Effects of four plant growth regulators on growth and cadmium accumulation in rice

Cadmium( Cd) pollution has become a serious problem following rapid industrial development. The increasing amounts of Cd in farmlands are the result of increased discharge of industrial waste,abuse of chemical fertilizers,and other man-made sources. Cd likely causes damage to crop physiology when its concentration in soil exceeds the maximum tolerable limit,resulting in growth inhibition and grain yield reduction. Continuous intake of Cd causes human health problems.Therefore,reducing Cd concentration in rice grain,a staple food for half of the world's population,is extremely important and urgent. Plant growth regulators( PGRs) are chemicals-plant endogenous hormones and artificially synthetic growth regulators-that affect and regulate plant growth and / or development at trace levels. Some PGRs play important roles in inducing plant tolerance to drought,salt,low temperature,high temperature,and heavy metals. In this study,the roles of four PGRs,abscisic acid( ABA),ethylene( ETH),salicylic acid( SA),and methyl jasmonate( MeJ A),were investigated during stress responses to Cd treatments in rice. Rice seedlings,grown in heavy metal-contaminated soil,were sprayed with the four PGRs on leaves twice,one time each during tillering and filling stages. On the second day after the PGR treatments during the filling stage,the photosynthesis indices and malondialdehyde( MDA) contents of the upperleaves were analyzed. After harvesting,the roots,shoots,and grains were collected to investigate Cd content,biomass,and yield. The results were as follows:( 1) The ABA treatment at 5 mg / L maintained normal rice growth and yield,while the ABA treatment at 15 mg / L showed the opposite effects. Treatment with two different levels of ETH significantly decreased the grain yield compared to that of the control. However,SA and MeJ A high-level treatments maintained normal yields.( 2)The exogenous application of the four PGRs inhibited stomatal opening and reduced the transpiration and photosynthetic rates. Interestingly,the most obvious inhibitory action was observed following the treatment with 0. 56 mg / L MeJ A.( 3)Both the SA treatments,5 mg / L ABA and 0. 56 mg / L MeJ A treatments,reduced MDA production and prevented plasma membrane peroxidation of leaves at the tillering stage.( 4) Decreases in the Cd concentrations were observed in rice grain treated with the four PGRs at their appropriate levels,and the ABA treatment at 5 mg / L showed the strongest inhibitory effect. The