Mitigation Effects Of Exogenous Ca²⁺ On Callus Of Nitraria Sibirica Pall. Under Salt Stress

In this study the Nitraria sibirica Pall.callus were studied under the different concentration of exogenous Ca²⁺(0,5,10,15 mmol·L^-1)with different concentration of salt stress(50,100,150,200 mmol·L^-1)under the N.sibirica callus growth,degree of membrane peroxidation,antioxidant enzymes system,osmotic regulation substances,the influence of ion content and activity of membrane ion pump,discusses the N.sibirica callus salt tolerance mechanism and regulatory role of exogenous Ca²⁺,the following conclusions:（1）With the increase of salt stress,the relative growth rate,relative water content,SOD and CAT activities of the callus showed a trend of first increase and then decrease,while the cell membrane permeability,MDA content,POD activity and osmotic regulatory substances increased gradually.When the salt concentration is no higher than 150 mmol·L^-1,the application of Ca²⁺(≤10mmol·L^-1)at a certain concentration can increase the relative growth rate and relative water content of the callus,improve the activity of SOD,POD and CAT,reduce the electrolyte exosmosis rate,reduce MDA content,and increase the accumulation of osmotic regulatory substances,and this trend increases with the increase of Ca²⁺ concentration.However,the high concentration of Ca²⁺(>10 mmol·L^-1)showed no significant or varying degree of relieving effect on all physiological indexes of N.sibirica.The results showed that the appropriate concentration of Ca²⁺could effectively alleviate the damage caused by salt stress to the N.sibirica callus,and the excessive application of Ca²⁺ had no significant mitigation effect,or even showed inhibitory effect.（2）With the increase of salt stress,the contents of Na⁺ and Cl^-were significantly increased,while the contents of K⁺ and Ca²⁺ were gradually decreased.The addition of exogenous Ca²⁺effectively restrain the N.sibirica callus of Na⁺ and Cl^-absorption,improve the absorption of K⁺and Ca²⁺,effectively reduce the Na⁺ content in the callus,and thus improve the K⁺/Na⁺,Ca²⁺/Na⁺,make the permeability of inorganic ions can be used as a regulator to maintain cell osmotic pressure,showed that exogenous Ca²⁺ can effectively reduce the level of Na⁺ in the plant cells,slow down the salt stress on plant damage.（3）Salt stress could significantly affect the plasma membrane H⁺-ATPase and Ca²⁺-ATPase activities of N.sibirica callus.When Na Cl concentration was less than 150 mmol·L^-1,their activities first increased and then decreased.With the increase of exogenous Ca²⁺ concentration,the plasma membrane H⁺-ATPase activity increased first and then decreased.When Na Cl concentration was less than 100 mmol·L^-1,the plasma membrane H⁺-ATPase activity reached itsmaximum when Ca²⁺ concentration was 5 mmol·L^-1,and when Na Cl concentration was more than100 mmol·L^-1,the plasma membrane H⁺-ATPase activity reached its maximum when Ca²⁺concentration was 10 mmol·L^-1,then decreased.The activity of Ca²⁺-ATPase in plasma membrane continued to increase with the increase of Ca²⁺ concentration.The results showed that under salt stress,plants promoted Na⁺ pumping out cells by increasing ion pump activity on plasma membrane,reduced intracellular salt concentration,protected the structure of plasma membrane and maintained the stability of membrane system.A certain concentration of exogenous Ca²⁺ can effectively improve the activity of ion pump and salt tolerance of plants.