Hydrogen peroxide content and vanadium-dependent haloperoxidase activity in thalli of six species of Fucales (Phaeophyceae)

Abstract

:Patterns of hydrogen peroxide content and vanadium-dependent haloperoxidase (V-HPO) activity were investigated in thalli of six species of Fucales (Fucus vesiculosus, F. serratus, F. edentatus, F. distichus, Ascophyllum nodosum and Pelvetia canaliculata). H2O2 levels in all species were similar to those of photosynthesizing tissues of unstressed terrestrial plants. The highest H2O2 content (up to 0.7 μM g FW−1) was in F. distichus and Pelvetia. H2O2 content in the basal and middle zones of fronds was generally higher than in vegetative apices and receptacles. Similar trends were detected for V-HPO activity with both bromide and iodide. Intrathallus profiles of H2O2 content and V-HPO activity may be attributed to the physiological condition of the respective thallus zones, i.e. photosynthetic activity and stage of cell differentiation. Steady-state kinetics showed significant variation of V-HPO parameters between fucoid species, suggesting that they contain different forms of the enzyme. V-HPO from high-intertidal Pelvetia and F. distichus exhibited the highest Km values for both halide and H2O2. The enzyme form with the maximum kinetic efficiency occurred in the mid-intertidal fucoids. For all investigated species, the iodination activities were two to four times lower than for bromination. Apparently, V-HPOs contribute significantly to the control of reactive oxygen species accumulation in Fucales. The similarity of the longitudinal profiles of H2O2 content and peroxidase activity between Fucales and terrestrial plants suggests a physiological analogy of V-HPO and secretory peroxidases.