CHAPTER IV. 



THE SYNTHESIS OF PROTEINS. 



In view of our limited knowledge of the chemistry of proteins, 

 the degree of our ignorance respecting their synthesis in plants 

 is not surprising. 



It is generally agreed that the leaves are the important 

 centres of protein formation, and they show a periodicity in 

 their nitrogen content. Otto and Kooper,* Le Clerc du 

 Sablon f and others J found that there is a gradually decreas- 

 ing amount of nitrogen from the spring to the autumn, and 

 that leaves of several different plants, even in different stages 

 of development, exhibit a greater nitrogen content in the 

 morning than in the evening. These observations are con- 

 firmed by Chibnall, § who found that a definite fall in the pro- 

 tein content of the leaves of the runner bean occurs during the 

 night, a fall due to the translocation of the dissociation pro- 

 ducts of the proteins effected by the presence in the leaves of 

 proteolytic enzymes. || 



This same author ^f also has investigated the relationship 

 between the various combinations of nitrogen in the leaves 

 of Phaseolus vulgaris var. multiflorus at different times of the 

 day and in different stages of development. 



With respect to age, Rippel ** found that the protein 

 content of the leaves of Populns canadensis suddenly dimin- 

 ishes as the yellow autumnal colour is assumed, a diminution 

 due to the cessation of protein synthesis rather than to an 

 increased rate of transportation. 



* Otto and Kooper : " Landwirthsch. Jahrb.," 1910, 39, 167. 

 t Le Clerc du Sablon : " Rev. Gen. Bot.," 1904, 16, 341. 

 X See Chibnall : " Ann. Bot.," 1923, 37, 511. 

 § Chibnall : " Biochem. Journ.," 1924, 18, 387, 395, 405. 

 || Ibid., 1922, 16, 599, 608. If Ibid., 1922, 16, 344. 



** Rippel : " Biol. Zentrlbl.," 1921, 41, 508. 



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