Journal Article

Different regulation of haloperoxidation during agar oligosaccharide-activated defence mechanisms in two related red algae, <i>Gracilaria</i> sp. and <i>Gracilaria chilensis</i>

Florian Weinberger, Boris Coquempot, Sandra Forner, Pascal Morin, Bernard Kloareg and Philippe Potin

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 58, issue 15-16, pages 4365-4372
Published in print December 2007 | ISSN: 0022-0957
Published online December 2007 | e-ISSN: 1460-2431 | DOI: http://dx.doi.org/10.1093/jxb/erm303
Different regulation of haloperoxidation during agar oligosaccharide-activated defence mechanisms in two related red algae, Gracilaria sp. and Gracilaria chilensis

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The related red seaweeds Gracilaria sp. from the eastern Mediterranean and Gracilaria chilensis from Chile were similar in their enzymatic inventory for halogenation. In both species, halogenation was dependent upon H2O2 and thus driven by haloperoxidases. These could be inhibited with phosphate and reversibly inhibited with azide and were therefore apparently dependent upon vanadate. Both species generated in the first line bromoform and other brominated halocarbons. Gel electrophoresis under non-denaturating conditions demonstrated that both species expressed halogenating peroxidases. Elicitation of Gracilaria sp. with agar oligosaccharides resulted in marked increases in bromination, iodination, and chlorination. Production rates of volatile halocarbons and phenol red bromination both increased by a factor of eight, presumably due to increased availability for haloperoxidases of H2O2 during the oxidative burst response. Elicitation of Gracilaria sp. also triggered a release of bromide ions through DIDS-sensitive anion channels, which allowed for some bromination in bromide-free medium. However, this effect was relatively limited. By contrast, agar oligosaccharide oxidation in G. chilensis did not increase halogenation. Obviously, agar oligosaccharide oxidation does not provide sufficient amounts of hypohalous acids for such increases, because it does not deliver H2O2 at the active site of vanadium-dependent haloperoxidases. These results correlate with earlier findings that the agar oligosaccharide-elicited oxidative burst controls microorganisms while agar oligosaccharide oxidation does not.

Keywords: Bromination; Gracilaria; halogenation; haloperoxidase; iodination; seaweed–microbe interactions

Journal Article.  4460 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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