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 responses 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."