Effect of Sugar on the Process of Cold-Acclimation-Induced Freezing Tolerance of Populus tomentosa

Populus tomentosa seedlings for cold-acclimating were pretreated with orwithout 20% saccharose. Changes in the concentrations of total soluble sugar, the survival rates, and freezing tolerance of seedlings during cold acclimation were investigated.The results showed that cold acclimation increased the concentrations of total soluble sugar, the survival rates and freezing tolerance. Cold acclimation, combined with the saccharose-pretreatment, enhanced the above-mentioned effect of cold acclimation, and obviously increased the concentrations of total soluble sugar, the survival rates and freezing tolerance of seedlings. Further analysis found that the concentrations of total soluble sugar in branches increased greater than that in leavesduring both cold acclimation with orwithout the pretreatment of saccharose. Moreover, an increase of the concentrations of total soluble sugar in branches and le aves was closely related to the freezing tolerance of seedlings.The results indicate the accumulation of soluble sugar in seedlings induced by cold acclimation may be involved in the induction of freezing tolerance.