VOL. 12 (1953) SOLUBLE NITROGEN FRACTION IN PEA PLANT AND ALDER 183 



These results will be discussed in another paper. We have also paid special attention to 

 changes taking place in the soluble nitrogen fraction when keeping the plants in the 

 dark. In two days great increase occurred in the soluble nitrogen fraction of all tissues 

 of growing pea, as appears from the results in Table I. 



TABLE I 



NITROGEN SOLUBLE IN 70% BY WT. ETHANOL 



{/iig N per 100 mg. dry wt.) Peas in full bloom, 43 days old 



- , ,, ,, N of all determined* free amino 



Soluble N ' . ■ 1 ■ , i 1 



after 2 davs ""'^^^ '" '"'"^^ 



in normal light /„t,^aark in normal light 'JSJ£'^' 



* Several amino acids could not be determined quantitatively. 



As the assimilation of carbon dioxide ceases in the dark, the decomposition pro- 

 cesses set in and the breakdown of proteins and deamination of amino acids are detectable. 

 In connection with them the synthesis of amino acids through transamination, reductive 

 amination of keto-acids etc. will possibly affect the soluble N-fraction in another way 

 than in plants grown in light when free amino acids are continuously removed through 

 the protein synthesis. It is therefore interesting to follow the changes in the soluble 

 nitrogen fraction caused by the darkness. Our experiments so far have been carried 

 out with pea plants growing in sand without combined nitrogen, solely with atmospheric 

 nitrogen fixed in their root nodules. Parallel experiments with nitrate or ammonium 

 nitrogen have not yet been made. Since the red nitrogen-fixing nodules of pea lose their 

 activity in the dark^** at breaking of the porphin ring of leghemoglobin through oxida- 

 tion2i.22_ the pea plants in these experiments have no longer received any nitrogen 

 nutrition. 



The darkening affected the proportions of free amino acids in pea plants in the fol- 

 lowing manner. As a rule the concentration of those amino acids, which normally are 

 either absent or present only in minute amounts in free state, rose most. Thus, arginine 

 and lysine appeared, and the quantities of leucine, woleucine, phenylalanine, and valine 

 rose to approximately 5-10-fold. Some free histidine was also found in the leaves of 

 darkened plants, normally it is completely absent from the plants. Glycine, threonine, 

 tyrosine, and methionine, which have not been found free in the leaves of pea growing 

 in light, became distinctly detectable during the darkening and their concentration 

 rose in the nodules. The amount of free aspartic acid increased during the darkness to 

 about 20-fold in the leaves ; in the roots it remained unchanged but in the nodules de- 

 creased. Similar changes occurred in glutamic acid but its increase in the leaves was 

 only about 3-fold. Amides and y-AB were affected in approximately the same way. 



Such amino acids as occur liberally in free state in normal plants, e.g. alanine and 

 serine, increased only in approximately the same proportion as soluble nitrogen. Darken- 

 ing did not essentially affect the amount of homoserine. 



The interpretation of the obtained results is difficult because many different reac- 

 tions affect the mutual relations of amino acids during the darkness. The general im- 

 References p. i8y. 



