Osmotic effects of NaCl on cell hydraulic conductivity of corn roots.

In this study, whether the effect of salt (NaCl) stress on cell hydraulic conductivity (L(p)) is via osmotic pressure or ion toxicity and whether abscisic acid (ABA) can release the salt adverse effect were tested. Immediate effects of NaCl and ABA on root cortical cell L(p) of maize (Zea mays L.) were detected by measuring changes in half time of water exchange (T(1/2)) and turgor of individual single cells with a cell pressure probe for at least 1 h. The results showed that stepwise additions of NaCl (50 mM) significantly (P < 0.01) reduced the water permeability. One-step addition of 50 mM NaCl even more drastically decreased L(p). ABA was not able to instantaneously reverse the low water permeability induced by the salt stress. Long-term effects of NaCl, mannitol and sorbitol, and ABA on L(p) were measured for 6 days. Both NaCl and a mixture of mannitol and sorbitol, with the same osmotic strength of 0.25 MPa, significantly reduced L(p) at the early stage of the treatments. The declined L(p) in the salinized cell gradually and partially recovered after 2 days, whereas the L(p) with the mannitol and sorbitol mixture treatment was all time inhibited. With long-time treatment, ABA (500 nM) significantly (P < 0.01) increased turgor and L(p) of the NaCl-treated cells. In general, NaCl reduced water permeability of corn root cortical cells most likely by an osmotic stress. ABA could not instantaneously change water permeability of the corn root cortical cell subjected to NaCl stress; however, with long-time treatment, ABA was able to in part relieve the salt stress likely by osmotic adjustment.