Normal-12 and Brown Midrib-12 Sorghum. I. Variations in Tissue Digestibility
1986
Akin, D. E. | Hanna, W. W. | Rigsby, L. L.
Reduced lignin contents in brown midrib (bmr) mutants of sorghum (Sorghum bicolor L. Moench.) are reported to improve the digestibility of this forage. The objective of this study was to evaluate microscopically leaf blades of normal-(N) 12 and bmr-12 sorghum for variations in anatomy, histological reactions of tissues for lignin, and specific tissue digestion to elucidate the contribution of the bmr- 12 mutation to improved forage quality. No differences in anatomy or histology of lignified tissues was observed between N-12 and bmr- 12 plants. Midribs of N and bmr plants, examined by scanning electron microscopy after a 48 to 72 h incubation with rumen fluid were partially degraded, with a tendency for parenchyma in bmr leaf blades to be more degraded than that in N leaf blades. Other tissues, i.e., epidermis and xylem, were not degraded in either plant type. In the non-midrib portion of blades, the parenchyma bundle sheaths and adaxial sclerenchyma areas were degraded to a greater extent in bmr plants by mixed rumen microorganisms and by a pure culture of the cell wall-degrading rumen bacterium Ruminococcus flavefaciens FD-1. Epidermis and mesophyll at times more rapidly degraded in bmr plants. In leaf sheaths, no marked differences in digestion between N and bmr plants were found with parenchyma totally degraded in both plant types. Xylem and other tissues normally highly resistant to microbial degradation were not degraded in plant parts of either N or bmr types. The bmr-12 mutation did not result in changes in leaf blade anatomy or histological reactions for lignin and did not result in susceptibility to microbial degradation of the most resistant tissues. The bmr-12 mutation did allow an improved microbial degradation of marginally digestible tissue, i.e., those tissues usually only poorly degraded.
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