Membrane recycling and calcium dynamics during settlement and adhesion of zoospores of the green alga Ulva linza.
Recruitment of individuals of the marine alga Ulva linza on to a suitable habitat involves the settlement of motile zoospores on to a substratum during which a preformed adhesive is secreted by vesicular exocytosis. The fluorescent styryl dye FM 1-43 and fluorescent Ca(2+) indicators were used to follow membrane cycling and changes in cytosolic Ca(2+) ([Ca(2+)](cyt)) associated with settlement. When swimming zoospores were exposed continuously to FM 1-43, the plasma membrane was preferentially labelled. During settlement, FM 1-43-labelled plasma membrane was rapidly internalized reflecting high membrane turnover. The internalized membrane was focused into a discrete region indicating targeting of membrane to an endosome-like compartment. Acetoxymethyl (AM)-ester derivatives were found to be unsuitable for monitoring [Ca(2+)](cyt) because the dyes were rapidly sequestered from the cytoplasm into sub-cellular compartments. [Ca(2+)](cyt) was, however, reliably measured using dextran-conjugated calcium indicators delivered into cells using a biolistic technique. Cells loaded with Oregon Green BAPTA-1 dextran (Invitrogen, Paisley, UK) showed diffuse cytosolic loading and reliably responded to imposed changes in [Ca(2+)](cyt). During settlement, zoospores exhibited both localized and diffuse increases in [Ca(2+)](cyt) implying a role for [Ca(2+)](cyt) in exocytosis of the adhesive.
Thompson
S E M
SE
School of Biosciences, The University of Birmingham, Birmingham, and Marine Biological Association, The Laboratory, Citadel Hill, Plymouth, UK.
Callow
J A
JA
Callow
M E
ME
Wheeler
G L
GL
Taylor
A R
AR
Brownlee
C
C
D002118:Calcium / Q000378:metabolism*; D002448:Cell Adhesion; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology; D000460:Chlorophyta / Q000378:metabolism / Q000502:physiology*; D004705:Endocytosis; D013170:Spores
D002118:Calcium