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Int. J. Mol. Sci. 2017, 18(10), 2045;

Integration of C1 and C2 Metabolism in Trees

Climate Science Department, Earth Science Division, Lawrence Berkeley National Laboratory, One Cyclotron Rd, building 64-241, Berkeley, CA 94720, USA
National Institute for Amazon Research, Ave. Andre Araujo 2936, Manaus, AM 69060-001, Brazil
Department of Earth and Environmental Sciences, California State University, East Bay, North Science 329, 25800 Carlos Bee Boulevard, Hayward, CA 94542, USA
Department of Plant Physiology, Estonian University of Life Sciences, Kreutzwaldi 1, 51014 Tartu, Estonia
Estonian Academy of Sciences, Kohtu 6, 10130 Tallinn, Estonia
Department of Geography, University of California Berkeley, 507 McCone Hall #4740, Berkeley, CA 94720, USA
Author to whom correspondence should be addressed.
Received: 18 August 2017 / Revised: 16 September 2017 / Accepted: 21 September 2017 / Published: 23 September 2017
(This article belongs to the Section Molecular Plant Sciences)
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C1 metabolism in plants is known to be involved in photorespiration, nitrogen and amino acid metabolism, as well as methylation and biosynthesis of metabolites and biopolymers. Although the flux of carbon through the C1 pathway is thought to be large, its intermediates are difficult to measure and relatively little is known about this potentially ubiquitous pathway. In this study, we evaluated the C1 pathway and its integration with the central metabolism using aqueous solutions of 13C-labeled C1 and C2 intermediates delivered to branches of the tropical species Inga edulis via the transpiration stream. Delivery of [13C]methanol and [13C]formaldehyde rapidly stimulated leaf emissions of [13C]methanol, [13C]formaldehyde, [13C]formic acid, and 13CO2, confirming the existence of the C1 pathway and rapid interconversion between methanol and formaldehyde. However, while [13C]formate solutions stimulated emissions of 13CO2, emissions of [13C]methanol or [13C]formaldehyde were not detected, suggesting that once oxidation to formate occurs it is rapidly oxidized to CO2 within chloroplasts. 13C-labeling of isoprene, a known photosynthetic product, was linearly related to 13CO2 across C1 and C2 ([13C2]acetate and [2-13C]glycine) substrates, consistent with reassimilation of C1, respiratory, and photorespiratory CO2. Moreover, [13C]methanol and [13C]formaldehyde induced a quantitative labeling of both carbon atoms of acetic acid emissions, possibly through the rapid turnover of the chloroplastic acetyl-CoA pool via glycolate oxidation. The results support a role of the C1 pathway to provide an alternative carbon source for glycine methylation in photorespiration, enhance CO2 concentrations within chloroplasts, and produce key C2 intermediates (e.g., acetyl-CoA) central to anabolic and catabolic metabolism. View Full-Text
Keywords: internal recycling of carbon; volatile emissions; central metabolism; plant growth and senescence; methanol; acetic acid internal recycling of carbon; volatile emissions; central metabolism; plant growth and senescence; methanol; acetic acid

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Jardine, K.J.; Fernandes de Souza, V.; Oikawa, P.; Higuchi, N.; Bill, M.; Porras, R.; Niinemets, Ü.; Chambers, J.Q. Integration of C1 and C2 Metabolism in Trees. Int. J. Mol. Sci. 2017, 18, 2045.

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