Ecotypes metal-tolerant

Two processes are involved in speciation. Firstly, the two populations must evolve sufficient ecological differences that they do not suffer from competitive exclusion. In the case of metal-tolerant ecotypes, this condition has been fulfilled. Secondly, they must evolve sufficient barriers to gene exchange that the two gene pools are effectively isolated, and will evolve independently. There are a number of ways in which this could occur, and the first stages of this have been observed in a number of studies of metal-tolerant plants. 

Heavy metal tolerance remains one of the clearest examples of microevolution, and one of the best systems to study the relationship between adaptation and ecology. It provides a model for the evolution of ecotypes and edaphic endemics. At the physiological and biochemical level, it is a model system for the study of the mechanisms of resistance to stress and pollution. Many questions remain unanswered, however, among the principal ones of which are ... 

There have been many attempts to reduce the migration of toxic metals from soils, and at the same time improve the appearance of derelict sites by the introduction of metal-tolerant ecotypes (Bradshaw et al., 1965 Gemmel, 1977 Bradshaw and Chadwick, 1980). Many such sites are poor in micronutrients and must first be treated with soil amendments such as lime and fertilisers. The maintenance of plant cover at such sites minimises soil erosion and reduces contamination from wind-blown dust. It has... 

Lead is considered to be a non-essential metal to plants, and only a small proportion of the lead in soils is biovailable to plants (Alloway, 1990). Visible symptoms of toxicity, though unspecific to Pb, are smaller leaves and a stunted growth. Leaves may become chlorotic and reddish with necrosis and the roots may turn black. Several plant species, ecotypes and bacterial strains have been known to develop Pb tolerance. The phytotoxicity of Pb is low as it has very limited availability and uptake from soil and soil solutions. However, plant roots are usually able to take up and accumulate large quantities of Pb2+ in soil and culture solutions but translocation to aerial shoots is generally limited due to binding at root surfaces and cell walls (Lagerwerff, 1971 Jones et al., 1973 Lane and Martin, 1977). 

---