The effect of zinc contamination from electricity pylons. Genetic constraints on selection for zinc tolerance

Abstract

Zinc tolerance, based on root growth in zinc-containing solutions, was examined in samples of 30 Agrostis capillaris L. individuals collected from populations beneath five electricity pylons in North Wales. The populations were found to vary in zinc tolerance. Three of them contained individuals whose tolerance ranged from low to high, one population consisted of individuals with low to moderate tolerance, whilst the fifth population (ZK-180) contained no tolerant individuals. Differences in zinc tolerance were also found between seedlings raised from five seed populations collected from plants growing in the uncontaminated pasture areas adjacent to four of those pylons, and one further pylon in the same area. The population adjacent to pylon ZK-1 80 consistently showed little sign of tolerant individuals. Samples of seeds collected from the populations in the uncontaminated areas surrounding each pylon, and likely to have been the origin of the pylon populations were grown at a concentration of 15 ,ug Zn cm and root lengths of 105 randomly chosen seedlings from each were measured. The means and variance of tolerances of four of the five did not differ, but all were significantly higher than that adjacent to pylon ZK-1 80. Two cycles of selection and breeding for increased zinc tolerance were carried out using seed samples collected from four of the five populations of adults collected beneath pylons examined previously, and including population ZK-180. Marked increases in tolerance were effected in three of the four populations; no corresponding increase in tolerance was achieved for population ZK-180. It is concluded from these findings that the lack of zinc tolerance beneath pylon ZK-180 is due to the absence of appropriate variation in zinc tolerance within that population, and in potential colonizing material adjacent to it, a situation which contrasts with that for the other three pylons.

The genetics of metal tolerance in vascular plants

“…This variation is highly heritable. Al-Hiyaly et al (1993) showed there to be a realized heritability of about 40 °o for Zn tolerance in three A. capillaris populations from beneath electricity pylons, and remarkably Macnair, et al (1993) have found exactly the same value for the heritability of the within-mine variation of Cu tolerance in M. guttatus at Copperopolis. Rocovitch & West (1975) found a correlation between As content of the soil and arsenate tolerance of plants at the individual level, and Macnair (1987i) details a number of other similar examples.…”

“…Not all species that exhibited Zn tolerance were present at each pylon. The difference appears to be in the local populations surrounding the pylons; those that had a low frequency of tolerance genes could produce a tolerant population under the pylon, while those that did not, could not (Al-Hiyaly et al, 1993).…”

Evolution of herbicide resistance in weeds: initial frequency of target site-based resistance to acetolactate synthase-inhibiting herbicides in Lolium rigidum

“…Major genes contribute to some examples of metal tolerance and must be present within populations for selection to occur (Macnair, 1993). Studies have demonstrated that some plant populations will evolve metal tolerance at some sites and not others (Al-Hiyaly et al, 1993). As rare genes will not be present in all small populations, large populations or a large number of populations will need to be treated to select for these rare genes.…”

Microevolution on Anthropogenically Changed Areas on the Example of Biscutella laevigata Plants from Calamine Waste Heap in Poland

“…The emergence of such forms of plants, which have the capacity to grow and reproduce effectively in areas with increased metal content in the soil, has usually ranged from a few dozen to several decades [65][66][67]. It should be noted, however, that the adaptations disclosed in these populations concerned only the physiological adjustment to the increased metal concentration.…”