GROWTH, DEVELOPMENT, AND DIFFERENTIATION 197 



effects of pH (see accompanying tabulation); the pH alone has little effect 

 on growth. The malonate inhibition is satisfactorily reversed by fumarate. 



pH Mean growth (mm) in malonate 3 mM 



6.5 1.56 



6.0 1.70 



5.5 1.55 



5.0 0.22 



4.5 0.16 



The mitotic activity of the excised roots of the garden pea {Pisum sativum) 

 is stimulated by glucose. This is very strongly blocked by malonate at pH 

 5.5. A concentration of 0.01 mM delays the action of glucose 2 hr but does 

 not inhibit mitosis; 0.1 mM inhibits mitotic activity around 50%; 0.5 milf 

 almost completely inhibits mi^-^ses; and 1 mi!f not only inhibits completely 

 but produces some toxic effects (Wilson et al., 1959). It was postulated 

 that the initiation of mitosis is dependent on the cycle, since once mitosis 

 began it proceeded to telophase normally. The progression through mitosis 

 may be coupled with a more anaerobic type of metabolism. The growth 

 and cell proliferation in tissue cultures of the crown galls of various plants 

 (marigold, Paris daisy, periwinkle, and sunflower) are inhibited to different 

 degrees by malonate. Cultures from normal tobacco stem are inhibited 

 similarly. At 10 mM, the following inhibitions may be estimated from the 

 curves given by Hildebrandt et al. (1954): sunflower 0%, marigold 29%, 

 tobacco 40%, Paris daisy 60%, and periwinkle 67%. At 80 mM malonate, 

 all are inhibited completely. A question arises again as to whether these 

 effects are related to cycle inhibition, since succinate, pyruvate, acetate, 

 and other organic anions inhibit also. The pH was 6.0 so that acid effects 

 should not be important. 



Egg Cleavage and Embryogenesis 



The best and most interesting work on the growth responses to malonate 

 has been done with marine invertebrate eggs and embryos. Since this work 

 was done in sea water, we must bear in mind that the concentration of 

 free malonate is much less than the total concentration due to the high 

 amounts of Ca++ and Mg+"'". When malonate is added at a total concen- 

 tration of 25 mM, it is likely that the free malonate is around 4 mM (see 

 Table 1-5). In addition, the pH of sea water is near 8.2 and this is unfavor- 

 able to malonate penetration into the cells. Considering these factors, it is 

 surprising that such definite and characteristic effects of malonate have 

 been observed. 



