ANION ACCUMULATION BY THE MOSS HYLOCOMIUM SPLENDENS: UPTAKE AND COMPETITION STUDIES INVOLVING ARSENATE, SELENATE, SELENITE, PHOSPHATE, SULPHATE AND SULPHITE

Abstract

SummaryArsenic and selenium uptake by the moss Hylocomium splendens (Hedw.) Br. et Sch. from solutions containing arsenate, selenite or selenate ions was investigated. Arsenate and selenite were accumulated only by living shoots. This moss was unable to take up selenate. Arsenate uptake was optimal between pH 3 and 5 whilst selenate uptake was greatest at pH 3. This difference is discussed in terms of speciation of these anions in solution.Uptake of arsenate and selenite displayed saturation kinetics at pH 5 which could be described in terms of Michaelis‐Menten parameters with Km values of 418 ± 56 μM and 451±93 μM for arsenate and selenite respectively.Competition studies revealed that pre‐incubation of moss shoots in phosphate solutions did not affect the subsequent uptake of either arsenate or selenite. However, the uptake of the latter ions was decreased if phosphate was included in the incubation medium. Phosphate was a competitive inhibitor of arsenate uptake with an inhibition constant (Km phosphate) of 82 μM. Phosphate and arsenate were non‐competitive inhibitors of selenite uptake with inhibition constants of 225 and 43 μM for phosphate and arsenate respectively. The results suggest that arsenate and selenite were accumulated via separate transport systems in H. splendens and it is proposed that these systems may normally be responsible, in part, for phosphate uptake by this moss.