The Role Of Chloride In The Xerophyte Pugionium Cornutum Adapting To Salt And Drought Stresses

The frequent drought and continuous soil salinization are main environmental factors that had seriously restricted the construction of ecological environment and the sustainable development of agriculture in desert regions of Northwest China.Comparing with most of crops and forages which have grown in abundant farming conditions for a long period,desert xerophytes have developed various mechanisms during the process of long-term evolution,so that they can successfully adapt to harsh living conditions.The resource plant Pugionium cornutum,as one kind of succulent xerophyte species that is widely distributed throughout the desert regions of Northwestern China,can well cope with salinity soil,moreover,has a strong adaptability to arid environments.Our previous investigations showed that Cl^-concentration in shoots and the contribution of Cl^-to leaf omostic potential were significantly increased with the increase of external Na Cl concentrations,which contributes to enhancing the osmotic adjustment capacity of P.cornutum under salt treatments,indicating that Cl^-might has positive effects for P.cornutum adapting to salt stress.However,the possible function of Cl^-in P.cornutum adapting to salt stress is not yet clear,and the role of Cl^-in the drought resistance of P.cornutum has not been reported.The aims of this project,therefore,are to investigate the physiological mechanisms of Cl^-involved in the adaptation to salt and drought stresses in P.cornutum.The main findings are as follows:1.Compared with 50 m M Na Cl,50 m M Na⁺significantly increased Na⁺concentration,but decreased K⁺and Ca²⁺concentrations in shoots of P.cornutum seedlings,and inhibited the photosynthetic capacity and the growth of P.cornutum;whereas,50 m M Cl^-could significantly increasing Cl^-concentration in shoots to maintain better water status,and had no influences on the photosynthesis of P.cornutum seedlings.The above results indicated that,compared with Na⁺,Cl^-was a beneficial and efficient osmoregulatory substance for P.cornutum under salt stress.2.Under 50 m M Na Cl treatment,the addition of 20?M DIDS and Nif,the inhibitors of Cl^-channels,had no effects on K⁺,Na⁺concentrations and their contributions to leaf omostic potential,but significantly decreased the net Cl^-uptake rate,Cl^-concentration in shoots and the contribution of Cl^-to leaf omostic potential in P.cornutum,and as a result,inhibited plant growth.3.Compared with control,the net Cl^-uptake rate,Cl^-concentration in shoots and its contribution to leaf omostic potential in P.cornutum seedlings were significantly increased under-0.3 MPa osmotic stress,suggesting that absorbing Cl^-and then transporting Cl^-to shoots for osmotic adjustment is one of the effective strategies for P.cornutum adapting to drought conditions.4.Under-0.3 MPa osmotic stress,the addition of 20 m M Na Cl significantly increased the shoot water content and net photothythesis rate of P.cornutum seedlings by 9%and 25%,repectively;the further addition of 20?M DIDS significantly reduced Cl^-concentration in shoots and the contribution of Cl^-to omostic potential,and consequently,counteracted the mitigative effect of Na Cl on the osmotic stress-induced growth inhibition of P.cornutum.All the above results indicated that P.cornutum can maintain better tissue water status and alleviate Na⁺toxicity by absorbing a great quantity of Cl^-and transporting them to shoots as an efficient osmoregulatory substance,which may be one of the effective strategies for P.cornutum adapting to salinity environments.Besides,the increase in Cl^-concentration in shoots and contribution of Cl^-to leaf omostic potential were the important physiological mechanisms for P.cornutum to adapt drought conditions.