Abstract

Sorghum plant synthesizes the cyanogenic glucoside dhurrin (β-D-glucopyranosyloxy-(S)-hydroxymandelonitrile), from the amino acid L-tyrosine. The biosynthesis of dhurrin involves two multifunctional cytochromes P-450s (CYP79A1 and CYP71E1) and a UDP-glucose glycosyltransferase (UGT85B1). The plant use this secondary metabolite to defence itself against herbivores and pest. In this project the synthesis of dhurrin has been analysed during different steps of plant growth: seeds in their different development stages, seedlings and old plant. With the aim to see the activity of dhurrin-metabolon, a in situ PCR was performed, for localize the mRNA encoding CYP79A1 and an assay to localize the enzyme (dhurrinase) involved in the dhurrin catabolism. A hydroponic system was setted up to analyze the production of sorgoleone. The results of the experiments showed that the dhurrin is synthesized in young developing tissue, probably because they are weak and more easily attacked by pests. When the plant is older the synthesis stops, this was observed with the microsomes where any activity was seen, but the dhurrin remains accumulated in the tissues. The dhurrin and the enzyme are present in different tissues and the production of HCN occurs when the plant is attached by pest and the two compounds are mixed. The plant produced also an other secondary metabolite called sorgoleone, used as defence against the surrounding plants.

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