EFFECTS ON MITOSIS, GROWTH, DIFFERENTIATION 965 



outer cortical zones, this to some extent simulating radiation injury (Hicks, 

 1953). 



There is no evidence that mercurials disturb development by generally 

 depressing metabolism. Ornstein and Gregg (1952) observed no effect of 

 p-MB on dorsal lip explant respiration at a concentration blocking differen- 

 tiation, and Brock et al. (1939) found that to inhibit sea urchin egg respira- 

 tion requires 20 times the Hg++ concentration necessary for cleavage block. 

 The latter concluded that this points to a nuclear effect as the basis for the 

 inhibition of division, but this does not follow. However, the difference be- 

 tween SH reagents is well shown here, in that arsenite depresses respiration 

 more readily than division. Haas (1941) also inclined to a primary nuclear 

 effect, since Hg++ produces demonstrable damage to the nucleus at 0.00074 

 vaM, while 0.037 mM is required for cytoplasmic damage in Anodonta 

 (fresh-water clam) eggs. Without denying that Hg++ can damage the nu- 

 cleus, one must be pessimistic as to the reliability of determining the site 

 of action of an inhibitor by visual inspection; e.g., the action could have been 

 on the plasma membrane and be microscopically undetectable, or a good 

 deal of disturbance in the cytoplasm might have been caused without being 

 immediately evident. Landau et al. (1954) stated that mersalyl is an effec- 

 tive ATPase inhibitor and hence was tried on the cleavage of Arbacia and 

 Chaetopterus eggs. Fertilized eggs placed in 2 mM mersalyl complete the 

 first 3-4 cleavages, but the furrowing strength is reduced, as measured by 

 the pressure increases required to prevent furrowing, so an inhibition of the 

 gelation of the cortex in the equatorial region by mersalyl was postulated, 

 this presumably being mediated through an interference with ATP utiliza- 

 tion. Since the ATPases from different sources vary a good deal in sensi- 

 tivity to mercurials, one does not know what inhibition to expect in these 

 eggs, and the mercurial concentration is so extremely high that many me- 

 tabolic and functional processes must be affected. Heilbrun and Wilson 

 (1955) explained the block of cleavage by mercurials as an inhibition of the 

 proteolytic enzyme system involved in gelation, without obvious evidence. 

 The direct effects of Hg++ on fibrous proteins extracted by sea urchin eggs 

 by Sakai (1962) are meaningless because a concentration of 10 mM was 

 used. 



Plants 



Many organic mercurials are applied to seeds, bulbs, or plants as fungi- 

 cides, but occasionally the plant tissues may be damaged and growth de- 

 pressed. The persistence of the mercurial in the plant is often remarkable. 

 For example, carnation seeds treated with radioactive PM at a concentra- 

 tion causing growth abnormalities in the seedlings produces plants which 

 at 8-9 weeks contain the mercurial in the cotyledon leaves, the hypocotyl, 

 and the root adjacent to the hypocotyl (Robson and Fenn, 1961). A very 

 interesting effect, and one illustrating that the mechanisms by which mer- 



