Glutamate Receptor–Like Genes Form Ca 2+ Channels in Pollen Tubes and Are Regulated by Pistil d -Serine

Amino acid modulation of Ca 2+ signaling guides growth of plant pollen tubes. Elevations in cytosolic free calcium concentration ([Ca 2+ ] cyt ) constitute a fundamental signal transduction mechanism in eukaryotic cells, but the molecular identity of Ca 2+ channels initiating this signal in plants is still under debate. Here, we show by pharmacology and loss-of-function mutants that in tobacco and Arabidopsis , glutamate receptor–like channels ( GLR s) facilitate Ca 2+ influx across the plasma membrane, modulate apical [Ca 2+ ] cyt gradient, and consequently affect pollen tube growth and morphogenesis. Additionally, wild-type pollen tubes grown in pistils of knock-out mutants for serine-racemase ( SR1 ) displayed growth defects consistent with a decrease in GLR activity. Our findings reveal a novel plant signaling mechanism between male gametophyte and pistil tissue similar to amino acid–mediated communication commonly observed in animal nervous systems.