Inhibition and regulation of shikonin biosynthesis in suspension cultures of Lithospermum

The accumulation of acetylshikonin, p-hydroxybenzoic acid-O-glucoside (PHB-Glc) and rosmarinic acid (RA) was investigated in cell suspension cultures of Lithospermum erythrorhizon under the influence of blue and white light, of in vivo inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase) and phenylalanine ammonia lyase (PAL), and of the effecters methyl jasmonate and arsenate. The activities of p-hydroxybenzoate geranyltransferase, p-hydroxybenzoate O-glucosyltransferase and HMG-CoA reductase were assayed. 2-Aminoindan-2-phosphonic acid, an inhibitor of PAL, completely suppressed the formation of acetylshikonin, PHB-Glc and RA. Mevinolin, an inhibitor of HMG-CoA reductase specifically blocked the formation of acetylshikonin, thereby increasing the formation of PHB-Glc. The activity of p-hydroxybenzoate-O-glucosyltransferase was not regulated by the intracellular concentration of p-hydroxybenzoate, but directly by light. White light rather than blue light induced the activity of this glucosyltransferase, whereas PHB geranyltransferase activity was repressed by blue light. The activity of HMG-CoA reductase correlated with the production of acetylshikonin, This suggests a regulatory role for HMG-CoA reductase in the isoprenoid part of shikonin biosynthesis.