The Regulation Of Cytokinin On Nitrogen Distribution And Leaf Senescence In Rice Seedlings Under Nitrogen Deficiency

Nitrogen(N)plays a key role in the formation of rice yield and quality,application of nitrogen fertilization is necessary for higher yield of rice.The higher utilization rate of nitrogen fertilizer is beneficial to the sustainable development of agriculture.Understanding the mechanism of nitrogen absorption,transport and redistribution is of great significance for improving the utilization efficiency of nitrogen fertilizer and guiding the application of nitrogen fertilizer in agriculture.It has kuown that there is a very close relationship between nitrogen nutrition?cytokinin levels and leaf senescence.However,the regulation mechanism of cytokinin on nitrogen absorption,transport and redistribution and leaf senescence in rice seedlings under nitrogen deficiency stress remains unclear.With the Oryza sativa rice 9311 as the experiment material,we investigated the effect of nitrogen deficiency stress on cytokinin and the regulation mechanism of cytokinin on nitrogen distribution and leaf senescence in the rice seedling under nitrogen deficiency stress.The main results are as follows:1.Nitrogen deficiency stress inhibited the expression of isopentenyl transferase gene in the basal leaf(leaves grown before nitrogen deficiency treatment),the young leaf(leaves grown after nitrogen deficiency treatment)and the root of rice seedings,inhibited the biosynthesis of cytokinin,thereby reduced the cytokinin content.The decrease of cytokinin content was positively related to the down-regulated expression of isopentenyl transferase gene.Nitrogen deficiency treatment inhibited the expression of cytokinin oxidase gene,which maybe the feedback regulation of the decrease of cytokinin content.2.Nitrogen deprivation stress reduced cytokinin content,and then regulated the nitrogen distribution in rice seedlings,promoted the decrease of nitrogen content and dry weight in the basal leaf.Compared with the control,nitrogen deficiency stress decreased cytokinin content,inhibited the expression of nitrogen input related genes and enhanced the expression of nitrogen output related genes,resulting in less nitrogen input and increased output in the basal leaves of rice seedlings,and then reduced the nitrogen content and dry weight in the basal leaves of rice seedlings.After treating the basal leaf with exogenous 6-BA,the regulation effect on the nitrogen content and dry weight in the basal leaves of rice seedlings under nitrogen deprivation stress was alleviated.3.Nitrogen deprivation stress induce the ratio of cytokinin content in the young leaves to the basal leaves increasing,and then promoted the redistribution of nitrogen transporting from the basal leaf to the young leaf.Compared with the control,nitrogendeficiency stress promoted the decrease of cytokinin content in basal leaves of rice seedlings significantly higher than that in young leaves,which resulting in the ratio of cytokinin content in the young leaves to the basal leaves increasment,and then promoted the redistribution of nitrogen transporting from the basal leaf to the young leaf in rice seedlings.After treating the basal leaf with 6-BA,the promotion of the redistribution of nitrogen transporting from the basal leaf to the young leaf in rice seedlings under nitrogen deprivation stress was alleviated and inhibited the young leaf growth.4.Nitrogen deprivation stress reduced cytokinin content,and then promoted the decrease of chlorophyll content and promoted senescence of the basal leaf in rice seedings.Compared with the control,nitrogen deficiency stress reduced cytokinin content,enhanced the expression of chlorophyll degradation and senescence related genes,inhibited the expression of chlorophyll biosynthesis related genes,reduced the chlorophyll content and promoted yellowing of the basal leaf in rice seedings.After treating the basal leaf with exogenous 6-BA,the regulation effect on the decrease of chlorophyll content and senescence in the basal leaves of rice seedlings under nitrogen deprivation stress was alleviated.5.Nitrogen deprivation stress reduced cytokinin content of the root,and then promoted the root growth of rice seedings.Compared with the control,nitrogen deficiency stress reduced cytokinin content of the root and increase many index of root growth(root number,root length,root surface area,root volume,root dry weight and root/shoot ratio).After treating the root with exogenous 6-BA,the promotion effect on the root growth of rice seedlings under nitrogen deprivation stress was alleviated.After treating the basal leaf with exogenous 6-BA,the promotion effect on the root growth of rice seedlings under nitrogen deprivation stress was enhanced.In this study,we found nitrogen deprivation stress reduced cytokinin content of the basal leaf,and then promoted the decrease of nitrogen content,chlorophyll content and dry weight in the basal leaf.Nitrogen deprivation stress induce the ratio of cytokinin content in the young leaves to the basal leaves increasing,and then promoted the redistribution of nitrogen transporting from the basal leaf to the young leaf.Nitrogen deprivation stress reduced cytokinin content of the root,and then promoted root growth of rice seedings.