Articles | Volume 12, issue 6
Technical note
23 Mar 2015
Technical note |  | 23 Mar 2015

Technical Note: Methionine, a precursor of methane in living plants

K. Lenhart, F. Althoff, M. Greule, and F. Keppler

Abstract. When terrestrial plants were identified as producers of the greenhouse gas methane, much discussion and debate ensued not only about their contribution to the global methane budget but also with regard to the validity of the observation itself. Although the phenomenon has now become more accepted for both living and dead plants, the mechanism of methane formation in living plants remains to be elucidated and its precursor compounds to be identified. We made use of stable isotope techniques to verify the in vivo formation of methane, and, in order to identify the carbon precursor, 13C positionally labeled organic compounds were employed. Here we show that the amino acid L-methionine acts as a methane precursor in living plants. Employing 13C-labeled methionine clearly identified the sulfur-bound methyl group of methionine as a carbon precursor of methane released from lavender (Lavandula angustifolia). Furthermore, when lavender plants were stressed physically, methane release rates and the stable carbon isotope values of the emitted methane greatly increased. Our results provide additional support that plants possess a mechanism for methane production and suggest that methionine might play an important role in the formation of methane in living plants, particularly under stress conditions.

Short summary
Plants are known as a source of methane (CH4), but the biochemical mechanisms involved in CH4 formation are still unknown. Employing 13C-labelled methionine clearly identified the sulfur-bound methyl group of methionine as a carbon precursor of CH4 released from lavender plants. When relating CH4 emission rates to dark respiration of intact plants, we found a molar CH4:CO2 emission ratio of 2.0 ±1.1 (pmol:µmol). After physical stress CH4 release rates greatly increased.
Final-revised paper