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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Influence of Leaf Tolerance Mechanisms and Rain on Boron Toxicity in Barley and Wheat^1,[C]

School of Earth and Environmental Sciences, University of Adelaide, Adelaide 5005, Australia

Boron (B) toxicity is common in many areas of the world. Plant tolerance to high B varies widely and has previously been attributed to reduced uptake of B, most commonly as a result of B efflux from roots. In this study, it is shown that the expression of genes encoding B efflux transporters in leaves of wheat (Triticum aestivum) and barley (Hordeum vulgare) is associated with an ability of leaf tissues to withstand higher concentrations of B. In tolerant cultivars, necrosis in leaves occurred at B concentrations more than 2-fold higher than in sensitive cultivars. It is hypothesized that this leaf tolerance is achieved via redistribution of B by efflux transporters from sensitive symplastic compartments into the leaf apoplast. Measurements of B concentrations in leaf protoplasts, and of B released following infiltration of leaves, support this hypothesis. It was also shown that under B-toxic conditions, leaching of B from leaves by rain had a strong positive effect on growth of both roots and shoots. Measurements of rates of guttation and the concentration of B in guttation droplets indicated that the impact of guttation on the alleviation of B toxicity would be small.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Rob Reid (robert.reid{at}adelaide.edu.au).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.141069

^* Corresponding author; e-mail robert.reid{at}adelaide.edu.au.

Received May 7, 2009; accepted July 14, 2009; published July 22, 2009.