Selenium hyperaccumulation by Astragalus (Fabaceae) does not inhibit root nodule symbiosis

Am J Bot. 2012 Dec;99(12):1930-41. doi: 10.3732/ajb.1200124. Epub 2012 Nov 30.

Abstract

Premise of study: A survey of the root-nodule symbiosis in Astragalus and its interaction with selenium (Se) has not been conducted before. Such studies can provide insight into how edaphic conditions modify symbiotic interactions and influence partner coevolution. In this paper plant-organ Se concentration ([Se]) was investigated to assess potential Se exposure to endophytes. •

Methods: Selenium distribution and molecular speciation of root nodules from Se-hyperaccumulators Astragalus bisulcatus, A. praelongus, and A. racemosus was determined by Se K-edge x-ray absorption spectroscopy. A series of greenhouse experiments were conducted to characterize the response of root-nodule symbiosis in Se-hyperaccumulators and nonhyperaccumulators. •

Key results: Nodules in three Se-hyperaccumulators (Astragalus crotalariae, A. praelongus, and A. preussii) are reported for the first time. Leaves, flowers, and fruits from Se-hyperaccumulators were routinely above the hyperaccumulator threshold (1,000 µg Se g(-1) DW), but root samples rarely contained that amount, and nodules never exceeded 110 µg Se g(-1) DW. Nodules from A. bisulcatus, A. praelongus, and A. racemosus had Se throughout, with a majority stored in C-Se-C form. Finally, an evaluation of nodulation in Se-hyperaccumulators and nonhyperaccumulators indicated that there was no nodulation inhibition because of plant Se tolerance. Rather, we found that in Se-hyperaccumulators higher levels of Se treatment (up to 100 µM Se) corresponded with higher nodule counts, indicating a potential role for dinitrogen fixation in Se-hyperaccumulation. The effect was not found in nonhyperaccumulators. •

Conclusions: As the evolution of Se hyperaccumulation in Astragalus developed, root-nodule symbiosis may have played an integral role.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Arizona
  • Astragalus Plant / drug effects
  • Astragalus Plant / growth & development
  • Astragalus Plant / microbiology
  • Astragalus Plant / physiology*
  • Bacteria / drug effects
  • Bacteria / metabolism
  • Colorado
  • Endophytes / drug effects
  • Endophytes / metabolism
  • Fabaceae / drug effects
  • Fabaceae / growth & development
  • Fabaceae / microbiology
  • Fabaceae / physiology
  • Nitrogen Fixation / drug effects
  • Plant Roots / drug effects
  • Plant Roots / metabolism
  • Plant Roots / microbiology
  • Selenium / pharmacology*
  • Soil / chemistry*
  • Species Specificity
  • Symbiosis / drug effects*
  • Washington
  • X-Ray Absorption Spectroscopy

Substances

  • Soil
  • Selenium