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We have used top-down metabolic control analysis to investigate the control of carbon flux through potato (Solanum tuberosum) plants during tuberisation. The metabolism of the potato plant was divided into two blocks of reactions (the source and sink blocks) that communicate through the leaf apoplastic sucrose pool. Flux was measured as the transfer of 14C from CO2 to the tuber. Flux and apoplastic sucrose concentration were varied either by changing the light intensity or using transgenic manipulations that specifically affect the source or sink blocks, and elasticity coefficients were measured. We have provided evidence in support of our assumption that apoplastic sucrose is the only communicating metabolite between the source and sink blocks. The elasticity coefficients were used to calculate the flux control coefficients of the source and sink blocks, which were 0.8 and 0.2, respectively. This work suggests that the best strategy for the manipulation of tuber yield in potato will involve increases in photosynthetic capacity, rather than sink metabolism.

Most applications of thermodynamic databases to materials design are limited to ambient pressure. The consideration of elastic contributions to thermodynamic stability is highly desirable but not straight-forward to realise. We present examples of existing physical models for pressure-dependent thermodynamic functions and discuss the requirements for future implementations given the existing results of experiments and first-principles calculations. We briefly summarize the calculation of elastic constants and point out examples of nonlinear variation with pressure, temperature and chemical composition that would need to be accounted for in thermodynamic databases. This is particularly the case if a system melts from different phases at different pressures. Similar relations exist between pressure and magnetism and hence set the need to also include magnetic effects in thermodynamic databases for finite pressure. We present examples to illustrate that the effect of magnetism on stability is strongly coupled to pressure, temperature, and external fields. As a further complication we discuss dynamical instabilities that may appear at finite pressure. While imaginary phonon frequencies may render a structure unstable and destroy a crystal lattice, the anharmonic effects may stabilize it again at finite temperature. Finally, we also outline a possible implementation scheme for strain effects in thermodynamic databases.

Potato tubers are modified stems that have differentiated into storage organs. Factors such as day-length, nitrogen supply, and levels of the phytohormones cytokinin and gibberellic acid, are known to control tuberization. Morphological changes during tuber initiation are accompanied by the accumulation of a characteristic set of proteins, thought to be involved in N-storage (i.e. patatin) or defense against microbial or insect attack (i.e. proteinase inhibitor II). Additionally, deposition of large amounts of starch occurs during tuber formation, which is paralleled by an increase in sucrose synthase and other enzymes involved in starch biosynthesis (i.e. ADP-glucose pyrophosphorylase, starch synthases, and branching enzyme). Potential controlling mechanisms for genes expressed during tuberization are discussed.

A chimaeric antisense construct was used to reduce the activities of the two major starch-synthase isoforms in potato tubers simultaneously. A range of reductions in total starch-synthase activities were found in the resulting transgenic plants, up to a maximum of 90% inhibition. The reduction in starch-synthase activity had a profound effect on the starch granules, which became extremely distorted in appearance compared with the control lines. Analysis of the starch indicated that the amounts produced in the tubers, and the amylose content of the starch, were not affected by the reduction in activity. In order to understand why the starch granules were distorted, amylopectin was isolated and the constituent chain lengths analysed. This indicated that the amylopectin was very different to that of the control. It contained more chains of fewer than 15 glucose units in length, and fewer of between 15 and 80 glucose units. In addition, the amylopectin contained more very long chains. Amylopectin from plants repressed in just one of the activities of the two starch-synthase isoforms, which we have reported upon previously, were also analysed. Using a technique different to that used previously we show that both isoforms also affect the amylopectin, but in a way that is different to when both isoforms are repressed together.

The leaf boundary layer, i. e. the layer of air adjacent to a leaf surface in which gas flow is significantly influenced by the leaf, considerably affects leaf gas exchange. Numerous factors, both external conditions and leaf properties, have a strong influence on boundary layer characteristics and the challenge to develop a reliable model of this link in the leaf gas exchange pathway has persisted for decades. Two parameters, the boundary layer thickness, d, and the ratio, B, of the diffusion coefficients of gases in the boundary layer and in the intercellular space, were shown to be sufficient to represent the effect of the boundary layer in a two-dimensional leaf gas exchange model 2DLEAF. An algorithm for calculation of these parameters is described and applied to simulate the transpiration rate of leaves in normal (cv. Desiree) and transgenic (expressing a mRNA antisense construct targeted to the cp-fructose-6-bisphosphate phosphatase) potato plants (Solanum tuberosum). For these leaves, both gas exchange and leaf anatomy have been studied. Parameters d and B were different for normal and transgenic leaves, and they expressed real differences in anatomy and surface properties.

In 2003 the Plant Research Department (PRD) at Risø National Laboratory was involved in establishing the consortium Plant Biotech Denmark, which is unifying most of the Danish Plant Biotechnology activities. Within the consortium, PRD has the uniqueopportunity to be the only life science department located in an environment that is largely dominated by physicists. PRD is challenged to optimally interface Plant Biology with the different fields of expertise that are established at Risø NationalLaboratory. These activities are mainly related to develop novel post-genomic tools to assign function to genes, which are widely applicable in the life sciences, such as non-invasive and non-destructive technologies to determine metabolite concentrationswith high spatial and temporal resolution. The Plant Research Department applies these and state-of-the-art technologies to increase knowledge to develop crops with improved agronomic traits and to engineer high-value compound containing plants.

The Plant Research Department integrates modern post-genomic tools to improve our understanding of plants. The aim is to develop crops with improved agronomic traits and to engineer high-value plants, which are able to meet the growth conditions of thefuture environment. The department is divided into six research programmes that are linked through their individual expertise delivered to the rest of the department. Three programmes are engaged in improving the agronomic performance of plants. Genetictools are being developed to enhance the nutrient efficiency of plants, to strengthen the ability of plants to resist fungal attack, and to optimise flowering time. Two programmes are devoted to improving the market value of plant products. Plants withenhanced nutritional value, or that contain novel renewable resources, are designed to add value to the European Agro-Industries. A sixth programme studies the effects of the future climate on plant growth, and the performance of newly designed crops andtheir interaction with the environment. Several activities in the area of Functional Genomics integrate the department. Each programme contains special expertise in the fields of genome, transcriptome, proteome, and metabolome analyses, which aredelivered throughout the department. The Plant Research Department is unique in that these activities are supplemented with a broad expertise in environmental analysis, allowing the interpretation of large biological data sets in the context of factorsaffecting plant growth.

The Department of Plant Biology and Biogeochemistry is engaged in basic and applied research to improve the scientific basis for developing new methods and technology for an environmentally benign industrial and agricultural production in the future. TheDepartment's expertise covers a wide range of areas needed to develop crops that meet the demands to increase agricultural production for a growing population, to produce plants with improved nutritional value, to develop crops that deliver renewableresources to the industry, and to generate plants that are adapted to the future climate. The projects are organized in six research programmes that are linked to each other through the individual expertise that is delivered by each of the programs tothe rest of the department.