Potassium activities in cell compartments of salt-grown barley

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Compatible solute accumulation and stress-mitigating effects in barley genotypes contrasting in their salt tolerance

The accumulation of compatible solutes is often regarded as a basic strategy for the protection and survival of plants under abiotic stress conditions, including both salinity and oxidative stress. In this work, a possible causal link between the ability of contrasting barley genotypes to accumulate/synthesize compatible solutes and their salinity stress tolerance was investigated. The impact of HO (one of the components of salt stress) on K flux (a measure of stress 'severity') and the mitigating effects of glycine betaine and proline on NaCl-induced K efflux were found to be significantly higher in salt-sensitive barley genotypes. At the same time, a 2-fold higher accumulation of leaf and root proline and leaf glycine betaine was found in salt-sensitive cultivars. The total amino acid content was also less affected by salinity in salt-tolerant cultivars. In these, potassium was found to be the main contributor to cytoplasmic osmolality, while in salt-sensitive genotypes, glycine betaine and proline contributed substantially to cell osmolality, compensating for reduced cytosolic K . Significant negative correlations (r= -0.89 and -0.94) were observed between Na-induced K efflux (an indicator of salt tolerance) and leaf glycine betaine and proline. These results indicate that hyperaccumulation of known major compatible solutes in barley does not appear to play a major role in salt-tolerance, but rather, may be a symptom of salt-susceptibility

Correlation between net mean K efflux measured from 6-d-old wheat seedlings and final plant yield at harvest (A) and the magnitude of membrane depolarization 60 min after 80 mM NaCl application (B)

Each point represents a different cultivar.<p><b>Copyright information:</b></p><p>Taken from "A root's ability to retain K correlates with salt tolerance in wheat"</p><p></p><p>Journal of Experimental Botany 2008;59(10):2697-2706.</p><p>Published online 20 May 2008</p><p>PMCID:PMC2486465.</p><p></p

Nax loci affect SOS1-like Na+^{+}/H+^{+} exchanger expression and activity in wheat

Salinity stress tolerance in durum wheat is strongly associated with a plant’s ability to control Na$^{+}$ delivery to the shoot. Two loci, termed Nax1 and Nax2, were recently identified as being critical for this process and the sodium transporters HKT1;4 and HKT1;5 were identified as the respective candidate genes. These transporters retrieve Na$^{+}$ from the xylem, thus limiting the rates of Na$^{+}$ transport from the root to the shoot. In this work, we show that the Nax loci also affect activity and expression levels of the SOS1-like Na$^{+}$/H$^{+}$ exchanger in both root cortical and stelar tissues. Net Na$^{+}$ efflux measured in isolated steles from salt-treated plants, using the non-invasive ion flux measuring MIFE technique, decreased in the sequence: Tamaroi (parental line)>Nax1=Nax2>Nax1:Nax2 lines. This efflux was sensitive to amiloride (a known inhibitor of the Na$^{+}$/H$^{+}$ exchanger) and was mirrored by net H$^{+}$ flux changes. TdSOS1 relative transcript levels were 6–10-fold lower in Nax lines compared with Tamaroi. Thus, it appears that Nax loci confer two highly complementary mechanisms, both of which contribute towards reducing the xylem Na$^{+}$ content. One enhances the retrieval of Na$^{+}$ back into the root stele via HKT1;4 or HKT1;5, whilst the other reduces the rate of Na$^{+}$ loading into the xylem via SOS1. It is suggested that such duality plays an important adaptive role with greater versatility for responding to a changing environment and controlling Na$^{+}$ delivery to the shoot

(A) The effects of 80 mM NaCl application on membrane potential in the mature zone of 6-d-old Baart 46 seedlings

(B) Steady-state membrane depolarization 60 min after salt application measured in all four cultivars. Mean ±SE (=6).<p><b>Copyright information:</b></p><p>Taken from "A root's ability to retain K correlates with salt tolerance in wheat"</p><p></p><p>Journal of Experimental Botany 2008;59(10):2697-2706.</p><p>Published online 20 May 2008</p><p>PMCID:PMC2486465.</p><p></p

Eight-week-old wheat cultivars used in this study after 6 weeks of salt treatment

The growth of salt-treated plants (shown on the left hand side of each picture) is severely restricted compared with control plants (shown on the right).<p><b>Copyright information:</b></p><p>Taken from "A root's ability to retain K correlates with salt tolerance in wheat"</p><p></p><p>Journal of Experimental Botany 2008;59(10):2697-2706.</p><p>Published online 20 May 2008</p><p>PMCID:PMC2486465.</p><p></p

(A) Net K and H flux kinetics measured in 6-d-old seedlings of Baart 46 cultivar following 80 mM NaCl treatment

Fluxes were measured in the mature zone, about 10 mm from the root tip. Means ±SE (=6). (B) Mean net K flux from each of the four cultivars over the first 60 min after NaCl application (80 mM). Means ±SE (=6). (C) Peak H efflux values measured 2 min after NaCl stress onset in four wheat cultivars. Means ±SE (=6). In all MIFE measurements, the sign convention is efflux negative.<p><b>Copyright information:</b></p><p>Taken from "A root's ability to retain K correlates with salt tolerance in wheat"</p><p></p><p>Journal of Experimental Botany 2008;59(10):2697-2706.</p><p>Published online 20 May 2008</p><p>PMCID:PMC2486465.</p><p></p