Biogenetic implication of lupin alkaloid biosynthesis in bitter and sweet forms of Lupinus luteus and L. albus

Abstract

The concentrations of lupin alkaloids, l-lysine and cadaverine were determined by a capillary GC-MS and an amino acid analyser in bitter and sweet plants of Lupinus luteus and L. albus. The contents of total crude alkaloids were ca four-fold higher in bitter plants than those in sweet plants; by contrast, the alkaloid patterns were similar in bitter and sweet plants. However, the cellular concentrations of l-lysine and cadaverine, a precursor amino acid and a decarboxylated intermediate for biosynthesis of the alkaloids, did not differ markedly between bitter and sweet plants. The enzymatic activities of acyltransferases for formation of (-)- p-coumaroyllupinine and (+)- 13α-tigloyloxylupanine were also the same in the cell-free extracts of bitter and sweet plants. These results suggest that the biosynthetic steps of ring closure forming initial cyclic alkaloids such as (-)-lupinine and (+)-lupanine from cadaverine are blocked in sweet plants, but the steps prior to cadaverine and the later steps for modification of the cyclized alkaloids are not altere