86 THE SYNTHESIS OF PROTEINS 



organic food materials and salts, but lacking potassium, 

 show but poor development and no protein synthesis. In 

 similar cultural conditions seedlings of the beet showed seven 

 times less protein and eighteen times less sugar, when grown 

 without potassium, as compared with the controls ; when 

 grown in sterile conditions in a culture medium containing 

 a sugar and supplied with known amounts of carbon dioxide, 

 it was found that those grown in the light were independent 

 of potassium as regards the synthesis of protein, and that the 

 addition of sugar to the culture medium resulted in an increase 

 of protein. In darkness, on the other hand, a less vigorous 

 development occurred and only those plants supplied with 

 potassium salts showed protein formation. 



It would therefore appear that the action of potassium 

 is partly indirect, and only in darkness does it play an important 

 role in the production of proteins. Since potassium is mildly 

 radioactive, it may possibly serve as a source of energy in 

 promoting metabolic activity, but, as has been remarked on 

 a previous page, no definite conclusion can be drawn from the 

 available evidence.* 



OCCURRENCE OF NITRATE. 



The obvious essentiality of nitrogen in the building of 

 proteins and the fact that in general the element is absorbed 

 by the plant in the form of nitrate has been remarked upon. 



The work of Anderson f and earlier authors has demon- 

 strated the presence of nitrate in a large number of plants ; 

 but a review of the literature shows some discordance, which 

 is probably due to the fact that the amount of discernible 

 nitrate in leaves varies according to the season of the year, 

 the richness of the soil, and the conditions of growth, more 

 especially the degree of insolation. To cite but two examples : 

 Suaeda fruticosa growing in its natural habitat, a shingle beach 

 from which salts are readily leached and exposed to maximum 

 insolation, gave negative results when tested for nitrate ; the 

 same plant growing in garden soil and in a certain amount 



* See Stoklasa : " Biochem. Zeit.," 1916, 73, 107. 

 1 Anderson : " Ann. Bot.," 1924, 38, 699. 



