328 2. MALEATE 



ment. It is somewhat selective in that grasses are generally more susceptible 

 than broad-leaved plants, and young plants are more susceptible than 

 older plants. A few examples will give an idea of the types and potency 

 of the effects. Vicia faba roots treated with 0.5 milf maleic hydrazide show 

 no mitoses for 2 days (Darlington and McLeish, 1951), the growth of bean 

 and tomato seedlings is inhibited 85-90% by 15 vaM maleic hydrazide 

 used as a dip (Greulach, 1953), the growth of crown gall on carrot roots 

 is suppressed for several days after exposure to 2.67 mM maleic hydrazide 

 (Waggoner and Dimond, 1953), the germination of lettuce seeds is reduced 

 over 90% by 15 mM maleic hydrazide (Haber and White, 1960), the growth 

 of young corn i)lants is completely stopped by spraying with 8.9 m.M 

 maleic hydrazide (Tatum and Curme, 1951), and the growth of moss 

 sporogonia is reduced 50% by 4.4 mM maleic hydrazide (Bopp, 1954). 

 It has been observed several times that the leaves of treated plants become 

 a darker green or in some cases develop an anthocyanin pigmentation 

 (Currier and Crafts, 1950; Tatum and Curme, 1951; Crafts, 1961 a). Many 

 morphological changes have been reported, including abnormally shaped 

 leaves, disruption of phloem, stomatal degeneration, chloroplast disin- 

 tegration and reduction, and general stunting. In some instances it ap- 

 pears that mitosis is blocked but cell enlargement is not affected, occa- 

 sionally resulting in abnormally large cells. One of the best reviews of such 

 changes is by Gifford (1956) who describes the effects of maleic hydrazide 

 on barley seedlings in detail. Three days after spraying there is inhibition 

 of mitoses in the terminal tips, and nuclear aberrations appear in the cells 

 of the protoderm and ground meristem; there is precocious growth of the 

 axillary buds brought about by cell enlargement; by 7 days the cells in 

 the shoot axis have thickened walls, and there is necrosis in the mesophyll 

 parenchyma; after 2 weeks the plants are stunted, and the leaves are thicker 

 greener, and brittler; finally there is necrosis in the pith and extensive 

 obliteration of the phloem. He compared some of these effects to plant 

 diseases produced by viruses. 



Crafts (1961 a) has postulated that perhaps one of the principal effects 

 of maleic hydrazide is a disorganization of the vascular system of the plants, 

 this eventually leading to the necrotic changes seen in the phloem. In this 

 connection, it may be noted that maleic hydrazide alters the transport of 

 Ca++ applied to foliage in apricot trees (Kessler et al., 1961), and it is likely 

 that the uptake of essential ions by the roots is also inhibited. Undoubtedly 

 the primary effect is on mitotic processes in the growing regions of the 

 plant and perhaps on the formation, transport, or utilization of auxins. 



Absorption, Distribution, and Metabolism of Maleic Hydrazide 



Maleic hydrazide enters young growing roots readily and, after foliar 

 application, penetrates into leaves through aqueous pathways; it is not 



