Effects of nitric oxide and hydrogen peroxide on induction of a defense response in the root tips and root border cells of soybean plants to Al toxicity

Abstract

Aims Nitric oxide (NO) and hydrogen peroxide (H2O2) function as signaling molecules in plants. A role for NO and H2O2 in the regulation of many abiotic stress responses, including drought, salt, heat, heavy metal and Al stresses, has been proposed. Our objective was to investigate (a) the Al-dependent accumulation of endogenous NO and H2O2 in root tips and (b) the role of exogenous NO and H2O2 in alleviating Al toxicity in root tips and root border cells (RBCs). Methods Seedlings of soybean (Glycine max) 'Zhechun No. 3' were divided into two groups for hydroponic and aeroponic cultured experiments. In order to investigate the response of endogenous NO and H2O2 in root tips to 50 μmol·L -1 Al, we determined root elongation, Al content in root apexes, endogenous NO and H2O2 content and their location in hydroponic cultured experiments. In the aeroponic culture experiments, seedlings were pretreated with exogenous NO and H2O2, then RBCs viability as well as the indicators in hydroponic cultured experiments were tested to clarify the role of exogenous NO and H2O2 on alleviating Al toxicity in root tips and RBCs. Important findings Al inhibited root elongation, increased Al content in root apexes and induced endogenous NO and H2O2 accumulation with the hydroponic culture. Results of the aeroponic experiments demonstrated that both 0.25 mmol·L -1 NO donor sodium nitroprusside (SNP) and 0.1 mmol·L -1 H2O2 alleviated the inhibitory effect of Al, decreased Al accumulation in root tips and enhanced RBCs viability. The 0.05 mmol·L -1 NO scavenger cPTIO (carboxy-PTIO) and 150 U·mL -1 H2O2 scavenger CAT (catalase) reversed the alleviating effect. Further- more, the results indicated that exogenous NO promoted the accumulation of H2O2 in root apexes, while exoge- nous H2O2 did not significantly affect NO content in root apexes. All of these results suggested that the rise of NO and H2O2 were in accordance with defense response in root apexes and RBCs to Al toxicity in soybean, and the