STUDIES ON THE ULTRASTRUCTURE OF THE GUARD CELLS OF OPUNTIA

The guard cells of Opuntia contain numerous mitochondria, elements of endoplasmic reticulum, dictyosomes, and microbodies. A complex array of small to large vacuoles which contain small, membrane-bounded vesicles occur in each guard cell. The variety of cytoplasmic constituents and vacuoles suggest that the guard cells are complex in function. A highly reduced grana-fretwork system within the plastids indicates that the photosynthetic capacity of the guard cells is probably rather low. No plasmodesmata occur in the walls between the guard cells and the subsidiary cells while there are numerous invaginations of the guard cell plasmalemmas. Many of the variations in the plasmalemma probably indicate that the plasmalemma is a highly active interface.