Previous studies have shown that mitochondrial petites of the yeast Saccharomyces cerevisiae appear to have some advantage over their wild type counterparts in terms of fermentative performance. In this thesis evidence is presented that inhibition of the respiratory chain by chemical or genetic means leads to an increase in ethanol formed per unit sugar and a decrease in biomass per unit sugar. The genetic studies involve a mutation in formation of subunit III of the cytochrome £ oxidase complex (pet!22) and a mutation in putative mitochondrial pyruvate transport (tpyl). The chemical study involves inhibition of mitochondrial pyruvate transport by a specific inhibitor alpha-cyano-4-hydroxycinnamic acid. To try and discover more of the nature of the tpyl mutation a gene was cloned from a yeast centromeric genomic library which complemented the mutation. The insert containing the complementing gene was reduced in size and sequenced. An open reading frame containing 1698 nucleotides coding for 566 amino acids was discovered. After comparison to databases the gene appeared to be undiscovered to date. No similarity was found between the translated protein and others on databases with the exception of the FAS2 gene of Penicillium patulum. Studies of isolated mitochondria and cell growth pattern, of the tpyl mutant, revealed data typical of a classical petite mutation rather than a mutation in a regulatory gene as described by the original paper describing the mutant.

The uptake and transport of vanadium in several higher plant species has been examined. Studies utilizing excised Hordeum roots have revealed the uptake patterns of two different ionic species of vanadium (V02+ and V03) to be similar. Both ionic forms exhibited a large extracellular component in their uptake. This extracellular component was shown to be exchangeable with a number of agents but was most effectively removed by a post uptake treatment in a solution of chromium(VI). This removal of extracellular vanadium by chromium was considered to be a genuine exchange process although the mechanism involved is unclear. The effect of temperature, pH, metabolic inhibitors and complexing agents were also examined and found to be similar for the two ionic forms considered. Concentration dependent uptake of the two ionic forms was also examined. Saturation kinetics were observed when a wide concentration range of vanadium (0.1-5.0 MM) was employed. These results were considered suggestive of conversion of vanadium to a common form within root tissues. Whole plant studies utilizing Zea and Vicia also revealed highly similar uptake patterns for the two different ionic species of vanadium. Irrespective of the ionic form of vanadium supplied to the plant marked retention of vanadium within the root tissues was observed. Analysis of vanadium root-shoot transport patterns in plants supplied with different ionic species of vanadium suggested that a common form of vanadium was being transported in both cases. Possible interactions between vanadium and other ions within the plant are briefly considered. ESR studies utilizing Hordeum clearly illustrated the ability of plant roots to reduce pentavalent vanadium to the tetravalent form. Evidence from all three lines of study is discussed and considered to support the suggestion that vanadium within plant roots exists in the reduced tetravalent form. This is thought to be of prime importance in determining the mobility of vanadium within plant tissues.

Interactions between above ground and root-feeding herbivores can be influenced by changes in plant traits, such as tissue chemistry and morphology. Environmental heterogeneity and perturbations also affect these plant-mediated interactions. Climate change is a multi-faceted phenomenon; increases in atmospheric carbon dioxide (CO2) concentrations lead to increased global mean temperature and an associated higher frequency of extreme weather events. These factors can potentially perturb ecosystem function by altering both plant–herbivore and herbivore–herbivore interactions. A detailed understanding of whether above–belowground interactions are affected by climate change remains lacking. In an attempt to fill knowledge gaps in this understudied area of ecology, this thesis investigates, through a series of glasshouse experiments, the effects of elevated CO2 and other aspects of climate change, such as altered phenology, on the interspecific interaction between the aboveground large raspberry aphid (Amphorophora idaei) and the root feeding larvae of the vine weevil (Otiorhynchus sulcatus), mediated by the shared raspberry (Rubus idaeus) host-plant. Under ambient climate conditions, reciprocal feeding facilitation was observed to occur between aphids and vine weevil larvae feeding on raspberry, with the presence of one increasing the abundance of the other herbivore, and vice versa. This occurred regardless of plant cultivar and order of herbivore arrival on the plant. It is likely that this facilitative relationship is driven by over-compensatory plant growth in response to herbivory. Although tougher, adult vine weevils show a feeding preference for leaves grown in elevated CO2. Herbivory may be more influential than CO2 in determining plant–herbivore interaction outcomes. Aphids affect plant intraspecific competition to a greater extent than elevated CO2 by altering plant biomass of both infested and non-infested plants. In conclusion, this particular plant–herbivore system would seem to be relatively robust in the face of possible future CO2 concentration scenarios.

The protein bodies of the endosperm of the seeds of the castor oil plant Ricinus cannon is contain a variety of storage proteins, along with two lectins, ricin and Ricinus communis agglutinin. Ricin is a heterodimer consisting of an A chain which is toxic to cell-free translation systems, and a B chain which has galactose-binding activity; the whole molecule is toxic to cells and animals by virtue of the ability of the A chain to enzymatically inactivate ribosomes after it crosses the cell membrane, this latter being achieved after binding of the molecule to cell surfaces by the B chain. The agglutinin consists of two ricin-like species linked non-covalently, is divalent, and is not significantly toxic to cells. Previous work on the synthesis of the lectins indicated diet each subunit had its own precursor, each being co-translationally segregated and glycosylated, and assembly of the lectins was thought to occur after transport to the protein bodies. However, the putative B chain precursor was far larger than the mature B chains, and further protein-based evidence Indicated that It contains both A and B chain sequences. The former A chain precursor was Identified as an albumin which contaminated lectin preparations used for raising antisera. The work reported here confirms that the putative B chain precursor contains A and B chain sequences, by means of the cloning of cDNA complementary to lectin-specific mRNA. Clones of nearly full length have been obtained and sequenced, and the precursor is shown to have an N-terminal signal sequence, which is followed by the A chain sequence, and then by the B chain sequence. A linker of 12 amino acids is shown to be present between the two chains. Sequences corresponding to both lectins are reported, and the similarities and differences between them are discussed. The sequences are placed into context by comparison with other plant nucleotide and protein sequences. Literature on the castor bean lectins is reviewed, and the uses of the clones are discussed, with special reference to their possible use in immunotoxins for cancer therapy.

No description available.

The action of ricin A chain on eukaryotic ribosomes was investigated from a number of different angles. It was shown that ricin A chain modified the rRNA from the 60S subunit of a number of eukaryotic ribosomes, including plant ribosomes, and that the site of action was at the same position in a highly conserved sequence which had previously been identified as the site of action in rat liver 28S rRNA. Investigations into the partial reactions of protein synthesis inhibited in ricin A chain-treated ribosomes showed that both initiation and elongation were inhibited, contradicting the assumption based on previous work that ricin A chain inhibited just the elongation cycle. In a rabbit reticulocyte lysate it was found that whilst elongation was severely inhibited by ricin A chain, the rate of initiation was also reduced approximately six-fold relative to that seen with an inhibitor of just elongation. Furthermore, experiments carried out to investigate the inhibition of elongation showed that this was most likely due to the inhibition of the elongation factor 2 catalysed step. Using an assay which allowed the N-glycosidase activity of ricin A chain to be measured directly it was possible to show that ribosomes from a number of different sources varied markedly in their sensitivity to ricin A chain. Wheat germ ribosomes were shown to be in the order of 1000 times less sensitive to modification than those from either yeast or rabbit reticulocytes. However, this difference does not seem to be a reflection of the differential affinity of ricin A chain for the various substrates but rather a consequence of the ability of the toxin to modify the rRNA once it has bound. This is because kinetic experiments showed that the Km for the reaction on wheat germ ribosomes was similar to that which had been published for the action of ricin A chain on rat liver or rabbit ribosomes. The Kcat, however, was approximately 3 orders of magnitude smaller. A similar picture was seen with the type 1 RIP dianthin 32. It was shown directly that elongation factor 2 bound irreversibly to the ribosome could protect the ribosome from the action of ricin A chain and that in a wheat germ lysate this ability to compete out ricin A chain seemed to be a property of just this supernatant protein. This protection is reflected in the finding that the elongation factor 2 content of purified ribosomes determines their sensitivity to depurination by ricin A chain and that the removal of this protein with high salt sensitises the ribosomes to modification.

The foliar uptake by wheat of the wild oat herbicide flampropmethyl has been studied following application of ul droplets of an aqueous solution. The results show that over the time required for the drop to dry the compound does not partition into the surface waxes and crystallises as an external deposit. This deposit is stable to volatilization and photochemical and biochemical degradation, and is depleted by foliar penetration. Adsorbtion by the leaf surface wax is initially rapid and thereafter occurs at a relatively constant rate until the almost complete exhaustion of the surface deposit. Penetration of the epicuticular wax layer generally proceeds at a slower rate than does adsorption of the surface deposit and the herbicide is accumulated in the wax layer. The compound is lost from the epicuticular waxes only slowly to the leaf tissues. Movement within the leaf tissues away from the area of uptake is predominantly acropetal to the leaf tip and it is presumed that the compound moves with the transpiration stream. A similar fate befalls the compound when aqueous solutions of flamprop-methyl are applied as ul droplets to barley or wild oat, no evidence of selectivity between wheat, barley and wild oat as a consequence of preferential uptake was found. Foliar uptake of flamprop-methyl is shown to depend on the amount of compound applied to un1 t area of leaf surface and to increase as the amount applied is increased or as the area to which application is made is increased. These trends are discussed in terms of compartmental model of foliar uptake. Foliar uptake of flamprop-methyl is also shown to be slightly influenced by environmental factors; in an environment in which maximum daily temperatures exceeded 35 o C penetration was especially rapid and tended to completion within 24 hours. The surface properties of aqueous solutions of selected polyoxyethylene non-ionic surfactants have been studied prior to investigating the effect of these compounds on the foliar uptake by cereals of flamprop-methyl. Two types of non-ionic surfactant were included in this study, the alkylphenol ethoxylates as exemplified by the Triton X products (ex Rohn and Haas) and alcohol ethoxylates as exemplified by the Brij products (ex Atlas Chemical Industries). Products from both sources were analysed using instrumental and separational methods; the results of these analyses supported the manufacturers description of the compounds. Surface and interfacial tensions of aqueous solutions of the surfactants were determined at various concentrations. Maximum"reduction of surface tension in the alkylphenol ethoxylate solutions was found with Triton X-35 and Triton X-45. Maximum reduction of surface tension in the alcohol ethoxylate solutions was found with the tetraoxyethylene dodecyl ether (Brij 30) and was reduced with increasing oxyethylene content with anyone hydrophobe. At constant oxyethylene content it was shown that surface activ1 ty was dependent on the nature of the hydrophobe. Critical micelle concentrations were determined from plots of surface tension vs concentration for alkylphenol and alcohol ethoxylates. The spreading and wetting properties of aqueous solutions of alkylphenol ethoxylates were investigated by the Draves test and in terms of calculated spreading coefficients. The foliar uptake by wheat of ethoxy1ated non-ionic surface active agents has been studied following topical application of aqueous solutions. The permeability of the cereal leaf to these compounds has been demonstrated. the rate of uptake was shown to depend on the mean oxyethy1ene content of the surfactant, decreasing as the oxyethy1ene content was increased within the Triton X series of compounds. In quali tati ve terms the trend in uptake was paralleled by changes in both partition coefficient and (estimated) diffusion coefficient. The distribution of oligomers within anyone surfactant was apparently retained during transcuticular movement. Movement of the surfactant across the epicuticular waxes resulted in an accumulation of the penetrant in the tissues underlying the site of application. Movement of the surfactant in treated leaves was acropetal. The foliar uptake of f1amprop-methy1 by wheat has been studied following topical application of the herbicide formulated in aqueous surfactant solutions. Non-ionic ethoxylated surfactants have been found to markedly enhance transcuticular movement of the herbicide but do not promote transport of the compound wi thin treated leaves. The extent to which uptake was enhanced was largely influenced by the concentration of the formulation with respect to the surfactant, was much less dependant on either hydrophobe or hydrophile structure and was apparently independant, within experimental limits, of the herbicide concentration. Optimum surfactant concentrat1ons were between 100 and 1000 ppm. Correlation between penetration enhancement and the surface properties of the formulations was non-existent. The effect of the surfactant on penetration is discussed in terms of a surfactant/lipid interaction which facilitated diffusion of the herbicide. At high surfactant concentrations a variety of responses were identified ranging from varying degrees of enhancement through to an inhibition of transcuticular movement: these responses were shown to correlate with the resistance to uptake afforded by a persistent surfactant residue on the leaf surface.

Field isolates of Botrytis cinerea Pers. from tomato crops gave rise to two distinct morphological types after successive single spore isolations; type 1 (T1) characterised by regular, rapidly growing mycelium and type 2 (T2) characterised by sparse, often distorted, slow growing mycelium. The frequency with which isolates produced these morphological types varied considerably. The reaction to benomyl of both types obtained remained the same as that of the parent isolate through successive single spore isolations on fungicide free agar over 10 generations. Benomyl tolerant field isolates could not be distinguished from sensitive isolates on the basis of colony morphology. Examination of 188 isolates of B. cinerea collected from 10 different tomato crops showed that sensitive isolates tended to be more pathogenic to detached tomato cotyledons and grew faster in vitro than tolerant isolates. In vitro and in vivo studies revealed no difference in the competitive ability of benomyl tolerant and sensitive isolates in mixed culture. In a study of 17 Lancashire tomato crops all were found to contain benomyl tolerant strains of B. cinerea although in some cases benzimidazole fungicides had not been used on the nursery for up to three years. Examination of B. cinerea in tomato crops suggested that the majority of stem lesions arose from infected leaf scars and were non-aggressive. Side shoot stumps or scars were also liable to infection and the resulting lesions were more likely to become aggressive than lesions at leaf scars. Conidia were considered to be the major source of inoculum although lesions at leaf scars could take up to 61 days to develop after deleafing. This delay was attributed to latent infection. Artificial infection of the petiole with B. cinerea prior to deleafing greatly reduced the susceptibility of the resulting leaf scar to subsequent attack by B. cinerea. Extracts from infected stems were shown to delay the germination of B. cinerea conidia when compared to extracts from healthy stems. This inhibition of germination was attributed to a resistance factor (RF) produced by the fungus or host in response to infection.

Phytoremediation is a plant-based remediation process for treating contaminated soils. The overall aim of this thesis was to determine whether phytoremediation could be applied to co-contaminated soils. Copper (Cu) and pyrene, and Chromium (Cr) and Benzo[a]pyrene (B[a]P) were used as contaminants. The first study involved the joint effect of Cu and pyrene or Cr and B[a]P on the early seedling growth of Lolium perenne. Results suggest that co-contamination showed several types of interactions for seedling growth with different combinations of the pollutants. The second study involved the role Brassica juncea and Zea mays during the remediation of Cu and/or pyrene, and Cr and/or B[a]P co-contaminated soils respectively. Brassica juncea and Z. mays showed contrasting results for metal and polycyclic aromatic hydrocarbon (PAH) remediation. The third study compared freshly spiked soils and aged soils. Ageing affected the plant biomass, metal phytoextraction and PAH dissipation in different ways when compared to fresh soils. Finally, the efficiency of ethylenediaminetetraacetic acid-EDTA and/or citric acid as chelators in co-contaminated soils was studied. The combined application of EDTA and citric acid was more effective in co-contaminated soils. The overall findings from the four studies suggest that phytoremediation could be applied to co-contaminated soils.

Liriomyza bryoniae is an economically important pest of vegetable and ornamental crops in European glasshouse agriculture. Diglyphus isaea is a parasitoid of Liriomyza leaf miners and is commercially available as a biological control agent. Anecdotal reports made to commercial producers of the parasitoid suggest that the efficacy of D. isaea varies between crops. This study examines the tritrophic interactions between crop plant, L. bryoniae and D. isaea. Host plant was found to influence the abundance of L. bryoniae and D. isaea with larger populations establishing in the culturing host than in the novel host, tomato. Individual size of L. bryoniae also varies with host plant. These patterns are consistent in L. bryoniae across three generations of rearing on tomato. Habituation of L. bryoniae to tomato does not affect D. isaea efficacy nor does the natal plant host of D. isaea. Both L. bryoniae and D. isaea are affected by plant host ontogenetic stage, becoming most numerous on juvenile plants. The D. isaea natal insect-plant complex showed no effect on D. isaea olfactory preferences. Diglyphus isaea demonstrated greater thermal tolerance than its host. These results are discussed in relation to biological control and also in terms of their wider ecological implications.