Differential contribution of cytoplasmic Ca2+ and Ca2+ influx to gamete fusion and egg activation in maize.
In multicellular organisms, gamete fusion triggers a set of events, collectively known as egg activation, that leads to the development of a new individual. Every species that has been studied shows at least one rise in cytoplasmic Ca2+ concentration ([Ca2+]Cyt) after gamete fusion which is believed to be involved in activation. Yet the source and regulation of this Ca2+ signal and the way it is transduced inside the zygote are controversial. In higher plants, in vitro fertilization (IVF) has enabled the description of a rise in [Ca2+]Cyt (ref. 4) that is sufficient for activation, and of a Ca2+ influx that spreads as a wavefront from the fusion site The relationship between these two responses is unknown. Using a new combination of methods that simultaneously monitor the extracellular flux with a Ca2+-vibrating probe, and [Ca2+]Cyt by widefield imaging, we directly determined that the Ca2+ influx precedes the [Ca2+]Cyt elevation by 40-120 s. In addition, results from experiments using the Ca2+-channel inhibitor gadolinium (Gd3+) suggest that the Ca2+ influx may be necessary for sperm incorporation. We also present evidence for a putative sperm-dependent Gd3+-insensitive localized Ca2+ influx confined to the fusion point.
Antoine
A F
AF
Laboratoire Reproduction et Développement des Plantes, UMR 5667 CNRS/INRA/ENS/Université Lyon I, Ecole Normale Supérieure de Lyon, 46 allée d'Italie, F-69364 Lyon, France. anne-frederique.antoine@univ-lille.fr
Faure
J E
JE
Dumas
C
C
Feijó
J A
JA
D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000502:physiology*; D003593:Cytoplasm / Q000378:metabolism; D005306:Fertilization / Q000502:physiology*; D005307:Fertilization in Vitro; D005682:Gadolinium / Q000494:pharmacology; D012639:Seeds / Q000378:metabolism; D003313:Zea mays / Q000254:growth & development*
D002121:Calcium Channel Blockers; D005682:Gadolinium; C038958:gadolinium chloride