PROTEINS AND LIPOIDS IN CHLOROPLASTS 



371 



from a known quantity of leaves, or indirectly, as in the method used by 

 Neish (I9391) and Menke (19400- They extracted chlorophyll (or the 

 carotenoids) from the flocculated " chloroplastic fraction" on the one 

 hand, and from an equal mass of whole leaves on the other hand; knowing 

 that all pigments were originally associated with the chloroplasts, they 

 calculated the total quantity of chloroplastic matter from a comparison 

 of the concentration of the pigments in the two extracts. Table 14.1 

 shows the results. 



According to Menke's data, the proportion of chloroplastic matter in 

 dry spinach leaves is 30% (if water-soluble components — carbohydrates, 

 acids, salts, etc. — are excluded from the total). Since most of the 

 soluble compounds are contained in the vacuolar sap or in the cytoplasm, 

 chloroplastic matter must constitute about 20% of the total dry weight 

 of spinach leaves. Neish's figures are somewhat higher, 25 to 35% of 

 the total dry weight. These results can be further compared with an 

 estimate of the relative volume of the cytoplasm, the chloroplast, and 

 the nucleus in a palisade cell of Tropaeolum majus made by Meyer (1917) 

 on the basis of microscopic measurements. He found for the chloroplasts 

 — an average volume of 9.4 ^t^; average number in a cell, 54; average 

 total volume, 508 /x^; for the nucleus — an average volume of 54 11^; and 

 for the cytoplasm— Sin average volume of 244 /x^ This corresponds to a 

 volume ratio of 2 : 1 between the chloroplasts and the cytoplasm. 

 Menke's value for the corresponding mass ratio in spinach leaves is closer 

 to 1, while Chibnall (1939) gave a value of 2.3 (for the same species). 



2. Proteins and Lipoids in the Cytoplasm and the Chloroplasts 



The main constituents of the chloroplasts are proteins and "lipoids." 

 The latter term is used in a very wide sense, embracing all compounds 

 soluble in ether or in an ether-alcohol mixture. It was previously 

 assumed that chloroplasts are the main protein carriers in plants, since 

 a statistical parallel was found between the size of the chloroplasts and 

 the nitrogen content of the leaves. The correctness of this rule was, 

 however, contested by Schumacher (1929); and the analytical data of 

 Menke, Neish, Bot, and Comar show that, while the chloroplasts contain 

 about 40-50% protein, the cytoplasm is almost pure protein, so that 



Table 14.11 

 Distribution of Proteins Between Spinach Leaf Constituents (after Menke) 



