THE NUCLEIC ACID CONTENT OF TISSUES AND CELLS 41 



found 32.5 % of the total P in the hot TCA extract of the tissue residue. 

 According to Fries,^'* the NAP concentration per unit dry weight in the 

 leaves of a variety of deciduous trees varies between 0.12 and 0.78 mg./g. 

 dry weight. During discoloration of the leaves, the NAP concentration de- 

 creased by 20 to 40 %, and about 400 mg. nucleic acid eventually falls on 

 each square mile of soil every year. 



Following Pirie's observations^^^ that the greatest yield of nucleoprotein 

 came from the smallest leaves, Holden^"" applied a modification of the Ogur 

 and Rosen^'* method to the leaves from tobacco plants and found that the 

 concentration of both PNA and DNA was at least four times as high in the 

 small as in the large leaves. There were three to four times the number of 

 cells per unit area in the small leaves, and leaf size increased by cell enlarge- 

 ment and not by cell proliferation. Of the total phosphorus of the leaf, 30 % 

 is PNA-P, two-thirds of which is located in the fiber. DNA-P accounts for 

 7 % and could not be detected in the chloroplasts.^"" Metzner.^^i using cyto- 

 chemical methods, claims that both PNA and DNA are present in chloro- 

 plasts. 



XI. Bacteria and Viruses 



A number of reviews have appeared which deal particularly with the 

 nucleic acid content of bacteria.^' ^°^- ^°^ There is, however, not nearly as 

 much detailed information about bacterial cell composition as is available 

 for metazoan tissues. 



According to Belozersky^"^ the total nucleic acid concentrations (on a dry 

 weight basis) of such bacteria as Micrococci, Staphylococci, and E. coli vary 

 between 10 and 22 %, whereas for yeasts and various molds the concentra- 

 tions are below 10%. In general agreement ^vith these values are Vend- 

 rely's202 results, which also show that the PNA/DNA ratio ranges from 2 

 for E. coli to nearly 13 for baker's yeast. Mitchell and Moyle^*^ report ratios 

 of the same order for a large series of micro organisms. 



It must be remembered, however, that the nucleic acids will vary in 

 amount with the physiological state of the culture. The concentrations of 

 PNA and DNA are reported to increase in rapidly growing yeast cells^''* 

 and to reach a maximum just before the onset of cell multiplication in cul- 



198 N. Fries, Plant and Soil 4, 29 (1952). 



199 N. W. Pirie, Biochem. J. 47, 614 (1950). 

 "» C. Holden, Biochem. J. 51, 441 (1952). 



201 H. Metzner, Naturwissenschaften 39, 64 (1952). 



"'^ R. Vendrely, "Un symposium sur les prot^ines," p. 165. Massonet Cie, Paris, 1946. 



2" A. N. Belozersky, Cold Spring Harbor Symposia Quant. Biol. 12, 1 (1947). 



"^ P. Mitchell and J. Moyle, Nature 166, 218 (1950). 



"5 F. J. Di Carlo and A. S. Schultz, Arch. Biochem. 17, 293 (1948). 



