Ja. Wilmer et al., REGULATION OF ELONGASE ACTIVITY BY ABSCISIC-ACID AND TEMPERATURE IN MICROSPORE-DERIVED EMBRYOS OF OILSEED RAPE (BRASSICA-NAPUS), Physiologia Plantarum, 102(2), 1998, pp. 185-191
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.