Non-selective cation channel activity of aquaporin AtPIP2;1 regulated by Ca2+ and pH.

The aquaporin AtPIP2;1 is an abundant plasma membrane intrinsic protein in Arabidopsis thaliana that is implicated in stomatal closure, and is highly expressed in plasma membranes of root epidermal cells. When expressed in Xenopus laevis oocytes, AtPIP2;1 increased water permeability and induced a non-selective cation conductance mainly associated with Na+ . A mutation in the water pore, G103W, prevented both the ionic conductance and water permeability of PIP2;1. Co-expression of AtPIP2;1 with AtPIP1;2 increased water permeability but abolished the ionic conductance. AtPIP2;2 (93% identical to AtPIP2;1) similarly increased water permeability but not ionic conductance. The ionic conductance was inhibited by the application of extracellular Ca2+ and Cd2+ , with Ca2+ giving a biphasic dose-response with a prominent IC50 of 0.32 mм comparable with a previous report of Ca2+ sensitivity of a non-selective cation channel (NSCC) in Arabidopsis root protoplasts. Low external pH also inhibited ionic conductance (IC50 pH 6.8). Xenopus oocytes and Saccharomyces cerevisiae expressing AtPIP2;1 accumulated more Na+ than controls. Establishing whether AtPIP2;1 has dual ion and water permeability in planta will be important in understanding the roles of this aquaporin and if AtPIP2;1 is a candidate for a previously reported NSCC responsible for Ca2+ and pH sensitive Na+ entry into roots.

Association between water and carbon dioxide transport in leaf plasma membranes: assessing the role of aquaporins.

The role of some aquaporins as CO2 permeable channels has been controversial. Low CO2 permeability of plant membranes has been criticized because of unstirred layers and other limitations. Here we measured both water and CO2 permeability (Pos , PCO2 ) using stopped flow on plasma membrane vesicles (pmv) isolated from Pisum sativum (pea) and Arabidopsis thaliana leaves. We excluded the chemical limitation of carbonic anhydrase (CA) in the vesicle acidification technique for PCO2 using different temperatures and CA concentrations. Unstirred layers were excluded based on small vesicle size and the positive correlation between vesicle diameter and PCO2 . We observed high aquaporin activity (Pos 0.06 to 0.22 cm s-1 ) for pea pmv based on all the criteria for their function using inhibitors and temperature dependence. Inhibitors of Pos did not alter PCO2 . PCO2 ranged from 0.001 to 0.012 cm s-1 (mean 0.0079 + 0.0007 cm s-1 ) with activation energy of 30.2 kJ mol-1 . Intrinsic variation between pmv batches from normally grown or stressed plants revealed a weak (R2 = 0.27) positive linear correlation between Pos and PCO2 . Despite the low PCO2 , aquaporins may facilitate CO2 transport across plasma membranes, but probably via a different pathway than for water.

Correction: A pH-driven, reconfigurable DNA nanotriangle.

Correction for 'A pH-driven, reconfigurable DNA nanotriangle' by Wenxing Wang et al., Chem. Commun., 2009, 824-826.

A pH-driven, reconfigurable DNA nanotriangle.

A simple and robust DNA nanotriangle that can be conveniently reconfigured by environmental pH changes is demonstrated.

Continuous on-site label-free ATP fluorometric assay based on aggregation-induced emission of silole.

In this letter, we have described the establishment of a label-free fluorometric assay to detect adenosine triphosphate (ATP), which can enable the monitoring of the ATP hydrolysis process continuously and in situ. This assay is based on a silole derivative with positively charged modifications, compound 1, that can aggregate on the negative charged ATP template through charge-charge interaction. Because the silole group has strong aggregation-induced fluorescence emission (AIE), we have found that the aggregation could induce strong fluorescence emission and its intensity is positively and linearly related to the ATP concentration. Meanwhile, 1 also shows good discrimination for ATP, where its hydrolysis products ADP, AMP, and adenosine could not induce sufficient aggregation to produce a strong fluorescence signal. These characteristics are sufficient to build up a sensitive fluorescence assay to monitor the ATP concentration change in solution in situ, and we have also verified its usability in studying the reaction process of phosphatase.

DNA-templated CMV viral capsid proteins assemble into nanotubes.

This communication describes the in vitro assembly of genetically recombinant Cucumber Mosaic Virus (CMV) viral capsid proteins (CPs) into biological nanotubes, several micrometres long yet with a diameter of only approximately 17 nm, triggered by double-stranded DNAs of different lengths.