All-granal Chloroplasts of Apple-fruit

Abstract

The occurrence of viable chloroplasts in the internal tissues of the apple-fruits has been inferred since a long time (Ulrich, 1952) and was later experimentally proven (Phan, 1970). The internal chloroplasts manifested themselves to our attention, for the first time by their ability to produce oxygen, which interfered with respiration measurements made on plugs of internal tissues of the apple-fruits. However, because of their scarcity among the bulk of non-photosynthetically active cells of the parenchyma of the fruit, and of the high content of phenols of these tissues, pure preparations of internal chloroplasts are hard to obtain and therefore biochemical work has not been successfully done on them. Electron microscopy was therefore used, and, to our great surprise, revealed a vary particular structure of the internal chloroplasts (see Fig. 1). At that time, we were impressed by the fact that all the lamellae were parallel; with the then new data of the C₄-photosynthesis and the high content of malic acid in the apple-fruit, a thought occurred to us that the apple species could be a C₄-plant. But this idea was soon rejected when we found, in a number of cells of a cut apple left in light for one day, the presence in the same cell of chloroplasts with the parallel-lamellar structure and others having the “normal” structure with lamellae and grana (Phan, 1973). We soon found out that the parallel-lamellar structure was the indication of a partial etiolation caused by the lack of light; we speak of partial etiolation because we have shown that some light did reach the internal regions of the apple-fruit through the calix and the peduncle ends. When the apple was cut into parts which were exposed to light, the internal chloroplasts acquired the granal structure, which is typical of the C₃-plants. We were then struck by the fact that the lamellae of the internal chloroplasts were not only parallel, but also all stacked together on their whole lengths. They are thus definitely not “chloroplasts with parallel lamellae” typical of C₄-plants, but chloroplasts with one huge granum; we therefore called them “all-granal chloroplasts”, and the one granum, hypergranum.