ST1-06: Topochemical distribution of lignin and hydroxycinnamic acids in sugar cane cell walls and its contents in varied sugar cane experimental breeds

Cellular UV-microspectrophotometry was used to detect lignin and hydroxycinnamic acids in individual fiber, vessel and parenchyma cell walls of sugar cane. UV measurements from fiber cell walls showed typical absorbance spectra of grass lignin with a band at 278 nm and a pronounced shoulder at 315 nm assigned to the presence of hydroxycinnamic (ferulic and p-coumaric) acids. Vessels presented the highest lignified cell walls, followed by fibers and parenchyma. Pith parenchyma cell walls presented very low absorbance values at 278 nm, however a distinct maximum at 315 nm indicated that pith parenchyma is not extensively lignified but contains significant amounts of hydroxycinnamic acids. Cellular UV image profiles scanned with the absorbance intensity maximum at 278 nm or 315 nm showed the pattern of lignin or hydroxycinnamic acids distribution in the individual cell walls with the highest concentrations of both in middle lamella and cell corners. Eleven sugar cane experimental breeds were also evaluated according to their chemical composition. Cellulose, hemicellulose, lignin and extractives contents varied between 39-43%, 26-32%, 17–24% and 1.6-8.7%, respectively. Hydroxycinnamic acids were also quantified based on two types of alkaline treatments. Mild treatment released esters linked to methylglucuronoxylans whereas a severe treatment was used to release the total hydroxycinnamic acids. Severe alkaline extraction required an especial calibration protocol for computing decomposition of part of the hydroxycinnamic acids. The total amount of hydroxycinnamic acids varied from 5.4 to 8.3% in the breeds and were not correlated with the lignin contents of the same samples.