Lipolytic and Glyoxysomal Enzyme Activities in Cotyledons of Ripening and Germinating Sunflower (Helianthus annuus L.) Seeds

Abstract

Summary In cotyledons of sunflower (Helianthus annuus L.) seeds glyoxysomal enzyme activities were shown to develop already during seed maturation. Glyoxysomes isolated from cotyledons 30 d after anthesis exhibited activities of monoacylglycerol lipase, hydroxyacyl-CoA dehydrogenase, catalase, and malate synthase, while apparent isocitrate lyase activity could be measured only in the supernatant fluid of the sucrose density gradients yet not in the crude homogenates. This indicates the presence of a probably unspecific inhibitor especially since glyoxysomes from cotyledons 40 d after anthesis showed isocitrate lyase activity although still no activity could be detected in the crude homogenates. After dehydration of the mature seeds a glyoxysomal fraction could not be isolated which presumably is due to damage of the organelles by the strong forces required for tissue disintegration, for low activities of all but one glyoxysomal enzyme activities measured were present in the crude homogenates. Comparison of glyoxysomes from maturing seeds to those from germinating seeds revealed, in contrast to earlier reports in the literature, that during seed ripening low but substantial activities of all key enzymes for glyoxysomes are present in the organelles. It is suggested that these glyoxysomes function as intermediate forms immediately after seed imbibition and start of germination until the pleomorphic population of germination related glyoxysomes is developed.