Different activities of SPS and PEPC in oilseed rape with different nitrogen use efficiency and their influence on seed yield and oil-content

【Objectives】 Transportation of carbon skeleton into carbon metabolism pathway and nitrogen metabolism circulation were respectively controlled by SPS (sucrose phosphate synthase) and PEPC (phosphoenolpyruvate carboxylase), and then the yield and grain quality of crop were affected by the two enzymes. In order to elucidate the regulation mechanism of contradiction between seed protein and oil during the high nitrogen use efficiency (NUE) progress in oilseed rape with high N efficiency, the different activities of SPS and PEPC and their influence on seed yield and oil content in oilseed rape with different NUE were studied in this paper.【Methods】 Variety No.27 with high NUE (H) and variety No.6 with low NUE (L) were cultured in soil under different nitrogen conditions normal nitrogen condition(N) and nitrogen stress condition(S) to study the difference of enzyme activities (SPS and PEPC) in leaf from seedling stage to flowering stage, in silique at early silique stage and in grain and silique husk at silique mid-term stage between the two NUE rape varieties as well as carbon (C) transportation amount and rate and their seed yield and seed oil content. 【Results】The test results showed that seed yield and seed oil content of high NUE (No.27) variety were significantly higher than those of low NUE (No.6) variety under two nitrogen conditions(normal nitrogen and nitrogen stress), the high NUE rape showed obvious variety advantage. Moreover, activities of SPS and PEPC of high NUE (No.27) variety in leaf from seedling stage to flowering stage were higher than those of low NUE (No.6) variety under two nitrogen conditions, the same tendency was found in silique at early silique stage as well as in grain and silique husk at silique mid-term stage. While the SPS/PEPC of the two variety rape was changed at different growth periods, SPS/PEPC of high NUE (No.27) variety in leaf at vegetative stage was higher than those of low NUE (No.6) variety, SPS/PEPC of the two varieties rape was similar in leaf at flowering stage, instead SPS/PEPC in main reproduction organs at silique stage of high NUE (No.27) variety was lower compared to low NUE (No.6) variety, which revealed that amount of delivery of carbon skeleton to C metabolism and N assimilation of high NUE (No.27) variety was more than those of low NUE (No.6) variety during the whole growth period and the response of C metabolism to N assimilation of high NUE (No.27) variety was higher than those of low NUE (No.6) variety at early growth stage, while at late growth stage the response of response of high NUE (No.27) variety was lower than that of low NUE (No.6) variety. Meanwhile C transportation amount and rate of high NUE (No.27) variety were significantly higher than those of low NUE (No.6) variety, which might be the vital physiological mechanism that regulatingthe contradiction between seed protein and oil during the high nitrogen use efficiency (NUE) progress in oilseed rape with high N efficiency. As for influence of different nitrogen conditions on items which we tested above, the results showed that seed yield, activity of PEPC, carbon transportation amount and rate were higher under normal nitrogen condition than under nitrogen stress condition, but seed oil content, activity of SPS, SPS/PEPC showed an inverse law, these phenomena appeared in the two rape varieties.【Conclusions】Compared to low NUE (No.6) variety, more carbon skeleton was transported into C and N metabolism pathway in high NUE (No.27) variety during the whole growth stage. This was the important premise for HNUE variety to coordinate the contradiction between C and N metabolisms. Response of C metabolism to N assimilation was higher during earlier growth stage than during later growth stage. Meanwhile, higher proportion of C in vegetative organs was transported into seed during later growth stage, which met the demands of carbon skeleton in C and N metabolism and coordinated the contradiction between seed oil and protein contents during later growth stage.