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 acid (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 whether this temperature effect is mediated by changes in the level of or sensitivity to abscisic acid (ABA). For this purpose we measured endogenous levels of ABA in developing seeds and MDEs. In addition, 22:1 accumulation was determined in MDEs exposed to a range of concentrations 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 sensitivity in MDEs occurred. Further evaluation using dose-response curves showed that at both 15 and 25°C the half-maximum increase in 22: 1 level in MDEs was observed at about 0.3 umol/L ABA, though throughout the concentration range tested levels of 22:1 were about 10 mol % higher at 15°C than at 25°C. This indicates that the sensitivity to ABA remains the same in this temperature range. Independent from the temperature effect, exogenously applied ABA induces an increase of about 10 mol % in 22:1 within the range of 10 to 25°C. In addition to this effect on 22:1 level, ABA stimulates the production of triglycerides in MDEs, whereas temperature has no effect on oil accumulation. In combination, our data indicate that growth temperature and ABA are independent and additive stimuli in regulating the level of 22:1 in oilseed rape.