Microspectrophotometry of Phenolic Compounds in Bermudagrass Cell Walls in Relation to Rumen Microbial Digestion

Abstract

Listen

Translate article

The amount and location of phenolic compounds within plant cell walls are important factors in limiting forage digestibility. The present study was undertaken to evaluate phenolic compounds within plant cell wall types that differed in digestibility in leaf blades of ‘Coastal’ (CB) and ‘Coastcross‐1’ (CX) bermudagrasses [Cynodon dactylon (L.) Pers]. The ultraviolet (UV) spectra of the cell wall types in bermudagrass leaf blades were obtained by microspectrophotometry and the results related to their digestibilities (measured by microscopy after in vitro incubation in rumen fluid) and to their histochemical reactions for phenolic compounds. Cell walls of all tissues gave three absorption peaks in the ranges of 317 to 324, 285 to 293, and 244 to 254 nm. Indigestible cell walls (sclerenchyma and mestomc sheath) had high UV absorbance (ca. 1.8 at 320 nm) and had positive tests with histochemical reagents for phenolics. In contrast, totally digestible cell walls (mesophyll and phloem) had low UV absorbance (ca. 0.2 at 320 nm) and had negative or weak reactions for phenolics. Partially digestible cell walls (parenchyma bundle sheath and epidermis) had intermediate UV absorbance (ca. 0.45 at 320 nm) and were positive for phenolics with chlorine‐sulfite and diazotized sulfanilic acid reagents. Comparison of cell wall types in leaf blades of CB and the more highly digestible CX showed that corresponding tissues of the two cultivars had similar UV absorbance values, with the exception of parenchyma bundle sheath; the parenchyma bundle sheath cell walls of CX had approximately two‐thirds the UV absorbance values of those of CB and were more digestible. Hence, improved digestibility of CX leaf blades appears to result from a lower concentration of phenolic compounds within cell walls of parenchyma bundle sheaths.