Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The aim of this study was to elucidate the control of flowering in Protea spp. The main factor that
makes studying flowering in this diverse genus so challenging is the fact that most Protea spp. and
their commercial hybrids have very dissimilar flowering times. The carbon input into floral organ
formation and support is expensive as flowers from Protea spp are arranged in a very large
‘flowerhead’ (50 mm by 130 mm for ‘Carnival’) that can take up to two months to develop fully.
Therefore the carbon needed for structural formation, metabolic respiration and the sugar-rich nectar
production make these structures extremely expensive to form and maintain. Protea is a
sclerophyllous, woody perennial shrub with a seasonal flush growth habit. The leathery leaves (source
tissue) produce most of the carbon needed for support and growth of the new leaves, roots and flowers
(sink tissue). In the case of expensive structures, such as the inflorescences, remobilization from stored
reserves, probably from underground storage systems, can be observed for structural development and
maintenance. At all times the flush subtending the apical meristem or florally developing bud provides
the largest proportion of carbon for support of the heterotrophic structures. Protea apical meristems
stay dormant during the winter months, but BA (benzyl adenine, 6-benzylaminopurine) application to
the apical meristem of the Protea hybrid ‘Carnival’ has shown to be effective in the release of
dormancy and subsequently shift flowering two months earlier than the natural harvesting time. BA is
thought to shift source/sink relationships by stimulating the remobilization of carbon to the resting
meristem. Although no direct evidence was found for this in our assay, possible reasons for a weak
assay are discussed. This study combined physiological research with the use of molecular tools. An
homologue of the Arabidopsis thaliana meristem identity gene, LEAFY, was identified in Proteaceae.
PROFL (PROTEA FLORICAULA LEAFY) is expressed in both vegetative and reproductive meristems
as well as leaves. PROFL expression in leaves may have an inhibitory effect on vegetative growth, as
the expression was high at the same time as the expression in the apical meristem increased marking
the transition to reproductive growth. In perennial species such as Protea, the availability of carbon is
thought to be the main factor controlling floral development. Possible mechanisms of control may be
through the direct control of meristem identity genes such as PROFL through sugar signaling. BA did
not have a direct effect on PROFL expression although the expression pattern was one month in
advance when compared to the natural system. PROFL expression seems to be consistent with that
found for other woody perennial species and would therefore be a convenient marker for floral
transition. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om die inisiëring van blomvorming in Protea spp. te ondersoek. Die
verskil in blomtyd tussen Protea spp. en hul kommersieel ontwikkelde hibriede maak die studie van
hierdie genus ‘n groot uitdaging. Die groot hoeveelheid koolstof wat benodig word vir blomvorming in
Protea is hoofsaaklik as gevolg van die grootte (50 mm by 130 mm vir ‘Carnival’) van die blomkop
waarin individuele blomme geranskik is. Hierdie blomkoppe kan tot 2 maande neem om
volwassenheid te bereik. Die koolstof benodig vir strukturele ontwikkeling, metaboliese respirasie en
produksie van suiker-ryke nektar maak die vorming van hierdie structure ongelooflik duur. Protea is
‘n bladhoudende, houtagtige bos met ‘n seisoenale groeipatroon. Die leeragtige blare voorsien die
grootste hoeveelheid koolstof vir die ontwikkelende blare, wortels en blomme. Koolstof vir die
ontwikkeling en ondersteuning van die groot stukture soos die blomkoppe word gedeeltelik deur die
huidige fotosinfaat voorsien en bewyse vir die remobilisasie van gestoorde koolstof, heel waarskynlik
vanaf ondergrondse stukture, is gevind. Die blare van die stemsegment wat die apikale meristeem of
ontwikkelende blom dra, voorsien altyd die grootse hoeveelheid koolhidrate aan die ontwikkelende
struktuur. Die apikale meristeme van Protea bly dormant gedurende die winter maande, maar
applikasie van BA (bensieladenien, 6-bensielaminopurien) aan die apikale meristeme van die Protea
hibried ‘Carnival’ verbreek dormansie en die blomtyd van hierdie gemanipuleerde plante is daarom
twee maande vroeër as die natuurlike oestyd. Daar word gespekuleer dat BA applikasie aan die apikale
meristeem die hoeveelheid koolstof wat na die dormante meristeem gestuur word verhoog wat dan die
dormansie verbreek. Hierdie studie beproef ongelukkig hierdie hipotese swak en redes hiervoor word
bespreek. In hierdie studie word fisiologiese analises met molekulêre studies gekombineer. ‘n
Meristeem identiteits gene wat homologie wys met LEAFY (LFY) in Arabidopsis thaliana
(Arabidopsis), PROFL (PROTEA FLORICAULA LEAFY), is in Proteaceae geïdentifiseer. PROFL
word uitgedruk in reproduktiewe meristeme so wel as die vegetatiewe meristeme en blare. PROFL
uitdrukking in blare mag dalk ‘n inhiberende effek hê op die vorming van nuwe blare, omdat die
uitdrukking hoog was op die selfde tyd as wat blominisiëring plaasgevind het in die apikale meristeem.
Die transisie tot reproduktiewe groei word gekenmerk deur ‘n verhoging in PROFL uitdrukking in die
apikale meristeem. In meerjarige plante soos Protea spp word daar verwag dat die teenwoordigheid
van voldoende koolstof die oorskakeling na reproduktiewe groei inisieer. Dit mag wees deur die
direkte aksie van suikers met gene soos PROFL wat die finale skakel na reproduktiewe groei beheer.
Alhoewel BA applikasie geen direkte effek gehad het op PROFL uitdrukking nie, was die blomtyd met
twee maande vervroeg. PROFL uitdrukking was vergelykbaar met die uitdrukking van LFY homoloë in ander houtagtige, meerjarige plante en kan gebruik word as ‘n merker vir blominisiëring in Protea
spp.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20942 |
| Date | 04 1900 |
| Creators | Smart, Mariette |
| Contributors | Cramer, M.D., Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 73 leaves : ill. |
| Rights | Stellenbosch University |
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