SECRETARY'S REPORT 175 



fraction. A number of sugars and neuraminic acids were demon- 

 strated to be bound to the EN A. 



The morphological development of plastids in the presence of a 

 carbohydrate substrate has been demonstrated to be controlled by the 

 phytochrome pigment system which is photosensitive to red and far- 

 red radiant energy. Microscopic examinations of leaf preparations 

 sliow a red light-induced disappearance of starch from within young 

 etiolated plastids. This observation has been substantiated by bio- 

 chemical analysis which also indicated that starch degradation was 

 preceded by a similar loss in total soluble sugars. In addition, these 

 changes, which are appreciable in 6 hours and maximal in 12 hours fol- 

 lowing a 3-minute exposure to light, correlate with the pronounced 

 photomorphogenic leaf expansion. Studies of the kinetics of these 

 changes, of temperature sensitivity and energy requirements for in- 

 duction and reversal, have been completed as a necessary preliminary 

 to an intensive study of the enzyme systems involved. 



Attempts to correlate physiological responses in a number of tissues 

 to reported in vivo measurements of phytochrome concentrations have 

 led to the conclusion that a simple one-pigment system appears to be 

 inadequate in explaining the observed results. A far-red dose re- 

 sponse curve was determined immediately after, and 1^^ hours after 

 red induction. The data show a significant increase in sensitivity to 

 far-red after 11/^ hours in both lettuce seed germination and bean hy- 

 pocotyl hook opening. It was also observed that complete reversal of 

 the induced response can be obtained with sufficiently large amomits 

 of far-red energy from 2^ hours to 4% hours after induction for both 

 lettuce and bean. Further, there is significant reversal of the red 

 induction for at least a 10-hour period in both. 



Experiments using Avena mesocotyl inhibition in wliich non- 

 inhibitory pretreatments of red irradiation were given 24 hours prior 

 to inhibitory red treatments did not produce any change in sensitivity. 

 The published in vivo measurements indicate that such pretreatments 

 should have significantly reduced the level of phytochrome so that the 

 sensitivity should have changed. Also, experiments in which red 

 treatments were divided into two doses separated by 4-hour dark inter- 

 vals, or given as one continuous dose, showed marked differences in 

 the sensitivity to far-red reversal. These data do not fit reasonably 

 with a single pigment system. 



Many biological responses, such as flowering, pigment synthesis, 

 seed germination, stem elongation, and leaf expansion are controlled 

 by photochemical reactions initiated by various portions of the visible 

 spectrum. In a program of study never previously undertaken an)'^- 

 where, measurements of specific spectral regions of sim and sky radia- 



