Cellular structure and light absorbtion in leaves of Frithia pulchra (Mesembryanthemaceae)

In order to quantify the structural differences between cell types of leaves from a ' window' plant, an ultrastructural morphometric analysis was made of the epidermal, window and chlorenchyma tissues of Frithia pulchra. Epidermal cells are the largest cells found in Frithia leaves and are characterized by the presence of a thick outer tangential cell wall and numerous vacuolar inclusions. Epidermal tissue has an optical density of 0.30. The transparent window tissue (i.e. optical density = 0.08) has a uniform ultrastructure throughout the length of the leaf. The vacuome comprises aproximately 97 per cent of the protoplasmic volume of window cells. Chlorenchyma cells possess thin cell walls and are surrounded by numerous intercellular spaces. Cells of the apical chlorenchyma tissue possess approximately 30 plastids per cell. These chloroplasts have an average individual volume of 220 μm². Cells of the basal chlorenchyma tissue contain chloroplasts that are five to six times smaller and more numerous than those in cells of the apical chlorenchyma. The increased volume of chloroplasts in the apical compared with basal chlorenchyma cells (i.e. 31.4 and 20.2 per cent of the protoplasm, respectively) is positively correlated with their optical densities of 1.46 and 0.97, respectively.