Alteration of pectic polysaccharides in cell walls, extracellular polysaccharides, and glycan-hydrolytic enzymes of growth-restricted carrot cells under calcium deficiency

Abstract

Suspension-cultured carrot (Daucus carota L. cv. Kintoki) cells were grown in calcium (Ca 2 + )-deficient and normal liquid media. Cell growth was limited by the Ca 2+ deficiency. Similar amounts of pectic fractions were extracted from the walls of control and Ca 2+ -deprived cells, but the fractions from the walls of Ca 2+ -deprived cells showed a substantial decrease in galacturonic acid content. However, after 15 days of culture, Ca 2+ -deprived cells released galacturonic acid-rich extracellular polysaccharides at twice the rate of control cells. The polysaccharides consisted of a mixture of several polymers containing predominantly arabinose, galactose and galacturonic acid. Ca 2+ -deprived cells also secreted three times more extracellular proteins, containing many glycan-hydrolytic enzymes, into the medium than did normal cells. SDS-PAGE analysis revealed several distinct changes in the polypeptide pattern in the medium of control and Ca 2+ -deprived cells. Activities of α-galactosidase, β-glucosidase and exo-polygalacturonase increased considerably during Ca 2+ deficiency, whereas α-L-arabinofuranosidase and #-galactosidase activities were much reduced.