Effects Of Exogenous Selenium On The Growth Of Cucumber Under Drought Stress

Drought is one of the most important environmental factors that limits the growth and development of plants.Cucumber?Cucumis sativus L.?is an important vegetable crop in China,which require a lot of water and cannot endure drought.Drought stress has the bad effect on the growth and development of cucumber,which leads to the decrease of the yield and quality of cucumber,finally reduces the economic benefit.Selenium is an essential trace element for human beings and animals.It has many biological functions,such as anti-aging,anti-oxidation and immunity enhancement.Exogenous selenium can reduce the harmful effects of stress on plants by eliminating stress,and it is an important way to improve drought resistance of plants by using exogenous selenium.In the cucumber seed germination stage and seedling stage separately,and in the PEG-6000 simulated drought stress situation,the effects of Methionine-Selenium(0?10?20?30?40 mg·L^-1)and Na₂SeO₃(0?1?2.5?5?10 mg·L^-1)on “Qingbai”and“Jinshuai”cucumber seed germination and radicle growth,seedling growth and physiological characteristics were studied to select the optimum concentration of two kinds of exogenous selenium.Then the effects of two kinds of exogenous selenium concentration comparatively studied on cucumber yield,fruit quality and selenium content under drought stress.The mechanism of exogenous selenium in drought tolerance of cucumber was comprehensively discussed.The results of the experiment can provide theoretical and practical basis for exogenous selenium to alleviate drought stress for Cucumber.The main results obtained are as follows:1.The seed germination potential,germination rate,germination index,vigor index,the growth of seedling morphology and root vigor were inhibited under PEG-6000 simulated drought stress,Among them,the drought tolerance of “Qingbai”variety was slightly better than “Jinshuai”variety.The Methionine-Selenium and Na₂SeO₃ soaking could improve seed germination potential,germination rate,germination index,vigor index and seedling height,stem diameter,root vigor and seedling index in different degrees,while the best seed soaking concentration of Methionine-Selenium was 20 mg·L^-1;the best soaking concentration of Na₂SeO₃ was 5 mg·L^-1.2.Under PEG-6000 simulated drought stress,the growth of cucumber seedlings was inhibited and the cell membrane was damaged.With the increase of stress time,the relative water content of leaves decreased continuously,and the contents of REC and MDA were increased,while the contents of Proline and soluble sugar were significantly higher than those of normal conditions,Among them,the drought tolerance of “Qingbai”variety was slightly better than the“Jinshuai”variety.The suitable concentration of Methionine-Selenium and Na₂SeO₃ spraying treatment could promote seedling growth,reduce REC and MDA content of cucumber,increase Pro and SSC content,alleviate the damage of drought stress to cell membrane and improve the ability of osmotic adjustment,so as to increase the drought resistance of cucumber seedlings.3.The leaves of cucumber seedlings O2-production rate and H2O2 accumulation were increased under PEG-6000 simulated drought stress,furthermore,antioxidant enzymes?SOD,POD,CAT?and the activity of antioxidant substances?AsA,GSH?content were increased in the early stage of drought stress in varying degrees,and were decreased significantly later,indicating that short-term stress could induce the drought resistance of cucumber seedlings.But with time prolonged stress caused serious damage to cucumber seedlings.Suitable concentration of Methionine-Selenium and Na₂SeO₃ spraying treatment could reduce MDA and H2O2 accumulation;at the same time,they could improve the antioxidant enzymes?SOD,POD,CAT?activity and increase antioxidant substances?AsA,GSH?content,improve the drought resistance of cucumber seedlings.High concentration of selenium and sodium selenite reduced drought tolerance of cucumber seedlings.On the whole,the best treatment concentration of Methionine-Selenium was 20 mg·L^-1;the best treatment concentration of Na₂SeO₃ was 5 mg·L^-1.4.The suitable concentration of Methionine-Selenium and Na₂SeO₃ spraying treatment could effectively alleviate the drought stress on “Qingbai”and “Jinshuai” cucumber seedlings chlorophyll degradation,increase leaf net photosynthetic rate,stomatal conductance,transpiration rate and reduce intercellular CO₂ concentration,so as to enhance the photosynthesis of cucumber seedlings under drought stress.5.After drought stress at seedling stage of cucumber,the average fruit weight,fruit number,plot yield,fruit shape index,Vc content and soluble sugar content were significantly lower than that in normal growth conditions?CK1?.However,20 mg·L^-1 Methionine-Selenium and 5 mg·L^-1 Na₂SeO₃ could effectively repair the damage and improve the yield and quality of fruits,reduce the rate of deformed fruit.The content of selenium in fruit could meet the requirements of classification standard of China food selenium content(0.01⁰.9 mg·kg^-1).