Studies On The Effects Of Exogenous Salicylic Acid On Rice Seedlings Growth From Lead Toxicity

Plumbum (Pb) was a highly toxic and persistent environmental poison, its increasing level in soil environment exerted a wild range of adverse effects on plants and even the healthy of human beings by food chains. Salicylic acid (SA), considered as a hormone-like substance, played an important role in the regulation of plant growth and development which not only served as a critical signalling molecule in the pathways leading to local and systemic disease resisteance, but also played a positive role in modulation of acclimation responses to abiotic stressors. It was proposed that one of the mechanisms involved in SA effect on plants from adverse stress was the up-regulation of H₂O₂ level.The possible effects of SA on rice seedlings growth under Pb stress were studied. The pre-treatment with 0.1 mmol/L SA for 48 h partially protected seedlings from18 d Pb stress from 0.05 to 0.25 mmol/L which were considered as low and moderately toxic concentrations. Endogenesis SA content of rice seedlings had a rapidly response to Pb stress and exogenous SA treatment. SA pre-treatment significantly reduce the Pb accumulation in rice seedlings, and the chlorophyll contents in leaves were significantly higher than that of Pb-exposed plants at the same Pb intensity. SA modulated the H₂O₂ level in leaves of seedlings by up-regulating the activity of superoxide dismutase(SOD) and repressing the activity of catalase(CAT) and ascorbate peroxidase(APX) which could take response to Pb stress.The effects of SA on the seeds germination under Pb stress were investigated during the first 7 d of germination. Pb had mild inhibition on the gemination index(GI) and embryo development, but serious toxicity on radicle. SA concentration of 0.01 mmol/L adding to the solution of Pb had prominently improved the growth of embryo and radicle from 0.75mmol/L Pb²⁺ toxicity. SA pre-soaking at low concentration from 0.01 to 0.1 mmol/L could significanly increase the activities of α-amylase in rice seeds during early stages of germination, also it alleviated the sharp decline of chlorophyll contents of embryo from Pb toxicity.