High rates of extracellular superoxide production in bryophytes and lichens, and an oxidative burst in response to rehydration following desiccation

Abstract

Summary The mechanism of extracellular superoxide radical (O2·−) formation and the role of the oxidative burst in response to desiccation stress is reported here in bryophytes and lichens from habitats of contrasting water availability. Rates of extracellular production of O2·− radicals were measured, before and after desiccation stress, by the oxidation of epinephrine to adrenochrome, determined spectrophotometrically. Several desiccation‐sensitive lichens and bryophytes that grow in very wet microhabitats produced O2·− extracellularly at high rates, even when they were not stressed. In addition, some species showed a powerful burst of O2·− production during rehydration following desiccation. Production of high levels of O2·− and the existence of an inducible oxidative burst was best developed in cyanobacterial lichens, a hornwort and the two thalloid liverworts tested. Extracellular production of O2·− was almost absent from all mosses tested, a leafy liverwort, a filmy fern and from desiccation‐tolerant lichens. Patterns of O2·− production are discussed in terms of their possible role as a defence against pathogenic fungi and bacteria.