Florigen hypothesis 2 Phytochrome hypothesis(光敏色素假说) Phytochrome activates specific gene expression 3. Carbon and nitrogen ratio hypothesis(碳氮 比假说) C/N high: flowering C/N low: non-flowering or delayed flowering2. Phytochrome hypothesis （光敏色素假说） Phytochrome activates specific gene expression 3. Carbon and nitrogen ratio hypothesis (碳氮 比假说） C/N high: flowering C/N low: non-flowering or delayed flowering Florigen hypothesis