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

The simultaneous measurement of the induction curves of chlorophyllfluorescence, its responses to saturating flashes, light-scatteringat 532 nm, and plasmalemma voltage supports previous findings(Hansen, Kolbowski, and Dau, 1987), that light-induced uptakeof protons into the inner thylakoid space causes the rapid (5to 20 s) light-induced depolarization at the plasmalemma viasubstrate depletion of the electrogenic H⁺-pump. These conclusionsare based on kinetic studies which enable the separation ofindividual components in complex signals by means of their assignmentto different time-constants. In contrast to the previous investigation,binary noise was used for modulation of the actinic light. Thenew input signal not only increased the reliability of the previousresults obtained by sine-waves, but also led to the detectionof three additional time-constants. One of these is probablyrelated to the action of light on the potassium channel of theplasmalemma. The others are assigned to the quencher Q and toa still unknown process. Key words: Chlorophyll fluorescence, plasmalemma potential, proton fluxes, noise, scattering, spinach, state-transitions, thylakoid membrane