Light‐Induced Proton Transport by Chloroplasts Suspended in Fluid Media at Sub‐Zero Temperatures: Kinetics and Stoichiometry

Abstract

Chloroplasts suspended in a medium containing ethanediol and water (1:1, v/v) at –16°C show light‐induced proton uptake and subsequent dark efflux. Proton uptake in continuous light showed biphasic kinetics. A 1 ms flash caused a single turnover of the photochemical centres at –16 °C. Under the same conditions 3 H+ were taken up from the external medium in the presence of methyl viologen as electron acceptor. The flash‐induced proton uptake was exponential and monophasic with t1/2= 3 s. The flash‐induced proton release into the thylakoid interior was biphasic, with half‐times of less than 0.1 s and 3 s. The fast phase represented approximately 30% of the total release and may be correlated with the oxidation of water. The half‐time of reduction of cytochrome f in the dark following illumination in the presence of 2 mM NH4Cl (2.5 s) is similar to the half‐time of the slow phase of proton release, suggesting a correlation between the kinetics of cytochrome f reduction and plastoquinol oxidation.

The Effect of Some Inhibitors of Photosynthetic Electron Transport on the Kinetics of Redox Changes of the Reaction Centre Chlorophyll of Photosystem I (P700) and of Cytochrome f at Sub-Zero Temperatures

“…2A shows semilogarithmic plots generated by the computer of the kinetics of reduction of cytochrome f following illumination in control chloroplasts and in chloroplasts treated with HgCI2. In both cases the kinetics are strictly pseudo first-order as reported previously [24,26,27]. Unexpectedly HgC12 inhibits the rate of reduction of cytochrome f as well as its level of oxidation in saturating continuous light.…”

“…Unexpectedly HgC12 inhibits the rate of reduction of cytochrome f as well as its level of oxidation in saturating continuous light. The reduction of P700 following continuous light is also pseudo first-order with a rate 3-4-times faster than the reduction of cytochrome f [24,26,27,30]. Fig.…”

“…Chloroplasts from spinach (Spinacea olevacea) were prepared and stored frozen in liquid nitrogen as described previously [26]. Absorbance changes were measured using a dual-wavelength spectrophotometer (Hitchi-Parkin Elmer 356) linked to a minicomputer through an interface containing analog inputs for sampling of the signal from the spectrophotometer and logic outputs for control of a shutter permitting actinic illumination.…”

Composition and spectral properties of a cytochrome-enriched fraction obtained from chloroplasts by digitonin treatment

“…Chloroplasts were isolated from spinach (Spinacea oleracea) and stored in liquid N2 as described previously (Olsen & Cox, 1979). The cytochromeenriched fraction was prepared from the thawed chloroplasts essentially by following the early stages of the procedure of Nelson & Neumann (1972).…”