Thesis (PhD (Microbiology))--University of Stellenbosch, 2010. / Dissertation presented for the degree of Doctor of Philosophy
in Microbiology at the University of Stellenbosch. / ENGLISH ABSTRACT: The interaction between a soil yeast, Cryptococcus laurentii and a medicinal plant,
Agathosma betulina (Berg.) Pillans (Rutaceae), was studied. Cryptococcus laurentii CAB
578 was isolated from the rhizosphere of wild A. betulina and liquid chromatographytandem
mass spectrometry analysis revealed that the yeast was capable of producing
polyamines such as cadaverine and spermine. Since the exogenous application of
polyamines are known to impact on root growth, these findings supported the results
obtained when A. betulina seedlings grown under axenic and low nutrient conditions were
inoculated with C. laurentii CAB 578 and cultivated for five months under glasshouse
conditions. The presence of the yeast increased root growth by 51%. Using soil dilution
plates, it was demonstrated that yeast numbers were greater in the vicinity of the roots than
in the bulk soil. Furthermore, fluoromicroscopy, in combination with the fluorescent
probes Calcofluor White and Fungolight revealed the presence of metabolic active yeast
colonies on the rhizoplane. The first part of the study thus provided evidence for a
symbiosis between A. betulina and C. laurentii CAB 578.
During the second part of the investigation, the effect of this symbiosis on quantitative
elemental distribution in A. betulina roots grown under axenic, nutrient-poor conditions
was assessed using micro-particle-induced x-ray emission spectrometry. To aid in the
interpretation of heterogeneous elemental distribution patterns, apoplastic barriers and
endophytic C. laurentii CAB 578 in root tissues were located using fluorescence
microscopy and transmission electron microscopy, respectively. The results showed that
the average concentrations of iron, manganese and phosphorus were significantly (P <
0.05) higher within roots of yeast-inoculated plants, compared to control plants. It was
shown that the yeast was not a root endophyte and that elemental enrichment in the
epi/exodermal-outer cortical tissues correlated with the presence of Casparian bands in the
exodermal cells of both treatments. This was the first report describing the role of a soil
yeast as a plant nutrient-scavenging microsymbiont.
In the final part of the investigation, the effect of C. laurentii CAB 578 on the
photosynthetic nitrogen, phosphorus and water-use efficiencies, as well as the carbon
economy of A. betulina was studied. Agathosma betulina plants inoculated with
C. laurentii CAB 578, as well as controls, were grown under axenic conditions and the
following parameters measured: Apparent photon yield, foliar nitrogen and phosphorus
concentrations, leaf dark respiration, maximum photosynthetic rate, photosynthetic
nitrogen-use efficiency, photosynthetic phosphorus-use efficiency, photosynthetic wateruse
efficiency, root construction cost, stomatal conductance, substomatal CO2 and
transpiration rate. The data showed that the higher photosynthetic resource-use
efficiencies in yeast-inoculated plants were a consequence of higher maximum rates of
CO2 assimilation, which was not related to foliar nitrogen and phosphorus content. We
hypothesize that photosynthetic stimulation in yeast-inoculated plants was a result of the
increased demand for photosynthates of the yeast-root symbiosis. In summary, the study
revealed that a symbiosis exists between A. betulina and the soil yeast C. laurentii CAB
578. This interaction has a significant effect on the size of the yeast population as well as
on the physiology of the plant. / AFRIKAANSE OPSOMMING: Die interaksie tussen ‘n grondgis, Cryptococcus laurentii, en ‘n medisinale plant,
Agathosma betulina (Berg.) Pillans, is ondersoek. Cryptococcus laurentii CAB 578 is
vanuit die risosfeer van A. betulina in sy natuurlike omgewing geisoleer en vloeistof
chromatografie tandem massa spektrofotometriese analise het bewys dat die gis poliamiene
insluitend kadaverien en spermien produseer. Dit is bevind dat die eksogene
aanwending van poli-amiene wortelgroei bevorder. Hierdie bevinding staaf die
waargenome 51% verhoging in wortelgroei van mikroob-vrye A. betulina saailinge
geinokuleer met C. laurentii CAB 578 en gekweek vir vyf maande onder lae nutriënt
kondisies in ‘n glashuis. Met gebruik van die grond verdunningsplaat-metode, is dit
verder bewys dat gisgetalle hoër was in die teenwoordigheid van wortels as in die
omliggende grond. Dit is ook bewys met die gebruik van die fluoressente peilers
Calcofluor White en Fungolight, in kombinasie met fluoressensie-mikroskopie, dat
metabolies aktiewe giste die wortels se oppervlak gekoloniseer het. Die eerste deel van
die studie het dus bewys dat ‘n simbiose tussen A. betulina en C. laurentii CAB 578
bestaan.
Tydens die tweede deel van die ondersoek is die effek van C. laurentii CAB 578 op
die konsentrasie en verspreiding van elemente binne A. betulina wortels, gekweek onder
lae-nutriënt, mikroob-vrye kondisies, bepaal met behulp van mikro-partikel geinduseerde
X-straal emissie spektrofotometrie. Om die interpretasie van heterogene verspreidingspatrone
van die onderskeie elemente te ondersteun, is daar met behulp van fluoressensie en
transmissie-elektron-mikroskopie vir apoplastiese versperrings en endofitiese C. laurentii
CAB 578 in die wortelweefsel getoets. Dit is bevind dat die gemiddelde konsentrasie van
fosfaat, mangaan en yster beduidend (P < 0.05) hoër was in gis-geinokuleerde plante, as in
kontrole plante. Die gis was nie ‘n wortel endofiet nie en elementale verryking in die
epi/eksodermale-buitenste korteks weefsels het gekorreleer met Casparian bande in die
eksodermale selle van beide behandelings. Hierdie was die eerste verslag wat die rol van
‘n grondgis as ‘n nutriënt-bekommende mikrosimbiont vir plante beskryf het.
In die laaste gedeelte van hierdie ondersoek is die effek van C. laurentii CAB 578 op
die fotosintetiese fosfaat, stikstof en water-verbruiksdoeltreffendheid, asook die koolstof
ekonomie in mikroob-vrye Agathosma betulina plante geinokuleer met C. laurentii CAB
578 asook kontrole plante bestudeer. Die volgende parameters is getoets: Blaar donker
respirasie, blaar fosfaat en stikstof konsentrasies, fotosintetiese fosfaatverbruiksdoeltreffendheid,
fotosintetiese stikstof-verbruiksdoeltreffendheid, fotosintetiese
water-verbruiksdoeltreffendheid, huidmond konduktansie, huidmond CO2 konsentrasie,
klaarblyklike foton opbrengs, maksimum fotosintetiese spoed, wortel konstruksie-koste, en
transpirasie spoed. Die resultate het getoon dat die hoër maksimum fotosintestiese spoed
in gis-geinokuleerde plante gelei het tot ‘n hoër fotosintetiese verbruiksdoeltreffendheid
van fosfaat, stikstof en water en dat dit nie verband gehou het met blaar fosfaat en stikstof
konsentrasies nie. Dit word voorgestel dat die stimulasie van fotosintese in gisgeinokuleerde
plante ‘n gevolg is van die verhoogde aanvraag na fotosintaat deur die giswortel
simbiose. Om op te som, die bevindings van hierdie studie het bewys dat ‘n
simbiose tussen A. betulina en C. laurentii CAB 578 bestaan. Hierdie simbiose het ‘n
beduidende effek op die populasie grootte van die gis sowel as die fisiologie van die plant.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5467 |
| Date | 12 1900 |
| Creators | Cloete, Karen Jacqueline |
| Contributors | Botha, Alfred, Valentine, Alexander J., Przybylowicz, Wojchiech J., Mesjasz-Przybylowicz, Jolanta, University of Stellenbosch. Faculty of Science. Dept. of Microbiology |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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