Aphids use light to produce ATP, but they are not making photosynthesis

Coming back from holidays, I found a very intriguing paper published by Alain Robichon in Scientific Reports regarding the occurrence of photosynthesis in aphids. Actually, as reported by the research group of Alain Robichon, “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 could be a basal archaic photosynthetic system consisting of photo-emitted electrons that are in fine funnelled into the mitochondrial reducing power in order to synthesize ATP molecules, even if, as clearly stated in the comment of Peter Perrytree, this is an evidence of “phototrophy”, not “photosynthesis”. Photosynthesis implies the transformation of CO2 into organic compounds, whereas Robichon et al have not evidence of photosynthesis. Instead, they have proofs of the production of ATP, a way of producing ATP (energy), named “phototrophy”.

A second criticism made by Perrytree is related to the occurrence of similar phenomena in animals, coincidentaly in insects. In particular he reported that in the paper “Solar energy harvesting in the epicuticle of the oriental hornet (Vespa orientalis)” Plotkin, Boden and Galushko reported that “rigorous coupled wave analysis simulations to show that the cuticle surfaces are structured to reduced reflectance and act as diffraction gratings to trap light and increase the amount absorbed in the cuticle. A dye-sensitized solar cell (DSSC) was constructed in order to show the ability of xanthopterin to serve as a light-harvesting molecule”.

Indeed, aphids, like other insects, are equipped with different pigments that for aphids include a pathway for processing the full carotene synthesis, together with many other pigments, such as xantho-, erythro- and proto-aphins, which display red (alkaline pH) or yellow (neutral pH) colours and strong yellow fluorescence when they are excited by UV light. Up to date, the physiological roles in aphids and other insects are yet poorly documented so that the present paper of Robichon (together that of Plotkin et al) could open intriguing perspectives of research to better understand the functional roles of these molecules very common in the insect cuticle. At this regard, the use of morphological analysis is essential (even if we are in the genomic era), since the distribution of these pigments is functionally related. Indeed, Robichon observed that “carotene molecules are disposed as a bilayer under the cuticule from 0 to 40 µM in depth, suggesting that this structure might present an optimal efficiency to harvest light energy”.

References

Plotkin M, Hod I, Zaban A, Boden SA, Bagnall DM, Galushko D, & Bergman DJ (2010). Solar energy harvesting in the epicuticle of the oriental hornet (Vespa orientalis). Die Naturwissenschaften, 97 (12), 1067-76 PMID: 21052618

Valmalette JC, Dombrovsky A, Brat P, Mertz C, Capovilla M, Robichon A (2012). Light- induced electron transfer and ATP synthesis in a carotene synthesizing insect Scientific Reports DOI: 10.1038/srep00579

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