Characterisation of the metacaspase gene family in Arabidopsis thaliana

Caspases are known to be involved in animal programmed cell death (PCD). The objective of this thesis was to use gene expression analysis and reverse genetics to determine if Arabidopsis metacaspase (AtMC) genes play a role in plant PCD. The majority of AtMC genes were found to be expressed nearly constitutively in various tissues, developmental stages, and under various inductive treatments. Transgenic Arabidopsis plants generated with AtMCpromoter::AtMCgene::GUS fusions showed expression of the reporter gene in leaves, vasculature, trichomes, siliques, anthers, and during embryo development. Preliminary phenotypic characterization of single and double Arabidopsis AtMC loss-of-function mutants suggested that the expression of the AtMC genes are highly functionally redundant. Nevertheless, our results suggest that AtMC1, 2, 4, 6 and 9 may be directly involved in rosette and/or stem development. Although this study does not provide a definitive role of MCs in plant PCD, it lays the foundation for their further in-depth analysis.

Evolutionary demography of long-lived monocarpic perennials: a time-lagged integral projection model

1. The evolution of flowering strategies (when and at what size to flower) in monocarpic perennials is determined by balancing current reproduction with expected future reproduction, and these are largely determined by size-specific patterns of growth and survival. However, because of the difficulty in following long-lived individuals throughout their lives, this theory has largely been tested using short-lived species (< 5 years). 2. Here, we tested this theory using the long-lived monocarpic perennial Campanula thyrsoides which can live up to 16 years. We used a novel approach that combined permanent plot and herb chronology data from a 3-year field study to parameterize and validate integral projection models (IPMs). 3. Similar to other monocarpic species, the rosette leaves of C. thyrsoides wither over winter and so size cannot be measured in the year of flowering. We therefore extended the existing IPM framework to incorporate an additional time delay that arises because flowering demography must be predicted from rosette size in the year before flowering. 4. We found that all main demographic functions (growth, survival probability, flowering probability and fecundity) were strongly size-dependent and there was a pronounced threshold size of flowering. There was good agreement between the predicted distribution of flowering ages obtained from the IPMs and that estimated in the field. Mostly, there was good agreement between the IPM predictions and the direct quantitative field measurements regarding the demographic parameters lambda, R-0 and T. We therefore conclude that the model captures the main demographic features of the field populations. 5. Elasticity analysis indicated that changes in the survival and growth function had the largest effect (c. 80%) on lambda and this was considerably larger than in short-lived monocarps. We found only weak selection pressure operating on the observed flowering strategy which was close to the predicted evolutionary stable strategy. 6. Synthesis. The extended IPM accurately described the demography of a long-lived monocarpic perennial using data collected over a relatively short period. We could show that the evolution of flowering strategies in short- and long-lived monocarps seem to follow the same general rules but with a longevity-related emphasis on survival over fecundity.

Piriformospora indica and Sebacina vermifera increase growth performance at the expense of herbivore resistance in Nicotiana attenuata

A Sebacinales species was recovered from a clone library made from a pooled rhizosphere sample of Nicotiana attenuata plants from 14 native populations. Axenic cultures of the related species, Piriformospora indica and Sebacina vermifera, were used to examine their effects on plant performance. Inoculation of N. attenuata seeds with either fungus species stimulated seed germination and increased growth and stalk elongation. S. vermifera inoculated plants flowered earlier, produced more flowers and matured more seed capsules than did non-inoculated plants. Jasmonate treatment during rosette-stage growth, which slows growth and elicits herbivore resistance traits, erased differences in vegetative, but not reproductive performance resulting from S. vermifera inoculation. Total nitrogen and phosphorous contents did not differ between inoculated and control plants, suggesting that the performance benefits of fungal inoculation did not result from improvements in nutritional status. Since the expression of trypsin proteinase inhibitors (TPI), defensive proteins which confer resistance to attack from Manduca sexta larvae, incur significant growth and fitness costs for the plant, we examined the effect of S. vermifera inoculation on herbivore resistance and TPI activity. After 10 days of feeding on S. vermifera-inoculated plants, larval mass was 46% higher and TPI activity was 48% lower than that on non-inoculated plants. These results suggest that Sebacina spp. may interfere with defense signaling and allow plants to increase growth rates at the expense of herbivore resistance mediated by TPIs.

Lithothamnion Prolifer Foslie: A Common Non-Geniculate Coralline Alga (Rhodophyta: Corallinaceae) from the Tropical and Subtropical Indo-Pacific

A little-known, but ecologically important non-geniculate coralline, Lithothamnion prolifer, is recorded from a number of tropical Indo-Pacific sites, including Fiji, Australia, Kiribati and Indonesia. The species occurs primarily on vertical walls of caves and overhangs in Fiji and Australia, but was also found as rhodoliths in Kiribati. Lithothamnion prolifer is characterized by the combination of characters which follow. The thallus is extremely glossy, smooth, and rosy coloured. Thalli usually produce complanate protuberances, but protuberances become terete when growing on well lit, horizontal substrata, when unattached, or when growing on loose substrata. Conceptacles occur mainly on the tips of protuberances, and tetra/bisporangial conceptacles are large (to 1300 mu m external diameter, with chambers up to 1100 mu m diameter). The tetra/bisporangial conceptacles are flush or only slightly raised, and often extensive and irregularly shaped (resembling small sori). They lack a raised rim, and have flattened pore plates. The rosette cells surrounding the tetra/bisporangial pore appear somewhat sunken below the surrounding roof cells in SEM, and the cells of filaments lining the pore canals of tetra/bisporangial conceptacles do not differ from the cells of filaments making up the rest of the roof. Old conceptacles persist and become buried in the thallus, and are then usually completely filled in by irregularly arranged calcified cells.