Theme 3: Metabolism and Adaptation

The central role of plants in nature is based on the fact that plants and plant-based products are essential nutrition elements for man and animals or starting material for chemical-industrial activity, both for food and non-food applications. The extraordinary and very specific biosynthetic capacities of plants, yield compounds that are used as e.g. medicines, pigments or insect deterrents. Therefore, large research efforts are focussed on the unravelling of the metabolic path-ways involved in the production of these plant-specific primary and secondary metabolites and the regulation of their production; at the same time attention is drawn to many related fundamental physiological problems such as the tissue specificity of the various production pathways, the partitioning of precursors to the sites of synthesis and the coordinated growth and induction of specific storage cells, tissues and organs involved. An important challenge is the unravelling of the role of this large array of metabolites in the life cycle of the plant, not only from the point view of the experimental botanist who is interested in the fundamental basis of plant functioning but also to get better insight into the possibilities to steer the biosynthetic potentials of plants into other directions without affecting proper plant functioning.

In this field integrative approaches become more and more important. The combination of knowledge of the metabolic pathways, their (molecular-biological) regulation and role in the life cycle of the plant and their importance for plant survival, is needed for the sustainable production of plants. These plants form the basis for integrated plant conversion.

An important issue in this respect is the incorporation of this knowledge in the stategies of 'total chain approach' that are becoming more and more important nowadays: at the end of a production chain, the plant material used as starting material often needs a set of treatments or processing steps to isolate or purify the final product or to meet otherwise the needs of the consumer.

Instead of executing a large array of (often environmentally hazardous/undesirable) processing steps, it might be possible to adapt the properties of the plants used as starting material, e.g. by adapting lipid, starch or protein composition of specific organs or changing the spectrum or site of synthesis of secondary metabolites. A second issue fitting closely within this approach is emphasis on agrification, especially on non-food applications for existing (and new) crops.

In such an integrative approach, information is urgently needed about the in vivo changes in metabolic pathway activity, dynamics of various regulatory mechanisms and transfer of precursors and products at the level of the whole plant and its organs at a rapid time scale. Therefore, the development of advanced non-invasive measurement techniques has to be further promoted.

A field of research that is closely related to the integrated approach, is the background of the large variation of physiological performance and properties between plants. This variation manifests itself not only in differences in the occurrence of cell components but also in the adaptative potentials of plants: as a result of all kinds of variations within the same general metabolic framework, plant species show specific adaptations to their environment leading to differences in performance ranging from differences in growth rate to a changed plant architecture. Also their plasticity in relation to the reaction on all kinds of stress conditions shows great variation and a large range of specific adaptations to stress appears to have developed in the plant kingdom. Study of the underlying mechanisms is not only of interest from a fundamental point of view but might also give indications about the possibilities of adapting (crop) plant properties in a way that they can be grown under unfavourable climatic conditions.

The theme on metabolism and adaptation is subdivided in three subthemes.

Subtheme 3a:

Metabolites and Metabolic Pathways

One of the challenges is to unravel the mechanisms and the regulation of the various metabolic processes, and the interactions in the plant between these. Understanding of these regulatory mechanisms makes it possible to direct the 'metabolic composition' of plants either by optimizing environmental conditions or genetically by using genetic variation and/or genetic modification.

Research is focused on a number of important processes such as:

• Control of primary metabolism. The enzymology of primary metabolism has been well established, but attempts for modifications in a predictable way have mostly failed due to lack of whole pathway control. Therefore metabolite sensing and metabolite induced signal transduction leading to pathway, development, and growth control, are major items.
• Regulation and manipulation of the biosynthesis of secondary compounds (also in relation to primary metabolism), such as terpenoids and alkaloids, with special attention given to the octadecanoid signalling pathway. In this research both model plants and cultivated plants are used.

Within this subtheme further attention is for:

• 'Strategies of total chain approach' including the definition/design of plant properties causing less derivatisation steps during industrial processing.
• 'Agrification', especially in relation to non-food application of plant products.
• Using the 'plant as a plant' and the development of combinatorial chemistry in planta.
• Relation between growth and production processes: the competition within a cell or tissue between the synthesis of components and the various primary and/or secondary metabolites.
• Development of non-invasive methods to measure and track the activity of various metabolic pathways in vivo, in the living, functional plant organ, in order to characterize their regulation. Various methods (i.e. NMR and optical spectroscopy) should be optimized and integrated.

Subtheme 3b:

Partitioning, Storage and Transport

The unraveling of the mechanisms and the regulation of the translocation of water, nutrients and assimilates in xylem and phloem, as well as intercellular transport processes are investigated. This research also includes the induction and growth of vegetative storage organs such as tubers and roots or generative storage organs such as seeds. Induction and development of these storage organs is accompanied with important changes in carbohydrate, amino acid and fatty acid metabolism.

To study the factors that regulate partitioning and transport, it is essential to measure water and carbon fluxes in vivo at the whole plant level in order to get an integrated picture of the processes involved. The unique facilities of the Wageningen Plant NMR Centre are used for this type of measurements, together with related facilities at other departments. In depth studies of the molecular, biochemical and biophysical processes involved with emphasis on membrane transport of sugars and amino acids are carried out. The integration of these in vivo and in vitro measurements will create the opportunity to characterize changes in transport and partitioning of metabolites in relation to plant functioning and plant growth.

Such an integrated characterization of the essential properties of the processes regulating transport and partitioning will make it possible to pinpoint steps that limit optimization and design optimal conditions for plant performance.

Subtheme 3c:

Plasticity and Stress

Within this subtheme, fundamental processes are studied that form the basis of the potential of plants to adapt to a large array of growth conditions and even to temporarily suspend active metabolism in order to withstand environmental conditions, not suitable for 'normal life'. In this way e.g. the acquisition of desiccation tolerance during the development of seeds and somatic embryos and the specific (sub)cellular characteristics which are responsible for this property forms one of the areas of research.

Part of these adaptive mechanisms can be identified on the level of enzymatic activities, gene expression, plant growth regulators etc., while others are in fact developmentally regulated and comprise the induction and development of changes in plant architecture and special structures such as seeds, vegetative storage organs and dormant buds. In fact, plasticity of plants is directly related to the switching on and off of various developmental programmes and linked to the theme on developmental biology.

Plants are able to grow in different environments providing different growth conditions. Insight into the fundamental life processes that form the basis of the potential of plants to sense and adapt to a large array of growth conditions is essential. The responsive adaptations of plant species to their environments lead to differences in growth rate and productivity and to differences in water or nitrogen use efficiency ('plant plasticity'). Ultimately adaptation will result in increased survival and reproduction. Unravelling the mechanisms involved and the background of these differences, at the biochemical, biophysical and molecular level, is essential for the understanding of the physiological background of plant performance in different environments.

The ability of plants or parts of plants to adapt to adverse environmental circumstances is also investigated. Stress parameters that affect primary processes are studied. These comprise a.o. drought, desiccation, UV-B, light, temperature, air pollution, herbicides, flooding and nutrient limitation. The application and integration of invasive and non-invasive techniques necessary to analyze the sensory mechanisms used to cope stress conditions as well as survival strategies for adaptations get special emphasis.