Physiological Response Of Puccinellia Tenuiflora To Osmotic And Isotonic Salt Stress

Salt and drought are the most important abiotic stresses that limit plant growth and agricultural development.The salt-excluding plant,Puccinellia tenuiflora,is a rare gramineous halophyte,which is closely related to important crops such as rice and wheat.Previous studies have found that P.tenuiflora can reduce the net accumulation of Na~+in the tissue through stronger selectivity for K~+over Na~+of root endodermis.What's more,PtNHX1,PtSOS1 and PtHKT1;5 could improve its salt tolerance by synergistically maintain the Na~+stability at the whole plant level.In addition,the endodermis is a major obstacle to limit ions enter into pericycle in P.tenuiflora,which is significantly thickened under high salt treatment.The suberin deposition on the surface of root endodermis is enhanced by various stresses.The relationship between the salt-tolerant ability of P.tenuiflora and the thickening of the root endothelium and the deposition of suberin is still unclear.What's more,although the salt-tolerant study of P.tenuiflora has been extensive,but it is not clear that why it could respond to salt but not drought,and the difference in P.tenuiflora respond to drought(osmotic stress)and salt as well as how the suberin deposition changes under the same osmotic potential is also not clear.Therefore,this study compares the growth and physiological responses of P.tenuiflora to osmotic stress and isotonic salt stress to reveal its physiological principles of why it is salt tolerant but not drought tolerant,and explains its structural reasons for its strong resistance by comparing component and content of suberin with Arabidopsis thaliana.The main results are as follows:1.When treated by iso-osmotic stress,the growth is better in salt stress than in osmotic stress.Plant height,root length,biomass and tissue water content are all better than osmotic stress.While the osmotic potential of leaves is lower and the inhibition of photosynthesis is also more serious under osmotic stress.2.The leaf membrane system of P.tenuiflora was destroyed under 150 mM NaCl and-0.8 MPa.Under the treatment of-0.8 MPa,the root plasma membrane was also seriously damaged,resulting in root electrolyte leakage rate increasing.3.Under the salt treatment,P.tenuiflora accumulated more Na~+in shoot and its contribution rate to the osmotic potential increased obviously.Under the osmotic stress with consistent osmotic potential,there are more soluble sugar was accumulated in shoot and a significant increase in its contribution to the osmotic potential.4.Compared with the control,the water transported by the apoplasts under the various treatments was reduced.Although the apoplast pathway is restricted,the root Na~+could be also transported through the symplast pathway to the shoots for osmotic adjustment under salt treatment.5.Under the osmotic stress and isotonic salt stress,the suberin's content was not significantly induced to increase in P.tenuiflora.While compared with Arabidopsis,its root suberin contains more phenolic compounds,which may be the reason why P.tenuiflora's apoplastic barrier is more effective against abiotic stress than Arabidopsis.