14 



STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



In our own experiments with mature leaves of Helianthus annuus 

 we found that the amino-acid content of the leaves was higher than 

 that of the stems, while the carbohydrate-content was considerably 

 higher in the stems. 



Comparing seedUngs which had developed in the light with those 

 grown in the dark, Schulze and Castoro found that the amount of 

 amino-acids in etiolated seedlings 7 days old was higher than in the 

 green plants twice as old, while the amount of asparagine was about 

 the same in both. In general, it would seem from these investigations 

 that the amount of amino-acid formation and protein breakdown is 

 considerably reduced when there are carbohydrates present or the 

 power of carbohydrate formation through photosynthesis is available 

 to the seedlings. This substantiates the general principle that 

 carbohydrates are protein-sparers, which has been found by other 



Table 4. — Distribution of nitrogen compounds in 

 leaves and stems according to Schidze's analysis. 



investigators. 1 These studies by Schulze have, however, only an 

 indirect bearing on our investigations, because Schulze was dealing 

 largely with the germination of seeds in which reserve proteinaceous 

 material was in the course of the metabolic activity of the plant 

 resolved into simpler compounds, and the plants were not mature 

 self-supporting organisms. Schulze^ has made some extensive 

 investigations of the amino-acid transformations in young plants. 

 In seedlings of the Vicia saliva, Pisum sativum, Lwpinus luteus, 

 and Lupinus alhus grown in the dark there occurs a marked accumu- 

 lation of amino-acids. The nature of the amino-acids changes with 

 the length of time the plants are allowed to remain in the dark. 

 Seedlings left in the dark 6 to 7 days contain leucin, asparagine, 

 arginine, histidine, lysine, and tyrosine in small quantities. After 

 remaining in the dark for longer periods, 2 to 3 weeks, leucine, tyro- 

 sine, and arginine decrease, while the amount of asparagine is greatly 

 increased. Schulze considers leucine, arginine, histidine, and lysine 

 as the primary products of the protein breakdown in leaves, and that 

 these substances in turn are converted into asparagine and glutamine 



» Deleano, N. T. Jahr. f. wiss. BoL, SI, 541-592 (1912). 



* Schulze, E. Ueber den Umsatz der Eiweissstoffe in der lebenden Pflanze. 

 chem., 30, 241-312 (1900). 



Zeit. physio. 



