466 PLANT GROWTH AND PLANT COMMUNITIES 



Proline 

 (15) 



Hydroxyprollne Glutamic Acid 



(24) (3) 



Aspartic Acid 

 (2) 



o 



I 

 o 



"53 

 o 

 < 



o 



c 

 a 



CD 



Phenol -Water 



Figure 5. Radioautograph of a chromatogram of the hydrolysate of total 

 protein in growing carrot explants which have incorporated C^'*-prohne. 

 (From Pollard and Steward, 1959.) 



method of preparation) are indeed the active organelles of accumula- 

 tion in situ, it would seem that they ought to approach the activity of 

 the whole cells at least within orders of magnitude! However, these 

 discrepancies are such as to inspire no confidence whatsoever in the 

 idea that mitochondria, as conventionally isolated, have any real role 

 as the active organs of salt intake in the cells. Their role as the pro- 

 ducers of energy-storing compounds which may be used in processes 

 elsewhere in the cell is, however, another question. 



Nucleate vs. enucleate states. The importance of the complete 

 cellular organization for the study of vital functions may be assessed 

 in other ways. Some cells {e.g., mammalian red blood cells) become 

 enucleate when mature. From others (amoebae, certain animal eggs, 

 Acetabularia) nucleated and enucleated fragments may be compared 

 as to their physiology. In still other systems the changes that occur in 

 metabolism may be traced throughout the ontogeny of the cells as they 

 pass from the state in which they are fully competent to divide to the 

 fully mature state in which they may become incapable of division. 

 Brown and Broadbent (1951) have traced these changes in cells as 

 they occur along the axis of angiosperm roots. Some conclusions can 

 also be drawn from the diflFerent metabolism of potato tuber cells as 

 they occur in thin disks, according to the prior treatment of the tubers. 



Old ideas of the nucleus as presiding over the metabolism of the 

 cell, and particularly as the center of cellular oxidation and of protein 

 synthesis, have given place to diflFerent ideas. These now recognize that 

 the nucleus may exert an influence over the RNA of the cytoplasm. 



