334 2. MALEATE 



rectly since the rate in terms of chlorophyll content is changed. The aug- 

 mented photosynthesis was considered to be important in the action of 

 maleic hydrazide, but how this could contribute to an inhibition of growth 

 is not clear. 



Chromosomal Effects 



The similarities between the actions of maleic hydrazide and X-radiation 

 led Darlington and McLeish (1951) to study possible changes in the mitotic 

 processes in Vicia faba roots. Low concentrations of maleic hydrazide 

 (0.1 raM) only partially block mitosis but cause chromosomal breakage; 

 at 24 hr there is around 0,47 break per cell. Breakage is most frequent in 

 certain chromosomes and regions, and is confined to the heterochromatin. 

 The chromosomes, however, do not become sticky, as with many other 

 antimitotic agents, and the effects are quite different from those produced 

 by X-radiation. It was suggested that maleic hydrazide might be useful 

 for defining specific genes in the heterochromatic regions. A concentration 

 of 0.2 mM gives a high breakage frequency but allows the subsequent 

 resumption of mitosis and growth (McLeish, 1954). Various factors affecting 

 the chromosomal responses to maleic hydrazide were studied by Kihlman 

 (1956). The number of isolocus breaks in Vicia roots increases with the 

 temperature, as does the mitotic inhibition, and decreases with increase 

 in the pH from 4.3 to 7.3, indicating that penetration is a factor here. 

 Removal of Og reduces the abnormal metaphase count from 66% to 20% 

 at 24 hr, and both azide and 2,4-dinitrophenol markedly reduce the effects 

 of maleic hydrazide. The absorption of anions by roots depends on oxidative 

 metabolism, and Kilhman felt that the anaerobiosis, azide, and 2,4-dini- 

 trophenol might inhibit the uptake of maleic hydrazide, but also consid- 

 ered the possibilty that ATP is involved in chromosomal breakage. 



Graf (1957) confirmed the heterochromatic site for the action of maleic 

 hydrazide in corn root cells by showing that the number of anaphase 

 bridges induced is correlated with the number of heterochromatic knobs 

 in the strain of corn used. He also showed that certain derivatives, par- 

 ticularly A^-benzoyl maleic hydrazide, are more potent than maleic hydra- 

 zide, due possibly to their greater lipid solubility. On the other hand, 

 Dodge (1964) found no chromosomal aberrations or anaphase bridges 

 in the dinoflagellate Prorocentrum micans treated with 0.1 mM to 1 mM 

 maleic hydrazide, although nuclear division is strongly inhibited. There 

 is no heterochromatin in the nucleus, but this is not sufficient reason for 

 the lack of effects on the chromosomes. 



The superficial structural similarity between maleic hydrazide and py- 

 rimidines such as uracil was noted by Deysson and Deysson (1953), but 

 they could demonstrate no antagonism of maleic hydrazide by uracil in 

 the inhibition of growth and mitosis in onion roots. Biesele (1958) remarked 

 on the structural resemblance of maleic hydrazide to the purines and the 



