Study of Mitigative and Physiological Effects by Arbuscular Mycorrhiz Fungi in Cucumber Plants under Salt Stress
|School||Nanjing Agricultural College|
|Keywords||Cucumber Salt stress Arbuscular mycorrhiz fungi Antioxidant enzyme Ascorbat-glutahione cycle Mineral nutrition|
Soil salinization seriously restricted the developing of modern agriculture. It was the main limitation factor of the crops growth and yield. High salty might course the yield reduction and the death of plants, effect the quality of vegetables. Increased the salt resistance of plants was very important to the sustainable development of agriculture. As the combo of the soil mycorrhiz and higher-plant roots, arbuscular mycorrhiz fingu (AMF) could infect most of the plants. It was recognized that AMF vaccinated could increase the absorptive amount of N, P and minor elements in plants, raise the yield and quatilty of vegetables, improve the resistance of environmental stress. However, the mechanism was still not well established in physiological regulation role of AMF in its adaptation to salt stress in cucumber seedlings.In the present study, salt-sensitive cultivar’Jinchun No.2’was chosen as experimental materials. In order to elucidate the mechanism of AMF in improving tolerance of cucumber to salinity, and develop suitable methods to whether infection seedlings with AMF could enhance the resistance of cucumber plants, we investigated the effects of different kinds of AMF on the growth, photosynthesis and mineral element contents in cucumber seedlings, and the relationship between AMF infection and the growth, photosynthesis, mineral element, reactive oxygen metabolism and ascorbat-glutahione cycle in cucumber seedlings under salt stress. Main research results were as follows:After treating with different levels of NaCl (0%,0.3%,0.6%,0.9% and 1.2%) both height, stem diameter and net photosynthetic rate (Pn) decreased, cell membrane damage rate and MDA contents increased, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activity improved, and the change of each index increases with the increase of NaCl concentrations. Under high concentration (0.9%,1.2%) NaCl treatment, the growth of leaves were distinctly inhibited, the survival rate of seedlings falled, and each physiological indices of the seedlings significant changed comparing with control.0.3% NaCl treatment had little effect on the growth and physiological indices. Under 0.6% and more concentration of NaCI treatment, biomass significantly decreased.Inoculation four kinds of AMF all could promote the growth of cucumber, chlorophyll a, chlorophyll b, carotenoid contents and photo synthetic rate of leaves, and the mineral element contents of shoots and roots were higher than control. It was illustrated that the inoculation of AMF might promote the growth of plant by enhancing the photosynthesis, the water and nutrients absorption of cucumber seedlings. GMA was the best one to promote the growth of cucumber seedlings.Inoculated AMF could effectively promote the growth and mineral nutrient absorption in cucumber plants, increase its yield and fruit quality. Salt stress might inhibit the growth of cucumber, reduce the mineral element contents and K+/Na+ of plants, and decrease the yield and quality of fruit. AMF inoculation could alleviate the inhibition of cucumber plants by salt stress, improve the mineral element contents and K+/Na+ of plants, and increase the yield and quality of fruits. It showed that by promoting the absorption of mineral nutrients in cucumber plants under salt stress, AMF could expedite the growth of plant and increase the yield and quality of fruit under stress conditions, consequently enhanced the salt stress tolerance in cucumber plants.Under salt stress, the height, the fresh and dry weight of shoots and roots decreased, and the net photosynthetic rate (Pn), stomatal conductance (Gs), stomatal limitation (Ls), transpiration rate (Tr) and water use efficiency (WUE) reduced, while intercellular CO2 concentration (Ci) increased in cucumber seedlings. Under salt stress, after AMF-inoculation the growth index, Pn, Gs, Tr, Ci and WUE increased, however Ls decreased. It indicated that AMF could accelerate plant growth and enhance the salt stress tolerance of cucumber seedlings by promoting the photosynthesis and the absorption of water.Under salt stress, hydrogen peroxide (H2O2), ascorbic acid (AsA), dehydroascorbic acid (DHA) and oxidized glutathione (GSSG) contens, AsA/DHA ratio, superoxide dismutase(SOD), peroxidase(POD), catalase(CAT), ascorbate peroxidase (APX), glutathione reductase (GR), mondehydroascorbate reductase (MDAR), dehydroascorbaic reductase (DHAR) activity significantly increased, while glutathione (GSH) and malondialdehyde (MDA) contents, GSH/GSSG ratio, O2 production rate notablely decreased compared with control in leaves and roots of cucumber seedlings. Under salt stress, after AMF inoculation the AsA and GSH contents, AsA/DHA and GSH/GSSG ratio, SOD, POD, CAT, APX, GR, MDAR activities in leaves and roots were remarkablely higher than those of salt stress, while MDA, H2O2 and GSSG contents, O2-·production rates in leaves and roots were lower than that of salt stress. It was suggested that AMF could improve the antioxidant capacities of cucumber seedlings, then ease the injury of salt stress in cucumber seedlings.Under salt stress, after AMF-inoculation soluble protein, soluble sugar, proline and various mineral elements contents, K+/Na+ increased. It showed that AMF could enhance the osmotic adjustment mechanism of salt tolerance by promoting the mass accumulation of soluble protein, soluble sugar and proline contents, and improve the absorption of mineral element contents to alleviate the damage of salt stress in cucumber seedlings.