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ABSTRACT:

Using confocal microscopy, X-ray microanalysis and the scanning ion-selective electrode technique, we investigated the signalling of H₂O₂, cytosolic Ca²⁺ ([Ca2+]cyt) and the
PM H⁺-coupled transport system in K⁺/Na⁺ homeostasis control in NaCl-stressed calluses of Populus euphratica.An obvious Na⁺ /H⁺ antiport was seen in salinized cells;however, NaCl stress caused a net K⁺ efflux, because of the salt-induced membrane depolarization. H₂O₂ levels, regulated upwards by salinity, contributed to ionic homeostasis,because H₂O₂ restrictions by DPI or DMTU caused enhanced K⁺ efflux and decreased Na⁺ /H⁺ antiport activity. NaCl induced a net Ca²⁺ influx and a subsequent rise of [Ca²⁺]cyt, which is involved in H₂O₂-mediated K⁺/Na⁺ homeostasis in salinized P. euphratica cells. When callus cells were pretreated with inhibitors of the Na⁺ /H⁺ antiport system, the NaCl-induced elevation of H₂O₂ and [Ca²⁺]cyt was correspondingly restricted, leading to a greater K+ efflux and a more pronounced reduction in Na⁺ /H⁺ antiport activity. Results suggest that the PM H⁺-coupled transport system mediates H⁺ translocation and triggers the stress signalling of H₂O₂ and Ca²⁺, which results in a K⁺/Na⁺ homeostasis via mediations of K⁺ channels and the Na⁺ /H⁺ antiport system in the PM of NaCl-stressed cells. Accordingly, a salt stress signalling pathway of P. euphratica cells is proposed.