The role of ultraviolet radiation, photosensitizers, reactive oxygen species and ester groups in mechanisms of methane formation from pectin

Abstract

Ultraviolet (UV) radiation has recently been demonstrated to drive an aerobic production of methane (CH4) from plant tissues and pectins, as do agents that generate reactive oxygen species (ROS) in vivo independently of UV. As the major building-blocks of pectin do not absorb solar UV found at the earth's surface (i.e. >280 nm), we explored the hypothesis that UV radiation affects pectin indirectly via generation of ROS which themselves release CH4 from pectin. Decreasing the UV absorbance of commercial pectin by ethanol washing diminished UV-dependent CH4 production, and this was restored by the addition of the UV photosensitizer tryptophan.

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

“…However, the response of plants and their components to ROS yields many products and might enable CH 4 generation (Apel and Hirt, 2004;Moller et al, 2007). The observation that CH 4 emissions were significantly stimulated by ROS generators and constrained by ROS scavengers also implies the importance of ROS in plant CH 4 formation (Messenger et al, 2009). The disturbance of the electron transport chain (ETC) in plant cells can occur under stress conditions (Moller et al, 2007).…”

“…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).…”

“…Because the major components of pectin do not absorb UV radiation, and UV radiation can stimulate the production of gasses other than CH 4 (ethane, ethylene and CO 2 ) from plants , Messenger et al (2009) first proposed that ROS might be involved in the biochemical production of CH 4 . It is well established that adverse environmental factors can lead to ROS production via diverse metabolic pathways in vivo (Apel and Hirt, 2004).…”

“…pectin, lignin, cellulose and leaf surface wax) (Bruhn et al, 2014;Keppler et al, 2008;McLeod et al, 2008;Messenger et al, 2009;Vigano et al, 2009Vigano et al, , 2008 have been extensively tested. The majority of studies reported substantial CH 4 emissions, while Bowling et al (2009) reported no evidence for substantial CH 4 emissions by a conifer forest under high UV radiation, to which a soil CH 4 sink might contribute.…”

Abiotic methanogenesis from organosulphur compounds under ambient conditions

“…It has been shown that CH 4 can be produced abiotically from plant material by exposing it to ultraviolet (UV) irradiation [15][16][17][18] . A reaction of reactive oxygen species (ROS) with methoxyl groups of pectic polysaccharides was suggested as a possible route to CH 4 formation under UV radiation 19 . On the other hand, several recent studies 2,9,10 , using 13 C-labelled plant and fungal species, have demonstrated that there is also continuous formation of CH 4 in living plants and fungi without any microbial contribution.…”