Summary• The Afromontane understorey moss Atrichum androgynum is shown here to display an oxidative burst of hydrogen peroxide (H 2 O 2 ) during rehydration following desiccation.• Maximum rates of H 2 O 2 production, assayed spectrophotometrically using the xylenol orange assay, occurred during the first 15 min of rehydration. Although the production of H 2 O 2 increased with increasing desiccation times, the moss produced significant amounts of H 2 O 2 during rehydration after desiccation for times that did not inhibit photosynthesis or cause potassium (K + ) leakage. Atrichum androgynum also produces H 2 O 2 during desiccation; artificially induced desiccation, using polyethylene glycol, strongly stimulates H 2 O 2 production.• Experiments involving inhibitors and exogenously supplied reductants indicated that peroxidases might be responsible for the production of H 2 O 2 . Factors that influence the rate of H 2 O 2 production during rehydration included light and the hormone abscisic acid. Patterns of H 2 O 2 production in A. androgynum are discussed in terms of their possible role in defence against pathogenic fungi and bacteria.
Results indicate that the photobiont of P. polydactylon possesses inducible tolerance mechanisms that reduce desiccation-induced damage to carbon fixation, and will therefore improve the supply of carbohydrates to the whole thallus following stress. In this lichen, ABA is involved in signal transduction pathways that increase tolerance of the photobiont.
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