Effect Of Salinity On The Growth And Physiological Metabolism Of Mini-Watermelon And Alleviating Function Of Exogenous Cacium And Putrescine

The threat of salinization in soil to agriculture production is a focus problem in the globe,and one of the major factors limiting plant growth and production.The secondary salinization in soil is ubiquitious in the protected culture,it have seriously influenced the yield and quality of crops,and become a difficult problem imparetive to solve in the protected culture.Calcium is not only one of necessary nutrient elements,but also a second messenger in connecting external signals and the physiological and biochemical process within cell.Calcium can initiate a series of physiological and biochemical process by increasing free Ca²⁺ concentration in cytoplasm and by combining Ca²⁺ and CaM under stress condition,hence play an important role in the response of plant to stress.Polyamines are low molecular mass aliphatic nitrogen-containing compounds having biological activity, produced in nitrogen metabolism of living organism.PAs have an important function in regulating growth and development,controlling morphology building,enhancing stress resistance and delaying senescence,and so on.In this paper,author identified and classified the salt tolerance of 16 mini-watermelon (Citrullus lanatus M.) cultivars by using cluster analysis.A salt-tolerant watermelon cultivar 'XiuYa' and a salt-sensitive cultivar 'XiuLi' were selected as materials,the experiment was carried out to study the effects of NaCI stress on plant growth, photosynthesis,ions uptake and distribution,and metabolism of reactive oxygen speices of mini-watermelon in solution culture.At the same time,we analyzed the effect of Cacium sulphate and putrescine in alleviating growth inhibition of mini-watermelon under salinity, explored the physiological function of exogenous Ca and Put in regulating salt tolerance of mini-watermelon plant,and analyzed the feasibility of improving salt tolerance of miniwatermelon by using exogenous matters.Main results were as follows:1.Apart from root length,the morphological indicators and plant biomass of all mini-watermelon cultivars were dramasticly decreased under 100 mmol·L^-1 NaCl stress; relative membrane permeability,the contents of MDA,Pro and Chl were increased significantly,while root vigor of different cultivars displayed diverse response to salinity. With RV of dry mass and RVs of other growth and physiological indicators that were significantly correlated with RV of dry mass as variables,systematic cluster analysis divided tested mini-watermelon cultivars into 3 types,including more-tolerant cultivars, middle-tolerant cultivars,less-tolerant cultivars.2.NaCl treatments below 50 mmol·L^-1 concentration did not apparently influence the growth of 'XiuYa' seedlings,the growth was significantly inhibited above 75 mmol·L^-1; with increasing NaCl concentration,the growth of 'XiuLi' seedlilng was significantly reduced.With inceaseing NaCl concentration and prolonging stress time,salt indury index was clearly increased,and survival percent was dramatically decreased under NaCl stress above 75 mmol·L^-1 concentration.The range of growth reduction of 'XiuYa' seedlings was less,and survival percent was higher than 'XiuLi' under salinity,i.e.the acclimation of 'XiuYa' to salinity was stronger than 'XiuLi'.3.With increasing NaCl concentration,the contents of the photosynthetic pigments in leaves were increased under lower NaCl concentration,and decreased above 75 mmol·L^-1; Pn,Gs and Tr were significantly decreased,Ci was reduced under lower concentration,and increased above 75 mmol·L^-1;Ls and WUE were increased under lower concentration,and tended to stabilization for Ls,and declined for WUE above 100 mmol·L^-1 concentration. The reduction of Pn under lower concentration NaCl treatments was the result of stomatal limitation,non-stomatal limitation became the main limitation factor under higher salinity. Compared with 'XiuLi',the inhibited extent of 'XiuYa' photosynthesis was clearly lower, this was one of the main reasons for its better growth under salinity.4.With enhancing NaCl stress,Na⁺ and Cl^- contents dramasticly increased,K⁺,Ca²⁺ and Mg²⁺ contents and K⁺/Na⁺ and Ca²⁺/Na⁺ ratios significantly decreased in watermelon plant.All ions showed compartmentalization,Cl^-was mainly accumulated in stem,and Na⁺ was mainly in stem and root.Reduced extent of K⁺ content was maximum in stem,and minimum in leaf.Ca²⁺ and Mg²⁺ mainly existed in stem and leaf,the reduced ranges were minimum in leaf.Selective transportation of K⁺ and Ca²⁺ were declined for root to stem, and increased for stem to leaf,it contributed to alleviate salt damage to leaf.Compared with 'XiuLi',the reduced ranges of K⁺ and Ca²⁺ contents were less,Na⁺ content were lower in leaf of 'XiuYa',K⁺/Na⁺ and Ca²⁺/Na⁺ ratios were higher.Better ions compartmentalization among organs was one of main reasons for its more-tolerance to salinity.5.With increasing NaCl concentration,O₂(?)production rate,MDA content and relative membrane permeability significantly increased in leaf,CAT and APX activities dramasticly increased;POD activity declined under lower concentration,and increased under higher concentration;SOD activity showed different regulation for two mini-watermelon cultivars. The contents of Pro,soluble sugar and AsA clearly enhanced;soluble protein content increased under lower concentration,and decreased under higher concentration.The activities of antioxidative enzymes and the contents of osmotic regulation matters of 'XiuYa' were higher than "XiuLi",and O₂(?) production rate,MDA content and relative membrane permeability were lower than 'XiuLi' under higher salinity.The less extent of growth inhibition and lipid peroxidation of 'XiuLi'were closely correlated with higher activities of antioxidative enzymes and higher contents of osmotic regulation matters.6.Exogenous CaSO₄ and Put obviously influenced the plant growth and physiological metabolism of mini-watermelon under salinity,and showed apparent concentration effect.6 mmol·L^-1 Ca and 1.0 mmol·L^-1 Put in solution significantly improved the plant growth, reduced relative membrane permeability and MDA content,increased the contents of soluble protein and AsA in leaves of mini-watermelon seedlings under salinity,so 6 mmol·L^-1 and 1.0 mmol·L^-1 were the suitable concentrations to mitigate the salinity injury of mini-watermelon plant for Ca and Put,respectively.7.Exogenous Ca,Put and Ca+Put significantly improved the plant growth,regulated some physiological metabolism of mini-watermelon under salinity.Three exogenous supplement means clearly increased the contents of photosynthetic pigments in leaves, enhanced Pn,Gs,Ci,and Tr,declined Ls,not influenced WUE;siguificantly decreased the contents of Na⁺ and Cl^-,increased the contents of K⁺,Ca²⁺ and Mg²⁺,and the ratios of K⁺/Na⁺ and Ca²⁺/Na⁺ in all organs;dramatically reduced O₂(?) production rate and MDA content,increased the activities of SOD,POD,CAT and APX;obviously increased the contents of NO₃^--N and soluble protein,improved the activities of NR,GS and GDH, significantly declined NH₄⁺-N content;increased the contents of free Put,Spd and Spm, decreased the activities of three polyamine oxidases under salinity.The results revealed that exogenous Ca,Put and Ca+Put treatments clearly increased salt tolerance of miniwatermelon, alleviated the salinity damage by improving photosynthesis,enhancing ions compartmentalization,regulating the metabolism of reactive oxygen species,nitrogen and polyamines.For mitigating the salinity-induced injury of mini-watermelon,the effect of three supplement means were Ca+Put＞Ca＞Put in turn,and the effect for 'XiuLi' seedlings was more evident than 'XiuYa'.