Protoplasts prepared from aVinca roseasuspension culture regenerated cell walk in culture within 24 hr. Glycoproteins containing hydroxyproline were isolated from the protoplasts prior to regeneration of the cell walls. The glycoproteins were extracted, without a degradation procedure, with 0.05 M sodium acetate buffer, pH 5.6, containing 0.3 M NaCl. Newly synthesized hydroxyproline in protoplasts labelled with proline appeared almost exclusively in the glycoproteins. In this system, the hydroxylation of proline and the incorporation of arabinose into glycoproteins were suppressed by protein synthesis inhibitors. Inhibition of hydroxylation by the removal of Fe2+also caused suppression of arabinose incorporation into glycoproteins. These observations suggest that glycoproteins are precursors of extensin, a hydroxyproline-rich glycoprotein contained in the cell wall of plants. The precursors were heterogeneous in size and charge as determined by gel filtration and ion exchange chromatography.
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