The Levels of Boron-Uptake Proteins in Roots are Correlated with Tolerance to Boron Stress in Barley
2015
Mishra, Sasmita | Heckathorn, Scott | Krause, Charles
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 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 (deficiency or toxicity) is correlated with natural levels of B-uptake proteins in roots. We grew two barley (Hordeum vulgare L.) cultivars that differ in tolerance to low and high B (Schooner and Clipper, respectively) at three B levels (sub-, near-, and supraoptimal), and then we determined the concentration of BOR1 and NIP5;1 in roots using enzyme-linked immunosorbent assay (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 total protein concentration. BOR1 content per unit total protein and per gram of root was greater in Clipper than Schooner, while NIP5;1 content was greater in Schooner. The estimated activity of BOR1 (B uptake per BOR1) did not differ between cultivars. 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 and 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).
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