The cyclic nucleotide-gated channel AtCNGC10 transports Ca2+ and Mg2+ in Arabidopsis.

The suppression of the cyclic nucleotide-gated channel (CNGC) AtCNGC10 alters K(+) transport in Arabidopsis plants. Other CNGCs have been shown to transport Ca(2+), K(+), Li(+), Cs(+) and Rb(+) across the plasma membrane when expressed in heterologous systems; however, the ability of the AtCNGC10 channel to transport nutrients other than K(+) in plants has not been previously tested. The ion fluxes along different zones of the seedling roots, as estimated by the non-invasive ion-specific microelectrode technique, were significantly different in two AtCNGC10 antisense lines (A2 and A3) in comparison to the wild type (WT). Most notably, the influxes of H(+), Ca(2+) and Mg(2+) in the meristem and distal elongation zones of the antisense A2 and A3 lines were significantly lower than in the WT. The lower Ca(2+) influx from the external media corresponded to a lower intracellular Ca(2+) activity, which was estimated by fluorescence lifetime imaging measurements (FLIM). On the other hand, the intracellular pH values in the meristem zone of the roots of A2 and A3 seedlings were significantly lower (more acidic) than that of the WT, which might indicate a feedback block of H(+) influx into meristematic cells caused by low intracellular pH. Under the control conditions, mature plants from the A2 and A3 lines contained significantly higher K(+) and lower Ca(2+) and Mg(2+) content in the shoots, indicating disturbed long-distance ion transport of these cations, possibly because of changes in xylem loading/retrieval and/or phloem loading. Exposing the plants in the flowering stage to various K(+), Ca(2+) and Mg(2+) concentrations in the solution led to altered K(+), Ca(2+) and Mg(2+) content in the shoots of A2 and A3 plants in comparison with the WT, suggesting a primary role of AtCNGC10 in Ca(2+) (and probably Mg(2+)) transport in plants, which in turn regulates K(+) transporters' activities.

Na(+)/H(+) antiporter activity of the SOS1 gene: lifetime imaging analysis and electrophysiological studies on Arabidopsis seedlings.

Based on sequence analysis, the salt overly sensitive (SOS1) gene has been suggested to function as a Na(+)/H(+) antiporter located at the plasma membrane of plant cells, being expressed mostly in the meristem zone of the root and in the parenchyma cells surrounding the vascular tissue of the stem. In this study, we compared net H(+) and Ca(2+) fluxes and intracellular pH and [Ca(2+)](cyt) in the root meristem zone of Arabidopsis wild-type (WT) and sos mutants before and after salt stress. In addition, we studied the effect of pretreatment with amiloride (an inhibitor of Na(+)/H(+) antiporters) on net ion fluxes, intracellular pH and intracellular Ca(2+) activity ([Ca(2+)](cyt)) in WT plants and sos1 mutants before and after salt stress. Net ion fluxes were measured using microelectrode ion flux estimation (MIFE) and intracellular pH and [Ca(2+)](cyt) using fluorescence lifetime imaging microscopy (FLIM) techniques. During the first 15 min after NaCl application, sos1 mutants showed net H(+) efflux and intracellular alkalinization in the meristem zone, whereas sos2 and sos3 mutants and WT showed net H(+) influx and slight intracellular acidification in the meristem zone. Treatment with amiloride led to intracellular acidification and lower net H(+) flux in WT plants and to a decrease in intracellular Ca(2+) in WT and sos1 plants. WT plants pretreated with amiloride did not show positive net H(+) flux and intracellular acidification. After NaCl application, internal pH shifted to higher values in WT and sos1 plants. However, absolute values of H(+) fluxes were higher and internal pH values were lower in WT plants pretreated with amiloride compared with sos1 mutants. Therefore, the SOS1 transporter is involved in H(+) influx into the meristem zone of Arabidopsis roots, or it may function as a Na(+)/H(+) antiporter. Amiloride affects SOS1 and other Na(+)/H(+) antiporters in plant cells because of its ability to decrease the H(+) gradient across the plasma membrane.

The cyclic nucleotide-gated channel, AtCNGC10, influences salt tolerance in Arabidopsis.

Cyclic nucleotide-gated channels (CNGCs) in the plasma membrane transport K+ and other cations; however, their roles in the response and adaptation of plants to environmental salinity are unclear. Growth, cation contents, salt tolerance and K+ fluxes were assessed in wild-type and two AtCNGC10 antisense lines (A2 and A3) of Arabidopsis thaliana (L.) Heynh. Compared with the wild-type, mature plants of both antisense lines had altered K+ and Na+ concentrations in shoots and were more sensitive to salt stress, as assessed by biomass and Chl fluorescence. The shoots of A2 and A3 plants contained higher Na+ concentrations and significantly higher Na+/K+ ratios compared with wild-type, whereas roots contained higher K+ concentrations and lower Na+/K+ ratios. Four-day-old seedlings of both antisense lines exposed to salt stress had smaller Na+/K+ ratios and longer roots than the wild-type. Under sudden salt treatment, the Na+ efflux was higher and the K+ efflux was smaller in the antisense lines, indicating that AtCNGC10 might function as a channel providing Na+ influx and K+ efflux at the root/soil interface. We conclude that the AtCNGC10 channel is involved in Na+ and K+ transport during cation uptake in roots and in long-distance transport, such as phloem loading and/or xylem retrieval. Mature A2 and A3 plants became more salt sensitive than wild-type plants because of impaired photosynthesis induced by a higher Na+ concentration in the leaves.