Stress-induced production of volatile halogenated organic compounds in Eucheuma denticulatum (Rhodophyta) caused by elevated pH and high light intensities

Eucheuma denticulatum has been shown to release bromoform, diiodomethane, dibromochloromethane, perchloroethylene, chloroiodomethane, chloroform, sec-butyl iodide, methyl iodide, methylchloroform, carbon tetrachloride, trichloroethylene and butyl iodide into its growth media, with bromoform (310 +/- 25 mu g kg DW-1 h(-1)) and diiodomethane (182 +/- 9 mu g kg DW-1 h(-1)) being the dominant volatile halocarbons (VHCs). The production of VHCs was always higher at a photon flux density of 1500 than at 400 mu mol photon m(-2) s(-1). The influence of pH was minimal at 400 mu mol photon m(-2) s(-1). The addition of azide decreased mean VHC production at pH 8.2 +/- 0.2 and 8.8. Algae kept in media where extracellular hydrogen peroxide was decomposed by addition of manganese dioxide showed a decrease in VHC production at pH 8.2 +/- 0.2 and an increase at pH 8.8. We suggest that high light intensity and carbon dioxide deficiency caused by high pH in E. denticulatum promote VHC production through induction of hydrogen peroxide synthesis.