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Light- induced electron transfer and ATP synthesis in a carotene synthesizing insect.

Valmalette JC, Dombrovsky A, Brat P, Mertz C, Capovilla M, Robichon A - Sci Rep (2012)

Bottom Line: We report here that the capture of light energy in living aphids results in the photo induced electron transfer from excited chromophores to acceptor molecules.The redox potentials of molecules involved in this process would be compatible with the reduction of the NAD+ coenzyme.This appears as an archaic photosynthetic system consisting of photo-emitted electrons that are in fine funnelled into the mitochondrial reducing power in order to synthesize ATP molecules.

View Article: PubMed Central - PubMed

Affiliation: IM2NP UMR 7334 CNRS, Université du Sud Toulon Var, P.O. Box 20132, 83957 La Garde CEDEX, France.

ABSTRACT
A singular adaptive phenotype of a parthenogenetic insect species (Acyrthosiphon pisum) was selected in cold conditions and is characterized by a remarkable apparition of a greenish colour. The aphid pigments involve carotenoid genes well defined in chloroplasts and cyanobacteria and amazingly present in the aphid genome, likely by lateral transfer during evolution. The abundant carotenoid synthesis in aphids suggests strongly that a major and unknown physiological role is related to these compounds beyond their canonical anti-oxidant properties. We report here that the capture of light energy in living aphids results in the photo induced electron transfer from excited chromophores to acceptor molecules. The redox potentials of molecules involved in this process would be compatible with the reduction of the NAD+ coenzyme. This appears as an archaic photosynthetic system consisting of photo-emitted electrons that are in fine funnelled into the mitochondrial reducing power in order to synthesize ATP molecules.

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Tetrazolium (MTT) reduction by orange aphid extract.100 µl of tetrazolium solution (1 mM in water) were placed on a glass slide in which 10 µl of orange aphid extracts were added. The system was irradiated by visible light (A) for 30 min or kept in dark (B). Then, the medium was delicately washed out. Top: The photos show the border of the spots where the formazan precipitation is more intense. Unambiguously, an increase of MTT reduction, measured as formazan precipitation on the glass, is observed under light (A). Middle: higher magnification of the photograph above. Bottom: The light exposure of strongly pigmented ovarioles in presence of MTT (1 mM in water) is compared with white/pale ovarioles in the same conditions as above. Produced formazan by orange or white aphid extract (100 µg protein) under light or kept in dark was measured after solubilization in acid/ethanol (C and D). The representations are the mean of three separate experiments.
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f6: Tetrazolium (MTT) reduction by orange aphid extract.100 µl of tetrazolium solution (1 mM in water) were placed on a glass slide in which 10 µl of orange aphid extracts were added. The system was irradiated by visible light (A) for 30 min or kept in dark (B). Then, the medium was delicately washed out. Top: The photos show the border of the spots where the formazan precipitation is more intense. Unambiguously, an increase of MTT reduction, measured as formazan precipitation on the glass, is observed under light (A). Middle: higher magnification of the photograph above. Bottom: The light exposure of strongly pigmented ovarioles in presence of MTT (1 mM in water) is compared with white/pale ovarioles in the same conditions as above. Produced formazan by orange or white aphid extract (100 µg protein) under light or kept in dark was measured after solubilization in acid/ethanol (C and D). The representations are the mean of three separate experiments.

Mentions: To get more insight about the light-dependent reduction-oxidation (redox) process, orange aphid extracts were used to reduce tetrazolium salts (MTT) in presence or absence of light. Although the effect was moderate, an increase of MTT reduction in presence of light was obtained with the orange, but not with the white extract (figure 6). This trend was also obtained with orange embryos incubated with MTT and exposed to light whereas the white embryos in the same conditions display a weak fluctuation of the basal level (figure 6). The same results were observed when the experiments were conducted with pure molecules. Briefly, 100 µl of MTT solubilized in water were placed on a layer of dry β-carotene and illuminated by a regular electric light. The reduction of MTT in blue precipitated formazan was observed as the result of a capture of free electrons generated by the photoactivated carotene, which suggests that the energy of these free electrons is high enough to pass the barrier of the tetrazolium redox potential (see Supplementary Data, figure S5).


Light- induced electron transfer and ATP synthesis in a carotene synthesizing insect.

Valmalette JC, Dombrovsky A, Brat P, Mertz C, Capovilla M, Robichon A - Sci Rep (2012)

Tetrazolium (MTT) reduction by orange aphid extract.100 µl of tetrazolium solution (1 mM in water) were placed on a glass slide in which 10 µl of orange aphid extracts were added. The system was irradiated by visible light (A) for 30 min or kept in dark (B). Then, the medium was delicately washed out. Top: The photos show the border of the spots where the formazan precipitation is more intense. Unambiguously, an increase of MTT reduction, measured as formazan precipitation on the glass, is observed under light (A). Middle: higher magnification of the photograph above. Bottom: The light exposure of strongly pigmented ovarioles in presence of MTT (1 mM in water) is compared with white/pale ovarioles in the same conditions as above. Produced formazan by orange or white aphid extract (100 µg protein) under light or kept in dark was measured after solubilization in acid/ethanol (C and D). The representations are the mean of three separate experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3420219&req=5

f6: Tetrazolium (MTT) reduction by orange aphid extract.100 µl of tetrazolium solution (1 mM in water) were placed on a glass slide in which 10 µl of orange aphid extracts were added. The system was irradiated by visible light (A) for 30 min or kept in dark (B). Then, the medium was delicately washed out. Top: The photos show the border of the spots where the formazan precipitation is more intense. Unambiguously, an increase of MTT reduction, measured as formazan precipitation on the glass, is observed under light (A). Middle: higher magnification of the photograph above. Bottom: The light exposure of strongly pigmented ovarioles in presence of MTT (1 mM in water) is compared with white/pale ovarioles in the same conditions as above. Produced formazan by orange or white aphid extract (100 µg protein) under light or kept in dark was measured after solubilization in acid/ethanol (C and D). The representations are the mean of three separate experiments.
Mentions: To get more insight about the light-dependent reduction-oxidation (redox) process, orange aphid extracts were used to reduce tetrazolium salts (MTT) in presence or absence of light. Although the effect was moderate, an increase of MTT reduction in presence of light was obtained with the orange, but not with the white extract (figure 6). This trend was also obtained with orange embryos incubated with MTT and exposed to light whereas the white embryos in the same conditions display a weak fluctuation of the basal level (figure 6). The same results were observed when the experiments were conducted with pure molecules. Briefly, 100 µl of MTT solubilized in water were placed on a layer of dry β-carotene and illuminated by a regular electric light. The reduction of MTT in blue precipitated formazan was observed as the result of a capture of free electrons generated by the photoactivated carotene, which suggests that the energy of these free electrons is high enough to pass the barrier of the tetrazolium redox potential (see Supplementary Data, figure S5).

Bottom Line: We report here that the capture of light energy in living aphids results in the photo induced electron transfer from excited chromophores to acceptor molecules.The redox potentials of molecules involved in this process would be compatible with the reduction of the NAD+ coenzyme.This appears as an archaic photosynthetic system consisting of photo-emitted electrons that are in fine funnelled into the mitochondrial reducing power in order to synthesize ATP molecules.

View Article: PubMed Central - PubMed

Affiliation: IM2NP UMR 7334 CNRS, Université du Sud Toulon Var, P.O. Box 20132, 83957 La Garde CEDEX, France.

ABSTRACT
A singular adaptive phenotype of a parthenogenetic insect species (Acyrthosiphon pisum) was selected in cold conditions and is characterized by a remarkable apparition of a greenish colour. The aphid pigments involve carotenoid genes well defined in chloroplasts and cyanobacteria and amazingly present in the aphid genome, likely by lateral transfer during evolution. The abundant carotenoid synthesis in aphids suggests strongly that a major and unknown physiological role is related to these compounds beyond their canonical anti-oxidant properties. We report here that the capture of light energy in living aphids results in the photo induced electron transfer from excited chromophores to acceptor molecules. The redox potentials of molecules involved in this process would be compatible with the reduction of the NAD+ coenzyme. This appears as an archaic photosynthetic system consisting of photo-emitted electrons that are in fine funnelled into the mitochondrial reducing power in order to synthesize ATP molecules.

Show MeSH
Related in: MedlinePlus