Ultrastructural Development of Chromoplasts in Valencia Oranges

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Abstract
The development of chromoplasts from chloroplasts during ripening of Valencia oranges was followed with the electron microscope. The chloroplasts in the young, green fruit of Valencia were similar in structure to those in leaves of other plants. During ripening, there was a breakdown of the internal membrane system, the grana-fretwork system, and large, osmiophillc globules were formed. These globules apparently formed from breakdown products of the granal membranes as well as from carotenoids synthesized during ripening. During ripening, membranes developed from invagination of the inner part of the limiting membrane of the plastids. These membranes may be associated with chlorophyll that is synthesized during ripening. The breakdown of the grana-fretwork system seemed to be independent and not influenced by the limiting membrane of the plastid.