Figure 1

Dye calibration performed in situ in the H. annuus stem and leaf.

(a) The dependence of the fluorescence intensity on the K⁺-induced membrane potential. The K⁺ concentrations used were 1 mM, 5 mM, 10 mM, 50 mM, 100 mM and 200 mM and the intracellular recordings by the microelectrode were approximately −125 ± 5 mV, −78 ± 4 mV, −63 ± 4 mV, −30 ± 4 mV, −9 ± 3 mV and 10 ± 1 mV (n = 25 recording repeats, 6 plant samples, mean ± S.E.M.) respectively. (b) The fluorescence ratio, Fc/F, versus the K⁺-induced membrane potential (n = 6 plant samples, mean ± S.E.M.). (c) The dependence of the normalized fluorescence, ΔF/F and the membrane potential derived from (b).