Micro-particle-induced X-ray emission mapping of elemental distribution in roots of a Mediterranean-type sclerophyll, Agathosma betulina (Berg.) Pillans, colonized by Cryptococcus laurentii

• Published in: Plant, cell and environment cell and environment, 2010-06, Vol.33 (6), p.1005-1015
• Main Authors: CLOETE, KAREN J, PRZYBYLOWICZ, WOJCIECH J, MESJASZ-PRZYBYLOWICZ, JOLANTA, BARNABAS, ALBAN D, VALENTINE, ALEXANDER J, BOTHA, ALFRED
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Casparian bands; Colony Count, Microbial; Cryptococcus - growth & development; Cryptococcus laurentii; elemental imaging; Elements; Fundamental and applied biological sciences. Psychology; Mediterranean Region; micro-PIXE; Microscopy; mineral nutrients; nuclear microprobe; Plant Roots - cytology; Plant Roots - metabolism; Plant Roots - microbiology; Rutaceae - cytology; Rutaceae - microbiology; soil yeast; Spectrometry, X-Ray Emission; X-ray microanalysis
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/j.1365-3040.2010.02122.x

The role of rhizosphere yeasts as plant nutrient-scavenging microsymbionts in resource-limited Mediterranean-type heathlands is unknown. This study, therefore, focused on quantitative elemental distribution within the roots of a medicinal sclerophyll, Agathosma betulina (Berg.) Pillans, grown under nutrient-poor conditions, and colonized by Cryptococcus laurentii. Micro-particle-induced X-ray emission (PIXE) was used to assess quantitative elemental distribution within the roots of A. betulina inoculated with viable C. laurentii, as well as within roots of control plants that received autoclaved yeast. To aid in the interpretation of heterogeneous elemental distribution patterns, apoplastic barriers (Casparian bands) in root tissues were located using fluorescence microscopy. In addition, root cross-sections were examined for endophytic C. laurentii using light and transmission electron microscopy (TEM). The average concentrations of P, Fe and Mn were significantly (P < 0.05) higher in roots of yeast-inoculated plants, compared to control plants. Casparian bands were observed in the exodermal cells of both treatments, and the presence of these bands was correlated with elemental enrichment in the epi/exodermal-outer cortical tissues. Light and TEM micrographs revealed that the yeast was not a root endophyte. This is the first report describing the role of a soil yeast as a plant nutrient-scavenging microsymbiont.