Osmiophilic lamellae

When the mucous layer is appropriately preserved, it shows a smooth or slightly undulating surface, as shown in scanning electron micrographs (Fig. 8). By transmission electron microscopy, the top-most layer can be seen to be coated with an osmiophilic film (Fig. 9), which may appear multilayered (Fig. 10). Lamellar bodies and other lipid structures may be present in the sol layer (6,86 Fig. 11). The periodicity of these osmiophilic lamellae has been measured at approximately 40 A (6), suggesting structural homology with the alveolar lining layer. 

Heterocysts were found occasionally in the Nostoc symbionts of Leptogium hildenbrandii (Peveling, 1969c). They differ from other cells by a poor differentiation of thylakoids. The lamellae are short and few in number but many osmiophilic globuli are present. 

Fig. 2.16. Electron micrograph of a shadowed fragment of a Vicia leaf chloroplast. Note the appearance of the grana (G). On the surface of the granal lamellae can be seen small particles (Q) which may be identical to those seen in freeze-etched preparations. Osmiophilic globules (0) are also present. (From F. A. L. Clowes and B. E. Juniper, Plant Cells, Blackwell Scientific Publications, Oxford, 1968. Micrograph by Mr. A. D. Greenwood.)...

Fig. 2.17. Bottom left. Chloroplasts (P) in chlorenchyma of pea leaf. Note the large starch grains within the chloroplast (asterisks). IS, intercellular space V, vacuole. X 780. Right. Electron micrograph of a chloroplast of a leaf of spinach Spinacea oleracea). The chloroplast is surrounded by a double membrane (PM) and the internal membrane system is differentiated into grana (asterisks) and stroma lamellae (open arrows). Osmiophilic droplets (small black arrows) occur in the plastid stroma. The structure of the grana is shown in more detail in the inset top left) as are regions of continuity between the grana and stroma lamellae (large solid arrows). Key CM, cell membrane CW, cell wall SG, starch grain ...

Key CM, chloroplast double membrane (each 35—50 A thick) S, stroma G, granum (made up of a cylindrical pile of discs) SL, stroma lamella GL, grana lamella D, disc OD, osmiophilic droplet. 

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