Cell walls are the extracellular matrix of plant cells and are primarily composed of a heterogeneous mixture of polysaccharides that change in composition and structure during growth and development and between species. The wall is crucial to the development of tissues and organs and determines the form and function of plant cells. Walls are also crucial to everyday life in the form of dietary fibre, energy, paper and timber. Since grains of cereal crops are a major source of complex carbohydrates in the human diet understanding the biosynthesis and architecture of grass walls will assist with improving the quality of grains for human health.
Suspension-cultured cells (SCC) derived from endosperm of Italian rye grass, Lolium multiflorum, are a model system for studying grass wall biosynthesis and architecture. Arabinoxylan (AX) and (1,3;1,4)-β-glucan (MLG) are the major matrix phase polysaccharides. Lolium SCCs were enzymically protoplasted, and wall polysaccharide deposition was followed temporally and spatially using fluorescence immunolabelling, confocal and superresolution microscopy. Wall polysaccharide deposition begins at focal regions with cellulose microfibrils deposited within 1 h followed closely by AX in filaments, MLG in small puncta, and callose in random patches. Over time, deposition radiated outwards from these foci to form a continuous wall structure. From these observations we have developed a model of the temporal and spatial assembly of these walls.
In parallel we examined the architecture of actively dividing and elongating barley root and coleoptile tissues walls, which have a similar polysaccharide composition using antibodies together with TEM and electron tomography. Associations between the wall, the secretory system and, where possible, links with wall biosynthetic enzymes were analysed. An overview of the secretory system within barley cells was also investigated using serial block face SEM, which may lead to the identification of common morphologies at sites of wall assembly.