Pesticide Metabolism in Plants
29
©¢+Q6
OH
OH
CARBARYL
Figure 2.3. Oxidation of carbaryl in beans.
The rate of metabolism of carbamate insecticides differed greatly among
plant species. Carbofuran metabolism ranged from 68% of the injected carbofuran
within 3 days in beans (Dorough et ai., 1973a) to 80% of the translocated
carbofuran in mugho pine needles after 70 days (Pree and Saunders, 1974).
Within a species such as bean, carbaryl and carbofuran were metabolized much
faster than aldicarb and Croneton® (Marshall and Dorough, 1977). After 20
days, only 15-19% of the injected carbofuran and carbaryl remained in the
organosoluble fractions as compared to 46% and 58% for Croneton® and aldicarb
(Marshall and Dorough, 1977). The carbamate ester linkage of Croneton® and
aldicarb was hydrolyzed in contrast to that of carbofuran and carbaryl. Many of
the glycosides of hydroxylated carbamate insecticides yielded aglycones that
were potent anticholinesterase agents after cleavage with j3-glucosidase (Kuhr
and Casida, 1967).
Organophosphate insecticides are activated by oxidative reactions such as
desulfuration, sulfur oxidation, and N-dealkylation and inactivated by O-dealkylation and hydrolysis of the acid anhydride bond. The activation and inactivation reactions above occur in plants, but studies on their reaction mechanisms
with in vitro preparations from plants are lacking (Bull, 1972; Casida and Lykken,
1969). In plants, the desulfuration of the thiono sulfur apparently does not occur
as readily as the oxidation of thioether sulfur (Bull, 1972; Bull et al., 1976; Eto,
1974). Very little of the O-analogs of BAY NTN 9306® (sulprofos) (Fig. 2.4)
(Bull et ai., 1976), Dyfonate® (fonofos) (McBain et al., 1970) or dimethoate
(Narayan and Lichtenstein, 1973) were detected in plants. Generally, the alkyl
sulfur in pesticides is rapidly oxidized to the sulfoxide and more slowly to the
sulfone (Bull, 1972; Bull et al., 1976). The concentration of BAY NTN 9306®
sulfoxide in cotton leaves was much higher than its sulfone or its O-analog over
a 16-day treatment period (Bull et ai., 1976). However, cleavage of the thiophenyl group of Dyfonate® followed by S-methylation and oxidation gave methylphenyl sulfone as a major metabolite in potatoes (McBain et al., 1970).
29
©¢+Q6
OH
OH
CARBARYL
Figure 2.3. Oxidation of carbaryl in beans.
The rate of metabolism of carbamate insecticides differed greatly among
plant species. Carbofuran metabolism ranged from 68% of the injected carbofuran
within 3 days in beans (Dorough et ai., 1973a) to 80% of the translocated
carbofuran in mugho pine needles after 70 days (Pree and Saunders, 1974).
Within a species such as bean, carbaryl and carbofuran were metabolized much
faster than aldicarb and Croneton® (Marshall and Dorough, 1977). After 20
days, only 15-19% of the injected carbofuran and carbaryl remained in the
organosoluble fractions as compared to 46% and 58% for Croneton® and aldicarb
(Marshall and Dorough, 1977). The carbamate ester linkage of Croneton® and
aldicarb was hydrolyzed in contrast to that of carbofuran and carbaryl. Many of
the glycosides of hydroxylated carbamate insecticides yielded aglycones that
were potent anticholinesterase agents after cleavage with j3-glucosidase (Kuhr
and Casida, 1967).
Organophosphate insecticides are activated by oxidative reactions such as
desulfuration, sulfur oxidation, and N-dealkylation and inactivated by O-dealkylation and hydrolysis of the acid anhydride bond. The activation and inactivation reactions above occur in plants, but studies on their reaction mechanisms
with in vitro preparations from plants are lacking (Bull, 1972; Casida and Lykken,
1969). In plants, the desulfuration of the thiono sulfur apparently does not occur
as readily as the oxidation of thioether sulfur (Bull, 1972; Bull et al., 1976; Eto,
1974). Very little of the O-analogs of BAY NTN 9306® (sulprofos) (Fig. 2.4)
(Bull et ai., 1976), Dyfonate® (fonofos) (McBain et al., 1970) or dimethoate
(Narayan and Lichtenstein, 1973) were detected in plants. Generally, the alkyl
sulfur in pesticides is rapidly oxidized to the sulfoxide and more slowly to the
sulfone (Bull, 1972; Bull et al., 1976). The concentration of BAY NTN 9306®
sulfoxide in cotton leaves was much higher than its sulfone or its O-analog over
a 16-day treatment period (Bull et ai., 1976). However, cleavage of the thiophenyl group of Dyfonate® followed by S-methylation and oxidation gave methylphenyl sulfone as a major metabolite in potatoes (McBain et al., 1970).