Chloroplast development and nuclear gene expression in cotyledons of soybean seedlings

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Abstract
SUMMARY: With the greening of soybean cotyledons after germination, development of the photosynthetic membrane system and particularly granal stacking were correlated with decreasing chlorophyll a/b ratios. Chlorophyll a/b binding proteins are known to be localized mainly in the appressed membrane regions and to have a role in mediating granal membrane appression. The chlorophyll a/b binding protein genes became operative very early in the development of the photosynthetic membrane system and coincided with incipient granal formation. However, the accumulation of chlorophyll a/b binding protein mRNAs decreased as the chloroplasts approached full development. As predicted from the literature, an early amyloplast developmental stage was observed, and prolamellar‐like structures appeared early in the development of the chloroplasts, but subsequently disappeared. The reported amoeboid stage that follows the amyloplast phase was not observed, and starch persisted until quite late in development of the chloroplasts. Also, deformations in the shape of the developing chloroplasts indicated that they were amoeboid as they increased in size and as granal formation increased. Phytoferritin accumulations were observed at every stage of development, suggesting that it was not utilized during chloroplast development.