Mobilization of Ca2+ by cyclic ADP-ribose from the endoplasmic reticulum of cauliflower florets.
The NAD+ metabolite cADP-Rib (cADPR) elevates cytosolic free Ca2+ in plants and thereby plays a central role in signal transduction pathways evoked by the drought and stress hormone abscisic acid. cADPR is known to mobilize Ca2+ from the large vacuole of mature cells. To determine whether additional sites for cADPR-gated Ca2+ release reside in plant cells, microsomes from cauliflower (Brassica oleracea) inflorescences were subfractionated on sucrose density gradients, and the distribution of cADPR-elicited Ca2+ release was monitored. cADPR-gated Ca2+ release was detected in the heavy-density fractions associated with rough endoplasmic reticulum (ER). cADPR-dependent Ca2+ release co-migrated with two ER markers, calnexin and antimycin A-insensitive NADH-cytochrome c reductase activity. To investigate the possibility that contaminating plasma membrane in the ER-rich fractions was responsible for the observed release, plasma membrane vesicles were purified by aqueous two-phase partitioning, everted with Brij-58, and loaded with Ca2+: These vesicles failed to respond to cADPR. Ca2+ release evoked by cADPR at the ER was fully inhibited by ruthenium red and 8-NH2-cADPR, a specific antagonist of cADPR-gated Ca2+ release in animal cells. The presence of a Ca2+ release pathway activated by cADPR at higher plant ER reinforces the notion that, alongside the vacuole, the ER participates in Ca2+ signaling.
Navazio
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L
The Plant Laboratory, Department of Biology, University of York, P.O. Box 373, York YO10 5YW, United Kingdom.
Mariani
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P
Sanders
D
D
D000246:Adenosine Diphosphate Ribose / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D001937:Brassica / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002458:Cell Fractionation; D036563:Cyclic ADP-Ribose; D018870:Endoplasmic Reticulum, Rough / Q000187:drug effects / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008861:Microsomes / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D018547:Plant Stems / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism
D009243:NAD; D036563:Cyclic ADP-Ribose; D000246:Adenosine Diphosphate Ribose; D002118:Calcium