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