PLANT PHYSIOLOGY , Vol 102, Issue 2 609-613, Copyright © 1993 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Synthesis of Benzylglucosinolate in Tropaeolum majus L. (Isothiocyanates as Potent Enzyme Inhibitors)
J. Lykkesfeldt and B. L. Moller
Plant Biochemistry Laboratory, Department of Plant Biology, Royal Veterinary and Agricultural University, 40 Thorvaldsensvej, DK-1871 Frederiksberg C, Copenhagen, Denmark
Benzylglucosinolate accumulates in mature plants of Tropaeolum majus L. The
biosynthetic capacity for synthesis of benzylglucosinolate and the total
content of benzylglucosinolate have been investigated during plant
development and in different tissues. The content increased from 5 mg of
benzylglucosinolate in the fresh seed to between 200 and 400 mg in the
adult plant, depending on size. The biosynthetic capacity was measured
using L-[U-14C]phenylalanine as precursor. Incorporation levels of
approximately 30% were obtained with green leaves, whereas the
incorporation levels obtained with other tissues were in the range of 0 to
5%. Leaves were the primary site of benzylglucosinolate synthesis. The high
amounts of benzylglucosinolate accumulated in other tissues (e.g.
developing seeds) reflected transport of benzylglucosinolate from the
leaves. The initial steps in the biosynthesis of glucosinolates and
cyanogenic glycosides are thought to be similar and to be localized on
microsomal membranes. However, a microsomal system prepared from T. majus
was biosynthetically inactive. Inclusion of T. majus plant material during
preparation of sorghum microsomes also inhibited their activity.
Benzylisothiocyanate, generated by degradation of benzylglucosinolate
during the homogenization procedure, strongly inhibited the sorghum enzyme
system, and its presence may thus explain why the isolated T. majus
microsomal system is inactive.
