526 5. QUINONES 



groups per se are not sufficient for inhibitory activity and o-diphenols are 

 weak; only the Tpara compounds are highly active and this led Druckrey 

 to postulate a "para principle," which may be merely an expression of the 

 need for a structure which can react readily with SH groups or possesses 

 bifunctionality for cross-linking. The hydroquinones are somewhat more 

 potent than the corresponding quinones in the two instances tested and 

 it was stated that the oxidation of the hydroquinones is presumably not 

 necessary for activity, a conclusion not completely justified because of pos- 

 sible differences in permeability of the cells to the two forms. Another 

 factor may be the effect of the oxidation of the hydroquinones on the eggs, 

 since Runnstrom (1932) showed that sea urchin eggs can utilize hydroqui- 

 none as a carrier and that it is oxidized through a cyanide-sensitive system, 

 probably cytochrome oxidase. It may well be that in some cases one 

 cannot attribute activity solely to either the quinone or hydroquinone, 

 since the mechanism may involve a redox couple in which both forms are 

 equally important. 



Disturbances in Embryonic Development 



Several groups of substances are known which might be said to possess 

 two or more reactive groups and which interfere with mitosis, cause frag- 

 mentation and cross-linking of chromosomes, and in general duplicate the 

 effects of irradiation. Druckrey (1952) used 59-benzoquinone as a model 

 substance of bifunctional type and tested it on the development of free- 

 swimming blastulas of Paracentrotus lividus. A concentration of 0.01 n\M 

 causes a sticking together of the blastulas after several hours, conglomer- 

 ates of several blastulas after 1 day, and frequent giant blastulas of spherical 

 form after 3 days; these remain motile and capable of development. Af- 

 ter 9 days there are monsters composed of two or more embryos, and in 

 some cases giant plutei are formed. Earlier stages are more sensitive, because 

 egg cleavage would have been quite depressed by this concentration. It 

 appears, however, that such effects may be unrelated to nuclear, chromoso- 

 mal, or mutagenic activity, and are conceivably mediated through actions 

 on the membranes or cytoplasm of the cells; the results do not provide much 

 evidence for the validity of the polyfunctional group hypothesis. 



Abnormalities in morphogenesis are produced by 0.22-0.44 raM men- 

 adiol-diP in frog and chick embryos (Bellairs, 1954). Mitotic effects are 

 observed within 2 hr and a certain degree of cytoplasmic vacuolation is 

 evident. The most frequent abnormality is a failure of the neural folds to 

 close in the region of the presumptive hindbrain, due, it is suggested, to 

 interference with mitoses in the neural plate. Other abnormalities are 

 failure of the two sides of the foregut floor and the two heart vesicles to 

 unite ventrally, reduction in blood island formation, and decrease in the 

 embryonic size. 



