NaCl- and cold-induced stress activate different Ca2+-permeable channels in Arabidopsis thaliana

Salinity (NaCl) and low temperatures significantly affect plant growth, development, and agricultural productivity. Both these stresses trigger an increase in free cytosolic Ca2+ concentration ([Ca2+]i) via Ca2+ influx across the plasma membrane. However, the interaction between salinity- and low temperature-induced [Ca2+]i increases are still poorly understood. We used aequorin to investigate the NaCl- and cold-induced [Ca2+]i signals in Arabidopsis thaliana. We found that the combination of NaCl and cold stimuli induced a greater increase in [Ca2+]i than that by either NaCl or cold separately. Therefore, we showed that these factors had an additive effect on [Ca2+]i increase. Following a pre-treatment of either NaCl or cold, the increase in [Ca2+]i significantly declined in response to a second NaCl treatment or cold exposure. After pre-treatment with NaCl, a subsequent cold stimulus suppressed [Ca2+]i increase to a lesser degree than that by a second NaCl treatment. A similar response was observed after pre-treatment with cold and subsequent treatment with NaCl, but the peak [Ca2+]i differed between them. We propose that NaCl-induced Ca2+ channels differ from those induced by cold and that a feedback mechanism may exist between NaCl- and cold-evoked [Ca2+]i. The Ca2+-permeable channels activated by NaCl were similar to those induced by cold stress; however, they may be expressed in different cells and activated by different signaling pathways. Our results indicated that there is a cross-adaptation in [Ca2+]i changes in response to NaCl- and cold-induced stresses.