Isoflavone Dimers from Yeast Extract-Treated Cell Suspension Cultures of Pueraria lobata

The accumulation of phytoalexins against microbial attacks is one of the im portant defense responses in higher plants [1, 2], The induction of the phytoalexins which is triggered after the recog­ nition of signal materials “elicitors” by plant cells is initiated at the transcription level of specific genes. Synthesis of specific enzymes results in the de novo activation of a secondary metabolic path­ way leading to phytoalexins. Therefore, elicitortreated plant tissues and cell cultures are suitable model systems for studying the signal recognition mechanisms by plant cells, the regulation mecha­ nisms o f specific gene expression and the enzyme reaction mechanisms in the biosynthesis of second­ ary metabolites [3, 4]. In the course of our en­ zymatic studies on isoflavonoid biosynthesis in cell suspension cultures of Pueraria lobata (Japanese name kudzu), we attempted elicitor induction strategy to obtain cells of high activity in isofla­ vonoid biosynthesis. The treatment of P. lobata cells with a glycoprotein elicitor prepared from the fungus Phytophthora megasperma f. sp. glycinea (Pmg) resulted in the rapid accumulation of a pterocarpan tuberosin (1) which was reported as a phytoalexin of P. lobata leaves [5] and stems [6]. Similar responses were observed in experiments using CuCl2 treatment. However, cells obtained by Pmg elicitor or CuCl2 treatment were not suitable for enzymatic studies, because these conditions led to rapid death of P. lobata cells probably due to hypersensitive response of cells to glycoprotein elicitor and CuCl2 (these results will appear else­ where). Among all elicitors tested, the most desira­ ble results were obtained with an endogenous elic­ itor which was prepared by the hydrolysis of