STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 9 



nitrogen compounds. There are no nitrogenous excreta, and the 

 plant possesses the power, to a very highly developed degree, of 

 resynthesizing the decomposition products of proteins. The excep- 

 tion to these statements should be mentioned at once. Thus there 

 are the denitrifying actions of certain bacteria and the behavior of 

 the lower non-chlorophyllous plants. These organisms exhibit a 

 behavior toward the proteins which seems to differ in many funda- 

 mental aspects from that of the higher plants.^ 



In this study we are concerned primarily with the metabolism of 

 mature autotrophic leaves. A priori, the nitrogen metabolism of 

 such organs would seem to have but little similarity to that of ger- 

 minating seeds, in which it is primarily a question of the resorption 

 of stored proteinaceous material. In view of its great importance 

 it is surprising how very little work has been done on the protein 

 metabolism of leaves. 



Deleano's- investigations show that the total nitrogen-content 

 of leaves of Vitis vinifera did not change appreciably during 493 

 hours of respiration in the dark. He also found but very slight 

 variation in the protein nitrogen up to 87 hours. Thereafter these 

 values decreased. These determinations were made by means of 

 Stutzer's method, so that they represent coagulable protein, and no 

 information can be gained therefrom regarding the amino acid- 

 protein relations. 



Whether a sharp differentiation can be drawn between living and 

 inanimate protein, or better, perhaps, between protoplasmic and 

 non-protoplasmic protein, in the leaf appears exceedingly difficult. 

 It has also been impossible to determine in plants a factor corre- 

 sponding to the "protoplasmic mass," which has an important role 

 in the discussions of animal physiologists in considering the phe- 

 nomenon of respiration. What, finally, the function is of the total 

 protein or of the protoplasmic proteins in plants is a question on 

 which we have no direct experimental evidence. As has been stated, 

 one of the chief difficulties in this problem has been the inadequate 

 information that exists regarding the nature of the proteins of leaves. 



Palladin^ has attempted to establish a relation between the rate 

 of carbon-dioxid emission and of the proteins in wheat seedlings. 

 Based upon the old observations of Reinke,* Zacharias,'^ and 

 Schwartz,^ Palladin assumed that the protoplasmic proteins are 



* Mater, A. Agriculturchemie, Gaerungschemie, 138-139 (1902). 



Cf. also Irving, A., and R. Hankinson. Biochemical Jour., 3, 87, 1908. Ivanoff, N. N., 



Biochem. Zeitschr., 120, 1-80 (1921). 

 = Deleano, N. Jahrb. f. wiss. BoL, SI, 587 (1912). 

 ' Palladin, W. Recherches sur la correlation entre la respiration des plantes et les substances 



azotees actives. Rev. Gen. de Bot., 8, 222-284 (1896). 



* Reinke, J. Stiidien ueber das Protoplasma (1881). 



* Zacharias, E. Bot. Zeitung (1881) 169; (1883) 209. 



* Schwartz, F. Morphologische und chemische Zusammensetzung dcs Prutoplasmas. 1887. 



