Abiotic and biotic stresses cause alterations in the normal physiological processes of all plants, including the economically important crops. Plant damage and decrease in their productivity take place most often due to naturally occurring unfavorable factors of the environment (natural stress factors). These include extreme temperatures; water de fi cit or abundance; increased soil salinity; high solar irradiance; early autumn or late spring ground frosts; pathogens, etc. Along with these factors, plants are imposed to a large scale of new stressors related to human activity (anthropogenic stress factors) including, toxic pollutants such as pesticides, noxious gasses (SO2, NO, NO2, NOx, O3 and photochemical smog); photooxidants; soil acidi fi cation and mineral de fi cit due to acid rains; overdoses of fertilizers; heavy metals; intensi fi ed UV-B irradiation, etc. (Fig. 13.1 ). All these stresses cause an increased production of reactive oxygen species (ROS) in plants that alter their normal physiological functions, decrease the biosynthetic capacity of plant organisms, and cause damages which may lead to plant death (Mittler 2002 ; Ahmad et al. 2008 ; Gill and Tuteja 2010b ; Potters et al. 2010 ) .