Gating of aquaporins by heavy metals in Allium cepa L. epidermal cells

Changes in the water permeability, aquaporin (AQP) activity, of leaf cells were investigated in response to different heavy metals (Zn2+, Pb2+, Cd2+, Hg2+). The cell pressure probe experiments were performed on onion epidermal cells as a model system. Heavy metal solutions at different concentrations (0.05 μM–2 mM) were used in our experiments. We showed that the investigated metal ions can be arranged in order of decreasing toxicity (expressed as a decrease in water permeability) as follows: Hg>Cd>Pb>Zn. Our results showed that β-mercaptoethanol treatment (10 mM solution) partially reverses the effect of AQP gating. The magnitude of this reverse differed depending on the metal and its concentration. The time course studies of the process showed that the gating of AQPs occurred within the first 10 min after the application of a metal. We also showed that after 20–40 min from the onset of metal treatment, the water flow through AQPs stabilized and remained constant. We observed that irrespective of the metal applied, the effect of AQP gating can be recorded within the first 10 min after the administration of metal ions. More generally, our results indicate that the toxic effects of investigated metal ions on the cellular level may involve AQP gating

Variation in categorical variables describing the bedrock type, its pH and age for each species cluster.

<p>Values in bold are significantly different from those for the pooled data (p<0.05, χ² test). Abbreviations for age classes: <b>HoloSedi</b>-holocene sediments; <b>PostHist</b>-postglacial, historic, younger than AD 871; <b>PostPreHist</b>-postglacial, prehistoric, older than AD 871; <b>TertPleist</b>-Tertiary and Pleistocene, older 11000 years; <b>UppPleist</b>-Upper Pleistocene, younger than 0.8 m.y.; <b>UppLowPleist</b>-Upper Pliocene and Lower Pleistocene, 0.8–3.3 m.y.; <b>UppTerti</b>-Upper Tertiary, older than 3.3 m.y.; <b>Ind</b>–Indefinite.</p

Environmental (bioclimatic and topoclimatic) variables used in the present study.

[1]<p>The variable called isothermality represents temperature evenness over the course of year (e.g. areas with isothermality value of 100 represent sites where diurnal temperature range equals to the annual temperature range, whereas areas with isothermality value of 50 represent sites where diurnal temperature range is equal to half of the annual temperature range).</p

Distribution and biogeographical affinities of species clusters.

<p>Maps of species distribution in the clusters: <i>Luzula arcuata</i> (A), <i>Carex rupestris</i> (B), <i>Nardus stricta</i> (C), <i>Saxifraga aizoides</i> (D) (maps) and their biogeographical affinities (diagrams A’, B’, C’, D’). For explanations see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102916#pone-0102916-g001" target="_blank">Figure 1</a>.</p

Results of principal component analysis, correlations of variables and principal components.

<p>Correlations >0.8 are marked in bold face.</p

Number of species, number of threatened species according to IUCN criteria and percentage of different life forms in each plant cluster.

<p>G-geophytes, Ch-chamaephytes, He-hemicryptophytes, Hy-hydrophytes, Na-nanophanerophytes, Ph-phanerophytes, Th-therophytes. Percentages in IUCN species column reflect the proportion of threatened species in each cluster.</p

Environmental characteristics of the species clusters.

<p>Principal Component Analysis biplots: A. Bioclimatic variables PC2 vs. PC1, B. Bioclimatic variables PC3 vs. PC2, C. topographic variables PC2 vs. PC1.</p