Conversion to glycolic acid is thought to occur rapidly. Susceptible species of plants are 
considered to lack the ability to metabolize CDAA (63). 
Maleic hydrazide 
1,2-Dihydro-pyridazine-2,6-dione (maleic hydrazide, MH) appears to remain intact 
in plants for long periods, The persistence of MH in tissue was recently reviewed and 
discussed by Smith, et al (54). MH is, however, known to react with certain plant con- 
stituents (59). Of the total radioactivity 15 percent obtained from tissue extracts of 
young wheat leaves incubated with C 14_MH was associated on paper chromatograms with 
spot U 1, approximately 1 percent with spot U 2, and the remainder was present as un- 
altered MH, Spot U 1 was identified as a B-glycoside of MH since it could be hydrolyzed 
with acid or the enzyme, emulsin, to yield glucose and MH. The authors (59) considered 
that the sugar moiety could be a disaccharide of glucose, for example, gentiobiose. No 
indication of the identity of spot U 2 was given. The formation of the glycoside could be 
a detoxification mechanism, 
MH has also been shown to form complexes with other plant constituents (3). 
C14-MH (carbonyl labeled) was shown to bind with proteins, such as egg albumin, zein, 
and hexokinase, and RNA in vitro. Stronger bonds were formed and more MH was bound 
when the MH was introduced as the diethanolamine salt rather than as the potassium salt. 
Fractions obtained by an ammonium sulfate precipitation of homogenates obtained from 
plants treated with C14-MH were also found to contain labeled material, The radioactivity 
was not readily dissociated by overnight dialysis against either water or non-labeled MH, 
More radioactivity was present in fractions obtained from plants treated with the 
diethanolamine salt than from those treated with the potassium salt of MH. Forces in- 
volved in the binding action were considered to be physical rather than chemical, 
DISCUSSION 
Any organic chemical introduced into a plant is subject to possible degradation, 
alteration of structure, or conjugation with natural plant constituents. There are, of 
course, differences in the ability of various species of plants to metabolize any individual 
herbicide. These differences, in some instances, provide the basis for their selective 
action on plants. The selective action of 4-(2,4-dichlorophenoxy) butyric acid is apparently 
the result of differences in the ability of different plants to convert the inactive chemical 
to the active acetic acid derivative, Future research may prove that other activation 
mechanisms are involved in the selective action of other herbicides, 
Both resistant and susceptible species may be able to degrade herbicides such as 
simazine and probably others, The selective action of these chemicals may be due to 
differential absorption, translocation, and the rapidity with which various species ac- 
complish detoxification through complete degradation. Detoxification does not necessarily 
depend on processes of degradation or even on metabolic reactions, The herbicides may 
be absorbed to cell constituents or enzymatically combined with plant substrates. Phyto- 
toxic chemicals are known to be conjugated withproteins, carbohydrates, or amino acids. 
Formation of these complex conjugates may be a detoxification mechanism which com- 
pletely inactivates the toxic material. In other instances, the herbicide-metabolite retains 
some of its toxic properties but is less toxic than the parent molecule, 
Movement of the toxic material within the treated plant depends upon complex and 
interrelated morphological, physiological, biochemical, chemical, and physical factors. 
It has been suggested that certain herbicides do not move readily in plants unless metabo- 
lized to more translocable forms. Conjugation of herbicides with plant substrates may 
result in immobilization of the toxic material. Many herbicides seem to move primarily 
in association with carbohydrates, presumably in the phloem. Consequently, the general 
metabolic activity of the plant probably plays an important role in distribution of chemi- 
cals within the treated plants, 
128 
