The Ascomycete fungus Magnaporthe oryzae is the causative agent of Rice Blast, and has become the predominant model organism for study of fungal phytopathogens and other appressorium-forming fungi. I identified and attempted to elucidate the function of the six aquaporin genes in the M. oryzae genome. These small membrane channels have been implicated in the transport of water, glycerol, and a variety of other small molecules. We speculated that these functions might be important in the formation of the appressorium – a specialised infection structure that relies on the generation of turgor. The role of these proteins in general fungal biology is poorly understood, and this project endeavoured to correct this gap. A phylogenetic analysis of aquaporins in extant fungi revealed the significant expansion of this gene family in Pezizomycete and Basidiomycete fungi, with up to 17 genes in some species. I characterised the expression pattern of the six identified aquaporins in the M. oryzae genome during pathogenic development and found there to be substantial up-regulation co-incident with appressorial turgor generation. Single knock-outs of each aquaporin gene were fully pathogenic, with normal infection-related development and axenic growth. I speculated that the absence of a strong phenotype may have been caused by functional redundancy, and used qRT-PCR investigate the incidence of transcriptional up-regulation of remaining family members in the knock-out backgrounds. This uncovered a putative reciprocal relationship between two genes MoAQP1 and MoAQP2, suggesting that deletion of one results in up-regulation of the other. I subsequently tested the substrate permeability of this gene pair and found them to be permeable to hydrogen peroxide. However, deletion of one of these genes did not appear to affect the rate of flux of hydrogen peroxide across the plasma membrane. My attempt to characterise the cellular localisation of these proteins using GFP fusions was largely unsuccessful with the exception of a single gene, MoAGP2, which appears to be located on the endoplasmic reticulum.

Plant seeds progress through specific stages during germination, from quiescence in the dry state through water uptake, testa rupture and finally endosperm rupture. The stages of seed germination are fairly well classified but the underlying biochemical and mechanical processes are unknown. The ability to control a seeds progression through the stages of germination has implications on farming efficiency and so the following thesis explores Arabidopsis thaliana and Lepidium sativum seeds during the germination process. A systematic approach to analysing the shape of cells within the radicle (embryonic root tissue) is developed, using confocal imaging, in order to characterise the shape of cells in the different tissues of the radicle. The cell shape approximations are not refined enough to characterise the different cell tissues. With more data, this approach would hope to find the region in which cells alter through the germination process. Change in the activity of cell wall modifying enzymes within the endosperm, that surrounds the emerging embryo, is a key part of the germination process and temporally and spatially defined high resolution transcriptomics data-sets are available to inform models. Through the course of this thesis, biochemical networks are developed, with ordinary and partial differential equation models being constructed and analysed. The models highlight elements for further investigation as well as differences between the two species considered. The mathematical models, along with data from biomechanical experiments on the endosperm, inform discussion on how the cell wall biochemistry of a cell wall alters the cell wall properties. These discussions focus on cell wall permeability, extensibility and the final cell separation event associated with germination. From the considered proteins, polygalacturonase and pectin lyase arise as the only viable candidates to cause the cell separation event with the model framework.

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In the developing endosperm of bread wheat (Triticum aestivum), seed storage proteins are produced on the rough endoplasmic reticulum (ER) and transported to protein bodies, specialised vacuoles for the storage of protein. The important gluten proteins of wheat are transported to the protein bodies they are stored in by two distinct routes. One route consists of vesicles that bud directly off the ER, while the other involves transport through the Golgi (Arcalis et al, 2004). In plants, the RabD clade mediates ER to Golgi vesicle transport (Batoko et al, 2000). Available sequence information for Rab GTPases in Arabidopsis, rice, Brachypodium and bread wheat was compiled and compared in phenetic trees. Partial genetic sequences were assembled using the first draft of the Chinese Spring wheat genome. A suitable candidate gene from the RabD clade (TaRabD2a) was chosen for down-regulation by RNA interference (RNAi) and an RNAi construct was used to transform wheat plants. Using real time PCR, all four available RabD genes were shown to be knocked down in the developing endosperm of transgenic wheat. The transgenic grain was found to produce flour with significantly altered processing properties when measured by farinograph and extensograph. SE-HPLC found that a smaller proportion of HMW-GS and large LMW-GS are incorporated into the glutenin macropolymer in the transgenic dough. Lower protein content but a similar protein profile on SDS-PAGE was seen in the transgenic grain

The formation of lateral roots is an important post-embryonic developmental process that allows plants to adapt to their environment via exploitation of soil mineral resources. New lateral roots initiate as lateral root primordia (LRP) in the pericycle cell layer adjacent to the central vascular tissue in the primary root, and must pass through the outer cell layers of endodermis, cortex and epidermis to emerge as mature roots. A key regulator of emergence is the plant hormone auxin and it has been shown previously that in Arabidopsis the auxin induced expression of the auxin influx carrier LAX3 in specific cortical cells over LRP is required for emergence to occur, as this leads to the expression of cell wall remodelling enzymes such as polygalacturonase (PG). By developing mathematical models of auxin transport and LAX3 expression the work in the thesis aims to test the existing conceptual models for lateral root emergence, and provide testable hypotheses for the existence of additional gene regulatory components. An initial single cell model demonstrates that hysteresis and bistability may explain the experimentally observed 'all-or-nothing' LAX3 spatial expression pattern in cortical cells containing a gradient of auxin concentrations. By fitting model parameters against experimental data, the model is then used to show that some auxin homeostasis mechanism is present, with both endogenous and exogenous sources of homeostasis investigated. The single cell model also investigates the validity of several alternative gene regulatory networks for LAX3, and its apparent repression by a key mediator of the auxin response, ARF19. Finally, the model is extended to a multicellular context, in which the auxin distribution from a simulated LRP source cell is used as a basis for the expression of LAX3, leading to the expression of PG in specific cells between which the LRP must pass.

This research was conducted to determine the potential for using plants to obtain samples of boron isotopes from groundwater, sod moisture and fracture water. In essence, this work sought to ascertain whether plants can function as in-situ samplers for boron as an environmental isotope. At present, very little is known about the behavior of boron isotopes in plants so this study was designed to reveal any isotopic fractionation that might occur during plant uptake by a specific species under carefully controlled conditions. The relationship between the boron isotope ratios sequestered in the leaves of the species Atriplex canescens and the growth conditions of the plant were investigated using a semi-hydroponic greenhouse experiment. Nutrient boron concentration and solution pH were selected as experimental variables as these parameters span large ranges in nature. In addition, the mechanism through which plants take up anionic nutrients suggests that boron isotope fractionation could occur. The experimental setup was a randomized factorial block design and the plants were provided six different nutrient solutions with pH values ranging from 7.5 to 9.5 and boron concentrations varying from 0.1 mg/L to 10.0 mg/L. Boron concentration in the plant's leaf and stem samples followed expected patterns, with the highest boron amount in the leaves of the plants fed nutrient solution with 10.0 mg/L B. The stern samples of plants fed 0.1 mg/L B contained the least boron. The ratio of boron in plants fed 10.0 mg/L vs. 0.1 mg/L B was far less than the 100:1 ratio of boron in the nutrients, which implies that a component of uptake is actively controlled by the plant. Negative thermal ionization mass spectrometry was employed to analyze the minute amounts of boron extracted from digests of the plant tissues. Statistical tests were utilized to determine that, contrary to the hypothesis, no significant isotopic fractionation occurred during uptake at any treatment pH level. The results of this research indicate that the species Atriplex canescens can provide samples of boron isotopes which closely represent the isotopic signature of the plant's water source.

26 pp. / Geographically, Arizona can be divided roughly into four areas, southwest, central, southeast, and northern. These regions correspond with four climatic zones, allowing a large and diverse number of plants to be grown for landscaping purposes. But, interestingly, in this desert environment many of the parasitic diseases in landscape plants are caused by a limited number of plant pathogens. This publication discusses some of those diseases that are sufficiently important to the urban plants in all areas Arizona.

Water and fertilizers are the two major agricultural inputs limiting yields in the arid and semi-arid regions of the world. Proper knowledge of their influence on crops should be obtained for appreciable returns. Therefore, a field study was conducted to evaluate the effects of four nitrogen (N) treatments (0, 56, 112, and 168 kg N/ha), two water (M) levels (39 and 58 cm), and two varieties (V) (Funks G-522DR and Conlee Rusler) on dry matter production, total N concentration, and yield of grain sorghum (Sorghum bicolor (L.) Moench). Total N concentration, dry matter, and grain yield were increased by N treatments. Generally, the highest N rate gave the most significant effects; the other rates had statistically the same responses. Varieties were different in their dry matter and grain yields, but had the same total nitrogen contents, as was suggested by the ANOVA and means analysis. There were no detectable interactions among the factors. Moisture had minimal effect on dry matter and grain yields, but influenced total N concentration significantly. Nitrogen contents increased with the higher moisture level.