CHAPTER 9 



THE SYNTHESIS OF FLOWERING 

 HORMONE 



One of the most interesting aspects of the flowering process is the 

 synthesis of a chemical hormonal substance which will result in the 

 control of gene activity and the redirection of growth at the apical 

 tissues. Most of the other aspects of the flowering process (e.g. 

 timing and the pigment system) are quite closely related to other 

 phenomena in biology, and it may well be that synthesis of hormones 

 capable of directing diff'erentiation is also a general phenomenon, 

 but except for a few examples,!^ little is known about such things 

 compared to the other aspects. 



Evidences for The Flowering Hormone 



(3, 9, 14, 20, 21, 22, 25, 32, 38) 



As a matter of fact, we cannot be absolutely certain that a hormone 

 is involved in the flowering process. Such absolute certainty would 

 have to rest upon some understanding of its chemistry, and so far 

 attempts to isolate the elusive substance in a test tube have never 

 succeeded to the satisfaction of a majority of plant physiologists. 

 Nevertheless, three very compelling evidences for such a hormone are 

 presented below, and they allow us to go safely to the brink of 

 absolute certainty in acceptance of the flowering hormone concept. 



1" A similar situation, but one about which much more progress has been made 

 towards understanding, occurs in insects such as the silkworm. Metamorphosis 

 takes place in response to a specific hormone produced by the prothoracic glands. 

 During the very early stages of metamorphosis, a certain region of a large 

 chromosome found in the salivary gland cells enlarges, forming a "puff", while 

 another becomes smaller. It appears that one gene is being turned on while 

 another is being turned off as first steps in the morphogenesis which is about to 

 take place. Starting with 500 kg (more than half a ton!) of fresh silkworms, 

 workers in Tiibingen, Germany, isolated 25 mg of pure, crystalline hormone. 

 This material (called ecdysone) not only caused metamorphosis, but the significant 

 changes on the chromosome could be observed within 2 hr after its apphcation! 

 (See U. Clever and P. Karlson, 1960, Experimental Cell Research 20: 623-626). 



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