Generation Mechanisms of Reactive Oxygen Species in the Plant Cell

The inputs of natural and anthropogenic activities produce several biotic and abiotic stresses which lead to the overproduction of reactive oxygen species (ROS) such as O2 .ˉ, 1O2, H2O2 and •OH in plants system. They are highly reactive and toxic which damage to proteins, lipids, and nucleic acids and thus cause oxidative stress. Generally, formation of ROS in the plant system is due to leakage/splitting of electron from chloroplast, mitochondria, peroxisome and plasma membranes during their metabolic activity. On the other hand, plants protect themselves from these ROS induced damaging effect by inducing strong enzymatic (SOD, CAT, APX, GR, MDHAR, DHAR, GPX, GOPX and GST) as well as non-enzymatic (AsA; GSH; phenolic compounds, NP-SH) antioxidant defense system. Antioxidants control the expression of a number of stress responsive genes and enhance growth, the cell cycle, systemic signaling, metabolic activity, as well as biotic and abiotic stress responses. Therefore, to understand the whole mechanism behind this concept, in the present chapter, the biochemistry of ROS, their production sites, and ROS scavenging antioxidant defense machinery in plants have briefly been reviewed.