ACTIVITY OF PHENYLALANINE AMMONIA-LYASE, TYROSINE AMMONIA-LYASE, AND CINNAMYL ALCOHOL-DEHYDROGENASE IN THE MAIZE STALK

The relation between the activities of lignification enzymes and deposition of cell-wall components during progressive stages of development has not been demonstrated. In this study, phenylalanine ammonialyase (PAL), tyrosine ammonia-lyase (TAL), and cinnamyl alcohol:NADPH dehydrogenase (CAD) activities were determined in maize (Zea maize L.) internodes at several development stages, and the activities were correlated with cellulose, hemicellulose, and lignin concentrations. Growth-chamber grown. maize was harvested at the fourteenth leaf stage, enzyme activities were quantified, and cell-wall components were determined by the detergent system of fiber fractionation from the lower, middle, and upper sections of Internodes 7 through 14. Internode 7 was the second internode above the groundline. Cell-wall maturation proceeded basipetally within each internode or the stalk, and appeared to be regulated by a coordinated and basipetal sequence of enzyme activities. Activity of PAL and TAL was highest in internodes undergoing rapid elongation and differentiation (Internodes 14-13) and progressively diminished in Internodes 11 through 7, which were maturing following cessation of elongation. CAD activity was lowest in upper Internodes 14 through 12, but progressively increased in internodes that were halting elongation (Internodes 11-7) and were commencing cell-wall fiber deposition. The degree of lignification increased as CAD activity increased; hemicellulose, cellulose, and lignin depositions correlated strongly with CAD activity rather than with PAL and TAL. CAD activity appears committed to lignification specifically, and to secondary cell-waif formation, in general, whereas PAL and TAL activities appear to have no direct regulatory role.