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The levels of boron-uptake proteins in roots are correlated with tolerance to boron stress in barley

Mishra, Sasmita, Heckathorn, Scott, Krause, Charles
Crop science 2015 v.55 no.4 pp. 1741-1748
Hordeum vulgare, antibodies, barley, biomarkers, biomass, boric acid, boron, cultivars, enzyme-linked immunosorbent assay, genotype, growth and development, nutrient deficiencies, nutrient excess, nutrient uptake, phytoremediation, plant growth, plant stress, plasma membrane, roots, shoots, stress tolerance, toxicity, transporters, xylem
Boron (B) is an essential micronutrient required for plant growth and development. Recently, two major B-uptake proteins, BOR1 and NIP5;1 have been identified and partially characterized. BOR1 is a high-affinity B transporter involved in xylem loading in roots, and NIP5;1 acts is a major boric-acid channel in the plasma membrane. The aim of the present study was to determine if plant tolerance to B stress is correlated with natural levels of B-uptake proteins in roots. We grew two barley cultivars that differ in tolerance to low and high B (Schooner and Clipper) at three B levels (sub-, near-, and supra-optimal), and then we determined the concentration of BOR1 and NIP5;1 in roots, using ELISA and protein-specific antibodies that we developed. Shoot and root biomass in Schooner decreased at high B, while shoot mass in Clipper decreased in low B. Differences between cultivars in tolerance to B stress were unrelated to the concentration of B in plant tissue or to effects of B on root:shoot mass. BOR1 content per unit total protein and per g root was greater in Clipper compared to Schooner, while NIP5;1 content was greater in Schooner. The estimated activity of BOR1 (B uptake per BOR1) also differed between cultivars, but NIP5;1 activity did not. These results show that whole-plant tolerance to B deficiency and toxicity is correlated with levels of the major B-uptake proteins in roots (BOR1, NIP5;1). Hence, BOR1 and NIP5;1 can potentially be used as biomarkers to identify plant genotypes with enhanced tolerance to B stress (e.g., for agriculture or phytoremediation).