Physiological Response Of Mesembryanthemum Crystallinum Under Sodium Chloride,Sodium Salt And Chlorine Salt Treatment

Mesembryanthemum crystallinum L.is a salt-secreting halophyte belonging to the Aprilaceae family.Salt absorbed by M.crystallinum is stored the salt bladders to avoid salt damage.It is known that low concentration of NaCl treatment can promote its growth,while high concentrations of NaCl treatment inhibit its growth but can promote the transformation of photosynthetic carbon assimilation pathway from C3 to CAM.We don't know which ions(Na⁺,Cl^-,both Na⁺and Cl^-)play a major role in this process?Therefore,in this study,the effects of different concentrations of NaCl,sodium salts and chlorine salts on the vegetative growth and the transformation of photosynthetic pathway of M.crystallinum were studied.The main research results are as follows:1.Nutritional growth:Low concentration(100 mM)of NaCl and sodium salt significantly increased the biomass,leaf area,and photosynthetic rate of the species.Low concentration of chloride inhibited the growth,reduced leaf area,and photosynthetic rate.It showed that Na⁺played a major role in promoting nutritional growth when treated with low concentration NaCl.High concentration(400 mM)of NaCl,sodium salt and chlorine salt significantly inhibited the growth.Among these inhibition factors,chloride salt was the most serious,causing water loss,yellowing,and even death of leaves.High concentration of NaCl,sodium salt and chloride salt significantly reduced the density of the salt bladders,but increased the size of salt bladders.The ions in the salt bladders were mainly Na⁺and Cl^-under sodium chloride treatment,but only mainly Na⁺or Cl^-under sodium or chloride treatment respectively.NaCl,sodium salt and chloride salt treatment significantly increased the content of soluble organic matter,such as soluble sugar,proline and soluble protein in the species.low concentration of salt treatment significantly increased the activities of SOD,CAT,APX and POD,which can clear the H₂O₂ and O₂^-and keep low H₂O₂ and O₂^-content.However high concentration of salt treatment that exceeds the tolerance caused the activities of some antioxidant enzymes to increase first and then decrease.2.Conversion from C3 pathway to CAM pathway:Leaves were taken at specific time points(morning and evening)to determinate stomatal opening,intercellular CO₂ concentration,organic acid content and sugar content,the results showed that compared to the control,under the treatment of NaCl and sodium salt,stomatal opening increased significantly at night so that can absorb and fix CO₂,which leading to the significantly increase of intercellular CO₂concentration,organic acid content significantly increased and reached the maximum at dawn,and carbohydrate content significantly decreased by consumption at night.During the day,stomatal opening decreased significantly,intercellular CO₂concentration decreased,organic acids decarboxylation and release CO₂ for photosynthesis synthesis of starch,which causing organic acids content significantly decreased.Compared to the control,chloride salt treatment significantly increased organic acid content,but there was no significant difference in the content of organic acids between day and night.In addition,qPCR was performed to verify the expression of key genes regulating the CAM pathway(regulating CO₂ receptor synthesis gene PEPC,regulating circadian rhythm gene CCA,malate dehydrogenase gene MDH and regulating stomatal opening gene OST).The results showed that sodium stress significantly increased the expression of these key genes,which was consistent with physiological results.It was concluded that Na⁺played a major role in the process of the transformation from C3 to CAM pathway.In conclusion,the low concentration of NaCl promoted growth,while the high concentration of NaCl promoted the transformation from C3 to CAM pathway,in which Na⁺played a major role.