Regulating Mechanism Of Salicylic Acid On Aluminum Resistance In Soybean (Glycine Max L.)

Approximately 40% of the word's potentially arable soils are acidic and negatively impacted by the Aluminum (Al). It is a universal problem that Al toxicity has therefore been represented one of the major constraint on plant growth and crop production in acid soil worldwide. Al-induced citrate exudation has been identified as an important Al-resistance mechanism in plants. Salicylic acid (SA), considered as a crucial signal molecule, plays an important role in regulating the plant disease resistance. It has been proposed that SA can involve in modulation of acclimation responses to abiotic stresses such as low temperature, heat shock, drought, salinity, heavy metal toxicity. Thus, this study was to research the changes of endogenous SA under Al stress; clarify SA involved in the process of Al induced-citrate exudation from soybean roots; explore the effect of exogenous SA on the antioxidant system under Al stress.Root elongation is a rapid and efficient parameter to assessment of Al resistance. The obtained results indicated that Al-inhibited root elongation response to different concentrations of applied SA differs and the obvious relief in Al toxicity caused by exogenous 10μM SA. The proper concentration of SA is an important factor in determining plant response to Al stress. 10μM SA decreased the Al accumulation in soybean root tips. Endogenous SA content of soybean root tips have a rapidly response to Al stress and exogenous SA treatment. The data was shown that external supply of SA to roots is quickly taken up by the root. the SA content of the root tips increased up 4 h, and following decrease with the elongation of Al treatment duration. SAG accumulated gradually throughout the treatment period. In order to further elucidate the role of SA under Al stress, an inhibitor of SA biosynthesis (PAC) was used in this study. PAC application slightly but significantly reduced endogenous free SA content in root tips of Al and SA-treated plants. However the effect on SAG was less clear. Al and SA together treatment increased the amount of Al-induced citrate secretion from soybean roots, further decreased aconitase (ACO) activity and enhanced the transcriptional expression of Gm-MATE1 compared to the sole Al treatment. From the above results, it is suggested that SA production might act as an early signal to regulate the metabolism and transportation of citrate in soybean roots.SA modulated the H₂O₂ level in root tips of soybean by regulating the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) which could take response to Al stress. Exogenous SA decreased the Al-induced enhancement of MDA in soybean root tips. Taken together, the possible of mechanisms of SA under Al stress are reducing the ACO activity and increasing Gm-MATE1 gene expression, leading to enhance citrate efflux, and then, alleviated the Al-induced inhibition of root elongation and decreased the Al accumulation in soybean root tips. SA may also regulate the antioxidant system to alleviate Al toxicity.There is evidence that SA can be effective in regulating the transcription factor WRKY and NPR1 in the process of plants respond to stress.ABC transporter genes encoding membrane-bound protein, is the most widely known function of the ultra-protein family.ABC transporters are not only involved in hormones, lipids, metals, secondary metabolites and xenobiotic transport, but also play an important role in regulation of ion channels. In this study, according to microarray results, using real-time quantitative PCR technology, analysis the genes expression of transcription factors Gm-WRKY58 and Gm- NPR1 as well as ABC transporters Gm-STAR1 and Gm- PDR12 under Al and/or SA treatments. The results show that, Al induced an increase genes relative expression of Gm-WRKY58,Gm-NPR1,Gm-SATR1 and Gm-PDR12 rapidly;adding exogenous SA enhanced the Al induced these genes expression. The obtained results indicated that the genes expression of Gm-WRKY58 and Gm-NPR1 as well as Gm-SATR1 and Gm-PDR12 response to Al stress, may play a crucial role in SA regulate Al resistance in soybean roots.