218 ASCORBIC ACID 



nitrogenous fertilizers to fruit trees lowered the ascorbic acid content of 

 the fruit.^^ Observations on grapefruit indicated that there was an inverse 

 relationship between the nitrogen and ascorbic acid content. ^^ The effect 

 of nitrogenous fertilizers may, however, be overshadowed by the effect of 

 other environmental factors such as soil or light intensity. "*"• *^ Moreover, 

 the effect of nitrogen per se is difficult to assess, since fertilizers rich in 

 this element inevitably affect the size of crop, the amount of foliage, etc., 

 all of which have important indirect effects on the synthesis of the vitamin. 

 It has also been suggested that the higher rate of respiration usually induced 

 by higher nitrogen supply may also influence the concentration of ascorbic 

 acid by increasing its rate of consumption,'*^ or by depressing the photo- 

 synthetic products available for synthesis by stimulating other competitive 

 synthetic processes. ^^ 



The form in which nitrogen is supplied to the plant is equally important, 

 although contrary effects have been reported. Some reports indicate that 

 plants supplied with nitrate contain less ascorbic acid than those grown on 

 ammonium salts.^'* In other studies the reverse has been reported. With 

 cress seedlings the effect of ammonium nitrogen depends on the type of 

 ammonium salt fed. Ammonium sulfate and chloride depress the synthesis 

 of ascorbic acid, but ammonium bicarbonate, acetate, or succinate have 

 relatively little effect. Of a large number of salts tested, it has been shown 

 that they influence the synthesis of ascorbic acid by virtue of their effect 

 in altering the pH of the cell sap. When the cation of the salt is NII4 and 

 combined with a non-utilizable anion, there is a marked depressant effect, 

 which is reduced w^hen the cation is combined with a utilizable anion. 

 Conversely, calcium or potassium salts, when combined with a utilizable 

 anion, e.g., nitrate, succinate, bicarbonate, or acetate, increase the synthe- 

 sis to a greater extent than when they are supplied in combination with 

 non-utilizable anions, e.g., sulfate or chloride. ^^ 



38 W. W. Jones and E. R. Parker, Proc. Am. Soc. Hort. Sci. 50, 195 (1947); S. H. 

 Wittwer and A. D. Hibbard, Proc. Am. Soc. Hort. Sci. 49, 116 (1947). T. Wallace 

 and S. S. Zilva, Biochcm. J. 27, 693 (1933); W. Kessler, Garienbauwiss. 13, 619 

 (1939); A. H. Finch, W. W. Jones, and C. W. Van Horn, Proc. Am. Soc. Hort. Sci. 

 46, 314 (1945). 



39 W. W. Jones, C. W. Van Horn, A. H. Finch, M. C. Smith, and E. Caldwell, Science 

 99, 103 (1944). 



40 K. J. Kasihka, L. T. Dudgeon, and H. M. Hauch, /. Ayr. Research 68, 49 (1944). 

 •»! K. C. Hamner, L. Bernstein, and L. A. Maynard, J. Nutrition 29, 85 (1945). 



« H. Burstom, Arkiv. Botan. 32A, 7:1 (1945); G. T. Nightingale, Botan. Rev. 3, 85 

 (1937); 14, 185 (1948). 



« B. Aberg and I. Ekdahl, Physiol. Plantarum 1, 290 (1948). 



^4 W. W. Jones, W. P. Bitters, and A. H. Finch, Proc. Am. Soc. Hort. Sci. 45, 1 (1944); 

 A. H. Finch, W. W. Jones, and S. W. Van Horn, ibid. 46, 314 (1947); S. H. Wittwer, 

 R. A. Schroeder, and W. A. Albrecht, Soil Sci. 59, 329 (1945). 



