Further Evidence for the Relationship between Light-Induced Changes of Plasmalemma Transport and Transthylakoid Proton Uptake

Abstract

The simultaneous measurement of the induction curves of chlorophyll fluorescence, its responses to saturating flashes, light-scattering at 532 nm, and plasmalemma voltage supports previous findings (Hansen, Kolbowski, and Dau, 1987), that light-induced uptake of protons into the inner thylakoid space causes the rapid (5 to 20 s) light-induced depolarization at the plasmalemma via substrate depletion of the electrogenic H⁺-pump. These conclusions are based on kinetic studies which enable the separation of individual components in complex signals by means of their assignment to different time-constants. In contrast to the previous investigation, binary noise was used for modulation of the actinic light. The new input signal not only increased the reliability of the previous results obtained by sine-waves, but also led to the detection of three additional time-constants. One of these is probably related to the action of light on the potassium channel of the plasmalemma. The others are assigned to the quencher Q and to a still unknown process.