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.