THE ROLE OF METAL‐ION BINDING IN MODIFYING THE TOXIC EFFECTS OF SULPHUR DIOXIDE ON THE LICHEN UMBILICARIA MUHLENBERGII: II. 14 C‐FIXATION STUDIES

• Published in: The New phytologist 1979-05, Vol.82 (3), p.633-643
• Main Authors: RICHARDSON, D. H. S., NIEBOER, E., LAVOIE, P., PADOVAN, D.
• Format: Article
• Language: English
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.1979.tb01658.x

Total 14 C fixation in Umbilicaria muhlenbergii was not significantly affected at levels near the capacity of the first binding site ( c. 12 μmol g ‐1 ) of class A metal ions or borderline metal ions with class A characteristics: i.e. Sr 2+ , Mg 2+ , Ca 2+ , Ni 2+ , and Zn 2+ . Although both Cu 2+ and Pb 2+ are borderline ions with significant class B character, only Cu 2+ greatly reduced fixation. However Ni 2+ and Pb 2+ , as well as Cu 2+ , induced increased photosynthate release from lichen samples. Protection against damage due to SO 2 exposure was rendered by the uptake of class A ions and even borderline ions except those normally accumulated intracellularly (Mg 2+ , Zn 2+ ) or possessing the capacity to penetrate cells readily (Cu 2+ ). Of the borderline ions tested, Pb 2+ , Cu 2+ and Ni 2+ , as well as SO 2 , induced changes resulting in the incorporation of less 14 C into ribitol and more into sucrose and other sugars during photosynthesis by the lichen samples. The presence of the class A ion Ca 2+ caused a shift in the opposite direction. The presence of Ca 2+ , Ni 2+ , Pb 2+ , but not Cu 2+ , on the lichen tended to inhibit the large SO 2 ‐induced shift away from ribitol production. The threshold levels of various metals reported from field studies to result in visible damage are discussed in terms of the observed photosynthetic perturbations, K 2+ leakage and factors determining metal uptake by lichens. Finally, the ecological significance of the ability of Ca 2+ to protect lichens against the damaging effects of air pollution is discussed.