Effect of Phenolic Structures on the Degradability of Cell Walls Isolated from Newly Extended Apical Internode of Tall Fescue (Festuca arundinacea Schreb.)

Abstract

Apical internodes of tall fescue (Festuca arundinacea Schreb. var. Clarine) harvested at flowering were sectioned into 5 or 10 equal parts to study in situ degradability and cell wall composition, respectively. The basal (youngest) section had the greatest primary wall content. Cell walls in the upper (older) sections had the highest xylose/arabinose ratio and lignin content and a lignin rich in syringyl units, all typical of extensive secondary wall development. Almost all of the p-coumaric (p-CA) and about half of the ferulic acid (FA) were released by 1 M NaOH and presumed to be ester-linked. The total FA content was approximately double that of p-CA in all sections other than the youngest with a distribution similar to that of total p-CA. However, the ratio of esterified to ether and ether plus ester linked (Et & Et+Es) FA differed with age. Whereas the esterified form remained essentially constant ( approximately 4.5 g/kg of cell wall), Et & Et+Es ferulate increased with increasing age of the tissue and was significantly related to lignin deposition (r = 0.79, P < 0.01). The extent of cell wall degradation after 48 h of incubation in the rumen was inversely related to maturity, falling from 835 g/kg of dry matter in the youngest section to 396 g/kg in the oldest. Both the rate and extent of cell wall degradation were significantly negatively related to the ratio of xylose to arabinose, lignin content, proportion of syringyl units present in lignin, and concentration of Et & Et+Es FA present. A positive relationship between Et & Et+Es FA was also found, with the rate (P < 0.01) being better correlated than the extent (P < 0.05) of cell wall degradation. Application of the newly extended internode model to fescue produced results consistent with the view that both the lignin content and the extent to which lignin was covalently bound to the other wall polymers crucially influenced the rate and extent of degradation.

Is the basal area of maize internodes involved in borer resistance?

“…In cells, PCA is mainly esterified to the γ -position of phenylpropanoid sidechains of S units in lignin [33,59,60]. Although very small quantities of PCA are esterified to arabinoxylans in immature tissues, most PCA accretion occurs in tandem with lignification [61,62]. FA is intracellularly esterified to the C5-hydroxyl of α-L-arabinose sidechains of xylans and deposited into primary and secondary walls [43,63,64].…”

KNOX1 genes regulate lignin deposition and composition in monocots and dicots

“…It has also been shown that CAD down-regulation in several species including maize, Medicago sativa , Pinus taeda , tobacco, and poplar, chemically alters lignin resulting in greater alkaline solubility with unchanged total lignin content and without compromising strength. In the case of poplar, the wood was more amenable to industrial delignification processes including kraft pulping (Hibino et al, 1995; Baucher et al, 1999; MacKay et al, 1999; Vailhe et al, 2000; Marita et al, 2003), while faster growth and higher wood density was observed in loblolly pine (Cavell et al, 1998). Thus, KNOX1 genes may be a useful tool for altering total lignin levels, as well as modulating the lignin chemical makeup to improve forage or processing properties.…”

Role of Dehydrodiferulates in Maize Resistance to Pests and Diseases

“…p -Coumarate is mainly esterified to the γ–position of phenylpropanoid sidechains of S units in lignin [5–7]. Although very small quantities of p -coumarate are esterified to arabinoxylans in immature tissues, most p -coumarate accretion occurs in tandem with lignification [8,9], making p -coumarate accumulation a convenient indicator of lignin deposition. Ferulates are intracellularly esterified to the C5-hydroxyl of α- l -arabinose sidechains of xylans and deposited into primary and secondary walls of a variety of grass tissues [10–12].…”