Maria Köhler

Abstract

Plants are continuously attacked by a variety of pathogens. One group that attacks the roots are the pathogenic nematodes causing huge crop failures. In the last years research focused on cell wall components, polysaccharides and carbohydrates in plants to improve the resistance against nematodes. In the organism Arabidopsis thaliana the accumulation of some UDP-sugars and sugar derivatives seem to reduce the susceptibility for nematode infections. The myo-inositol pathway plays an important role in the production of UDP-glucuronic acid which is used as precursor for cell wall components. Myo-inositol is also involved in the synthesis of galactinol and raffinose, whose function in the plant is not yet completely clarified.
Galactinol is a sugar derivative and important as precursor and galactosyl donor for the raffinose family of oligosaccharides (RFOs) such as raffinose or stachyose. It is synthesized from UDP-α-D-galactose and myo-inositol and catalyzed by galactinol synthases. In A. thaliana ten genes are known coding for galactinol synthases (GolS). This work focuses on AtGolS2 since according to Taji et al. (2002) Arabidopsis plants overexpressing GolS2 show increased levels of galactinol and raffinose. These plants showed a significantly higher tolerance against drought. In general cold, heat and salt stressed wild type plants show significantly higher amounts of raffinose, galactinol and other carbohydrates than wild type plants. In a former project indications were found that plants with high amounts of galactinol and raffinose show decreased susceptibility to the nematode Heterodera schachtii. In order to investigate the influence of galactinol on biotic and abiotic stress resistance, Arabidopsis lines with significant higher levels of galactinol are generated. Therefore, the effect of different overexpressed genes coding for enzymes of the galactinol pathway, e.g. GolS2 or myo-inositolphosphate synthase 1 (MIPS1), are studied under certain stress conditions.