The Biogenesis of Chloroplasts in Tissue Cultures of a C_3 and a C_4 Plant

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The formation of chloroplasts during the greening of callus from a C_4 (Zea mays) and C_3 (Canavalia ensiformis) plant was the object of our study. Benzylaminopurine (BAP) accelerated the synthesis of chlorophyll, the growth of callus and the development of the photochemical activity of both types of tissue grown under continuous light. However, the characteristics of the synthesis of chlorophyll and photochemical activities are different in Z. mays and C. ensiformis calli during greening. Chlorophyll a/b ratios were 3.2 for Z. mays and 2.2 for C. ensiformis. Electron micrographs of the callus tissues during greening showed the biogenesis of chloroplasts of the C_3 type in C. ensiformis. Twenty-four times subcultured Z. mays calli grown under continuous illumination for 10 days revealed the formation of two types of chloroplasts: one with well-developed grana, like those in mesophyll cells of Z. mays leaves, and another with poorly developed grana, like the mature chloroplasts of bundle sheath cells or the undeveloped mesophyll chloroplasts of Z. mays leaves. After longer periods of illumination only granal chloroplasts could be found. One hundred and twenty times subcultured Z. mays calli showed only granal chloroplasts. Kranz anatomy was not observed at any stage of greening of Z. mays calli. The C_3 and C_4 types of callus showed early signs of senescence and undeveloped chloroplasts as compared to those in leaves.
日本植物生理学会の論文