No description available.

The studies reported in this thesis have been primarily concerned with the mechanism of the selective action of the substituted phenylurea herbicide chlortoluron (N 1-(3-chloro-4-methylphenyl)-N,N-dimethylurea) in cereals and monocotyledonous cereal weeds. The introduction reviews relevant aspects of photosynthetic electron transport, the use of the substituted phenylureas as herbicides and the mode of action of the substituted phenylureas with reference to structure/activity relationships. In addition, their selective properties are discussed particularly in relation to their metabolic fate in biological systems. Studies on the Hill activity of chloroplasts isolated from resistant and sensitive plants and incubated in vitro with chlortoluron or the related phenylurea isoproturon (NT-(3-chloro-4-isopropylphenyl)-N,N -dimethylurea) demonstrated a similar inhibition of DCPIP photoreduction in each case. Examination of the Hill activity of chloroplasts isolated from plantstreated with either chlortoluron or isoproturon, however, demonstrated a greater inhibition of DCPIP photoreduction in sensitive compared to resistant plants. Studies on the recovery of photosynthetic activity both in whole plants and in leaf segments following inhibition by prior treatment with chlortoluron or isoproturon demonstrated a greater ability to restore oxygen evolution in the case of resistant plants, suggesting a more rapid detoxification of the herbicides in these varieties. Metabolism studies made using (carbonyl-14C) chlortoluron indicated degradation by both N-demethylation and ring-methyl oxidation pathways, followed by conjugation. The ring-methyl oxidation pathway predominated in the resistant cereal varieties to a greater extent than in the sensitive cultivars. In contrast, the N-demethylation pathway constituted the major metabolic route in the case of the cereal weeds. Studies onthe inhibition of the Hill reaction by the metabolites of chlortoluron indicated that the initial product of N-demethylation retained significant phytotoxicity, whereas all products of ring-methyl oxidation were essentially non-phytotoxic. Further metabolism studies made using 14(carbonyl-C)diuron (N1-(3,4-dichlorophenyl)-N,N-dimethylurea) and 14(carbonyl-C) N1-(3-methyl-4-chlorophenyl)-N,N-dimethylurea emphasised the importance of both the presence and the positioning of the ring-methyl group in the selective action of the substituted phenylureas. Studies on the polar conjugated metabolites of chlortoluron revealed that the glycone moiety was B-D-glucose in each case. In vitro experiments indicated that chlortoluron metabolism was achieved by a microsomal-linked system requiring molecular oxygen and NADPH as cofactors. Experiments on the absorption of chlortoluron from both soil and nutrient media indicated a greater uptake of the herbicide by the cereal weeds compared to the cereal varieties examined. A sub-cellular organelle localisation study of absorbed chlortoluron and its metabolites demonstrated the association of significantly larger amounts of phytotoxic material with the chloroplasts of sensitive compared to resistant plants. In addition, post-mitochondrial fractions prepared from resistant plants contained correspondingly larger quantities of non-phytotoxic metabolites. The various experimental results are discussed in terms of their significance in accounting for the observed differences in the response of cereals and cereal weeds to chlortoluron.

The uptake of the auxins indole-3-acetic acid (IAA) and 1-naphthylacetic acid (NAA) was investigated using fluorimetric methods of assay. Uptake by the following plant material was examined - segments of Avena coleoptile, maize mesocotyl and the hypocotyl of Phaseolus radiatus. The growth regulating substances 2,4-dichlorophenoxyacetic acid, triiodobenzoic acid (TIBA), N-l-naphthyl-phthalamic acid, (1-naphthyl-methyl-sulphide) - propionic acid, and 3:5-diiodo- and 3:5-dibromo-4-hydroxybenzonitrile were examined for their effects on the entry and accumulation of IAA and NAA. Experiments were conducted to distinguish between the initial physical phase of uptake and subsequent metabolic uptake by pretreatment of the tissue with metabolic inhibitors and poisons. As fluorescence assay can be employed, under the experimental conditions, only for measuring loss of the auxins from the external medium, C14-labelled IAA and I131-labelled TIBA were used to assay actual uptake by the plant material. As it was suspected that the effects of TIBA on the uptake of IAA were exerted through metabolic action on a sulfhydryl-enzyme system, various SH-enzyme protectors (2,3-dimercaptopropanol, cysteine) were tested in attempts towards tracing the mechanism of TIBA action. Chromatographic and fluorimetric analysis of variously treated material has been undertaken. Autoradiographic analysis to check the nature and degree of IAA metabolism and the effects of TIBA on it was conducted, and measurements made of respiratory decarboxylation of IAA - C14 under the experimental conditions. The results have been critically discussed with reference to the literature dealing with synergism and antagonism between growth regulators, uptake and transport of auxins, mechanism of auxin action in growth, general aspects of membrane permeability and solute transport, and auxin kinetics.

With an expanding population and uncertain consequences of climate change, the need to both stabilise and increase crop yields is important. The relationship between biomass production and radiation interception suggests one target for improvement. Under optimal growing conditions, biomass production is determined by the amount of light intercepted and the efficiency with which this is converted into dry matter. The amount of light at a given photosynthetic surface is dependent upon solar movement, weather patterns and the structure of the plant, amongst others. Optimising canopy structure provides a method by which we can improve and optimise both radiation interception and also the distribution of light among canopy layers that contribute to net photosynthesis. This requires knowledge of how canopy structure determines light distribution and therefore photosynthetic capacity of a given crop species. The aim of this thesis was to assess the relationships between canopy architecture, the light environment and photosynthesis. This focused on two core areas: the effect of varietal selection and management practices on canopy structure and the light environment and; the effect of variable light on select photosynthetic processes (photoinhibition and acclimation). An image-based reconstruction method based on stereocameras was employed with a forward ray tracing algorithm in order to model canopy structure and light distributions in high-resolution. Empirical models were then applied using parameterisation from manually measured data to predict the effects of variable light on photosynthesis. The plasticity of plants means that the physical structure of the canopy is dependent upon many different factors. Detailed descriptions of canopy architecture are integral to predicting whole canopy photosynthesis due to the spatial and temporal differences in light profiles between canopies. This inherent complexity of the canopy means that previous methods for calculating light interception are often not suitable. 3-dimensional modelling can provide a quick and easy method to retain this complexity by preserving small variations. This provides a means to more accurately quantify light interception and enable the scaling of cellular level processes up to the whole canopy. Results indicate that a canopy with more upright leaves enables greater light penetration to lower canopy layers, and thus higher photosynthetic productivity. This structural characteristic can also limit radiation-induced damage by preventing exposure to high light, particularly around midday. Whilst these features may lead to higher photosynthetic rates per unit leaf area, per unit ground area, photosynthesis is usually determined by total leaf area of the canopies, and within this study, the erect canopies tended to have lower total leaf areas than the more horizontal canopies. The structural arrangement of plant material often led to low levels of light within the lower canopy layers which were punctuated by infrequent, high light events. However, the slow response of photosynthesis to a change in light levels meant that these sun flecks cannot be used by the plant and thus the optimal strategy should be geared towards light harvesting and efficient photosynthesis under low light conditions. The results of this study contribute to our understanding of photosynthetic processes within the whole canopy and provide a foundation for future work in this area.

Plants establish associations with beneficial fungi in order to overcome abiotic and biotic stresses. An example is Serendipita indica, which colonises the roots of a broad range of plant species, including Arabidopsis thaliana. S. indica has been shown to increase crop yield, induce tolerance against drought and salinity, and enhance pathogen resistance in plants. However, the underlying molecular mechanism, utilised by S. indica to confer these beneficial effects to the host plant, is unknown. S. indica may induce beneficial effects in plants, through the use of effector proteins. Sequencing of the S. indica genome, revealed 386 putative effectors. To elucidate the full sequences of these effector candidates, the S. indica transcriptome was sequenced. A shortlist of 150 S. indica effector candidates was generated for experimental investigation. The potential A. thaliana targets of these 150 putative effectors, were identified through Yeast-two hybrid screening, and by identifying differentially regulated genes from RNA-seq data. Only 38 A. thaliana proteins, that were targeted by the S. indica effector candidates, are known pathogen effector targets. Therefore, the majority of S. indica plant targets are novel, and may not be affected by plant pathogens. These novel targets provide new opportunities, for scientists to engineer crop plants that produce greater yields, and exhibit enhanced resistance to drought, salinity and disease. One pathogen S. indica is known to induce resistance against, is the necrotrophic pathogen Fusarium graminearum. To identify if any S. indica effector candidates, were responsible for protecting barley from F. graminearum, a screening process was set up. This involved the optimisation of a stable barley root transformation system, and the adaptation of F. graminearum inoculation procedures. A metabolite extraction procedure was also developed, to determine if any S. indica specialised metabolites were involved in promoting F. graminearum resistance in barley.

No description available.

In spite of constant technological advancements, world hunger remains a major challenge due to exponential population growth, and the loss of e effectiveness of crop treatments such as pesticides. As such, comprehending the plant response to stress is of great importance in breeding more resilient crops. Whilst different stresses elicit distinct responses from the plant, a core set of regulatory interactions are conserved across multiple responses and operate as networks. In this thesis, computational approaches were used to elucidate such regulatory interactions from time course expression datasets, predominantly through identification of genes co-expressed across multiple stimuli responses as a footprint of shared network co-regulation. The identification of such network footprints was tackled through Wigwams, a data mining algorithm capable of detecting groups of genes co-regulated across multiple datasets. In contrast to other algorithms, Wigwams assesses whether the co-expression it detects is likely to reflect co-regulation. The modules it found were significantly enriched in functionality and cis-regulatory elements, indicating actual co-regulation. Wigwams and other computational approaches were applied to time course expression data capturing Arabidopsis thaliana response to Pseudomonas syringae pv. tomato DC3000. The presence of a virulent and avirulent strain in the experiment allowed for the temporal deconstruction of the regulatory events underlying the virulent strain's attempts to overcome plant defence through effector action. This analysis led to the detection of a number of effector-specific transcription changes stifling the defence response and manipulating the host's gene and protein expression. A transcription factor-only regulatory network model was proposed to explain the detected network footprints. The inference of causal regulatory networks from expression data is a daunting task, and transcription factor-only models are a good computational compromise by capturing the key regulatory events taking place. However, they are lacking in target genes that carry out the functionality induced by the signalling, making functional assessment di cult. Wigwams was used to introduce the network footprint components into the corresponding transcription factor-only models, resulting in enhanced network models carrying information about downstream regulated genes. This allows for functional assessment to be used to identify nodes of interest within the network, and propose concise follow-up experiments.

Most plants complete their life cycle in a single location and therefore are affected by the changing environment. As a result, plants have evolved physiological and developmental adaptations to overcome stress. The work presented in this thesis has examined the regulation of photosynthetic electron transport in barley, rice and Thellungiella salsuginea. Barley is considered as a crop which is comparatively tolerant to soil salinity. The focus of this study was to evaluate the physiological responses of photosynthesis in barley under salinity and to characterize traits responsible for the regulation of photosynthesis. At low salt concentrations, barley plants protect PSII centres from excitation pressure by down-regulating the electron transport chain and maintaining ΔpH, by cyclic electron transport associated with PSI, to support nonphotochemical quenching (NPQ). However, at the highest concentration of salt examined, this regulation starts to fail. The failure might result from a specific loss of PSI, resulting in reduced cyclic electron flow, or an increase in the leakiness of the thylakoid membranes, resulting in loss of ΔpH. The effects of salinity on the regulation of electron transport through Photosystem I and Photosystem II have been studied in two rice varieties from Sri Lanka. The regulation of photosynthesis in the salt-tolerant At-354 is more prominent than in the salt-sensitive Bg-352 when plants are exposed to salt. Exposure of Bg-352 to salt resulted in a substantial decrease in gas exchange, PSII photochemistry, leaf area and loss of chlorophylls. The decrease in the photosynthesis in AT-354 is caused by stomatal limitations, which restrict the CO2 entry into the plants, whereas the decrease of photosynthesis in Bg-352 is caused by non-stomatal limitations. Results suggest that At-354 protects PSII centres from excitation pressure by down-regulating the electron transport chain and maintaining ΔpH by cyclic electron transport associated with PSI to support NPQ. At high salt concentration, this regulation starts to fail in Bg-352.Tolerance to abiotic and biotic stress has evolved in many wild plant species, termed extremophiles. These plants contain essential genes which may used to improve crop production in changing environments. Thellungiella salsuginea is an extremophile, able to grow and reproduce in extreme environments. Stepien and Johnson (2009) identified a protein, known as the plastid terminal oxidase (PTOX) which acts as an alternative electron sink in T. salsuginea under salt stress. The current study showed that, in addition to salt, T. salsuginea showed increases in PTOX protein content and activity when exposed to drought, different growth irradiances and cold with high light. Semi-natural conditions also triggered the activity of PTOX. This study also showed that salt caused an up-regulation of PTOX gene transcripts in the leaves of salt treated T. salsuginea plants compared to control plants. Direct electron transport from PSII to PTOX and then to oxygen via the PQ pool accounted for up to 30% of total PSII electron flow in T. salsuginea (Stepien and Johnson, 2009). Efficient electron flow from PSII to PTOX would however, probably require co-location of these complexes in the same thylakoid fraction. To examine the location of PTOX in the thylakoid membrane, immunoblot analyses were performed, to test for changes in other protein complexes which may be associated with PTOX. In addition blue-native polyacrylamide gel electrophoresis and immunoblots were performed to isolate and detect the PTOX protein with any associated complexes. Although immunoblot analysis showed a prominent signal, mass spectrometry data did not allow identification of PTOX. This results suggests that further studies are needed to identify the precise localisation of the PTOX protein in the thylakoid membranes in T. salsuginea.

謝雪梅. / 手稿本 (cops. 2-3複印本). / Thesis (M.A.)--香港中文大學硏究院中國語文學部. / Shou gao ben (cops. 2-3 fu yin ben). / Includes bibliographical references (leaves 315-323). / Xie Xuemei. / Thesis (M.A.)--Xianggang Zhong wen da xue yan jiu yuan Zhongguo yu wen xue bu. / Chapter 一 --- 引言 --- p.1 / Chapter 二 --- 庾信生平簡介 --- p.7 / Chapter 三 --- 哀江南賦之寫作年代與背景 --- p.12 / Chapter 四 --- 哀江南賦之題解與結構 --- p.26 / Chapter 五 --- 哀江南賦之主旨　 --- p.43 / Chapter 六 --- 哀江南賦之字句 / Chapter （1) --- 對仗分析 --- p.52 / Chapter （2) --- 句式分析 --- p.68 / Chapter （3) --- 散行運用分析 --- p.78 / Chapter （4) --- 虛字運用分析 --- p.85 / Chapter 七 --- 哀江南賦之事類 --- p.94 / Chapter （1) --- 用事之手法 --- p.98 / Chapter （2) --- 事類之編排 --- p.104 / Chapter （3) --- 用事之特色 --- p.109 / Chapter （4) --- 用事之評價 --- p.131 / Chapter 八 --- 哀江南賦之聲律 / Chapter （1) --- 用韻參差 --- p.143 / Chapter （2) --- 平仄諧協 --- p.166 / Chapter （3) --- 聲情相配 --- p.169 / Chapter 九 --- 哀賦與離騷之比較 --- p.176 / Chapter （1) --- 內容(事、義、情、志) --- p.177 / Chapter （2) --- 技巧(想象、對比、穿插、急流轉棹) --- p.200 / Chapter 十 --- 歸魂賦、觀我生賦與哀江南賦之比較 --- p.221 / Chapter 十一 --- 哀賦與擬連珠、擬詠懷及傷心賦之匯通 --- p.266 / Chapter 十二 --- 哀江南賦之評價及其影響 --- p.286 / 注釋 --- p.306 / 參考書目 --- p.315 / 參考論文 --- p.322 / Chapter 附錄： --- 哀賦異解札記 --- p.324

Thesis (M.A.)--香港中文大學. / Manuscript. / Includes bibliographical references (p. 1-5 (4th group)). / Thesis (M.A.)--Xianggang Zhong wen da xue. / 自　序 / 例　言 / Chapter 第一編 --- 緒論 / Chapter 第一章 --- 駢文之名義及其特質　 --- p.1 / Chapter 第二章 --- 駢文之起源 --- p.20 / Chapter 第三章 --- 六朝後期駢文之特色 --- p.36 / Chapter 第二編 --- 庚信生平 / Chapter 第一章 --- 信之先世 --- p.46 / Chapter 第二章 --- 南朝之仕 --- p.54 / Chapter 第三章 --- 北朝之仕 --- p.68 / Chapter 第四章 --- 信之家屬 --- p.76 / Chapter 第三編 --- 庾信賦論 / Chapter 第一章 --- 賦之緣起標準及其至六朝之流變 --- p.80 / Chapter 第二章 --- 前後期作品之異 --- p.91 / Chapter 第三章 --- 前期賦作　 --- p.97 / Chapter 第一節 --- 春　賦　 --- p.97 / Chapter 第二節 --- 燈賦鏡賦及鴛鴦賦 --- p.103 / Chapter 第三節 --- 七夕賦對燭賦及蕩子賦 --- p.111 / Chapter 第四章 --- 後期賦作（哀江南賦除外） --- p.116 / Chapter 第一節 --- 小園賦　 --- p.116 / Chapter 第二節 --- 枯樹賦 --- p.134 / Chapter 第三節 --- 傷心賦 --- p.151 / Chapter 第四節 --- 竹杖賦與邛竹杖賦 --- p.156 / Chapter 第五節 --- 象戲賦及馬射賦 --- p.164 / Chapter 第五章 --- 哀江南賦 --- p.175 / Chapter 第一節 --- 寫作動機´ؤ´ؤ試評陳寅恪先生之說 --- p.175 / Chapter 第二節 --- 結構及主題 --- p.210 / Chapter 第三節 --- 評價　 --- p.226 / Chapter 第四編 --- 各體駢文分論（上） / Chapter 第一章 --- 表序 --- p.241 / Chapter 第一節 --- 表序之緣起及標準 --- p.241 / Chapter 第二節 --- 慶賀之表 --- p.248 / Chapter 第三節 --- 懇請之表　 --- p.259 / Chapter 第四節 --- 進貢之表 --- p.271 / Chapter 第五節 --- 趙國公集序 --- p.281 / Chapter 第二章 --- 書啟 --- p.285 / Chapter 第一節 --- 書啟之緣起及標準　 --- p.285 / Chapter 第二節 --- 答謝滕王諸啟 --- p.291 / Chapter 第三節 --- 答謝趙王諸啟 --- p.298 / Chapter 第四節 --- 其他 --- p.311 / Chapter 第三章 --- 連珠 --- p.318 / Chapter 第一節 --- 連珠之緣起及標準 --- p.318 / Chapter 第二節 --- 擬連珠四十四首　　 --- p.323 / Chapter 第五編 --- 各體駢文分論（下） / Chapter 第一章 --- 銘 --- p.338 / Chapter 第一節 --- 銘之緣起及標準 --- p.338 / Chapter 第二節 --- 梁東宮諸山銘 --- p.342 / Chapter 第三節 --- 思舊銘　 --- p.349 / Chapter 第四節 --- 其他 --- p.358 / Chapter 第二章 --- 碑 --- p.364 / Chapter 第一節 --- 碑之緣起及標準 --- p.364 / Chapter 第二節 --- 陝州弘農郡王張寺經藏碑及溫湯碑 --- p.371 / Chapter 第三節 --- 神道碑（上） --- p.379 / Chapter 第四節 --- 神道碑（下）　 --- p.395 / Chapter 第三章 --- 誌銘　 --- p.415 / Chapter 第一節 --- 誌銘之緣起及標準 --- p.415 / Chapter 第二節 --- 名臣誌銘（上） --- p.428 / Chapter 第三節 --- 名臣誌銘（下） --- p.433 / Chapter 第四節 --- 司馬裔鄭常神道碑與墓誌銘之比較 --- p.443 / Chapter 第五節 --- 夫人誌銘 --- p.453 / Chapter 第六編 --- 庾信與徐陵 / Chapter 第一章 --- 徐庾體與宮體　 --- p.468 / Chapter 第二章 --- 身世之比較 --- p.476 / Chapter 第三章 --- 作品之比較 --- p.485 / Chapter 第一節 --- 賦銘 --- p.485 / Chapter 第二節 --- 表序 --- p.488 / Chapter 第三節 --- 碑誌　 --- p.493 / Chapter 第四節 --- 書啟 --- p.497 / Chapter 第四章 --- 總結 --- p.505 / Chapter 第七編 --- 結　論 / Chapter 第一章 --- 庾信駢文對後世影響舉隅 --- p.516 / Chapter 第一節 --- 初唐四傑 --- p.516 / Chapter 第二節 --- 陳維崧與王闓連 --- p.529 / Chapter 第二章 --- 庾信在中國文學史之地位 --- p.542 / Chapter 第一節 --- 駢文之價值 --- p.542 / Chapter 第二節 --- 庾信駢文之評價 --- p.551 / 參考書目 / 參考論文