Oxaziclomefone [OAC; IUPAC: 3-(3,5-dichlorophenyl)-1-methylethyl)-2,3-dihydro-6-methyl-5-phenyl-4H-1,3-oxazin-4-one] is a new herbicide recently released onto the market by Aventis, in Japan. OAC is very effective in controlling <i>Echinochloa</i> sp., a weed which is particularly prevalent in paddy fields and which can substantially reduce the yield of rice. OAC inhibits growth of graminaceous monocots but is relatively ineffective on most dicots. OAC was found to inhibit cell expansion in maize cell suspension cultures (CSCs) and roots within 8 h of exposure and has an ID₅₀ (inhibition dose) of ~ 7 nM. Cell expansion is promoted and regulated by turgor pressure, cell wall loosening and tightening. OAC did not reduce turgor pressure in maize CSCs or impede water transport across cell membranes. The herbicide did not promote the activity, apoplastic action or secretion of peroxidase, which can effect cell wall tightening by catalysing the formation of diferulate and di-isodityrosine. OAC did not inhibit the activity, action or secretion of XET, which may promote cell wall loosening via transglycosylation of xyloglucan chains. The herbicide did not reduce the consumption of extracellular ascorbate by maize CSCs, suggesting that OAC did not inhibit the formation of ^*OH (generated via the Fenton reaction which requires the presence of ascorbate) believed to cause polysaccharide scission and therefore effect cell wall loosening. OAC did reduce acid-dependent creep in methanol-killed maize silks (though not consistently) but not in methanol-killed celery petiole vascular bundles. OAC also reduced acid-dependent creep in frozen, thawed maize roots but again not consistently. However, OAC did inhibit the action of β-expansin (aqueously extracted from <i>Zea mays</i> pollen) on boiled maize silks and roots, assayed using an extensiometer. OAC may inhibit cell expansion by suppressing β-expansin-mediated cell wall loosening.

The hypothesis that allocation between the main tree components is controlled by the relative uptake rates of carbon dioxide and nutrient was tested by growing one-year-old sycamore seedlings (<I>Acer pseudoplatanus</I> L.) at elevated and ambient CO<SUB>2</SUB> concentrations and at two nutrient addition rates which were modelled in accordance with a predicted optimal growth function. Elevated CO<SUB>2</SUB> concentration significantly increased the leaf dry mass but did not significantly change the dry mass of any other component. In contrast nutrient addition rate had large effects on all biomass components with the exception of the root. Allocation was strongly affected by nutrient addition rate although CO<SUB>2</SUB> treatment only affected the allocation to the stem. Nutrient concentrations were reduced by growth at elevated CO<SUB>2</SUB> concentrations. Leaf starch concentrations were larger at elevated CO<SUB>2</SUB> concentrations. There were no differences in soluble leaf carbohydrate concentrations between treatments. There was evidence of downregulation of photosynthesis at the low nutrient addition rate but not at elevated CO<SUB>2</SUB> concentrations. In conclusion, the growth concentration of CO<SUB>2</SUB> and nutrient and water availabilities are important in the control of allocation. Increases in atmospheric CO<SUB>2</SUB> concentrations are likely to be accompanied by shifts in allocation towards the root and stem although the magnitude of these changes will be determined by the nutrient availability of soils. The effects of perturbations in these variables are also determined by differences in growth and allocation between clones of the same species, between species and by the development of allocation patterns which are dependent on phenology. The functional balance is useful in predicting changes in allocation, although it does not fully explain the observed patterns.

No description available.

<I>Idriella bolleyi</I> strains, T560, J10 and AB1, differed considerably in their tolerance to water-stress - this was apparent in both osmotic and matric potentials and in all aspects of their growth cycle. The level of tolerance for one strain, T560, was comparable to the take-all pathogen <I>Gaeumannomyces graminis</I> var. <I>tritici</I>, which is associated with low water-stress tolerance, and another strain, AB1, was comparable to the foot-rot pathogen <I>Fusarium culmorum</I>, known to be highly tolerant of drought conditions. Variation in response to osmotic potential was also observed in root and stem base field isolates of <I>I. bolleyi</I>. The field isolates differed in the level of mycelial growth and sporulation at potentials of -1.5 MPa (control) and -5.0 MPa. Isolates from the same plant were found to have different levels of sporulation - this may have been related to the degree of microcycle conidiation they exhibited. <I>Idriella bolleyi</I> isolates, T560 and AR1, were able to colonise straw in soil at different matrix potentials down to -7.0 MPa. Straw colonisation was found to increase from 2 to 8 weeks, indicating that both strains were actively growing at all water potentials during this period. A number of other fungal species were isolated from the straw along with <I>I. bolleyi</I>, suggesting that a high degree of competition was associated with colonisation. Water potential appeared to be the most influencing factor with regard to the activity of each species. <I>Idriella bolleyi</I> could increase its population on unsterilised wheat seeds buried in soil. <I>Idriella bolleyi</I> was inoculated onto the seeds as either an alginate or water suspension. For both seed treatments the detectable level of conidia increased exponentially on the seeds over five days, this increase coinciding with the production of young wheat roots. As the seed aged the detectable level of conidia decreased.

This thesis is concerned with the following areas: first, the nature of the developmental modulations in mitochondrial function, and the role of coarse control, at the level of protein synthesis, in bringing them about; and secondly, the importance of mitochondrial reactions in the regulation of cellular metabolism. Changes in respiratory physiology in developing cotyledons have been characterised and correlated with changing metabolic phases. During lipid mobilisation, carbon is diverted away from the decarboxylating reactions of the TCA cycle, whereas the capacity exists for full cycle operation in the photosynthetic phase. Mitochondrial glycine oxidation, necessary for the maintenance of the photorespiratory cycle, is induced during photosynthetic development. The non-phosphorylating pathway of electron transport, via the alternative oxidase, is present, and the access of substrates to this pathway appears to be regulated such that high rates of succinate and glycine oxidation can occur simultaneously. These changes are brought about, at least in part, by protein synthesis. The steps regulating succinate oxidation by isolated cotyledon mitochondria have been determined using the quantitative techniques of metabolic control theory. During lipid mobilisation, succinate metabolism is regulated by the adenine nucleotide translocator and the processes of succinate uptake into the mitochondria. A mitochondrial r^ole in the integration of biosynthesis and degradation is proposed in the light of these results. In the photosynthetic phase, the regulation of succinate oxidation is by the steps of the respiratory chain. There is evidence to suggest that variation in succinate oxidation rates during development is a result of the synthesis of specific proteins. Studies into the pathway of pyruvate metabolism in developing cotyledons indicate that carbon may be diverted into the TCA cycle during chloroplast biogenesis, through pyruvate production by the mitochondrially located NAD-malic enzyme. It is suggested that this mitochondrial route of carbon entry would enable TCA cycle flux to be regulated by the demand for intermediates required for biosynthetic pathways, rather than the rate of sucrose production from lipid. Evidence is presented for the more conventional route of carbon entry into the TCA cycle from cytosolic pyruvate during the photosynthetic phase. Results indicate that the developmental modulation of pyruvate metabolism is regulated at the level of protein synthesis. Application of metabolic control theory to <i>in vitro</i> systems capable of hexose production from organic acids, provides further support for the proposed r^ole of mitochondria during lipid mobilisation. The adenine nucleotide translocator and other mitochondrial steps have significant flux control coefficients for hexose production <i>in vitro</i>. The results presented are used as the basis for the development of a hypothesis concerning the importance of mitochondria in the regulation of plant metabolism.

There has been much research into the impact of rising [CO<SUB>2</SUB>] on growth and physiology of plants. Trees, being long-lived organisms which often exist in nutrient-limited soils, are especially relevant to the study of the long-term impact of rising [CO<SUB>2</SUB>], not least because they play an important role in the global carbon cycle. Their response to rising [CO<SUB>2</SUB>] is complex and often species-specific, because of interactions with other variables such as nutrients, temperature or the ability to fix atmospheric nitrogen. In particular, nitrogen-fixing trees grown in elevated [CO<SUB>2</SUB>] should grow better than non-fixers, since they can uncouple growth from soil nutrient availability and use the extra carbon to run the expensive nitrogen-fixing apparatus with greater efficiency and output. The aim of this thesis was to investigate the effects of nutrient uptake and nitrogen fixation on growth and biochemistry in two temperate tree species: <I>Alnus glutinosa </I>and <I>Pinus sylvestris. </I>The former is a nitrogen-fixing deciduous species, the latter a mycorrhizal conifer. One short-term experiment (15 weeks) and one long-term experiment (three years) were set up, both using seedlings grown in open top chambers (OTCs). In the short-term experiment, <I>c</I>. 90 one-year old <I>Alnus</I> seedlings (alder) and 85 one-year old <I>Pinus </I>seedlings (Scots pine) in pots were exposed to either ambient or ambient + 350 μmol mol<SUP>-</SUP>1 [CO<SUB>2</SUB>] for fifteen weeks. They were supplied with either a high nitrogen (N) fertiliser designed to allow maximum growth, or a low nitrogen fertiliser. Growth was measured weekly and two harvests were made, one at the beginning and one at the end of the experiment. Other variables measured were leaf area, stem basal diameter, chlorophyll concentrations, nutrient concentrations, and soluble carbohydrate and starch concentrations.

No description available.

Evolution has a major influence on the plant cell wall and variation in primary cell wall (PCW) composition is known to exist between different angiosperm taxa. The PCWs of lower land plants have not been well studied. It is of interest to see what changes have taken place in PCW composition during plant evolution. One of the main qualitative variables within angiosperms is the presence of mixed-linkage b-(1(r)3),(1(r)4)-glucan (MLG) in gramineous monocots and apparent absence from non-gramineous monocots and dicots. Anomolously, the presence of MLG had been reported in the dicot <i>Phaseolus aureus. </i>In the present work, MLG was not detected (< 0.02% w/w of the cell wall) in <i>P. aureus </i>hypocotyls or in PCWs of all non-gramineous land plants tested (dicots, monocots, pteridophytes and bryophytes). One exception was <i>Flagellaria guineensis,</i> a close relative of the gramineous monocots, which on licheninase digestion produced the characteristic tri- and tetrasaccharide of MLG. MLG is therefore restricted to the Poaceae and some closely related members of the Poales. Xyloglucan was found in all land plants tested including bryophytes. Methylation analysis had indicated some of the glycosyl linkages typically found in xyloglucan are present in a cell wall polymer from the charophyte <i>Nitella. </i>However, Driselase-digestible xyloglucan was not detected (< 0.01% w/w of the cell wall) in <i>Chara</i>, a charophyte, thought to be closely related to land plants. In addition, PCWs of <i>Chara</i>, two other charophytes and <i>Ulva lactuca</i> were not digested to xyloglucan-derived oligosaccharides by cellulase or xyloglucan-specific endoglucanase. Land plants are thought to have organised from a single species of charophyte: it is therefore likely the putative ancestor, unlike other charophytes, had xyloglucan in its cell walls.

This thesis employs two techniques to investigate the influence of carbon dioxide concentration on carbon assimilation in tropical tree species. To investigate the response of tropical tree species to elevated CO<SUB>2</SUB> concentration, seedlings of <I>Cedrela odorata</I> L. (Meliaceae) were grown in open-top chambers and exposed to atmospheric CO<SUB>2</SUB> at either ambient or twice ambient concentrations. Nutrient supply rate was also altered to investigate its interaction with elevated CO<SUB>2</SUB> concentration. This experiment was repeated on different seedlings over two years, 1995 and 1996, with <I>C. odorata</I> showing an acclimation response to elevated CO<SUB>2</SUB> concentration in the second year of the experiment but not in the first. Plants grown in elevated CO<SUB>2</SUB> concentration were larger than those grown in ambient CO<SUB>2</SUB> concentration in 1995 only with a high rate of nutrient supply. It is hypothesised that high vapour pressure deficits restricted stomatal conductance and consequent photosynthesis in both years but that this effect was particularly pronounced in 1996 when combined with a nutrient regime of excessively high concentration for the rate of growth. These effects are hypothesised to have triggered acclimation, or a reduction in CO<SUB>2</SUB> fixation capacity, as indicated by changes in derived values for the enzyme kinetic parameters of the carboxylation enzyme, ribulose 1,5 bisphosphate carboxylase-oxygenase (Rubisco). A biochemical model of photosynthesis was used to assess photosynthetic acclimation to elevated CO<SUB>2</SUB> concentration. The derived parameters for maximum rate of electron transport (<I>J<SUB>max</SUB></I>) and maximum velocity of the Rubisco enzyme (<I>V<SUB>max</SUB></I>) were compared between treatment CO<SUB>2</SUB> concentrations and both were significantly lower (<I>p</I> < 0.05) in plants that had been grown in elevated CO<SUB>2</SUB> concentration in 1996. Whole-plant gas exchange was monitored in 1996, where a decrease in net CO<SUB>2</SUB> uptake of plants grown in elevated CO<SUB>2</SUB> concentration was observed.

No description available.