The Peroxisomal Ascorbate–Glutathione Pathway: Molecular Identification and Insights into Its Essential Role Under Environmental Stress Conditions

Abstract

Peroxisomes are unique organelles with intricate biochemical machinery­ involved in oxidative stress management and signaling. Peroxisomal metabolism is characterized by its plasticity because the organelle’s enzyme composition varies depending on the cell type, stage of development, and environmental conditions. The present chapter reviews recent progress in understanding the metabolism of reactive oxygen species (ROS) in plant peroxisomes. The ascorbate–glutathione (AsA–GSH) cycle is the second line of defense to cope with hydrogen peroxide (H2O2) generated by peroxisomal flavin oxidases particularly under stress conditions when catalase becomes inactivated. The cycle has been studied comprehensively at the biochemical and physiological level and its role been elucidated under biotic and abiotic stress conditions. The last two members of the peroxisomal AsA–GSH cycle, glutathione reductase and dehydroascorbate reductase, have recently been identified by proteome analysis of Arabidopsis leaf peroxisomes and been established as peroxisomal proteins by in vivo targeting analysis. The identification of all cycle members now opens new doors with which to study the function of the cycle in vivo, including reverse genetics. The release of ROS signaling molecules, such as H2O2, from plant peroxisomes adds new functions in the cross-talk events among organelles and cells under physiological and stress conditions.