REACTIVE OXYGEN PRODUCTION AND DAMAGE IN INTERTIDAL FUCUS SPP. (PHAEOPHYCEAE)

The research described in this paper was designed to test the hypothesis that the differential stress tolerance associated with the vertical zonation of intertidal seaweeds is attributable to reactive oxygen metabolism. To do so, we measured the production of, and damage caused by, reactive oxygen in three species of intertidal brown seaweeds— Fucus spiralis L., F. evanescens C. Ag., and F. distichus L.— that differ in their ability to withstand freezing, desiccation, and high light stress. Fucus spiralis is the most stress-tolerant species and F. distichus the least. Reactive oxygen production was determined by measuring the production of H₂O₂ and the oxidation of dichlorohydrofluorescein diacetate to dichlorofluorescein. Damage caused by freezing, desiccation, and high-light stress was assessed by measuring variable fluorescence (F_v/F_m) and lipid peroxidation. Production of reactive oxygen increased following freezing, desiccation, or high-light stress. In general, the data were consistent with the hypothesis that reactive oxygen metabolism is involved in stress tolerance. The production of reactive oxygen was relatively low in unstressed seaweeds, and there was little difference between species. Fucus distichus showed the greatest increase in reactive oxygen production after desiccation and freezing stress. Fucus evanescens produced more reactive oxygen production after desiccation than F. spiralis. Although F. evanescens and F. spiralis produced similar amounts of reactive oxygen after freezing, this treatment resulted in an increase in lipid peroxidation only in F. evanescens (and F. distichus ).