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 depos ition 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 dehydr ogenase (CAD) activities were determined in maize (Zea maize L.) inter nodes at several development stages, and the activities were correlate d with cellulose, hemicellulose, and lignin concentrations. Growth-cha mber grown. maize was harvested at the fourteenth leaf stage, enzyme a ctivities were quantified, and cell-wall components were determined by the detergent system of fiber fractionation from the lower, middle, a nd upper sections of Internodes 7 through 14. Internode 7 was the seco nd internode above the groundline. Cell-wall maturation proceeded basi petally within each internode or the stalk, and appeared to be regulat ed by a coordinated and basipetal sequence of enzyme activities. Activ ity of PAL and TAL was highest in internodes undergoing rapid elongati on and differentiation (Internodes 14-13) and progressively diminished in Internodes 11 through 7, which were maturing following cessation o f elongation. CAD activity was lowest in upper Internodes 14 through 1 2, but progressively increased in internodes that were halting elongat ion (Internodes 11-7) and were commencing cell-wall fiber deposition. The degree of lignification increased as CAD activity increased; hemic ellulose, cellulose, and lignin depositions correlated strongly with C AD activity rather than with PAL and TAL. CAD activity appears committ ed to lignification specifically, and to secondary cell-waif formation , in general, whereas PAL and TAL activities appear to have no direct regulatory role.