Uptake of Boron and Silicon by Barley Genotypes with Differing Susceptibilities to Boron Toxicity

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Abstract
In long-term experiments with whole plants, boron uptake by barley genotypes was linearly related to boron supply over a range of boron concentrations from normal to excessive. The comparative susceptibility of genotypes to boron toxicity was reflected by the relative differences in boron uptake rates over the entire range of boron supply. Root temperature over the range 5–25 °C markedly affected plant growth but had no effect on the relative susceptibility of genotypes to boron toxicity. Concentrations of boron in genotypes were likewise unaffected by root temperature. Uptake of silicon differed greatly amongst genotypes and also reflected the relative susceptibility to boron toxicity and boron uptake. No competitive interaction was observed in the uptake of boron and silicon. The variation in boron accumulation, which governs susceptibility to boron toxicity amongst barley genotypes, is the result of differences in passive boron uptake via a mechanism which apparently also governs silicon uptake. The nature of this mechanism is discussed in relation to the permeability of plant membranes to both boron and silicon.