Silicate Inhibits the Cytosolic Influx of Chloride in Protoplasts of Wheat and Affects the Chloride Transporters, TaCLC1 and TaNPF2.4/2.5

Abstract

Chloride is an essential nutrient for plants, but high concentrations can be harmful. Silicon ameliorates both abiotic and biotic stresses in plants, but it is unknown if it can prevent cellular increase of chloride. Therefore, we investigated the influx of Cl− ions in two wheat cultivars different in salt sensitivity, by epifluorescence microscopy and a highly Cl−-sensitive dye, MQAE, N-[ethoxycarbonylmethyl]-6-methoxy-quinolinium bromide, in absence and presence of potassium silicate, K2SiO3. The Cl−-influx was higher in the salt-sensitive cv. Vinjett, than in the salt-tolerant cv. S-24, and silicate pre-treatment of protoplasts inhibited the Cl−-influx in both cultivars, but more in the sensitive cv. Vinjett. To investigate if the Cl−-transporters TaCLC1 and TaNPF2.4/2.5 are affected by silicate, expression analyses by RT-qPCR were undertaken of TaCLC1 and TaNPF 2.4/2.5 transcripts in the absence and presence of 100 mM NaCl, with and without the presence of K2SiO3. The results show that both transporter genes were expressed in roots and shoots of wheat seedlings, but their expressions were differently affected by silicate. The TaNPF2.4/2.5 expression in leaves was markedly depressed by silicate. These findings demonstrate that less chloride accumulates in the cytosol of leaf mesophyll by Si treatment and increases salt tolerance.

Ion Changes and Signaling under Salt Stress in Wheat and Other Important Crops

“…The Cl − absorption in the salt-stressed wheat cultivar Vinjett was decreased by silicon supplementation, revealing that Cl transport from roots to shoots is regulated. Additionally, it was noted that the wheat cultivar Vinjett expresses two Cl-transporter genes, TaCLC1 and TaNPF2.4/2.5, in both the roots and the shoots [ 160 ]. Since TaCLC1 was more highly expressed in roots than in shoots, it is most likely that more Cl − is accumulated in the root cell vacuoles and less is transferred to the shoots as a result of Si action.…”

“…It is hypothesized that this makes the wheat plant more resistant to high Cl − concentrations when Si is added. While vacuolar chloride is not harmful, high quantities of chloride present in the cytosol are toxic [160]. The coordinated symport of K + , Na + , and Cl − , is catalyzed by cation Cl − cotransporter proteins.…”