Effects of light during low temperature treatment and water stress on freezing tolerance and sugar contents in cabbage seedlings

Cabbage seedlings exposed to non-freezing low temperature (5 degreesC) under a 12 h photoperiod acquired the freezing tolerance, while the plants exposed to non-freezing low temperature in the dark did not acquire the freezing tolerance. On the contrary, in the case of reversal from cold acclimation, the freezing tolerance of the plants was reduced by exposure to normal growth temperature (20/15 degreesC) regardless of light conditions. These changes in freezing tolerance coincided with the changes in the sugar contents of cabbage leaves. The plants subjected to water stress by withholding water displayed a higher degree of freezing tolerance and increase of sugar contents compared with the watered plants. Thus, it was assumed that cabbage seedlings required light to acquire the freezing tolerance after exposure to low temperature, while de-acclimation was induced without light and it was confirmed that water stress increased to a certain extent the freezing tolerance in cabbage seedlings.