258 1. lODOACETATE AND lODOACETAMIDE 



and 2.5 mM, respectively (Zottl, 1953), and Niedergang-Kamien and Leo- 

 pold (1957) observed no respiratory inhibition in sunflower stems with 1 mM 

 iodoacetate over 4 hr, although auxin transport is well depressed. 



The number of cells per root tip in Cucurhita pepo is increased from 

 8.2 X 10* to around 8.7 X 10* by low concentrations (0.004-0.04 mM ) of 

 iodoacetate, but is decreased to 7.35 X 10* and 6.47 X 10* by 0.41 and 

 1 mM, respectively (Hopkins, 1952). The decrease in the number of cells 

 by 1 mM iodoacetate (21%) is not as much as the decrease in elongation 

 (63%), indicating some changes in cell size or form. Iodoacetate also reduces 

 the amount of cell wall deposited by apical pea stems, and this does not 

 correlate well with the changes in carbohydrate utilization (Christiansen 

 and Thimann, 1950 a). Meiosis in the excised anthers of Lilium lienryi is 

 inhibited quite strongly as the iodoacetate concentration is raised from 

 0.01 mM to 1 mM (Pereira and Linskens, 1963). The only histological study 

 of the effects of iodoacetate was made by Torrey (1953) in isolated pea root 

 tips. There is acceleration of the maturation of xylem tissue, with absence 

 of mitotic cells along the root in the apical meristem. Secondary wall forma- 

 tion is abnormal, the newly formed protoxylem being thin and having de- 

 ficient lignification. The maturation of the sieve tube elements in the phloem 

 is normal, but again there is less secondary thickening of the walls in the 

 mature cells. Finally, iodoacetate at fairly low concentration (0.3 mM) in- 

 hibits the uptake of water by discs of potato (Hackett and Thimann, 1950) 

 and artichoke (Hackett and Thimann, 1952). All of these observations may 

 well be of importance in determining the fundamental action of iodoacetate 

 on over-all growth, but at the present time it is impossible to localize the 

 basic lesion or process affected. 



Inhibition of Fertilization, Egg Cleavage, and Embryogenesis 



Inasmuch as much of the work has been done with marine animals, it is 

 important to realize that the intracellular concentration of iodoacetate may 

 be much less than in the surrounding sea water, and thus that high concen- 

 trations are often necessary. If the cells are permeable only to the un-ionized 

 iodoacetic acid, and if the cells are sufficiently buffered against pH change 

 (which is probably true under the conditions), it can be calculated that the 

 intracellular concentration will be about 1/400 the external (assuming the 

 pH of sea water as 8.2 and of the cell as 6.8). Of course cells may be per- 

 meable to varying degrees to the ionized iodoacetate. 



The effects of iodoacetate on egg and embryo metabolism were discussed 

 in earlier sections of this chapter, but inspection of the tables shows that 

 relatively little has been done and that the critical enzymes have seldom 

 been tested. The resistance of marine egg glycolysis and respiration to iodo- 

 acetate is sometimes surprising, since it occurs even when the pH is low- 

 ered, or in extracts or homogenates. One can conclude only that the 



