STRESS RESPONSES IN ALFALFA (MEDICAGO-SATIVA L) .20. TRANSCRIPTIONAL ACTIVATION OF PHENYLPROPANOID PATHWAY GENES IN ELICITOR-INDUCED CELL-SUSPENSION CULTURES

Nuclear transcript run-on analysis was used to investigate the relativ e transcription rates of genes encoding enzymes of isoflavonoid phytoa lexin biosynthesis and related pathways in elicitor-treated alfalfa (M edicago sativa L.) cell suspension cultures. Genes encoding L-phenylal anine ammonia-lyase (PAL), chalcone synthase (CHS) and chalcone reduct ase (CHR) were most rapidly activated, with increases in transcription measurable within 10-20 min after elicitation. Cinnamic acid 4-hydrox ylase (C4H), chalcone isomerase (CHI), isoflavone reductase (IFR) and caffeic acid 3-O-methyltransferase (COMT) genes were also rapidly acti vated, but at a slower initial rate. Transcription of chalcone 2'-O-me thyltransferase (CHOMT), and 1,3-beta-D-glucanase genes was less rapid , with lag periods of 60 and 30 min post-elicitation, respectively. Tr eatment of cells with the PAL inhibitor L-alpha-aminooxy-beta-phenylpr opionic acid (AOPP) resulted in increased transcription of PAL, CHS an d CHR, but reduced transcription of CHOMT, indicating a role for pheny lpropanoid products as both negative and positive regulators of gene e xpression within the phenylpropanoid pathway.