UV Absorption microspectrophotometry and digestibility of cell types of bermudagrass internodes at different stages of maturity

The walls of sclerenchyma, vascular bundle sheaths, and parenchyma at different maturities (internodes 2, 5, and 7 from the apex) of bermudagrass [Cynodon dactylon (L) Pers] were analyzed by UV absorption microspectrophotometry, and the results were related to wall digestibility. Sclerenchyma walls from internode 2 were degraded by rumen microorganisms, with only the middle lamella remaining. Undegraded sclerenchyma walls gave a UV absorption spectrum similar to that of p‐coumaroyl and feruloyl arabinoxylo‐trisaccharides isolated from bermudagrass cell walls. Absorption maxima occurred at ˜ 245 and 320 nm, together with a shoulder at ˜ 280 nm. Sclerenchyma from the older internodes 5 and 7 showed only partial degradation of the secondary wall adjacent to the lumen. Spectra of undegraded walls from these internodes showed absorption maxima at ˜ 245 and 285 nm with a shoulder at ˜ 320 nm. Spectra of sclerenchyma walls that included the middle lamellae gave a higher absorption at ˜ 320 nm than did wall layers excluding the middle lamellae. Vascular bundle sheaths generally were similar in digestion patterns and spectra to those of sclerenchyma. Parenchyma cells in internode 2, which were totally degradable, gave low absorbance. Parenchyma cell walls from internodes 5 and 7 were degraded except for the middle lamellae in cells nearest to the sclerenchyma; parenchyma cells nearest to the stem centre were totally degraded. Spectra of parenchyma wall regions that included middle lamellae were similar to the p‐coumaroyl and feruloyl arabinoxylo‐trisaccharides, and absorbance values were low compared with sclerenchyma and vascular walls. Results suggested that esteror ether‐linked phenolic acids accounted for most of the UV absorption in young sclerenchyma and young and old parenchyma; lignin‐like aromatics increased in older, poorly digested sclerenchyma as ester/ether‐type compounds decreased. An estimation of the amount of ‘ferulic acid equivalents’ of the walls was made assuming all the absorbance at ˜ λmax 320 nm was due to ferulic acid; older sclerenchyma walls had the highest values (160 mg g−1 walls) and parenchyma walls the lowest (11 mg g−1 walls).