Redox Homeostasis and Antioxidant Signaling: A Metabolic Interface between Stress Perception and Physiological Responses

Abstract

Efficient flux through plant electron transport cascades requires the simultaneous presence of both oxidized and reduced forms of electron carriers. This requirement, known as redox poising, involves a continuous flux of electrons to molecular oxygen from multiple sites in the photosynthetic and respiratory electron transport chains. Apart from the specialized water-producing reactions catalyzed by specific oxidases, the initial product of this flux is superoxide, from which other ROS are subsequently produced (Table 1). Singlet oxygen is also formed during light capture and photochemistry. Numerous enzyme systems produce superoxide or H₂O₂. The reactive nature of these intermediates means not only that their accumulation must be controlled but also that they are able to act as signaling molecules.