INVESTIGATION OF THE ESTER-LINKED AND ETHER-LINKED PHENOLIC CONSTITUENTS OF CELL-WALL TYPES OF NORMAL AND BROWN MIDRIB PEARL-MILLET USING CHEMICAL ISOLATION, MICROSPECTROPHOTOMETRY AND C-13 NMR-SPECTROSCOPY

The cell walls of rind, parenchyma and vascular bundle fractions of pe arl millet (Pennisetum glaucum (L) R Br) were isolated from two brown midrib mutants and their normal (N) near-isogeneic line. The walls wer e sequentially treated with 1 M NaOH at 25-degrees-C for 20 h to deter mine ester-linked phenolic acids and then with 4 M NaOH at 170-degrees -C for 2 h to determine ether-linked phenolic constituents. The untrea ted walls and their residues resulting from each treatment were analyz ed by microspectrophotometry and C-13 NMR spectroscopy. The amount of ester-linked p-coumaric acid was determined by chemical analysis and f ound to be two to six times higher in the N line with no difference am ong lines in ferulic acid content. Ether-linked ferulic acid was about 30 % higher in the rind in the N line and ether-linked p-coumaric aci d was only slightly higher with the greatest difference found in the r ind tissue. Microspectrophotometry of the untreated tissues showed abs orption maxima at 232-238 nm, 288 292 nm and 312-324 nm. Treatment wit h 1 M NaOH generally reduced or eliminated the 312-324 nm absorption, with 4 M NaOH removing the remainder of the 288-292 nm absorption. C-1 3 NMR confirmed these reductions of aromatic functionalities by alkali treatments. The combination of techniques provides excellent correlat ion of two types of spectral data with chemical identification and qua ntitation and establishes that bmr mutants have less ester-linked p-co umaric acid and less ether-linked ferulic acid, thus providing a bette r understanding of the factors contributing to biodegradability.