ANTIMITOTIC ACTIONS 537 



p-benzohydroquinone, and this demonstrates well the specificity which 

 may be achieved on actively dividing cells. 



Antimitotic Actions in Plant Cells 



p-Benzoqiiinone has been found to inhibit the germination of seeds and 

 the growth of seedlings and roots, but very different degrees of potency 

 have been reported. For example, wheat seedlings are inhibited and injured 

 by 0.0092 niM /j-benzoquinone (Schreiner and Reed, 1907), but the ger- 

 mination of cress seeds is not affected at 1 mM, although it is blocked 

 completely at 10 mM (Schmid, 1944). Much of the variation is probably 

 due to the experimental differences in the treatment of the seeds, the dura- 

 tions of exposure, and other factors. Hoffmann-Ostenhof and Reitmaier 

 (1948) compared the effects of various quinones on the germination and 

 growth of cress seeds, and generally found the naphthoquinones to be more 

 potent inhibitors than the benzoquinones, both 1,2- and 1,4-naphthoquinone 

 depressing growth around 50% at 0.1 mM. js-Xyloquinone is only a little 

 less active, while p-benzoquinone is one of the weakest quinones, toluquinone 

 being the least active of all. The proliferation of blue-green algae is sup- 

 pressed very potently by 2,3-dichloro-l,4-naphthoquinone, the most active 

 of all the inhibitors examined, 0.00009 mM being effective (Fitzgerald et al., 

 1952). It is difficult to interpret studies of over-all growth depression, 

 because several types of mechanism may be imagined, and one cannot 

 attribute the results to an antimitotic action without direct evidence. 



Mitotic effects have been reported several times and the findings may 

 help to throw some light on the problem of antimitotic mechanisms. Nybom 

 and Knutson (1947) observed an unusual type of mitotic abnormality in 

 onion root cells treated with menadione; the chromosomes divide into two 

 or more groups at the poles during anaphase, and this was called "distrib- 

 uted c-mitosis" (c-mitosis designates a colchicine-like effect). This was more 

 extensively studied by Levan and Tjio (1948), who showed that p-benzo- 

 quinone, p-benzohydroquinone, catechol, :p-phenylenediamine, and related 

 compounds are all active. Two types of chromosomal fragmentation occur: 

 free fragments left at the equator at anaphase, and attached fragments 

 that retain a vestige of connection to the parent chromosomes. Trans- 

 locations are quite rare and reattachment occurs in only a few instances. 

 In addition, it was thought that impeded division of the centromeres of 

 the longest chromosomes contributes to the abnormal mitosis. p-Benzo- 

 hydroquinone causes c-mitosis in concentrations from 5 to 100 mM, so 

 that these cells are not nearly as sensitive as mammalian cells. p-Benzo- 

 quinone is active at about one tenth these concentrations and some frag- 

 mentation occurs at 0.02 mM. Loveless and Revell (1949) could detect 

 no chromosome breakage in Vicia roots treated with /^-benzohydroquinone 

 and felt that the quinones are not radiomimetic, a conclusion supported 



