Physiological Alleviating Effects Of Exogenous Nitric Oxide On The Chinese Cabbage Under Copper Stress

As a member of Crueiferae Brassica, chinese cabbage(Brassica capestris L.) is a one or two years herbage plant. Along with the frequently use of baeterieide and a great deal of eontamination, more and more copper was in poured into the entironment. It is resulted in the pollution of soil and worse vegetable. Studies showed that nitric oxide was involved in various physiological processes of plants, such as respiration, photomorphogenic, responses, seed germination, senescence, stress responses, programmed cell death,disease resistance in plants. The relationship between nitric oxide and resistance, especially the relationship between nitric oxide and copper tolerance of plants is a research focus in recent years. To the present, information about the effects of nitric oxide in physiological processes of plants is very limited. There are hardly reports about the relationship between copper tolerance of horticulture plants and nitric oxide.In the present experiment, by using exogenous sodium nitroprusside (SNP), a nitric oxide donor, and Nitro-L-arginine, a nitric seavenger the effects of nitric oxide on copper tolerance of chinese cabbage cultivar seedlings were investigated under copper stress. Chinese cabbage was chosen as an experimental material. The relation ship between nitric oxide and seedling growth, photosynthetic characteristics, nitrogen metabolism, antioxidative system in adaptation to copper stress was discussed. Main research results were as follows:1.300μmol·L-1 exogenous sodium nitroprusside, were investigated on the growth, leaf protective enzymatic activities superoxide dismutase(SOD), peroxidase (POD), catalase (CAT) , and oxidative damage in Chinese cabbage seedlings under 100 -1000μmol·L-1 copper stress condition. The results showed that the best effect on the alleviation of 300μmol·L-1copper stress damage was observed in the treatment of 300μmol·L-1 SNP. At this concentration, the seedling growth, chlorophyll content, activities of protective enzymes in leaves were significantly increased, while malondialdehyde (MDA) content in leaves were significantly decreased. The above results indicated that dosage effect of exogenous nitric oxide donor (SNP) existed on the alleviation of copper stress in chinese cabbage seedlings, and the best alleviating effect was found at 300μmol·L-1copper stress, which elevated the tolerance of plants.2.By the treatment of exogenous nitric oxide,photochemical efficiency of PSII (Fv/Fm), potential photochemical efficiency(Fv/Fo),were increased, minimal fluorescence (Fo), was obviously in the leaves of chinese cabbage seedlings decreased under 300μmol·L-1 copper stress condition. Copper treatment alone had significant effects on upper indexes. The results showed that NO could alleviate the damage of PSII caused by copper stress and play an important role in enhancing copper resistance in chinese cabbage seedlings.3. exogenous sodium nitroprusside increased net photosynthetic rate (Pn), the content of photosynthetic pigment in leaves and the contents of soluble protein in leaves of chinese cabbage seedlings under 300μmol·L-1 copper stress significantly. Meanwhile, exogenous nitric oxide markedly decreased intercellular CO2 concentration (Ci) under 300μmol·L-1 copper stress, but Nitro-L-arginine blocked these effects of sodium nitroprusside in some extent.4. Sodium nitroprusside significantly increased activity of SOD, POD, CAT in leaves of chinese cabbage seedlings under 300μmol·L-1 copper stress. Nitro-L-arginine blocked the effects of nitric oxide on adjusting antioxitant system. However, exogenous nitric oxide markedly decreased membrane permeability, the content of MDA and H2O2 under 300μmol·L-1 copper stress.