Salt stress-induced expression of rice AOX1a is mediated through an accumulation of hydrogen peroxide

Treatment with 300 mM NaCl increased the capacity of the alternative respiratory pathway and induced the expression of AOX1a of the leaves of rice (Oryza sativa L.) seedlings. A significant increase in the content of hydrogen peroxide (H(2)O(2)) was observed in rice leaves treated with 300 mM NaCl. However, NaCl at 150 mM did not significantly affect the capacity of the alternative respiratory pathway, the content of H(2)O(2), and the transcript level of AOX1a. Exogenous application of H(2)O(2) enhanced the levels of the capacity of the alternative respiratory pathway and AOX1a expression. The accumulation of H(2)O(2) in rice leaves in response to 300 mM NaCl was inhibited by the pretreatment with dimethylthiourea (DMTU, scavenger of H(2)O(2)). This treatment also suppressed the induction of AOX1a expression and the increase in the capacity of the alternative respiratory pathway under 300 mM NaCl stress. Moreover, the salt-stressed (300 mM NaCl) seedlings pretreated with 1 mM salicylhydroxamic acid (SHAM, a special inhibitor of alternative oxidase) had higher level of H(2)O(2) production than the seedlings either subjected to 300 mM NaCl stress or SHAM treatment alone did. These observations suggest that the expression of AOX1a in response to higher salt stress is mediated through an accumulation of H(2)O(2) and alternative oxidase could play a role in antioxidant protection under the condition of higher salt stress.