USE OF THE ENRICHED STABLE ISOTOPE ³⁴S TO STUDY SULPHUR UPTAKE AND DISTRIBUTION IN WHEAT

Abstract

Elemental sulfur (S) highly enriched in the stable isotope ³⁴S (90 atom %) was converted quantitatively to sulfate and used as a tracer to investigate S uptake and distribution in wheat (Triticum aestivum L. cv. Axona). The ³⁴S label was fed to wheat for 24 h at different growth stages in hydroponic culture. The ³⁴S abundance in plant samples was determined using a continuous flow elemental analyzer coupled with an isotope ratio mass spectrometer. The unlabeled plant tissues showed very similar S isotope composition to the S source used in the nutrient solution, whereas labeled plants contained 0.43–18.88 atom % excess ³⁴S over the background. Total amounts of the ³⁴S label in the whole plants did not differ significantly between those harvested immediately after the labeling period and those harvested at anthesis. Stems and roots were the main contributors of the ³⁴S label to ears up to the anthesis stage. This study shows that highly enriched ³⁴S can be reliably used in plant nutrition studies.

ACKNOWLEDGMENT

IACR-Rothamsted receives grant-aided support from the Biotechnology and Biological Sciences Research Council of the United Kingdom.

Notes

^*Natural abundance of ³⁴S is normally expressed on the δ³⁴S (‰) scale: δ³⁴S (‰) = [(R _sample – R _standard)/R _standard] × 1000, where R refers to ³⁴S/³²S and R _standard has the value of 0.0450045. Atom % ³⁴S and δ³⁴S (‰) can be inter-converted using the above and following equations: Atom % ³⁴S=[R _sample/(R _ssample + 1)] × 100.