Effects And Mechanism Of Exogenous Ascorbic Acid,Glutathiose On The Resistance Physiology Of Dianthus Chinensis Seedlings Exposed To Cadmium In The Soil

Different degrees of Cd pollutions are existing in the urban soil here and there, and urban ground cover ornamental plants were grown in the Cd contaminated soil inevitably. Therefore, it is very meaningful to define the effects of Cd stress on the growth of urban ground cover plant and explore the way to alleviate the Cd toxicity. A greenhouse pot experiment was conducted to explore the effects of different concentrations (0,0.3,1,3,10,30,50mg/kg) Cd and (0,20,40,60,80and100mg/L) of exogenous AsA, GSH on the growth of Dianthus chinensis seedlings. comparing the regulation mechanism of the exogenous AsA, GSH on Dianthus chinensis seedlings exposed to Cd (50mg/kg), we got the best applied concentration of the two exogenous substances to ease the Cd toxicity of urban ground cover plants. It provided a theoretical basis for defining the effects of Cd stress on the growth of urban ground cover plant and exploring the way to alleviate the Cd toxicity. The experimental results showed that:(1) The tiller number, height and biomass of Dianthus chinensis seedlings lived in the different concentrations Cd contaminated soil exhibited significant "low promoting suppression" phenomenon. This phenomenon resulted from the activity of SOD, APX, MDAR, DHAR, GR and some other antioxidant enzyme increased against gradually increasing reactive oxygen species in Dianthus chinensis seedlings leaves in the low concentration (≤1mg/kg) soil Cd stress and stress beginning period; With the increasing of the Cd concentration (50mg/kg was the critical concentration) and cadmium stress time prolonging, the activity of the SOD, APX, MDAR, DHAR and GR decreased leading to excessive reactive oxygen species can not be removed by their own antioxidant system in a effective way, because of O2(?), H2O2and some other reactive oxygen species outbreaking. It Caused membrane lipid peroxidation and stress damage, eventually.(2) Spraying exogenous AsA (≤40mg/L) markedly eased the stress effect of Cd (50mg/kg). Exogenous AsA significantly increased the activities of the CAT, POD, APX, MDAR, DHAR and GR. Compared with Dianthus chinensis seedlings exposed to Cd, exogenous AsA also significantly increased the biomass, plant height, number of tillers, and the contents of AsA and GSH. Exogenous AsA markedly reduced the cell membrane permeability, the shoots Cd content, production rates and accumulative amount of H2O2. However, the alleviating effect of exogenous AsA was showed as quadratic curve. With higher concentration, the exogenous AsA showed pro-oxidant effects.(3) Spraying exogenous (≤40mg/L) GSH could significantly ease Cd (50mg/kg) stress on Dianthus chinensis seedlings. The activity of the CAT, POD, APX, MDAR, DHAR and GR, AsA and GSH content, biomass, plant height, number of tillers were significantly higher than Dianthus chinensis seedlings under Cd stress. The MDA, cell membrane permeability, Cd content, production rates and accumulated amount of H2O2significantly were lower than Dianthus chinensis seedlings under Cd stress. However, with the exogenous GSH concentration increasing, the mitigative effects reflected a downward trend.(4) Spraying suitable concentration of exogenous ASA, GSH could effectively ease the Dianthus chinensis seedlings cadmium toxicity (50mg/kg), so that improve its growth. Suitable concentration exogenous AsA significantly improved the Dianthus chinensis seedlings’biomass, plant height, number of tillers, the activity of the antioxidant enzymes, AsA and GSH contents. However, with the exogenous AsA concentration increasing, effects of alleviating decreased and produced prooxidant effects. Exogenous GSH could replenish the non-enzymatic antioxidants of Dianthus chinensis seedlings, but the activities of the antioxidant enzymes only had a little small changes relatively. Its main mechanisms to alleviate Cd toxicity might promote root PCs synthesis, thereby reducing the Cd contents in the seedlings. Because of the limited range of exogenous GSH concentration in the experimental design, further research is needed to research whether higher concentrations of exogenous GSH oxidative stress Dianthus chinensis seedlings synergistic with Cd.(5) Taking all factors, it indicated that35-45mg/L exogenous AsA was better than55-65mg/L of exogenous GSH to ease the Dianthus chinensis seedlings Cd toxicity, but taking the overall effects, the exogenous GSH was superior to exogenous AsA.