20 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



Chloroplasts 



Chloroplasts, like mitochondria, provide the cell biologist with 

 an organelle showing orderly and consistent membranous struc- 

 ture amenable to integrated morphological and biochemical 

 analysis. If such studies involving electron microscopy at first 

 seemed to lag because of difficulties encountered in the preserva- 

 tion of plant tissues, the weight and vigor of interest in photo- 

 synthesis nonetheless are pushing them to a high level of 

 sophistication (see Calvin, 1959; Hodge, 1959; Wolken, 1959). 



The pigmented phytoflagellates appear to occupy a gratifyingly 

 intermediate position in a scale of increasing differentiation of 

 chloroplast structure. In the photosynthetic bacteria, bacterio- 

 chlorophyll and carotenoids are localized in chromatophores that 

 are minute (about 32 m/x in diameter) spheres with dense 

 peripheries and low-density interiors (Bergeron, 1959). In the 

 blue-green algae Nostoc (Hodge, 1959) and Calothrix (Ris and 

 Singh, 1961), a membrane system ramifying through the cytoplasm 

 is assumed to bear the enzymes that in eucells are localized in 

 membranes of mitochondria and chloroplasts. In Anabaena and 

 Anacjstis, studied by the same authors, some of these membranes 

 assume the form of wide, flat lamellae embedded in the general 

 cytoplasm but often running in parallel below the cell membrane. 



Primitive red algae (Brody and Vatter, 1959; Gibbs, 1960 and 

 personal communication) have developed true chloroplasts, 

 inasmuch as lamellar discs resembling those of the blue-greens 

 now are segregated from the surrounding cytoplasm by two 

 parallel limiting membranes. In all other algae (Gibbs, 1960) discs 

 within the chloroplasts are very intimately associated in bands of 

 two or more. 



In various chrysomonad flagellates studied by Parke, Manton, 

 and Clarke (1958, 1959), by Rouiller and Faure-Fremiet (1958a), 

 and by Manton and co-workers (see citations in Chapter 4) the 

 lamellar bands run roughly parallel to the long axis of the 

 chloroplast or to its curvature where it is cup-shaped. They 

 converge at the two ends of the organelle, but some discs may 

 extend less than its full length. The bands in these micrographs 

 are rather sinuous and separated by spaces of varying width ; to 

 what extent this may be an artifact of fixation is uncertain. 



