TRACE GAS PRODUCTION BY SEAWEEDS: DEFENSE, OXIDATIVE STRESS, SIGNALLING AND ATMOSPHERIC SIGNIFICANCE

Malin, G. 1 , Küpper F. C. 2 , Carpenter, L. 1 , Baker, A. 1 , Broadgate, W. 1 , Kloareg, B. 2 & Liss, P. S. 11 School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ. U.K. 2UMR 1931 CNRS‐Goëmar, Station Biologique de Roscoff, BP 74, F‐29682 Roscoff, Bretagne, France For some years it has been known that seawater contains a range of volatile halogenated compounds which are produced by phytoplankton and macroalgae. The total production for some of these compounds is estimated to be of the order of Tg per year, and the resulting flux of trace gases to the air is highly significant for global atmospheric chemistry, since the volatiles are an important source of halogen free radicals which impact on oxidant chemistry and participate in ozone destruction reactions. Ongoing research seeks to determine the physiological basis of the production of halogens by seaweeds. However, debate continues as to whether the algal production of these trace gases has a particular functional value or should be considered an ‘accident’ of photoautotrophy which serves to sequester reactive oxygen species. This talk will focus on our recent research on the production of volatile iodinated halocarbons and inorganic iodine species by sporophytes of Laminaria digitata. In this species elicitor compounds such as Oligoguluronates (oligomeric degra‐dation products of cell wall alginate), trigger a strong, transient burst of active oxygen species, which is recognised as a ubiquitous defence characteristic in animal and higher plant phyla. In Laminaria digitata, which accumulates very high levels of iodine the oxidative burst rapidly induces a massive efflux of inorganic iodine which is accompanied by elevated production of volatile iodinated compounds. Our data also suggest that the iodine release is a component of the seaweeds defence system against pathogens.