The Cellular Localisation of Elements in Leaf Cells of Sphagnum with the Scanning Proton Microprobe

Abstract

Scanning proton microprobe analysis was used to investigate the spatial distribution of elements at the cellular level in leaf cells of Sphagnum squarrosum Crome. Light micrographs of the areas scanned enabled cell types to be identified and the cellular locations characterised. The scans revealed that iron was bound at high concentrations in extracellular locations. Pretreatment of moss shoots by submersion in 0.5 mM FeC1 resulted in a concentration of 85 mM of iron per liter of hydrated tissue, approximately 170 times the concentration of the surrounding solution. Calcium was present within living cells at high concentrations, and in the cell walls. Potassium occurred intracellularly. This new technique has potentialfor increasing our understanding of metal ion uptake by mosses. Mineral uptake by bryophytes is characterised by the large part played by ion exchange sites in the cell walls (Brown 1982). Cations, in particular, but also anions to a lesser extent, are absorbed from a bathing solution by the nonliving cell walls. The process is similar to that occurring in ion exchange resins, being independent of the activities of living cells and with the greatest affinity shown between the exchange sites and cations of highest valency (Bell 1959). The exchange sites are acidic residues of polyuronic acids in the cell walls. Clymo (1963) estimated quantities of unesterified uronic acid in Sphagnum samples and found a correlation between