LAUSR

Mitochondrial alternative oxidase is an important protein involved in maintaining cellular metabolic and energy balance, especially under stress conditions. AOX-genes knockout is aimed at revealing the functions of AOX genes. Under unfavorable conditions, AOX-suppressed plants (mainly based on Arabidopsis AOX1a-knockout lines) usually experience strong oxidative stress. However, a compensation effect, which consists in the absence of AOX1a leading to an increase in defense response mechanisms concomitant with a decrease in reactive oxygen species contents has also been demonstrated. This review briefly describes the possible mechanisms underlying the compensation effect upon the suppression of AOX1a. Information about mitochondrial retrograde regulation of AOX is given. The importance of reactive oxygen species and mitochondrial membrane potential in triggering the signal transmitting from mitochondria in the absence of AOX or disturbance of mitochondrial electron transport chain functions is indicated. The few available data on the response of the cell in response to the absence of AOX at the level of changes in the hormonal balance and the reactions of chloroplasts are presented. The decrease in the relative amount of the reduced ascorbate at stable reactive-oxygen-species levels as a result of compensation in AOX1a-suppressed plants is proposed to be a sign of stress development. Obtaining direct evidence on the mechanisms and signaling pathways involved in AOX modulation in the genome should facilitate a deeper understanding of the role of AOX in the integration of cellular signaling pathways.