SUMMARY: Chlorophyll formation in non-growing etiolated cells of var. is inhibited by certain antimetabolite analogues of purines, pyrimidines and amino acids. The inhibitory effects of bromo- and nitro-uracils were annulled by uracil and thymine; those of fluoro- and thio-urneils were not. Ethionine inhibition was completely annulled by methionine. All the base analogues were more inhibitory for the dark growth of the alga than in the light and an adaptation to these antimetabolites was apparent during growth. The growth inhibitory effects of some of these base analogues was annulled by several Krebs's cycle intermediates; the latter in themselves stimulated growth of photosynthesizing euglenas although they were not utilized in the dark with any degree of efficiency. Long-term exposure of non-proliferating euglenas, green or etiolated, to 5-fluoro-uracil had a profound effect on the chloroplast integrity of the organisms. Such euglenas on further subculture in an adequate growth medium were permanently bleached. The effect of 5-bromo-uracil, though similar, was less marked.


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