CELL-WALL COMPOSITION OF MAIZE INTERNODES OF VARYING MATURITY

Incorporation of polysaccharides, hydroxycinnamic acids, and lignin we re quantified in successive internodes along the maize (Zea mays L.) s tall;, which displayed progressively greater cellular development. Rin d and pith tissues of growth chamber-grown plants were dissected from internodes at the 15th leaf stage of development and cell-wall neutral sugars, uronic acids, Klason lignin, syringyl-to-guaiacyl (S/G) ratio , and ferulic acid (FA) and p-coumaric acid (PCA) ester and ether conc entrations were determined. From the youngest internode (I13) to the o ldest (I7), cell-walt concentrations increased in rind tissue, whereas in pith tissue concentrations increased through I10, then plateaued. Cell-wall lignin concentrations increased from 75 to 140 g kg(-1) and neutral sugar and uronic acid concentrations decreased from 836 and 10 1 g kg(-1) to 759 and 36 g kg(-1) cell wall, respectively. Rind vascul ar tissue, which lignified earlier and to a greater extent than pith t issue, had significantly higher levels of FA and PCA esters. Ferulic a cid ester levels rose in younger I13 through IIO, peaking at 6.6 g kg( -1) cell wall, but declined to 3.6 g kg(-1) cell wall in older, lignif ying I9 through I7. Ferulic acid ether levels rose and peaked early in lignification, but fell during subsequent maturation. Concentrations of PCA esters rose with internode maturity (from 1.8-23 g kg(-1) cell wall) and this pattern mirrored a steady rise in S/G ratio of the lign in. Our results suggest that FA is laid down in ester linkages to prim ary cell-wall polysaccharides and provides ether-linkage initiation si tes for lignin.