MALEIC HYDRAZIDE 



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hydrazide at 10 mg/crock/day (Shaw et al, 1958). It may be mentioned 

 that maleic hydrazide does not inhibit the respiration of mammalian skin 

 at concentrations up to 10 mM (Barnes et al, 1957), which is in conformity 

 with the general lack of toxicity to animals. 



Maleic hydrazide retards development of the floral buds of magnolia 

 and the degree of effect is correlated with the quantity of starch in the 

 perianth segments at the time of application (Griesel, 1954). Furthermore, 

 in treated flowers the starch disappears less rapidly than normally, and 

 it was thought that this suppression of starch utilization might explain 

 the respiratory depression observed in other plants. The C-l/C-6 ratio 

 in wheat leaf discs is not altered by maleic hydrazide, although the res- 

 piration is somewhat stimulated (Shaw et al., 1958), so we have little evi- 

 dence for an effect on the pathways of carbohydrate breakdown. The 

 protein content of potatoes obtained from sprayed plants is some 20% 

 greater than in the controls, but during 60-day storage the protein content 

 falls much faster than in the controls (Yasuda et al, 1955). The inhibition 

 of sprouting by maleic hydrazide was thought to be due to this disturbance 

 of protein metabolism. No inhibition of the incorporation of amino acids 

 into protein in pea root mitochondria by maleic hydrazide was observed 

 by Baker (1961). At low concentrations (0.3-1 mM) maleic hydrazide has 

 little effect on either O.^ uptake or phosphorylation in cucumber hypocotyl 

 mitochondria, and the P:0 ratio is actually elevated slightly (Stemlid and 

 Saddik, 1962). 



The effects of maleic hydrazide on photosynthetic processes are partic- 

 ularly interesting. It has been mentioned that the leaves of plants treated 

 with maleic hydrazide usually become greener, but that there is some re- 

 duction of chloroplast number. In Swiss chard sprayed with maleic hydra- 

 zide, the number of chloroplasts is decreased by 35-40% while the chloro- 

 plast diameter is increased 23% (Callaghan and Van Norman, 1956). 

 Similar changes occur in tobacco plants and here the changes in chloro- 

 phyll (chl) content and photosynthesis were investigated (see accompa- 

 nying tabulation). The photosynthetic mechanism must be affected di- 



