1734 CHLOROPLASTS, CHROMOPLASTS AND CHROMATOPLASM CHAP. 37A 



All these calculations have a wide range of uncertainty, particularly if 

 they combine chloroplast numbers, counted by one observer in one plant, 

 with chloroplast dimensions, determined by someone else on another plant, 

 and grana dimensions, measured by a third person with still different plant 

 material. For example, values Vjetween 20 and 50 m^ can be used for the 

 chloroplast volume, those between 50 and 200 for the number of grana in a 

 chloroplast, and those between 0.03 and 0.1 n^ for the volume of a granum. 



Starch-free chloroplasts are known to contain, under normal conditions 

 of nutrition, 50-60% of "proteinaceous" and 30-44% of "lipide" material 

 (c/. below). The "lipides" — i. e., compounds soluble in ether or alcohol, in- 

 cluding chlorophylls and the carotenoids — appear to be more abundant in 

 the grana than in the stroma. However, it was mentioned above that the 

 grana cannot be purely lipide and the stroma purely proteinaceous (as one 

 may be tempted to suggest), for two reasons: First, the total content of 

 lipides in the chloroplasts is so high that all of them cannot find place in the 

 grana; second, grana are still visible after treatment with lipophilic sol- 

 vents, indicating that they contain a proteinaceous "skeleton." Certain 

 lipophilic stains, such as Sudan red, color only the grana (c/. Vol. I, p. 361) ; 

 this does not prove, according to Frey-Wyssling, that the stroma is lipide- 

 free, but can be explained by the assumption that the stroma lipides are 

 tied up in lipoproteins. 



Dispersion and fractionation of chloroplast material has never yet pro- 

 duced a purely lipide or a purely proteinaceous pigment-bearing fraction. 

 The "chloroplastin" of Stoll (cf. Vol. 1, p. 385 and section 6(a) below) con- 

 tained proteins, pigments, and lipophilic materials in approximately the 

 same proportion as whole chloroplasts. Similarly, no significant shifts in 

 the [nitrogen] : [chlorophyll] ratio could be observed in the fractionation of 

 dispersed chloroplast material by French, Holt and others {cf. Chapter 35, 

 pages 1555-1556). 



It was postulated by Hubert (1936) and Frey-Wyssling (1938) that 

 grana contain proteinaceous and lipide material in the form of alternate 

 layers, with chlorophyll molecules attached to protein layers by their 

 chlorophyllin "heads" (made polar by the presence of magnesium and of 

 carbonyl groups), and to lipide layer by their non-polar phj^tol "tails." 



Granick and Porter pointed out that, if less than one-half of the grana 

 material is proteinaceous, and all pigments are concentrated in the grana, 

 the ratio [protein] : [chlorophyll] in the grana must be less than one-half 

 of the average — in itself very low — ratio of these two components in the 

 chloroplasts as a whole. (For the discussion of this ratio, see Vol. 1, p. 

 389.) Frey-Wyssling (1953) estimated that grana contain 9 chlorophyll 

 molecules per "Svedberg unit" of protein (table 14. IX shows other 

 estimates, ranging from 1 to 22). 



