Pesticide Metabolism in Plants
31
S
S
0
II
II
II
C2H50-~-S-CH2-S-C2H5 - - _ .. CZH50-~-S-CHZ-S-C2H5
CZHSO
Cz HSO
PHORATE
fH3
R
R fH3
R
CH 3 -S- y -CH=N-O-C-NHCH 3 -
CH 3 -S- y -CH=N-O-C-NHCH 3
~3
~3
ALDICARB
Figure 2.5. Sulfoxidation of phorate, aldicarb, and prometryne.
with herbicides such as prometryne, sulfoxidation is probably the initial step
toward complete detoxication since the methylmercaptan is the herbicidally active
molecule (Esser et al., 1975).
Organophosphate insecticides are readily metabolized by apparent mfo-catalyzed hydrolysis and conjugation to water-soluble metabolites in plants (Bull,
1972; Bull et al., 1976; McBain et al., 1970; Narayan and Lichtenstein, 1973).
In pea roots 81-91 % of the recovered 1 4 C from [14C]Dyfonate® was in the
organosoluble fraction after 8 days of treatment. However, in the shoots 47-71 %
of the 14C was in water-soluble metabolites and 19-47% was in a "bound"
insoluble residue (Narayan and Lichtenstein, 1973). The water-soluble metabolites were associated primarily with proteins. Water-soluble metabolites of BAY
NTN 9306® were primarily glycosides of the different phenols (Fig. 2.4), and
they accounted for 34% of the 1 4 C in cotton leaf extracts after 16 days (Bull et
al., 1976).
The hydrolysis of the acid anhydride bond and O-dealkylation of ring substituents of phosphorothionates occur readily in plants (Casida and Lykken,
1969). These reactions were demonstrated with etrimfos in beans and corn (Fig.
2.6) (Akram et al., 1978). Only small amounts of the O-analog of etrimfos were
detected. Most of the EEHP (Fig. 2.6) may be derived after desulfuration of
etrimfos (Casida and Lykken, 1969).
The removal of alkyl groups on substituted amide and amino nitrogens of
pesticides is well-established in plants, insects, and mammals (Baldwin, 1977;
Bull, 1972; Menzer, 1973). The N-hydroxymethyl intermediates of dicrotophos
(Menzer and Casida, 1965) and carbaryl (Kuhr and Casida, 1967) have been
isolated from plants. The N-demethylation of monuron in cotton is the one
31
S
S
0
II
II
II
C2H50-~-S-CH2-S-C2H5 - - _ .. CZH50-~-S-CHZ-S-C2H5
CZHSO
Cz HSO
PHORATE
fH3
R
R fH3
R
CH 3 -S- y -CH=N-O-C-NHCH 3 -
CH 3 -S- y -CH=N-O-C-NHCH 3
~3
~3
ALDICARB
Figure 2.5. Sulfoxidation of phorate, aldicarb, and prometryne.
with herbicides such as prometryne, sulfoxidation is probably the initial step
toward complete detoxication since the methylmercaptan is the herbicidally active
molecule (Esser et al., 1975).
Organophosphate insecticides are readily metabolized by apparent mfo-catalyzed hydrolysis and conjugation to water-soluble metabolites in plants (Bull,
1972; Bull et al., 1976; McBain et al., 1970; Narayan and Lichtenstein, 1973).
In pea roots 81-91 % of the recovered 1 4 C from [14C]Dyfonate® was in the
organosoluble fraction after 8 days of treatment. However, in the shoots 47-71 %
of the 14C was in water-soluble metabolites and 19-47% was in a "bound"
insoluble residue (Narayan and Lichtenstein, 1973). The water-soluble metabolites were associated primarily with proteins. Water-soluble metabolites of BAY
NTN 9306® were primarily glycosides of the different phenols (Fig. 2.4), and
they accounted for 34% of the 1 4 C in cotton leaf extracts after 16 days (Bull et
al., 1976).
The hydrolysis of the acid anhydride bond and O-dealkylation of ring substituents of phosphorothionates occur readily in plants (Casida and Lykken,
1969). These reactions were demonstrated with etrimfos in beans and corn (Fig.
2.6) (Akram et al., 1978). Only small amounts of the O-analog of etrimfos were
detected. Most of the EEHP (Fig. 2.6) may be derived after desulfuration of
etrimfos (Casida and Lykken, 1969).
The removal of alkyl groups on substituted amide and amino nitrogens of
pesticides is well-established in plants, insects, and mammals (Baldwin, 1977;
Bull, 1972; Menzer, 1973). The N-hydroxymethyl intermediates of dicrotophos
(Menzer and Casida, 1965) and carbaryl (Kuhr and Casida, 1967) have been
isolated from plants. The N-demethylation of monuron in cotton is the one