Abstract: Seasonal changes in the contents of water and organic osmotica were examined in the leaves of Sabina przewalskii and Sabina chinensis, aimed to probe into their relationships with freezing tolerance. The results showed that the relative water content (RWC) and free water content (FWC) decreased during hardening in autumn, but bound water content (BWC) and organic osmotica accumulated and remained relatively higher level over winter. In spring, RWC and FWC increased, BWC decreased, and organic osmotica accumulated again. These seasonal patterns were consistent with winter hardening and dehardening. Organic osmotica may supply nutrients to regrowth in spring and contribute to the stabilization of the cell membrane by preventing lipid peroxidation and by binding the tissue water. The results also suggested that a better capacity for osmoregulation in S. przewalskii might account for its greater capacity for freezing tolerance than S. chinensis.

Key words: Sabina, evergreen woody plants, water, organic osmotica, freezing tolerance