Characterization of calcium fluxes across the envelope of intact spinach chloroplasts

Publisher Website
Google Scholar
Abstract
Calcium fluxes across the envelope of intact spinach chloroplasts (Spinacia oleracea L.) in the light and in the dark were investigated using the metallochromic indicator arsenazo III. Light induces Ca2+ influx into chloroplasts. The action spectrum of light-induced Ca2+ influx and the inhibitory effect of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU) indicate an involement of photosynthetic electron transport in this process. The driving force for light-induced Ca2+ influx is most likely a change in the membrane potential component of the proton motive force. This was demonstrated by the use of agents modifying the membrane potential (lipophilic cations, ionophores, different KCl concentrations). The activation energy of the observed Ca2+ influx is about 92 kJ mol-1. Verapamil and nifedipine, two Ca2+-channel blockers, have no inhibitory effect on light-induced Ca2+ influx, but enhance ferricyanide-dependent oxygen evolution. Inhibition of Ca2+ influx by ruthenium red reduces the light-dependent decrease in stromal NAD+ level.