The Relationship Of Abscisic Acid, Phospholipase D? And Nitric Oxide In Arabidopsis Thaliana Under Drought Stress

The growth and development of plants are affected by environmental non biological factors,such as drought,high salinity and low temperature.In these abiotic stresses,drought is the most serious environmental factor limiting plant growth and crop yield.The content of abscisic acid(ABA)in plant cells increased under drought stress.The accumulation of ABA can significantly increase the adaptability and tolerance of plants to drought stress.The relationship of the ABA and various signaling molecules is very complex.Understanding the relationship between signal molecules will help us better understand the ABA responding mechanism to drought stress,and provide the theoretical basis for enhancing drought resistance of crops and improving agricultural production.Phospholipase is a kind of hydrolytic enzyme for the degradation of phospholipids,and Phospholipase D(PLD)is one of key enzyme in phospholipase's family.PLD and its product phospholipids(PA)play important roles in maintaining the stability of cell membrane and regulating the signal conduction function of various stresses.There are 12 different types of PLD genes in Arabidopsis thaliana,which have different biochemical,regulatory and structural characteristics,and participate in different cell processes.Nitric oxide(NO),as a very simple lipid-soluble gas molecule,is easy to diffuse through cell membranes and transmits signals,which plays an important role in plant growth and abiotic stress.PLD and NO are the important signal molecules that have been found in ABA signaling pathway.The stomatal closure induced by ABA will be inhibited when PLD?1 dysfunction or endogenous NO inhibition.However,the specific regulation mechanism of ABA on PLD? and the signal position relationship of PLD? and NO in drought stress are not clear yet.To sum up,we have Arabidopsis wild type(WT),ABA1-deficient mutant(aba1),nitric oxide synthase(NOS)-deficient mutant(noa1),nitrate reductase(NR)-deficient mutant(nia1,nia2),and phospholipase D?(PLD?)-deficient mutant(pld?)seedling as material,using molecular biology,cell biology and plant physiology method,the regulation mechanism of ABA on PLD? and the signal transduction relationshipbetween PLD? and NO responding the 0.3 M mannitol simulated drought stress were studied.The results are as follows:1.The content of ABA and the expression of ABA1 gene increased significantly under drought stress.Both ABA and Ca Cl2 significantly promoted the activity of PLD and PLD? gene expression in WT and aba1 seedlings under drought stress.Ca2+inhibitors(EGTA,La Cl3 and RR)significantly inhibited the PLD activity and PLD?gene expression in WT and aba1 seedlings.Ca2+ inhibitors significantly inhibited the effect of ABA on PLD activity and PLD? relative expression in WT and aba1 seedlings,and the inhibition effect of La Cl3 was most obvious.These show that ABA can activate PLD? gene expression by Ca2+,and then promote the PLD activity under drought stress.The influx of calcium from the plasmic membrane Ca2+passage plays a major role in this process.2.NO content,PLD and NR activity with PLD?,NOA1,NIA1 and NIA2 expression were significantly increased under drought stress,while pld? and nia2 are more sensitive than other mutants(noa1 and nia1)to drought stress.Sodium nitroprusside(SNP),as an exogenous NO donor,can improve the seed germination of WT,nia2 and pld?.The exogenous phosphatidic acid(PA)can promote seed germination of WT and pld? under drought stress except nia2.Besides,in compensation experiment,PA can promote the production of NO in WT and pld?under drought stress,but not in nia2.Therefore,it is speculated that PLD?/PA located at the upstream of NO signal passage under drought stress,and the NO produced by NR2 is the main way for PLD?/PA to promote Arabidopsis seed germination under drought stress.3.The promoting effect of exogenous NO donor(SNP)on the antioxidant activity,free proline,soluble protein,NR activity and endogenous NO content in WT was more obvious than that in nia2 under drought stress.The endogenous NO produced by the NR2 pathway involved in the regulation of antioxidant enzyme activities and the accumulation of osmolyte in Arabidopsis thaliana under drought stress.These results indicated that exogenous NO can regulate endogenous NO by promoting NR2 activity,and the endogenous NO protects the plants from drought stress by maintaining the balance of reactive oxygen species and the stability ofosmotic pressure of Arabidopsis thaliana under drought stress.