Cold calcium signaling in Arabidopsis involves two cellular pools and a change in calcium signature after acclimation

Cold shock elicits an immediate rise in cytosolic free calcium concentration ([Ca2+](cyt)) in both chilling-resistant Arabidopsis and chilling-sensitive tobacco (Nicotiana plumbaginifolia). In Arabidopsis, lanthanum or EGTA caused a partial inhibition of both cold shock [Ca2+](cyt) elevation and cold-dependent kin1 gene expression. This suggested that calcium influx plays a major role in the cold shock [Ca2+](cyt) response and that an intracellular calcium source also might be involved. To investigate whether the vacuole (the major intracellular calcium store in plants) is involved, we targeted the calcium-dependent photoprotein aequorin to the cytosolic face of the vacuolar membrane. Cold shock calcium kinetics in this microdomain were consistent with a cold-induced vacuolar release of calcium. Treatment with neomycin or lithium, which interferes with phosphoinositide cycling, resulted in cold shock [Ca2+](cyt) kinetics consistent with the involvement of inositol trisphosphate and inositide phosphate signaling in this response. We also investigated the effects of repeated and prolonged low temperature on cold shock [Ca2+](cyt). Differences were observed between the response of Arabidopsis and N. plum baginifolia to repeated cold stimulation. Acclimation of Arabidopsis by pretreatment with cold or hydrogen peroxide caused a modified calcium signature to subsequent cold shock. This suggests that acclimation involves modification of plant calcium signaling to provide a ''cold memory.