Studies On Physiological Mechanisms Of The Improved Tolerance To NaCl By Polyamines In Cucumber (Cucumis Sativus L.)

In our study, we investigated the effects of exogenous polyamines and inhibitor applications on cucumber (Cucumis sativus L. cv. Jinyan No.4) seedlings exposed to salt stress. The seedlings were cultivated in plastic containers filled with continuously aerated full-strength Hoagland nutrient solution. The present work was aimed to study the effects of polyamines on plant growth, ion content, leave water status, photosynthesis , activities of antioxidant enzymes and carbohydrate metabolite under salt stress. The major results were as follows:1 Plant growth was significantly inhibited by salt stress (100-200 mM NaCl), and high salt concentration (200 mM NaCl) even induced the death of cucumber plants. Interestingly, Put completely alleviated the inhibition of root growth. However, it was not effective on relieving the growth inhibitions of leaf and stem by salt stress. There was a significant decline in stomatal conductance and net photosynthetic rate when plants were subjected to salt stress. However, plants with Put pretreatment showed less extent of inhibition in photosynthesis and Put induced a large restoration of stomatal conductance in the presence of salt.2 Leaf water potential and water content decreased dramatically with salt stress, and nutritional imbalance in cucumber plants were also found. Thus, Put pretreatment insalt-stressed plants may improved the plant growth through preventing overaccumulation of Na+ in roots and increasing K+ and Mn uptake.3 There was a sharp increase in total sugar content in cucumber roots exposed 100 mM NaCl, possibly as a result of the adaptive mechanism of plant under salt stress. However, the increase of starch content in leaves may give rise to counter effect on net photosynthetic rate. Put pretreatment in salt-stressed plants decreased the total sugar andstarch content.4 We found that NaCl significantly increased the MDA and H2O2 content and this enhancement was alleviated by Put pretreatment. However, the reduced accumulation of reactive oxygen species (ROS) was not accompanied by the increase in ROS scavenging capacity. Put might reduce the membrane peroxidation and avoid injuries of salt stress through other pathways, such as stabilization of cellular membrane, direct scavenging of ROS and alleviation of Mn deficit.