Microbial degradation of the apical internode of Co125 and W401 maize in the rumen
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文摘
The internodes of maize lines Co125 and W401, harvested five days after anthesis were cut into three fragments of equal length. In the internodes of Gramineae there is a gradient of maturity from the base upwards. Measurements of digestibility made in situ with the nylon bag method showed that the bases of the internodes were more digestible than their tops and that line Co125 was more digestible than line W401. Lignin-specific histological stains showed clear differences in staining between the sclerenchyma, fibres and xylem. The parenchyma was never stained. Lignification of tissues occurred first in the xylem and then in the fibres and sclerenchyma. There were great differences in the percentage of area stained by acid phloroglucinol, in relation to total stem area, in the bases, which were of comparable digestibility. Conversely, the percentage of area stained in the tops, which were not of comparable digestibility, differed little. SEM and TEM observations showed that the cell walls of lignified tissues were thicker in the tops than in the bases in both maize lines. They also showed that the most intensely stained tissues were the most resistant to microbial degradation. The parenchyma was degraded very rapidly but not at the same rate in all samples (base Co125 > top Co125 > base W401 > top W401) whereas the xylem was never degraded. The most extensively degraded tissues in all samples were the fibres and the parenchyma. The bases of the two maize lines were more degraded than the tops. Of the cell walls that reacted positively to lignin-specific stains only the secondary walls of the fibres and sclerenchyma were sometimes degraded. However, the sclerenchyma secondary wall was not always degraded in the top of maize W401. The phenolic compounds seemed to have different characteristics in the bases and tops of the two maize lines. This study shows the suitability of the internode as a model for observing the growth and lignification of cell walls and for determining the effects on digestibility.