Cold acclimation enhances the activity of plasma membrane Ca2+ ATPase in winter rye leaves

Exposure of plant cells and tissues to low or freezing temperatures often l ead to uncontrolled and detrimental ion leakage. Therefore, when plants acc limate to low temperatures, processes that control ionic homeostasis are im portant. Here we characterized H+ ATPase and ATP-dependent Ca2+ transport a ctivities in isolated plasma membranes of cold-acclimated and non-acclimate d winter rye leaves (Secale cereale L. cv. Voima). Cold acclimation resulte d in a two-fold higher Ca2+ transport activity, significantly different (P = 0.021) from that of non-acclimated rye, whereas only a small increase in H+ ATPase activity, measured as ATP hydrolysis, was observed in cold-acclim ated compared to non-acclimated preparations. In plasma membranes, extensiv ely washed with EDTA and Brij 58 to remove endogenous calmodulin, Ca2+ tran sport activity increased to about double by calmodulin addition, with both non-acclimated. and cold-acclimated material. Uptake of Ca2+ was seen withi n the pH range analyzed (pH 6-8), with an optimum at pH 7.2 with both mater ials, and both in the absence and in the presence of calmodulin. The increa se in activity of ATP-dependent Ca2+ transport in cold-acclimated rye plasm a membranes probably reflects the capacity needed to sustain the resting le vel: of cytosolic Ca2+ concentration that is characteristic to the cold-acc limated situation. (C) Elsevier, Paris.