Fig. 1.

Blue light induces transient membrane potential depolarizations in Arabidopsis thaliana mesophyll cells. (A) Diagram showing the experimental setup for recording blue light-induced membrane potential changes in A. thaliana mesophyll cells. Note: Leaves were mounted with the adaxial side on the microscope slide and the abaxial epidermis up, facing the bath medium. (B) Representative trace of membrane potential recordings using microelectrode impalement of mesophyll cells in intact leaves in response to a 50-s blue light pulse. Upon impalement, typical membrane potentials of ca. −160 to −180 mV were recorded. Upon 50 s of illumination with blue light, fast membrane potential depolarizations to about −60 mV were triggered as a singular event. Membrane potential depolarizations were followed by fast repolarization and transient hyperpolarization, before cells returned to prestimulus membrane potential levels. The mean depolarization (ΔV) triggered by extended blue light pulses was about 101.2 ± 3.3 mV, while the observed hyperpolarization, relative to the recorded resting membrane potential was about −32.5 ± 2.3 mV (Inset). (C) No difference in kinetics is observed when comparing the blue light-induced depolarization under the same experimental conditions as in B between A. thaliana WT (Col-0) and the gork1-2 mutant, indicating that the mesophyll K⁺ efflux channel does not contribute to blue light-induced membrane potential changes. External solution was composed of 1 mM KCl, 1 mM CaCl₂, 10 mM MES/BTP, pH 6.0. Blue light was applied via fiber optics at an intensity density of 17.5 mW·mm⁻².