Adaptation to metals in widespread and endemic plants.

Abstract

Bryophytes, including the mosses, liverworts, and hornworts, occur in a variety of habitats with high concentrations of metals and have other characteristics that are advantageous for studies of metal tolerance. Mosses may evolve genetically specialized, metal-tolerant races less frequently than flowering plants. Some species of mosses appear to have inherently high levels of metal tolerance even in individuals that have not been subjected to natural selection in contaminated environments. Scopelophila cataractae, one of the so-called copper mosses, not only tolerates extremely high concentrations of metals in its substrates, but requires these substrates for optimum growth. This species should be included in mechanistic studies of tolerance at the cellular and molecular levels. - 274-3474. evolve in just a few generations, and high levels of tolerance tend to be metal-specific. Tolerance mechanisms are varied and the genetic basis for infraspecific differences in tolerance may also be varied. Major genes with modifiers seem to be involved in several species but additional genetic analyses are needed. Tolerance in Widespread MossesMany species of bryophytes are known to tolerate habitats with high concentrations of environmental pollutants (7) and the effects of metals such as copper, zinc, and lead have been most thoroughly studied under experimental conditions. Genetically specialized ecotypes tolerant of copper have been described in the liverwort, Solenostomum crenulatum (8) Other studies on several species of mosses suggest that in addition to, or sometimes instead of, the evolution of genetically adapted ecotypes, inherently broad tolerances permit plants to colonize and thrive in metal-contaminated environments. Shaw (9) studied tolerance of copper, zinc, cadmium, and nickel in plants from eight populations of Funaria hygrometrica. There was strong evidence of ecotypic differentiation for copper tolerance; populations could be clearly segregated as either tolerant or relatively nontolerant. Tolerant plants were restricted to copperenriched sites. These observations provide solid, if indirect, evidence of responses to natural selection for tolerance at contaminated sites.The same populations were genetically variable with regard to cadmium and zinc tolerance, but the relationships between tolerance levels and concentrations of these metals in the natural habitats of populations were less clear than for copper. For cadmium, plants from one population that originated at a cadmium-enriched site were indeed relatively tolerant of this metal, but plants from several other populations growing at sites without cadmium enrichment were also tolerant. Plants that were tolerant of copper also tended to be tolerant of cadmium, even if cadmium was not present in high concentration in their substrates. This observation suggests cotolerances between metals, with obvious implications for mechanistic studies.Plants also exhibited variation in tolerance of zinc, but there appeared to be no relationship between toleran...

Soil influence on Cu and Co uptake and plant size in the cuprophytes Crepidorhopalon perennis and C. tenuis (Scrophulariaceae) in SC Africa

“…High tolerance to both Cu and Co has often been demonstrated in plant populations from Cu-enriched soil, but there was no clear evidence for elevated Cu requirements neither for pseudometallophyte (Hogan and Rauser 1979;Schat and Ten Bookum 1992;Macnair et al 1993;Lou et al 2004;but see Brej 1998) nor Cu specialists (Baker et al 1983). In the socalled "copper mosses", however, Shaw (1993Shaw ( , 1994 showed elevated copper requirements and growth stimulation in contaminated substrates.…”

Pleurozium schreberi as bioindicator of mercury pollution in heavily industrialized region

“…This result indicates a possible adaptation mechanism which allowed P. schreberi to survive the accumulation of high mercury levels (Fernándèz et al 2000). According to Shaw (1994) and Guschina and Harwood (2002), some specimens of mosses appear to have inherently a high level of metal tolerance, which permits them to colonize and thrive in metal-contaminated environments. The only exception was native moss at ten sites: 4-6, 8-9, 15, 18-19, 21, 26.…”

Genetic Susceptibility in Ecosystems: The Challenge for Ecotoxicology

“…In ecotoxicological terms, genetic susceptibility in ecosystems may be considered to exist in one of two forms: the result ofevents contributing to a reduction the natural variation found in any gene pool or the result of the effects of genetic damage ( Pollutant-induced selection of resistant genotypes has been demonstrated for fish (12), polychaetes (13)(14)(15)(16), insects (7,17), and a range of plants (8,18). Although the long-term ecological impact of such selection is not known with certainty, there are a number of possible implications of ecotoxicological significance.…”

“…A major criticism of this approach has been that it seldom considers the variability in susceptibility to chemical toxicity [17][18][19][20][21][22] March 1996 in Espoo, Finland. Manuscript received at EHP 5 November 1996; accepted 18 November 1996.exhibited by the large number of animal and plant species found in the natural environment.…”