Existence of Extracellular Calmodulin in the Lower Epidermis of the Leaves of Vicia faba and Its Role in Regulating Stomatal Movements

摘要

As a possible peptide primary messenger, extracellular calmodulin (CaM) may regulate processes such as cell proliferation, pollen germination and expression of some genes. Stomata open or close quickly in response to environmental stimuli. CaM was found to be extracellular both in guard cells of broad bean leaves and in epidermal cells by immuno-electron microscopy and immuno-fluorescence microscopy techniques. Exogenous purified CaM enhanced stomatal closure and inhibited stomatal opening with an optimal concentration of 10~(-8) mol/L; CaM antagonist W7-agarose and anti-CaM serum, which were membrane-impermeable macro-molecules , inhibited stomatal closure and promoted stomatal opening. All these data showed that endogenous extracellular CaM of guard cells did promote stomatal closure and inhibit stomatal opening, and could be active only outside the cells. Therefore under natural conditions, the endogenous extracellular CaM of guard cells might regulate stomatal movements as a primary messenger together with other signal molecules, and might be an important linkage between environmental stimuli and cell responses.