652 P. W. Brian and H. G. Hemming 



the response to GA, is dependent on high-intensity light. This can- 

 not be explained purely in terms of photosynthetic formation of su- 

 crose. This effect of light appears to be blocked by the inhibitors 

 AZS and DON, which are known to affect the pattern of photosyn- 

 thetic COo-fixation in algae in pathways other than those concerned 

 in sucrose formation. They also block the response of sections to GA. 

 From what is known of their mode of action in other systems, it can 

 be suggested that the effect of light on green section growth is per- 

 haps concerned with biosynthesis of purines or amino acids, path- 

 ways blocked by AZS or DON by their effect on transamination reac- 

 tions. In this connection it is interesting to note (2) that treatment of 

 germinating barley grain with gibberellic acid results in considerable 

 increases in transaminase content. 



Starvation of sections before use has little subsequent effect on ex- 

 tension if sucrose is supplied. Such sections no longer respond to ex- 

 ogenous GA, and it seems probable that they have been depleted of 

 some other substance necessary for the response to GA. 



It has already been suggested (4, 8) that other factors besides auxin 

 are involved in stem extension responses to GA. The results reported 

 above offer further support for this view. 



ACKNOWLEDGMENT 



We are indebted to Parke, Davis R: Co., Detroit, for the gift of 

 samples of azaserine and 6-diazo-5-oxo-L-norIeucine. 



LITERATURE CITED 



1. Barker, S. A., Bassham, J. A., Calvin, M., and Quarck, U. C. Sites of azaserine 

 inhibition during photosynthesis by Scenedesmus. Jour. Amer. Chem. Soc. 78: 

 4632^635. 1956. 



2. Bergqvist, G., StensgSrd, A.M., and Nielsen, N. The influence of gibberellic 

 acid on the transaminase content of germinating barley seeds. Physiol. Plant. 

 12: 386-389. 1959. 



3. Brian, P. W., and Hemming, H. G. The effect of gibberellic acid on shoot 

 growth of pea seedlings. Physiol. Plant. 8: 669-681. 1955. 



4. , and Hemming, H. G. Complementary action of gibberellic acid and 



auxins in pea internode extension. Ann. Bot. II. 22: 1-17. 1958. 



5. Clarke, D. A., Reilly, H. C, and Stock, C. C. A comparative study of 6-diazo- 

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 Chemother. 7: 653-671. 1957. 



6. Galston, A. W. Studies on indoleacctic acid oxidase and its inhibitor in light- 

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7. , and Baker, R. S. Studies on the physiology of light action. I\'. Light 



enhancement of auxin induced growth in green pc.is. Plant Phvsiol. 26: 

 311-317. 1951. 



8. . and Warburg, H. .\n analysis of auxin-gibberellin interaction in pea 



stem tissue. Plant Pliysiol. 31: 16-22. 1959. 



