Low temperature acclimation mediated by ethanol production is essential for chilling tolerance in rice roots

Rice seedlings (Oryza sativa L.) were subjected to low temperature pretreatment (LT-PT; 10 degrees C) for various length of time followed by a 48-h chilling temperature stress (2 degrees C). Chilling tolerance of rice roots was improved with increasing duration of LT-PT, but HT-PT longer than 12 h gave no additional improvement. LT-PT did not change in fatty acid composition in rice roots under the present experimental condition. Alcohol dehydrogenase (ADH) activity and ethanol concentration in the roots were increased with increasing duration of LT-PT up to 12 h, which indicates that LT-PT increased ethanol fermentation in the roots. 4-Methylpyrazole, a potent inhibitor of ADH, reduced the ethanol concentration and the chilling tolerance in the roots. This reduction of the chilling tolerance recovered with exogenously applied ethanol. Ethanol also induced 21- and 33-kD protein synthesis in the roots and these proteins may contribute the improvement of the tolerance. The present research suggests that LT-PT may increase chilling tolerance in rice roots owing to ethanol production, and ethanol may trigger a signal transduction cascade, which might lead to a decrease in membrane damage and injury.