Electrical Signals at the Plasma Membrane and Their Influence on Chlorophyll Fluorescence of Chara Chloroplasts in vivo

AbstractAction potentials of plant cells are engaged in the regulation of many cell processes, including photosynthesis and cytoplasmic streaming. Excitable cells of characean algae submerged in a medium with an elevated K+ content are capable of generating hyperpolarizing electrical responses. These active responses of plasma membrane originate upon the passage of inward electric current comparable in strength to natural currents circulating in illuminatedChara internodes. So far, it remained unknown whether the hyperpolarizing electrical signals inChara affect the photosynthetic activity. Here, we showed that the negative shift of cell membrane potential, which drives K+ influx into the cytoplasm, is accompanied by a delayed decrease in the actual yield of chlorophyll fluorescenceF′ and the maximal fluorescence yieldFm′ under low background light (12.5  µmol m–2 s–1). The transient changes inF ′ andFm′ were evident only under illumination, which suggests their close relation to the photosynthetic energy conversion in chloroplasts. Passing the inward current caused an increase in pH at the cell surface  (pHo), which reflected high H+/OH– conductance of the plasmalemma and indicated a decrease in cytoplasmic pH due to the H+ entry into the cell. The shifts in pHo arising in response to the first hyperpolarizing pulse disappeared upon repeated stimulation, thus indicating the long-term inactivation of plasmalemmal H+/OH– conductance. Suppression of plasmale...

Source: Biochemistry (Moscow) - October 1, 2023 Category: Biochemistry Source Type: research