EFFECT OF WHITE-LIGHT ON CELL EXPANSION AND LIPID-METABOLISM IN SUNFLOWER COTYLEDONS

The growth of the cotyledons of etiolated sunflower seedlings (Heliant hus annuus L.) is promoted by white light (WL). This process is due to an enhancement in the rate of cell expansion. The degradation of lipi d reserves is stimulated by WL. An analysis of different fractions of homogenized cotyledons revealed that the enzyme lipase is exclusively localized in the oil bodies (oleosomes) of the cells. In WL-treated se edlings, lipolytic activity was higher than in dark-grown controls. In contrast, the specific activity of isocitrate lyase, a key enzyme of the glyoxylate cycle, was reduced upon exposure to WL. The results are discussed with respect to the relationship between sugar accumulation and cell expansion in the cotyledons and the hypocotyl of the develop ing sunflower seedling.