[On the formation of stroma-like material and of thylakoids in the space between the outer and the inner part of the plastid limiting membrane].

The cross between Oenothera lamarckiana and Oenothera hookeri produces among others the hybrid velans · (h) hookeri with lamarckiana-plastids, which is characterized by an incompatibility between the genome and the plastome. The result of this incompatibility is a more or less distinct bleaching of the leaves in the juvenile stage of the plants.The cells in pale-green leaf regions contain many chloroplasts, which show a partial broadening of the normally narrow space between the two electron dense lines of the plastid envelope (Fig. 1, 3, 4). This enlarged intramembranous space may become bigger than the normal interior space of the chloroplasts (Fig. 11), and it is not separated by a membrane from the remaining normal narrow intramembranous space of the plastid envelope (Fig. 1, 5).According to the contrast after KMnO4-fixation, the material in the enlarged intramembranous region seems to be similar to the plastid stroma (Fig. 1, 4, 6). It is capable of storing starch (Fig. 14). The enlarged intramembranous spaces contain thylakoids which are sometimes arranged to grana. They cannot be distinguished from the thylakoids and grana in the normal interior space of the chloroplasts (Fig. 3, 4).Due to the transient incompatibility between the genome and the plastome, abnormalities in the thylakoid shape, e.g. vesiculation and/or an extraordinary elongation, occur in the chloroplasts. Such abnormalities are visible simultaneously in the normal interior space and in the enlarged intramembranous region of the same chloroplast (Fig. 4, 15).The thylakoids in the intramembranous space arise from evaginations of the inner membrane of the plastid envelope (Fig. 5b). This is completely analogous to the normal development of thylakoids, which takes place by an invagination of the same inner plastid membrane into the interior of the chloroplast (Fig. 5 a, 17). Vesicular thylakoids in the intramembranous space may occasionally produce small tubular invaginations (Fig. 6) and secondary vesicles by budding (Fig. 7).The possible formation of stroma-like material in the enlarged intramembranous region and some questions about the structure of thylakoid membranes are discussed.