Coordination and Solvation of the Au⁺ Cation: Infrared Photodissociation Spectroscopy of Mass-Selected Au(H₂O)_<i>n</i>⁺ (<i>n</i> = 1–8) Complexes

Gold cation–water complexes with attached argon atoms are produced via a laser vaporization supersonic cluster source. The [Au­(H₂O)_<i>n</i>Ar_<i>x</i>]⁺ (<i>n</i> = 1–8; <i>x</i> = 1 or 2) complexes are each mass selected and studied by infrared photodissociation spectroscopy in the OH stretching frequency region to explore the coordination and solvation structures of the Au⁺ cation. Density functional calculations have been performed, and the calculated vibrational spectra are compared to the experimental spectra to identify the gas-phase structures of the Au­(H₂O)_<i>n</i>⁺ complexes. Confirming previous theoretical predications, the first coordination shell of the Au⁺ cation contains two water molecules forming a linear O–Au⁺–O arrangement; subsequent water molecules bind to the two H₂O ligands of the Au­(H₂O)₂⁺ core ion via hydrogen bond forming of the second hydration shell, which is complete at <i>n</i> = 6. For the complexes with <i>n</i> ≤ 7, the experimental spectrum can in general be assigned to the predicted global minimum structure. However, the spectrum suggests that two or more conformers coexist for the <i>n</i> = 8 complex, indicating that the identification of a single global minimum becomes less important upon increasing the number of solvating water molecules

The lengths of the exons and introns in <i>GhMKK1</i> and <i>AtMKK1</i>.

<p>The lengths of the exons and introns in <i>GhMKK1</i> and <i>AtMKK1</i>.</p

Drought tolerance test comparing the wild-type and the <i>GhMKK1</i>-overexpressing <i>N. benthamiana</i> plants.

<p>(A) Seed germination on MS medium with 0, 50, 100, or 200 mM mannitol. (B–C) Germination rates of the WT and OE lines under normal and mannitol treatment conditions. Based on daily scoring, the results obtained on the MS medium containing 200 mM mannitol are presented. The presented data are the means ±SE of three independent experiments (<i>n</i> = 3). Asterisks (* or **) above the lines indicate (highly) significant differences (*<i>P</i><0.05; **<i>P</i><0.01) according to Duncan's multiple range test performed using SAS version 9.1 software. (D) Photograph of representative 10-week-old WT and OE plants grown in soil under drought conditions for 10 d, then watered for 2 d to allow them to recover. BD, before drought treatment; RW, rewatering. (E) The water loss from the detached leaves of WT and OE plants at the indicated times. The rate of water loss was calculated by the loss of fresh weight in the samples. The presented data are the means ±SE of three independent experiments (<i>n</i> = 6). Asterisks (**) above the lines indicate (highly) significant differences (<i>P</i><0.01) according to Duncan's multiple range test performed using SAS version 9.1 software. (F) Survival rates of WT and OE plants under drought stress. The presented data are the means ±SE of three independent experiments (<i>n</i>≥50). Different letters above the columns indicate significant differences (<i>P</i><0.0001) according to Duncan's multiple range test performed using SAS version 9.1 software. (G–I) Phenotype of roots subjected to drought stress for WT and OE plants, together with additional root lengths and fresh weights. The presented data are the means ±SE of three independent experiments (<i>n</i> = 6). Different letters above the columns indicate significant differences (<i>P</i><0.0001) according to Duncan's multiple range test performed using SAS version 9.1 software. (J–K) Stomatal changes observed with a microscope before and after drought treatment. The stomatal aperture is displayed. BD, before drought treatment; RW, rewatering. Bar  = 200 µm. The presented data are the means ±SE of three independent experiments (<i>n</i> = 6). Different letters above the columns indicate significant differences (<i>P</i><0.01) according to Duncan's multiple range test performed using SAS version 9.1 software.</p

Cotton <i>GhMKK1</i> Induces the Tolerance of Salt and Drought Stress, and Mediates Defence Responses to Pathogen Infection in Transgenic <i>Nicotiana benthamiana</i>

<div><p>Mitogen-activated protein kinase kinases (MAPKK) mediate a variety of stress responses in plants. So far little is known on the functional role of MAPKKs in cotton. In the present study, <i>Gossypium hirsutum MKK1</i> (<i>GhMKK1</i>) function was investigated. GhMKK1 protein may activate its specific targets in both the nucleus and cytoplasm. Treatments with salt, drought, and H₂O₂ induced the expression of <i>GhMKK1</i> and increased the activity of <i>GhMKK1</i>, while overexpression of <i>GhMKK1</i> in <i>Nicotiana benthamiana</i> enhanced its tolerance to salt and drought stresses as determined by many physiological data. Additionally, <i>GhMKK1</i> activity was found to up-regulate pathogen-associated biotic stress, and overexpression of <i>GhMKK1</i> increased the susceptibility of the transgenic plants to the pathogen <i>Ralstonia solanacearum</i> by reducing the expression of <i>PR</i> genes. Moreover, <i>GhMKK1</i>-overexpressing plants also exhibited an enhanced reactive oxygen species scavenging capability and markedly elevated activities of several antioxidant enzymes. These results indicate that <i>GhMKK1</i> is involved in plants defence responses and provide new data to further analyze the function of plant MAPK pathways.</p></div

Analysis of ROS accumulation in WT and OE plants in response to abiotic stresses.

<p>(A–B) Abiotic stress-induced H₂O₂ and O₂⁻ accumulation detected via DAB staining and NBT staining, respectively. (C) Leaf disks from WT and OE plants were incubated in different concentrations of MV (0, 200, or 400 µM) under greenhouse conditions. (D) Relative chlorophyll contents were determined in the leaf disks of WT and OE plants following MV treatments. Disks floated in water were used as a control. The presented data are the means ±SE of three independent experiments (<i>n</i> = 6). Different letters above the columns indicate significant differences (<i>P</i><0.0001) according to Duncan's multiple range test performed using SAS version 9.1 software.</p

Expression patterns of <i>GhMKK1</i> in different tissues, developmental stages and under different stress conditions.

<p>(A) The tissue-specific expression of <i>GhMKK1</i> was analysed via RT-PCR using total RNA extracted from the roots, stems, and cotyledon leaves of 7-day-old cotton seedlings. (B) The expression profiles of <i>GhMKK1</i> were measured in the cotyledon leaves of 7-day-old cotton seedlings. For the stress treatments, 7-day-old cotton seedlings were obtained from a hydroponic culture and were subjected to treatment with 100 mM NaCl (C), 15% PEG (D), wounding (E), 100 µM H₂O₂ (F), low temperature (4°C) (G), 2 mM SA (H), 100 µM ABA (I), 100 µM MeJA (J), 100 µM ET (K), release from ethephon, and <i>R. solanacearum</i> infection (L). Total RNA was isolated at the indicated times following the initiation of treatments and was subjected to RT-PCR analysis. The obtained PCR products were visualized via agarose gel electrophoresis, followed by ethidium bromide staining. The <i>18S rRNA</i> gene was employed as an internal control. This experiment was repeated at least twice.</p

Salt tolerance test comparing the wild-type and <i>GhMKK1</i>-overexpressing <i>N. benthamiana</i> plants.

<p>(A) Analysis of <i>GhMKK1</i> expression in wild-type (WT) and T₁ OE plants. (B) Seed germination on MS medium containing different concentrations of NaCl. (C–D) Germination rates of the WT and OE lines under normal and NaCl treatment conditions. Based on daily scoring, the results obtained using MS medium containing 200 mM NaCl are presented. The presented data are the means ±SE of three independent experiments (<i>n</i> = 3). Asterisks (* or **) above the lines indicate significant differences (*<i>P</i><0.05; **<i>P</i><0.01) according to Duncan's multiple range test performed in SAS version 9.1 software. (E) Post-germination seedling development of the WT and the OE lines on MS supplemented with different concentrations of NaCl. The seeds sown on MS medium that showed radicle emergence after 3 d were transferred to MS medium containing different concentrations of NaCl. The plates were oriented vertically, with seedlings kept upside down, and a photograph was taken 14 d after transfer. (F) Primary root lengths of the seedlings 14 d after germination in the presence of different NaCl concentrations. The presented data are the means ±SE of three independent experiments (<i>n</i> = 6). Different letters above the columns indicate significant differences (<i>P</i><0.05) according to Duncan's multiple range test performed using SAS version 9.1 software. (G) Photograph of representative 10-week-old WT and OE plants grown in soil containing 200 mM NaCl for 14 d. (H) Survival rates of 10-week-old plants treated with 200 mM NaCl for 14 d. The presented data are the means ±SE of three independent experiments (<i>n</i> = 6). Different letters above the columns indicate significant differences (<i>P</i><0.01) according to Duncan's multiple range test performed using SAS version 9.1 software.</p

Oligonucleotide primers used in this study.

<p>Oligonucleotide primers used in this study.</p

Subcellular localization of the GhMKK1 protein transiently expressed in onion epidermal cells.

<p>(A) Schematic diagram of the 35S-GhMKK1::GFP fusion construct and the control 35S-GFP construct. (B) Transient expression of the 35S-GhMKK1::GFP and 35S-GFP constructs in onion epidermal cells. Green fluorescence was observed using a confocal microscope 12 h after particle bombardment. The nuclei of the onion cells were visualized via DAPI staining. Bar  = 200 µm.</p

Infrared Photodissociation Spectroscopy of Mass-Selected Silver and Gold Nitrosyl Cation Complexes

The [M­(NO)_<i>n</i>]⁺ cation complexes (M = Au and Ag) are studied for exploring the coordination and bonding between nitric oxide and noble metal cations. These species are produced in a laser vaporization supersonic ion source and probed by infrared photodissociation spectroscopy in the NO stretching frequency region using a collinear tandem time-of-flight mass spectrometer. The geometric and electronic structures of these complexes are determined by comparison of the distinctive experimental spectra with simulated spectra derived from density functional theory calculations. All of these noble metal nitrosyl cation complexes are characterized to have bent NO ligands serving as one-electron donors. The spectrum of [Au­(NO)₂Ar]⁺ is consistent with 2-fold coordination with a near linear N–Au–N arrangement for this ion. The [Au­(NO)_<i>n</i>]⁺ (<i>n</i> = 3–4) cations are determined to be a mixture of 2-fold coordinated form and 3- or 4-fold coordinated form. In contrast, the spectra of [Ag­(NO)_<i>n</i>]⁺ (<i>n</i> = 3–6) provide evidence for the completion of the first coordination shell at <i>n</i> = 5. The high [Au­(NO)_<i>n</i>]⁺ and [Ag­(NO)_<i>n</i>]⁺ (<i>n</i> ≥ 3 for Au, <i>n</i> ≥ 4 for Ag) complexes each involve one or more (NO)₂ dimer ligands, as observed in the copper nitrosyl cation complexes, indicating that ligand–ligand coupling plays an important role in the structure and bonding of noble metal nitrosyl cation complexes