INTRAPROTOPLASMIC FERULOYLATION OF ARABINOXYLANS IN FESTUCA-ARUNDINACEA CELL-CULTURES

Graminaceous primary cell walls contain polysaccharides to which are e sterified feruloyl residues. Ester biosynthesis is highly specific and the present experiments were performed to ascertain the likely site o f feruloylation in living grass cell cultures. Cell cultures of tall f escue grass (Festuca arundinacea Schreber) incorporated exogenous L-[1 -H-3]arabinose into polymers at a linear rate after a short lag of app rox. 1-3 min. Radiolabelled polymers did not start to accumulate in th e culture medium until 20-35 min after [H-3]arabinose was supplied. Ho wever, polymer-bound feruloyl-arabinose residues began to accumulate H -3 after a lag of 1-3 min. Assuming that the onset of secretion of rad iolabelled polymers into the medium indicates the time before which es sentially all the radiolabel was internal to the plasma membrane, the results show that the polysaccharide-bound [H-3]arabinose residues mus t have been feruloylated within the protoplast.