Loss of arabinogalactan-proteins from the plasma membrane of NaCl-adapted tobacco cells

Abstract

Cultured cells of tobacco (Nicotiana tabacum L.) adapted to 428 mM NaCl exhibited a reduced rate of cell enlargement, which is probably due to decreased cell-wall extensibility. Arabinogalactan-protein (AGP) has been implicated as a cell-wall-loosening factor (Schopfer 1990). Levels of plasma membrane and extracellular AGPs that react with Yariv reagent were measured and compared between NaCl-adapted and unadapted tobacco cells. Unadapted cells contained a very high level of AGPs on the plasma membrane, which amounted to 0.16 μg·μg−1 membrane protein. In contrast, AGPs were virtually undetectable on the plasma membrane of NaCl-adapted cells. Accumulation of AGPs was also decreased in culture media of NaCl-adapted cells. These data support the hypothesis that AGPs participate in cell expansion. Possible mechanisms of the proposed cell-expansion role of AGPs are discussed.