Nitrogen Uptake And Utilization In Citrusrootstocks Ziyang Xiangcheng And Trifoliateorange

Ziyang xiangcheng[Citrus junos Sieb.ex Tanaka]and trifoliate orange[Poncirus trifoliata?L.?Raf.]are widely used as citrus rootstock in China.There is little information about the physiological and molecular basis of nitrogen utilization in two citrus rootstocks.The main findings are as follows:Effects on the nitrogen metabolism and expression of related genes in different citrus rootstocks under nitrogen stressCompared with the control,nitrogen deficiency significantly reduced the nitrogen accumulation in Ziyang Xiangcheng and excess nitrogen significantly increased the nitrogen accumulation in the two citrus rootstocks.The total nitrogen accumulation of Ziyang Xiangcheng was significantly higher than that of trifoliate orange.This result may be caused by the higher biomass and root hair density of Ziyang Xiangcheng.In roots and leaves,the nitrate content of Ziyang Xingcheng was significantly higher than that of trifoliate orange.However,in both trifoliate orange and Ziyang Xiangcheng leaves,the highest nitrate content was the high nitrogen treatment,followed by the control and low nitrogen treatment.Similar results were obtained for the ammonium content.We further measured the expression of nitrogen metabolism-related genes.The relative expression levels of genes such as Fd-GOGAT,NR,NiR and GDH2 in the leaves of trifoliate orange under N deficiency condition were significantly lower than those in the control,and nitrogen stress significantly increased the relative expression of genes such as NADH-GOGAT1,NADH-GOGAT2 and NADH-GOGAT3.Meanwhile,the relative expression levels of genes such as NR,NiR,GDH1,GS and GDH2 in Ziyang Xiangcheng leaves under nitrogen stress were significantly lower compared to those of the control.the relative expression levels of NR,NADH-GOGAT1,NADH-GOGAT3 and NADP-GDH genes were significantly lower than those in the control,while there was almost no change in expression levels of genes such as Fd-GOGAT and GDH1.Similarly,the relative expression level of the genes Fd-GOGAT,NR,NiR,NADH-GOGAT1,NADH-GOGAT2,NADH-GOGAT3 and NADP-GDH in the roots of Ziyang Xiangcheng were significantly lower than those in the control under nitrogen stress.The relative expression of the gene GDH2 was not significantly different from the control.We also found that the nitrogen deficiency and high nitrogen treatment significantly reduced nitrate reductase,nitrite reductase,glutamyl dehydrogenase and glutamate synthase in leaves and roots of Ziyang Xiangcheng and trifoliate orange.The trends in activities of NR,NiR,NADH-GDH,and GOGAT were consistent with those of NR,Ni R,NADH-GDH and GOGAT transcription,respectively.All above results showed that nitrogen stress significantly reduced the activities of nitrogen-related enzymes in trifoliate orange and Ziyang Xiangcheng,resulting in the reduction of nitrate absorption and ammonium production.Effect of newhall navel orange seedlings of trifoliate orange and Ziyang Xiangcheng rootstock on nitrogen absorption,distribution and utilizationIn the trifoliate orange and Ziyang xiangcheng root Newhall navel orange seedlings,the 15N distribution rate of each organ from root to root?including main root and fine root?>leaves>trunk>shoots is not affected by nitrogen levels.It also reflects the nitrogen distribution ratio of each organ of Newhall navel orange seedlings of the two rootstocks,indicating that most of the nitrogen was absorbed by the roots.The ¹⁵N distribution rate of the main roots of the Newhal navel orange seedlings of Ziyang xiangcheng Roots under three nitrogen levels of N16,N24,and N32 were 30.0%,53.3%,and 44.8%lower than those of the trifoliate orange Rootstocks.The trifoliate orange was 39.4%,35.3%,and 40.6%higher.The ¹⁵N utilization rate of Newhal navel orange seedlings from trifoliate orange and Ziyang xiangcheng showed significant differences under different nitrogen levels,from N16>N24>N32 to high.The ¹⁵N utilization rate of the Newhall navel orange seedlings from the anvil was 7.38%,3.64%,and 1.71%from high to low,respectively,and the Ziyang xiangcheng were 8.55%,5.36%,and 2.16%,respectively.At the same nitrogen level,the seedlings of Newhall navel orange in Ziyang xiangcheng were significantly higher than those in the trifoliate orange.Effect of Jinqiu shatangju of trifoliate orange and Ziyang xiangcheng rootstock on nitrogen absorption,distribution and utilizationThe ¹⁵N distribution rate of Jinqiu shatangju of Ziyang xiangcheng rootstock in tree trunks,main branches,annual branches,fine roots and fruits was significantly higher than that of trifoliate orange,and the ¹⁵N distribution rate of both in perennial branches and main roots was not significant.and in the leaves,the ¹⁵N distribution rate of Jinqiu shatangju of Ziyang xiangcheng rootstock is significantly higher than that of trifoliate orange.In addition,the ¹⁵N distribution rate of the two rootstocks,Jinqiu shatangju,was the highest among the fruits.The total nitrogen content of Jinqiu shatangju of Ziyang xiangcheng rootstock plant was 107.59g,the total absorption of ¹⁵N was 1.96g,and the ¹⁵N utilization rate of the plant was 35.44%,which were significantly higher than the 73.31g,1.2g and21.67%of trifoliate orange.Among them,the ¹⁵N utilization rate of Jinqiu shatangju of Ziyang xiangcheng rootstock plants was 1.64 times that of trifoliate orange.