Methoxyl groups of plant pectin as a precursor of atmospheric methane:: evidence from deuterium labelling studies

The observation that plants produce methane (CH4) under aerobic conditions has caused considerable controversy among the scientific community and the general public. It led to much discussion and debate not only about its contribution to the global CH4 budget but also about the authenticity of the observation itself. Previous results suggested that methoxyl groups of the abundant plant structural component pectin might play a key role in the in situ formation process of CH4. Here, this effect is investigated using an isotope labelling study. Polysaccharides, pectin and polygalacturonic acid, with varying degrees of trideuterium-labelled methyl groups in the methoxyl moieties, were investigated for CH4 formation under UV irradiation and heating. A strong deuterium signal in the emitted CH4 was observed from these labelled polysaccharides. Results clearly demonstrate that ester methyl groups of pectin can serve as a precursor of CH4, supporting the idea of a novel chemical route of CH4 formation in plants under oxic environmental conditions.