OXIDATIVE CROSS-LINKING OF PLASMA-MEMBRANE ARABINOGALACTAN PROTEINS

Monoclonal antibodies which recognize carbohydrate in arabinogalactan proteins (AGPs) have revealed that certain carbohydrate epitopes at th e outer plasma membrane surface are developmentally regulated. Some ep itopes are expressed according to cell position, and AGPs are thought to play a role in cell-cell interaction during development. This study demonstrates that sugar beet plasma membranes contain two subfamilies of AGPs, with apparent molecular masses of 82 and 97 kDa, and that ea ch sub-family consists of a small number of acidic AGP isoforms. Excis ion of leaves generates three additional AGP complexes with apparent m olecular masses of 120, 170 and 210 kDa, with the 170 kDa complex bein g the major form induced by excision. The addition of millimolar conce ntrations of H2O2 to a partially purified fraction of the 82 and 97 kD a AGPs also generates AGP complexes, with the 170 kDa complex as the m ajor form. These results indicate that the plasma membrane AGPs are a target for endogenous H2O2.