Oxidative stress reflects a disruption in redox homeostasis due to imbalance between the reactive oxygen species (ROS) production and a biological system's capability to scavenge ROS. However, oxidative stress occurs as a secondary outcome in most of the abiotic and biotic stresses. Although the high accumulation of the ROS is very hazardous for cellular functions, they are sometimes necessary to perceive of surrounding environments and also they can trigger singling pathways and regulate the genes expressions. It seems there are some cross talking between stress sensing pathways. Ca2+-dependent phosphorylation can considerably regulate the activity of NADPH oxidases as a well-known enzymatic source of ROS. However, launching the ROS signaling pathway and stimulation of the antioxidants are very different in various situations. Environmental stimuli cause ROS production and disturbance of the redox balance can stimulate expression, accumulation and activity of antioxidants. Non-enzymatic antioxidants are divided in water soluble antioxidants (e.g. ascorbate, glutathione, carotenoids, phenolic compounds and etc.) and membrane associated antioxidants (e.g. α-tocopherol, β-carotene, and ubiquinone). The major enzymatic antioxidants in plants are superoxide dismutase, catalases, ascorbate peroxidase, glutathione peroxidases, ascorbate peroxidase and glutathione reductase. In plant systems the selection and prioritization of the antioxidants for ROS scavenging are different and it may depended on genetic potential, growth statues and environmental conditions. In addition to the enzymatic and non-enzymatic antioxidants, ROS homeostasis can be manipulated by genetically modification in biosynthesis pathways some compound such as proline, polyamines (putrescine, spermidine, and spermine) and sugar metabolism (trehalose, galactinol, raffinose, fructans, mannitol and sorbitol). The functions of the ion channels, kinase cascades, accumulation of hormones-like substances such a
