Autolysis-Iike Release of Pectic Polysaccharides from Regions of Cell Walls Other Than the Middle Lamella

Abstract

Cell walls of a storage organ (potato tubers) showed autolysis-like activity. After 20 h of incubation in water at 35°C, the purified cell walls released approximately 10% of the cell wall dry weight as pectic polysaccharides containing about 40% of the total galacturonic acid present in the cell walls. Virtually no neutral polysaccharides were found in the soluble fraction. The pectic polysaccharides were heterogeneous in galacturonic acid content and had a very large molecular size. The release of pectic polymers was caused neither by enzymatic reactions nor by β-elimination, but by a chelation of Ca2+ and/or other metal ions during the cell wall isolation. Ultrastructural observations clearly showed that these pectic polysaccharides were released not from the middle lamella, but from the primary cell wall adjacent to the plasma membrane. These results indicate that nearly half of cell wall pectic polysaccharides are held in the primary wall only by Ca2+- and/or other metal-bridges and that these pectic polymers are not associated with the middle lamella.