RESUMO
Nuclear transcript run-on analysis was used to investigate++ the relative transcription rates of genes encoding enzymes of isoflavonoid phytoalexin biosynthesis and related pathways in elicitor-treated alfalfa (Medicago sativa L.) cell suspension cultures. Genes encoding L-phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) and chalcone reductase (CHR) were most rapidly activated, with increases in transcription measurable within 10-20 min after elicitation. Cinnamic acid 4-hydroxylase (C4H), chalcone isomerase (CHI), isoflavone reductase (IFR) and caffeic acid 3-0-methyltransferase (COMT) genes were also rapidly activated, but at a slower initial rate. Transcription of chalcone 2'-O-methyltransferase (CHOMT), and 1,3-beta-D-glucanase genes was less rapid, with lag periods of 60 and 30 min post-elicitation, respectively. Treatment of cells with a PAL inhibitor L-alpha-aminooxy-beta-phenylpropionic acid (AOPP) resulted in increased transcription of PAL, CHS and CHR, but reduced transcription of CHOMT, indicating a role for phenylpropanoid products as both negative and positive regulators of gene expression within the phenylpropanoid pathway.