Effect of Light Intensity on the Lipid Composition of Euglena gracilis*

Cultures of the phytoflagellate Eugfena gracitis were grown at light intensities varying from 120 to 610 footcandles. With increasing light intensity, the content of chlorophyll and of total lipids declined, whereas the percentage of 4,7, 10,13-hexadecatetraenoic acid and of ar-linolenic acid rose sharply. The increased content of the two polyunsaturated fatty acids was even more pronounced in the chloroplast lipids and was greatest when the monogalactosyl glyceride fraction was analyzed separately. In EugZena, in spinach, and in Chlorella vulgaris all of the CM polyunsaturated acids and the major portion of a-linolenic acid are localized in the monogalactosyl glyceride fraction. The finding that Hill reaction activity and lipid unsaturation show the same response to changes in light intensity is discussed with respect to the possible role of polyunsaturated fatty acids in photosynthetic oxygen evolution.