Gibberellin flowering

Abscisin II is a plant hormone which accelerates (in interaction with other factors) the abscission of young fruit of cotton. It can accelerate leaf senescence and abscission, inhibit flowering, and induce dormancy. It has no activity as an auxin or a gibberellin but counteracts the action of these hormones. Abscisin II was isolated from the acid fraction of an acetone extract by chromatographic procedures guided by an abscission bioassay. Its structure was determined from elemental analysis, mass spectrum, and infrared, ultraviolet, and nuclear magnetic resonance spectra. Comparisons of these with relevant spectra of isophorone and sorbic acid derivatives confirmed that abscisin II is 3-methyl-5-(1-hydroxy-4-oxo-2, 6, 6-trimethyl-2-cyclohexen-l-yl)-c s, trans-2, 4-pen-tadienoic acid. This carbon skeleton is shown to be unique among the known sesquiterpenes. 

WEST AND REILLY Gibberellins from Flowering Plants... 

West, C., Chemistry of Gibberellins from Flowering Plants in Plant Growth Regulation (Proc. of IVth International Conf. on Plant Growth Regulation), Iowa State University Press, Ames, Iowa, in press. 

The discovery of the effects of gibberellin on flower formation is closely linked 1 with older studies on the physiology of this process, particularly its regulation by certain external or environmental factors. 

Flower formation is usually obtained only after repeated applications of relatively substantial gibberellin doses. In lettuce, two treatments of 20 / g. each,... 

Figure 1. Effect of gibberellin on flowering in carrot (variety Early French Forcing), a cold-requiring plant (24)...

Most cold-dependent plants also possess a long-day requirement. The gibberellin treatment of these plants was usually conducted under long-day conditions, so that only the temperature-controlled block to flower formation was present. If the treatment was given under short-day conditions, only stem elongation was obtained it is evidently difficult to overcome the simultaneous presence of two blocks to flower formation. 

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-... 

The precise function of gibberellin in flower formation is by no means clear and may be indirect in nature. On the other hand, gibberellins are the first... 

Gibberellin Modification of Flower Sex Expression in Cucumis sativus L... 

Flower sex expression of cucumbers can be modified by treating seedlings with several growthregulating substances With the exception of gibberellin, chemicals tend to reduce the number, or suppress the development, of staminate flowers, and increase the number or accelerate the development of pistillate flowers Gibberellin, in contrast, increases the number of staminate flowers in monoecious cucumbers and results in the formation of staminate flowers on gynoecious cucumbers which otherwise would produce only pistillate flowers In promotive effects on staminate flower formation and vegetative extension, GA4 is approximately tenfold more active than GA3 ... 

Table II. Effect of Photoperiod and Gibberellin A3 on Flowering of Cucumis sativus L., var. Burpee Hybrid...

Studies reported herein are primarily concerned with the effects of gibberellin in extending the staminate stage of monoecious cucumbers and with the formation of staminate flowers on gynoecious cucumbers. 

Galun (8) has recently reported similar results for monoecious cucumbers differing in the normal duration of the staminate stage. He demonstrated a close relationship between gibberellin-induced vegetative elongation and modification of flower sex expression (8). 

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