MICROBIAL-DEGRADATION OF THE APICAL INTERNODE OF CO125 AND W401 MAIZEIN THE RUMEN

The internodes of maize lines Co125 and W401, harvested five days afte r anthesis were cut into three fragments of equal length. In the inter nodes of Gramineae there is a gradient of maturity from the base upwar ds. Measurements of digestibility made in situ with the nylon bag meth od showed that the bases of the internodes were more digestible than t heir tops and that line Co125 was more digestible than line W401. Lign in-specific histological stains showed clear differences in staining b etween the sclerenchyma, fibres and xylem. The parenchyma was never st ained. Lignification of tissues occurred first in the xylem and then i n the fibres and sclerenchyma. Then were great differences in the perc entage of area stained by acid phloroglucinol!, in relation to total s tem area, in the bases, which were of comparable digestibility. Conver sely, the percentage of area stained in the tops, which were not of co mparable digestibility, differed little, SEM and TEM observations show ed that the cell wails of lignified tissues were thicker in the tops t han in the bases in both maize lines, They also showed that the most i ntensely stained tissues were the most resistant to microbial degradat ion. The parenchyma was degraded very rapidly but not at the same rate in all samples (base Co125 > top Co125 > base W401 > top W401) wherea s the xylem was never degraded. The most extensively degraded tissues in all samples were the fibres and the parenchyma. The bases of the tw o 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 maiz e W401, The phenolic compounds seemed to have different characteristic s in the bases and tops of the two maize lines. This study shows the s uitability of the internode as a model for observing the growth and si gnification of cell walls and for determining the effects on digestibi lity.