| Farmland suffers from cadmium (Cd) pollution, causing crop growth inhibition, yield reduction, and more likely to result in excessive accumulation of Cd in crop products, affecting food quality. This investigation was carried out to study physiological mechanism of genotypic differences in Cd-toxicity, uptake and accumulation, and explored with the mitigation effect and mechanism of exogenous GSH-based materials on Cd toxicity of rice.1 Mitigation effect and optimal concentration of exogenous GSH and plant hormones on Cd toxicity in riceHydroponic experiment was performed to study the exogenous reduced glutathione (GSH), indole-3-acetic acid (IAA),6-benzylaminopurine (6-BA) and gibberellin (GA3) on the alleviation of Cd toxicity and optimize the concentration of alleviation. The results showed that 5μM Cd significantly reduced plant height and shoot dry weight and fresh weight. Different concentrations of GSH significantly elevated plant height and shoot dry weight of rice seedlings. FiftyμM GSH mostly resumed the shoot fresh weight. Low concentrations of IAA significantly increased the root fresh weight. The various concentrations of 6-BA and GA3 did not significantly alleviate the Cd induced growth inhibition in rice seedling. Further research showed that all the concentrations of GSH (except for 50μM), as well as 0.1 and 10μM IAA, significantly increased the chlorophyll content (SPAD value). The variety of concentrations of GSH and IAA could reduce the shoot/root Cd concentration. Comprehensive comparative analysis of results showed that concentrations of 50 and 200μM GSH and 10μM IAA concentrations could serve as an effective mitigation factor in Cd toxicity.2 Genotypic differences of Cd stress on the ultrastructure and antioxidative system of rice seedlings and mitigation effects of exogenous GSH and IAAHydroponic experiment was performed to study the effects of exogenous GSH and IAA on Cd stress on growth, ultrastructure. and antioxidant system activity in two different Cd-resistance rice genotypes (Xiushui63, cadmium-sensitive genotype; Bing97252, cadmium-resistant genotype). The results showed that 5μM Cd stress significantly inhibited the growth of rice seedlings, destroyed the structure of mesophyll and root tip cells, with cell matrix thinning, chloroplast lamellae loose, vacuole larger and increased, root EDG increased, and more severely inhibition was observed in sensitive genotype. Cd also increased shoot SOD (mainly Mn-SOD), and GST activity, GSH content, and enhanced the POD activity during 10 d treatment, while reduced the APX activity, root POD, CAT activity, shoot AsA content and AsA/DHA ratio. The shoot CAT was elvated in Bing97252, but decreased in Xiushui63 after Cd exposure. Moreover, the increased of accumulation of membrane lipid peroxidation product MDA was more in Xiushui63. Thus, the possible mechanism of Bing97252 showing stronger potential tolerance to Cd might be that it has the ability to transfer and held Cd in the vacuole and has an effective antioxidant system. Addition of GSH significantly relieved of Cd toxicity in rice with plant growth and cell structure restored, MDA accumulation reduced, and the recovery was better in Bing97252. GSH significantly increased root POD, CAT, APX activity, shoot AsA content and AsA/DHA ratios in the cadmium-resistant genotype, significantly reduced GST activity in roots, GSH content in shoots and Cu/Zn-SOD activity at thel5th d in the both genotypes. Addition of IAA also alleviated the Cd toxicity to some extent with significantly increase of root dry weight, cell structure recovery, reducing shoot MDA accumulation and Cd accumulation in plants. IAA increased root AsA content, decreased the GSH content, GST activity and shoot POD activity. Combined GSH and IAA treatment can also significantly alleviate the symptoms of cadmium toxicity on the growth of rice; the effect was similar to single addition of GSH. The differences are that Cu/Zn-SOD activity, GSH content, GST activity, shoot AsA content and AsA/DHA values were lower with Cd+GSH+IAA treatment. These results showed that exogenous GSH, IAA may both take part in chelation, the effect of GSH should be related to restoration of antioxidant system, but IAA appeared to have no effect on antioxidant system.3 Genotypic dependent effect of exogenous glutathione on Cd-induced changes in cadmium and mineral uptake and accumulation in rice seedlingsWe evaluated how the different rice genotypes respond to Cd toxicity in the presence of GSH. We studied the effects on growth, Cd and mineral uptake and accumulation. The results showed that Cd stress (5,50μM Cd) decreased plant fresh weight, reduced content of chlorophyll a, b and total carotenoids, with Cd-sensitive genotype being much sever than tolerant one. Cd significantly decreased concentration and accumulation of Mn in root/shoot, and Zn in shoot, but increased Cu concentration in root/shoot. Significantly negative correlation was discovered between shoot Zn concentration and shoot/root Cd concentration, and between root Cd and Mn concentration. Exogenous GSH significantly alleviated Cd-induced growth inhibition in both genotypes, and significantly reduced Cd concentration in roots and shoots. Meanwhile, in 5μM Cd, the concentrations of Ca, Mn in Bing97252, and Ca, Zn in Xiushui63 in roots were elevated by addition of GSH. In 50dM Cd, external GSH enhanced the translocation of Zn. The effects of GSH were different between genotypes and dose of Cd treatment.4 Difference in response to Cd toxicity in photosynthesis and phytochelatins between Cd tolerant and sensitive rice genotypes and as affected by exogenous glutathioneWe evaluated how the different genotypes responded in photosynthesis and phytochelatins to Cd toxicity in the presence of GSH. Plant height, chlorophyll content, net photosynthetic rate (Pn) were reduced in the treatments of 5 and 50μM Cd and Cd-sensitive genotype showed much severer in the reduction than tolerant one. Cd stress caused decrease in maximal photochemical efficiency of PSⅡ(Fν/Fm) and effective PSⅡquantum yield (Y(Ⅱ)) and increase in quantum yield of regulated energy dissipation (Y(NPQ)), with Cd-sensitive genotype being more evident. Cd-induced phytochelatins (PCs), GSH and Cysteine (Cys) accumulation was observed in roots of both genotypes, with a markedly higher level in PCs and GSH on day 5 in Bing97252 compared with that in Xiushui63. Exogenous GSH significantly alleviated growth inhibition in Xiushui63 under 5μM Cd, and both genotypes in 50μM Cd. External GSH significant enhanced chlorophyll content, Pn, Fv/Fm and Y(II) of the plants exposed to Cd, but decreased Y(NPQ) and the coefficient of nonphotochemical quenching (qN). GSH addition significantly increased root GSH levels of both genotypes during 15 d Cd exposure, except day 5 of 50μM Cd; induced up-regulation in PCs of 5μM Cd treated Bing97252 thoughtout 15 d and Xiushui63 of 5 d exposure. The results suggest that alleviation of Cd toxicity by GSH is related to a significant improvement in chlorophyll content, photosynthetic performance and root GSH levels.5 Proteomic analysis to unravel mild cadmium stress response in rice seedlings and as affected by exogenous glutathioneWe applied 5μM Cd to investigate the effect of environmentally realistic Cd concentration on proteomics in rice. A comparative analysis between two genotypes with proteomic approach revealed that proteins involved in anti-oxidative system, carbohydrate metabolism, membrane protection, protein synthesis, DNA expression and defense in roots; photosystem, ROS signaling, energy, and protein degradations in leaves are important in Cd tolerance. We also applied GSH to exam the alleviating effects on Cd toxicity. GSH enhanced the expressions of proteins involved in anti-oxidative system, carbohydrate metabolism, membrane protection, protein synthesis, DNA expression and defense in roots; Calvin cycle, protein and amino acid metabolism, heat shock responses in leaves. The results suggested GSH play an important role in elevating Cd tolerance of rice in these processes.
|
PDF Full Text Request