ABSTRACT
Abiotic stresses unfavorably influence the growth and yield of agricultural crop plants. The negative impact is elicited due to the overproduction of reactive oxygen species (ROS) which cause damage to carbohydrates, proteins, lipids and DNA. To scavenge ROS, plants have developed efficient enzymatic antioxidants (catalase, ascorbate peroxidase and superoxide dismutase) and several non-enzymatic antioxidants particularly glutathione-GSH, ascorbic acid-ASA (Vitamin C), α-Tocopherols (Vitamin E), carotenoids-Ct, phenolic compounds (flavonoids) and non-protein amino acids (Phytochelatins-PCs and Metallothioneins-MTs). GSH and ASA act as redox buffers and play roles in the synthesis of proteins and nucleic acids. Ct, Tocopherols and flavonoids have photoprotective roles as well as dissipating spare excitation energy as heat or by removing ROS and inhibiting lipid peroxidation. Metallo-proteins (PCs and MTs) defend plants against HMs by scavenging ROS, vacuolar sequestration and regulation of metalloenzymes. This chapter highlights various mechanisms by which non-enzymatic antioxidants enhance plant tolerance to heavy metals, salt, water and temperature stress.
Keywords – Ascorbic acid, glutathione, non-enzymatic antioxidants, reactive oxygen species, tocopherols
