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Histochemical Reactions, Autofluorescence, and Rumen Microbial Degradation of Tissues in Untreated and Delignified Bermudagrass Stems¹

Low digestibility of stems is due to large proportions of lignified cell walls, but lignified tissues vary in resistance to microbial degradation. The objective of the research was to characterize lignified tissues histologically and by autofluorescence, and to examine the influence of delignification with potassium permanganate (PM) on the histology, autofluorescence, and tissue degradation by rumen microorganisms in mature internodes of ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.]. Cell walls of epidermis, sclerenchyma ring, and vascular xylem gave a positive lignin test with acid phloroglucinol (AP+), while those the parenchyma gave a positive reaction to the chlorine-sulfite test (CS+). The maximum of the emission spectrum (E_max) of the autofluorescence after excitation at 365 nm was 452 to 455 nm for the sclerenchyma ring and about 460 nm for parenchyma. The intensity of the autofluorescence for the three internodes averaged 1.97 mV for the sclerenchyma ring, 1.50 mV for the middle parenchyma, and 1.27 mV for parenchyma cell walls nearer the stem center. Delignification resulted in lack of a histochemical reaction in parenchyma, but an AP+ reaction still occurred in epidermis, sclerenchyma ring, and xylem. Delignification reduced the E_max tO 450nm and the intensity to 1.28 mV for AP+ tissues and resulted in a total loss of autofluorescence in parenchyma. Treatment with PM resulted in almost total microbial degradation of the parenchyma, but AP + tissues were not degraded in untreated or PM-treated stem sections. Results indicate that variations exist in the retention of phenolic compounds in cell walls upon oxidation with PM, and these variations relate to quality differences in forage fiber.

Key Words: Cynodon dactylon (L.) Pers. • Lignin • Digestibility • Potassium permanganate

² Microbiologist and research chemist, Richard B. Russell Agric. Res. Center, ARS-USDA, P. O. Box 5677, Athens, GA 30613.

³ Botanist and head, Dep. of Plant Cytology and Morphology, Agricultural Univ., Arboretumlaan 4,6703 BDWageningen, The Netherlands.

Received for publication January 18, 1985.