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Subject: search.filters.subject.Abscisic acid (ABA)

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    Evaluation of the efficacy of the inducible over-expression of 9-cis-epoxycarotenoid dioxygenase1 (NCED1) to confer improved water use efficiency in transgenic plants : 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, 2013) Sixtus, Caleb D.
    In order to trial the concept of inducible overproduction of the plant hormone abscisic acid (ABA) to confer increased water use efficiency, the forage legume Trifolium repens (L.) (white clover) and the model plant species Nicotiana tabaccum (L.) (tobacco) were transformed with the construct 9-cis-epoxycarotenoid dioxgenase 1 (NCED1) gene from Solanum lycopersicon (SlNCED1) driven by the RUBISCO small subunit promoter (SSUp). For white clover, a total of 18 putatively genetically-independent transgenic lines were obtained through selection in tissue culture, and these were further cloned by vegetative propagation to give 56 plants in total. Ten of these tested positive for NCED1 insertion using polymerase chain reaction (PCR) with genomic DNA. Establishment of transgenic clover on soil was problematic, but seven putatively transformed lines were established. Of these, only one line potentially expressed SlNCED1, but the transcriptional levels were too low, as determined by semi-quantitative reverse-transcriptase dependent PCR (sqRT-PCR), for any further analysis. This low expression, and the fact that only one line was identified, led to the decision to discontinue investigations with white clover. In parallel, the more amenable tobacco transformation system was also used with the SlSSUp::NCED1 construct to act as proof-of-concept. Fourteen putatively genetically independent transgenic lines of tobacco were obtained through tissue culture, six of which were successfully established onto soil. A range of integrated gene copy numbers and NCED1 expression levels were identified in the To lines using genomic PCR and sqRT-PCR. Self-fertilised seed was collected from each transgenic line, but the germination rate from all of the transgenic lines was significantly lower than wild-type. Those lines that did germinate often displayed a range of aberrant growth phenotypes. After trialing methods to evaluate water use efficiency, a total of 47 T1 seedlings displaying a normal seedling phenotype were established on soil. A range of water use efficiencies were observed as determined by analysis of plant growth rates against water use, followed by a transpiration assay of plants deemed „efficient‟ and „poor‟ users of available water. No correlation of SlNCED1 expression with the more efficient users of available water was observed, and so ultimately it was concluded that the transgene was ineffective at raising the water use efficiency of tobacco as determined by the parameters measured in thesis.
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    Horticultural and physiological aspects of vigour control in apricot (Prunus armeniaca L.) under orchard and controlled environment conditions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (Ph.D) in Pomology and Fruit Tree Physiology at Massey University New Zealand
    (Massey University, 1994) Arzani, Kazem
    In the absence of dwarfing rootstocks for apricot, techniques which reduce vegetative growth are important in the orchard management system. Studies were conducted in the orchard and in controlled environment (CE) rooms in order to explore the horticultural and physiological responses of apricot (Prunus armeniaca L.) to some vigour control techniques. In the orchard in the humid climate of Palmerston North, New Zealand, five-year-old vigorous 'Sundrop' apricot trees on 'Golden Queen' peach seedlings trained on Tatura trellis at 1000 or 2000 tree ha-1 were used. The objectives were: a). to evaluate the trees' responses to 0.5 and 1.5 g. tree-1 soil applied Paclobutrazol (PBZ), dormant root-pruning and regulated deficit irrigation (RDI); b). to identify osmotic adjustment in fruits and leaves in response to internal water stress. Two-year-old 'Trevatt' apricot in an aeroponic system in CE rooms were used with the objectives: a). to examine the effects of root cytokinin and endogenous ABA on shoot growth and whole plant physiology; b). to study the mechanism of adaptation to high water stress. In the orchard all treatments reduced vegetative growth. PBZ was more effective than the other treatments, and the lower rate (0.5 g. tree-1) when applied annually gave more uniform growth reduction. The root-pruning and RDI had less effect, particularly in the second season of study. The deep soil, together with low temperature and evaporation, high rainfall and humid conditions during winter and early spring were limiting factors for RDI. The inhibitory effect of root-pruning was more persistent on wider spaced trees. In close planted trees root length density (RLD) declined with increasing depth, but roots were observed to 1.6 m explored soil depth. Root-pruning increased RLD, but no treatments effect was observed on root weight density (RWD) in the explored soil volume. PBZ increased dry matter partitioning into crop in both seasons on close spaced trees, and fruit growth and final fruit size were increased without any detrimental effect on fruit quality. In the second year PBZ advanced flowering by 2-4 days, and increased fruit set, final fruit number, crop density and yield efficiency. In general RDI had no negative effects on flowering, fruiting, yield and final fruit size. In the second year it generally enhanced flowering, fruit set and fruit number. Root-pruning did not affect other flowering and yield parameters, but reduced fruit size in the first season. There was some evidence of advanced fruit maturity and increased total soluble solids by all applied treatments. Generally fruiting characteristics were improved, and vegetative growth reduced, more by PBZ than by root-pruning and RDI. PBZ treated trees had the same water status as controls. Their net CO2 assimilation rate (A) and stomatal conductance (gs) were improved, and from later stage I and during stages II and III of fruit growth fruit carbohydrates were increased. RDI and root-pruning increased net CO2 assimilation rate (A) and stomatal conductance (gs) on some occasions. Root-pruned trees developed an increased internal water deficit in the leaves and fruits especially at the time of highest water demand during fruit stage III. There was evidence on occasions in RDI and root-pruning of osmotic adjustment in leaves and fruits maintaining turgor (ψp). An aeroponic system with intermittent misting gave good control of plant water stress. When water stress was developed gradually plants were able to maintain their turgor at high internal water deficit (-2.2 and -3.0 MPa of ψxylem and ψ1 respectively). Osmotic adjustment occurred in both partially and fully expanded leaves of all treatments, BAP combined with water stress showed bigger osmotic adjustment. Water stress reduced vegetative growth, and increased root:shoot ratio. Shoot tip ABA increased as water stress increased. BAP reduced the growth inhibition and rise in shoot ABA of water stressed plants, maintained net CO2 assimilation rate (A) and stomatal conductance (gs), and increased root:shoot ratio.