The Changes of G6PDHase, ATPase and Protein during Low Temperature -induced Freezing Tolerance of P. Suaveollens

The effect of cold acclim ation on the freezing tolerance of P. suaveollens seedlings and the changes of G6PDHase, ATPase, and protein in branches of P. suaveollens seedlings during cold acclima-tion were studied.In addition, the seedlings are pretreated with protein synthesis inhibitor (cycloheximide) before cold acclimation in order to examine whether cold acclimation-induced proteins play a role in the development of freezing tolerance.The results show that freezing tolerance of P. suaveollens seedlings could be obviously induced by cold acclimation, this cold acclimation will require experiencing two stages in order to acquire higher freezing tolerance. Although the first stage of cold acclimation, involving a temperature of -10℃, has few effects on the increase in freezing tolerance, it might provide the basis for acclimation at -20℃ of the second stage and the acquisition of freezing tolerance. Cold acclimation distinctly increased not only the activities of G6PDHase and ATPase, and the content of protein in branches of seedlings but also the freezing tolerance of seedlings. After 2 days of deacclimation, the freezing tolerance of seedlings decrease to the level of nonacclimation, but the activities of G6PDH ase and ATPase, and the content of protein in branches of seedlings still maintained a little higher than those in branches of nonacclimated seedlings. Protein synthesis and the acquisition of freezing tolerance are inhibited by cy cloheximide.Further analy sis found that low temperature-induced changes in the activities of G6PDHase and ATPase, and the content of protein directly correlated with the development of freezing tolerance.