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Leucine-derived cyano glucosides in barley
Kirsten Annette Nielsen1, Carl Erik Olsen, Katrine Pontoppidan
1Plant Biochemistry Laboratory, Department of Plant Biology, Royal Veterinary and Agricultural University, Frederiksberg, Copenhagen, Denmark. kani@kvl.dk
Plant Physiology
|July 13, 2002
Summary
Barley seedlings contain five cyanogenic glucosides derived from L-leucine. These compounds are primarily in leaf epidermis, with biosynthesis occurring elsewhere and translocation to the epidermis, suggesting a role beyond cyanide release in plant defense.
Area of Science:
- Plant biochemistry
- Metabolomics
- Agricultural science
Background:
- Barley (Hordeum vulgare) seedlings possess cyanogenic glucosides originating from L-leucine.
- Cyanogenic glucosides are known for their role in plant defense mechanisms via cyanide release.
Purpose of the Study:
- To investigate the chemical structure and relative abundance of cyanogenic glucosides in barley.
- To elucidate the biosynthesis and localization of these compounds within barley seedlings.
- To explore the functional significance of cyanogenic glucosides in barley, particularly concerning plant defense.
Main Methods:
- Liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) analyses were employed.
- Investigation utilized spring barley cultivars with varying cyanide potential.
- Enzyme assays using microsomal preparations from different barley tissues were conducted.
Main Results:
- A 10-fold difference in total cyanogenic glucoside content was observed across cultivars, with consistent relative proportions of individual compounds.
- Epiheterodendrin was identified as the sole cyanogenic glucoside, constituting 12-18% of the total.
- Cyanogenic glucosides were localized to the epidermis (99%) of barley leaf blades, with biosynthesis occurring in other cell types and subsequent translocation.
- A beta-glucosidase capable of degrading epiheterodendrin was found exclusively in the endosperm.
Conclusions:
- The biosynthesis of barley cyanogenic glucosides involves cytochrome P450 enzymes (CYP79 and CYP71E families) acting on L-leucine.
- Translocation of cyanogenic glucosides to the leaf epidermis suggests a specialized role.
- The absence of cyanide release in barley indicates that cyanogenic glucosides may not function in plant defense through this mechanism in this species.