72 PLANT PHYSIOLOGY 



> 



difficult to reproduce under artificial conditions, where it requires 

 many complex synthetic reactions. 



18. Metabolism of Proteins during Seed Germination. Proc- 

 esses of Decomposition and Synthesis. The Significance of 

 Ammonia and Asparagine. A General Outline of the Metab- 

 olism of Reserve Substances during Germination. — As has 

 been seen in Art. 15, the metabohsm of protein substances during 

 germination begins with an intensive decomposition of the reserve 

 proteins and with the accumulation of easily soluble crystalhne 

 products of their decomposition, the amino acids. 



It is especially convenient to follow the degradation of pro- 

 teins in seeds germinated in the dark, for in this case the processes 

 of synthesis that take place in hght are inhibited. By this 

 method, it was proved that over two-thirds of the total protein 

 is transformed to more simple products in spite of the fact that 

 germination even in the dark is accompanied by growth of the 

 seedlings, a considerable increase of the number of living cells, 

 and consequently an increase of the total amount of living 

 protoplasm. Prianishnikov found (1895) in one of his experi- 

 ments on the germination of vetch seeds in the dark that 10 days 

 after the beginning of germination, there remained only 50 per 

 cent of protein substances undecomposed; 10 days later, 

 40 per cent; another 10 days later, 33 per cent; and finally, 

 40 days after germination, when the seedlings were approaching 

 death from exhaustion, there remained 32 per cent. These 

 figures show that, in spite of extreme starvation, the protoplasm 

 persistently retains a part of the protein substances as such. 

 The reserve proteins of the seed were of course completely 

 decomposed by that time. The protein substances that have 

 not disintegrated with starvation belong chiefly to the group of 

 nucleoproteins, complex proteins representing compounds of 

 simple proteins with nuclein. 



Corresponding with this intensive disintegration of proteins 

 during germination, there is a rapid increase of the activity of the 

 proteolytic enzymes. According to the data of Bach and 

 Oparin (1923), on the third day of germination, the activity of 

 protease is 6 times its value in dormant seeds; on the sixth day, 

 30 times; and on the eighth day, 45 times its initial value. Later 

 on, the activity of protease slows down somewhat. 



