SummaryIt has been controversial for many years whether in the cellulose of higher plants, the microfibrils are aggregates of 'elementary fibrils', which have been suggested to be about 3.5 nm in diameter. Solid-state NMR spectroscopy was used to examine two celluloses whose fibril diameters had been established by electron microscopy: onion (8-10 nm, but containing 40% of xyloglucan as well as cellulose) and quince (2 nm cellulose core). Both of these forms of cellulose contained crystalline units of similar size, as estimated from the ratio of surface to interior chains, and the time required for proton magnetisation to diffuse from the surface to the interior. It is suggested that the onion microfibrils must therefore be constructed from a number of cellulose subunits 2 nm in diameter, smaller than the 'elementary fibrils' envisaged previously. The size of these subunits would permit a hexagonal arrangement resembling the cellulose synthase complex.
SummaryA laccase-type polyphenoloxidase (EC 1.1 0.3.2.), abundantly secreted by suspension-cultured sycamore (Acer pseudoplatanus) cells was purified t o homogeneity. This laccase form is a glycoprotein (molecular weight 110 000) with high mannose and complex glycans. The polypeptide moiety has a molecular weight of 66 000, indicating that the glycoprotein is 40% carbohydrate. Laccase is abundantly present in both the cell wall and the culture medium of suspensioncultured sycamore cells, but it is not detected in the cytoplasm, indicating that this large protein is efficiently secreted by the cells. Polyclonal rabbit antiserum was raised against the deglycosylated protein and was used to probe extracts of sycamore stem tissues. A second laccase form (molecular weight 56 OOO), antigenically related t o laccase from cell cultures, is abundant in the epidermis of sycamore stems. In addition, this 56 kDa laccase form co-localizes with lignin precursors on tissue prints from sycamore stems. A polypeptide (molecular weight 50 000-56 000), antigenically related t o sycamore laccase, was also immunodetected in most plant organs previously described in the literature as polyphenoloxidase-rich.
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