Chloroplast Development in Charophyceae

Members of the Charophyceae are particularly suited to studies on nuclear-chloroplast relationships . The chloroplasts in the elongated internodal cells are arranged in regular rows . Unlike the nuclei and most of the cytoplasm, they are stationary and do not participate in the active streaming of the protoplasm . It is thus possible to maintain plastids in one section of the cell in the dark and those of another segment under controlled illumination. In such an arrangement, the streaming nuclei and cytoplasm are exposed intermittently to both conditions . We recently made use of this subcellular arrangement to demonstrate that maintenance of full photosynthetic capability in mature chloroplasts of Nitella requires direct light stimulation . (1) Illumination of the nuclei, cytoplasm, and neighboring chloroplasts of the same cell is not sufficient. This report concerns further observations which indicate that the controls regulating the morphological and functional development of the chloroplasts are complex and that, furthermore, the development of chloroplasts can be reversed in this alga .