Format: ORAL

Michelle J Price1,2, Sylvain Loubery2, Mathilde Ruche1,2

1 Conservatory and Botanical Garden of Geneva, Chemin de l'Impératrice 1, 1292 Chambèsy-GE, Switzerland 2 Department of Plant Sciences, University of Geneva, Quai Ernest-Ansermet 30 1211 Geneva, Switzerland

The peristome in mosses plays a role in spore maturation and release. Arthrodontous peristomes are formed from one or two rings of cell-wall remnants of opposing cell layers that are divided into distinct, articulated teeth. These teeth are reactive to humidity and move in response to changes in the ambient water levels in their immediate surroundings. The hygroscopic movements of the peristome teeth are hypothesised to facilitate spore dispersal. Two main types of response of the peristome teeth to water availability extremes are documented, peristomes that are open when wet and closed when dry versus peristomes that are open when dry and closed when wet. Cell wall deposition patterns on the internal and external faces of the teeth influence the movements based on water diffusion patterns and absorption-loss dynamics. The presence of a hydrophobic substance between the two cell layers of the single or outer ring of teeth has been documented in certain moss species, with several hypotheses proposed to explain its function in the hygroscopic movements and what the substance may be composed of. Histological examination of peristomes from species across the Dicranidae allowed us to clarify the composition of the layer and, when present, clarify its role in the mediation of the hygroscopic movements. Reflections on the responses of peristomes, with and without the hydrophobic layer, revealed a potential link with ecological preferences.