Research On Physiological Response And Differential Gene Expression Of Nitrogen Efficient Utilization In Potato

Nitrogen is one of the indispensable elements in the normal growth and development of potatoes.However,excessive application of nitrogen fertilizer has also caused a series of environmental pollution problems.Therefore,the selection of nitrogen efficient varieties to improve nitrogen use efficiency and reduce the loss of nitrogen fertilizer has received great attention.Screening varieties with different nitrogen efficiency and understanding the differences in nitrogen efficiency,physiology,biochemistry and molecular mechanism among different varieties are the basis of nitrogen efficient cultivation and breeding.In this study,27 potato varieties were used as experimental materials to study the physiological and biochemical mechanism of nitrogen efficient on the basis of screening nitrogen efficient varieties and nitrogen inefficient varieties.And using high-throughput sequencing platform to analyze differential gene expression at different levels of nitrogen from the transcriptome.The main results are as follows:1.Combination of seedling screening and field validation,the nitrogen efficient varieties were Netherlands 14(HL14),Jizhangshu 12(JZ12)and Xingjia 2(XJ2),nitrogen inefficient varieties were Zaodabai(ZDB),Youjia 70(YJ70)and Kexin 4(KX4).Relative shoot dry matter,relative dry matter,relative root-shoot ratio,relative shoot nitrogen accumulation and relative root nitrogen accumulation can be used as screening indicators for potato nitrogen efficiency at seedling stage.2.The further study was carried out with nitrogen efficient variety JZ12 and nitrogen inefficient variety YJ70 as experimental materials.The results showed that the root dry weight,root volume,total absorption area,active absorption area and distribution of deep roots of nitrogen efficient varieties were significantly higher than nitrogen inefficient varieties.Root activity,root nitrate reductase activity,and root glutamine synthetase activity were significantly higher than nitrogen inefficient varieties under low nitrogen and no nitrogen treatment.Under the condition of nitrogen reduction,the influence degree of nitrogen efficient varieties was less than that of nitrogen inefficient varieties.Nitrogen accumulation of nitrogen efficient cultivars was significantly higher than that of nitrogen inefficient cultivars,and there was a significant positive correlation between nitrogen accumulation and root dry weight,root volume,root activity,root absorption area,root active absorption area,root nitrate reductase activity and root dry weight in all soil layers.3.The chlorophyll,photosynthetic rate,stomatal conductance,transpiration rate,nitrate reductase activity and glutamate synthetase activity of nitrogen efficient variety JZ12 were significantly higher than that of nitrogen inefficient variety YJ70 under low nitrogen and no nitrogen treatments.The activities of nitrite reductase and glutamine synthetase of nitrogen efficient cultivar JZ12 were significantly higher than those of nitrogen inefficient cultivar YJ70 under three nitrogen treatments.Under the condition of nitrogen reduction,the influence degree of nitrogen efficient varieties was less than that of nitrogen inefficient varieties.Compared with nitrogen inefficient cultivars,midday depression of photosynthesis of nitrogen efficient cultivars was lighter.The dry matter accumulation and yield of nitrogen efficient varieties were significantly higher than those of nitrogen inefficient varieties.4.The contents of Mn,Mo,La,Ce,Pr,Sm,Gd,Tb,Dy,Er,Yb and Y in the leaves of nitrogen efficient variety JZ12 were higher than those in the nitrogen inefficient variety YJ70,The content of Mn,Mo,La,Ce,Pr,Sm,Gd,Tb,Dy,Er,Yb and Y in stems of nitrogen efficient varieties was lower than that of nitrogen inefficient varieties.Under the condition of nitrogen reduction,the content of each nutrient element was reduced,and the reduction of nitrogen efficient variety JZ12 was greater than that of nitrogen inefficient variety YJ70.5.Compared with conventional nitrogen,after 30 days of low nitrogen treatment,6173 differentially expressed genes were detected in leaves of nitrogen inefficient variety Youjia70.There are 160 GO terms with significant enrichment of these differentially expressed genes,including biological processes,catalytic activities,chloroplast.There are 15 Pathways with significant enrichment of differentially expressed genes,including protein processing in endoplasmic reticulum,carbon fixation in photosynthetic organisms,biosynthesis of amino acids,porphyrin and chlorophyll metabolism.3455 differentially expressed genes were detected in leaves of nitrogen efficient variety Jizhangshu 12.There are 112 GO terms with significant enrichment of these differentially expressed genes,which are mainly enriched in metabolic processes,organonitrogen compound metabolic process,catalytic activities,plastid,and so on.There are 4 Pathway with significant enrichment of differential genes,including ribosome,alanine,aspartate and glutamate metabolism,ribosome biogenesis in eukaryotes and biosynthesis of amino acids.6.Compared with conventional nitrogen treatment,after 30 days of low nitrogen treatment,249 differentially expressed genes were detected in roots of nitrogen inefficient variety Youjia70.There were 12 GO terms which were significantly enriched,mainly in transport,amide transport,oligopeptide transport and oxidoreductase activity.There are 8 Pathways with significant enrichment,including carotenoid biosynthesis,phenylpropanoid biosynthesis and steroid biosynthesis.1990 differentially expressed genes were detected in roots of nitrogen efficient variety Jizhangshu 12.There were 18 GO terms which were significantly enriched,mainly in response to stress,glutamine family amino acid metabolic process,amine metabolism and oxidoreductase activity.There are 12 Pathways with significant enrichment,including zeatin biosynthesis,nitrogen metabolism and phenylpropanoid biosynthesis.7.Low nitrogen treatment increased the gene expression level of high affinity NRT in two cultivars.The genes encoding nitrite reductase in roots of high nitrogen inefficient variety were significantly down-regulated,and the genes related to glutamine synthase and glutamate synthase in roots and leaves were significantly up-regulated.It indicated that nitrogen efficient variety had energy-saving nitrogen assimilation patterns and high nitrogen assimilation capacity.The expression levels of key genes encoding chlorophyll synthesis,light-harvesting complexes Lhca5,Lhcb3,Lhcb6,Lhcb7 and ribulose diphosphate carboxylase in carboxylation stage of nitrogen inefficient variety were significantly down-regulated,while those of high nitrogen efficient variety were significantly up-regulated or unchanged,indicating that nitrogen efficient variety maintained high chlorophyll synthesis level,enhanced light intensity,absorption and transmission of energy,strengthening carbon sequestration capacity.