Absorption and distribution of boron in Arabidopsis thaliana

Abstract

We investigated the absorption and distribution of boron (B) by tracer experiments in Arabidopsis thaliana, a model plant for molecular genetic studies. Plants were grown hydroponically in the presence of B at 12, 30 and 100µM (¹⁰B/¹¹B = 19.9/80.1 atom%) for 4 weeks. Then, they were transferred to solutions containing 30µM of ¹⁰B enriched boric acid (¹⁰B/¹¹ B = 95.9/4.1 atom%) and incubated for 48 hours (pulse labeling). Old rosette leaves (leaves 1–4), young rosette leaves (leaves 5–10) and shoot apices were harvested before and after the labeling. The ¹⁰B and ¹¹B contents were determined by inductively coupled plasma mass spectrometry (ICP-MS).

Regardless of the levels of B supply, the B concentration was lower at the top of the shoot than the bottom. The ratio of B concentration in shoot apices to that in old leaves increased as B supply became restricted, suggesting that B translocation is regulated not only by transpiration stream but also by other mechanisms. Percent boron derived from tracer (%BDFT) ranged from 48.0 to 57.2% and from 6.8 to 14.9% in shoot apices and in old leaves, respectively. The amounts of B contained in shoot apices before the labeling were estimated to be 31.6 to 39.6% of those after the labeling, suggesting that most of the increase in B amount during the period of the labeling can be explained by tracer derived B.

These findings suggest that translocation and distribution of B in A. thaliana do not contradict to general patterns of B distribution in higher plants. Thus molecular genetic studies on B nutrition using A. thaliana are likely to provide us with further understanding of B functions in higher plants.

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