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Bromophenols in Rhodomela larix : a study in chemical ecology Phillips, David William


In this study aspects of the ecology, biology and chemistry of Rhodomela larix (Turner) C. Agardh are investigated and an effort made to relate the findings to a determination of the reasons for the production of bromophenols by red algae. Environmental factors occurring, in local tide-pools which might affect the production or exudation of bromophenols by this alga were examined in summer over a three month period. Measurements of algal biomass and levels of total phenols in the pools show that R. larix produces and exudes copious amounts of these compounds. The ecological implications of this rate of release are introduced. Chemotaxonomic comparison of the morphologically different tidepool and low intertidal populations of R. larix indicates that the two are sufficiently similar to be considered the same species. Several bromophenols previously thought to be artifacts are now considered to be natural constituents of algae. A high-performance liquid chromatographic method was developed for the separation, identification and quantitative determination of red algal bromophenols. The method is evaluated on the basis of several chromatographic parameters, and steps in its development and improvement are discussed. Previous studies on red algal phenols have generally overlooked quantitative considerations. This study presents data for various aspects of the quantitative analysis of the major bromophenolic substance (lanosol, 2,3-dibromo-4,5-dihydroxybenzyl alcohol) in R. larix. Temporal determination of lanosol concentrations demonstrates that the highest levels occur in winter months. Populational differences were observed and the highest levels within a single plant were found to be in the youngest regions. Control of the exudation of bromophenols by R. larix was studied using artificial conditions which fell within the ranges of environmental conditions previously monitored. Exudation of lanosol is enhanced in light, at higher temperatures and at lower salinities. pH has little effect on exudation. The rates of exudation found in these experiments correspond to those measured in the tidepool. Examination of the broad spectrum antibiotic activity of lanosol proves this compound to be effective even at low levels against a wide variety of organisms. The effect is enhanced at low pH, and comparison with R. larix exudates suggests lanosol to be the major active component. A discussion of the ecological significance of bromophenol production is presented and an argument made for the production of these compounds as antibiotic substances. Comparison with previous experiments describing the temporal antibiotic activity of another Rhodomela species supports this conclusion.

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