Measurement of cation uptake into Arabidopsis guard cells upon blue light illumination

Abstract

Blue light-induced membrane hyperpolarization in guard cells through the activation of plasma membrane H⁺-ATPase drives K⁺ uptake and elicits stomatal opening. Hyperpolarization-activated Ca²⁺channel in guard cells has been reported, however, it is not investigated whether the membrane hyperpolarization induces the Ca²⁺ uptake through this type of Ca²⁺ channel. In this study, we showed the blue-light-induced changes in cytosolic Ca²⁺ concentration in guard cell protoplasts isolated from Arabidopsis thaliana, which has been transformed with Ca²⁺-sensitive luminescent protein, aequorin. At lower level than physiological concentration of extracellular K⁺, blue light-dependent Ca²⁺ uptake was observed, however, it was absent at the physiological level of K⁺. When we added the K⁺ channel blockers, the Ca²⁺ uptake was observed even in the presence of higher concentration of K⁺. These results indicate that blue light-dependent hyperpolarization can induce Ca²⁺ uptake but K⁺ uptake is predominant under physiological condition.