EFFECTS ON MITOSIS, GROWTH, DIFFERENTIATION 



255 



involved in cleavage. On the other hand, Beatty and Beatty (1959) could 

 find no effects of 1 mM iodoacetate on the chromosomes of Tradescantia 

 under aerobic conditions, although anaerobically some aberrations are 

 evident. 



Mitotic activity can be very significantly affected in vivo, as indicated 

 by the previously discussed effects on proliferating tissues, but is especially 

 well characterized in the studies of Cibis et al. (1957) on mitosis in lens 

 epithelium of rabbits, in which injections of 40 mg/kg iodoacetate produce 

 very marked and long-lasting effects (Fig. 1-27). The initial brief stimulation 

 is probably real, and such stimulation of mitotic activity by low concentra- 

 tions of SH reagents has often been observed. 



Fig. 1-27. Effects of iodoacetate (40 mg/kg) on 



the mitotic activity of lens epithelium in rabbits. 



(From Cibis et al., 1957.) 



Inhibition of Plant Tissue Growth 



Selected growth inhibitions, usually measured with respect to elongation, 

 are given in Table 1-40. These results are not of great quantitative signifi- 

 cance since the inhibitions depend so strongly on the pH. However, they 

 show that, when the pH is favorable to penetration, the growth is very 

 sensitive to iodoacetate. A stimulation of the growth at low concentrations 

 has often been noted (Commoner and Thimann, 1941; Hopkins, 1952). 

 This is particularly well seen in the biphasic curves for Avena coleoptiles, 

 where stimulation by as much as 50% is observed (Thimann and Bonner, 

 1948). Depending on the pH, the concentrations of iodoacetate that stim- 

 ulate are usually in the range 0.001-0.01 mM. No explanation of this 

 stimulation has been made or is evident. A slight depression of the EM 



