THE HETEROGENEITY OF THE PLASMA-MEMBRANE H-ATPASE RESPONSE TO AUXIN -AN ALTERNATIVE WAY TO ANALYZE SIGNAL PERCEPTION AND TRANSDUCTION()

The sensitivity of the plasma membrane H+-ATPase in tobacco was invest igated in vitro, both at the proton translocation level and the ATPase level, according to plant development and leaf location. Both activit ies are stimulated by auxin in all leaves, whatever the plant age and the leaf age. However, the sensitivity to auxin was heterogeneous with respect to plant development and leaf location. In parallel experimen ts using the same plasma membrane samples, polypeptides patterns were investigated by two-dimensional gel electrophoresis and image analysis was used to quantify the relative abundance of 110 peptides. Systemat ic analysis of the two kinds of data identified 8 polypeptides, the ab undance of which changed in a consistent way with the sensitivity, wha tever the plant developmental state and leaf location. These unknown p olypeptides are proposed as potential markers of the membrane response to auxin.