Perception of Light - Floral Induction

Stimulus Leaves are found to be organs that perceive light 'stimulus', K.C. Hamner and J. Bonner showed in 1938 that even if all the leaves are stripped in a cocklebur plant and only as little as one eighth of a leaf is allowed to stay on the plant would flower in response to one short day exposure. The 'stimulus' continues to stay even when the plants are brought under non-inductive conditions. Moreover, this stimulus can be 'transferred' to another plant through grafting. Chailakhyan's classical grafting experiment using short day Nicotiana species and long day Nicotiana species clearly established this point. He suggested for the existence of 'Florigen'-a flowering hormone. So far it has not been possible to isolate the flowering hormone, although there is evidence to suggest that it consist of

• Anthesin
• Gibberellin

For the present flowering may be considered to be controlled by the balance between GA, cytokinin and ABA.