Abstract: ObjectiveEffects of sucrose phosphate synthase(SPS)activity variation in rape silique on carbon and ni-trogen metabolite and rapeseed oil content were studied to provide reference for revealing the expression regulation mecha-nism of SPS,and contradiction between quality and yield of improved rape varieties.MethodRape varieties with low ni-trogen use efficiency and high nitrogen use efficiency were used in this experiment,and soil culture test under normal ni-trogen supply and nitrogen stress was carried out.During silique development period,rape siliques were smeared with SPS inhibitor,and those smeared with distilled water were set as control.SPS activity,soluble sugar content and free amino acid content in husk and grain were determined in the morning on day 3 after treatment,and grain oil yield at maturity stage was measured.ResultAfter smearing SPS inhibitor on silique,under different nitrogen supply conditions,SPS activity of rape varieties with different nitrogen use efficiencies decreased greatly,and the differences were significant(P<0.05). Under nitrogen stress,SPS activity of varieties with low nitrogen use efficiency was greatly inhibited,but under constant nitrogen condition,SPS activity of varieties with high nitrogen use efficiency was greatly inhibited.As for SPS activity of silique during development period,those in constant nitrogen condition were higher than those in nitrogen stress,and those of varieties with high nitrogen use efficiency were higher than those of varieties with low nitrogen use efficiency.The change of soluble sugar content was consistent with that of SPS activity. The difference of free amino acid content be-tween different nitrogen levels and varieties was consistent with SPS activity,but its reaction to SPS inhibitor was diffe-rent from SPS activity and soluble sugar content.That is,it increased when SPS activity was inhibited.Grain oil yield had the same variation trend with SPS activity.Under SPS inhibitor treatment,grain oil yield decreased greatly.Under nitro-gen stress,grain oil content of varieties with low nitrogen use efficiency and high nitrogen use efficiency reduced by 5.00% and 13.13%;under constant nitrogen condition,grain oil content of varieties with low nitrogen use efficiency and high nitrogen use efficiency reduced by 17.57% and 21.88%.Grain oil yield of rape varieties with high nitrogen use effi-ciency was larger than those with low nitrogen use efficiency,and grain oil yield under constant nitrogen condition was larger than that under nitrogen stress.ConclusionsRegardless of nitrogen level,when silique SPS activity of rape varie-ties with low and high nitrogen use efficiencies is inhibited,carbon metabolism of silique and grain weaken,nitrogen me-tabolism strengthens,and eventually grain oil yield reduces.