Entwicklung und Anwendung von verläßlichen Methoden zur Berechnung angeregter Zustände : von Lichtsammelkomplexen bis zu mittelgroßen Molekülen

Photo-initiated processes, like photo-excitation and -deexcitation, internal conversion, excitation energy transfer and electron transfer, are of importance in many areas of physics, chemistry and biology. For the understanding of such processes, detailed knowledge of excitation energies, potential energy surfaces and excited state properties of the involved molecules is an essential prerequisite. To obtain these informations, quantum chemical calculations are required. Several quantum chemical methods exist which allow for the calculation of excited states. Most of these methods are computationally costly what makes them only applicable to small molecules. However, many biological systems where photo-processes are of interest like light-harvesting complexes in photosynthesis or the reception of light in the human eye by rhodopsin are quite large. For large systems, however, only few theoretical methods remain applicable. The currently most widely used method is time-dependent density functional theory (TD-DFT), which can treat systems of up to 200–300 atoms with the excitation energies of some excited states exhibiting errors of less than 0.5 eV. Yet, TD-DFT has several drawbacks. The most severe failure of TD-DFT is the false description of charge transfer states which is particularly problematic in case of larger systems where it yields a multitude of artificially low-lying charge transfer states. But also Rydberg states and states with large double excitation character are not described correctly. Still, if these deficiencies are kept in mind during the interpretation of results, TD-DFT is a useful tool for the calculation of excited states. In my thesis, TD-DFT is applied in investigations of excitation energy and electron transfer processes in light-harvesting complexes. Since light-harvesting complexes, which consist of thousands of atoms, are by far too large to be calculated, model complexes for the processes of interest are constructed from available crystal structures. The model complexes are used to calculate potential energy curves along meaningful reaction coordinates. Artificial charge transfer states are corrected with the help of the so-called ∆DFT method. The resulting potential energy curves are then interpreted by comparison with experimental results. For the light-harvesting complex LH2 from purple bacteria the experimentally observed formation of carotenoid radical cations is studied. It is shown that the carotenoid radical cation is formed most likely via the optically forbidden S1 state of the carotenoid. In light-harvesting complex LHC-II of green plants the fast component of the so-called non-photochemical quenching (NPQ) is investigated. Two of several different hypotheses on the mechanism of NPQ, which have been proposed recently, are studied in detail. The first one suggests that NPQ proceeds via simple replacement of violaxanthin by zeaxanthin in the binding pocket in LHC-II. However, the calculated potential energy curves exhibit no difference between violaxanthin and zeaxanthin in the binding pocket. In combination with experimental results it is thus shown that simple replacement alone does not mediate NPQ in LHC-II. The second hypothesis proposes conformational changes of LHC-II that lead to quenching at the central lutein and chlorophyll molecules during NPQ. My TD-DFT calculations demonstrate that if this mechanism is operative, only the lutein 1 which is one of two central luteins present in LHC-II can take part in the quenching process. This is corroborated by recent experiments. Though several conclusions can be drawn from the investigations using TD-DFT, the interpretability of the results is limited due to the deficiencies of the method and of the models. To overcome the methodological deficiencies, more accurate methods have to be employed. Therefore, the so-called algebraic diagrammatic construction scheme (ADC) is implemented. ADC is a widely overlooked ab initio method for the calculation of excited states, which is based on propagator theory. Its theoretical derivation proceeds via perturbation expansion of the polarization propagator, which describes electronic excitations. This yields separate schemes for every order of perturbation theory. The second order scheme ADC(2), which is employed here, is the equivalent to the Møller-Plesset ground state method MP(2), but for excited states. It represents the computationally cheapest excited state method which can correctly describe doubly excited states, as well as Rydberg and charge transfer states. The quality of ADC(2) results is demonstrated in calculations on linear polyenes which serve as model systems for the larger carotenoid molecules. The calculations show that ADC(2) describes the three lowest excited states of polyenes sufficiently well, particularly the optically forbidden S1 state which is known to possess large double excitation character. Yet, the applicability of the method is limited compared to TD-DFT due to the much larger computational requirements. To facilitate the calculation of larger systems with ADC(2) a new variant of the method is developed and implemented. The variant employs the short-range behavior of electron correlation to reduce the computational effort. As a first step, the working equations of ADC(2) are transformed into a basis of local orbitals. In this basis negligible contributions of the equations which are due to electron correlation can be identified based on the distances of local orbitals. A so-called “bumping” scheme is implemented which removes the negligible parts during a calculation. This way, the computation times as well as the disk space requirements can be reduced. With the “bumping” scheme several new parameters are introduced that regulate the amount of “bumping” and thereby the speed and the accuracy of computations. To determine useful values for the parameters an evaluation is performed using the linear polyene octatetraene as test molecule. From the evaluation an optimal set of parameter values is obtained, so that the computation times become minimal, while the errors in the excitation energies due to the “bumping” do not exceed 0.15 eV. With further calculations on various molecules of different sizes it is tested if these parameter values are universal, i.e. if they can be used for all molecules. The test calculations show that the errors in the excitation energies are below 0.15 eV for all test systems. Additionally, no trend is visible for the errors that their magnitude might depend on the system. In contrast, the amount of disregarded contributions in the calculations increases drastically with growing system size. Thus, the local variant of ADC(2) can be used in future to reliably calculate excited states of systems which are not accessible with conventional ADC(2).Lichtinduzierte Prozesse, wie Absorption, Emission, interne Konversion und Energie- und Elektrontransfer, sind in vielen Bereichen von Physik, Chemie und Biologie von Bedeutung. Zum Verständnis solcher Prozesse ist die genaue Kenntnis von Anregungsenergien, Potentialenergieflächen und Eigenschaften angeregter Zustände unabdingbar. Zum Erwerb dieser Informationen werden quantenchemische Verfahren benötigt, die die Berechnung angeregter Zustände erlauben. Die meisten der entsprechenden Methoden sind aufgrund ihrer Hardware-Anforderungen nur auf kleine Moleküle anwendbar. Viele der hier interessierenden Systeme, wie z.B. die Lichtsammelkomplexe in Pflanzen oder das Rhodopsin im menschlichen Auge, sind jedoch sehr groß, so dass nur wenige Methoden für die Berechnung dieser Systeme in Frage kommen. Eine häufig verwendete Methode ist die zeitabhängige Dichtefunktionaltheorie (TD-DFT), mit deren Hilfe sich Systeme von bis zu 200–300 Atomen berechnen lassen, ohne dass die Fehler in den Anregungsenergien mancher Zustände 0.5 eV überschreiten. Allerdings, hat TD-DFT auch einige Nachteile. Der schwerwiegendste davon ist das Versagen bei der Berechnung von Ladungstransferzuständen, was besonders für große Systeme zu einer Fülle solcher Zustände mit viel zu niedrigen Anregungsenergien führt. Desweiteren können auch sogenannte Rydberg-Zustände und Zustände mit starkem Doppelanregungscharakter nicht richtig beschrieben werden. Trotzdem lässt sich die Methode gut zur Berechnung von angeregten Zuständen einsetzen, wenn man bei der Interpretation der entsprechenden Ergebnisse die vorhandenen Probleme berücksichtigt. In dieser Arbeit wird TD-DFT zur Untersuchung von Energie- und Elektronentransferprozessen in Lichtsammelkomplexen eingesetzt. Da Lichtsammelkomplexe mit ihren weit über 1000 Atomen auch für TD-DFT viel zu groß sind, werden zunächst anhand von Röntgenstrukturen Modellkomplexe für die jeweiligen Prozesse konstruiert. Mit diesen werden dann Potentialenergiekurven entlang geeigneter Reaktionskoordinaten berechnet. Die dabei auftretenden, schon erwähnten artifiziellen Ladungstransferzustände werden mit Hilfe der sogenannten ∆DFT-Methode korrigiert bzw. aussortiert. Durch Vergleich mit experimentellen Daten lassen sich die Potentialenergiekurven interpretieren. Beim in Purpurbakterien vorkommenden Lichtsammelkomplex LH2 wurde die photoinduzierte Bildung von Radikalkationen von Karotenoiden theoretisch studiert. Dabei zeigt sich, dass die Radikalkationen höchstwahrscheinlich über die S1 Zustände der jeweiligen Karotenoide entstehen. Desweiteren wurde der Mechanismus des nicht-photochemischen Quenchens (NPQ) in Lichtsammelkomplexen LHC-II von Pflanzen untersucht. Für den NPQ werden verschiedene mögliche Prozesse diskutiert, von denen hier zwei betrachtet wurden. Bei dem einen soll NPQ schon durch bloßen Austausch von Violaxanthin gegen Zeaxanthin in der Bindungstasche des LHC-II ablaufen. Allerdings zeigen die berechneten Potentialenergiekurven für Violaxanthin und Zeaxanthin keine entsprechenden Unterschiede. Daher lässt sich, gestützt durch weitere experimentelle Befunde, folgern, dass dieser einfache Mechanismus für NPQ nicht in Frage kommt. Beim zweiten Prozess lässt eine Konformationsänderung des LHC-II das Quenchen an den zentralen Lutein- und Chlorophyll-Molekülen stattfinden. Aus den Rechnungen dazu ergibt sich, dass, sollte dies der maßgebliche Mechanismus für NPQ sein, höchstens eins der zwei zentralen Luteine im LHC-II, das Lutein 1, am Quenchen teilnehmen kann. Trotz der obigen, aus TD-DFT-Rechnungen gewonnenen Erkenntnisse, bleibt die Interpretierbarkeit der Ergebnisse aufgrund der Unzulänglichkeiten der Methode und den stark vereinfachten Modellen doch beschränkt. Um die Probleme von TD-DFT zu umgehen, ist die Verwendung genauerer Methoden unausweichlich. Daher wurde hier als genauere Methode zur Berechnung angeregter Zustände die algebraisch-diagrammatische Konstruktion (ADC) weiterentwickelt. ADC ist eine weitgehend übersehene ab initio-Methode zur Berechnung angeregter Zustände, die auf dem Propagator-Formalismus beruht. Die Herleitung der Methode erfolgt über die störungstheoretische Entwicklung des Polarisationspropagators, der elektronische Anregungen beschreibt. Dabei ergibt sich für jede Ordnung der Störungstheorie eine neue Variante von ADC. In zweiter Ordnung ist das die im Folgenden verwendete ADC(2)-Methode. Sie entspricht für angeregte Zustände in etwa dem, was die bekannte Møller-Plesset-Störungstheorie MP(2) für Grundzustände darstellt. ADC(2) ist außerdem die am wenigsten aufwändige Methode, mit der doppelt angeregte Zustände, als auch Rydberg- und Ladungstransferzustände prinzipiell richtig beschrieben werden können. Die Qualität der ADC(2)-Ergebnisse wird in dieser Arbeit durch Rechnungen an linearen Polyenen demonstriert, die als Modelle für Karotenoide dienen. Die dabei erhaltenen, niedrigsten drei angeregten Zustände weisen eine ausreichende Genauigkeit auf. Allerdings lässt sich ADC(2) aufgrund des erhöhten Rechenaufwands nur auf wesentlich kleinere Systeme anwenden als TD-DFT. Um auch größere Systeme mit ADC(2) beschreiben zu können, habe ich in meiner Arbeit eine neue lokale Variante von ADC(2) entwickelt und implementiert. Diese Variante nutzt die Kurzreichweitigkeit der Elektronenkorrelation, um Rechenaufwand zu verringern. Für die Implementierung der Variante wurden die ADC-Gleichungen zunächst in eine Basis aus lokalen Orbitalen transformiert. In dieser Basis können mit Hilfe eines sogenannten ,,Bumping”-Schemas Teile der Berechnungen aufgrund des Abstandes der lokalen Orbitale vernachlässigt werden, was sowohl Rechenzeit verkürzt, als auch benötigten Speicher reduziert. Die Einführung des ,,Bumping”-Schemas resultiert in einer Reihe zusätzlicher Parameter. Diese Parameter sollten so gewählt sein, dass möglichst viel vernachlässigt werden kann, ohne dass jedoch der durch das ,,Bumping”-Schema verursachte Fehler in den Anregungsenergien 0.15 eV übersteigt. Ein Satz optimaler Parameterwerte wurde mittels Rechnungen an trans-Octatetraen bestimmt. Anschließend wurde die Qualität der Parameterwerte durch Rechnungen an mehreren, verschieden großen Molekülen überprüft. Dabei zeigt sich, dass die Fehler in den Anregungsenergien unabhängig vom Molekül etwa konstant bleiben. Gleichzeitig lässt sich bei den Rechnungen mit wachsender Systemgröße aber immer mehr vernachlässigen. Daher können mit der neuen, lokalen Variante von ADC(2) Rechnungen an Systemen durchgeführt werden, die mit dem konventionellen Verfahren nicht möglich sind, ohne dass dabei die Qualität der Ergebnisse leidet

Advances in molecular quantum chemistry contained in the Q-Chem 4 program package

A summary of the technical advances that are incorporated in the fourth major release of the Q-CHEM quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and open-shell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order Møller–Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly correlated Cr2 dimer, exploring zeolite-catalysed ethane dehydrogenation, energy decomposition analysis of a charged ter-molecular complex arising from glycerol photoionisation, and natural transition orbitals for a Frenkel exciton state in a nine-unit model of a self-assembling nanotube

Cell Wall Damage-Induced Lignin Biosynthesis Is Regulated by a Reactive Oxygen Species- and Jasmonic Acid-Dependent Process in Arabidopsis

The plant cell wall is a dynamic and complex structure whose functional integrity is constantly being monitored and maintained during development and interactions with the environment. In response to cell wall damage (CWD), putatively compensatory responses, such as lignin production, are initiated. In this context, lignin deposition could reinforce the cell wall to maintain functional integrity. Lignin is important for the plant’s response to environmental stress, for reinforcement during secondary cell wall formation, and for long-distance water transport. Here, we identify two stages and several components of a genetic network that regulate CWD-induced lignin production in Arabidopsis (Arabidopsis thaliana). During the early stage, calcium and diphenyleneiodonium-sensitive reactive oxygen species (ROS) production are required to induce a secondary ROS burst and jasmonic acid (JA) accumulation. During the second stage, ROS derived from the NADPH oxidase RESPIRATORY BURST OXIDASE HOMOLOG D and JA-isoleucine generated by JASMONIC ACID RESISTANT1, form a negative feedback loop that can repress each other’s production. This feedback loop in turn seems to influence lignin accumulation. Our results characterize a genetic network enabling plants to regulate lignin biosynthesis in response to CWD through dynamic interactions between JA and ROS

Photocatalytic water splitting with acridine dyes: Guidelines from computational chemistry

AbstractThe photocatalytic splitting of water into H and OH radicals in hydrogen-bonded chromophore-water complexes has been explored with computational methods for the chromophores acridine orange (AO) and benzacridine (BA). These dyes are strong absorbers within the range of the solar spectrum. It is shown that low-lying charge-transfer excited states exist in the hydrogen-bonded AOH2O and BAH2O complexes which drive the transfer of a proton from water to the chromophore, which results in AOHOH or BAHOH biradicals. The AOH and BAH radicals possess bright ππ∗ excited states with vertical excitation energies near 3.0eV which are predissociated by a low-lying repulsive πσ∗ state. The conical intersections of the πσ∗ state with the ππ∗ excited states and the ground state provide a mechanism for the photodetachment of the H-atom by a second photon. Our results indicate that AO and BA are promising chromophores for water splitting with visible light

Reduced expression of a gene encoding a Golgi localized monosaccharide transporter (OsGMST1) confers hypersensitivity to salt in rice (Oryza sativa)

Sugar transport is critical for normal plant development and stress responses. However, functional evidence for the roles of monosaccharide transporters in rice (Oryza sativa) has not previously been presented. In this study, reversed genetics was used to identify OsGMST1 as a member of the monosaccharide transporter family in rice. The predicted 481 amino acid protein has the typical features of a sugar transporter in the plastid glucose transporter subfamily consistent with reduced monosaccharide accumulation in plants with reduced OsGMST1 expression. OsGMST1-green fluorescent protein is localized to the Golgi apparatus. OsGMST1 expression is induced by salt treatment and reduced expression confers hypersensitivity to salt stress in rice. OsGMST1 may play a direct or an indirect role in tolerance to salt stress in rice

TaReCa – Cascade utilization of horticultural biomass for a resource efficient production of valuable bioactive substances

Viele pflanzliche Sekundärmetabolite haben antioxidative oder andere bioaktive Eigenschaften, weshalb sie einerseits wichtige Bestandteile der menschlichen Ernährung sind, andererseits aber auch als pharmazeutische Verbindungen oder als Substrat für die chemische Synthese von bioaktiven Substanzen verwendet werden. Pflanzen induzieren die Produktion solcher nutzbaren Sekundärmetabolite wie z.B. Flavonoiden als Reaktion auf abiotischen Stress. Die Produktion von Gemüse und Früchten in Gewächshäusern hinterlässt große Mengen an ungenutzter pflanzlicher Biomasse, welche eine potentielle Ressource für die Gewinnung wertvoller Metabolite darstellt. Durch eine kaskadenartige Verwendung von Gartenbaukulturen zur Produktion von Früchten und Gemüse mit einer anschließenden Gewinnung hochwertiger Substanzen aus der verbleibenden Restbiomasse würde ein erheblicher Mehrwert generiert. Das Projekt TaReCa bearbeitet die Entwicklung einer maßgeschneiderten Kaskadenverwertung von Paprikapflanzen-Restbiomasse aus dem Gartenbau. Dabei soll der pflanzliche Sekundärmetabolismus durch spezifische abiotische Stressbedingungen nach der Fruchternte gezielt induziert werden, um die Konzentrationen der Zielmetaboliten zu steigern. Durch umweltfreundliche und wirtschaftliche Extraktionsprozesse und eine anschließende Verwertung des verbleibenden Pflanzenmaterials in einer Bioraffinerie wird die Wertschöpfungskette erweitert. Eine Analyse der Anwendungsgebiete sowie Untersuchungen zur Akzeptanz der induzierten Inhaltsstoffe, Prozesse und Technologien werden helfen, das Marktpotenzial der Restbiomasse für die Nutzung in Kaskaden zu evaluieren. Die maßgeschneiderte Nutzung von Gartenbaubiomasse durch Lebensmittelproduktion, Extraktion bioaktiver Sekundärmetabolite und Bioraffinerien kann wirtschaftlich relevante, biobasierte Produkte für industrielle Anwendungen erzeugen und somit zur Entwicklung einer nachhaltigen, effizienten und integrierten Bioökonomie beitragen, ohne mit der Lebensmittelproduktion zu konkurrieren.Many plant secondary metabolites have antioxidant or pharmaceutically relevant properties, which makes them important components of the human diet, but also as pharmaceutical compounds or for the chemical synthesis of bioactive substances. Plants induce the production of secondary metabolites, e.g. flavonoids in response to environmental stress stimuli. The production of vegetables and fruits in greenhouses leaves huge amounts of so far under-utilized biomass after fruit harvest, which is a potential source for production of valuable metabolites. A cascade utilization of horticultural crops to produce fruits and vegetables with subsequent extraction of high quality compounds would generate significant added value. The project TaReCa is working on the development of a tailored cascade utilization of bell pepper plant residues from horticulture. The secondary metabolism will be induced by specific abiotic stress treatments after the last fruit harvest, in order to increase the concentrations of the target metabolites. Eco-friendly and economical extraction processes and subsequent utilization of the remaining plant material in a biorefinery will expand the value chain. An analysis of the application areas as well as studies on the acceptance of the induced ingredients, processes and technologies will help to evaluate the market potential of the residual biomass for the proposed cascaded use. The tailored utilization of horticultural biomass in food production, extraction of bioactive secondary metabolites and biorefineries can produce economically relevant bio-based products for industrial applications and thus contribute to the development of a sustainable, efficient and integrated bioeconomy without competing with food production

Expression analysis and functional characterization of the monosaccharide transporters, OsTMTs, involving vacuolar sugar transport in rice (Oryza sativa)

In Arabidopsis, the compartmentation of sugars into vacuoles is known to be facilitated by sugar transporters. However, vacuolar sugar transporters have not been studied in detail in other plant species. To characterize the rice (Oryza sativa) tonoplast monosaccharide transporters, OsTMT1 and OsTMT2, we analysed their subcellular localization using green fluorescent protein (GFP) and expression patterns using reverse-transcription polymerase chain reaction (RT-PCR), performed histochemical beta-glucuronidase (GUS) assay and in situ hybridization analysis, and assessed sugar transport ability using isolated vacuoles. Expression of OsTMT-GFP fusion protein in rice and Arabidopsis revealed that the OsTMTs localize at the tonoplast. Analyses of OsTMT promoter-GUS transgenic rice indicated that OsTMT1 and OsTMT2 are highly expressed in bundle sheath cells, and in vascular parenchyma and companion cells in leaves, respectively. Both genes were found to be preferentially expressed in the vascular tissues of roots, the palea/lemma of spikelets, and in the main vascular tissues and nucellar projections on the dorsal side of the seed coats. Glucose uptake studies using vacuoles isolated from transgenic mutant Arabidopsis (tmt1-2-3) expressing OsTMT1 demonstrated that OsTMTs are capable of transporting glucose into vacuoles. Based on expression analysis and functional characterization, our present findings suggest that the OsTMTs play a role in vacuolar glucose storage in rice

Exploring the structure of the N-terminal domain of CP29 with ultrafast fluorescence spectroscopy

A high-throughput Förster resonance energy transfer (FRET) study was performed on the approximately 100 amino acids long N-terminal domain of the photosynthetic complex CP29 of higher plants. For this purpose, CP29 was singly mutated along its N-terminal domain, replacing one-by-one native amino acids by a cysteine, which was labeled with a BODIPY fluorescent probe, and reconstituted with the natural pigments of CP9, chlorophylls and xanthophylls. Picosecond fluorescence experiments revealed rapid energy transfer (~20–70 ps) from BODIPY at amino-acid positions 4, 22, 33, 40, 56, 65, 74, 90, and 97 to Chl a molecules in the hydrophobic part of the protein. From the energy transfer times, distances were estimated between label and chlorophyll molecules, using the Förster equation. When the label was attached to amino acids 4, 56, and 97, it was found to be located very close to the protein core (~15 Å), whereas labels at positions 15, 22, 33, 40, 65, 74, and 90 were found at somewhat larger distances. It is concluded that the entire N-terminal domain is in close contact with the hydrophobic core and that there is no loop sticking out into the stroma. Most of the results support a recently proposed topological model for the N-terminus of CP29, which was based on electron-spin-resonance measurements on spin-labeled CP29 with and without its natural pigment content. The present results lead to a slight refinement of that model

Expression Patterns of Genes Involved in Sugar Metabolism and Accumulation during Apple Fruit Development

Both sorbitol and sucrose are imported into apple fruit from leaves. The metabolism of sorbitol and sucrose fuels fruit growth and development, and accumulation of sugars in fruit is central to the edible quality of apple. However, our understanding of the mechanisms controlling sugar metabolism and accumulation in apple remains quite limited. We identified members of various gene families encoding key enzymes or transporters involved in sugar metabolism and accumulation in apple fruit using homology searches and comparison of their expression patterns in different tissues, and analyzed the relationship of their transcripts with enzyme activities and sugar accumulation during fruit development. At the early stage of fruit development, the transcript levels of sorbitol dehydrogenase, cell wall invertase, neutral invertase, sucrose synthase, fructokinase and hexokinase are high, and the resulting high enzyme activities are responsible for the rapid utilization of the imported sorbitol and sucrose for fruit growth, with low levels of sugar accumulation. As the fruit continues to grow due to cell expansion, the transcript levels and activities of these enzymes are down-regulated, with concomitant accumulation of fructose and elevated transcript levels of tonoplast monosaccharide transporters (TMTs), MdTMT1 and MdTMT2; the excess carbon is converted into starch. At the late stage of fruit development, sucrose accumulation is enhanced, consistent with the elevated expression of sucrose-phosphate synthase (SPS), MdSPS5 and MdSPS6, and an increase in its total activity. Our data indicate that sugar metabolism and accumulation in apple fruit is developmentally regulated. This represents a comprehensive analysis of the genes involved in sugar metabolism and accumulation in apple, which will serve as a platform for further studies on the functions of these genes and subsequent manipulation of sugar metabolism and fruit quality traits related to carbohydrates