Oxidative Stress and Chilling Tolerance in Tomato Seedlings

Abstract

Diurnal variation in the chilling sensitivity of tomato seedlings was examined. Sensitivity to chilling in tomato seedlings is a response to light and not under the control of a circadian rhythm. Chilling sensitivity is highest in seedlings chilled at the end of the dark period, and these seedlings become more resistant to chilling injury upon exposure to the light. Diurnal variation in chilling sensitivity was associated with changes in catalase and superoxide dismutase activities. The results show an increase in catalase and superoxide dismutase activities at the end of the light period. The recovery of the net photosynthesis rate following chilling was faster in seedlings chilled at the end of the light period. It is suggested that an increase in catalase and superoxide dismutase activities at the end of light period before the chilling plays a role in the resistance to chilling stress in tomato seedlings. Forty-eight hours of 14°C acclimation or hydrogen peroxide pretreatment conferred chilling tolerance to tomato seedlings and were correlated with elevated catalase activity. Acclimated seedlings still exhibited diurnal variation in chilling sensitivity while hydrogen peroxide treated seedlings showed little evidence of a diurnal variation in chilling sensitivity. Transgenic tomato plants expressing an antisense catalase gene were generated. A several-fold decrease in total catalase has been detected in the leaf extracts of transformants. Preliminary analysis of these plants indicated that modification of reactive oxygen species scavenging in plant system can lead to change in oxidative stress tolerance.