Physiological Alleviating Effect Of Exogenous Nitric Oxide On Cucumber And Chinese Cabbage Under Cadmium

Cucumber (Cucumis sativus L.) and Chinese cabbage (Brassica campestris L.) are main vegetables, planted widely in greenhouse and outdoor in China. Cadmium is one of the most aggressive and persistent heavy metals that may be present in natural environments as a by-product of human activities; among them, application of phosphoric fertilizers, pesticides and sewage farming constitute the major Cd inputs into agricultural soils. Cd concentration in soil is over standard in many places. Excess Cd inhibited the growth and yield of plants, including cucumber. Nitric oxide (NO) is a versatile signal molecule that functions through interaction with cellular targets via either redox or additive chemistry, and is involved in many key physiological processes of plants, such as growth, development, disease resistance and stress resistance. In this experiment, we studied the effects and the mechanism of that NO alleviate the toxic hazard that Cd to cucumber and chinese cabbage. The main results were as follows:1 Plant growth, chlorophyll and carotenoid contents, net photosynthetic rate (Pn) and stomatal conductance (Gs) of cucumber and chinese cabbage decreased with increasing concentration of Cd, while intracellular CO2 (Ci) significantly increased. The primary maximum photochemical efficiency of PSII(Fv/Fm), the maximum yield of the photosystem II photochemical reactions (Fv/Fm) and the quantum yield of photosysytem II electron transport (ΦPSII) were significantly inhibited by excess Cd, and was more significant with the increasing concentration of Cd. MDA and Pro contents, increased, superoxide dismutase (SOD) and catalase (CAT) activities decreased with the increasing concentration of Cd. Low concentration of Cd increased POD activity while high concentration dramatically inhibited its activity. The results showed that the Cd concentration of 300μmol·L-1 had the most significant effect.2 Application of SNP significantly alleviated the inhibition of plant growth of cucumber and chinese cabbage seedlings under Cd stress, and increased the contents of photosynthetic pigment significantly. Pn, Fv/Fm, Fv/Fo,ΦPSII and activities of SOD, CAT and POD increased with application of SNP, whereas MDA content decreased with application of SNP. The results showed that 300μmol·L-1 concentration of SNP had the most significant relief effect. However the application of SNP was different, this indicated that the by-products of SNP had inhibition. Potassium ferricyanide (SF) as the by-products of simulates SNP, which offered CN- affected the seedlings.3 Application of inhibitors significantly decreased photosynthetic pigment content, Pn, Fv/Fm, Fv/Fo,ΦPSII, and POD activity. At the same time, inhibitors increased the content of MDA and Pro, which indicated that inhibitors aggravated the stress of Cd to cucumber and chinese cabbage seedling. Thus, we can see that application of SNP was an effective way to alleviate the toxic hazard of Cd to cucumber and chinese cabbage seedlings.