ZINC TOLERANCE IN BETULA SPP.

Abstract

SUMMARYClones of Betula pendula Roth, and B. pubescens Ehrh., collected as seed from zinc-contaminated mine tailings, were grown aseptically in a liquid/perlite medium. Three zinc-tolerant and four non-tolerant genotypes were compared with respect to extension growth and zinc uptake over a range of external concentrations of zinc. The effect of increasing zinc concentration on total root length and root cell length was also examined. Extension growth declined rectilinearly as the external zinc concentration increased, but the relationship between uptake and external concentration was not rectilinear. After an initial proportional increase, concentrations of zinc in tissues remained constant over much of the range of external concentrations at which some growth was possible. Fresh weight concentrations of zinc in tolerant and non-tolerant genotypes were similar at similar external concentrations. However, at a characteristic threshold external concentration, control of uptake broke down and plants were inundated with zinc. The decrease in extension growth was found to be due mainly to a progressive inhibition of cell elongation. Zinc tolerance in Betula lies in an ability to maintain proportionally more extension growth at similar internal and external zinc concentrations. Neither a tolerance mechanism involving internal detoxification, nor binding of zinc ions to electronegative sites in the cell walls, are consistent with the results. However, these findings are compatible with a tolerance mechanism involving control of uptake operating at the endodermis.

Zinc isotopic fractionation in Phragmites australis in response to toxic levels of zinc

“…The lower BCF, the accumulation of Zn in roots, and the limitation to Zn export to the green tissues comprise an avoidance response that confers increased tolerance to Zn excess (Denny and Wilkins, 1987; Maestri et al , 2010). The higher BCF of dead roots in Zn+ is consistent with the use of root senescence to release Zn, an excretion mechanism of tolerant plants (Duarte et al , 2010).…”

Rapid evolution towards heavy metal resistance by mountain birch around two subarctic copper–nickel smelters

“…Both seedling height and leaf length data indicate that 60–70 years of pollution impact near the smelters in Monchegorsk and Nikel have resulted in mountain birch populations adapting to HM stress. To my knowledge, this is one of the few examples of long‐lived trees adapting to anthropogenic pollution stress (but see: Denny & Wilkins, 1987; Watmough & Dickinson, 1995; Punshon et al. , 1995).…”

“…The exact mechanisms behind the detected adaptation can not be solved with the current data either, but there are several possibilities. These include physiological tolerance of the HM compounds (Denny & Wilkins, 1987), better use of mycorrhizal fungi that have been shown to be beneficial to birch trees in HM polluted habitats (Brown & Wilkins, 1985; Jones & Hutchinson, 1986), and reduced HM uptake by seedlings originating from polluted habitats (Punshon et al. , 1995; Watmough & Dickinson, 1995).…”

“…, 1991; Turner & Dickinson, 1993). However, there are some examples of long‐lived trees adapting to anthropogenic pollution stress, especially in genera Betula (birches) and Salix (willows) (Denny & Wilkins, 1987; Punshon et al. , 1995; Utriainen et al.…”

Mountain birch under multiple stressors – heavy metal‐resistant populations co‐resistant to biotic stress but maladapted to abiotic stress

“…one to two generations) HM resistance in mountain birch populations may be based on reduced HM uptake. This study, together with the study by Eränen (2008), is among the few studies showing HM adaptation in long‐lived trees (but see Denny & Wilkins, 1987; Punshon et al. , 1995; Utriainen et al.…”