Involvement of ethylene and hydrogen peroxide in induction of alternative respiratory pathway in salt-treated Arabidopsis calluses.

The role of ethylene and hydrogen peroxide (H₂O₂) in the induction of the alternative respiratory pathway (AP) in calluses from wild-type (WT) Arabidopsis and ethylene-insensitive mutant etr1-3 under salt stress was investigated. The capacity and the contribution of the AP to the total respiration were significantly induced by 100 mM sodium chloride (NaCl) in WT calluses but only slightly induced in etr1-3 calluses. Ethylene emission was enhanced in WT calluses under salt stress. Application of 1-aminocyclopropane-1-carboxylic acid (an ethylene precursor) further increased the AP capacity in WT calluses but not in etr1-3 calluses under salt stress. Reduction of ethylene production by aminooxyacetic acid (AOA, an ethylene biosynthesis inhibitor) in WT calluses eliminated the NaCl-induced increase of ethylene emission and inhibited AP induction under salt stress, suggesting that ethylene is required for AP induction. H₂O₂ enhanced ethylene production while ethylene reduced H₂O₂ generation in WT calluses under salt stress. In addition, ethylene and H₂O₂ modulated NaCl-induced alternative oxidase gene (AOX1a) expression and the increase in pyruvate content in WT calluses. Inhibition of the AP by salicylhydroxamic acid in WT calluses under salt stress resulted in severe cellular damage as indicated by the high content of H₂O₂, malondialdehyde and more electrolyte leakage. Taken together, ethylene and H₂O₂ are involved in the salt-induced increase of the AP, which plays an important role in salt tolerance in WT calluses, and ethylene may be acting downstream of H₂O₂.