RELATIONSHIP BETWEEN STRUCTURAL DEVELOPMENT OF CELL-WALLS AND DEGRADATION OF TISSUES IN MAIZE STEMS

Sections of internodes of growing maize stems were used to study the behaviour of cell walls of different tissues during in-vitro degradation with rumen fluid. Tissues with primary cell walls-middle lamellae, at early stages of development, were degraded completely. In specific tissues, newly synthesised secondary walls were highly digestible whereas the primary walls middle lamellae of these tissues were indigestible. These primary walls-middle lamellae stained positively with acid phloroglucinol but showed no fluorescence. At pollination, when secondary walls were of considerable thickness, these walls were still completely digestible even though they stained intensely with acid phloroglucinol and showed reduced fluorescence. However, at some distance from the cut end of sections, the secondary walls of the elongated tube-like cells of sclerenchyma tissue showed considerable reduction in digestibility. Cross-sectional area and dry weight measurements of different stem tissues revealed the importance of secondary wall digestion of sclerenchyma compared with the thin-walled parenchyma. Chemical treatment with KMnO4 or NaOH resulted in colourless secondary walls after staining whereas primary walls still reacted positively. It was concluded that very small amounts of phenolic compounds (lignin) located in the primary wall-middle lamella that are not removed by KMnO4 and NaOH treatment are responsible for the decrease in digestibility of tissues during plant development. Histochemical 'lignin' reactions and fluorescence just detect phenolic compounds and cannot be correlated with degradation.