Influence of Gibberellic Acid on lAA Disappearance 



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lAA SPARING, ABSORPTION UNITS /3 HRS. 



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Fig. 6. Average rate of indole-3-acetic acid (lAA) destruction over the first 3 hr. 

 period (vertical axis) plotted against the difference between the average rates of 

 destruction over the same period in the presence or absence of gibberellic acid 

 (horizontal axis). Curves (a) and (c) represent experiments (1957) with stem sections 

 from light-grown material; curve (b) represents section experiments (1958) from 

 dark-grown material; curves (d) and (e) represent experiments (1958) with apical 

 tissues. Experiments shown in (a) were carried out with "Lincoln' peas; experiments 

 shown in curves (b) to (e) with 'Progress No. 9' peas. Experiments of curves (d) and 

 (e) were carried out with light- and dark-grown material, respectively. The letter 

 over each point indicates whether the experiment was conducted in light (L) or in 

 darkness (D). 



ond factor was the differing amounts of leaf tissue removed when 

 apical tissues were being prepared for excision. Other factors may be 

 associated with distinbances resulting from excision, a point discussed 

 by Brian and Hemming (5). 



As the present data are consistent with an inhibitor interpretation 

 in the scheme of Figure 5 (top), it is profitable to consider this system 

 further. The formation of / is influenced by a red/near infrared re- 

 action, and it is constructive to consider the literature. Johnson and 

 Liverman (13) state that near infrared-induced dormancy in summer- 

 grown tomatoes can be reversed by GA producing a striking effect on 

 stem elongation; the same dormancy can be broken also by red light, 

 auxins, or cool weather (19). Lockhart (22) notes that the GA-in- 

 duced elongation of dwarf bean seedlings may be markedly enhanced 

 by a 2 to 5 min. exposure of the plants to red light. This effect may 

 be reversed by subsequent exposure of the plants to near infrared 



