UltraStrutture E Stadi Involutivi Di Alcuni Tipi Di CromoplaSti

Abstract

Fine structure of some types of chromoplasts and of their involutive changes. — The structures of the chromoplasts, of flowers and fruits in pumpkin (Cucurbita pepo L., cv. Small. Sugar), of fruits in pumpkin (Cucurbita maxima Duch., cv. Gialla Mammoth), in rose (Rosa sp. horticultural variety) and in Sioux tomato (Lycopersicon esculentum Mill.) were studied at the electron microscope. New chromoplasts types were found among these. In the chromoplasts of the fruits (but not in the flowers) of both Cucurbita species the main feature is the presence of vesicles both sparsely distributed and crowded together into bulky pro-vesicular bodies. These bodies are found also in the young stages of the chromoplasts formation. Large needle- or stick-shaped crystals, distributed with no apparent order, are also frequently observed. Different structures appear in chromoplasts of the pumpkin flowers and, similarly, in rose fruits: groups of long and parallel tubules are set along the main axis of the chromoplasts in pumpkin flowers, or irregurarly distributed in rose fruits. Each tubule is formed by a thicker outer layer, very opaque to the electron beams and by a more transparent internal portion. The chromoplasts of the tomato fruits are relatively poorly .structured having only large crystalline bodies. These patterns change greatly during the plastid involution. The involution processes start usually with the formation of vesicles, in several points, between the two membranes of the plastid: such vesicles can be lately detached. In other cases, as in rose chromoplasts, similar interlayer vesicles are formed into the plastid itself in irregular membrane invaginations : such invaginations lend in later stages to a fragmentation of the plastid in portions containing both vesicles and lamellar elements.