NaCl-elicited, vacuolar Ca2+ release facilitates prolonged cytosolic Ca2+ signaling in the salt response of Populus euphratica cells

• Vacuolar Ca2+ signaling networks were established in salt-stressed poplar cells.
• The salt-induced vacuolar Ca2+ release depends on eATP, Ca2+ influx, H2O2, and NO.
• NaCl-altered Ca2+ mobilizations were mediated by IP3 and cADPR but not by SV channel.
• The salt-elicited vacuolar Ca2+ release mediates ionic homeostasis in poplar cells.
• IP3/cADPR-mediated vacuolar Ca2+ release enhances salt-responsive genes expression.

High environmental salt elicits an increase in cytosolic Ca2+ ([Ca2+]cyt) in plants, which is generated by extracellular Ca2+ influx and Ca2+ release from intracellular stores, such as vacuole and endoplasmic reticulum. This study aimed to determine the physiological mechanisms underlying Ca2+ release from vacuoles and its role in ionic homeostasis in Populus euphratica. In vivo Ca2+ imaging showed that NaCl treatment induced a rapid elevation in [Ca2+]cyt, which was accompanied by a subsequent release of vacuolar Ca2+. In cell cultures, NaCl-altered intracellular Ca2+ mobilization was abolished by antagonists of inositol (1, 4, 5) trisphosphate (IP3) and cyclic adenosine diphosphate ribose (cADPR) signaling pathways, but not by slow vacuolar (SV) channel blockers. Furthermore, the NaCl-induced vacuolar Ca2+ release was dependent on extracellular ATP, extracellular Ca2+ influx, H2O2, and NO. In vitro Ca2+ flux recordings confirmed that IP3, cADPR, and Ca2+ induced substantial Ca2+ efflux from intact vacuoles, but this vacuolar Ca2+ flux did not directly respond to ATP, H2O2, or NO. Moreover, the IP3/cADPR-mediated vacuolar Ca2+ release enhanced the expression of salt-responsive genes that regulated a wide range of cellular processes required for ion homeostasis, including cytosolic K+ maintenance, Na+ and Cl− exclusion across the plasma membrane, and Na+/H+ and Cl−/H+ exchanges across the vacuolar membrane.

A schematic diagram of the proposed model showing the NaCl-elicited mechanisms involved in vacuolar Ca2+ release, and the roles of vacuolar-generated Ca2+ in mediating ionic homeostasis in Populus euphratica cells.Figure optionsDownload as PowerPoint slide