Relationship Between Stimuli, IAA and Growth

Abstract

“Ohne Wuchsstoff kein Wachstum”: without auxin no growth [e.g. 32]. A particularly valuable test of this dictum was made by Dolk [e.g. 32] who showed that double decapitation of the A vena coleoptile stopped growth. Growth could then be partially restored by means of applied auxin. As beautiful as this experiment is, it is important to test the conclusion by determining if there is a quantitative relationship between endogenous IAA and growth. The relationship between numbers of coleoptile tips placed on a receiver block and growth induced by applying the receiver block to shoot stumps does not establish this relationship, since the tip supplies both free IAA and IAA derived from the seed auxin precursor [2, 23] presumably by hydrolysis of bound IAA [28]. Thus, we wish to make a quantitative test of the dictum by determining the relationship between growth rate and amount of free IAA. We wish further to determine the effect of various environmental stimuli on the amount of IAA in the tissue. In that manner we can determine the extent to which the transduction of environmental stimuli is accomplished by varying the amount of free IAA in the experimental system. Lastly, we wish to understand how the plant can so precisely regulate its IAA levels so as to have more IAA on one side than on the other of a tropically stimulated stem. Lastly, we wish to understand tropic curvatures in terms of IAA metabolism and transport.