STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



13 



accumulation of amino-acids has been the subject of numerous inves- 

 tigations and the basis of much speculation regarding the function 

 and fate of proteins in plant respiration. ^ Suzuki^ is also of the 

 opinion that during the night the proteins of the leaf are broken 

 down to amino-acids and that these migrate to other parts of the 

 plant. This seems to be very near to the actual state of affairs, 

 although the extent to which this takes place is still an undecided 

 question. The solution thereof is made very difficult because other 

 processes, such as photosynthesis during the day and respiration 

 at night, may often mask any definite results observable in the 

 analytical data. 



Since the development of protein chemistry the improved methods 

 of isolating and determining the various amino-acids have made it 

 possible to establish what compounds are formed in the decomposition 

 of the proteins of plants when these are left in the dark. Most of 

 the investigations have been carried out on germinating seeds, so 

 that many of the results are not altogether applicable to mature 

 leaves. However, Schulze for many years has been working on the 

 amino-acid content of plants and he has obtained some very valuable 

 results. Seedlings of Lupinus grown for 14 days in the open were 

 reported by Schulze and Castoro^ to contain nitrogen compounds, 

 as follows : 



Table 3. 



Schulze attributes the great difference in the asparagine content 

 between the stems (21.12 per cent) and the leaves (6.65 per cent) 

 to the photosynthetic action of the leaves, which in the presence of 

 carbohydrates convert the asparagine into proteins. In harmony 

 with this it is pointed out that the protein-content of the leaves is 

 2.5 times as great as in the stems. 



1 Pfeffer, W. Untersuchungen ueber die Bedeutung des Asparagins beim Keimen der Samen. 

 Jahrb. f. wiss. BoL, 8, 429-574 (1880). 

 Meuniek, F. fitude sur I'asparagine. Ann. Agron., 6, 275-281 (1880). 



Borodin, J. Ueber die physiologische Rolle und die Verbreitung des Asparagins im Pflanzen- 

 reiche. Bot. Zeit., 36, 801-832 (1878). 

 » Suzuki, W. Bull. Coll. Agr. Tokyo 2, 458 (1896). 



' Schulze, E., and N. Castoro. Beitrege zur Kenntniss der Zusammensetzung und des Stoff- 

 wechsels der Keimpflanzen. Zeit. physiol. chem., 38, 244 (1903). 

 Also KiESEL, A., Zeit. physiol chem., 49, 72-80 (1906) ; Andr6, G., Compt. rend., 148, 1685-1687; 

 Thompson, S. G., Jour. Amer. Chem. Soc., 37 230-235 (1915). 



