Ca(2+) shuttling in vesicles during tip growth in Neurospora crassa.
Tip-growing organisms maintain an apparently essential tip-high gradient of cytoplasmic Ca(2+). In the oomycete Saprolegnia ferax, in pollen tubes and root hairs, the gradient is produced by a tip-localized Ca(2+) influx from the external medium. Such a gradient is normally dispensable for Neurospora crassa hyphae, which may maintain their Ca(2+) gradient by some form of internal recycling. We localized Ca(2+) in N. crassa hyphae at the ultrastructural level using two techniques (a) electron spectroscopic imaging of freeze-dried hyphae and (b) pyroantimoniate precipitation. The results of both methods support the presence of Ca(2+) in the wall vesicles and Golgi body equivalents, providing a plausible mechanism for the generation and maintenance of the gradient by Ca(2+) shuttling in vesicles to the apex, without exogenous Ca(2+) influx. Ca(2+) sequestration into the vesicles seems to be dependent on Ca(2+)-ATPases since cyclopiazonic acid, a specific inhibitor of Ca(2+) pumps, eliminated all Ca(2+) deposits from the vesicles of N. crassa.
Torralba
S
S
Department of Biology, York University, Toronto, Ontario, M3J 1P3, Canada.
Heath
I B
IB
Ottensmeyer
F P
FP
D000965:Antimony / Q000737:chemistry; D002118:Calcium / Q000378:metabolism*; D011232:Chemical Precipitation; D004577:Electron Probe Microanalysis; D005612:Freeze Drying; D006056:Golgi Apparatus / Q000378:metabolism / Q000648:ultrastructure; D008854:Microscopy, Electron / Q000295:instrumentation / Q000379:methods; D009492:Neurospora crassa / Q000254:growth & development* / Q000378:metabolism* / Q000648:ultrastructure; D015388:Organelles / Q000378:metabolism* / Q000648:ultrastructure
C009133:pyroantimonate; D000965:Antimony; D002118:Calcium