A sodium-dependent, fast block to polyspermy occurs in eggs of fucoid algae.
More than 70% of Pelvetia fastigiata eggs and about 15% of Fucus distichus eggs become polyspermic when fertilized at natural sperm concentrations in a low-sodium (2.5 mM Na+, 450 mM N-methyl glucamine) artificial seawater. Natural levels of polyspermy are 1-3% for both species. Polyspermic eggs germinate and respond to photopolarization, but do not develop beyond an abnormal, "stumpy," four-cell stage. They die within 1-1.5 weeks. The sodium-dependent block is a fast block, and it is replaced by a second block (probably cell wall formation) no later than 9 min (Pelvetia) after eggs are shed. The sodium-dependent block in Pelvetia is very efficient; when external sodium is raised to only 47.5 mM, the level of polyspermy drops to about 25%. These results are compared with data on marine invertebrates in the context of factors such as the sperm/egg concentration at fertilization and natural, osmotic (salinity) stress.
Brawley
S H
SH
Department of General Biology, Vanderbilt University, Nashville, Tennessee 37235.
D056890:Eukaryota / Q000502:physiology*; D005260:Female; D005306:Fertilization; D008297:Male; D008564:Membrane Potentials; D000459:Phaeophyceae / Q000502:physiology*; D012623:Seawater; D012964:Sodium / Q000502:physiology; D013084:Sperm-Ovum Interactions; D013997:Time Factors
D012964:Sodium