Hydroxynitrile glucosides in barley and their involvement in disease resistance
M. LYNGKJAER (1), E. Eva Knoch (1), P. Roelsgaard (1), C. Olsen (1) (1) Department of Plant and Environmental Science, University of Copenhagen, Denmark

Barley contains five hydroxynitrile glucosides (HNGs): Epiheterodendrin, Epidermin, Sutherlandin, Osmaronin and Dihydroosmaronin. HNGs are known plant defense compounds that include the cyanogenic glucosides, which can release hydrogen cyanide (Epiheterodendrin is a cyanogenic glucoside). In barley, HNGs accumulates in the epidermal tissue and may constitute more than 90% of the soluble epidermal sugars. Total HNG content varies between barley cultivars, ranging from low to high, but the ratio between the five compounds within one plant is constant. It has been suggested that increased HNG content in barley correlates with increased susceptibility to Blumeria graminis f. sp. hordei, the cause of powdery mildew. However, we have found that high HNG producing barley lines are more resistant to B. graminis infection, possibly due to the toxicity of their breakdown products, and that the compounds are induced in response to infection. To learn about the synthesis of HNGs and their importance in relation to disease susceptibility we have identified candidates for the HNG biosynthetic enzymes in barley and found that the genes are localized in a gene clusters. Transient expression of the candidate genes, five cytochrome P450 enzymes and two UDP-glucosyltransferases, in tobacco results in the production of HNGs specific to barley. Application of the HNG compounds to barley leaves strongly limited fungal colony growth implying a role of the HNG compounds in fungal defense.

Abstract Number: P7-190
Session Type: Poster