EFFECTS ON GROWTH AND MITOSIS 771 



and attributed to an increase in thymonucleic acid, while simultaneously 

 no cytoplasmic changes could be detected (Rybinsky and Zrykina, 1935). 

 Some cells, such as yeast, do not readily exhibit nuclear damage with the 

 arsenicals (Janke and Garzuly-Janke, 1936), but it is difficult to determine 

 whether this is due to a natural resistance or difficulty in nuclear visuali- 

 zation. Arsenite at 1 mM does not induce the yeast — > mycelium conver- 

 sion, although growth is well inhibited; since mitotic inhibition generally 

 diverts the cells from division to growth without division, this might indicate 

 that mitosis is not specifically blocked and that growth processes are simul- 

 taneously affected (Nickerson and Van Rij, 1949). 



In most instances, both nuclear and cytoplasmic damage can occur but, 

 in others, at least a partially specific effect on the nucleus may be achieved. 

 From what little we know of the nature of the structural and contractile 

 elements of the mitotic spindle, it certainly seems likely that arsenicals 

 might interfere with its formation or function. It is difficult from cy to- 

 logical studies to localize the site of action, inasmuch as the nuclear- 

 cytoplasmic relationship is such that changes in one can bring about changes 

 in the other. Arsenicals, in common with other antimitotic agents, more 

 readily depress mitosis in rapidly than in slowly proliferating cells, and 

 Florijn (1950) has discussed this in terms of the greater metabolism and 

 energy requirements of proliferating tissues, although earlier work on 

 the metabolism of dividing cells indicates that a qualitative, as well as 

 a quantitative, change in pattern occurs. 



A series of reports from Thimann and his collaborators at Harvard has 

 contributed to our understanding of plant growth and the effects of arsenite. 

 Sections of pea stem about 20 mm long, floated on water in the dark for 

 24 hr, grow in length about 4 mm and with added auxin about 10 mm. 

 Arsenite seems to suppress the stimulation brought about by auxin, although 

 this cannot be definitely shown from the data since the effects of arsenite 

 in the absence of auxin were not observed (see accompanying tabulation) 



Auxin + % Change in the 



Water Auxin 



arsenite auxin response 



(Christiansen et al., 1949). The arsenite concentration used here is 0.1 mM; 

 the growth is somewhat inhibited by 0.01 mM and almost completely pre- 

 vented by 1 mM (Thimann and Bonner, 1949). The auxin-stimulated 



