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

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 identified. We made use of stable isotope techniques to verify in vivo formation of methane and, in order to identify the carbon precursor, 13C-positionally labelled organic compounds were employed. Here we show that the amino acid L-methionine acts as a methane precursor in living plants. Employing 13C-labelled methionine clearly identified the sulphur-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.

A novel pathway of direct methane production and emission by eukaryotes including plants, animals and fungi: An overview

“…By assuming UV radiation-induced CH 4 emissions from pectin as representing foliar CH 4 emissions, Bloom et al (2010) suggested a global contribution of 0.2e1.0 Tg plantderived CH 4 yr À1 . However, clear evidence shows that pectin is not the only precursor (Carmichael et al, 2014;Lenhart et al, 2014;Vigano et al, 2009), and several environmental stresses in addition to UV radiation have been observed to induce CH 4 production. Thus, whether Bloom et al (2010) underestimated the magnitude of this plant source of CH 4 has been a subject of debate (Bruhn et al, 2012;Fraser et al, 2015).…”

“…In the second step, demethylation of the sulphoxide leads to methyl radical ( CH 3 ) formation via homolytic bond cleavage, and then to CH 4 (Table 1). This potential route of CH 4 production may exist in both plants and fungi because methionine has been identified as a common precursor of plant-and fungus-derived CH 4 (Lenhart et al, 2014. Accordingly, several stress factors (e.g.…”

“…soil or plant water) and whether plants have their own mechanism(s) to produce CH 4 have been debated (Bruhn et al, 2012;Keppler et al, 2009;Nisbet et al, 2009). Evidence is now accumulating to indicate that plants can produce CH 4 even in the presence of oxygen (Bruggemann et al, 2009;Bruhn et al, 2009Bruhn et al, , 2014Cao et al, 2008;Fraser et al, 2015;Keppler et al, 2008;Lenhart et al, 2014;McLeod et al, 2008;Messenger et al, 2009;Mikkelsen et al, 2011;Reid, 2009, 2011;Sanhueza and Donoso, 2006;Sinha et al, 2007;Vigano et al, 2009Vigano et al, , 2008Wang et al, 2009aWang et al, , 2009bWang et al, , 2011aWatanabe et al, 2012;Wishkerman et al, 2011).…”

“…2). Employing 13 C positionally labelled methionine, Lenhart et al (2014) verified the sulphur-bound methyl group (eSeCH 3 ) of methionine as a potential carbon precursor of plant-derived CH 4 . The number of the potential source substrates for CH 4 may be much greater than anticipated (Vigano et al, 2010).…”

“…A series of experiments have been conducted on the effects of physical injuries and hypoxia on CH 4 emissions (Lenhart et al, 2014;Qaderi and Reid, 2011;Wang et al, 2009bWang et al, , 2011a. Insect activity, human damage and extreme weather can result in the physical injury of plants.…”