CHEMICAL COMPOSITION OF PLANTS 75 



poor in nonnitrogenous reserves, are unable to form asparagine 

 from ammonia, since the necessary carbohydrates are lacking. 

 There may even be observed a decrease in the synthesis of 

 asparagine in the presence of ammonium salts. But if the seeds 

 of lupine are given carbohydrates, one of the best methods of 

 doing which is to germinate them in light, they may display 

 an intense synthesis of asparagine in the presence of ammonium 

 chloride, in other words, with ammonia presented from sources 

 outside of the seed. 



Prianishnikov illustrated the interrelations between the protein 

 substances, asparagine, and ammonia in the following diagram: 



amino acids — > proteins — > amino acids 



T i 



NH3 ^- asparagine ^- NH3 



The left side of this diagram gives a picture of the synthesis 

 of proteins in plants from the products of disintegration. The 

 right side represents the course of disintegration. This diagram 

 gives a very clear picture of the unity of two opposite processes 

 of decomposition and synthesis of proteins and the role of 

 asparagine as a connecting link between decomposition and 

 synthesis. 



According to the picturesque expression of Prianishnikov, NH3 

 must be considered the alpha and omega of the metabolism of 

 protein substances in plants. It is liberated from amino acids 

 and represents the final product of disintegration of nitrogenous 

 substances. But it represents likewise the initial substance with 

 which there starts the synthesis of nitrogenous compounds from 

 nitrogen-free substances, the first product of this synthesis being 

 asparagine. 



In some plants, especially in fungi, that are rich in proteins 

 and poor in nitrogen-free substances, the intermediate product 

 of the protein metabolism, asparagine, is replaced by urea. In 

 this respect, they function somewhat like the animal organism. 

 Especially large amounts of urea are accumulated in the fruiting 

 bodies of Lycoperdon, in which it constitutes 10 per cent or more 

 of the total dry weight. In plants whose cells are very rich in 

 organic acids, the ammonium salts of these acids are accumulated 

 instead of asparagine. 



This analogy between asparagine and urea emphasizes a very 

 important physiological difference between animals and plants. 



