Kunihiko Okada

Freezing tolerance and soluble sugar contents affected by water stress during cold-acclimation and de-acclimation in cabbage seedlings

The effect of water stress on freezing tolerance during cold-acclimation and de-acclimation in cabbage seedlings were studied. The seedlings were subjected to water stress by withholding water. The treatment wilted the seedlings and decreased the water content of their shoots. Exposure of seedlings to low temperatures (5°C) for 7 days induced freezing tolerance. Water stress promoted the increase in freezing tolerance during cold-acclimation. However, the interruption of water stress by rewatering decreased freezing tolerance rapidly to the same level as for continually watered seedlings. Exposure of cold-acclimated seedlings to normal growth temperature (20°C/15°C) reduced freezing tolerance within a day. Water stress during the de-acclimation period prevented the loss of freezing tolerance. Changes in glucose, fructose and sucrose contents were related to variations in freezing tolerance of seedlings. These results suggest that water stress affects freezing tolerance and is accompanied by changes in sugar contents during cold-acclimation and de-acclimation.