ANNEXIN-MEDIATED SECRETORY VESICLE AGGREGATION IN PLANTS

The mechanism by which membranes fuse during vesicle-mediated secretio n is of considerable importance for plant cell growth, but remains unk nown. We have identified Ca2+-dependent phospholipid-binding proteins (annexins) from maize (Zea mays), that may play a part in this process . An assay for Ca2+-dependent binding of annexins to liposomes, reveal ed that the maize proteins (p23, p33 and p35) and annexins from bovine lung, bind over a similar range of Ca2+ concentrations. Turbidity ass ays further revealed that both maize and bovine annexins induced lipos ome aggregation and that the plant annexins were also effective at agg regating plant secretory vesicles. This aggregation occurred at levels of free Ca2+ Similar to that required for die binding of annexins p33 and p35. We discuss the significance of these results for the plant s ecretory apparatus.