Degradability of parenchyma and sclerenchyma cell walls isolated at different developmental stages from a newly extended maize internode

Abstract

Parenchyma and sclerenchyma cell walls were mechanically isolated from sections of a newly extended maize internode containing cells at different stages of maturity. Internodes were divided into four equal segments (A[top]-D[bottom]) and preparations of both cell types obtained from each segment. The lignin content of sclerenchyma (57.5–108.3 g kg−1) was greater than that of parenchyma (48.0–86.8 g kg−1) at all stages of development. The extent of lignification increased with age in both cell types but was similar in cells taken from segments A and B. The ratio of the saponifiable phenolic acids differed with age with levels of (E+Z)-ferulic acid remaining essentially constant while the (E+Z)-p-coumaric acid content increased in parallel with lignification. The extent to which commercial ‘cellulase’ was able to degrade both cell types decreased with age and extent of lignification. Sclerenchyma walls were less degradable than parenchyma walls isolated from the same segment. The fitted rate constant calculated for the period 2–72 h, however, was independent of both age and cell type. The mean thickness of sclerenchyma walls increased with age because of secondary wall formation (confirmed by image analysis of sections prepared for microscopy) while parenchyma remained thin walled. The consequences of lignification appeared to be essentially the same for both cell types and, by implication, for both primary and secondary wall layers.