... communication. Although pollen tube growth is regulated by the cytoplasmic Ca 2+ concentration ([Ca 2+ ] cyt ), it is not known whether [Ca 2+ ] cyt is involved in pollen tube guidance and reception. Using Arabidopsis expressing the GFP-based Ca 2+ -sensor yellow cameleon 3.60 (YC3.60) in pollen tubes...

..., releasing two sperm that fertilize an egg and a central cell. Here, we identified the gene encoding Arabidopsis HAP2, demonstrating that it is allelic to GCS1. HAP2 is expressed only in the haploid sperm and is required for efficient pollen tube guidance to ovules. We identified an insertion ( hap2-1...