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DEVELOPMENTAL ANATOMY OF EPIDERMAL AND MESOPHYLL CHLOROPLASTS IN OPUNTIA BASILARIS LEAVES

A B S T R A C T Developmental studies of Opuntia basilaris Engelm. & Bigel. leaves revealed the presence of three morphologically distinct types of plastids. All epidermal cells examined contained chloroplasts. After 13 days of growth in the dark the plastids of epidermal and mesophyll cells were characterized by the presence of a prolamellar body and fibril inclusions. Epidermal plastids which developed under light conditions contained large stromacentres and a limited grana-fret membrane system. Guard cell plastids developed under similar conditions had a much poorer developed grana system with fibril inclusions apparent only during the developmental stages. At maturity these plastids appeared swollen or dilated. Mesophyll plastids had fibril inclusions during all stages of development and at maturity contained a very extensive grana-fret membrane system. Microbodies were found in association with the mesophyll plastids. Starch accumulation was common in subsidiary cell and guard cell plastids. CHLOROPLASTS have been found in the epidermal cells of a wide variety of plants, including both aquatic (Sculthorpe, 1967) and terrestrial (Meyer, 1962) angiosperms. Mikulska (1959a, b) has described epidermal chloroplasts in a large number of both monocotyledonous and dicotyledonous plants. Of 184 species of dicotyledonous plants examined Mikulska noted that 94 % had epidermal plastids which were capable of starch synthesis. Wylie (1948) concluded that the epidermal cells of certain species of Adiantum constituted the major photosynthetic tissue of the leaf. The relationship between guard cell plastids and the stomatal mechanism has been reviewed by Zucker (1963), and ultrastructural investigations