Reactive Oxygen Species, Antioxidants, Sulfur Metabolites and their Agro-biotechnological Potential to Enhance Stress Resistance of Crop Plants

Reactive oxygen species (ROS) are by-products of aerobic metabolism. At physiological concent ration, ROS mediate intracellular signaling cascades and redox regulation. Their excessive production leads to oxidative stress, loss of cell function, and ultimately apoptosis or necrosis. A balance between oxidant and antioxidant in intracellular systems is vital for cell function, regulation, and adaptation to diverse growth conditions. A core ubiquitous oxidoreductase system with antioxidant and redox regulator roles comprises of thioredoxin reductase (TrxR) and thioredoxin (Trx). TrxR has a highly reactive active site - selenocysteine residue, to reduce several substrates in addition to Trx. It catalyzes regeneration of several antioxidants - ascorbic acid, selenium-containing substances, lipoic acid, and ubiquinone (Q10). Formation of ROS is one of the active defense re sponses of plants to pathogen invasion and linked to hypersensitive response (HR) resulting in cell necrosis/lesion. Accumulation of phytoalexins inhibits pathogens in or adjacent to HR cells. Various sulfur metabolites- thiols, alliins, glucosinolates, phytoalexins, phytochelatins, proteins (defensins and thionins) constitute the innate defense mechanism of plants to resist abiotic stress and pests and have the biotechnological potential to enhance resistance of crop plants.