Abstract
Ultrastructural and histochemical studies of the enlarged, refractive glandular cells of O. californica provided structural evidence for their function. Most of the cell volume is occupied by a large vacuole containing a homogeneous, electron dense, proteinaceous material. The vacuole develops by the swelling and coalescence of smooth-surfaced cisternae. Incomplete coalescence of the cisternae frequently results in the formation of numerous cytoplasmic channels which penetrate the vacuole. The channels characteristically contain a crystalline array of cytoplasmic tubules (29 nm total diameter). Well-developed chloroplasts are present in the peripheral cytoplasm, but dictyosomes are absent. In contrast to the vegetative outer cortical cells, the gland cells are multinucleate. Because neither vacuolar breakdown nor organelles for extracellular secretion were observed in mature cells, the gland cells of Opuntiella appear specialized for storage rather than secretion.

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