ARS | Publication request: BORON-ISOTOPE FRACTIONATION IN PLANTS

Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 1997
Publication Date: N/A

Interpretive Summary: All mineral elements are composed of one or more naturally occurring isotopes and radioactive isotopes can be prepared for most elements. Both stable and radioactive isotopes play critical roles in human nutrition studies. The element boron has two stable isotopes, but no radioactive isotopes. Because boron might have a function in human nutrition, we have e been developing the techniques for using the stable isotopes of boron in nutrition studies. Isotope fractionation is observed in plants and animals for isotopes such as carbon, nitrogen, and oxygen. For example, a plant will contain more carbon-12 than carbon-13. To conduct a stable isotope experiment with carbon, a correction must be made for fractionation. Fractionation is also a concern for boron. We have raised broccoli, corn, and wheat in hydroponic solutions and measured the isotopes of boron in various tissues. We have discovered that in all three plants, boron fractionation has occurred; there is more boron than expected with an atomic weight of 11 than with an atomic weight of 10 in plants. This implies that future plant experiments with boron isotopes will need to correct for naturally occurring fractionation. This work also suggests that boron fractionation in animals must be investigated before further animal studies are conducted.

Technical Abstract: Naturally-occurring variations in the abundance of stable isotopes of carbon, nitrogen, oxygen, and other elements in plants have been reported and are now used to understand various physiological processes in plants and animals. Boron (B) isotopic variation in several plant species has been documented, but no determination as to whether plants fractionate the e stable isotopes of boron, B-11 and B-10, has been made. Here, we report that plants with differing boron requirements (wheat, corn, and broccoli) fractionate boron. With respect to the nutrient solution, the whole plant is enriched in B-11, and with respect to the xylem sap, the leaves are enriched in B-10 and the stem in B-11. Although, at present, a mechanistic role for boron in plants is uncertain, potential fractionating mechanisms are discussed.