370 



CHLOROPLASTS AND CHROMOPLASTS 



CHAP. 14 



breaks the chloroplasts and releases the grana, then upon fractionation the stroma may- 

 follow either the grana or the cytoplasm, depending on its state of dispersion and the 

 relative strength of its hydrophobic character. Since the stroma probably contains 

 less hydrophobic material than the grana (c/. page 361), it may have a tendency to 

 associate itself with the cytoplasm in fractional coagulation. 



This uncertainty casts some doubt on the pubhshed analytical data. Obviously, 

 much depends on how the grinding was carried out. Neish (1939^ asserted that 

 grinding under water produces free grana (because chloroplasts swell and rupture in 

 distilled water), while grinding in glucose solution keeps the chloroplasts intact. Granick, 

 who used a 0.5 molar glucose solution, described his " chloroplastic matter" as con- 

 sisting of whole and broken chloroplasts. Menke (1938'), who carried out the grinding 

 under water, nevertheless obtained a small fraction consisting of more or less intact 

 chloroplasts (c/. Table 14.IIIB). He had no doubts that the "chloroplastic matter" 

 obtained by fractional coagulation included all constituents of the chloroplasts (together 

 with 15% of the cytoplasm); while Mommaerts (1938) and Bot (1942) have asserted 

 that they have obtained preparations which consisted entirely of free grana. However, 

 the fact that the chlorophyll content of these allegedly pure grana fractions was not 

 higher (and sometimes even lower) than the chlorophyll concentration in the chloro- 

 plastic matter as a whole (c/. Table 14.X), supports the opinion of Menke (1940i) that 

 no separation of stroma and grana takes place in the fractionation. 



Determination of the total quantity of chloroplastic matter in the leaves 

 can be carried out either directly, by weighing the fractions obtained 



Table 14.1 



Proportion of Chloroplastic Matter in Green Leaves 



A. AFTER Menke 



B. AFTER Neish 



" Corrected for 15% coprecipitated cytoplasm; cf. page 369. 



