A remarkable constancy in the relative amount of stroma lamellae of chloroplasts from plants, and its functional significance

A model is presented which gives a quantitative picture of the distribution of the photosynthetic components in the thylakoid membrane of higher plants. The model is based on fragmentation and separation analysis together with microscopy. A salient feature of the model is that over 80 per cent of the pigments are located in the grana where the two photosystems 1 and 2 produce oxygen, NADPH and ATP by the linear electron transport pathway while the stroma lamellae, which harbour less than 20 per cent of the pigments, carry out Photosystem 1 mediated cyclic electron transport coupled to ATP production. This arrangement derives from the observation that more pigments are associated with Photosystem 1 which therefore captures more quanta than Photosystem 2. The excess pigments associated with Photosystem 1 are suggested to be located in the stroma lamellae. Tentative numbers of the different photosystem and cytochrome b.f. complexes located in the different domains of the thylakoid membrane will be presented.