Biology Reference
In-Depth Information
To determine how speciÝc enzymatic activities are enhanced in the symbiotic strain, two
hypotheses were tested: (1) that aposymbiotic insect genetic drift and mitochondrial expression
failure may occur after the heat treatment of the symbiotic strain while obtaining the aposymbiotic
insects and (2) that nutritional interaction would occur between the host and the symbiont. The
former hypothesis was ruled out by performing backcrosses between symbiotic and aposymbiotic
insects and measuring mitochondrial enzymatic activities (Heddi and Lefebvre, 1990b; Heddi
et al.,
1993) and by studying mitochondrial protein neosynthesis (Heddi and Nardon, 1993). The nutri-
tional hypothesis was tested with vitamin (pantothenic acid and riboÞavin)-supplementation exper-
iments conducted on wheat-Þour artiÝcial pellets (Heddi
et al., 1999). These experiments showed
clearly that differences between symbiotic and aposymbiotic strains were attenuated or became
nonsigniÝcant when insects were reared on vitamin-supplemented pellets (Figure 5.4). It was
therefore concluded that SOPE improved mitochondrial oxidative phosphorylation in a nutritional
way (Heddi
et al., 1999). Indeed, by supplying the host with vitamins that are in low quantities in
A
5
S
A
4
3
2
1
0
SCR
GCR
PDH CGDH
B
C
5
6
5
4
4
*
3
*
3
2
2
1
1
0
0
SCR
GCR
PDH
CGDH
SCR
GCR
PDH
CGDH
FIGURE 5.4
SpeciÝc enzymatic activities of mitochondrial suspensions isolated from symbiotic (S) and
aposymbiotic (A) adults of the weevil
S. oryzae
. Insects were reared for one generation on wheat Þour artiÝcial
pellets supplemented or not with vitamins. (A) Control pellets without any supplementation. (B) Pellets
supplemented with pantothenic acid. (C) Pellets supplemented with riboÞavin. SCR = succinate cytochrome
c
reductase (y unit = ´mol mg
Ï1
s
Ï1
), GCR = glycerol-3-phosphate cytochrome
c
reductase (y = 0.5 ´mol
mg
Ï1
s
Ï1
), PDH: pyruvate dehydrogenase (y = 0.1 ´mol mg
Ï1
s
Ï1
), KGDH = b-ketoglutarate dehydrogenase
(y = 0.2 ´mol mg
Ï1
s
Ï1
). Data are expressed as the mean of ten measurements ° tsvn. + = No signiÝcant
difference between symbiotic and aposymbiotic insects (
t
test, b! = 0.05) [ModiÝed from Heddi, A., Lefebvre,
F., and Nardon, P. (1993).
Insect Biochem. Mol. Biol
.
23:
403Ï411 and Heddi, A., Grenier, A.M.,
Khatchadourian, C., Charles, H., and Nardon, P. (1999).
Proc. Natl. Acad. Sci
.
U.S.A.
96:
6814Ï6819.]
