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

Abstract

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 crosssections 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.

The role of Cryptococcus laurentii and mycorrhizal fungi in the nutritional physiology of Lupinus angustifolius L. hosting N2-fixing nodules

“…In addition, the high root RGR and increased BGA observed for these plants indicate that C. laurentii CAB 91 stimulated root growth of blue lupin. This concurs with the work of Cloete et al (2009) where it was found that another C. laurentii strain could improve root growth of buchu, which was attributed to the ability of the yeast to act as a nutrient scavenging symbiont of its host (Cloete et al 2010). It was speculated that this yeast increased the plant's P concentration by accumulating short chain inorganic polyphosphates.…”

“…Therefore, it was not surprising that representatives of C. friedmannii and C. laurentii were isolated from the rhizosphere of free-growing blue lupin during this study. Since some C. laurentii strains are able to improve growth of leguminous (Sampedro et al 2004;Boby et al 2008) and non-leguminous (Cloete et al 2009;Cloete et al 2010) plants, it seemed likely that C. laurentii CAB 91 may act as a PGPY of blue lupin. Therefore, this yeast strain was used during experimentation in the present study and assessed for two plant growth promoting traits.…”

“…However, when mycorrhizal fungi are absent other microorganisms, such as yeasts, may aid plant survival (Botha 2011). These unicellular fungi are known to benefit growth of various plants (Vassileva et al 2000;Vassilev et al 2001;Medina et al 2004a;Medina et al 2004b;Nassar et al 2005;El-Tarabily and Sivasithamparam 2006;Cloete et al 2009;Azcon et al 2010;Cloete et al 2010;Souchie et al 2010;Amprayn et al, 2012;Azzam et al 2012;Morsy et al 2014;Mukherjee and Sen 2014;Morsy 2015) and some soil yeasts may also act as P-acquiring symbionts of plants. For example, it was shown that the plant growth promoting yeast (PGPY) Cryptococcus laurentii increased the root P concentration of a plant occurring in the nutrient poor Fynbos ecosystem, i.e.…”

“…buchu (Agathosma betulina (Berg.) Pillans) (Cloete et al 2010). Similarly, it was demonstrated that the rock-phosphate solubilizing yeast Yarrowia lipolytica (Vassileva et al 2000) enhances growth of the shrub, prostrate canary clover (Dorycnium pentaphyllum Scop.…”

Yeasts Biodiversity and Its Significance: Case Studies in Natural and Human-Related Environments, Ex Situ Preservation, Applications and Challenges

“…Results from inoculation experiments showed an effect of the spore-associated yeasts on the root growth of rice, suggesting potential tripartite interactions with mycorrhizal fungi and plants (Alonso et al 2008). Cloete et al (2010) studied the role of rhizosphere yeasts as plant nutrient-scavenging microsymbionts in roots of a medicinal sclerophyll, Agathosma betulina, grown under nutrient-poor conditions, and colonized by Cryptococcus laurentii. The average concentrations of P, Fe and Mn were significantly higher in roots of yeast-inoculated plants, compared to control plants that received autoclaved yeast.…”