Percentage of Tissue Types in Tropical and Temperate Grass Leaf Blades and Degradation of Tissues by Rumen Microorganisms¹

Abstract

Tropical and temperate grasses were investigated for the amounts and the relative ease of degradation of tis. sue types in leaf blades to relate microanatomy to digestibility. Leaf blades of five tropical and six temperate grasses, grown in different locations but harvested at four weeks of summer regrowth, were examined by light microscopy for cross sectional percentages of total vascular tissue, lignified vascular tissue, phloem, epidermis, sclerenchyma, and mesophyll. Leaf blades of four of the tropical grasses and the six temperate species were evaluated for in vitro degradation of tissue types by tureen microorganisms using scanning electron microscopy.Bermudagrasses, Cynodon dactylon (L.) Pers. possessed about 36% total vascular tissue with 27% of the leaf blade section composed of parenchymal bundle sheaths; totals of vascular tissue for the other grasses were lower, ranging from 11.0% to 22.1%. The parenchymal bundle sheaths, which occupied > 50% of the area for total vascular tissue in tropical grasses but < 50% in all temperate species, were more rigid and usually digested at a slower rate in the tropical grasses. In all grasses, mesophyll and phloem were degraded before the other tissues but were degraded more rapidly in the temperate species. Leaf blades of tropical grasses had an average of 22 percentage units less of the easily digested tissue (mesophyll and phloem) and 25 percentage units more of the slowly digested tissues (epidermis and parenchymal bundle sheath) than temperate species. Except for the bermudagrasses, the percentages of lignified tissue were higher in temperate species. Differences in the ease of degradation were apparent between similar tissues of different grass types, species, and cultivars. Results indicated that leaf blade microanatomy and inherent characteristics of cell walls affect digestibility by rumen microorganisms.

Sward structural resistance and biting effort in grazing ruminants

“…The critical disparity between the leaf anatomy of grasses from the C 3 and C 4 photosynthetic pathways lies in the greater number of veins, and smaller interveinal distance [62,78], and a higher proportion of sclerenchyma [1,78] in C 4 species. These structural characteristics strengthen plant tissues [72].…”

Fractions of carbohydrates and of nitrogenous compounds of tropical grasses at different cutting ages

“…Plant tissues became lignified as age increases, changing the composition of the cellular wall of the vegetables (Akin & Burdick, 1975).…”

Degradação in vitro de tecidos da lâmina foliar e do colmo de gramíneas forrageiras tropicais, em função do estádio de desenvolvimento

“…Células com parede delgada e não-lignificada, como as do FLO e as do MES, geralmente apresentam completa digestão após período de incubação de 12 a 24 horas (Akin et al, 1983;Hartest et al, 1983), apesar de que, algumas vezes, a digestão não se completa após incubação por 48 horas (Twidwell et al, 1989;Wilson et al, 1991;Lempp et al, 1998). Para a BPF e a EPI, a digestão é parcial após período de incubação entre 24 e 48 horas (Akin et al, 1983;Bohn et al, 1988;Wilson et al, 1991), embora alguns autores tenham encontrado desaparecimento total das células da epiderme após incubação por 24 h (Akin & Burdick, 1975;Akin et al, 1983). Os tecidos que apresentam células com paredes espessadas e lignificadas, como o XIL e o ESC, são praticamente indigestíveis, permanecendo aparentemente intactos após longo tempo de incubação em líquido ruminal (Wilson et al, 1991;Brito et al, 1999).…”