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    A molecular analysis of flowering in Metrosideros : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology at Massey University, Palmerston North, New Zealand
    (Massey University, 2005) Jury, Alexa
    A calendar of floral and vegetative developmental events has been previously determined for the woody perennial Metrosideros excelsa. M. excelsa flowers just once a year in summer and bud development has been related to seasonality and gene expression. M. collina cv. Tahiti is closely related to M. excelsa but appeared to flower sporadically through out the year. Using histology, the bud development of M. collina has been analysed and a developmental sequence determined. Periodicity of bud development has also been observed by obtaining bud measurements. While it is difficult to relate bud size to developmental phase or determine whether the bud is vegetative or floral, it appears that M. collina goes through two periods of bud development in one year and that flowering may be related to warm temperature. The genetic interactions between pathways controlling floral meristem development have been analysed in the herbaceous annual model plant Arabidopsis thaliana. In Arabidopsis, expression of the floral meristem identity gene, LEAFY (LFY), is regulated directly by the florally promotive gibberellin and photoperiodic pathways. LFY expression in Arabidopsis was upregulated in response to gibberellin application, which hastened the transition from vegetative to floral meristem. Another floral meristem identity gene, APETALA1 (AP1) is upregulated by LFY to promote formation of the floral meristem. However, exogenous application of gibberellic acid (GA3 ) to woody perennial trees, including M. collina, inhibits flowering. Due to the differences between Arabidopsis and woody perennial species, it is important to determine if the Arabidopsis model is a useful tool to analyse flowering in Metrosideros species. LFY and AP1 homologues were isolated previously from M. excelsa, and from M. collina in this project. The responsiveness of MEL (M. excelsa LFY-like) and MESAPI (M. excelsa AP1-like) and MCL (M. collina LFY-like) and MTAP1 (M. collina AP1-like) to GA3 , and other growth regulators and hormones was examined in juvenile and adult Metrosideros. MEL or MCL expression was not detected in juvenile or adult GA3 -treated Metrosideros, which supports GA3 inhibition of flowering in perennials. It appears that the gibberellin component of the Arabidopsis model does not represent appropriately, the response of perennial woody species to gibberellins in terms of flowering.
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    Phase change, flowering and postharvest characteristics of Metrosideros excelsa (Myrtaceae) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Biology at the Institute of Molecular BioSciences, Massey University, Palmerston North, New Zealand
    (Massey University, 2001) Henriod, Robert E.
    The development of Metrosideros excelsa (pohutukawa) as an ornamental crop has been limited by a lack of knowledge on the cultural requirements and underlying physiological processes associated with: (a) vegetative phase change (maturation) following micropropagation, (b) the environmental control of flowering, and (c) the postharvest characteristics of the cut-flower. These three concerns were addressed in this thesis. First, plantlets of M. excelsa that had undergone rejuvenation following micropropagation, were subjected to shoot and root restriction treatments to accelerate vegetative phase change. Leaves of shoot-restricted, single-stemmed plants became progressively more adult with increasing node position, whereas root restriction reduced root growth but did not accelerate vegetative phase change. In single-stemmed plants, light saturated maximum rate of photosynthesis and leaf carbon isotope discrimination decreased within increasing node position. However, carbon isotope composition in leaves of these plants diverged away from those exhibited by leaves of adult plants, possibly reflecting physiological changes resulting from altered source/sink relations. Second, the effects of photoperiod, temperature and irradiance on floral initiation and development were examined in M. excelsa by manipulating these parameters in controlled and greenhouse environments. M. excelsa responded as a facultative short-day plant with maximum flowering occurring following a 15 weeks cool (mean 15° C) short-day (10 h) inductive treatment. An irradiance of 567 µmol m-2 s-1 during induction provided the optimal conditions for floral primordial growth and subsequent flower development. Buds initially 2.0-3.0 mm in diameter had the highest probability of becoming floral, whilst those less than 2.0 mm in diameter were more likely to remain vegetative or to not break. Finally, the postharvest characteristics of M. excelsa as a cut flower were assessed. Generally, holding solution treatments containing sucrose extended vase life, whereas those containing HQC (applied alone or as a pulse) were detrimental. Cut flowers were sensitive to exogenous ethylene and pre-treatment with inhibitors of ethylene action (STS and 1-MCP) conferred significant protection. This thesis has contributed significantly to furthering our understanding and knowledge of cultural and physiological factors that underlie vegetative phase change, flowering and vase life characteristics in flowers of M. excelsa.
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    Quantitative markers of phase change, and modelling the size and complexity of trees : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Biology at the Institute of Molecular BioSciences, Massey University, Palmerston North, New Zealand
    (Massey University, 2001) Sismilich, Miloš
    Quantitative markers of ontogenetic phase change were sought to track the restoration of the adult state in plants of Metrosideros excelsa (pohutukawa) that had been rejuvenated by micropropagation (plantlets). The potential markers of leaf carbon isotope discrimination and tree architecture were examined in association with leaf morphology for plantlets, and juvenile and adult plants at a range of temperatures (32/24, 24/16 and 16/8 ଌ day/night). Changes in leaf morphology of plantlets and juvenile plants that were indicative of vegetative phase change were associated with a decrease in carbon isotope discrimination. Phase change, judged by these two markers, occurred most rapidly at 24/16 ଌ and in plantlets faster than in juvenile plants. Adult plants showed long-term stability. It was hypothesised that phase change could be quantified by changes in plant growth rate, expressed through canopy topological size and complexity parameters. A model of tree architecture (the Metrosideros Model) was developed that would allow tree size and 2D structural complexity to be recorded and analysed quantitatively. A further hypothesis was that juvenile plants and plantlets must attain a certain size and/or structural complexity before passing to the adult state and this was evaluated using the Metrosideros Model. Dynamics of growth and structural change were examined using both non-linear and linear analyses. The Metrosideros Model was successfully tested, confirming the hypothesis of quantitative differences between juvenile plants, plantlets and adult plants in structural complexity and branching patterns. The model was able to separate parameters of plant size from those of structural complexity. Complexity was indicative of ontogenetic state, and tracked the progress of phase change in juvenile plants and plantlets independently of temperature. Adult plant parameters of structural complexity, as δ13C, also remained stable at all temperatures. On the other hand, the growth rate of size parameters was not associated with phase change, but was responsive to temperature. It was concluded that while leaf morphology, carbon isotope discrimination and crown architecture can be used to track phase change, each relates to a program of change that might occur largely independently of others. Crown architecture was less affected by temperature than were leaf characteristics, and was, therefore, the most reliable marker of phase change of those studied.
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    Morphological, physiological, and molecular studies on the effect of shoot architecture on phase change and floral transition in Eucalyptus occidentalis and Metrosideros excelsa : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Biology at Massey University, Palmerston North, New Zealand
    (Massey University, 2007) Jaya, Elizabeth S.K.D.
    Shoot morphogenesis in Eucalyptus occidentalis and Metrosideros excelsa was analysed at the morphological, physiological and molecular levels to understand the regulation of phase change and the floral transition. Study of the regulation of these developmental plant processes is limited in woody species due to their long juvenile phase. Six ecotypes of E. occidentalis were grown to two predetermined architectures (free branching or single stem). Free branching plants of ecotype 13648 displayed adult shoot phenology (lanceolate leaves) earlier than single stem counterparts. In addition, changes in leaf morphology in free branching plants were accompanied with changes in leaf anatomy and gas exchange signifying that in E. occidentalis complexity of shoot architecture had a significant effect on rate of phase change. Flowering was observed in all but one ecotype irrespective of architecture demonstrating that vegetative phase change and floral transition are temporally uncoupled in this species. To understand the floral transition at the molecular level in E. occidentalis, partial homologues of the inflorescence meristem identity gene TERMINAL FLOWER1 and floral meristem identity genes LEAFY and APETALA1 were isolated. The expression patterns of these meristem identity genes during development of free branching and single stem plants were analysed by quantitative real-time PCR. Increased levels of expression of EOLFY and EOAP 1 (relative to α -TUBULIN) were displayed at more proximal nodes in free branching plants than in single stem plants. Elevated floral meristem identity gene expression levels correlated with flower initiation. Further, effects of architecture and environment on gene expression were monitored in E. occidentalis. The overriding effect of shoot architecture on the floral transition was observed under warm long day and ambient environments. Elevated levels of EOLFY and EOAP 1 were correlated with floral bud score and EOAP1 was found to be a reliable marker of floral transition in E. occidentalis. Low levels of EOTFLI expression were detected in buds irrespective of their position on the plant leading to the suggestion that this might have contributed to the precocious flowering observed in this species. In contrast to E. occidentalis, M excelsa attained adult shoot phenology (pubescent leaves) faster when grown as single stem plants than as free branching plants. It appears that growth as height is required for vegetative phase change in this species. However, floral transition occurred only once single stem plants were allowed to branch. Vegetative phase change and the transition to flowering seem to be coordinated in this species with the former being a pre-requisite for the latter.