Cell wall composition of vascular and parenchyma tissues in broccoli stems

Broccoli stems can become tough and stringy owing to excessive development of the vascular ring. Thickened cell walls from the vascular ring were isolated and their composition was determined. They were derived principally from anatomically recognisable xylem vessels, fibres and tracheids but contained an assemblage of polysaccharides typical of primary cell walls. Their pectin content was particularly high and they contained only 6% lignin as estimated by solid state 13C NMR spectroscopy. They did not differ markedly in composition from parenchyma cell walls within the same stems. Thus, despite their thickness and anatomical appearance, these cell walls resembled the walls of non-woody cells in their polymer composition.