May aid fertilization by loosening the cell wall of the stigma and style, thereby facilitating penetration of the pollen tube. Acts selectively on grass cell walls, which are relatively poor in pectins and xyloglucans and rich in glucuronoarabinoxylans and (1-3),(1-4)-beta-D-glucans, when compared with cell walls of other angiosperms, including other monocots. Expressed in anthers and pollen. Expression low before and high after pollen mitosis. Causes an allergic reaction in human. Causes maize pollen allergy. Beta-expansin 1 extension activity grass cell wall is enhanced by dithiothreitol (DTT) and EDTA, inhibited by Cu(2+) and Hg(2+), and resistant to denaturation by methanol boiling and heat treatments. Belongs to the expansin family. Expansin B subfamily.