Abstract: The cold-acclimation effects on the Ca2 + -ATPase activities in plasmolemma of the winter wheat seedlings ( Triticum aestivum L. ) were studied with electromicmscopic-cytochemical assay in which cerium trichloride precipitation method was adopted. The main conclusions are: (1) The plasmolemma Ca2+ -ATPase activities of the wheat seedlings treated at –9 ℃ for 3 h decreased considerably as compared with those of the seedlings grown at the optimal temperature of 20 ℃. A further impediment of the enzyme activities was observed when the cold-stress was prolonged to 12 h at –9 ℃. And complete enzyme inactivation as well as damage of ultrastructure of cells occurred when the seedlings were subjected to cold-stress at –9 ℃ for 24 h. (2) If seedlings were cold-ac- climated at 2 ℃ for 15 d, the plasmolemma Ca2 + -ATPase activities were higher than those of the non-acclimated seedlings. When the cold-acclimated seedlings were then treated at –9 ℃ for 3 h, the enzyme activities decreased less markedly than those of the non-acclimated seedings under the same treatment condition. Similarly, under prolonged cold-stress of both seedlings at – 9 ℃ for 12 h, the enzyme activities of the cold-acclimated seedlings still kept higher than those of the non-ac- climated ones. Finally, when the cold-stress lasted for 24 h at – 9 ℃, the enzyme activities of the cold acclimated seedlings remained active, and the cellular ultrastructure also remained unchanged. The above results indicate that cold-acclimation has enhanced the stability of the plasmolemma Ca2 + -ATPase activities of the winter seedlings under low temperature stress.

Key words: Wheat seedlings, Plasmolemma, Ca2+-ATPase, Cold acclimation, Low temperature stress