© 2017 by the authors. Licensee MDPI, Basel, Switzerland. C1metabolism 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 C1pathway 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 C1pathway and its integration with the central metabolism using aqueous solutions of13C-labeled C1and C2intermediates 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, and13CO2, confirming the existence of the C1pathway and rapid interconversion between methanol and formaldehyde. However, while [13C]formate solutions stimulated emissions of13CO2, emissions of [13C]methanol or [13C]formaldehyde were not detected, suggesting that once oxidation to formate occurs it is rapidly oxidized to CO2within chloroplasts.13C-labeling of isoprene, a known photosynthetic product, was linearly related to13CO2across 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 C1pathway to provide an alternative carbon source for glycine methylation in photorespiration, enhance CO2concentrations within chloroplasts, and produce key C2intermediates (e.g., acetyl-CoA) central to anabolic and catabolic metabolism.