER EXPRESSION OF CONSTANS (SOC1)的表达，其基因产物进而触发了开花控制基因的活化。 另外，拟南芥及其他植物的春化反应也受 DNA 甲基化/去甲基化的调节。由低温处理而导致的基因增 强子区的去甲基化以及随后引发的一系列其他基因的活化对植物生殖生长的启动十分重要。 11.3 Photoperiodism 光周期现象 11.3.1 Definition of photoperiodism（光周期现象的概念） Photoperiod is the duration of daily period of light and dark. In most latitudes there are seasonal changes in the length of the photoperiod, photoperiodism is the developmental responses of plants to the relative lengths of the light and dark periods, Plant responses controlled by photoperiodism are numerous, including the initiation of flowering, asexual reproduction, the formation of storage organs, and the onset of dormancy. Photoperiodism is primarily associated with longer-lived species that survive for at least a single growing season. Development of such species can often depend on photoperiod to synchronize flowering to ensure that flowering occurs at a specific time of year in order to allow successful seed set and maturation along with cross-pollination. 光周期是指一昼夜的光暗交替。地球上大多数纬度地区存在昼夜长短的季节性变化，光周期现象
即为植物对白天和黑夜的相对长度的反应。植物的很多生理活动都受光周期的调控,如开花的诱导 无性生殖,贮藏器官的形成,休眠的开始等。光周期现象主要表现在寿命较长的植物种类上,该植物 至少能存活一个生长季节。这类植物依靠光周期使开花发生在特定的时期,从而确保伴随着异花授粉 的实现,植物可以顺利地结实与成熟。 113.2 Three types of Photoperiodic Responses(三种光周期反应类型 Plants are classified into three categories: short-day(long-night), long-day(short-night), or day-neutral depending on their response to the day length for flowering: 1. Short-day plants (SDPs)require shorter than a certain number of hours of light to induce flowering. In general, short-day plants flower as days grow shorter, which is during summer or fall in the northern hemisphere. 2. Long-day plants(LDPs)require longer than a certain number of hours of light in each 24-hour period to induce flowering. These plants typically flower in the northern hemisphere during late spring or early summer as days are getting longer 3. Day-neutral plants(DNPs)such as cucumbers, roses and tomatoes, do not initiate flowering based on photoperiodism at all; they flower regardless of the day length. They may initiate flowering after attaining a certain overall developmental stage or age, or in response to alternative environmental stimuli, for example, many desert annuals, such as Castilleja chromos(desert paintbrush), evolved to germinate, grow, and flower quickly whenever sufficient water is available. Further, some species exhibit a dual requirement for successful flowering, i. e. they may require a prescribed sequence of inductive conditions such as SD-LD (short day-long day)or LD-SD 根据植物在日照长短变化时的开花反应可将其分为三个类型:短日(长夜)植物,长日(短夜) 植物及日中性植物。短日植物在光照时间短于一定时数时才能成花。一般而言,北半球的夏末和秋季 白天逐渐变短,短日植物可在这段时间开花。长日植物在每一个24h昼夜周期中光照时间长于一定时 数时才能成花。因此,这些植物往往在北半球的春末夏初白天变长时开花。日中性植物如黄瓜、玫瑰 番茄等,成花不受光周期现象的影响,在任何长度的日照下均可进行。这类植物通常在发育到一定的 生长阶段或者接受一定的环境刺激后即可开花。例如沙漠画笔等许多沙漠一年生植物,无论何时, 要有足够的水分便可发芽生长,然后迅速开花。 另外,还有一些植物对成花有着双重需求,它们可能需要短日-长日或者长日-短日的双重诱导。 113.3 Critical day length(临界日长) Ithough plants are grouped as short day or long day plants, the distinction between Sd plant and LD plant is not based on the absolute length of day. Whether a plant is classified as a Sd plant or LD plant depends on its behavior relative to a certain duration, called the critical day length. Critical day length can be defined as the maximum day length a short-day plant, and the minimum day length a long-day plant, require to initiate flowering. Thus flowering in LDPs is promoted only when the day length exceeds the critical day length, whereas promotion of flowering in SDPs requires a day length that is less than the critical day length. The absolute value of the critical day length varies widely among species 植物被分为短日或长日植物的依据并非绝对日长,而是临界日长,它们对一定时间的日照会产生 不同的反应。临界日长指的是诱导短日植物开花的最长日照或者诱导长日植物开花的最短日照。对于 长日植物而言,只有当日长大于临界日长时才能开花:而对于短日植物而言,只有当日长小于临界日 长时才能开花。临界日长的具体数值存在种间差异。 1l34 Important role of the night length(夜长在光周期现象中的重要性) Under natural conditions, day and night lengths configure a 24-hour cycle of light and darkness. The term photoperiodism implies that plants measure the relative lengths of day and night, which is misleading In fact, a plant measures neither the relative length of day and night nor the duration of daylight, it measures the length of dark period. This was elegantly demonstrated by the experiments of Hamner and Bonner(1938) and Hamner(1940)where flowering of cocklebur, a short day plant, occurred only when night length exceed
即为植物对白天和黑夜的相对长度的反应。植物的很多生理活动都受光周期的调控，如开花的诱导， 无性生殖，贮藏器官的形成，休眠的开始等。光周期现象主要表现在寿命较长的植物种类上，该植物 至少能存活一个生长季节。这类植物依靠光周期使开花发生在特定的时期，从而确保伴随着异花授粉 的实现，植物可以顺利地结实与成熟。 11.3.2 Three types of Photoperiodic Responses（三种光周期反应类型） Plants are classified into three categories: short-day (long-night), long-day (short-night), or day-neutral, depending on their response to the day length for flowering: 1. Short-day plants (SDPs) require shorter than a certain number of hours of light to induce flowering. In general, short-day plants flower as days grow shorter, which is during summer or fall in the northern hemisphere. 2. Long-day plants (LDPs) require longer than a certain number of hours of light in each 24-hour period to induce flowering. These plants typically flower in the northern hemisphere during late spring or early summer as days are getting longer. 3. Day-neutral plants (DNPs) such as cucumbers, roses and tomatoes, do not initiate flowering based on photoperiodism at all; they flower regardless of the day length. They may initiate flowering after attaining a certain overall developmental stage or age, or in response to alternative environmental stimuli, for example, many desert annuals, such as Castilleja chromosa (desert paintbrush), evolved to germinate, grow, and flower quickly whenever sufficient water is available. Further, some species exhibit a dual requirement for successful flowering, i. e. they may require a prescribed sequence of inductive conditions such as SD-LD (short day-long day) or LD-SD. 根据植物在日照长短变化时的开花反应可将其分为三个类型：短日（长夜）植物，长日（短夜） 植物及日中性植物。短日植物在光照时间短于一定时数时才能成花。一般而言，北半球的夏末和秋季 白天逐渐变短，短日植物可在这段时间开花。长日植物在每一个24h昼夜周期中光照时间长于一定时 数时才能成花。因此，这些植物往往在北半球的春末夏初白天变长时开花。日中性植物如黄瓜、玫瑰、 番茄等，成花不受光周期现象的影响，在任何长度的日照下均可进行。这类植物通常在发育到一定的 生长阶段或者接受一定的环境刺激后即可开花。例如沙漠画笔等许多沙漠一年生植物，无论何时，只 要有足够的水分便可发芽生长，然后迅速开花。 另外，还有一些植物对成花有着双重需求，它们可能需要短日-长日或者长日-短日的双重诱导。 11.3.3 Critical day length（临界日长） Although plants are grouped as short day or long day plants, the distinction between SD plant and LD plant is not based on the absolute length of day. Whether a plant is classified as a SD plant or LD plant depends on its behavior relative to a certain duration, called the critical day length. Critical day length can be defined as the maximum day length a short-day plant, and the minimum day length a long-day plant, require to initiate flowering. Thus flowering in LDPs is promoted only when the day length exceeds the critical day length, whereas promotion of flowering in SDPs requires a day length that is less than the critical day length. The absolute value of the critical day length varies widely among species. 植物被分为短日或长日植物的依据并非绝对日长，而是临界日长，它们对一定时间的日照会产生 不同的反应。临界日长指的是诱导短日植物开花的最长日照或者诱导长日植物开花的最短日照。对于 长日植物而言，只有当日长大于临界日长时才能开花；而对于短日植物而言，只有当日长小于临界日 长时才能开花。临界日长的具体数值存在种间差异。 11.3.4 Important role of the night length （夜长在光周期现象中的重要性） Under natural conditions, day and night lengths configure a 24-hour cycle of light and darkness. The term photoperiodism implies that plants measure the relative lengths of day and night，which is misleading. In fact, a plant measures neither the relative length of day and night nor the duration of daylight, it measures the length of dark period. This was elegantly demonstrated by the experiments of Hamner and Bonner (1938) and Hamner (1940) where flowering of cocklebur, a short day plant, occurred only when night length exceed
8.5 h, but remained vegetative on a schedule of 16 h light and 8 h darkness. On schedule of 4 h light-8 h darkness, plants remained vegetative even though the 4 h day length is much shorter than the 15.5 h critical day length. On the other hand, schedule of 16 h light-32 h darkness induced rapid flowering even thoug the day length exceeded the critical day length. Night break lighting of cocklebur of as little as a few minutes prevented flowering even when the total night length was sufficient to promote flowering. Similarly, night break lighting can result in stimulation of flowering in LDP. But much longer lengths of time of a night break are often required to promote flowering in LDPs. So a SDP could actually be a LNP(long night plant) and a LDP could really be a SNP(short night plant 在自然条件下,昼夜总是在24h的周期内交替出现。依据“光周期现象”的定义可知,植物可以 估量白天与黑夜的相对长度,这其实是不准确的。事实上,植物既不能估量白天与黑夜的相对长度 也不能估量白天的绝对长度,它只能估量夜晚的长度。这一理论可以完美地解释 Hamner and Bonner (1938)与 Hamner(1940)利用苍耳所做的成花诱导实验。苍耳是短日植物,只有在夜长超过8h时才可 开花,当日长为l6h且夜长为$h时,其进行营养性生长,不开花:当日长为4h且夜长为8h时,其仍为 营养性生长,此时4h已远远短于临界日长155h。但另一方面,当日长为16h且夜长为32h时,其很快 便开花了,即使此时16h已超过临界日长。在足够引起苍耳开花的暗期内,即使一个短至几分钟的夜 间断也能阻断其开花。与此类似,夜间断也可以影响长日植物的成花诱导,但较长时间的夜间断通常 可以促进其开花。因此,短日植物实际是长夜植物,长日植物实际是短夜植物 113.5 Perception of the photoperiodic signal(光周期信号的感知) The photoperiodic stimulus in both LDPs and SDPs is perceived not by the stem apex, where the actual change from vegetative to reproductive growth occur, but by the leaves. This has been demonstrated experimentally. For example, SDP cocklebur stripped of all but one leaf could be induced to flower if the remaining leaf were provided the appropriate photoperiod, even when the rest of the plant is exposed to long days. Photoperiodic induction can take place in a leaf that has been separated from the plant. For example, in the SDP Perilla crispa, an excised leaf exposed to short days can cause flowering when subsequently grafted to a noninduced plant maintained in long days(Zeevaart and Boyer 1987). This result indicates that photoperiodic induction depends on events that take place exclusively in the leaf. 实验证明,长日植物与短日植物感受光周期刺激的部位不是茎尖端生长点(从营养生长转变为生 殖生长的发生部位),而是叶片。例如,将短日植物苍耳的叶片去除到只剩一片叶子,将这片叶子用 合适的光诱导周期处理,即使该植物的其他部位处于长日照下,植物仍能开花。光周期诱导还可发生 在离体的叶片上。例如,将一片离体的紫苏(短日植物)叶片用短日照处理后嫁接于一株未诱导的长 日照植物上,可引起后者开花。这个现象表明光周期诱导仅与叶片上发生的反应有关。 113.6 Photoperiodic induction(光周期诱导) The photoperiod-regulated processes that occur in the leaves resulting in the transmission of a floral tumulus to the shoot apex are referred to collectively as photoperiodic induction. The appropriate photoperiod is referred to as an inductive treatment. The number of inductive treatments required to induce flowering varies with species. Some plants, such as cocklebur, will proceed to flower even if the plant is returned to unfavorable photoperiods after a single inductive treatment, many other plants require more or less continuous inductive treatments to induce flowering Induction is not an all-or-none process, but can be achieved in degrees. For example, the flowering of cocklebur can be induced by a single inductive treatment but the flower initiation can be more rapid and prolific if more inductive treatments are given 发生在叶片上的反应产生成花物质并传导到茎尖端,这一受光周期调控的过程统称为光周期诱 导。适宜的光周期便是一次诱导处理。开花所需的诱导次数因植物种类而异。有些植物(如苍耳)在 次诱导处理后,即使被置于不适宜的光周期下也仍能开花,另外一些植物或多或少需要连续几次的 诱导处理才能开花。诱导处理并非一个“全或无”的过程,可以表现为梯度式。如苍耳可以在接受
8.5 h, but remained vegetative on a schedule of 16 h light and 8 h darkness. On schedule of 4 h light-8 h darkness, plants remained vegetative even though the 4 h day length is much shorter than the 15.5 h critical day length. On the other hand, schedule of 16 h light-32 h darkness induced rapid flowering even thoug the day length exceeded the critical day length. Night break lighting of cocklebur of as little as a few minutes prevented flowering even when the total night length was sufficient to promote flowering. Similarly, night break lighting can result in stimulation of flowering in LDP. But much longer lengths of time of a night break are often required to promote flowering in LDPs. So a SDP could actually be a LNP (long night plant), and a LDP could really be a SNP (short night plant). 在自然条件下，昼夜总是在24h的周期内交替出现。依据“光周期现象”的定义可知，植物可以 估量白天与黑夜的相对长度，这其实是不准确的。事实上，植物既不能估量白天与黑夜的相对长度， 也不能估量白天的绝对长度，它只能估量夜晚的长度。这一理论可以完美地解释Hamner and Bonner (1938) 与Hamner (1940)利用苍耳所做的成花诱导实验。苍耳是短日植物，只有在夜长超过8.5h时才可 开花，当日长为16h且夜长为8h时，其进行营养性生长，不开花；当日长为4h且夜长为8h时，其仍为 营养性生长，此时4h已远远短于临界日长15.5h。但另一方面，当日长为16h且夜长为32h时，其很快 便开花了，即使此时16h已超过临界日长。在足够引起苍耳开花的暗期内，即使一个短至几分钟的夜 间断也能阻断其开花。与此类似，夜间断也可以影响长日植物的成花诱导，但较长时间的夜间断通常 可以促进其开花。因此，短日植物实际是长夜植物，长日植物实际是短夜植物。 11.3.5 Perception of the photoperiodic signal（光周期信号的感知） The photoperiodic stimulus in both LDPs and SDPs is perceived not by the stem apex, where the actual change from vegetative to reproductive growth occur, but by the leaves. This has been demonstrated experimentally. For example, SDP cocklebur stripped of all but one leaf could be induced to flower if the remaining leaf were provided the appropriate photoperiod, even when the rest of the plant is exposed to long days. Photoperiodic induction can take place in a leaf that has been separated from the plant. For example, in the SDP Perilla crispa, an excised leaf exposed to short days can cause flowering when subsequently grafted to a noninduced plant maintained in long days (Zeevaart and Boyer 1987). This result indicates that photoperiodic induction depends on events that take place exclusively in the leaf. 实验证明，长日植物与短日植物感受光周期刺激的部位不是茎尖端生长点（从营养生长转变为生 殖生长的发生部位），而是叶片。例如，将短日植物苍耳的叶片去除到只剩一片叶子，将这片叶子用 合适的光诱导周期处理，即使该植物的其他部位处于长日照下，植物仍能开花。光周期诱导还可发生 在离体的叶片上。例如，将一片离体的紫苏（短日植物）叶片用短日照处理后嫁接于一株未诱导的长 日照植物上，可引起后者开花。这个现象表明光周期诱导仅与叶片上发生的反应有关。 11.3.6 Photoperiodic induction（光周期诱导） The photoperiod-regulated processes that occur in the leaves resulting in the transmission of a floral stimulus to the shoot apex are referred to collectively as photoperiodic induction. The appropriate photoperiod is referred to as an inductive treatment. The number of inductive treatments required to induce flowering varies with species. Some plants, such as cocklebur, will proceed to flower even if the plant is returned to unfavorable photoperiods after a single inductive treatment, many other plants require more or less continuous inductive treatments to induce flowering. Induction is not an all-or-none process, but can be achieved in degrees. For example, the flowering of cocklebur can be induced by a single inductive treatment, but the flower initiation can be more rapid and prolific if more inductive treatments are given. 发生在叶片上的反应产生成花物质并传导到茎尖端，这一受光周期调控的过程统称为光周期诱 导。适宜的光周期便是一次诱导处理。开花所需的诱导次数因植物种类而异。有些植物（如苍耳）在 一次诱导处理后，即使被置于不适宜的光周期下也仍能开花，另外一些植物或多或少需要连续几次的 诱导处理才能开花。诱导处理并非一个“全或无”的过程，可以表现为梯度式。如苍耳可以在接受一
次诱导处理后开花,但在接受多次诱导处理后其开花更为迅速及高产 The role of phytochrome in photoperiodism(光周期现象中光敏色素的作用) It is known that photoperiodism is a response to the length of a dark period, but the length of the dark period is determined by the timing of light-off and light-on signals. The nature of the pigment involved in photoperiodism was first studied by determining the action spectrum of the inhibition of flowering in SDP by night break. Action spectra on several SD plants indicated that red light was most effective as a light-break to inhibit flowering. And a subsequent exposure to far-red light restores the flowering response Red and far-red reversibility has also been demonstrated in some LDPs. In these plants, a night break of red light promoted flowering, and a subsequent exposure to far-red light prevented this response. Red, far-red photoreversibility of the light break clearly confirm the role of phytochrome as the photoreceptor that is involved in the photoperiodic timing process 我们知道光周期现象是植物对夜长的反应,但是夜长的长度是由明暗信号的定时转换决定的。有 实验通过确定夜间断对短日植物开花产生抑制的作用光谱首次研究了光周期现象中涉及的光敏色素 结果表明,红光作为暗期间断在抑制短日植物开花时是最有效的,但随后照以远红光可以抵消其作用。 在某些长日植物上也存在红光远红光的可逆效应。用红光对这些长日植物进行夜间断可以促进开花, 随后照以远红光可以阻碍此反应。红光与远红光在暗期间断中的光逆转性证明了光敏色素可以作为光 周期中定时反应的光感受器。 Florigen(成花素 The observation that photoperiodic perception occurs in the leaves and flowering occurs in the meristem suggested the existence of a moving signal termed"florigen "formed in leaves and reaching the meristem. Molecular genetic studies in Arabidopsis and other species have provided the identify of florigen which is small protein(23KD)encoded by FLOERING LOCUS T(FT) in Arabidopsis. According to the current model, FT mRNA moves via the phloem from the leaves to the meristem under inductive photoperiods. Once in the meristem, the FT mRNA is translated into FT protein, and the FT protein forms a complex with another protein called FD. The complex of FT and FD then activates floral identity genes such as APETALA 1. It is also possible that FT protein can be translocated from leaves to the meristem 感受光周期剌激的部位是叶片,而开花却是在茎尖端分生组织,这一现象表明有一种可被转移的 信号物质一成花素在叶片中形成并可被运输到茎尖端。对于拟南芥及其他一些物种的分子遗传学方面 的研究证实了成花素的存在。在拟南芥中,成花素是一个由 FLOERING LOCUS T(FT)编码的23KD的 蛋白质。根据现有实验模型,在光周期剌激下, FTmRNA从叶片中经韧皮部到达茎尖端分生组织 然后转录为FT蛋白。FT蛋白与FD蛋白构成一个复合物,该复合物可以激活花器官决定基因如 APETALA1的表达。FT蛋白也可在形成后直接从叶片运输到茎尖端。 Floral hormones(与成花有关的激素 Of the several classes of plant hormones, gibberellins(GAs) have shown a strong influence on flowering in a wide variety of species. When exogenous gibberellin was applied to the apex of LDPs like Arabidopsis, or to dual-day length plants such as Bryophyllum, flowering responses can be elicited under short days. In addition, applied gibberellins promote or induce flowering in cold-requiring plants that have not been vernalized. GA can also be used for cone induction in juvenile plants of several gymnosperm families. Thus, in some plants, exogenous Ga induction of flowering is a pathway that bypasses the endogenous trigger of age in autonomous flowering, and runs in parallel to vernalization and photoperiodic duction 在几类植物激素中,赤霉素(GAs)对多种植物的成花均有重要影响。用外源赤霉素处理长日植 物如拟南芥或者双重日长植物如大叶落地生根的茎尖,几天后便可开花。另外,赤霉素还可使某些冬 性植物不经春化即可开花,或者促进一些幼年期裸子植物球果的形成。因此,使用外源赤霉素可以代
次诱导处理后开花，但在接受多次诱导处理后其开花更为迅速及高产。 The role of phytochrome in photoperiodism（光周期现象中光敏色素的作用） It is known that photoperiodism is a response to the length of a dark period, but the length of the dark period is determined by the timing of light-off and light-on signals. The nature of the pigment involved in photoperiodism was first studied by determining the action spectrum of the inhibition of flowering in SDP by night break. Action spectra on several SD plants indicated that red light was most effective as a light-break to inhibit flowering. And a subsequent exposure to far-red light restores the flowering response. Red and far-red reversibility has also been demonstrated in some LDPs. In these plants, a night break of red light promoted flowering, and a subsequent exposure to far-red light prevented this response. Red, far-red photoreversibility of the light break clearly confirm the role of phytochrome as the photoreceptor that is involved in the photoperiodic timing process. 我们知道光周期现象是植物对夜长的反应，但是夜长的长度是由明暗信号的定时转换决定的。有 实验通过确定夜间断对短日植物开花产生抑制的作用光谱首次研究了光周期现象中涉及的光敏色素。 结果表明，红光作为暗期间断在抑制短日植物开花时是最有效的，但随后照以远红光可以抵消其作用。 在某些长日植物上也存在红光-远红光的可逆效应。用红光对这些长日植物进行夜间断可以促进开花， 随后照以远红光可以阻碍此反应。红光与远红光在暗期间断中的光逆转性证明了光敏色素可以作为光 周期中定时反应的光感受器。 Florigen（成花素） The observation that photoperiodic perception occurs in the leaves and flowering occurs in the meristem suggested the existence of a moving signal termed “florigen” formed in leaves and reaching the meristem. Molecular genetic studies in Arabidopsis and other species have provided the identify of florigen, which is small protein (23KD) encoded by FLOERING LOCUS T (FT) in Arabidopsis. According to the current model, FT mRNA moves via the phloem from the leaves to the meristem under inductive photoperiods. Once in the meristem, the FT mRNA is translated into FT protein, and the FT protein forms a complex with another protein called FD. The complex of FT and FD then activates floral identity genes such as APETALA 1. It is also possible that FT protein can be translocated from leaves to the meristem. 感受光周期刺激的部位是叶片，而开花却是在茎尖端分生组织，这一现象表明有一种可被转移的 信号物质—成花素在叶片中形成并可被运输到茎尖端。对于拟南芥及其他一些物种的分子遗传学方面 的研究证实了成花素的存在。在拟南芥中，成花素是一个由FLOERING LOCUS T (FT)编码的23KD的 蛋白质。根据现有实验模型，在光周期刺激下，FT mRNA从叶片中经韧皮部到达茎尖端分生组织， 然后转录为FT蛋白。FT蛋白与FD蛋白构成一个复合物，该复合物可以激活花器官决定基因如 APETALA 1的表达。FT蛋白也可在形成后直接从叶片运输到茎尖端。 Floral hormones （与成花有关的激素） Of the several classes of plant hormones, gibberellins (GAs) have shown a strong influence on flowering in a wide variety of species. When exogenous gibberellin was applied to the apex of LDPs like Arabidopsis, or to dual–day length plants such as Bryophyllum, flowering responses can be elicited under short days. In addition, applied gibberellins promote or induce flowering in cold-requiring plants that have not been vernalized. GA can also be used for cone induction in juvenile plants of several gymnosperm families. Thus, in some plants, exogenous GA induction of flowering is a pathway that bypasses the endogenous trigger of age in autonomous flowering, and runs in parallel to vernalization and photoperiodic induction. 在几类植物激素中，赤霉素（GAs）对多种植物的成花均有重要影响。用外源赤霉素处理长日植 物如拟南芥或者双重日长植物如大叶落地生根的茎尖，几天后便可开花。另外，赤霉素还可使某些冬 性植物不经春化即可开花，或者促进一些幼年期裸子植物球果的形成。因此，使用外源赤霉素可以代
替春化作用、光周期剌激而诱导成花,也可代替足日龄引发的自发开花而使植物成花 第三节花器官的形成 Once flowering has been induced, the apical meristem produces whorls of floral organ primordia, and ultimately leads to the production of the four different types of floral organs--sepals, petals, stamens, and 旦成花诱导实现,茎尖端分生组织便开始产生轮生的花器官原基,后者最终分化为四种不同的 花器官:萼片,花瓣,雄蕊及心皮。 The developmental fate of floral organs is controlled by the floral organ identity genes, which were identified through analysis of the genetic mutations that alter the specification of floral development. Five floral organ identity genes have been identified as in Arabidopsis: APETALAl(AP1), APETALA2 (AP2), APETALA3(AP3), PISTILLATA(PD, and AGAMOUS (AG). Generally mutations in these gene of foral mutations in API or AP2 affect the development of sepals and petals(see Figure), such that carpels replace petals in the second whorl; and carpels instead of stamens in the third whorl. And defective alleles of AG identity genes are therefore divided into three classes, depending on which organs they affect. Mutations in class a genes affect sepals and petals. Mutations in class B genes affect petals and stamens, while those in class C affect stamens and carpels 花器官的分化命运是受器官决定基因控制的,对于花器官发育不正常的突变体的分析在寻找器官 决定基因中起了重要作用。在拟南芥中发现有五种器官决定基因: APETALAl(AP1)、 APETAla2 (AP2)、 APETALA3(AP3)、 PISTILLATA(PD及 AGAMOUS(AG)。这些基因的突变体可以使相邻两 轮的花器官形态发生异常。例如,AP1或AP2的突变体影响萼片与花瓣的发育,使萼片变为心皮, 花瓣变为雄蕊。AP3或PI的突变体与之类似,使第二轮的花瓣变为萼片,第三轮的雄蕊变为心皮。 缺乏AG基因的突变体影响第三、第四轮花器官的发育,丧失雄蕊和心皮。因此,根据所影响的 器官将花器官决定基因分为三类:A类基因影响萼片与花瓣的发育,B类基因影响花瓣与雄蕊的 发育,C类基因影响雄蕊与心皮的发育 ABC model and ABCDE model(ABC模型与 ABCDER模型) Based on the observation of mutants with defects in floral organ development, the ABC model of flower development was formulated. The model posits that three types of genes, termed A, B, and C regulate floral development. Each whorl of a flower is determined by a unique combination of the three organ identity gene functions, the function of A alone specifies sepals. Functions of both A and B are equired for the formation of petals. Functions of B and C form stamens. Function of C alone specifies rpels. The model further suggests that Aand C functions mutually repress each other(see Figure 24.6); that is, the A function prevents the C function, and vice versa. The ABC model has recently been extended by the inclusion of two other gene classes, namely D and E, which are involved in ovule development, and petal stamen and carpel development, respectively. Mutations in class D genes lack ovule. Mutations in class genes affect petal, stamen and carpel development; that is all the other three whirls of floral organs are transformed into sepals ABC模型是根据不同类型的突变体对花器官的形成有不同的影响这一现象提出的。该模型假设有 三种类型的基因A、B和C调控花器官的形成。每一轮花器官的形成是由三类器官决定基因的一个唯 的组合而决定的。其中,A类基因单独决定萼片的形成,A类与B类基因共同决定花瓣的形成,B类与 C类基因共同决定雄蕊的形成,C类基因单独决定心皮的形成。值得说明的是,A类基因与C类基因相 互拮抗,即A类基因的功能会阻抑C类基因的功能,反之亦然。随着研究的深入,D与E基因也被补充
替春化作用、光周期刺激而诱导成花，也可代替足日龄引发的自发开花而使植物成花。 第三节 花器官的形成 Once flowering has been induced, the apical meristem produces whorls of floral organ primordia, and ultimately leads to the production of the four different types of floral organs—sepals, petals, stamens, and carpels. 一旦成花诱导实现，茎尖端分生组织便开始产生轮生的花器官原基，后者最终分化为四种不同的 花器官：萼片，花瓣，雄蕊及心皮。 The developmental fate of floral organs is controlled by the floral organ identity genes, which were identified through analysis of the genetic mutations that alter the specification of floral development. Five floral organ identity genes have been identified as in Arabidopsis: APETALA1 (AP1), APETALA2 (AP2), APETALA3 (AP3), PISTILLATA (PI), and AGAMOUS (AG). Generally mutations in these genes result in reduced, altered, or misplaced development of floral organs in two adjacent whorls. For example, mutations in AP1 or AP2 affect the development of sepals and petals (see Figure), such that carpels replace sepals; and stamens replace petals. Phenotypes of ap3 or pi mutations are similar, producing sepals instead of petals in the second whorl; and carpels instead of stamens in the third whorl. And defective alleles of AG affect flower development in the third and fourth whorls, lacking both stamens and carpels. Floral organ identity genes are therefore divided into three classes, depending on which organs they affect. Mutations in class A genes affect sepals and petals. Mutations in class B genes affect petals and stamens, while those in class C affect stamens and carpels. 花器官的分化命运是受器官决定基因控制的，对于花器官发育不正常的突变体的分析在寻找器官 决定基因中起了重要作用。在拟南芥中发现有五种器官决定基因：APETALA1 (AP1)、APETALA2 (AP2)、APETALA3 (AP3)、PISTILLATA (PI)及AGAMOUS (AG)。这些基因的突变体可以使相邻两 轮的花器官形态发生异常。例如，AP1或AP2的突变体影响萼片与花瓣的发育，使萼片变为心皮， 花瓣变为雄蕊。AP3或PI的突变体与之类似，使第二轮的花瓣变为萼片，第三轮的雄蕊变为心皮。 缺乏AG基因的突变体影响第三、第四轮花器官的发育，丧失雄蕊和心皮。因此，根据所影响的 器官将花器官决定基因分为三类：A类基因影响萼片与花瓣的发育，B类基因影响花瓣与雄蕊的 发育，C类基因影响雄蕊与心皮的发育。 ABC model and ABCDE model（ABC模型与ABCDE模型） Based on the observation of mutants with defects in floral organ development, the ABC model of flower development was formulated. The model posits that three types of genes, termed A, B, and C, regulate floral development. Each whorl of a flower is determined by a unique combination of the three organ identity gene functions, the function of A alone specifies sepals. Functions of both A and B are required for the formation of petals. Functions of B and C form stamens. Function of C alone specifies carpels. The model further suggests that Aand C functions mutually repress each other (see Figure 24.6); that is, the A function prevents the C function, and vice versa. The ABC model has recently been extended by the inclusion of two other gene classes, namely D and E, which are involved in ovule development, and petal, stamen and carpel development, respectively. Mutations in class D genes lack ovule. Mutations in class E genes affect petal, stamen and carpel development; that is all the other three whirls of floral organs are transformed into sepals. ABC模型是根据不同类型的突变体对花器官的形成有不同的影响这一现象提出的。该模型假设有 三种类型的基因A、B和C调控花器官的形成。每一轮花器官的形成是由三类器官决定基因的一个唯一 的组合而决定的。其中，A类基因单独决定萼片的形成，A类与B类基因共同决定花瓣的形成，B类与 C类基因共同决定雄蕊的形成，C类基因单独决定心皮的形成。值得说明的是，A类基因与C类基因相 互拮抗，即A类基因的功能会阻抑C类基因的功能，反之亦然。随着研究的深入，D与E基因也被补充
入ABC模型,D与胚珠的形成有关,E可调控花瓣、雄蕊及心皮的发育。D突变体缺乏胚珠。E突变体 使花瓣、雄蕊及心皮发育异常,即这三轮花器官全部变为萼片。 Formation of gametes(配子的形成 Following flower development, the next step in plants reproductive cycle is the formation of gametes The male gametes are produced in a sac-like structure known as the anther. The division of a diploid sporogenic cell results in two cells-the tapetal initial cell and the pollen mother cell. The pollen mother cell undergoes meiosis, giving rise to microspores, a tetrad of haploid cells. Subsequently, microspores underg two mitotic division, the first one is asymmetric, creating a larger vegetative cell and a small generative cell A second mitotic division of the generative cell yields two sperm cells. At what point this second division occurs is species specific. In the majority of flowering plants, it is during pollen tube growth. However, in the case of the crucifers and grasses, the division occurs while the pollen grain is still in the anther. In most species, pollen is released in a partially hydrated state and becomes fully hydrated upon contact with the stigma. The vegetative cell extends the pollen tube by tip growth, ultimately delivering the sperm cells to the embryo sac and completing the pollen development process 在植物的生殖周期中,紧接着开花的下一个阶段便是配子的形成。雄性配子是在花粉囊中形成的 一个二倍体造孢细胞分裂为两个子细胞:绒毡层初始细胞和花粉母细胞。花粉母细胞经过减数分裂形 成四分体的单倍体小孢子,随后小孢子进行两次有丝分裂,第一次为不对称的分裂,形成一个大的营 养细胞和一个小的生殖细胞,生殖细胞经第二次有丝分裂形成两个精子细胞。第二次有丝分裂的发生 时间因植物种类而异。对大多数开花植物而言,第二次有丝分裂发生在花粉管生长时:但十字花科及 禾本科植物的第二次有丝分裂在花粉粒还在花粉囊中时就已开始。大多数植物的花粉在部分水合状态 时即被释放,当其与柱头接触时达到完全水合的状态。营养细胞通过顶端生长使花粉管延伸,最终将 精子细胞运输到胚囊中,从而完成花粉的发育过程 Female gamete development occurs over two phases referred to as megasporogenesis and megagametogenesis. During megasporogenesis, the diploid mega gives rise to four haploid nuclei. Angiosperms exhibit three main patterns of megasporogenesis, referred to as monosporic, bisporic, and tetrasporic, differing mainly in whether cell plate formation occurs after these divisions. The monosporic pattern is the most common form, in which both meiotic divisions are accompanied by cell plate formation, resulting in four one-nucleate megaspores. Subsequently, three megaspores generally undergo cell death. During megagametogenesis, the surviving megaspore undergoes three mitotic division to produce the female gametophyte, or embryo sac. The female gametophyte is typically a seven-celled structure at maturity three antipodal cells, two synergids, a central cell (containing two of the haploid nuclei), and the egg cell. 雌性配子的发育经过大孢子发生与配子体形成这两个过程。大孢子发生时,二倍体的孢母细胞经 过减数分裂产生四个单倍体的细胞核。被子植物有三种产生大孢子的方式:单孢子式、双孢子式及四 孢子式,划分依据是在相应的分裂期是否形成细胞板。单孢子式是最普遍的形式,按此方式形成大孢 子时,细胞板的形成伴随减数分裂过程同时发生,结果形成四个单核孢子,其中三个孢子最终凋亡 在配子体形成时,仅存的孢子进行三次有丝分裂后产生雌性配子体或胚囊。成熟的雌性配子体是一个 七细胞结构:三个反足细胞,两个助细胞,一个中心细胞(包括两个单倍体核)以及一个卵细胞。 Germination of pollen(花粉的萌发) a pollen grain must hydrate and grow a pollen tube toward the ovule after landing on a stigma Stigmas can be classified into two categories, wet and dry, according to whether there is surface secretion The first step in pollen tube germination is pollen hydration, to which the lipids of the pollen coat have been thought to be essential, especially in plants with so-called"dry"stigma Upon hydration, Ca flows into the pollen grain; resulting in the formation of a cytoplasmic gradient of Ca" beneath the site of germination; this
入ABC模型，D与胚珠的形成有关，E可调控花瓣、雄蕊及心皮的发育。D突变体缺乏胚珠。E突变体 使花瓣、雄蕊及心皮发育异常，即这三轮花器官全部变为萼片。 Formation of gametes （配子的形成） Following flower development, the next step in plant’s reproductive cycle is the formation of gametes. The male gametes are produced in a sac-like structure known as the anther. The division of a diploid sporogenic cell results in two cells—the tapetal initial cell and the pollen mother cell. The pollen mother cell undergoes meiosis, giving rise to microspores, a tetrad of haploid cells. Subsequently, microspores undergo two mitotic division, the first one is asymmetric, creating a larger vegetative cell and a small generative cell. A second mitotic division of the generative cell yields two sperm cells. At what point this second division occurs is species specific. In the majority of flowering plants, it is during pollen tube growth. However, in the case of the crucifers and grasses, the division occurs while the pollen grain is still in the anther. In most species, pollen is released in a partially hydrated state and becomes fully hydrated upon contact with the stigma. The vegetative cell extends the pollen tube by tip growth, ultimately delivering the sperm cells to the embryo sac and completing the pollen development process. 在植物的生殖周期中，紧接着开花的下一个阶段便是配子的形成。雄性配子是在花粉囊中形成的。 一个二倍体造孢细胞分裂为两个子细胞：绒毡层初始细胞和花粉母细胞。花粉母细胞经过减数分裂形 成四分体的单倍体小孢子，随后小孢子进行两次有丝分裂，第一次为不对称的分裂，形成一个大的营 养细胞和一个小的生殖细胞，生殖细胞经第二次有丝分裂形成两个精子细胞。第二次有丝分裂的发生 时间因植物种类而异。对大多数开花植物而言，第二次有丝分裂发生在花粉管生长时；但十字花科及 禾本科植物的第二次有丝分裂在花粉粒还在花粉囊中时就已开始。大多数植物的花粉在部分水合状态 时即被释放，当其与柱头接触时达到完全水合的状态。营养细胞通过顶端生长使花粉管延伸，最终将 精子细胞运输到胚囊中，从而完成花粉的发育过程。 Female gamete development occurs over two phases referred to as megasporogenesis and megagametogenesis. During megasporogenesis, the diploid megaspore mother cell undergoes meiosis and gives rise to four haploid nuclei. Angiosperms exhibit three main patterns of megasporogenesis, referred to as monosporic, bisporic, and tetrasporic, differing mainly in whether cell plate formation occurs after these divisions. The monosporic pattern is the most common form, in which both meiotic divisions are accompanied by cell plate formation, resulting in four one-nucleate megaspores. Subsequently, three megaspores generally undergo cell death. During megagametogenesis, the surviving megaspore undergoes three mitotic division to produce the female gametophyte, or embryo sac. The female gametophyte is typically a seven-celled structure at maturity: three antipodal cells, two synergids, a central cell (containing two of the haploid nuclei), and the egg cell. 雌性配子的发育经过大孢子发生与配子体形成这两个过程。大孢子发生时，二倍体的孢母细胞经 过减数分裂产生四个单倍体的细胞核。被子植物有三种产生大孢子的方式：单孢子式、双孢子式及四 孢子式，划分依据是在相应的分裂期是否形成细胞板。单孢子式是最普遍的形式，按此方式形成大孢 子时，细胞板的形成伴随减数分裂过程同时发生，结果形成四个单核孢子，其中三个孢子最终凋亡。 在配子体形成时，仅存的孢子进行三次有丝分裂后产生雌性配子体或胚囊。成熟的雌性配子体是一个 七细胞结构：三个反足细胞，两个助细胞，一个中心细胞（包括两个单倍体核）以及一个卵细胞。 Germination of pollen（花粉的萌发） A pollen grain must hydrate and grow a pollen tube toward the ovule after landing on a stigma. Stigmas can be classified into two categories, wet and dry, according to whether there is surface secretion. The first step in pollen tube germination is pollen hydration, to which the lipids of the pollen coat have been thought to be essential, especially in plants with so-called “dry” stigma. Upon hydration, Ca2+ flows into the pollen grain; resulting in the formation of a cytoplasmic gradient of Ca2+beneath the site of germination; this
gradient is critical for polar tip growth. As pollen tubes grow, the cytoplasm is concentrated near the tip, and the tube closest to the grain is blocked off by deposition of callose plugs. The pollen tube wall is an extension of the inner pollen wall, and is composed largely of callose. The pollen tube extends by tip growth through the pistil to deliver the sperm to the embryo sac 花粉落到柱头上后必须水合化并且产生一个朝向胚珠的花粉管。柱头根据表面有无分泌物可被分 为两种类型:湿柱头与干柱头。花粉管生长的第一步是花粉的水合化,花粉外壁的脂质在这个过程中 十分重要,对于花粉落在干柱头上的植物尤其如此。经过水合化,Ca2流入花粉粒,在花粉萌发位置 之下的细胞质内形成Ca2浓度梯度,该梯度对于极性的顶端生长是必需的。在花粉管生长时,细胞 质集中于顶端区,而管的基部则被胼胝质堵住。由胼胝质构成的花粉管壁由内部的花粉壁延伸而成。 花粉管通过顶端生长而伸长,从而将精子通过雌蕊运输到胚囊中, Fertilization(受精) The pollen tube grows downward toward the ovary through special tissues in the style. After reaching the ovule, the pollen tube releases its two sperm into one of the two synergid cells, which begins to degenerate as the pollen tube enters it. The two sperm cells have different targets for fertilization. One sperm cell fertilizes the haploid egg cell to form a diploid zygote, from which the embryo develops. The other sperm unites with the two nuclei located in a single cell at the center of the embryo sac. Together these nuclei form the triploid nucleus of the cell from which the endosperm develops. Double fertilization in th form is unique to the angiosperms 花粉管通过花柱内的特殊组织朝向子房生长。到达胚珠后,花粉管进入其中的一个助细胞,该细 胞开始退化,使花粉管内的两个精子得以进入胚囊。这两个精子分别受精,其中一个与单倍体的卵细 胞结合形成二倍体的受精卵,开始胚胎发育。另外一个精子与两个中央细胞极核结合,形成一个三细 胞核的细胞,该细胞将发育成胚乳。被子植物的这种双受精在自然界是独一无二的。 Self-incompatibility(自交不亲和性 Self-incompatibility is a widespread mechanism in flowering plants that prevents self-fertilization and thus encourage outcrossing. In plants with SI, when a pollen grain produced in a plant reaches a stigma of the same plant or another plant with a similar genotype, the process of pollen germination, pollen tube growth, ovule fertilization, and embryo development is halted at one of its stages, and consequently no seeds are produced 自交不亲和性是开花植物避免自体受精而支持远源杂交的一种广泛应用的机制。对于自交不亲和 的植物,当一种植物的花粉粒落到同种植物或者具有相似基因型的植物的柱头上时,花粉的萌发、花 粉管的生长、胚珠的受精、受精卵的发育等其中的某一过程将被中断,最终导致无法结实。 The self-incompatibility response is genetically controlled by a single genetic locus termed S, which has multiple alleles, and relies on a series of complex cellular interactions between the self-incompatible pollen and pistil. Differences in the proteins encoded by coding regions of the S-locus are thought to be the basis for the recongnition of incompatibility or compatibility 遗传学上的自交不亲和性受一个具有复等位基因的S基因座控制,并依赖一系列雌雄细胞间的相 互作用而实现。S基因编码的不同蛋白质是自交不亲和或亲和的识别基础 There are two major types of self-incompatibility gametophytic self-incompatibility(GSI)and rophytic self-incompatibility(SSI). GSI is more common, existing in the families: Solanaceae, Rosaceae, Plantaginaceae, Fabaceae, Onagraceae, Campanulaceae, Papaveraceae and Poaceae. Two GSI mechanisms that have been well-studied rely on RNase and S-glycoprotein respectively. In this form of elf-incompatibility, pollen is successful only when the genotype of the pollen does not match the genotype of the female(figure ) In many cases of GSI, the incompatible pollen tube is able to initiate growth through the style before it arrests
gradient is critical for polar tip growth. As pollen tubes grow, the cytoplasm is concentrated near the tip, and the tube closest to the grain is blocked off by deposition of callose plugs. The pollen tube wall is an extension of the inner pollen wall, and is composed largely of callose. The pollen tube extends by tip growth through the pistil to deliver the sperm to the embryo sac. 花粉落到柱头上后必须水合化并且产生一个朝向胚珠的花粉管。柱头根据表面有无分泌物可被分 为两种类型：湿柱头与干柱头。花粉管生长的第一步是花粉的水合化，花粉外壁的脂质在这个过程中 十分重要，对于花粉落在干柱头上的植物尤其如此。经过水合化，Ca2+流入花粉粒，在花粉萌发位置 之下的细胞质内形成 Ca2+浓度梯度，该梯度对于极性的顶端生长是必需的。在花粉管生长时，细胞 质集中于顶端区，而管的基部则被胼胝质堵住。由胼胝质构成的花粉管壁由内部的花粉壁延伸而成。 花粉管通过顶端生长而伸长，从而将精子通过雌蕊运输到胚囊中。 Fertilization（受精） The pollen tube grows downward toward the ovary through special tissues in the style. After reaching the ovule, the pollen tube releases its two sperm into one of the two synergid cells, which begins to degenerate as the pollen tube enters it. The two sperm cells have different targets for fertilization. One sperm cell fertilizes the haploid egg cell to form a diploid zygote, from which the embryo develops. The other sperm unites with the two nuclei located in a single cell at the center of the embryo sac. Together these nuclei form the triploid nucleus of the cell from which the endosperm develops. Double fertilization in this form is unique to the angiosperms. 花粉管通过花柱内的特殊组织朝向子房生长。到达胚珠后，花粉管进入其中的一个助细胞，该细 胞开始退化，使花粉管内的两个精子得以进入胚囊。这两个精子分别受精，其中一个与单倍体的卵细 胞结合形成二倍体的受精卵，开始胚胎发育。另外一个精子与两个中央细胞极核结合，形成一个三细 胞核的细胞，该细胞将发育成胚乳。被子植物的这种双受精在自然界是独一无二的。 Self-incompatibility（自交不亲和性） Self-incompatibility is a widespread mechanism in flowering plants that prevents self-fertilization and thus encourage outcrossing. In plants with SI, when a pollen grain produced in a plant reaches a stigma of the same plant or another plant with a similar genotype, the process of pollen germination, pollen tube growth, ovule fertilization, and embryo development is halted at one of its stages, and consequently no seeds are produced. 自交不亲和性是开花植物避免自体受精而支持远源杂交的一种广泛应用的机制。对于自交不亲和 的植物，当一种植物的花粉粒落到同种植物或者具有相似基因型的植物的柱头上时，花粉的萌发、花 粉管的生长、胚珠的受精、受精卵的发育等其中的某一过程将被中断，最终导致无法结实。 The self-incompatibility response is genetically controlled by a single genetic locus termed S, which has multiple alleles, and relies on a series of complex cellular interactions between the self-incompatible pollen and pistil. Differences in the proteins encoded by coding regions of the S-locus are thought to be the basis for the recongnition of incompatibility or compatibility. 遗传学上的自交不亲和性受一个具有复等位基因的 S 基因座控制，并依赖一系列雌雄细胞间的相 互作用而实现。S 基因编码的不同蛋白质是自交不亲和或亲和的识别基础。 There are two major types of self-incompatibility. gametophytic self-incompatibility(GSI) and sporophytic self-incompatibility (SSI). GSI is more common, existing in the families: Solanaceae, Rosaceae, Plantaginaceae, Fabaceae, Onagraceae, Campanulaceae, Papaveraceae and Poaceae.Two GSI mechanisms that have been well-studied rely on RNase and S–glycoprotein respectively. In this form of self-incompatibility, pollen is successful only when the genotype of the pollen does not match the genotype of the female (figure ). In many cases of GSI, the incompatible pollen tube is able to initiate growth through the style before it arrests
自交不亲和性可分为配子体型自交不亲和性(GSI)和孢子体型自交不亲和性(SSI)两类。GSI更为 普遍,属于此类的植物有茄科、蔷薇科、车前草科、豆科、柳叶菜科、桔梗科、罂粟科及禾本科等。 关于GSI的两种作用机制已被阐明,分别与核酸酶及S-糖蛋白有关。对于GSI的植物而言,只有当 花粉的基因型与卵细胞的基因型不同时传粉才能成功。许多GSI植物的花粉管在生长被阻断前在花柱 中可以进行短暂的伸长。 SSI was identified in the families of Brassicaceae. Asteraceae. Convolvulaceae Betulaceae, Caryophyllaceae, Sterculiaceae and Polemoniaceae. In SSl, rejection of self pollen is controlled by the diploid genotype of the anther( the sporophyte)in which it was created. Pollen grains can germinate and grow tubes only when they do not carry determinants that match the genotype of the female. The interaction occurs early in pollen-pistil interactions often blocks pollen hydration or pollen tube emergence at the stigma surface. 属于SSⅠ型的植物有十字花科、菊科、旋花科、桦木科、石竹科、梧桐科及花葱科等。SSI植物 对自身花粉的排斥是受它的二倍体花药(孢子)的基因型控制的。只有当花粉粒不含有可与雌细胞匹 配的基因型时其才可正常萌发并长出花粉管。自体花粉与雌蕊接触后的早期相互作用表现为在柱头表 面花粉水合化及花粉管的出现被阻碍 Various methods, such as: bud irradiation, delayed self-pollination, high temperature treatment, hormone application, induced polyploidy, are successfully employed to overcome self-incompatibility 许多方法可以打破自交不亲和性,如辐射花芽,延迟自花授粉,高温处理,应用激素,多倍体诱 导等 Summary(总结) In flowering plants, post-embryonic life is characterized by at least three distinct phases of shoot development-a juvenile vegetative phase, an adult vegetative phase and a reproductive phase. The primary while the former is reproductively incompetent. Environmental signals can induce floral initiation in competent plants. The two major signals for inducing flowering are light(photoperiod) and temperature (cold treatment ). Photoperiodism is the developmental responses of plants to the relative lengths of the light and dark periods. Plants are classified into three categories: short-day, long-day, or day-neutral, depending on their response to the day length for flowering. In photoperiodism, what plants measures is actually the length of dark period. Short-day plants flower when a critical dark length is exceeded. Flowering in ong-day plants requires a dark length that is less than the critical dark length. The photoperiodic stimulus in both LDPs and SDPs is perceived in leaves and induces a moving signal, called florigen, that moves through the phloem to the shoot apex, where it causes flowering. Plant growth hormones, especially the gibberellins, can also modify flowering in many plants. Vernalization refers to the promotion of flowering by low perature, It occurs most nly in winter annuals and biennials. The site of perception of vernalization is the shoot apical meristem. The four whorls of floral organs(sepals, petals, stamens, and arpels)are initiated after flowering has been induced. The ABC model explains how the floral organ identity genes control organ identity through the unique combinations of their products. The model posits that three types of genes, termed A, B, and C, regulate floral development. Type a genes control sepals and petals. Type B genes control petals and stamens. Stamens and captels are controlled by type C activity. The ABC model has recently been extended to become the aBCDE model by the inclusion of two other gene classes, namely D and E, which are involved in ovule development, and petal, stamen and carpel development, respectively. Following flower development, the next step in plant s reproductive cycle is the formation of gametes. The male gamete is produced via two mitotic divisions; resulting a vegetative cell and two sperm cells. Female gamete development occurs over two phases referred to as megasporogenesis
自交不亲和性可分为配子体型自交不亲和性(GSI)和孢子体型自交不亲和性(SSI)两类。GSI 更为 普遍，属于此类的植物有茄科、蔷薇科、车前草科、豆科、柳叶菜科、桔梗科、罂粟科及禾本科等。 关于 GSI 的两种作用机制已被阐明，分别与核酸酶及 S-糖蛋白有关。对于 GSI 的植物而言，只有当 花粉的基因型与卵细胞的基因型不同时传粉才能成功。许多 GSI 植物的花粉管在生长被阻断前在花柱 中可以进行短暂的伸长。 SSI was identified in the families of Brassicaceae, Asteraceae, Convolvulaceae, Betulaceae,Caryophyllaceae, Sterculiaceae and Polemoniaceae. In SSI, rejection of self pollen is controlled by the diploid genotype of the anther (the sporophyte) in which it was created. Pollen grains can germinate and grow tubes only when they do not carry determinants that match the genotype of the female. The interaction occurs early in pollen-pistil interactions often blocks pollen hydration or pollen tube emergence at the stigma surface. 属于 SSI 型的植物有十字花科、菊科、旋花科、桦木科、石竹科、梧桐科及花荵科等。SSI 植物 对自身花粉的排斥是受它的二倍体花药（孢子）的基因型控制的。只有当花粉粒不含有可与雌细胞匹 配的基因型时其才可正常萌发并长出花粉管。自体花粉与雌蕊接触后的早期相互作用表现为在柱头表 面花粉水合化及花粉管的出现被阻碍。 Various methods, such as: bud irradiation, delayed self-pollination, high temperature treatment, hormone application, induced polyploidy, are successfully employed to overcome self-incompatibility. 许多方法可以打破自交不亲和性，如辐射花芽，延迟自花授粉，高温处理，应用激素，多倍体诱 导等。 Summary（总结） In flowering plants, post-embryonic life is characterized by at least three distinct phases of shoot development – a juvenile vegetative phase, an adult vegetative phase and a reproductive phase. The primary distinction between the juvenile and the adult vegetative phases is that the latter is reproductively competent, while the former is reproductively incompetent. Environmental signals can induce floral initiation in competent plants. The two major signals for inducing flowering are light (photoperiod) and temperature (cold treatment). Photoperiodism is the developmental responses of plants to the relative lengths of the light and dark periods. Plants are classified into three categories: short-day, long-day, or day-neutral, depending on their response to the day length for flowering. In photoperiodism, what plants measures is actually the length of dark period. Short-day plants flower when a critical dark length is exceeded. Flowering in Long-day plants requires a dark length that is less than the critical dark length. The photoperiodic stimulus in both LDPs and SDPs is perceived in leaves and induces a moving signal, called florigen, that moves through the phloem to the shoot apex, where it causes flowering. Plant growth hormones, especially the gibberellins, can also modify flowering in many plants. Vernalization refers to the promotion of flowering by low temperature, it occurs most commonly in winter annuals and biennials. The site of perception of vernalization is the shoot apical meristem. The four whorls of floral organs (sepals, petals, stamens, and carpels) are initiated after flowering has been induced. The ABC model explains how the floral organ identity genes control organ identity through the unique combinations of their products. The model posits that three types of genes, termed A, B, and C, regulate floral development. Type A genes control sepals and petals. Type B genes control petals and stamens. Stamens and captels are controlled by type C activity. The ABC model has recently been extended to become the ABCDE model by the inclusion of two other gene classes, namely D and E, which are involved in ovule development, and petal, stamen and carpel development, respectively. Following flower development, the next step in plant’s reproductive cycle is the formation of gametes. The male gamete is produced via two mitotic divisions; resulting a vegetative cell and two sperm cells. Female gamete development occurs over two phases referred to as megasporogenesis