The leaf tissue organization and ultrastructure of Portulaca oleracea L. from Korea was examined. Their succulent leaves exhibit a typical Kranz structure with distinct three cell types. The bundle sheath cells completely enclose the vascular bundles and consist of 5-9 large cells, showing centripetally oriented cellular organelles. The mesophyll cells concentrically surround the bundle sheath with 11-20 small cells whose organelles are peripherally arranged in the thin layer of the cytoplasm. The watery cells are the ground tissue of the leaf. These watery cells are usually elongated and very large with big vacuoles, and only a few organelles are present. Peripheral reticulum (PR) was observed in the chloroplasts of all cell types, but relatively well-developed PR was found in the mesophyll chloroplasts. Grana are well established in the bundle sheath chloroplasts and the mesophyll chloroplasts only. Agranal to rudimentary grana were frequently observed in the watery and the vascular parenchyma cells. Phytoferritin-like structures (Pf) are, sometimes, appeared in all cell types, especially in the vascular parenchyma where the abundant Pf appear as aggregates.
Temporal variation of the starch grains in the chloroplasts of each cell type was noticed when materials fixed in the morning and in the afternoon were compared. In the materials fixed in the afternoon, considerable reduction in number and size of the chloroplast starches were detected. The only cell type showing some starches in the afternoon is the bundle sheath cells and the other cell types contain almost none to little starches, if any.
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