Poster: Nutrient Biology

Abs # 400: B tolerance in wheat genotypes: uptake and allocation of B during vegetative and reproductive development

Presenter:	Wimmer, Monika A., m.wimmer@uni-bonn.de
Authors	Wimmer, Monika A. (A)   Lauchli, Andre  (B)   Brown, Patrick H. (C)
Affiliations:	(A): Institute of Plant Nutrition, University of Bonn (B): Department of Land, Air and Water Resources, University of California, Davis (C): Department of Pomology, University of California, Davis

Wheat has been shown to exhibit a wide range of genotypic variations in response to toxic B levels. The underlying physiological mechanisms are still unknown, but have been thought to be associated with the ability to restrict B accumulation in the plant. We present evidence that a variety of mechanisms to reduce B accumulation is expressed in wheat genotypes. The degree of overall B tolerance is likely a result of the combined effects of these mechanisms. Three wheat genotypes ranging from B sensitive to B tolerant were grown hydroponically and supplied with 0.2 mM boric acid. The three genotypes differed in the duration of their vegetative development. Using the stable isotope ¹⁰B, we determined B uptake rates and the allocation of B within the plant at early and late reproductive growth. The following results were obtained: 1. All wheat genotypes were more B tolerant during reproductive than during vegetative growth. 2. B sensitivity appeared to be related to high B uptake rate and to the accumulation of B in leaves, stems and flag leaves. 3. B tolerance appeared to be associated with partial B exclusion from flag leaves, but there was no correlation between B tolerance and the allocation of B in reproductive organs. 4. Tolerant genotypes differed in the predominant mechanism of B tolerance which may involve low B uptake rate, reduced B translocation, B exclusion from certain plant parts, or rapid plant development. 5. In leaves, the extent of B accumulation may be related to Ca accumulation. 6. Measuring ¹⁰B/¹¹B ratios after supplying the plant with enriched ¹⁰B is useful to assess B uptake and tissue allocation during specific stages of development.