Mobilization of Ca2+ by Cyclic ADP-Ribose from the Endoplasmic Reticulum of Cauliflower Florets

Abstract

The NAD ϩ metabolite cADP-Rib (cADPR) elevates cytosolic free Ca 2ϩ 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 Ca 2ϩ from the large vacuole of mature cells. To determine whether additional sites for cADPR-gated Ca 2ϩ release reside in plant cells, microsomes from cauliflower (Brassica oleracea) inflorescences were subfractionated on sucrose density gradients, and the distribution of cADPR-elicited Ca 2ϩ release was monitored. cADPR-gated Ca 2ϩ release was detected in the heavy-density fractions associated with rough endoplasmic reticulum (ER). cADPR-dependent Ca 2ϩ 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 Ca 2ϩ

Analyses of Ca2+ Accumulation and Dynamics in the Endoplasmic Reticulum of Arabidopsis Root Cells Using a Genetically Encoded Cameleon Sensor

“…The subsequent decrease in [Ca 2+ ] ER , which is especially evident with L-Glu, low ATP concentration, and NaCl treatments, occurs only after the initial accumulation and is likely to be dependent on the activity of ER membrane-resident Ca 2+ -permeable channels (Klüsener et al, 1995(Klüsener et al, , 1997Muir and Sanders, 1997;Navazio et al, 2000Navazio et al, , 2001 (Fig. 2G).…”

“…Despite some biochemical evidence for Ca 2+ release in response to IP3, nicotinic acid adenine dinucleotide phosphate, and cyclic adenosine diphosphoribose (Muir and Sanders, 1997;Navazio et al, 2000Navazio et al, , 2001, electrophysiological analyses supporting the existence of voltage-gated ER-localized Ca 2+ channels (Klüsener et al, 1995(Klüsener et al, , 1997, homologous for the respective IP3 and ryanodine receptors, are missing in higher plants (Wheeler and Brownlee, 2008;Kudla et al, 2010 Geisler et al, 2000;Sze et al, 2000;Bonza and De Michelis, 2011). Plant genomes encode different isoforms of both ECAs and ACAs.…”

Inositol hexakisphosphate mobilizes an endomembrane store of calcium in guard cells

“…Among the different agents reported to increase guard cell [Ca 2ϩ ] cyt , both Ins(1,4,5)P 3 and cADPR are believed to target endomembranes (25,30). Thus both agents activate calcium release from the vacuole (30) but also from other endomembranes such as the endoplasmic reticulum (ER) (7,31). A further Ca 2ϩ -mobilizing agent in higher plants, nicotinic acid adenine dinucleotide phosphate, is active exclusively at the ER (32).…”

Endoplasmic reticulum stress-induced programmed cell death in soybean cells

“…Although the ER has a smaller Ca 2+ storage capacity than the vacuole, its importance in Ca 2+ release during signaling has recently been suggested (Navazio et al, 2000;Navazio et al, 2001). In plant cells two distinct subtypes of Ca 2+ -ATPases have been found in the ER: ECA1, a type IIA ER-type Ca 2+ /Mn 2+ pump, which is sensitive to CPA (Sze et al, 2000;Pittman and Hirschi, 2003); and ACA2, a CaM-regulated type IIB Ca 2+ pump, which is insensitive to CPA (Harper et al, 1998;Pittman and Hirschi, 2003).…”