Arabidopsis ABCG28 is required for the apical accumulation of reactive oxygen species in growing pollen tubes

resulted in defective pollen tube growth, failure to localize polyamine and ROS to the growing pollen tube tip, and complete male sterility, whereas ectopic expression of this gene in root hair could recover ROS accumulation at the tip and improved the growth under high-pH conditions, which normally prevent ROS accumulation and tip growth. Together, these data suggest that AtABCG28 is critical for localizing polyamine and ROS at the growing tip. In addition, this function of AtABCG28 is likely to protect the pollen tube from the cytotoxicity of polyamine and contribute to the delivery of polyamine to the growing tip for incorporation into the expanding cell wall.