We are interested in the molecular physiology of seed development and focus our work on understanding the genetic and metabolic regulation of developmental and metabolic processes in seeds. In more detail we ask: How is seed development governed by genetic programmes? How is gene expression related to differentiation and to physiological processes? How is metabolism connected to growth and development? What roles play metabolites like soluble sugars in regulatory networks? How are biosynthetic pathways controlled by assimilate transport processes? How can we manipulate developmental and metabolic processes to modify, for example, seed sink capacity and composition of storage products?
Studies on seeds at the Gatersleben institute have a long history. The group's work was originally focused on the structure, function and regulation of storage protein gene expression in the faba bean (Vicia faba L.) seed as part of an integrated institutional approach to better understand and manipulate seed storage functions. Beginning in the early 1990's the approach was broadened to include physiological, metabolic and biochemical aspects of seed development in general.
Seed development and metabolism is presently preferably studied in dicot grain legumes (faba bean Vicia faba, narbon bean Vicia narbonensis and pea Pisum sativum) as well as in monocot cereals (barley Hordeum vulgare and in applied projects wheat Triticum aestivum).
A major focus of our earlier work was to better understand the role of metabolites, especially soluble sugars, as signal molecules during development. We suggested that sugar gradients are important developmental triggers and formulated the invertase control hypothesis of seed development (Weber et al. 1997a). This hypothesis suggests that in faba beans a cell-wall-bound invertase in the thin-walled parenchyma of the seed coat (VfCWINV1) determines the changing hexoses to sucrose ratio in the developing cotyledons (Weber et al. 1995). That in turn acts as a developmental trigger. The working model was initially based on a detailed correlative analysis of expression patterns of storage protein genes, genes involved in carbohydrate metabolism, enzyme activities and sugar concentrations. The data nicely correlated with developmental gradients of mitotic figures, endopolyploidization patterns and histo-differentiation (Borisjuk et al. 1995). Furthermore, the model was strongly supported by high resolution, histographical mapping of glucose (Borisjuk et al. 1998) and sucrose concentrations (Borisjuk et al. 2002) in developing faba bean cotyledons.

Similar molecular-physiological studies were carried out in developing barley caryopses leading to principally similar results (Weschke et al. 2000, 2003).

Three different experimental approaches were used in most of our work: (1) Detailed correlative analysis of as many as possible molecular, biochemical, histological and physiological parameters in wild-type and mutant seeds of faba bean, pea and barley; (2) Experimental analysis of explanted cotyledons and seed coats of different age in media with varying concentrations of hexoses, sucrose, amino acid nitrogen and hormones; (3) Programmed changes of seed metabolism by transgen overexpression and repression in narbon beans, peas, barley and wheat.

To add a new dimension of analysis, our and other IPK groups developed genomics tools mainly for barley within the frame of the German plant genome research programme GABI (see, for instance, Zhang et al. 2004). This enabled us to carry out initial transcriptome studies of developing caryopses (Sreenivasulu et al. 2002, 2004). The data implied an important role for photosynthesis in seed development and led to define a specific developmental period, the intermediary or transition phase, in which a dramatic reprogramming of the genetic machinery takes place.

Seed photosynthesis and the related oxygen distribution in the hypoxic seeds as well as the spatial pattern of energy production were extensively studied in pea (see Rolletschek et al. 2003) and barley (Rolletschek et al. 2004). It was concluded that the local energy state plays an important role in the regulation of storage product synthesis in the developing seeds.

The combined data worked out for legumes and barley were included in two recent reviews (barley: Wobus et al. 2004; grain legumes: Weber et al. 2005).

A more comprehensive description of our work is found in the IPK Annual Reports (English versions since 2002).