Vieillissement de l'appareil photosynthétique I. Effet synergique de la lumière et du vieillissement in vitro sur les changements de volume de chloroplastes isolés d'épinard


In: Plant and Cell Physiology, 1969, vol. 10, no. 4, p. 801-810

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    In view of the difficulty of studying all of the aspects of ageing of the photosynthetic apparatus in vivo and of the action of light upon this phenomenon, the consequences of chloroplast ageing were investigated in vitro, especially on the volume of these organelles. It was found that at 20°C in a Tris-NaCl medium, chloroplast swelling occurred slowly in the dark for the 6 hr experimental period, while it was activated in the light, with an optimum after 90 min. The most characteristic feature of these 2 curves is that they cross each other after 5 hr, indicating that, independent of the previous treatments (dark or light), the chloroplasts in vitro reach the same volume after a few hours. Special attention was devoted to the pH effect. In dark and light conditions, swelling was found to be maximum at pH 7.5 to 8.5 and was independent of the buffer used. There was no major difference between swelling in Tris and Tricine. A marked depression in the chloroplast volume was observed at pH 4.5 in the dark and at pH 5.5 in the light. Simultaneous with the swelling phenomenon, the capacity of chloroplasts to carry out light-dependent shrinkage diminished. There was a striking parallelism between swelling rate and loss of chloroplast shrinkage capacity. The action of light is synergetic on both these processes in that it accelerated to the same extent both the dark-swelling and the inhibition of light-dependent shrinking in chloroplasts incubated in the dark