Effect of Light on Glucose Utilization by Euglena gracilis

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Abstract
The effect of light on glucose consumption by wild-type E. gracilis Z. and mutant cells was studied. When dark- or light-grown wild-type cells are transferred from a medium containing sodium butyrate as the only C source to a glucose-containing medium, glucose consumption is blocked for 6-7 days when cultures are incubated under a light intensity of at least 600 lx. During this time cells multiply at the same rate as controls kept on media devoid of any utilizable organic C source. This light-induced inhibition of glucose consumption and of growth on glucose-containing medium is not related to photosynthesis since: glucose consumption is inhibited by light intensities much lower than those required for high phototrophic growth; the inhibition of photosynthesis by 3-(3,4-dichlorophenyl)-1,1-dimethylurea does not overcome the inhibition of glucose consumption; and nonphototrophic-growing mutants also show light-induced inhibition of glucose consumption and of growth on glucose-containing medium. This inhibition of growth by light might be explained by modification in the permeability of the cellular membrane.