Mass Spectrometry & Purification Techniques
Open Access

Abstract

Boron Isotope Fractionation in Bell Pepper

Sonja Geilert, Jochen Vogl, Martin Rosner, Susanne Voerkelius and Thomas Eichert

Various plant compartments of a single bell pepper plant were studied to verify the variability of boron isotope composition in plants and to identify possible intra-plant isotope fractionation. Boron mass fractions varied from 9.8 mg/kg in the fruits to 70.0 mg/kg in the leaves. Boron (B) isotope ratios reported as ?11B ranged from -11.0? to +16.0? (U ? 1.9?, k=2) and showed a distinct trend to heavier ?11B values the higher the plant compartments were located in the plant. A fractionation of ?11Bleaf-roots = 27? existed in the studied bell pepper plant, which represents about about 1/3 of the overall natural boron isotope variation (ca. 80?). Two simultaneous operating processes are a possible explanation for the observed systematic intra-plant ?11B variation: 1) B is fixed in cell walls in its tetrahedral form (borate), which preferentially incorporates the light B isotope and the remaining xylem sap gets enriched in the heavy B isotope and 2) certain transporter preferentially transport the trigonal 11B-enriched boric acid molecule and thereby the heavy 11B towards young plant compartments which were situated distal of the roots and typically high in the plant. Consequently, an enrichment of the heavy 11B isotope in the upper young plant parts located at the top of the plant could explain the observed isotope systematic. The identification and understanding of the processes generating systematic intra-plant ?11B variations will potentially enable the use of B isotope for plant metabolism studies.