Upregulation of mitochondrial alternative oxidase pathway protects photosynthetic apparatus against photodamage under chilling stress in Rumex K-1 leaves

This study aimed to clarify the role of mitochondrial alternative oxidase (AOX) pathway upregulation in photoprotection under chilling stress in Rumex K-1 leaves. Malate-oxaloacetate shuttleꞌs activity and AOX pathwayꞌs capacity were synchronously enhanced with light intensity increase both in control and chilling-treated leaves. Besides, the AOX pathway was upregulated more significantly when irradiated by light in chilling-treated leaves than that of control. These results suggested that excess reducing equivalents generated by photosynthesis were exported from chloroplasts and oxidized by the AOX pathway at a potentially higher rate in chilling-treated leaves than in control, which avoided the overaccumulation of excess reducing equivalents under light conditions. Also, inhibition of the AOX pathway led to more severe accumulation of hydrogen peroxide in chilling-treated leaves than that in control. Therefore, the mitochondrial AOX pathway was specifically upregulated and employed for sinking excess reducing equivalents produced by photosynthesis, which protected photosynthetic apparatus from photodamage under chilling stress in Rumex K-1 leaves.