Binds to actin filaments and promotes cross-linking into thick bundles. Has an actin-stabilizing activity. Associates predominantly with long and dynamic actin bundles in the shank of growing pollen tubes. The actin regulatory activities are inhibited by pH > 6.8 and/or high [Ca(2+)]. Interacts with F-actin. Exclusively expressed in pollen grains. The C-terminal domain (159-213) is required for the ability to respond to pH and calcium variations. Cross-links actin with a constant of dissociation of 1.5 uM.