Effects Of Exogenous MT And Ca²⁺ On Improving Salt Tolerance Of Melon

Cucumis melo L.is also known as melon,annual muskmelon vine herbaceous plant genus of Cucurbitaceae,high nutritional value,is a type of important fruit vegetables.With the popularization of greenhouse,plastic greenhouse,and other agricultural facilities melon cultivation area in our country is very broad.However,the secondary salinization of soil caused by unreasonable irrigation and fertilization has seriously restricted the sustainable development of melon cultivation.Therefore,the research chose melon as test material,by spraying MT and Ca²⁺ under NaCl stress,studying the melon seedlings growth,photosynthesis,and antioxidant enzyme activity under different treatments.To conclude the MT and Ca²⁺ concentration that best suitable for alleviating the muskmelon salt stress,and clarify the interaction mechanism between MT and Ca²⁺.The main results were listed as follows:1.By taking ’horn crisp’ melon seedlings as test material under the salt stress of 100mmol·L-1,melon seedlings’ growth was inhibited.The growth indexes,such as lower plant height and stem diameter reduced,and so did the physiological indexes,such as root activity and nitrate reductase activity.However,leaf relative conductivity,MDA and peroxide content increased.2.By spraying different contribution of MT under salt stress condition,measure and analyse the seeding’ growth and physiological characteristics to screen the optimum concentration of MT.he results showed that compared with SS+0 group,melon seedling shoot fresh weight,chlorophyll content,net photosynthetic rate（Pn）,root activity,and nitrate reductase activity under the treatment of 100μmol·L-1 of MT were increased by 47%,24.3%,27%,25.7%and 26.8%,respectively.Alleviation effect was better than other treatments.By comprehensive analysis and comparison,it could be concluded that 100mo1·L-1 MT was the best concentration to alleviate the salt stress of melon seedlings.3.By spraying different contribution of Ca²⁺ under salt stress condition,measure and analyse the seeding’ growth and physiological characteristics to screen the optimum concentration of Ca²⁺.The results showed that compared with SS+0 group,the plant height,stem diameter,shoot fresh weight and root fresh weight under the treatment of 5mmol·L-1 of CaCl₂ were increased by 30.3%、3.1%、23.9%、79.6%,respectively.Alleviation effect was better than other treatments.By comprehensive analysis and comparison,it was found that 5mmol·L-1 CaCl₂was the best concentration for melon seedlings.4.Compared with controls,salt stress significantly inhibited growth of the melon seedlings,increased contents of Cl^-and Na⁺ in roots and leaves,and decreased contents of K⁺,Mg²⁺ and Ca²⁺.Under salt stress condition,MT and Ca²⁺ treatment could remarkably reduce the contents of Cl^-and Na⁺ in roots and leaves,and increase the contents of K⁺,Mg²⁺ and Ca²⁺,making the ratio of Na⁺/K⁺,Na⁺/Ca²⁺ and Na⁺/Mg²⁺decrease.Additionally,exogenous MT or Ca²⁺ increased H+-ATP activity and osmotic adjustments,and further alleviated cell membrane injuries imposed by salt stress:lower MDA content and relative conductivity.In short,single or combined applications of exogenous MT and Ca²⁺ effectively reduced the content of Cl-and Na+,improved ion balance by enhancing H+-ATP activities,increased the content of osmotic adjustment substances,reduced the contents of O₂^-、H₂O₂ and ameliorated membrane lipid peroxidation.The result showed that combined applications of exogenous MT and Ca²⁺,was better performance than other treatment due to the synergistic effect on increasing salt tolerance in melon seedlings.5.Compared with SS+MT and SS+MT+Ca,adding calcium inhibitors（LaCl₃）made physiological indexes of melon seedlings change.The relative conductivity increased,antioxidant enzyme activity decreased and the content of MDA 和 O₂^-raised.These aggravated melon seedlings’ degree of membrane peroxidation.However,exogenous application of MT or Ca²⁺ could improve kmelon seedlings plasma membrane’s protection capability,reduce relative conductivity and plasma membrane permeability,increase antioxidant enzyme activity.The result showed that Ca²⁺,combined with CaM,had the synergistic effect with MT.It could adjust plasma membrane permeability,and reduce relative conductivity.Ca²⁺ and MT could work together to eliminate MDA,O₂^-,H₂O₂ caused by salt stress,reduce the degree of membrane lipid peroxidation,and ease the oxidative damage of melon seedlings to reduce the effect of salt stress to them.The study played an important role in increasing melon yield and economic benefit.