Lamina Cell Shape and Cell Wall Thickness Are Useful Indicators for Metal Tolerance-An Example in Bryophytes.

Bryophytes are widely used to monitor air quality. Due to the lack of a cuticle, their cells can be compared to the roots of crop plants. This study aimed to test a hypothetical relation between metal tolerance and cell shape in biomonitoring mosses (, , ) and metal sensitive species (, ). The tolerance experiments were conducted on leafy gametophytes exposed to solutions of ZnSO4, ZnCl, and FeSO in graded concentrations of 1 M to 10 M. Plasmolysis in D-mannitol (0.8 M) was used as a viability measure. The selected species differed significantly in lamina cell shape, cell wall thickness, and metal tolerance. In those tested mosses, the lamina cell shape correlated significantly with the heavy metal tolerance, and we found differences for ZnSO4 and ZnCl. Biomonitoring species with long and thin cells proved more tolerant than species with isodiametric cells. For the latter, "death zones" at intermediate metal concentrations were found upon exposure to ZnSO4. Species with a greater tolerance towards FeSO and ZnSO had thicker cell walls than less tolerant species. Hence, cell shape as a protoplast-to-wall ratio, in combination with cell wall thickness, could be a good marker for metal tolerance.