Physiological Action of Gibberelli?! 



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AA + K3 



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GA + K3 



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CONCN., lAA, MG./L. 



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CONCN.,GA, MG./L. 



Fig. 4. Interaction of 2-methyl-l,4-dihydronaphthoquinone (K3) with lAA and 

 gibberellic acid in the elongation of pea stem sections (13). 



The series of experiments so far presented may suggest that the 

 reaction sequence caused in tissues by gibberellin differs from that 

 caused by auxin, or more specifically, that probably the physiological 

 receptor for gibberellin is different from that for auxin. Curtis (6) 

 found that, using Phaseolus vulgaris 'Black Valentine,' the inhibitory 

 effect of the filtrate from the culture medium of Aspergillus niger 

 could be reversed by GA but not by lAA, and inferred that GA 

 operates through a system different from that of lAA. 



The complete inhibition of the GA-induced elongation by anti- 

 auxins, as described above, was reversed by the concomitant addi- 

 tion of lAA or indole-3-acetamide. This reversing effect of lAA, how- 

 ever, could not be substituted by other growth factors such as amino 

 acids (L-leucine, L-histidine, tyrosine, L-phenylalanine, L-methionine, 

 DL-threonine, L-hydroxyproline, DL-iso-leucine, aspartic acid, dl- 

 ornithine, L-arginine, L-alanine, L-proline, glycine, L-lysine, DL-va- 

 line, L-glutamic acid), vitamins (thiamine, riboflavin, ascorbic acid, 

 vitamin E, vitamin K, pyridoxine, pantothenic acid, folic acid, nicotin- 

 amide, vitamin B^g), diphenylurea, biotin, casein hydrolysate, and 

 yeast extract. Hence the effect of GA seems to be caused by some 

 process involving auxin, as already suggested by Brian and Hemming 

 (4), Kuse (15), and Galston and Warburg (8). 



On the other hand, Applegate (2), using seedlings of Zinnia ele- 



