Effects of Fungal Elicitor on Lignin Biosynthesis in Cell Suspension Cultures of Soybean

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Abstract
Soybean (G. max L.) cells cultured in B5 medium produce extremely low amounts of lignin. Modification in the growth medium, by lowering the concentration of NO3- and PO42-, results in the lignification of these cells without affecting levels of cell wall-esterified 4-coumaric and ferulic acid. The production of an extracellular, macromolecular complex by the cultured soybean cells (Moore, 1973) allows a rapid, nondestructive solubilization of the lignin which can be estimated by reaction with phloroglucinol in free solution. This system was used to study the effects of fungal elicitor on the synthesis of lignin in soybean cells. The inclusion of very low levels of an elicitor fraction from the cell walls of Phytophthora megasperma in the medium in which lignification of the soybean cells occurs suppressed both the accumulation of extracellular lignin and phloroglucinol staining of the cell walls without affecting the levels of bound hydroxycinnamic acid. The activity profiles of phenylalanine ammonia-lyase (EC 4.3.1.5) and isoenzymes of 4-coumarate:CoA ligase (EC 6.2.1.12) were compared in lignifying and elicitor-treated cell cultures as was the activity of chalcone synthase, an enzyme of flavonoid biosynthesis. The measured activities of these enzymes in cell cultures treated with elicitor were considerably lower than in untreated cells.