The alternative oxidase pathway participates in seagrass seedling establishment by regulating photosynthetic and respiratory metabolism

The roles of the alternative oxidase (AOX) pathway in plant physiology and metabolism are of increasing interest. AOX was found to regulate the growth of Enhalus acoroides seedlings, but its specific mechanism and physiological significance are unclear. In this study, the roles of the AOX pathway during E. acoroides seedling establishment were clarified by investigating the relationships between metabolism and the AOX pathway at the physiological and molecular levels. Results showed that inhibiting the AOX pathway causes the accumulation of reducing equivalents, and further results in the inactivation of the PSII reaction center and destruction of the PSII electron receptor side in E. acoroides seedlings, which decreased photosynthetic activity and increased H2O2 content. Meanwhile, the accumulation of reducing equivalents also restricted mitochondrial respiratory metabolism (including glycolysis, the tricarboxylic acid cycle, the pentose phosphate pathway and oxidative phosphorylation). In addition, when the AOX pathway was inhibited, the gene expressions related to photosynthesis and respiratory metabolism were generally down-regulated. The above results indicate that inhibiting the AOX pathway affected metabolism through disturbing photosynthetic and respiratory metabolic processes, resulting in an inability to satisfy the material (saccharides, proteins, lipids, and nucleotides) and energy requirements of various physiological processes, thus stunting the growth of seagrass seedlings. This study reveals that the AOX pathway accelerates the production of intermediate metabolites in key metabolic pathways through energy redistribution in seagrass, which has a very positive significance for the establishment of seagrass seedlings.