40 I. LESLIE 



the same time the PNA/DNA ratio was increased. ^^^' ^^° In rat spleen^^^ and 

 mouse thymus^' X-ray irradiation produced a large reduction in the PNA 

 and DNA contents per organ. The exposure of rabbit bone marrow to 

 7-radiation reduced the concentrations of PNA and DNA but did not alter 

 the average amount of DNA per nucleus in marrow cells. ^^' The PNA per 

 unit protein was decreased in the mitochondrial, microsome, and super- 

 natant fractions of the cytoplasm in rabbit bone marrow, and in mouse 

 spleen after X-ray irradiation. ^^^ j^ ^g suggested that irradiation causes a 

 selective elimination of cell types with high concentrations of PNA. 



4. Drug Action 



The nitrogen mustard HN2 [methylbis(/3-chloroethyl)-amine] prevents 

 the normal increase of DNA in amphibian embryos. '^^ Administration of 

 HN2 to rats 1 hr. after hepatectomy caused a decrease in cellularity below 

 control level at 36 hr., and at the same time raised the average DNA per 

 cell by 19 % and PNA per cell by 23 %."* Ultmann et al. concluded that 

 HN2 has a "temporary inhibitory action on mitosis when a single dose of 

 the drug is given." 



Injection of phenylhydrazine leads to the destruction of mature erythro- 

 cytes and the liberation into blood of immature reticulocytes, resulting in 

 a 10- to 30-fold increase in nucleic acid (mostly PNA) concentration in 

 blood .^^' ^^^ An anesthetic dose of sodium phenobarbitol increased the total 

 nucleic acid content of spleen and reduced by almost half the PNA/DNA 

 ratio." The PNA, DNA, and total protein per liver increase appreciably 

 24 hr. after the injection of carbon tetrachloride into rats, probably as a 

 result of proliferation of new cells in the periphery of the liver lobules. ^^^ 



X. Plant Tissues 



Very little information about the nucleic acid content of plants is avail- 

 able so far. Von Euler and Hahn^'^ have shown that the PNA-P concentra- 

 tion decreases in rye-plants from the roots to the tip, and that it is lower 

 in triploid than in diploid aspen. The ratio of PNA/DNA is 6.2 in the corn 

 root tip meristem.^"* 



Wildman et al.^^'' applied the Schneider procedure to spinach leaves and 



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