Synthesis and oxidative insolubilization of cell-wall proteins during osmotic stress

The cell walls in the new white roots of jack pine (Pinus banksiana Lamb.) were observed to constrict around the shrinking protoplast of osmotically s tressed roots, and pressure was maintained via an apparent adjustment of ce ll-wall size and elasticity. These elastic alterations of the cell wall per mitted the root cells to maintain full turgor despite the loss of most of t he water in the tissue. The constriction of the root cell wall around the d ehydrating protoplasts to maintain turgor may reflect changes in cell wall structure. We found that these shrinking root cells synthesize and secrete into the intercellular fluid a set of proteins. These proteins become tight ly associated (i.e. guanidine HCl- and sodium dodecyl sulfate-insoluble) wi th the cell wall but can be released from the matrix, after briefly boiling in 0.1% sodium dodecyl sulfate, by the combination of guanidine HCl, CaCl2 and dithiothreitol. However, these cell-wall proteins became insoluble wit h time. The proteins could subsequently be destructively extracted from the wall with acid NaClO2 treatments. After these proteins were incorporated i nto the cell walls, the roots adopted a new, smaller maximal tissue volume and elastic coefficients returned to normal levels.