Physiological and biochemical controls over methyl halide emissions from rice plants

Abstract

[1] This paper investigates physiological and biochemical aspects of methyl halide production in rice plants over two growing seasons. Multiple separate mechanisms appear to be responsible for production of methyl halides in rice plant tissues. Evidence for multiple mechanisms is found in timing of peak emissions of methyl halides from rice, inconsistent effects of competitive inhibitors on methyl halide emissions, and large differences in methyl halide emission rates when compared to plant tissue halide concentrations. Other results show that chloride, bromide, and iodide ion concentrations in plant tissue appear to be regulated throughout the season, and observed changes in leaf tissue concentration cannot explain observed methyl halide emissions. The K m for methyl iodide formation in leaf tissue cell-free extract is 0.018 mM, suggesting a very efficient mechanism. Of the seven competitive inhibitors used, only thiol had a consistently strong effect on both methyl iodide and methyl bromide.

Rice OsHOL1 and OsHOL2 proteins have S-adenosyl-L-methionine-dependent methyltransferase activities toward iodide ions

“…Therefore, when the kinetic parameters and halide concentrations in vivo are considered, both HOL proteins should mainly methylate iodide ions and not bromide ions. Previous studies have shown methyl iodide emissions from rice paddies (Muramatsu and Yoshida 1995) and from rice tissues (Redeker et al 2004). ese phenomena could be because of enzymatic activity of OsHOL proteins in accordance with our biochemical results showing that both OsHOL1 and OsHOL2 actually have SAM-dependent methyltransferase activity toward iodide ions and synthesize methyl iodide.…”

Microbial metabolism directly affects trace gases in (sub) polar snowpacks

“…To date, only prokaryotes (bacteria) have been observed to consume methyl chloride and methyl bromide [13] and they are able to use these compounds as their sole energy substrate. Methyl iodide has been observed to be produced by bacteria [14], fungi [9] and plants [11], and is preferentially generated relative to the other methyl halides in most cases. Genetic sequences and enzymatic mechanisms for bacterial consumption of methyl chloride and methyl bromide have been identified [15], as well as a suite of homologues for methyl halide production in plants [16].…”

“…Genetic sequences and enzymatic mechanisms for bacterial consumption of methyl chloride and methyl bromide have been identified [15], as well as a suite of homologues for methyl halide production in plants [16]. There remains uncertainty regarding whether all primary mechanisms for monohalogenated metabolism have been identified [11,17].…”

“…Methyl iodide affects local air quality and influences atmospheric degradation rates for longer-lived compounds such as methane through its influence on hydroxyl radical concentrations [6]. Methyl chloride and methyl bromide can be formed directly through chemical interactions in soil [7], but are more commonly produced through active metabolism of eukaryotic organisms (fungi: [8,9]; plants: [10][11][12]). To date, only prokaryotes (bacteria) have been observed to consume methyl chloride and methyl bromide [13] and they are able to use these compounds as their sole energy substrate.…”

Methyl chloride isotopic signatures from Irish forest soils and a comparison between abiotic and biogenic methyl halide soil fluxes

“…Temperate forests incorporate the potential for fungal emissions, bacterial degradation and abiotic production within the soil column combined with the potential for subsurface plant emissions within the soil (root emissions; Redeker et al, 2004b) and canopy (leaf and stem emissions; Redeker et al, 2004b). Temperate forests incorporate the potential for fungal emissions, bacterial degradation and abiotic production within the soil column combined with the potential for subsurface plant emissions within the soil (root emissions; Redeker et al, 2004b) and canopy (leaf and stem emissions; Redeker et al, 2004b).…”