PHOTOREACTION AND ASSOCIATED CHANGES 437 



anthocyanin formation in cotyledons and hypocotyls of red cabbage 

 seedlings (Siegelman and Hendricks, 1957), the concave side of 

 isolated plumular hooks (Klein et aL, 1956), sections of A vena 

 coleoptiles (Liverman and Bonner, 1953), discs from primary leaves 

 of bean plants (Miller, 1952; Liverman et aL, 1955), and the region 

 near the micropile of germinating seed (Toole et al., 1956; Koller, 

 1956). Translocation of some type-controlling response is clearly indi- 

 cated by the absence of a phototropic response of dark-grown seedlings 

 to unilateral irradiation with red light. We have repeatedly been enticed 

 into looking for a phototropic response with red light and have been 

 encouraged by initial indications which have always been eliminated 

 by rigorous exclusion of blue light. 



CONCLUSION 



The reaction controlling photomorphogenic responses is photore- 

 versible. It is probably a photohydrogenation with the quantum effi- 

 ciencies being determined by the ratios of the oxidants and reductants. 

 The molar absorptior) coefficients of the red- and far-red-absorbing 

 forms of the responsive pigment are 2.0 X 10\ Physiological re- 

 sponse is associated with the far-red-absorbing form of the pigment. 

 The reaction is probably ubiquitous for seed plants but need not be 

 recognizable for all types of responses in a given plant. 



REFERENCES 



Borthwick, H. A., S. B. Hendricks, E. H. Toole, and V. K. Toole. 1954. Action 



of light on lettuce seed germination. Botan. Gaz., 115, 205-25. 

 Downs, R. J., S. B. Hendricks, and H. A. Borthwick. 1957. Photoreversible 



control of elongation of pinto beans and other plants under normal conditions 



of growth. Botan. Gaz., 118, 199-208. 

 Haxo, P., C. O'h Eocha. and P. Norris. 1955. Comparative studies of chroma- 



tographically separated phycoerythrins and phycocyanins. Arch. BiocJiem., 



54, 162-73. 

 Hendricks, S. B., H. A. Borthwick, and R. J. Downs. 1956. Pigment conversion 



in formative reaction of plants to radiation. Proc. Natl. Acad. Sci. U. S., 42, 



19-26. 

 Klein, W. H., R. B. Withrow, and V. B. Elstad. 1956. Response of the hypocotyl 



hook of bean seedlings to radiant energy and other factors. Plant Physiol., 



31, 289-94. 



