[On the three-dimensional form of the thylakoid system in chloroplasts]

An investigation of extensive series of adjacent ultrathin sections through the plastids of the Oenothera hybrid Oe. (lamarckianaxhookeri) velans· (h) hookeri with Lamarckiana-plastids and through the plastids of the two parents, Oe. lamarckiana and Oe. hookeri, made it possible to reconstruct the thylakoid system in the chloroplasts. It proved to be very similar to the thylakoid system of the chloroplasts of some higher plants previously described by other authors. 1. The grana are composed of small thylakoids (=grana-thylakoids) with an average diameter of 0,4-0,6 μ, and of large thylakoids (=stroma-thylakoids), which extend into the stroma and also into some of the neighbouring grana with narrow appendages of varying length as well as with broad perforate parts. 2. Extensive series of adjacent sections throught many grana showed that certainly the inner spaces of some thylakoids may be continuous with another, but not the inner spaces of all thylakoids in a granum or even in a chloroplast. 3. In electron micrographs of single cross sections some aspects of the thylakoids are difficult to interpret. They become clear, however, in models constructed from serial sections. Such reconstructions may also give some indications concerning the development of the arrangement of thylakoids in the grana. It is whown that thylakoids lying closely superimposed are the result of invaginations of thylakoid membranes as described by MENKE, and probably also of processes of overlapping growth in agreement with the findings of WEHRMEYER. 4. The influence of the fixation medium on the appearance of the thylakoid system is discussed. The perforations in the stroma-thylakoids which are known to appear after a potassium-permanganate fixation of 2 hrs are not significantly reduced after glutaraldehyde fixation.-Besides the region occupied by stroma-and grana-thylakoids, many chloroplasts contain a relatively large area filled almost only with stroma material. However, a few large stroma-thylakoids which show no perforations are sometimes to be seen there. Thus the same chloroplast contains 2 different types of stroma-thylakoids, namely, one with and one without perforations. 5. After fixation with glutaraldehyde several slightly contrasted regions, which are separated from each other, are visible in the chloroplasts. They show fine fibrils, and, in accordance with observations already known, they are interpreted as being nucleoplasm-like, DNA-containing areas.