Abstract
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.