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.