Dissecting blue light signal transduction pathway in leaf epidermis using a pharmacological approach

Main conclusion: Blue light signalling pathway in broad bean leaf epidermal cells includes key membrane transporters: plasma- and endomembrane channels and pumps of H⁺, Ca²⁺and K⁺ions, and plasma membrane redox system. Blue light signalling pathway in epidermal tissue isolated from the abaxial side of fully developed Vicia faba leaves was dissected by measuring the effect of inhibitors of second messengers on net K⁺, Ca²⁺ and H⁺ fluxes using non-invasive ion-selective microelectrodes (the MIFE system). Switching the blue light on–off caused transient changes of the ion fluxes. The effects of seven groups of inhibitors were tested in this study: CaM antagonists, ATPase inhibitors, Ca²⁺ anatagonists or chelators, agents affecting IP₃ formation, redox system inhibitors, inhibitors of endomembrane Ca²⁺ transport systems and an inhibitor of plasma membrane Ca²⁺-permeable channels. Most of the inhibitors had a significant effect on steady-state (basal) net fluxes, as well as on the magnitude of the transient ion flux responses to blue light fluctuations. The data presented in this study suggest that redox signalling and, specifically, plasma membrane NADPH oxidase and coupled Ca²⁺ and K⁺ fluxes play an essential role in blue light signal transduction.