Physiological Mechanisms Of Salt Tolerance Improved By NO In Cucumber (Cucumis Sativus L.)

Nitric Oxide (NO) is an important active molecule in biology. It is firstly described as a diffusible multifunctional second messenger in animals since it plays various functions including the relaxation of blood vessels, neurotransmission and defense during immune response etc. It is now being evident that NO is also a ubiquitous signal molecule in plant kingdom. It was proved to participate in many key physiological processes such as seed germination, hypocotyls elongation, leaf expansion, root growth, lateral root initialation, programmed cell death, and stress tolerance. However, its disease-resistant physiological mechanisms in plants are still vague at present. Recently, it has been reported that the addition of NO increased the salt tolerance of crops in experiments within wheat (Triticum aestivum), maize (Zea mays) and rice (Oryza sativa), lupin (Lupinus luteus), reed (Phragmites communis trin.). However, information is still lacking regarding the effects of NO on salt tolerance of cucumber (Cucumis sativus L.) and its mechanism. Therefore, the effects of NO donor on the physiological and biochemical mechanisms in hydroponic cucumber seedlings under salt stress were investigated, in order to clarify the possible mechanisms of enhancing salt-tolerance in plants. The main results were presented as follows:1. The cucumber (Cucumis sativus L.) plants were grown in a hydroponics culture system for the investigation of exogenous NO on plant growth and the activities of major antioxidation enzymes [ superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT), dehydroascorbate reductase (DR) and glutathione reductase (GR) ] in seedling leaves under salt stress. The results showed that salt stress significantly decreased plant growth and soluble protein content, and increased electrolytic leakage percentage, H2O2 and MDA contents in leaves of cucumber seedlings, while NO treatment significantly decreased electrolytic leakage percentage, H2O2 and MDA contents under salt stress. Compared with the plants treated with salt alone, NO treatment significantly enhanced the activities of SOD, GPX, CAT and APX in salt-stressed cucumber leaves. It could be concluded that higher activieties of SOD, GPX, CAT, APX...