Research Group: Plant Nutrition
Molecular Plant Nutrition
Membrane proteins involved in transport of metals and metalloids
Ongoing projects focuses on transmembrane channel proteins belonging to the Major Intrinsic Protein (MIP) family, comprising aquaporins and aquaglyceroporins. We have documented that specific plant MIPs are permeable for hydrogen peroxide, arsenite and antimonite and are currently in the process of clarifying the physiological function and regulation of these MIPs in yeast and Arabidopsis.
Another line of research deals with manganese (Mn) transporters in barley. Mn deficiency is an important plant nutritional disorder resulting in substantial yield and quality reductions in many parts of the world. Barley (Hordeum vulgare) genotypes differ considerably in tolerance to growth in soils with a low availability of Mn (Hebbern et al., 2005), but the specific mechanisms underlying these differences are not yet fully understood. Recently, we have shown that barley genotypes differ in the kinetics of the high-affinity Mn2+ uptake system (HATS), which is active in the low Mn concentration range usually found in the soil solution (Pedas et al., 2005). We have recently identified and characterized the first barley gene encoding a plasma membrane localized metal transport protein with specificity for Mn2+ (Pedas et al. 2008, submitted).
Ammonium homeostasis in plants
Ammonium is the cross point of nitrogen metabolism in plants. NH4+ can be absorbed from the soil, or produced by mechanisms such as protein turnover, photorespiration and lignin biosynthesis and can accumulate to millimolar levels in the cell. However, elevated levels of cytoplasmic NH4+ may result in excessive, energy-requiring cycling and, eventually, efflux of NH3 across the plasma membrane. Efficient compartmentalization and/or assimilation of NH4+ /NH3 in plants may thus provide a means to avoid both futile recycling and ammonia emission from the foliage. We study on the molecular level transport mechanisms underlying the fluxes of NH4+/NH3 across different membranes in plants. We have discovered that aquaporins in the subfamily of Tonoplast Intrinsic Proteins (TIPs) are permeable for NH3 (Jahn et al. 2004). The functional role of TIPs are now being investigated using knock-out mutants in Arabidopsis and over-expression strategies in Arabidopsis in rye-grass and Arabidopsis.
Improved nitrogen use efficiency
The genetic and physiological basis of nitrogen use efficiency is investigated in barley, wheat and oilseed rape. Special attention is given to the role of glutamine synthetase (GS) isoforms (Bernard et al. 2008). The approach involves over-expression of GS1 in barley and rye-grass using not only transgenic strategies but also the cisgenesis concept in which only the plant’s own genes are used. A new project starting in 2008 involves studies of allelic variations in GS1 genes and other candidate genes for N-use-efficiency in selected wheat genotypes with contrasting N harvest index, grain protein content and composition.
Plant Nutritional Metabolomics
High-throughput elemental profiling of plant tissues and yeast
Plants contain >70 elements. We are developing tools for rapid and reliable analysis of their concentration in small quantities of plant tissue, e.g. grain components or material from Arabidopsis mutants. ICP-MS and ICP-OES are used. The ICP-MS is housed in newly constructed ISO-certified clean-room facilities and is equipped with an octopole reaction cell enabling accurate measurements at the ppt-level of even problematic elements as Fe and Se. Modern support equipment such as accelerated solvent extractor, microwave oven, sub-boiling device for solvent clean-up and a Milli-Q element purification unit for ultra-clean water production are also available.
Metal speciation in grain tissues
Most elements in plants are bound to different organic compounds. These organic species are governing the mobility of essential nutrients and toxic elements in plants and their subsequent bio-availability in food and feed products. We use HPLC-ICP-MS for analysis of major binding forms of Fe, Zn, Cd and Se in the cereal grain. For identification of unknown metal-ligand complexes ESI-MS is used and in collaboration with other research groups at KU-LIFE we have access to MALDI-TOF-MS and HPLC-electrospray tandem MS instruments.
Quality and traceability of vegetable food products
Trace elements, bioactive secondary metabolites and vitamins are among the most important quality parameters in plants. Yet, very little information is available on their content, bioavailability and health effects in plant products. We study the impact of different agricultural management practises on the ability of cereal, vegetable and fruit crops to absorb trace elements from the soil. The variability and optimum levels of bioactive compounds such as molecular species of the elements iron (Fe), zinc (Zn), selenium (Se), sulphur (S) and phytates are investigated and multivariate statistical methods used to reveal differences between farming systems (e.g. organic vs. conventional).
Plant Nutritional Physiology
Plant nutrition in relation to quality of plants for food, feed and bio-fuel
The supply of different macro- and micronutrients has a profound influence biosynthesis of compounds important for the quality of plant products. In addition to the 17 essential elements governing plant development, growth and productivity, plants also contain a large number of bio-active trace elements unknown functions in biological organisms. Our ongoing research focuses on iron, zinc, selenium and cadmium deposition and bioavailability in cereal grain and vegetable plants. Furthermore, the causal links between nutrient supply and key processes in biosynthesis of compounds important for the quality of plant products are studied. The emphasis is on seed protein composition in cereal species as affected by altered patterns of nitrogen redistribution during generative growth. Interactions between plant nitrogen status and cell wall biosynthesis are highly important for bio-fuel crops and will be covered in a project starting September 2008.
Diagnostic tools to characterize the nutritional status of plants
Nutrient imbalances in plants are a world-wide problem for crop production. Diagnosis of nutritional disorders is traditionally based on visible symptoms or the use of chemical analyses of the total dry matter content of the nutrients under consideration. These methods are neither sufficiently sensitive nor precise to allow for an early detection and amendment of latent nutrient deficiencies. They can therefore not be implemented as a general tool in fertilizer recommendations. By implementing knowledge on the specific functions of elements in specific physiological processes much more sensitive, specific and versatile methods can be developed. We have developed a sensitive tool for detection of early manganese deficiency based on chlorophyll fluorescence. In addition, elemental profiling by use of ICP-MS and ICP-OES are implemented for analysis of a large number of plant and soil samples received from KU-LIFE research groups as well as from companies and research Institutions outside KU-LIFE.
Plant-atmosphere exchange of ammonia and bio-indicators for N-deposition
Plant-atmosphere NH3 exchange has over the past years been a key topic in our research. As part of the NitroEurope project, we are currently focusing on quantification of leaf-atmosphere NH3 and N2O fluxes of single leaves. The NH3 flux measurements are combined with studies of leaf apoplastic solution, stomatal conductance to NH3 diffusion, photorespiration, photosynthesis, glutamine synthetase activity, leaf senescence, xylem translocation, and root N influx in order to establish a mechanistic basis for the interpretation of the physiological regulation of the NH3 exchange.
Please contact Professor Jan K. Schjørring on further information.