| In order to investigate the effect of Sucrose photophate synthase（SPS）and phosphoenolpyruvate carboxylase（PEPC）activities and carbon-nitrogen（C-N）accumulation on the oil content and grain yield in Brassica napus,Brassica napus genotypes with contrasting nitrogen use efficiency（NUE）was used to conduct the experiments.（1）Pot experiments was conducted to study the effects of SPS and PEPC activities on soluble sugar,free amino acid,oil content and grain yield by alternatively suppressing the activity of SPS and PEPC;（2）Sand culture experiment was conducted to investigate the effects of C-N accumulation and reutilization on the oil content and grain yield in Brassica napus through13C and 15N isotope tracer method,the results of the test are as follows:1.The results of SPS and PEPC activity and their gene expression showed that:After silique of SPS inhibitors,SPS activity of husks and grains of two rapeseed varieties decreased significantly under two nitrogen levels,but the activity of PEPC increased,in all treatments,the activity of SPS was the largest in the husk of low NUE varieties under nitrogen stress,with a decrease of 30.55%;After silique of PEPC inhibitors,PEPC activity showed a decreasing trend,and SPS activity had no consistent change.The difference of SPS and PEPC activity among different rape varieties showed that,no matter how the inhibitors were treated,the SPS and PEPC activities of the low NUE varieties were generally higher than those of the high NUE varieties;Most of the two enzyme activities at different nitrogen levels were normal nitrogen higher than nitrogen stress level.2.The determination of soluble sugar and free amino acid showed that:The content of soluble sugar in husks and grains were significantly decreased after SPS inhibitor was applied;when the PEPC inhibitor was applied to the silique,the soluble sugar content of the two varieties husk increased slightly under nitrogen stress,but decreased under the normal nitrogen level.The soluble sugar content of all treatments was higher than that of low NUE varieties,and reached a significant level in most cases;the soluble sugar content of normal nitrogen treatment was slightly higher than that of nitrogen stress,and the soluble sugar content of grains reached a significant level between different nitrogen levels.The effect of enzyme inhibitors on soluble sugar content of high NUE varieties was greater than that low NUE varieties,and the effect on soluble sugar content of grains was greater than that of siliques.The free amino acid rule was opposite to the soluble sugar content,when the SPS inhibitor was applied to the silique,the content of free acid amino acids increased in the normal nitrogen condition and decreased under the nitrogen stress condition;When PEPC inhibitor was applied,the free amino acid content of the two varieties silique was increased by 0.27 and 0.22 percentage points under nitrogen stress level,and the content of free amino acids in the other treatments decreased in varying degrees.The content of free amino acids in high NUE varieties was greater than that of low NUE varieties,only the treatment of individual varieties reached significant level,and the content of free amino acids in the silique and grain of two varieties were all higher than that of nitrogen stress treatment,and the difference reached significant level.Under the condition of enzyme inhibition,the regularity of the results between the varieties and nitrogen levels was consistent.3.The results of seed oil and grain yield showed that:After silique of SPS inhibitors,the oil content is all significantly reduced,while the oil content in the nitrogen stress level increased significantly under the treatment of PEPC inhibitor,and the oil content in the normal nitrogen level had no significant change,and the inhibitory effect of SPS activity on the oil content was greater than that of the PEPC activity inhibition.The grain yield decreased in varying degrees under the two enzyme inhibition treatments,There was no significant difference in low NUE varieties except nitrogen stress,the other treatments were significantly different;The grain yield of high NUE was significantly higher than that of low NUE varieties,grain yield at normal nitrogen level was significantly higher than that under nitrogen stress.4.The dynamics of C-N and dry matter accumulation in rapeseed were studied:The C content of organs with different varieties and nitrogen levels,and N content of organs in different varieties under the same nitrogen level had little difference,while the N content in the organs by normal nitrogen was higher than that of nitrogen stress treatment.The cumulative dynamic of C-N and dry matter at different growth stages,the cumulative percentage of high NUE varieties at the bolting and flowering stage under nitrogen stress was significantly higher than that of low NUE varieties,the C accumulation rate was higher5.68 and 11.37 percentage points,the N accumulation rate was higher 5.68 and 11.37percentage points respectively,and the dry matter accumulated rate higher 6.47 and 11.87percentage points,there is no significant difference between the two varieties at the normal nitrogen level,the silique stage and the harvest stage are the opposite.It shows that nitrogen stress has a stronger accumulation capacity of C-N and dry matter in the early growth period of nitrogen under the condition of nitrogen stress,which lays a good foundation for the transport of reproductive organs in the late growth stage.5.The results of dynamic determination of C-N reutilization show that:The C transport rate and transport amount showed that the high NUE varieties were significantly higher than those of low NUE at the normal nitrogen level,the C transport rates were higher 1.47 and 3.47 percentage points in the silique stage and harvest stage,and the carbon transport amounts were higher 35.16%and 34.64%respectively,while the two varieties had no difference at the level of nitrogen stress.N transport rate and transport amount were significantly higher than that of low NUE varieties at two nitrogen levels,in the harvest stage,the N transport rates and transport amounts were higher 8.91 percentage points and31.75%under the normal nitrogen level,and higher 24.44 percentage points and 49.07%under the nitrogen stress level.6.The results of dynamic measurement of C-N loss showed that:The difference between the C loss rate and the loss amount showed that the low NUE varieties were larger than the high NUE varieties,and mainly reflected in the flowering stage;The difference of C loss rate and loss amount at different nitrogen levels showed that normal nitrogen level was higher than nitrogen stress level,but the difference of C loss rate was only reflected in flowering stage.N loss rate was higher than that of high NUE variety,but the difference reached significant level only at the normal nitrogen level,and there was no difference in N loss rate at different nitrogen levels;there was no difference in N loss amount among varieties,and normal nitrogen level was higher than nitrogen stress level. |
