96 THE SYNTHESIS OF PROTEINS 



in the maize, whilst in the sunflower there was a diminution 

 of protein. Woodman and Engledow,* in their detailed 

 biochemical study of the development of the wheat grain, 

 found that there was a regular increase in total nitrogen and 

 in the percentage of protein nitrogen during development. 

 The nitrogen enters the developing grain, which contains no 

 nitrate, in the form of asparagine, and they conclude that the 

 asparagine is oxidized to ammonia which is the starting- 

 point of the protein synthesis. They also observed that 

 gliadine was greater in amount than glutenine, and that these 

 two substances increased at much the same rate until the be- 

 ginning of the desiccation of the grain, after which the glute- 

 nine remained constant and gluten appeared. Smirnow f 

 compared the nitrogen metabolism of etiolated seedlings of 

 high carbohydrate content, e.g. barley, and of low carbohy- 

 drate content, e.g. lupin, which were grown in sterile culture 

 solutions in controlled conditions. It was found that the 

 barley seedlings readily absorb ammonia, which is followed by 

 an increase in the amount of asparagine. The rate of absorp- 

 tion depends on the amount of sugar contained in the plant ; 

 at first it is rapid and then falls off and stops as the sugar 

 content diminishes to a certain limit. The presence of calcium 

 salts promotes the formation of asparagine, but the process 

 ends sooner since the sugar is more rapidly used up. 



The degree of uptake of ammonia by lupin seedlings is 

 dependent on the presence of sugar in the culture medium. 

 Seedlings given ammonium salts and glucose show a higher 

 asparagine content, a higher protein content, and a lesser 

 accumulation of ammonia in the tissues than seedlings given 

 ammonium salts but no sugar. Further, the ratio of aspara- 

 gine nitrogen to ammonium nitrogen is twice as great in the 

 seedlings given sugar in addition to the ammonium salts. 

 Younger seedlings after being given ammonium and glucose 

 also showed a higher amino acid content, but the amount fell 

 off with age as the proteins arc regenerated. 



These works indicate that in the plant amides and amino 



* Woodman and Engledow : " Journ. Agric. Sci.," 1924, 14, 563. 

 f Smirnow : " Biochem. Zcit.," 1923, 137, 1. 



