Flowering hormone

A postulated flowering hormone, florigen, has not been isolated 366 Flowering seems to be controlled by a variety of different hormonal effects.369 Jasmonic... 

Can we say anything more precise about the function of gibberellins in flower formation Most plant biologists feel that flower formation is controlled by specific, hormone-like substances, so-called flower hormones. Attempts at ex-... 

Facilitated diffusion, 247 Fate maps, 101, 102 Flowering hormone (florigen), 231, 232... 

Within less than two decades after the discovery of photoperiodism in 1920, the hypothesis developed that one or more specific flowering hormones are responsible for floral initiation (23,36-39). 

The classic P. are Auxins (see), Cibberellins (see), Antheridiogen (see), Cytokinins (see), Abscisic acid (see). Flowering hormone (see) and Fruit ripening hormone (see). 

The light stimulus is received by the leaf but the pivotal event takes place in the shoot meristem. This finding alone suggests the existence of a flowering hormone even in plants that are dependent on day length, which migrates from the leaves to the apical meristem. Another experi-... 

In view of apparently convincing indications of the existence of a flowering hormone it is reasonable to ask whether this substance has... 

Fig. 241. Evidence for the migration of the flowering hormone from the leaf to the apical meristem in Pharbitis nil. The test for migration consisted of the removal of the cotyledons at different tirnes after the beginning of the inductive dark period. Pharbitis is a short day plant in which even the cotyledons can be induced (modified from Zeevaart as presented in Beermann et al. 1966).

Thus, gibberellins can substitute for either the effect of cold or the long day as shown in point 2 but seldom both at the same time. Usually the short day cannot be replaced by gibberellins. We can also exclude with certainty the possibility that the gibberellins might be identical with the much sought after flowering hormone. The reasons for this are ... 

The administration of antimetabolities of transcription and translation inhibits the induction of flowering in plants that are dependent on the length of day just as it does in those requiring vernalization. The inhibitors produce their effect partly in the leaf, partly in the shoot meristem. As far as their activity in the leaf is concerned, it may be assumed that they impair the activity of the genes that are involved in the synthesis of the flowering hormone. At least in part their effectiveness in the shoot meristem has to do with subsequent flower differentiation rather than with flower induction the activity of the genes for flower differentiation is interferred with. 

Traumatic acid was proposed in some early works as "florigen", the plant flowering hormone. The new literature data revealed the complex picture of flowering induction. At the same time, if not the sole, traumatic acid is one of the flowering initiation factors [1]. Recently the jasmonic acid derivative, 12-(5 - 8-D-glucopyranosyloxy)-jasmonate ... 

Is the list of interacting plant growth hormones complete Almost certainly it is not. Only very recently abscisic acid (Fig. 9.8), which is involved in leaf and fruit abscission and in bud dormancy in woody plants, was discovered. There is considerable evidence for the involvement of a flowering hormone (florigen) in the induction of flower initiation and for the involvement of additional hormones in the functioning of vascular cambia. 

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