IV. BIOCHEMICAL SYSTEMS 221 



light, and moreover carhoii dioxide was necessary for its accumulation." 

 In general, factors which favor photosynthesis also favor biosynthesis of 

 ascorl)ic acid, although the connection between these metabolic activities 

 may be indirect. If sugar serves as the precursor of ascorbic acid it is only 

 natural that its formation should be accelerated under conditions in which 

 sugar is being formed. This does not exclude the possibility that other, 

 more active intermediates may be formed during photosynthesis. Aberg^^ 

 has suggested that there are two different routes for ascorbic acid synthesis 

 in the plant: (a) a synthesis independent of light, which occurs mainly in 

 germinating seeds and (b) a light-conditioned synthesis w'hich is connected 

 with the assimilation of carbon dioxide. 



c. Relation between Sijnthesis of Carotenoids and Ascorbic Acid 



Fruits richest in carotenoids are also usually rich in ascorbic acid.^- Seed- 

 lings grown at low temperature were found to form much ascorbic acid and 

 also carotenoids, but little chlorophyll.^' With cress seedlings the effect of 

 different nutrients salts had a similar effect on the synthesis of both ascorbic 

 acid and carotene.'* It is difficult, however, to establish a direct chemical 

 relationship on the one hand, or on the other to decide whether this parallel- 

 ism is pure chance. The suggestion*' has been made that carotene may pro- 

 tect ascorbic acid from oxidation, thus causing an accumulation of the 

 vitamin in the cell. 



/. Relation to Sucrose 



In detached leaves kept in the dark the ascorbic acid content falls; this 

 fall may be arrested and an increase of ascorbic may in some cases actually 

 occur by floating the leaves in a 10% sucrose solution.*^ With submerged 

 leaves in water the fall of ascorbic acid is not arrested but even accentuated, 

 but there is no indication as to whether this treatment increases the sucrose 

 content inside the cell. Other evidence, however, points to some relation 

 between sucrose and ascorbic acid. With detached leaves placed in the dark 

 and supplied with weak solutions of iodoacetate, fluoride, or arsenite, a 

 marked fall in the ascorbic acid of the leaf occurred, and the fall was ac- 

 companied or even slightly preceded by a parallel fall in sucrose.*^ The same 

 process appears to go on in leaves left in the dark and supplied w^ith water 

 alone, although the rate of change is much slower. A correlation between 

 ascorbic acid and sucrose content has also been observed in potato tul)ers 

 sul)jected to temperatures of —0.8° to +1° to induce sweetening," Under 



"A. Giroud, Proloplasma (Monogr.) 16, 1 (1938); A. Giroud, R. Ratismamanga, 



R. Leblond, H. Chalopin, and M. Rabinowicz, Bui. soc. chim. biol. 18, 573 (1936). 

 " B. Aberg, Physiol. Plantarum 2, 164 (1949). 

 " L. W. Mapson and J. Barker, Unpublished data. 

 " J. Barker and L. W. Mapson, New Phytulogist 49, 283 (1950). 



