The Regulation Mechanism Of Hydrogen Peroxide On Aluminum Tolerance Of Soybean And Its Interaction With Salicylic Acid Under Aluminum Stress

Approximately50%of the world’s potentially arable lands are acidic, in whichaluminum （Al） toxicity is an important factor in limiting crop production. Root apexis a target for Al toxicity, and Al-activated exudation of organic acid anions whichbased on Al exclusion from the root apex was considered as one of the most importantAl resistance mechanisms in plants. The regulation mechanism of Al-induced organicacid secretion still needs further research.Hydrogen peroxide （H₂O₂） is one molecule of the reactive oxygen species （ROS）.It plays important role in a variety of physiological and biochemical processes ofplants. There are more and more evidences that H₂O₂functions as a signaling agent.Salicylic acid （SA） is also a very important signal molecule in resist both biotic andabiotic stresses. Our preliminary experiment proved that Al could increase the contentof endogenous SA in soybean root. SA was suggested to involve in both metabolismand transportation of citrate to alleviate Al toxicity in soybean root. This studyfocused on the interaction between H₂O₂and SA in the process of soybean resistanceto aluminum. We measured root elongation, Al content, malondialdehyde （MDA）content, citrate secretion rate, relative expression of transporter gene and antioxidantenzyme activity in soybean root with H₂O₂pretreatment under aluminum stress. Theresults are as follows:1.The regulation of H₂O₂in Al resistance of soybeanThe results show that pretreated with low concentration of H₂O₂（10μM） couldsignificantly alleviate the inhibition of root elongation and reduce Al accumulation insoybean root tip under Al stress. Meanwhile, this pretreatment can alleviateAl-induced oxidative stress by reducing endogenous H₂O₂content and MDA content.This paper tried to clarify the relationship between citrate transport and citratesecretion in soybean root with H₂O₂pretreatment under Al stress. The results showedthat the H₂O₂pretreatment can increase citrate secretion at the early stage, improvethe expression level of citrate transporter gene Gm-MATE1. we suggested that Al-induced Gm-MATE1expression may be a premise in the process of citatesecretion.2. The interaction between H₂O₂and SA under Al stressUnder Al stress, exogenous SA increased endogenous H₂O₂accumulation insoybean root within6h, but keep decreased within12h and24h. However, H₂O₂preatment just weakly increased endogenous SA at6h, but subsequently decreasedunder Al stress. And endogenous combination state SA （SAG） content did not changesignificantly. Meanwhile, the activity of SA synthesis key ezmye （L-phenylalaninammonia-lyase, PAL） also had no significantly change. Based on the experimentalresults, we speculated that H₂O₂may be involved in and as downstream signalingmolecule of SA signal transduction pathway in soybean under Al stress.Exogenous SA could decrease the MDA content, and alleviate Al toxicity. Inaddition, exogenous H₂O₂scavager DMTU reversed the effect of SA on the activity ofAPX and SOD except CAT, these further illustrated that H₂O₂took part in themodulation of antioxidant system by SA under Al stress. Further more, H₂O₂pretreatment increased the activity of APX and SOD, and had no effect on the activityof CAT, these were consistent with the DMTU’s results. All of these conclusionsshowed that H₂O₂might be as downstream signal molecule involved in soybeanresistance to Al regulated by SA.