CHAPTER 10 



THE MOVEMENT AND ACTION OF 

 THE FLOWERING HORMONE 



Some of the topics which relate to processes taking place subsequent 

 to synthesis of flowering hormone have already been alluded to in 

 previous chapters. Thus translocation of the flowering hormone and 

 its activity in causing the bud to become reproductive have been 

 mentioned a number of times. An interesting part of the flowering 

 process which has not been discussed in any detail, however, concerns 

 the status and activity of the flowering hormone after it is synthesized 

 during the dark period. We will discuss five aspects of this topic. 



Translocation Rate of the Flowering Hormone 



(3, 32, 38) 



As shown in Fig. 9-1, measurement of the rate of flowering 

 hormone movement out of the leaf can be made by defoliating 

 different groups of plants at various time intervals following an 

 inductive dark period. Experiments such as this have indicated that 

 movement out of the leaf may begin within 2 to 4 hr after plants are 

 moved from darkness to sunlight; that this period of translocation 

 often requires anywhere from 12 hr to 2 to 3 days; and that the rate 

 of movement is probably rather slow. Figure 10-1 shows that the 

 rate is highly temperature dependent, as would be expected for 

 movement in the phloem. 



A defoliation experiment is, not however, a good way to measure 

 the linear rate of flowering hormone movement, since we are not 

 making the measurement over a linear distance. We are only 

 determining a portion of the hormone which has entered the stem 

 at any given time interval, providing there is sufficient to cause 

 flower development. Other slightly more direct methods have been 

 used to measure rate of movement of the hormone over a linear 

 distance. One way is to utilize two-branched plants, in which one 



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