Mechanisms Regulating the Production and Emission of Methanol in Lycopersion esculentum

Phytogenic methanol (MeOH) emission is the largest source of MeOH to the atmosphere, where it is the second most abundant organic compound, after methane. MeOH is believed to be a by-product of pectin methylesterase (PME) activity in cell walls. Immature leaves are known to have higher MeOH emission rates than mature leaves and are believed to produce MeOH within leaf tissue via PME activity. The source of MeOH from mature leaves, however, is unknown and has been suggested to be derived from below-ground sources. MeOH emissions are known to increase with stomatal conductance, light, and wounding. The mechanisms controlling MeOH production and emission, however, are not well understood. In my dissertation, I pursued questions concerning the source of MeOH emissions from mature leaves, the ability of PME activity to predict MeOH flux, the direct influence of light on MeOH production and emission, and the influence of mechanical damage on local and systemic MeOH production and emission. Results suggested that MeOH from mature and immature leaves was derived from the same biosynthetic pathway. Enriched isotopic signatures of MeOH emission relative to the isotopic signature of the pectin methoxyl pool, as well as unexplained variance in PME activity and concentrations of MeOH in plant tissue, suggested the presence of a MeOH sink (e.g. MeOH catabolism). PME activity was related to MeOH emission but was not a good predictor of MeOH emission. Results suggested that below-ground production of MeOH was not a significant source to mature leaves. Light did not directly influence MeOH production or emission over short time scales. Mechanical damage significantly increased MeOH emission, but no significant II changes in PME activity were detected. PME transcription was locally and systemically down-regulated in response to damage. My dissertation contributes to basic biological knowledge concerning the production and emission of MeOH, an important biogenic flux to the atmosphere.

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