EFFECTS OF ABSCISIC-ACID AND TEMPERATURE ON ERUCIC-ACID ACCUMULATION IN OILSEED RAPE (BRASSICA-NAPUS L)

The qualitative effect of growth temperature on the level of erucic ac id (22:1) is similar in seeds and microspore-derived embryos (MDEs) of oilseed rape, as we have previously shown (Wilmer et al., 1996), but absolute levels of 22:1 are lower in MDEs. In this paper we studied wh ether this temperature effect is mediated by changes in the level of o r sensitivity to abscisic acid (ABA). For this purpose we measured end ogenous levels of ABA in developing seeds and MDEs. In addition, 22:1 accumulation was determined in MDEs exposed to a range of concentratio ns of ABA. The endogenous level of ABA in seeds, about 5 to 10 nmol/g FW, was twentyfold higher than the concentration at which maximum sens itivity in MDEs occurred. Further evaluation using dose-response curve s showed that at both 15 and 25 degrees C the half-maximum increase in 22:1 level in MDEs was observed at about 0.3 mu mol/L ABA, though thr oughout the concentration range tested levels of 22:1 were about 10 mo l% higher at 15 degrees C than at 25 degrees C. This indicates that th e sensitivity to ABA remains the same in this temperature range. Indep endent from the temperature effect, exogenously applied ABA induces an increase of about 10 mol % in 22:1 within the range of 10 to 25 degre es C. In addition to this effect on 22:1 level, ABA stimulates the pro duction of triglycerides in MDEs, whereas temperature has no effect on oil accumulation. In combination, our data indicate that growth tempe rature and ABA are independent and additive stimuli in regulating the level of 22:1 in oilseed rape.