Exogenous salicylic acid treatment induces cold tolerance in wheat through promotion of antioxidant enzyme activity and proline accumulation

The phytohormone salicylic acid (SA) plays a critical role in plant development and involved in the protection of the plants against various stresses. The research was directed on the study of the effects of exogenous SA on cold tolerance, activity of antioxidant enzymes and proline (Pro) accumulation in winter wheat at low hardening temperature (4 degrees C). Exogenous application of SA (100 mu M) promoted wheat cold tolerance before hardening and during all periods of cold exposure. At 4 degrees C, the activity of superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase(GPOD), and Pro content in wheat leaves was increased while malondialdehyde (MDA) and hydrogen peroxide (H2O2) content were increased at first and then were decreased. Moreover, the levels of TaMnSOD, TaFeSOD and TaCAT gene transcripts were increased under cold stress condition. Application of SA prevented the MDA and H2O2 accumulation during cold hardening period and promoted the activity of antioxidant enzymes and the accumulation of transcripts of their encoding genes in the leaves at normal temperature and at hardening conditions. Furthermore, the Pro level in SA-treated wheat plants was higher at 4 degrees C than at SA-untreated seedlings. These results suggested that SA improved the cold tolerance in wheat by up-regulating the activity of antioxidant enzymes and Pro accumulation.