Ultraviolet radiation drives methane emissions from terrestrial plant pectins

Recent studies demonstrating an in situ formation of methane (CH4) within foliage and separate observations that soil-derived CH4 can be released from the stems of trees have continued the debate about the role of vegetation in CH4 emissions to the atmosphere. Here, a study of the role of ultraviolet (UV) radiation in the formation of CH4 and other trace gases from plant pectins in vitro and from leaves of tobacco (Nicotiana tabacum) in planta is reported. Plant pectins were investigated for CH4 production under UV irradiation before and after de-methylesterification and with and without the singlet oxygen scavenger 1,4-diazabicyclo[2.2.2]octane (DABCO). Leaves of tobacco were also investigated under UV irradiation and following leaf infiltration with the singlet oxygen generator rose bengal or the bacterial pathogen Pseudomonas syringae. Results demonstrated production of CH4, ethane and ethylene from pectins and from tobacco leaves following all treatments, that methyl-ester groups of pectin are a source of CH4, and that reactive oxygen species (ROS) arising from environmental stresses have a potential role in mechanisms of CH4 formation. Rates of CH4 production were lower than those previously reported for intact plants in sunlight but the results clearly show that foliage can emit CH4 under aerobic conditions.