Chilling-induced oxidative stress and polyamines regulatory role in two wheat varieties

Fifteen-day-old seedlings of two wheat varieties (Side 1 & Gimmiza 7) were randomly separated into three equal groups to investigate the effect of chilling stress on their antioxidant defense system. Moreover, the possible role of polyamines (PAs) pretreatment during alleviating chilling injuries. The first group was kept in a green house at 21/15 degrees C (day/night) and 10: 14h light/dark (-ve control). Second seedlings group were chilled at 5 degrees C for 6 or 9 hours (+ve control). The Seedlings of the third group were divided into three sub-groups and sprayed with 0.5, 1.0 and 2.0mM spermidine (Spd). After 12 hours of polyamine pre-treatments, the seedlings were incubated at 5 degrees C for 6 or 9 hours. At the end of the chilling period, the treated plants were transferred to the pre-experimental conditions in the greenhouse where they recovered for 10 days. Chilling stress induced a significant increase of lipid peroxidation, membrane leakage and hydrogen peroxide level, while Spd treatments resulted in a significant decrease. In addition, endogenous PA level increased in response to chilling stress. Activities of catalase, peroxidase and ascorbate peroxidase declined after the exposure to chilling whereas glutathione and free ascorbate increased. Spd treatments alleviated the injury caused by chilling stress by preventing the decrease in the activity of the antioxidant enzymes. It can be concluded that the stress protection caused by spermidine treatment probably contributes to the enhancement of the activity of the free-radical scavenging systems. Moreover, it was clear that the Sids-1 cultivar was more tolerant to chilling stress than Gemmieza-7cultivar.