The Expression Of Alternative Oxidase Genes And The Function Of Alternative Pathway Under Environmental Stress And Light-Induced Conditions

In mitochondrial respiration, there exists an alternative respiratory pathway (cyanide-resistant respiration), which is connected with the respiratory chain by an additional terminal Oxidase-alternative Oxidase (AOX). To date, our knowledge about the precise regulation and function of AOX and its expression are still limited.With use of the specific probes for rice AOX1a, AOX1b and AOX1c, the differential expression of AOX1 multigene family was investigated with various environmental and chemical treatments. In the present work, respiratory inhibitor treatment caused an induction of all AOX1 genes. Water stress and pathogen infection induced the expression of AOX1a and AOX1b. Exogenous H₂O₂ or SA application induced AOX1a and AOX1b expression, whereas no expression of AOX1 genes was detected in the leaves of seedlings treated with exogenous ABA.During initial greening steps of plant, the transition from dark to light activated the AOX1 transcripts and the capacity of alternative pathway. The induction of cyanide-resistant respiration with light is associated with chloroplasts development. Following futher development of leaves with light, an increased alternative pathway and AOX1c transcripts in photosynthetic organisms may also be necessary for maintaining the photosynthetic functional state. AOX would have a flexible role and regulated mechanism in photosynthetic organisms.Under low temperature stress, the alternative pathway not only contributes to maintain the structure of chloroplast, but also lows the ROS production in chloroplast. H₂O₂ pretreatment could effectively induce chilling tolerance. Moreover, the capacity of the alternative respiratory pathway and the expression of the AOX1 gene were substantially elevated by H₂O₂ treatment under either normal or chilling condition. The adaptability of plants under chilling and the acquired tolerance to chilling due to oxidative shock might be related to the enhanced alternative respiratory pathway. Water stress significantly enhanced the capacity of alternative respiratory pathway and induced AOX1 transcript. The enhancement of cyanide-resistant respiration under drought might be partially mediated by ROS and the cyanide-resistant respiration could play a role in antioxidant protection under the condition of drought.