Effects Of Salt Stress On Photosynthetic Physiology Characters Of PeMPK7 Transgenic Poplar Seedlings

Due to human activities and global climate change,more and more land appears salinization problem,which brings increasing serious losses to the development of agricultural and forestry.Salt stress can cause damage to plants,such as ion imbalance,osmotic stress and oxidative stress,which leads to the decline of plant biomass and even the death of plants.Therefore,it is of great significance to study the mechanism of plant salt tolerance and improve the ability of plant salt tolerance to improve forestry productivity.The area of Poplar plantation in Chinaranks the first in the world,and Poplar has become an important tree species to solve the problem of wood supply in China.In recent years,as a model tree species of forest genetic engineering,poplar has been widely studied.In the previous study,the'84K Yang'transgenic plantswith the overexpression of MPK7 gene(P_35S::MPK7^OE)have been obtained by our team.In this study,a hydroponic system was used to study the changes of physiological and biochemical indexes of P_35S::MPK7^OEE transgenic poplar seedlings under different concentrations of NaCl stress and different stress time.The results are as follows:?1?High salt stress significantly inhibited the leaf phenotype of Poplar.When NaCl concentration was 0¹00 mM,there was no significant phenotypic change in Poplar leaves.When NaCl concentration was 150 mM,the contrast seedlings were severely stressed,and the leaf wilted due to water loss,However,the stress level of OE 3-3and OE 1-6 transgenic poplar seedlings was significantly lower than that of the control plants,and with the amount of expression increasing,the stress phenotype was lower,showing that the salt-tolerant ability of transgenic poplar with overexpression of PeMPK7 was than that of the control plants.?2?Different concentrations of NaCl stress significantly reduced the photosynthetic capacity of Poplar.With the NaCl concentration increasing,the photosynthetic rate?P_n?,transpiration rate?T_r?,stomatal conductance?G_s?and water use efficiency?WUE?of poplar decreased significantly,and the decrease of P_n in transgenic Poplars with overexpression of PeMPK7 was significantly lower than that of control plants;indicating that PeMPK7alleviated the inhibition of NaCl stress on P_n and the damage of salt stress on photosynthetic system to a certain extent.When NaCl concentration was 50 mM,P_n decreased,C_i decreased and L_s increased;when NaCl concentration was greater than 50 mM,C_i increased and L_s decreased,indicating that NaCl concentration of 50 mM was the turning point concentration of photosynthetic rate from stomatal restriction to non-stomatal restriction.?3?The photochemical efficiency and electron transfer efficiency of Poplar were significantly reduced by different concentrations of NaCl stress.With the NaCl concentration increasing,the PeMPK7 transgenic poplars and control plants have almost the same change trend,namely the maximum fluorescence?F_m?,the actual photochemical efficiency(?_PS?)and the maximal photochemical efficiency?F_v/F_m?,potential photochemical efficiency?F_v/F_o?and photochemical quenching?qP?were significantly lower,minimal fluorescence?F_o?and photochemical quenching?NPQ?increased significantly,indicating that salt stress led to the Poplar photoinhibition;The change range of PeMPK7 transgenic Poplar was better than that of control plants.Above showed that overexpression plants could alleviate the problems of light inhibition,closure of PS?reaction center and low electron transfer efficiency caused by high concentration of NaCl stress,and the higher the expression quantity,the more obvious the alleviate degree.?4?The concentration and duration time of NaCl stress led to oxidative stress and osmotic stress in Poplars.With the NaCl concentration and stress time increasing,malondialdehyde?MDA?content increased.At this time,the plant would resist oxidative stress and osmotic stress by increasing the content of soluble sugar,soluble protein and antioxidant enzyme activity.The change trend of PeMPK7 transgenic Poplar was basically the same as that of control plants,but the increase of MDA content in PeMPK7 transgenic Poplar was lower than that of control plants,indicating that the degree of membrane damage of transgenic Poplar was less than that of control plants,and the PeMPK7 played a certain role in the maintenance of membrane function,and the higher the expression level,the greater the protective effected on cell membrane.The content of soluble sugar,soluble protein and the activity of antioxidant enzymes increase significantly higher than that of control plants,and the higher the expression of PeMPK7 gene,the higher the content of soluble sugar and protein and the activity of antioxidant enzyme,indicating that PeMPK7 could maintain the osmotic regulation of genetically Poplar,inhance the ability of scavenging active oxygen,and improve the salt resistance of'84K Yang'to some extent,and the higher the expression level,the stronger activity of the antioxidant enzymes.