Biology Reference
In-Depth Information
18.4.4 Photodynamic Effects of Proto Accumulation
on Mitochondrial Function in T. ni
To determine the possible photodynamic effects of mitochondrial Proto accumulation
upon mitochondrial function, mitochondria were isolated from fifth-instar
T
.
ni
larvae
which were dark-treated for 17 h with ALA (4 mM) and Oph (3 mM). The isolated
mitochondrial suspension was exposed to 900 W/m
2
of white fluorescent light for
30 min at 25
C before monitoring the activity of various mitochondrial marker
enzymes, namely: succinate oxidase, NADH dehydrogenase and NADH-cytochrome
c
reductase. All three-enzyme activities decreased significantly in a time-dependent
manner in comparison to darkmitochondrial controls. These results strongly indicated
that Proto accumulation in mitochondria triggers mitochondrial damage in the light
and may contribute significantly to photodynamic damage in treated insects (Lee and
Rebeiz
1995
).
18.5 Screening of Other Porphyric Insecticide Modulators
and Their Effects on Four Different Insect Species
Earlier photodynamic herbicide structure-function studies described elsewhere led
to the assembly of two databases of commercially available compounds with
potential photodynamic herbicidal properties (Rebeiz et al.
1990b
,
1991
). These
databases consisted of a set of 6-membered N-heterocyclic compounds (Rebeiz
et al.
1991
) and a set of 5-membered N-heterocyclics (Rebeiz et al.
1990b
).
A substructure computer search of these databases identified 322 putative photody-
namic herbicide modulators (see Chap.
17
). Extensive testing of these modulators
on a variety of plant species led to the identification of about 150 modulators with
excellent photodynamic herbicidal properties (Rebeiz et al.
1990b
). Encouraged by
these results, a screening effort was undertaken to determine whether these
150 modulators exhibited porphyric insecticidal properties. Screening by food
ingestion was performed on the German cockroach, cotton boll weevil, corn
earworm and cabbage looper as described below.
For
T
.
ni
and H. zea, ALA (4 mM) and a modulator (3 mM) were added to
liquefied Waldbauer's medium (Waldbauer et al.
1984
) at 55-60
C. The mixture
was blended for 2 min in a Sorval Omnimixer. The treated and control diets
(the latter lacking ALA and modulators) were poured into 12-ml plastic molds
and were allowed to cool down and to solidify before storage in a refrigerator at
4
C. The food was generally used within 2 days, and was never stored for more
than 2 weeks. Treatment of
T
.
ni
consisted of placing 15-20 third-instar larvae with
one block of control or treated food, in a cardboard cup (about 9 cm h
10 cm
diameter) sealed with a plastic lid. Each treatment was replicated three times.
Treatment of
H
.
zea
entailed placing a 3 ml control or treated diet cube and a single
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