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Leaf senescence is a sensitive and dynamic process that is both genetically and environmentally controlled. Environmentally, factors such as daylength and nitrogen availability are understood to affect the timing of senescence, but the underlying genetic factors that initiate the processes that result in leaf death remain elusive. Sugars and nitrogen can act at the molecular level as signalling molecules which result in altered gene expression. Sugars were found to accumulate in senescing leaves suggesting that leaf senescence is not caused by sugar starvation. Nitrogen decreases in senescing leaves as it is exported to young leaves and the developing fruits. This study presents evidence that the alteration in the ratio between these two essential nutrients may act as the instigating signal for leaf senescence. On medium containing 2% glucose in combination with low nitrogen supply senescence was accelerated. The expression of a number of genes, functional during developmental senescence was altered by the addition of glucose. The expression of SAGI2. a senescence specific gene, confirmed that accelerated senescence was not caused by stress and also that glucose-induced senescence was representative of developmental senescence. Quantitative trait loci analysis was carried out on the Bay-0 x Shahdara population in response to treatment with low nitrogen plus 2 o glucose. The decline in maximum photosynthetic efficiency (F /Fm) was monitored by chlorophyll fluorescence imaging to determine the extent of senescence of the whole rosette. Using Fx/Fm as quantitative trait, two new loci, on Chromosomes II and IV. were mapped that regulate glucose-induced senescence. The use of near isogenic lines confirmed the locus on Chromosome IV. The study of flowering uncovered a strong link between flowering time and senescence in the RIL population. In one RIL. 310. flowering was severely retarded and glucose did not induce senescence. This was confirmed by the absence of SAG 12 expression in glucose-treated plants. Of particular interest was that FRIGIDA. a gene involved in vernalization- dependent flowering, mapped to the QTL on chromosome IV. This gene was subsequently nominated as a candidate gene.

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No description available.

In the face of global climate change and the need to urgently transition from fossil fuels to a low carbon economy, bioenergy derived from plant biomass has the potential to provide a diverse range of renewable and sustainable solid and liquid fuels. Second generation (2G) lignocellulosics are dedicated bioenergy crops; ideally cultivated on marginal lands with minimal agricultural inputs or competition with food production. The model tree poplar is a fast growing, genetically diverse and widespread hardwood and has great potential for commercial development as a feedstock for cellulosic biorefineries. At this time however, lignocellulosics such as poplar have not received the same research and breeding effort as many food crops. Chapter 2 of this work demonstrates that a substantial yield gap exists for 2G bioenergy crops, which will hamper commercialisation. This yield gap may be closed through sustainable intensification and advanced, molecular breeding techniques offer the potential to increase the efficiency and timeliness of this improvement process. These advanced breeding techniques require an understanding of the genetic basis of traits of interest. To this end Chapters 3 and 4 are centred on a natural, wide population of Populus nigra Linnaeus (black poplar) genotypes, drawn from across the western European range of this species. This highly diverse population has been cultivated under short rotation coppice (SRC) in two field trials in the UK and Italy and phenotyped for important bioenergy traits related to biomass yield, wood quality, leaf development and drought tolerance. The population has also been genotyped; firstly using an Illumina 12K BeadChip array and secondly with targeted, sequence capture genotyping by sequencing (GBS) of the annotated gene space. These single nucleotide polymorphisms (SNPs) have been employed to analyse the population genetic structure of European P. nigra and in genome wide association genetics; identifying trait-marker associations and candidate genes for quantified phenotypes. These data will be valuable for the molecular breeding and commercialisation of bioenergy poplar.

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Trichilia emetica seeds have already been utilised for oil extraction. This project investigated the chemistry of by-products, especially water after boiling the seeds and the defatted residue. The first part of the study was to subject the seed oils to physicochemical analysis using standard methods of food analysis. The data obtained were acid (0.4±0.0 and 0.4±0.1 mg KOH/g), iodine (69.2±2.1 and 64.6±2.8 gI2/100g), peroxide (10.3±0.5 and 9.2±0.4 %) and saponifiable value (195.4±5.4 and 197.3±4.6) for T. emetica seeds from Ghana and Mozambique and were comparable to those of other edible oils. The fatty acid composition of the seeds and shell oils was determined using different analytical methods. The result obtained using 1H and 13C NMR and GC-MS of fatty acid methyl esters are 56-65% saturated (C14:0, C16:0, C18:0), 27-34% monounsaturated (C18:1, ω-9) and 4-10% polyunsaturated (C18:2 ω-6, 9 and C18:3 ω-6, 9, and 12) are in good agreement between the different methods of analysis for the proportion of individual fatty acids. Linolenic acid methyl ester was not detected in the seed oil. Phytochemical investigation of the unsaponifiable fraction of T. emetica seed oil resulted in the isolation of two sterols, β-sitosterol and stigmasterol. The second part of the study was the phytochemical examination of the boiled water extract of the seed. This resulted in the isolation of one new flavanol glycoside, catechin-3-O-α-L-rhamnopyranosyl (1→4) β-D-glucopyranoside and eight known compounds; catechin, epicatechin, taxifolin, elephantorrhizol, catechin 3-O-β-D-glucopyranoside, taxifolin 4’-O-β-D-glucopyranoside and eriodictyol 4’-O-β-D-glucopyranoside. Similarly, three known compounds Naringenin, Quercetin and Quercetin 3-O-β-D-glucopyranoside were isolated from the stem. To the best of our knowledge, this is the first report on the phenolic content of T. emetica. The third part of the study was the use of Azadirachta indica seeds and the seeds oil of Millettia pinnata as a model to check the various methods used in the unsuccessful attempt to isolate a limonoids from the seeds of T. emetica. These resulted in the isolation of two known limonoids and three furanoflavonoids: azadirachtin, nimbin, karanjin, pongapin and lanceolatin. The structures of these compounds were determined on the basis of spectroscopic methods and by comparison of the data obtained with literature. Some compounds were confirmed with X-ray crystallography.

The glucosinolate-myrosinase system has been the subject of sustained focus and has been extensively reviewed over time. The system is characteristic of Brassicaceae. Diets rich in Brassica vegetables have been associated with a reduced risk of cancer, attributed to isothiocyanates, the degradation products of glucosinolates. Glucosinolates are water soluble sulfur rich compounds, which upon hydrolysis by endogenous myrosinase yields a variety of compounds with impact on human health and sensory attributes of these vegetables. However, the delivery of health beneficial hydrolysis products is hampered when Brassicaceae are thermally processed. This thesis was aimed at improving the formation of sulforaphane, and its bioavailability when brown mustard is added to cooked broccoli. Thermal and pressure inactivation of myrosinase enzymes extracted from black, brown and yellow mustard seeds was investigated to ascertain the stability of mustard myrosinase under processing conditions. Brown mustard had higher myrosinase activity than black and yellow mustard and the extent of enzyme inactivation increased with pressure and temperature for all the mustard seeds. However, at combinations of pressures {200-400 MPa) and high temperatures (60-80 °C), there was less inactivation. Application of 300 MPa and 70 °C for 10 minutes retained 20%, 80% and 65% activity in yellow, black and brown mustard, respectively, whereas the corresponding activity retentions when applying only heat (70 °C, 10 min) were 0%, 59% and 35%. Thus, application of moderate pressures (200-400 MPa) can potentially be used to retain myrosinase activity needed for subsequent glucosinolate hydrolysis. The impact of geographical origin on myrosinase activity and thermal inactivation in black, brown and yellow mustard seeds was studied. Mustard seeds from different geographical locations were grown under identical controlled conditions. There were significant increases in enzyme activity and protein content after cultivation. Myrosinase inactivation increased on heating the cultivated seeds. Myrosinase was stable below 60 °C in all the seeds. However, at 70 °C, activity loss was approximately 10% and over 70% loss at 90 °C. At 100 °C, only two brown seeds (China, Korea) and one yellow seed sample (France) had marginal myrosinase activity. This Implied that varietal differences in mustard myrosinase activity and thermal stability persisted after cultivation under identical controlled conditions.

This is one of the first studies on the relationship between pre-harvest environmental conditions found in the Mediterranean and postharvest characteristics of cut roses (Rosa hybrida L. ). Effects of storage temperature on vase life parameters were also studied for roses grown all year round. The postharvest storage of roses at low temperature is a useful practice, in terms of market flow regulation. However, a reduction in vase life and loss of flower quality has been recorded after storage due to Low Temperature Injury (LTI). LTI of roses is difficult to assess by visual observation. Relative chlorophyll fluorescence (F'IFR, ), which is a non-invasive technique that provides an index of stress effects on photosystem II (PS II) activity, was used to investigate LTI in roses. The plant growth regulator abscisic acid (ABA) can cause physiological responses that protect plants against CI or LTI. The overall objectives of this study were firstly to evaluate the pre-harvest environmental conditions affecting vase life and secondly to evaluate novel potential ABA treatments to protect cut roses against LTI. Vase life durations and Fv. /Fm ratios measured after low temperature storage for 'First Red' and 'Akito' roses were seasonally dependant. Vase lives of roses grown during winter were significantly (P _< 0.001) shorter compared to roses grown during the rest of the year. In autumn and winter experiments F.. IF.. ratios were generally reduced following storage at 1°C, suggesting LTI of roses. Thus, the fall of F,. /Fm was due to an interaction of growing season and storage at I. T. However, in second year experiments, growing temperature and PFD were relatively higher and, as a result, Fý/Fm did not decline for 'Akito' roses after low temperature storage, indicating a strong influence of environmental conditions. Higher PFD and temperature glasshouse during the year were positively and significantly correlated with maintenance of post-storage Fv. /Fm ratios and longer vase life. It is suggested that shorter vase lives and lower post-storage FV/Fm values after storage at 1°C are consequences of reduced photosynthesis and smaller carbohydrate pools in winter- harvested roses. Because of the lack of correlation between Fv. /Fm and post-storage vase life, it is concluded that the CF parameter F,. /Fm is not a practical index for assessing LTI in cold-stored roses. Growing roses in autumn and winter months increased flower blueing in red petals of 'First Red' roses and prevented flower opening for both cultivars. ABA applied as pulse treatment before storage or as vase solution during vase life generally improved vase life parameters. Pulsing 'Akito' roses with 10-1 M ABA before storage increased vase life and inhibited bent neck incidence. Also, the presence of ABA in vase solution increased vase life after storage at 1°C, reducing vase solution usage during vase life. Similarly, the synthetic ABA analogue PBI-365, as vase solution ingredient, was effective in extending vase life and reducing transpiration rates in roses after low temperature storage. Increased ABA levels were detected in leaves and petals using HPLC when roses were treated with exogenous ABA before storage and during vase life. Thus, it was assumed that ABA or PBI-365 acted on guard cells by causing stomatal closure. Electrolyte leakage and lipid peroxidation, measured after storage at 1°C, were markedly reduced by application of ABA. Both pulse ABA treatment and vase solutions containing ABA helped to recover F,, /Fm during vase life. Moreover, addition of PBI-365 in vase solution reduced the degree of lipid peroxidation in leaves and petals after storage at 1°C. These observations indicated a protection role of ABA against LTI for roses, which has also been observed in other crops. Further research at the cellular and/or molecular level may help in better understanding the physiological responses of roses to seasonal variation during the year and LTI. In addition, work is also required to look at the ABA and PBI-365 mode of action in roses. Additional research using a wide range of ABA concentrations and assays using exogenous radio-labelled ABA may help to better understand the nature of ABA efficacy.

The A6 gene family represents a distinct class of P-l,3-glucanase enzymes in higher plants (Hird et al., 1993). The genes differ from other known P-l,3-glucanases in both sequence characteristics and expression pattern. The DNA sequences encode proteins with a distinctive GINYG N-terminal motif and a long C-terminal extension. The A6 gene shows tapetum-specific expression, with maximum activity detected at the time of microspore release (Hird et al., 1993). The expression pattern of A6 suggests that this gene may be part of the callase enzyme complex required for the dissolution of the callose wall surrounding the tetrads of developing microspores within the anther (Hird et al., 1993). The preliminary work on the A6 gene family identified four anther-specific cDNAs from Brassica napus (Scott et al., 1991 Hird et al., 1993). As a continuation of this work, five A6 family genes have now been cloned and sequenced in Arabidopsis thaliana. All five are single copy genes, and the three genes that have been mapped to the Arabidopsis genome are located at unlinked positions on two different chromosomes. Analysis of the cDNAs corresponding to the A6 family genes has revealed considerable variation in expression pattern. Two of the A6 family genes show anther-specific expression, and three genes are constitutively expressed, indicating differential regulatory mechanisms for these genes. Two populations of T-DNA-tagged lines were screened for four of the Arabidopsis A6 family members in attempt to obtain lines carrying mutations in these genes, which may reveal more information on their biological function(s). One positive line was identified and later shown to contain an insertion At-A6 gene. Detailed analysis of this line showed that although the At-A6 transcript in the mutant line is shorter than wild type and does contain part of the T-DNA sequence, the hybrid mRNA is stable. No phenotype could be associated with the T-DNA insertion in At-A6.