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

K Lenhart,F Althoff,F Keppler,M Greule

doi:10.5194/bg-12-1907-2015

K Lenhart, F Althoff + Show 2 more

Open Access

https://doi.org/10.5194/bg-12-1907-2015

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Abstract

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.

Highlights

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, under stress conditions
We investigated CH4 emissions of L. angustifolia supplemented with 13C positionally labeled Met (13CH3-Met; only the methyl group −S−CH3 was enriched with 13C atoms). under stressed and non-stressed conditions
The employment of 13CH3-Met clearly showed that the sulfur-bonded carbon atom of the methyl group in methionine was transferred to CH4 in L. angustifolia

Summary

Introduction

The observation that plants produce methane (CH4) under aerobic conditions has caused considerable controversy in the scientific community (Keppler et al, 2006; Dueck et al, 2007; Evans, 2007; Beerling et al, 2008; Kirschbaum and Walcroft, 2008; McLeod et al, 2008; Vigano et al, 2008; Wang et al, 2008; Nisbet et al, 2009; Bloom et al, 2010; Covey et al, 2012; Zhang et al, 2014). Nonmicrobial CH4 release has been shown to occur from dry and detached fresh plant material under ultraviolet (UV) irradiation and elevated temperatures (McLeod et al, 2008; Vigano et al, 2008; Bruhn et al, 2009). CH4 can be derived from other structural components, as shown with commercially purified lignin and cellulose (Vigano et al, 2008), leaf surface waxes (Bruhn et al, 2014), and even with ascorbic acid under highly oxidative conditions (Althoff et al, 2010). For further information on CH4 formation from dry and fresh detached plant matter and specific plant structural compounds, the reader should refer to the recent reviews of Bruhn et al (2012) and Wang et al (2013)

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