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     

Analysis of Chlorophyll Fluorescence by Means of Noisy Light

Linearization is an efficient means of detecting individualcomponents in complex fluorescence induction curves. In a previousinvestigation based on sine-waves (Hansen, Kolbowski, and Dau,1987) the components related to the plastoquinone pool, thehigh-energy state of the thylakoid membrane and the state 1-state2 transition controller could be identified. In this paper,binary noise is used as an alternative input signal which canalso allow linearization by mathematical tools. Comparison withexperiments using sine-waves shows that curve-fitting of thenoise experiments yields the same data as the sine-wave analysis.Further, some additional components were revealed as labelledby the related time-constants whose values depended on lightintensity (e.g. 5, 15, 20, 70, 85, 550 s for spinach at 2.5W m^–2). The advantages of noise analysis are a shorter measuring time and the availability ofan on-line criterion which indicates when a sufficient signal-to-noiseratio is reached. Key words: Chlorophyll fluorescence, correlation functions, linearization, noise, spinach, time-constants     

The Effect of N-nutrients on the Acceptor Pool of PS I and Thylakoid Energization as Measured by Chlorophyll Fluorescence of Dunaliella salina

Changes of PS II chlorophyll fluorescence of Dunaliella salinawere used to study the effect of micromolar concentrations ofN-nutrients (nitrate, nitrite and ammonia) on photosyntheticelectron flow. The responses were evoked by changes in lightintensity which were controlled by a special protocol. Thisenabled the splitting of the overall response into individualcomponents by curve fitting and the assignment of these componentsto particular reactions of the photosynthetic apparatus. Byvirtue of a comparison with simultaneously measured changesin transmission at 532 ran, the identification could be madeof the component which is related to redox changes of the acceptorpool of PS I. The time-constant related to this acceptor pool was found toincrease by a factor of up to 5 after the addition of N-nutrients.The results indicate that the addition of N-nutrients increasesthe acceptor pool of PS I. The relationship between nutrientconcentration and effect is not consistent. In contrast to theelectron flow to the Calvin cycle, the electron flow to nitrogenassimilation is not related to a strong consumption of ATP.Thus, it gives rise to an increase in the transthylakoid pHgradient. The expected increase in the kinetic component ofchlorophyll fluorescence related to thylakoid energization isobserved after the addition of nitrate. Key words: Chlorophyll fluorescence, noise, N-nutrient metabolism, time-constants, thylakoid energization