The involvement of calmodulin and protein kinases in the upstream of cytosolic and nucleic calcium signaling induced by hypoosmotic shock in tobacco cells

Changes in Ca2+ concentrations in cytosol ([Ca2+](C)) or nucleus ([Ca2+](N)) may play some vital roles in plants under hypoosmotic shock (Hypo-OS). Here, we observed that Hypo-OS induces biphasic increases in [Ca2+](C) and [Ca2+](N) in two tobacco cell lines (BY-2) expressing apoaequorin either in the cytosol or in the nucleus. Both [Ca2+](C) and [Ca2+](N) were sensitively modulated by the inhibitors of calmodulin and protein kinases, supporting the view that calmodulin suppresses the 1st peaks and and protein kinases enhance 2nd peaks in [Ca2+](C) and [Ca2+](N). Data also suggested that the 1st and 2nd events depend on the internal and extracellular Ca2+ sources, respectively.