1750 CHLOROPLASTS, CHROMOPLASTS AND CHROMATOPLASM CHAP. 37A 



synthesis has repeatedly been suggested (c/. Chapter 10, section E2). 

 Experiments of Krasnovsky (Chapter 35, section A4) on photochemical 

 chlorophyll reduction by ascorbic acid in vitro have added some new inter- 

 est to these suggestions. We cannot review here the considerable new 

 literature on the ascor})ic acid content of green cells, and its variability, but 

 will mention a few relevant investigations. Aberg (1946) has studied the 

 effect of light and temperature on the ascorbic acid content of tomato and 

 kale leaves, and found on approximate proportionality of this content with 

 light intensity up to about 80 cal./cm.- min.; he noted a rapid decrease of 

 this content in darkness. Later (1945) he made similar studies also with 

 parsley and spinach leaves, and noted that the decrease of ascorbate con- 

 centration in dark could be largely prevented by feeding with sugar. 



Matuyama and Hirano (1944) determined the ascorbic acid content of 

 Chlorella, and found 2-3 mg. in 1 g. dry weight; 60-70% of it were in the 

 reduced form. In the dark, the ascorbate concentration went down, and 

 the percentage of the reduced form decreased, both increased markedly 

 after three hours exposure to light in the presence of carbon dioxide. The 

 percentage of the reduced form (but not the total content) could be raised 

 also by a supply of 5% CO2 in the dark. Iron-deficient, chlorotic algae 

 were found to contain more ascorbate than the normal ones, while Mg or 

 N-deficient cells showed a subnormal ascorbate content. 



The role of ascorbate in the Hill reaction and in Anion's et al. (1954) 

 "photosynthesis with whole chloroplasts" was described in Chapter 35, 

 sections 1 and 4. 



6. State of Pigments in Chloroplasts 



(a) Chloroplastin 



In section 2, it was tentatively suggested that chlorophyll may be 

 located on the protein-lipide interfaces in the grana discs (or lamina). 

 This picture, however plausible, is still speculative; and even if correct, 

 leaves open the question of the nature of the association between the pro- 

 tein, the pigment, and the lipoid constituents. Even less certain is the lo- 

 cation and state, in vivo, of the accessory pigments, in particular, of the 

 hydrophylie phycobilins. 



In Chapter 14 (sections C2 and C3), we reviewed the evidence for 

 (and, mainly, against) the assumption of a stoichiometric chlorophyll- 

 protein compound in chloroplasts. Since then some new experiments have 

 been published dealing with the pigment-protein-lipoid complex as ob- 

 tained from green cells. 



Stoll and Wiedemann (1947) gave some additional data on the properties 

 of "chloroplastin" prepared as described in their earlier papers (cf. Vol. I, 

 p. 385). The ether extract from salt-induced cleavage of Aspidistra 

 chloroplastin was analyzed and found to consist of 49% insoluble proteins. 



