Stomata Prioritize Their Responses to Multiple Biotic and Abiotic Signal Inputs

<div><p>Stomata are microscopic pores in leaf epidermis that regulate gas exchange between plants and the environment. Being natural openings on the leaf surface, stomata also serve as ports for the invasion of foliar pathogenic bacteria. Each stomatal pore is enclosed by a pair of guard cells that are able to sense a wide spectrum of biotic and abiotic stresses and respond by precisely adjusting the pore width. However, it is not clear whether stomatal responses to simultaneously imposed biotic and abiotic signals are mutually dependent on each other. Here we show that a genetically engineered <i>Escherichia coli</i> strain DH5α could trigger stomatal closure in <i>Vicia faba</i>, an innate immune response that might depend on NADPH oxidase-mediated ROS burst. DH5α-induced stomatal closure could be abolished or disguised under certain environmental conditions like low [CO₂], darkness, and drought, etc. Foliar spraying of high concentrations of ABA could reduce stomatal aperture in high humidity-treated faba bean plants. Consistently, the aggressive multiplication of DH5α bacteria in <i>Vicia faba</i> leaves under high humidity could be alleviated by exogenous application of ABA. Our data suggest that a successful colonization of bacteria on the leaf surface is correlated with stomatal aperture regulation by a specific set of environmental factors.</p></div

DH5α-triggered stomatal closure is disguised by darkness or drought treatment.

<p>A and B, Stomatal aperture and conductance in <i>V. faba</i> leaves dip-inoculated with mock or DH5α at 10⁸ CFU/ml under light/dark transition; C and D, Stomatal aperture and conductance in <i>V. faba</i> leaves dip-inoculated with mock or DH5α at 10⁸ CFU/ml under different field water content (FWC). Data from the epidermal bioassay are means of 120 stomatal aperture measurements from three replicates ±SEM. Data from the stomatal conductance experiment are means of measurements from 8–12 leaves (n = 4). Asterisks denote significant differences as analyzed by two-tailed <i>t</i>-test (***, <i>P</i><0.001; *, <i>P</i><0.05; ns, no statistical difference).</p

DH5α-induced stomatal closure involves ROS accumulation in guard cells.

<p>A, Stomatal aperture in <i>V. faba</i> epidermal peels incubated with different treatments. Data are means of 120 stomatal aperture measurements from three replicates ±SEM; B, ROS accumulation in intact guard cells detected by H₂DCF-DA fluorescence. The microscopic images represent fluorescent and DIC images of peels treated with mock (upper left and right), fluorescent image of peels treated with DH5α at 10⁸ CFU/ml (lower left), and fluorescent image of peels treated with 1 mM LPS (lower right). Bars  =  50 µm; C, Quantitation of generated ROS in <i>Vicia faba</i> guard cells as shown in B. Asterisks denote significant differences as analyzed by two-tailed <i>t</i>-test (***, <i>P</i><0.001; ns, no statistical difference).</p

DH5α-elicited stomatal closure is abolished by low [CO₂] or high RH treatment.

<p>A and B, Stomatal aperture and conductance in <i>V. faba</i> leaves dip-inoculated with mock or DH5α at 10⁸ CFU/ml under ambient or low CO₂ concentrations; C and D, Stomatal aperture and conductance in <i>V. faba</i> leaves dip-inoculated with mock or DH5α at 10⁸ CFU/ml under ambient and high RH conditions. Data from the epidermal bioassay are means of 120 stomatal aperture measurements from three replicates ±SEM. Data from the stomatal conductance experiment are means of measurements from 8–12 leaves (n = 4). Asterisks denote significant differences as analyzed by two-tailed t-test (***, P<0.001; **, P<0.01; *, P<0.05; ns, no statistical difference).</p

Exogenous ABA can reduce stomatal aperture and inhibit foliar bacterial growth under high RH.

<p>A, Stomatal aperture in <i>V. faba</i> leaves dip-inoculated with mock or DH5α (10⁸ CFU/ml) supplemented with the indicated concentrations of ABA under ambient and high RH conditions. Results represent means of three replicates ±SEM, (n = 120 stomata). “+” and “−” represent presence or absence of DH5α cells in the inoculum. Asterisks denote significant differences as analyzed by two-tailed <i>t</i>-test (**, <i>P</i><0.01; ns, no statistical difference); B, Bacterial population in <i>V. faba</i> leaves at day 3 after dip inoculation with DH5α. “+” and “−” represent presence or absence of ABA (20 µM) in the inoculum.</p

<i>E. coli</i> DH5α can trigger stomatal closure in <i>V. faba</i>.

<p>A, Stomatal aperture in <i>V. faba</i> epidermal peels incubated with DH5α at the indicated concentrations; B, Stomatal aperture in <i>V. faba</i> epidermal peels incubated with mock or DH5α at 10⁸ CFU/ml. Results represent means of three replicates ±SEM, (n = 120 stomata).</p

Pathogenicity of DC3118 in <i>Arabidopsis</i> can be modulated by extrinsic factors.

<p>A, Stomatal aperture in Col-0 leaves surface-inoculated with mock or DC3118 at 10⁸ CFU/ml under ambient or high RH; B, Stomatal aperture in Col-0 leaves surface-inoculated with different treatments under high RH. Data in A and B represent means of 120 stomatal aperture measurements from three replicates ±SEM. Asterisks denote significant differences as analyzed by two-tailed <i>t</i>-test (***, <i>P</i><0.001; ns, no statistical difference); C, Progression of disease symptom in Col-0 plants with the following treatments: (I) RH = 60%, mock; (II) RH≥90%, mock; (III) RH = 60%, DC3118 (10⁸ CFU/ml); (IV) RH≥90%, DC3118 (10⁸ CFU/ml); (V) RH≥90%, DC3118 (10⁸ CFU/ml) + ABA (20 µM).</p

Decontamination of Sr(II) on Magnetic Polyaniline/Graphene Oxide Composites: Evidence from Experimental, Spectroscopic, and Modeling Investigation

The interaction of Sr­(II) on magnetic polyaniline/graphene oxide (PANI/GO) composites was elucidated by batch, EXAFS, and surface complexation modeling techniques. The batch experiments showed that decreased uptake of Sr­(II) on magnetic PANI/GO composites was observed with increasing ionic strength at pH <5.0, whereas no effect of ionic strength on Sr­(II) uptake was shown at pH >5.0. The maximum uptake capacity of magnetic PANI/GO composites derived from the Langmuir model at pH 3.0 and 293 K was 37.17 mg/g. The outer-sphere surface complexation controlled the uptake of Sr­(II) on magnetic PANI/GO composites at pH 3.0 due to the similarity to the EXAFS spectra of Sr²⁺ in aqueous solutions, but the Sr­(II) uptake at pH 7.0 was inner sphere complexation owing to the occurrence of the Sr–C shell. According to the analysis of surface complexation modeling, uptake of Sr­(II) on magnetic PANI/GO composites was well simulated using a diffuse layer model with an outer-sphere complex (SOHSr²⁺ species) and two inner-sphere complexes (i.e., (SO)₂Sr­(OH)⁻ and SOSr⁺ species). These findings are crucial for the potential application of magnetic nanomaterials as a promising candidate for the uptake of radionuclides for environmental remediation