The Role Of NaCl In Photosynthesis Of Suaeda Salsa

With the impact of global climate change,the area of secondary salinization caused by agricultural activities in arid regions will increase,which will seriously affect agricultural production.The research on salt-tolerance mechanism of halophytes can help to improve the salt tolerance of crops and restoring saline land.Suaeda salsa L.is a C₃ plant,which is a typical euhalophyte with high salt tolerance,rich nutrition and high edible and medicinal value.It has been proved that the photosynthesis and biomass at 200 mM NaCl are significantly higher than that of the control?0 mM NaCl?,but the mechanism is not clear.In order to understand the reason why salinity can promote the photosynthetic capacity of S.salsa,the efficiency of light energy transfer and conversion and the change of key enzyme activity during carbon assimilation stage were investigated in the current study.The main findings are as follows:1.The effect of salinity on the biomass of S.salsaCompared with the control?0 mM NaCl?,200 mM NaCl had no significant effect on the shoot dry weight,but it was significantly reduced under 500 mM NaCl when seedlings were treated with salinity for 2 days.Under long-term salinity treatment?14 d?,the shoot dry weight at 200 mM NaCl increased significantly compared to the control,while 500 mM NaCl treatment had no significant effect on the value.The trend was consistent with the change in net photosynthetic rate?Pn?and starch accumulation in the leaves.2.Effect of salinity on photoreaction in S.salsaThe maximum efficiency of PSII photochemistry?Fv/Fm?and the electron transfer rate?ETR?of S.salsa were not affected by salinity.However,the chlorophyll content,ferredoxin-NADP oxidoreductase?FNR?activity,and chloroplast NADPH activity of S.salsa increased in comparison with the control under long-term salinity treatment?14 d?.This indicates that the photoreaction system of S.salsa under salt stress was protected.The structure and function of the photoreaction system can maintain a normal state,and the efficiency of light energy transfer and conversion,and the activity of related enzymes may be promoted under salinity.3.Effect of salinity on enzyme activity during carbon assimilation stageCompared with the control,the activities of ribulose-1,5-bisphosphate carboxylase?Rubisco?and rubisco activase?RCA?did not change at 200 mM NaCl,but decreased significantly at 500 mM NaCl when seedlings were treated with salinity for 2 days.After a long-term salinity treatment?14 d?,the enzyme activity increased significantly at 200 mM NaCl,but there was no difference between the control and500 mM NaCl.The trend of enzyme activity was the same as that of biomass and net photosynthetic rate?Pn?.High salinity?500 mM NaCl?increased the activities of3-phosphoglycerate kinase?PGK?and glyceraldehyde-3-phosphate dehydrogenase?GAPDH?after a long-term salinity treatment.Therefore,these enzymes especially Rubisco and RCA may play critical roles in the process of carbon assimilation to improve plant growth under salinity?e.g.,200 mM NaCl?in S.salsa.4.Effects of salinity on gene expression of certain enzymes during carbon assimilation stageThe expression of genes SsFNR,SsRbcl,SsRbcs,SsRCA,SsPGK,and SsGAPDH increased at 200 mM NaCl compared to the control,and 500 mM NaCl had no significant inhibition on the expression of genes during the time course?1,2 and 14 d?especially when seedlings were treated with salinity for 2 days.This indicates that 200mM NaCl upregulated the expression of these genes which may play important roles in promoting carbon assimilation under salinity in S.salsa.