SECRETARY'S REPORT 91 



Studies involving the reversal of red light induction by far-red 

 radiation at 25° C. show that there must be a time delay interposed be- 

 tween red and far-red light treatments before maximum reversal can 

 occur in hypocotyl hook of beans, in Arahidopsis seed germination, and 

 in leaf disc expansion. Lettuce seed germination and reversal by far- 

 red light at 25° C. does not require a time delay between light treat- 

 ments to obtain maximmn efficiency in reversal. However, when the 

 experiments are conducted at 2° C, a requirement for a time delay 

 between light treatments is manifested. 



The influence of such exogenous and endogenous factors as substrate, 

 age, ionizing radiation, and particularly the red, far-red photomor- 

 phogenic pigment system on the development of the chlorophyll-syn- 

 thesizing mechanism in etiolated leaf tissue, have all been previously 

 demonstrated in this laboratory. The apparent effect of the media- 

 tion of a photomorphogenic receptor on chlorophyll s^mthesis implies 

 a radiant energy stimulation of biochemical systems associated with 

 either pigment precursor synthesis and/or exo- or endoplastid enzyme 

 systems, resulting in observable gross morphological proplastid 

 changes. 



Light-microscope examination of com leaf tissue macerates have 

 revealed both biochemical and morphological changes within the de- 

 veloping proplastid. In the dark-grown seedling, proplastids con- 

 tinue to enlarge slowly and accumulate considerable starch internally 

 during the first several days of growth; a short pretreatment with 

 white light, on the other hand, induces an observable degradation of 

 accumulated starch, as well as considerable enlargement in proplastid 

 size. These light-induced proplastid changes can be correlated with 

 photomorphogenic leaf responses such as elongation and expansion. 



PUBUCATIONS 



Price, Leonard, and Klein, William H. Red, far-red response and chlorophyll 



synthesis. Plant Physiol., vol. 36, pp. 733-735, 1961. 

 Shropshire, Walter, Jr. The lens effect and phototropism of Phycomyces. 



Journ. Gen, Physiol., vol. 45, pp. 949-958, 1962. 

 Maegulies, Maurice M. The effect of chloramphenicol on the light dependent 



development of seedlings of Phaseolus vulgaris var. Black Valentine, with 



particular reference to the development of photosynthetic activity. Plant 



Physiol., vol. 37, pp. 473-480, 1962. 



OTHER ACTIVITIES 



The division was represented during this year at various confer- 

 ences of scientists and meetings of scientific societies. Drs. L. 

 Loercher and W. H. Klein were invited participants in the Gordon 

 Research Conferences on Biochemistry and Agriculture, Tilton, N.H., 



