Coumarin compounds in Ammi majus L. callus cultures.
Callus cultures of Ammi majus L. (bishop's weed), Apiaceae, were maintained on variants of Linsmaier-Skoog's (L-S) medium differing in the content of the phytohormones, alpha-naphthaleneacetic acid (NAA) and 6-benzylaminopurine (BAP) (0.1-10.0 mg/l). The increments of callus tissue fresh weight showed considerable differences (1.4 bis 4.4-fold) during 4-week subcultures on the media tested. HPLC analysis revealed the presence of six compounds in the extracts of callus tissues, which are known metabolites in plants growing under natural conditions: the linear furanocoumarins psoralen, bergapten, xanthotoxin, isopimpinellin, imperatorin and their precursor umbelliferone. The total contents of coumarin compounds under examination showed marked differences dependent on the phytohormone concentrations in the medium. They ranged from 40.95 to 871.05 mg/100 g of dry weight. Imperatorin was the metabolite dominating among the furanocoumarins in calli from almost all tested variants of L-S medium (maximum content of 169.27 mg/100 g). Callus tissue cultured on one of the variants (0.1 mg/l NAA, 0.1 mg/l BAP) yielded in high content of xanthotoxin (145.33 mg/100 g). On the majority of media, umbelliferone was also accumulated at high quantities (maximum content of 536.29 mg/100 g). The medium containing 0.1 mg/l NAA and 0.1 mg/l BAP was the best for the accumulation of analysed coumarins. This medium favoured the formation of embryogenic callus. Xanthotoxin also dominated quantitatively among the furanocoumarins in the tested vegetative organs and fruits of the plant grown under natural conditions (leaves: 26.10 mg, roots: 5.55 mg, fruits: 3010.41 mg/100 g). Maximum contents of this metabolite in in vitro culture were many times higher than those found in vegetative plant organs but manifold lower than in fruits. On the other hand, maximum contents of imperatorin obtained in in vitro culture were many times higher in comparison with those detected in vegetative organs and fruits (leaves: 14.10 mg, roots: 3.30 mg, fruits: 94.70 mg/100 g of dry weight.). The A. majus L. callus culture, established in the course of the present experiments, can be considered a valuable model for studies of the biosynthesis of coumarin compounds, and a potential source of the psoralen 8-alkoxy derivatives imperatorin and xanthotoxin and their precursor umbelliferone.