1744 CHLOROPLASTS, CHROMOPLASTS AND CHROMATOPLASM CHAP. 37A 



homogenates from tobacco leaves, the distribution of desoxy ribonucleic 

 acid followed, in general, that of chlorophyll. Metzner considered the 

 probable presence of desoxyribonucleic acid in the grana as important in 

 connection with Strugger's hypothesis that chloroplast propagation is 

 initiated and directed by a "plastidogen" (cf. section 1). 



Sisakyan and Chernyak (1952) obtained nucleic acid, from the chloro- 

 plast material of sugar beet leaves, by alkaline extraction and acetic acid 

 precipitation; color reaction with orcin was used to identify ribose. A 

 cytochemical test (formation of a fluorescent complex with acridine, which 

 is selectively absorbed by nucleoproteids), showed mostly red fluorescence 

 (typical of ribonucleic acid), and only in spots, green fluorescence (char- 

 acteristic of desoxyribonucleic acid) . 



In connection with the projects to grow large amounts of algae for food 

 or fuel, considerable study has been devoted to the possibility of directing 

 their metabolism toward the synthesis of increased quantities of proteins 

 or fats. It was found possible to vary the composition of algal cells very 

 widely by variation in culture conditions; but no studies have as yet been 

 made concerning the distribution of the accumulated fats and proteins be- 

 tween the cytoplasm and the plastides. 



Reviews of this subject by Milner, by Fogg and Collyer, and by others 

 are found in the monograph "Algal Culture, from Laboratory to Pilot 

 Plant" (1953), which also contains an extensive bibliography. 



(b) Enzymes 



From the point of view of photosynthesis one is most interested in the 

 presence in chloroplasts of enzymes whose activity could conceivably be 

 involved in the fixation and reduction of carbon dioxide, or in the liber- 

 ation of oxygen from water. 



Among the carbon dioxide-binding enzymes, we can first inquire about 

 carbonic anhydrase; we recall (Vol. I, p. 198) that the hydration of carbon 

 dioxide to H2CO3 has been considered a possible "bottleneck" in photo- 

 synthesis. It was mentioned in Volume I (p. 380) that no carbonic an- 

 hydrase was found in leaves by Burr and Mommaerts; but that it was 

 identified there by Neish. Neish's results have since been confirmed by 

 Day and Franklin (1945), Bradfield (1947), Steemann-Nielsen and Kris- 

 tiansen (1949), and Waygood and Clendenning (1950). They all found 

 that chloroplast material has an accelerating effect on the hydration of 

 carbon dioxide. Steemann-Nielsen and Kristiansen noted that carbonic 

 anhydrase appears to be present in Elodea as well as in Fontinalis, although 

 the first of these aquatic plants (according to Steemann-Nielsen) can use 

 HCOs" ions for photosynthesis, while the second one uses CO2 molecules 

 only (c/. Vol. II, part 1, p. 888). According to Waygood and Clendenning, 

 the carbonic anhydrase is located in the cytoplasm rather than in the 

 chloroplast. 



