Effects of light on cyanide-resistant respiration and alternative oxidase function in Arabidopsis seedlings

Mitochondrial alternative oxidase (AOX), the unique respiratory terminal oxidase in plants, catalyzes the energy wasteful cyanide (CN)-resistant respiration and plays a role in optimizing photosynthesis. Although it has been demonstrated that leaf AOX is upregulated after illumination, the in vivo mechanism of AOX upregulation by light and its physiological significance are still unknown. In this report, red light and blue light-induced AOX (especially AOX1a) expressions were characterized. Phytochromes, phototropins and cryptochromes, all these photoreceptors mediate the light-response of AOX1a gene. When aox1a mutant seedlings were grown under a high-light (HL) condition, photobleaching was more evident in the mutant than the wild-type plants. More reactive oxygen species (ROS) accumulation and inefficient dissipation of chloroplast reducing-equivalents in aox1a mutant may account for its worse adaptation to HL stress. When etiolated seedlings were exposed to illumination for 4 h, chlorophyll accumulation was largely delayed in aox1a plants. We first suggest that more reduction of the photosynthetic electron transport chain and more accumulation of reducing-equivalents in the mutant during de-etiolation might be the main reasons.