Xanthone biosynthesis and accumulation in calli and suspended cells of Hypercium androsaemum

Calli and suspended cells of Hypericum androsaemum accumulated high levels of 1,3,5,6 and 1,3,6,7 oxygenated xanthones. The major compounds include si mple oxygenated xanthones or derivatives with prenyl, pyran or methoxyl gro ups, four of them being new natural compounds. A hypothetical biosynthetic scheme is proposed based on the isolated compounds and statistical analysis . Xanthone accumulation was influenced greatly by medium factors, namely ho rmone supplementation. Calli grown with 4.5 mu M alpha-naphtaleneacetic aci d (NAA) + 2.3 mu M kinetin (KIN) had the highest specific xanthone producti on (1.3% biomass dry weight (DW)), whereas suspended cells grown in similar medium accumulated a lower amount (0.87% DW). Calli displayed a negative l inear relationship between total xanthone accumulation and NAA concentratio n, in the range of 4.5-22.5 mu M. However, in this range the xanthone 1,3,6 ,7/1,3,5,6 ratio and the biomass production showed a positive linear relati onship with NAA concentration. Substitution of 4.5 mu M of NAA by the same molar amount of 2,4-dichlorophenoxyacetic acid (2,4-D), in the presence of 2.3 mu M of KIN, caused a decrease in xanthone accumulation in calli. The u se of N-6-benzyladenine (BA) instead of KIN reduced xanthone production, in dependently of the auxin used. This effect was attenuated when both hormone s were present. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.