Disparate impact of salt stress and saline-alkali stress on key nitrogen metabolism enzyme activities and related gene expression in grape rootstock seedlings
[Objectives]We investigated the differences in the effects of salt stress and saline-alkali stress on the activities of nitrogen metabolism enzymes,and the expression of genes related to nitrogen absorption and assimilation in grape root stock seedlings.[Methods]Sand culture experiment was conducted using'5BB'rootstock seedlings as materials,which were under three treatments for 14 days,CK(normal nutrient solution),salt stress(nutrient solution containing 0.20 mol/L NaCl),and saline-alkali stress(nutrient solution containing 0.10 mol/L NaCl&0.10 mol/L NaHCO3).Plants were sampled for the measurement of dry and fresh weight,root morphology,SPAD value,Na+and K+content,activities of five nitrogen metabolism enzymes,15 N content,and the expression levels of nine genes.[Results]Compared with CK,saline-alkali stress significantly reduced the fresh weight of whole plants,and markedly decreased the SPAD values.Salt and saline-alkali stress increased Na+content to 1.50 and 2.50 fold in leaves,and 1.68 and 1.79 fold in roots,compared to CK,and were recorded higher Na+content in roots than in leaves.Saline-alkali stress was tested the highest leaf K+content,while CK was tested the highest root K+content.Compare with CK,salt and saline-alkali stress decreased the activities of enzymes in leaves and roots,and decreased NO3-,NH4+and total nitrogen content in different extent.Compare with CK,salt and saline-alkali stress decreased the NO3-and total N contents in leaves and roots,saline-alkali decreased the NH4+contents in leaves,salt and saline-alkali stress decreased the NH4+contents in roots.Salt and saline-alkali stress down-regulated the expression levels of nine nitrogen metabolism-related genes in leaves and roots.Compared with CK,the expression levels of leaf VvNIA decreased by 68.61%,92.55%,and VvNIR decreased by 66.26%,81.61%,respectively;both salt and saline-alkali stress decreased the expression levels of VvNRT1.1,VvNRT1.2,VvNRT2.1 and VvNRT2.2 in leaves,and the difference in the expression levels of the four genes was significant between salt and saline-alkali stress.Saline-alkali stress down-regulated the expression levels of VvNRT1.1 and VvNRT1.2 in roots,and salt and saline-alkali stress down-regulated the expression levels of VvNRT2.1 and VvNRT2.2 in roots.The result of K15 NO3 isotope labeling showed that 15 N use efficiency of grape rootstock seedlings under salt and saline-alkali stress were decreased by 63.83%and 75.95%,respectively.[Conclusions]Under salt and saline-alkali stress,grape seedlings would reduce the activities of key nitrogen metabolism enzymes in leaves and roots,down-regulate the expression levels of genes related to nitrogen absorption and assimilation to some extent,thus reduce the NO3-,NH4+and total N content in leaves and roots,and result in low 15 N use efficiency and growth of grape root stock seedlings.The adverse effect of saline-alkali stress is worse than salt stress on grape root stock seedlings.
grape root stock seedlingssaline-alkali stressnitrogen metabolism key enzyme15N use efficiencygene expression of nitrogen metabolism
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