Effects Of Different Nitrogen Levels On Chloroplast Structure And GS Expression In Different Sugarcane Varieties

Sugarcane is the most important sugar crop in China,and 90%of sugar comes from sugarcane in the country.In our sugarcane production,excessive application of chemical fertilizers,especially nitrogen not only declined in nitrogen use efficiency and increased the cost of sugarcane production,but also resulted in a series of negative effects such as cane quality degradation and agricultural environmental pollution.Glutamine synthase is a key enzyme in the process of plant nitrogen metabolism.GS has been a hot topic in plant physiology and nutrition,but mainly focused on enzyme activity.At molecular level,GS gene expression study is not much.The main gene and its expression characteristics of this enzyme are of great significance to understand the mechanism of nitrogen metabolism regulation and application in agricultural production.In this study,three sugarcane cultivars,GT11,ROC22 and GXB9,were planted in a greenhouse.Three nitrogen levels were set up,this is,0 kg/ha(low nitrogen level),150 kg/ha(medium nitrogen level)and 300 kg/ha(high nitrogen level)of urea,aiming to explore the response mechanism of agronomic traits,photosynthesis,and GS activity and expression to different nitrogen levels in different sugarcane varieties.The main results are as follows.1.The full-length CDS sequence of scGS I was successfully cloned from sugarcane leaves,which was 2529 bp in length and encoded 843 amino acids.The gene has been registered in GenBank with the accession number KY072794.The amino acids encoded by this gene have high homology with the GS I of other plants.2.The effects of nitrogen on the agronomic traits,chloroplast structure and photosynthetic rate in sugarcane cultivars GT11,ROC22 and GXB9 were studied.It was found that the plant height,stalk diameter,SPAD in GT11 and ROC22 increased with the increase of nitrogen application,while the plant height,stalk diameter and SPAD in GXB9 were the highest on medium nitrogen level.The leaf area in GX11,ROC22 and GXB9 increased significantly with the increase of nitrogen application.The leaf area of GXB9 was always higher than that of GT11 and ROC22 at the same nitrogen level.The photosynthetic rate of GT11 and ROC22 increased with the increase of nitrogen application,but that of GXB9 showed the highest on medium nitrogen level.The chloroplast structure in GT11 was normal on the high nitrogen level.ROC22 had the highest chloroplast number but significantly less grana lamella on medium nitrogen level compared with high nitrogen level.The chloroplast number in GXB9 was the highest,but the number of grana lamella showed no significant difference between medium and high nitrogen levels.3.The GS activity and GOG AT activity in GT11 and ROC22 increased with the increase of nitrogen application.The GS activity and GOGAT activity in GXB9 reached the highest on medium nitrogen level.Under the condition of low and medium nitrogen levels,the activities of GS and GOGAT were higher in GXB9 than in GT11 and ROC22.On the high nitrogen level,the activity of GS and GOGAT were the highest in ROC22.As the response of transcription level expression of scGSl.a and scGSl.b to nitrogen was down-regulated while the response of scGSl.c,scGS2 and scGS I to nitrogen was up-regulated.The expression of GS1 protein in GT11 increased with the increase of nitrogen application rate.The expression of GS1 protein in GXB9 was the highest on medium nitrogen level.Under low and medium nitrogen levels,the expression of GS1 was higher in GXB9 than in GT11 and ROC22 on low and medium nitrogen levels.