picture.gif (17583 bytes)
Maggie Walser

Chemical Engineering
and Chemistry

Interest in environmental issues was the motivation behind Maggie Walser’s research pursuits. Her interest in atmospheric chemistry led to her current study of agricultural emissions of trace gases, which allowed her to learn and apply aspects of earth science and biology and gain a variety of new skills. Maggie has taken on various roles during her undergraduate years, including guiding, advising and helping fellow students. She has been a University Studies discussion leader, a House Assistant in Arroyo Vista, and a Peer Academic Advisor for the School of Physical Sciences. Her advice to others is “Find something you care about and get involved!” triangle.gif (504 bytes)




Inorganic halogen radicals in the atmosphere play a role in stratospheric ozone destruction. Methyl halides act as transport vectors for halogen radicals from surface sources to the atmosphere, making knowledge of their budgets necessary. Atmospheric concentrations of methyl halides have been measured, but their fluxes are not yet fully quantified. Better estimation of methyl halide sources and atmospheric budgets can be gained from the measurement of emissions from agricultural and other terrestrial plants. This study sought an understanding of the metabolic mechanism(s) that produces methyl halides. The role of methyl transferases in methyl halide biosynthesis in rice was examined using leaf-disk enzyme inhibition assays with known methyl transferase substrates as possible competitive inhibitors. Only thiocyanate had a significant impact (p < 0.05) on methyl bromide generation, while methyl iodide synthesis was not significantly inhibited by any of the methyl transferase substrates surveyed. In all assays, methyl bromide production was inhibited more than that of methyl iodide, suggesting that either the enzyme(s) responsible for methyl halide synthesis binds iodide preferentially, or a suitable competitive substrate was not found. Methyl halide emissions from barley, corn, soybean, and wheat leaf disks were also investigated. The findings of this investigation increase knowledge of the biochemical production pathway(s) of methyl halides. triangle.gif (504 bytes)

back.gif (221 bytes) next


Faculty Mentor                                                                                                                
facultypicture.gif (12811 bytes)

Ralph J. Cicerone,

School of Physical

Maggie Walser’s research topic was unusually original so we could only guess what her experiments would show. Methyl bromide is a chemical that is produced industrially and used as an agricultural and structural fumigant. Its use is being banned worldwide due to its potential impact on the ozone layer. The ban was conceived before natural sources were investigated. We have found that methyl bromide and methyl iodide are emitted by rice plants, and our group set out to learn the metabolic mechanism of biochemical production of methyl halide gases by plants. Maggie used potential chemical inhibitors to see if they would impede the activity of methyl halide transferase enzymes in plant leaves. She made many difficult measurements that were true experiments, and she found that one of the chemicals inhibited methyl bromide production and that none of them significantly impeded formation of methyl iodide. Her research unveiled the complexity of this new topic. triangle.gif (504 bytes)

back.gif (221 bytes)

If you wish to view the paper in its entirety, please select the link given to the PDF file. pdf_logo.gif (126 bytes)[Maggie Walser.pdf]

If you wish to download the Adobe Acrobat Reader,
please go to Adobe’s website (

Back to Journal 2002 Index

Copyright 2002 by the Regents of the University of California.  All rights reserved.