RAPID ACTIVATION OF PHENYLPROPANOID METABOLISM IN ELICITOR-TREATED HYBRID POPLAR (POPULUS-TRICHOCARPA TORR AND GRAY X POPULUS-DELTOIDES MARSH) SUSPENSION-CULTURED CELLS

Elicitor induction of phenylpropanoid metabolism was investigated in suspension-cultured cells of the fast-growing poplar hybrid (Populus trichocarpa Torr. & Gray x Populus deltoides Marsh) H11-11. Treatment of cells with polygalacturonic acid lyase or two fungal elicitors resulted in rapid and transient increases in extractable L-phenylalanine ammonia lyase and 4-coumarate:coenzyme A ligase enzyme activities. The substrate specificity of the inducible 4-coumarate:coenzyme A ligase enzyme activity appeared to differ from substrate specificity of 4-coumarate:coenzyme A ligase enzyme activity in untreated control cells. Large and transient increases in the accumulation of L-phenylalanine ammonia-lyase and 4-coumarate:coenzyme A ligase mRNAs preceded the increases in enzyme activities and were detectable by 30 minutes after the start of elicitor treatment. Chalcone synthase, cinnamyl alcohol dehydrogenase, and coniferin beta-glucosidase enzyme activities were unaffected by the elicitors, but a large and transient increase in beta-glucosidase activity capable of hydrolyzing 4-nitrophenyl-beta-glucoside was observed. Subsequent to increases in L-phenylalanine ammonialyase and 4-coumarate:coenzyme A ligase enzyme activities, cell wall-bound thioglycolic acid-extractable compounds accumulated in elicitor-treated cultures, and these cells exhibited strong staining with phloroglucinol, suggesting the accumulation of wall-bound phenolic compounds.