Physiological Mechanisms Of Salt Tolerance Improved By Grafting In Tomato (Lycopersicon Esculentum Mill.)

In recent years,with the successive cultivation in the greenhouse,the secondary salinization in the soil is becoming heavier and has become one of main factors limiting the sustainable development of vegetable production.Tomato(Lycopersicon esculentum Mill.)is an important vegetable and is widely cultured in open field and greenhouse.There are some wild tomatos,which are more salt-tolerant than common cultivar.Grafting is an important agricultural technique,which has been widely used in crops,such as watermelon,melon,cucumber,tomato,eggplant and so on.Grafting plays an important role in the production of horticulture.Therefore,the research of salt tolerance in tomato is of theoretic and practical significance to direct the production of tomato and improve the use efficiency of greenhouse.Recently,it has been reported that grafting improved the salt tolerance of watermelon and tomato. However,the mechanisms of grafting on tomato in salt-tolerance are not clear. Therefore,using wild tomato as the rootstock,the effects of grafting on the physiological and biochemical mechanisms in hydroponic tomato seedlings under salt stress were investigated,in order to clarify the possible mechanisms of enhancing salt tolerance in plants.The main results were presented as follows:1.Under salt stress,grafting treatment significantly increased overground part of plant dry weight.100 mM NaCl stress significantly decreased photosynthetic rate (Pn),transpiration rate(Tr)and stomatal conductance(Gs)in leaves of tomato seedlings,and the grafted seedlings were significantly higher than non-grafted seedlings under 100 mM NaCl.Under salt stress,intercellular CO₂ concentration(Ci) essentially unchanged and the concentrations of grafted seedlings were same as non-grafted seedlings.The water use efficiency(WUE)significantly increased in grafted seedings while decreased in the non-grafted ones.Under 100 mM NaCl salt stress,the reduction degree of Fv/Fm and quantum yield of PSâ…¡(φPSâ…¡)of non-grafted seedlings is higher than grafted ones.Salt stress increased non-photochemical quenching of fluorescence(NPQ),and the non-grafted seedlings were significantly higher than grafted ones.The results showed that grafting could improve the capture and conversion of light energy and improve the osmotic adjustment ability of tomato seedlings under salt stress and improved plant growth.2.Under salt stress,relative electrolyte leakage and MDA content significantly increased and the increased extent of grafted seedlings was lower than non-grafted ones:Under salt stress,the activities of SOD significantly increased while the activities of CAT decreased in non-grrafted tomato leaves.But the enzymatic activities of grafted seedlings were higher than non-grafted ones.It could be concluded that higher activities of CAT,APX,DHAR,GR lower plasma membrane permeability and less contents of MDA in salt-stressed leaves induced by grafting may protect the plant tissues from membrane oxidative damage under salt stress,thus mitigating salt toxicity and improving the growth of tomato plants.3.Salt stress significantly decreased the absorption of potassium and increased the absorption of sodium.The increased extent of sodium in the root of grafted seedlings was higher than non-grafted ones,which indicated that grafting greatly improved the ability of avoiding sodium.Under salt stress,the content of K and K/Na ratio decreased,but grafted seedlings were higher than non-grafted ones,which indicated that grafting greatly improved the activities of selective absorbing potassium.In conclusion,roots were stronger and the activities of selective absorbing potassium were higher after grafted.The results showed that grafting improved tomato salt-resistance.