DEGRADATION OF 3 WARM-SEASON GRASSES IN A PREPARED CELLULASE SOLUTION

Information is needed on the relationship between anatomical structure and the rate and extent of cell wall degradation in warm-season forag e grasses, The objective was to study the pattern, rate, and extent of tissue degradation of three warm-season grasses in a prepared cellula se solution, using light microscopy. Most recent fully collared leaf b lades from field-grown big bluestem (Andropogon gerardii Vitman), indi angrass [Sorghastrum nutans (L.) Nash] and switchgrass (Panicum virgat um L.) were cut into 5-cm sections and digested in 10 mt prepared cell ulase solution with an acid-pepsin pretreatment. All material was in a vegetative state. Leaf segments were retrieved after 3, 9, 23, 48, an d 72 h incubation and prepared for light microscopy by fixation, dehyd ration and embedding in Spurr's low-viscosity resin, Sections 5 mu um thick were made using an ultramicrotome, and undigested tissues in cro ss section were measured with a computer-based image analysis system. The proportion of undigested tissue in cross section after 72 h incuba tion ranged from 25.4% in big bluestem to 35.0% in switchgrass. Switch grass contained a higher percentage of parenchyma bundle sheath tissue than either big bluestem or indiangrass, Digestion of all tissues exc ept mesophyll and phloem was delayed until after 24 h incubation, Diff erences among species tended to de greater in extent of digestion than in rate, Degradation of the parenchyma bundle sheath was significantl y less in switchgrass than in either big bluestem or indiangrass after 72 h incubation, Digestion of the abaxial epidermis was nearly comple te in big bluestem after 72 h incubation. The adaxial epidermis was mo re readily degraded than the abaxial epidermis, These results imply th at differences in digestibility among the three warm-season grasses co uld be attributed to differences in the degradation of their individua l tissue types.