Part 2 Long-Distance Transport o 2.1 Overview of diffusive and convective transport in plants o 2. 1. 1 Diffusion and convection are the basis for solute transport o Diffusion: An independent movement of molecules driven by a concentration gradient Convective transport: Bulk flow of solution driven by a pressure gradient
Part 2 Long-Distance Transport ⚫ 2.1 Overview of diffusive and convective transport in plants ⚫ 2.1.1 Diffusion and convection are the basis for solute transport. ⚫ Diffusion: An independent movement of molecules driven by a concentration gradient. ⚫ Convective transport: Bulk flow of solution driven by a pressure gradient
2.1.2 Water and solutes can move from cell to cell along either of two parallel aqueous pathways Cytosol Plasmodesmata Vacuole Cell wall Intercellular space
2.1.2 Water and solutes can move from cell to cell along either of two parallel aqueous pathways
2.1.3 The concept of water potential provides a thermodynamic basis for the study of water movement Equation 2. 1.3 ●V=Vb+。+vg+V ● w water potentia ppressure potential o Vs: solute(osmotic) potential Vg: gravitational potential Vm: matrix potential
2.1.3 The concept of water potential provides a thermodynamic basis for the study of water movement. ⚫ Equation 2.1.3 ⚫ ψw=ψp+ψs+ψg+ψm ⚫ ψw :water potential ⚫ Ψp : pressure potential ⚫ ψs : solute (osmotic) potential ⚫ ψg : gravitational potential ⚫ ψm: matrix potential
o 2. 1. 4 Concentration gradients over short distances tend to drive both diffusion and osmotically generated pressure flow(OGPF)
⚫ 2.1.4 Concentration gradients over short distances tend to drive both diffusion and osmotically generated pressure flow (OGPF)
A)Hydraulically C)Conducting cells olated cell 兀P asi ng P? 兀,P ecreasll 吗g从 (B)Hydraulically linked cells 兀,P termediate 兀P high 兀 intermediate 兀 lo 兀,P Solutes low Water
2.2 Comparison of xylem and phloem transport o 2. 2. 1 Some generalizations and useful comparisons can be o made about the composition of xylem and phloem exudates
2.2 Comparison of xylem and phloem transport ⚫ 2.2.1 Some generalizations and useful comparisons can be ⚫ made about the composition of xylem and phloem exudates
Xylem and phloem transport streams can be sampled by several methods (A) (B) Retaining C 8 tube Silicone rubber Stem Vacuum Pressure chamber Pot
Xylem and phloem transport streams can be sampled by several methods
A) 1 mm
Table 2.2 General characteristics of Xylem and phloem exudates Phloem exudates Xylem exudates Sugars 100-300g ● Amino acids5-40g1 01-2g Inorganics 0.2-4gl-1 ● otal solutes 250-1200mmol kg 10-100mmol kg ●pH p 7.3-8.0 5.0-6.5
Table 2.2 General characteristics of xylem and phloem exudates ⚫ Phloem exudates Xylem exudates ⚫ Sugars 100-300gl-1 0gl-1 ⚫ Amino acids 5-40gl-1 0.1-2gl-1 ⚫ Inorganics 1-5gl-1 0.2-4gl-1 ⚫ Total solutes 250-1200mmol kg-1 10-100mmol kg-1 ⚫ pH 7.3-8.0 5.0-6.5
