REGULATION OF ELONGASE ACTIVITY BY ABSCISIC-ACID AND TEMPERATURE IN MICROSPORE-DERIVED EMBRYOS OF OILSEED RAPE (BRASSICA-NAPUS)

Growth temperature and ABA both affect the level of erucic acid (22:1) in microspore-derived embryos (MDEs) of oilseed rape. We have previou sly shown that these stimuli act independently. In the present study w e investigated the effects of growth temperature (15 vs 25 degrees C) and ABA (0 vs 5 mu M) on the characteristics and activity of the elong ase complex, the enzymes synthesising 22:1. Due to inhibition by the s ubstrate oleoyl-CoA at low concentrations (< 10 mu M) it was not possi ble to determine values for K-m and V-max. Elongase activities from pr eparations extracted from MDEs grown under different conditions showed an optimum temperature higher than 30 degrees C, with a Q(10) value o f about 3. We found considerable effects of temperature and exogenous ABA on total elongase activity in MDEs. Our results suggest that the a ccumulation of 22:1 is regulated by the amount of elongase enzyme and not by changes in the intrinsic characteristics of the enzyme. Elongas e activity correlated closely with the absolute amount of 22:1 (mu mol ), whereas the correlation between elongase activity and the fraction of 22:1 (% of fatty acids) in oil was poorer. Including the total acti vity of acyltransferases did not improve the correlation. Acyltransfer ase activity itself correlated poorly with the total amount of oil for med.