Ionic and osmotic components of salt stress specifically modulate net ion fluxes from bean leaf mesophyll
Shabala, SN, Ionic and osmotic components of salt stress specifically modulate net ion fluxes from bean leaf mesophyll, Plant, Cell and Environment, 23, (8) pp. 825-837. ISSN 0140-7791 (2000) [Refereed Article]
Ionic mechanisms of salt stress perception were investigated by non-invasive measurements of net H+, K+, Ca2+, Na+, and Cl- fluxes from leaf mesophyll of broad bean (Vicia faba L.) plants using vibrating ion-selective microelectrodes (the MIFE technique). Treatment with 90 mM NaCl led to a significant increase in the net K+ efflux and enhanced activity of the plasma membrane H+-pump. Both these events were effectively prevented by high (10 mM) Ca2+ concentrations in the bath. At the same time, no significant difference in the net Na+ flux has been found between low- and high-calcium treatments. It is likely that plasma membrane K+ and H+ transporters, but not the VIC channels, play the key role in the amelioration of negative salt effects by Ca2+ in the bean mesophyll. Experiments with isotonic mannitol application showed that cell ionic responses to hyperosmotic treatment are highly stress-specific. The most striking difference in response was shown by K+ fluxes, which varied from an increased net K+ efflux (NaCl treatment) to a net K+ influx (mannitol treatment). It is concluded that different ionic mechanisms are involved in the perception of the 'ionic' and 'osmotic' components of salt stress.