The seed oil content of rapeseed is affected by insufficient light at pod-filling stage,while more seeds can be harvested with the increasing planting density.The interaction of pod shading and planting density on the mechanism that affecting seed oil content has not been reported.The objective of this study is to study the effect of density on seed carbon and lipid metabolism of shaded rapeseed at pod-filling stage.In this experiment,two varieties(Huayouza 62,H,and Fengyou 520,F)were selected,and three levels of densities(15×104,30×104,and 45×104 plants hm-2)and two light intensities(100％light transmission,LT100％,and 70％light transmission from 10-35 d after terminating flowering,LT70％)were conducted in a field trial.The results showed that pod shading caused a decrease in seed chlorophyll content,the activity of ribulose 1,5-bisphosphate carboxylase(Rubisco)at 25 days and 35 days after flowering(DAF)of both varieties,leading to 0.4％-27.9％decrease in glucose content.Meanwhile,the decrease in the activities of sucrose synthase-cleavage(SuSy)and sucrose phosphate synthase(SPS)under shading inhibited su-crose conversion and resulted in a decrease by 4.8％-24.5％in fructose content.The activities of seed phosphatidate phosphatase(PPase)and glucose-6-phosphate dehydrogenase(G6PDH)were also reduced,resulting in 2.1％-11.8％decline in seed oil content and 27.0％-35.3％decline in oil production.Compared with the shading under lower density,the reduction in content of seed chlorophyll,fructose,glucose,and activities of rubisco and SuSy became lower,while the decrease of seed G6PDH and PPase activities became higher at 35DAF,which aggravated the decrease of seed oil content under shading.However,the decline in oil yield was alleviated due to the increase in population yield with denser planting.
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