156 PHOTOCONTROL OF GROWTH 



leaves from light to dark results in a temporary rise in inhibitor, fol- 

 lowed by a fall. 



4. The quantity of inhibitor in young leaves of Alaska (tall) pea 

 plants greatly exceeds that in analogous portions of Laurel (dwarf) 

 pea plants. 



5. Treatment of intact Laurel or Alaska pea plants with gibberellic 

 acid (ca. 10"^M) resuks in an elevation of inhibitor content in the 

 young leaflets. Similar results, though not so marked, can be obtained 

 by application of GA to excised stem or leaflet tissue. 



6. Both the lAA oxidase inhibitor and cofactor (from which the 

 inhibitor may be made by a photoreaction) have been partially puri- 

 fied by solvent techniques and chromatography. The cofactor has been 

 resolved into two fractions, neither of which is active alone. 



7. The studies are being pursued in the hope that an understanding 

 of the nature of the inhibitor and of the mechanism of the light control 

 of its synthesis may shed some light on the intermediary biochemistry 

 of photomorphogenesis. 



REFERENCES 



Brian, P. W., and H. G. Hemming. 1955. The effect of gibberellic acid on 

 shoot growth of pea seedlings. Physiol. Plantarum, 8, 669-81. 



Galston,"A. W., and R. S. Baker. 1951. Studies on the physiology of light 

 action. III. Light activation of a flavoprotein enzyme by reversal of a naturally 

 occurring inhibition. Am. J. Botany, 38, 190-95. 



Galston, A. W., and L. Y. Dalberg. 1954. The adaptive formation and physio- 

 logical significance of indoleacetic acid oxidase. Am. J. Botany, 41, 373-80. 



Goldacre, P. L., A. W. Galston, and R. L. Weintraub. 1953. The effect of sub- 

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Kenten, R. H. 1955. The oxidation of indolyl-3-acetic acid by waxpod bean root 

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Mohr, H. 1957. Der Einfluss monochromatischer Strahlung auf das Langen- 

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Phinney, B. O. 1956. Growth response of single-gene dwarf mutants in maize to 

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