Browsing by Author "Smart, Mariette"
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- ItemPhysiology of floral induction in Protea spp(Stellenbosch : Stellenbosch University, 2005-04) Smart, Mariette; Cramer, M. D.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.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.