448 



NITROGEN METABOLISM 



cell sap such as begonia and rhubarb, ammonia often reacts with organic acids 

 forming salts (Ruhland and Wetzel, 1926, 1927). 



3. Asparagine and Glutamine. — The compound resulting if one of the 

 carboxyl groups of aspartic acid is replaced with an acid amide group is 

 called asparagine. A similar substitution in the molecule of glutamic acid 

 gives the compound glutamine^ thus: 



COOH 



I 

 CHNH2 



I 

 CH2 



I 

 COOH 



Aspartic acid 



COOH 



I 

 CHNH2 



CH2 



I 

 CH2 



COOH 



Glutamic acid 



COOH 



I 

 CHNH2 



I 

 CH2 



I 

 CONH2 



Asparagine 



COOH 



I 

 CHNH2 



I 

 CH2 



CH2 



CONH2 



Glutamine 



One or both of these compounds are apparently found in all species of 

 plants. The role of asparagine has been more exhaustively studied than that 

 of glutamine (Robinson, 1929, Murneek, 1935). Asparagine appears in 

 relatively large quantities in germinating seeds, being especially abundant in 

 those of legumes. The asparagine thus produced is apparently synthesized from 

 amino acids resulting from the digestion of proteins. Asparagine is formed 

 in plants only in the presence of oxygen. Protein hydrolysis will occur in the 

 absence of oxygen and under such conditions amino acids are produced but no 

 asparagine. 



Asparagine is a very mobile compound and is an important translocation 

 form of nitrogen. Much of the asparagine synthesized in seeds is translocated 

 to growing regions of the seedlings and there utilized in the synthesis of 

 proteins. Similarly when proteins are hydrolyzed in other organs of a plant 

 asparagine usually appears as a product along with amino acids. Asparagine 

 also serves as a temporary storage form of nitrogen in some plant organs. 



When plants are deficient in carbohydrates, amino acids produced as a 

 result of protein digestion may be oxidized in respiration (Chap. XXIX). 



