PRINCIPLES OF FLOWER FORMATION

An attempt is made to synthesize the mechanisms of flower formation of all seed plants, based on literature and own experience, especially on the concept that "flower-forming genes" are periodically inactivated and activated. Five partial processes in the "floral chain" are distinguished:

1. In vegetative plants floral-hormone forming genes are inactivated by an immobile blocking, occurring in different gene-determined intensities. Deblocking takes place by external factors, light, temperature, chemicals. After deblocking, the specific floral-hormone forming DNA is activated and forms specific RNA. Neutral plants have no blocking.
2. Floral hormone(s) is (are) formed via the specific RNA. Recent evidence (Bernier, 1976) shows that a floral hormone may consist of more than one component, that one of them may be a cytokinin, that in different plants different floral hormones or combinations of floral hormones may occur.
3. Besides the immobile blocking or inhibition sub 1, mobile floral inhibitors may be formed by genic action. In vegetative plants the inhibitor genes are active. Floral-hormone deblocking factors may block the inhibitor genes, but already formed inhibitors remain active. Abscisic acid may act as an inhibitor. Flower formation results from a competition between floral hormone(s) and inhibitor(s).
4. Floral hormones move upwards and downwards from leaves to apices through the phloem. Their movement may be hampered by the mass flow of assimilates and perhaps by inhibitors.
5. Flower formation results from an activation of floral genes in an apex ("evocation") by deblocking through floral hormone(s) and external factors.

A tentative scheme on the last page shows the mutual relationships of these partial processes.