ACTIVITY OF 2 LIGNIN BIOSYNTHESIS ENZYMES DURING DEVELOPMENT OF A MAIZE INTERNODE

To ascertain the temporal relationships of phenylpropanoid and lignin pathway enzymes, phenylalanine ammonia-lyase (PAL) and cinnamyl alcoho l-NADPH dehydrogenase (CAD), with lignin concentration, PAL and CAD ac tivities and lignin concentrations were assessed during progressive de velopment of the 10th internode in maize (Zea mays L). Enzyme activiti es were quantified and lignin concentrations were determined by the de tergent system of fiber fractionation from lower, middle, and upper se ctions of the elongating internode harvested 3, 5, 7, 9, 11, 13, and 1 5 days after the internode had reached 10 mm in length. Over 15 days, a coordinated, sequential, and basipetal pattern of enzyme activities and lignin accumulation evolved through the internode, spanning the st ages of rapid elongation cellular differentiation, and secondary cell wall formation. PAL activity was initiated first, rising to peak activ ity in elongating tissue, and falling basipetally in tissues as they m atured. CAD activity rose in fully elongated, maturing internode tissu e where PAL activity was waning following its peak activity. Lignin ac cumulated in tissues with high CAD activity. CAD activity and lignin d eposition patterns were similar: simultaneously increasing in activity and deposition over time while activity and deposition also shifting basipetally through the internode, keeping pace with secondary cell wa ll formation. Lignin concentration correlated significantly with CAD, but not with PAL.