Vieillissement de l'appareil photosynthétique II. Effet synergique de la lumière et du vieillissementin vitrosur les activit´es photochimiques de chloroplastes isolés d'épinard

摘要

The consequences of chloroplast ageingin vitrowere further investigated, especially on the photochemical activities of these organelles.Ageing of chloroplasts in dark was accompanied by decreases in activities for photohydrolysis and cyclic and non-cyclic syntheses of ATP, photoreduction of NADP+and O2evolution; but there was no decrease in ferricyanide photoreduction. The rates of decrease in these activities were comparable to the rate of increase in chloroplast volume. Complete inhibitions were reached when maximum chloroplast swelling had occurred,i.e.after 5 to 6 hr of incubation at 20°C in a Tris-NaCl (pH 8) medium. Ageing in the light resulted in much accelerated decreases in activities tested; the loss of capacity for light-induced shrinkage was also accelerated by the light during ageing. Thus, light acts synergetically towards the ageing process. Moreover, light and, to a less extent, dark ageing, resulted in an uncoupling of chloroplast photophosphorylation and associated electron flow measured by ferricyanide photoreduction. The part of the electron flow which is induced by coupling (+ADP, Pi, MgCl2, pH 8) or by uncoupling (+NH4C1, pH 7) was found to be very sensitive to light ageing. The NADP+photoreduction loss was restored by addition of the ascorbate-DCPIP electron donor system, suggesting that ageing interferes with the integrity of photosystem II.In many respects, these effects of ageing are comparable with the action of detergents and fatty acids on the structure and photochemical activities of chloroplasts, especially in that they attack the energy transducing mechanism in chloroplasts