Salt Tolerance Appraisal Of Tomato And Cucumber And Effects Of Salt Stress On Sucrose Metabolism And Ionic Uptake

Tomato and cucumber are moderate salt-sensitive crops that are cultivated widely in the world.As soil resource is becoming scarce day by day,saline soil gets more attention than ever before because of its prospect as a type a soil resource.At present,screening out and breeding salt-tolerant crop cultivars through tapping the salt-tolerant potential of germplasms is viewed as the most economic and effective approach to exploit saline soil.Therefore, salt-tolerant cultivars' selection and breeding,appraisal of salt tolerance,and enhancement of salt tolerance has become a research focus.Invertase is a versatile agent in plants,it acts as a catalyst in the process of sucrose's hydrolyzation,and it can help plants to resist hard environments through regulating osmosis pressure of the cell,playing roles in signal transduction as well as regulating genes expression.Ionic balance and normal metabolism are disrupted under salt stress.Salt tolerance indices of tomato and cucumber were appraised in this study,and effects of salt stress on invertase expression,sucrose metabolism,and photosynthetic pigments content as well as ionic uptake were studied,aiming at providing simple and convenient indices for early appraisal,and laying the theoretical foundation for physiological research relevant to salt tolerance.Findings of the study are showed as follows:1.By artificially simulated salt stress with NaCl aqueous solution,salt tolerance and salt tolerance indices of tomato and cucumber were appraised during their sprout and seedling stage.The results indicated that salt tolerance of tomato and cucumber differed between their sprout and seedling stage.Indices such as germination energy,germination rate,germination index,germination vigor index,hypocotyl lengh and the overground fresh weight were selected to appraise salt tolerance of tomato and cucumber during their sprout stage;and overground fresh weight,root fresh weight,overground dry weight,root dry weight,index of seedling growth as well as root/shoot were chosen to appraise salt tolerance of tomato and cucumber during their seedling stage.2.By studying seedlings of tomato and cucumber with different salt-tolarant potential, invertase expression in leaves and roots of tomato and cucumber were determined.The results showed that activity of cell wall invertase and soluble acid invetase were high in leaves and roots of tomato and cucumber.Invertase activity in cucumber was higher than that in tomato,and cell wall invertase in leaves and root of cucumber showed the highest activity, followed by invertase in tomato leaves,and invertase in tomato roots had the lowest activity. Cell wall invertase in cucumber leaves was in positive correlation with cucumber's salt tolerance,but no such correlation was showed by other types of invertase in the materials determinded.3.By artificially simulated salt stress with NaCl aqueous solution in controlled environment,effects of salt stress on invertase expression and sucrose metabolism of tomato and cucumber were studied.As was shown in the results,invertase activity,sucrose and hexose as well starch content in tomato and cucumber all increased before they fell,and the increase of invertse activity was seen earlier than the increase of sucrose,hexose and starch content.By affecting sucrose's hydrolyzation,invertase regulated sucrose/hexose to combat against salt stress.Sucrose and hexose content in salt-tolarant tomato and cucumber was higher than that in non-salt-tolerant ones.4.Photosynthetic pigments content in salt-tolerant tomato and cucumber were not so vulnerable to salt stress.Under moderate and low-level salt stress for a short period of time, chlorophyll content and chlorophyll a/b increased in both tomato and cucumber.Nevertheless, under high-level or moderate and low-level salt stress for a long time,total chlorophyll content and chlorophyll a/b decreased.Under salt stress,chlorophyll/carotenoids declined, and carotenoids were more vulnerable to salt stress than chlorophyll.5.Under salt stress,Ca²⁺ content in tomato seedlings went up,but K⁺ content went down, and Ca²⁺ content increased before a downward trend was seen.Nevertheless,Na⁺,K⁺ as well as Ca²⁺ content all showed a downward trend in cucumber.Increase of Ca²⁺ content in salt-tolerant materials was more than that in non-salt-tolerant ones,but the increase of Na⁺ content showed a reverse trend.