Osmiophilic globules

The histidine-rich sheath seems to act as a priming coat for distribution of intensely osmiophilic globules 49, 64). This osmiophilic matrix or cementing substance is probably sulfur-rich 64, 82) and has been observed as patchy deposits 49) that embed the 100-A filaments within 250-A fibrils 64, 70). Various evidence suggests that this osmiophilic... 

Besides the dense osmiophilic globules there are other positively or negatively stained bodies in the protoplast which appear mainly in the centroplasm. The function and origin of these different cellular inclusions are unknown. 

The main difference in protoplast differentiation between blue-green phycobionts and their free-living counterparts is the occurrence of osmiophilic globules. 

Fig. 22. Dark-grown C. reinhardi y-1 exposed to the light for 5 h (chlorophyll concentration 5.3 Mg/10 cells). Note the increase in number and length of disc profiles (d) and disc pairing (dp), the still limited fusion of discs to form grana (g), and the chloroplast ribosomes (cr). mb, plasma membrane o, osmiophilic globules sg, starch granules. (78,500x for experimental details see ref. 63.)...

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.)...

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