Glutamate Receptor–Like Genes Form Ca2+ Channels in Pollen Tubes

Elevations in cytosolic free calcium concentration ([Ca2+]cyt) constitute a fundamental signal transduction mechanism in eukaryotic cells, but the molecular identity of Ca2+ 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 (GLRs) facilitate Ca2+ influx across the plasma membrane, modulate apical [Ca2+]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. Pollen tubes are amodel system for tip growth,a cellular growth mechanism common to fis-sion yeast, filamentous fungi, neurons, and root hairs. Pollen tubes growing in vitro display reg-ular oscillations in many parameters with the same period but often with different phase relationships (1). These include vesicle trafficking, cell wall pre-cursor exocytosis, actin microfilament polymeriza