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Published on March 16, 2007; 10.1104/pp.106.094748

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Received December 13, 2006
Accepted March 9, 2007

Flavonoid Biosynthesis in Barley (Hordeum vulgare L.) Primary Leaves Requires the Presence of the Vacuole and Controls the Activity of Vacuolar Flavonoid transport

Krasimira Marinova , Katja Kleinschmidt , Gottfried Weissenböck , and Markus Klein *

Zurich Basel Plant Science Center, University of Zurich, Plant Biology, Zollikerstrasse 107, CH-8008 Zürich, Switzerland; University of Cologne, Botanical Institute, Gyrhofstrasse 51, D-50931 Cologne, Germany

* Corresponding author; email: markus.klein{at}botinst.unizh.ch.

Barley (Hordeum vulgare) primary leaves synthesize saponarin, a twofold glucosylated flavone (apigenin 6-C-glucosyl-7-O-glucoside), which is efficiently accumulated in vacuoles via a transport mechanism driven by the proton gradient. Vacuoles isolated from mesophyll protoplasts of the plant line ant310, which contains a mutation in the chalcone isomerase (CHI) gene that largely inhibits flavonoid biosynthesis, exhibit strongly reduced transport activity for saponarin and its precursor isovitexin (apigenin 6-C-glucoside). Incubation of ant310 primary leaf segments or isolated mesophyll protoplasts with naringenin, the product of the CHI reaction, restores saponarin biosynthesis almost completely, up to levels of the wildtype Ca33787. During reconstitution, saponarin accumulates to more than 90% in the vacuole. The capacity to synthesize saponarin from naringenin is strongly reduced in ant310 miniprotoplasts containing no central vacuole. Leaf segments and protoplasts from ant310 treated with naringenin, showed strong reactivation of saponarin or isovitexin uptake by vacuoles while the activity of the UDP-glucose: isovitexin 7-O-glucosyltransferase was not changed by this treatment. Our results demonstrate that efficient vacuolar flavonoid transport is linked to intact flavonoid biosynthesis in barley. Intact flavonoid biosynthesis exerts control over the activity of the vacuolar flavonoid/H+-antiporter. Thus, the barley ant310 mutant represents a novel model system to study the interplay between flavonoid biosynthesis and the vacuolar storage mechanism.




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