Effect of white light on cell expansion and lipid netabolism in sunflower cotyledons

Summary The growth of the cotyledons of etiolated sunflower seedlings ( Helianthus annuus L.) is promoted by white light (WL). This process is due to an enhancement in the rate of cell expansion. The degradation of lipid 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 seedlings, 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 developing sunflower seedling.