ENRICHMENT OF VITRONECTIN-LIKE AND FIBRONECTIN-LIKE PROTEINS IN NACL-ADAPTED PLANT-CELLS AND EVIDENCE FOR THEIR INVOLVEMENT IN PLASMA-MEMBRANE CELL-WALL ADHESION

Cells of tobacco adapted to grow in high concentrations of NaCl develo p tight zones of adhesion between the plasma membrane and cell wall, r evealed by concave plasmolysis in osmotic solutions. Unadapted cells e xhibit mostly convex plasmolysis and exhibit little or no adhesive cha racter. Wall-less protoplasts isolated from the adapted cells retain t he complementary adhesive character and adhere tightly to each other, whereas protoplasts from unadapted cells do not. The hexapeptide gly-a rg-gly-asp-ser-pro, in which the arg-gly-asp represents the integrin-b inding domain of several animal extracellular matrix proteins, specifi cally blocks adhesion of the protoplasts. A control hexapeptide, gly-a rg-gly-glu-ser-pro, is ineffective in blocking adhesion. Tobacco prote ins immunologically related to human vitronectin were found in cell wa lls and membranes of unadapted and NaCl-adapted cells, but the total e xtractable vitronectin-like protein was enriched in the adapted cells. Tobacco proteins immunologically related to human fibronectin were fo und in membranes and cell walls of NaCl-adapted cells but not in those from unadapted cells. Our observations indicate that plant cells poss ess cell-matrix adhesion complexes similar to animal cells, and these adhesion complexes accumulate in growth-limited cells adapted to salin e stress.