Impacts of Surface Depletion on the Plasmonic Properties of Doped Semiconductor Nanocrystals

Degenerately doped semiconductor nanocrystals (NCs) exhibit a localized surface plasmon resonance (LSPR) in the infrared range of the electromagnetic spectrum. Unlike metals, semiconductor NCs offer tunable LSPR characteristics enabled by doping, or via electrochemical or photochemical charging. Tuning plasmonic properties through carrier density modulation suggests potential applications in smart optoelectronics, catalysis, and sensing. Here, we elucidate fundamental aspects of LSPR modulation through dynamic carrier density tuning in Sn-doped Indium Oxide NCs. Monodisperse Sn-doped Indium Oxide NCs with various doping level and sizes were synthesized and assembled in uniform films. NC films were then charged in an in situ electrochemical cell and the LSPR modulation spectra were monitored. Based on spectral shifts and intensity modulation of the LSPR, combined with optical modeling, it was found that often-neglected semiconductor properties, specifically band structure modification due to doping and surface states, strongly affect LSPR modulation. Fermi level pinning by surface defect states creates a surface depletion layer that alters the LSPR properties; it determines the extent of LSPR frequency modulation, diminishes the expected near field enhancement, and strongly reduces sensitivity of the LSPR to the surroundings

Biochemical and physiological assays of plants overexpressing the <i>GhSnRK2</i> gene.

<p>(A) Rate of water loss from <i>GhSnRK2</i> transgenic plants. Six plants of each transgenic and WT line were analyzed. Three biological replicates produced similar results. Asterisk denotes a significant difference (P<0.05). (B) The RWC of <i>GhSnRK2</i> transgenic plants. (C) Stomata aperture size of WT and <i>GhSnRK2</i> transgenic plants treated with different concentrations of ABA (D) The stomata apertures were measured after 2 h of treatment with different concentrations of ABA, and the mean values of the WT and transgenic lines at each ABA concentration were compared using Student's T-test (P<0.05). Asterisk denotes a significant difference (P<0.05). (E) Proline accumulation in WT and <i>GhSnRK2</i> transgenic plants. The proline content of <i>GhSnRK2</i> transgenic lines was consistently higher than that of the WT line. Student's T-test revealed a significant difference (p<0.05) between the transgenic and WT lines (n = 3). (F) The chlorophyll content of the WT and <i>GhSnRK2</i> transgenic plants. The mean values were compared using Student's “t-test”. Asterisk denotes a significant difference (P<0.05).</p

Seed germination of the WT and <i>GhSnRK2</i> plants subjected to NaCl and exogenous ABA treatment and biomass accumulation of these plants.

<p>(A) Seed germination frequency of the WT and <i>GhSnRK2</i> transgenic plants cultured on MS medium supplemented with different concentrations of NaCl (50 mM or 100 mM) or ABA (0 µM, 0.3 µM, or 0.5 µM). (B) The survival rate of the WT and <i>GhSnRK2</i> transgenic plants cultured in MS medium containing 50 mM or100 mMNaCl. The mean values were compared using Student's T-test (p<0.05). (C) The germination rate in MS medium supplemented with 0.3 µM or 0.5 µM ABA. The values are presented as the mean germination rates (%) of approximately 200 seeds. Asterisk denotes a significant difference (P<0.05). (D) Biomass accumulation of the <i>GhSnRK2</i> transgenic and WT plants. For dry weight biomass, the dry weight in the roots and shoots was recorded after drying in an oven to a constant weight at 70°C for 48 h. (E) Fresh weight biomass of <i>GhSnRK2</i> transgenic plants and corresponding WT plants. The fresh weight of the roots and shoots was measured immediately after harvesting. Each of the three biological replicates consisted of 12 plants. Student's T-test was performed. Asterisk denotes a significant difference (P<0.05).</p

Phylogenetic analysis, subcellular localization, and expression pattern of <i>GhSnRK2</i> in cotton plant.

<p>(A) A phylogenetic tree of <i>GhSnRK2</i> and other <i>SnRK2</i> proteins from different plants was constructed using the neighbor-joining method with MEGA 5. The sequences used for analysis are listed by accession number: <i>Litchi chinensis</i> (<i>LcSnRK2</i>), AFX72761.1; <i>Arabidopsis thaliana</i> (<i>AtSNRK2.2</i>), CP002686.1; <i>Arabidopsis thaliana</i> (<i>AtSnRK2.3</i>), AED98274.1; <i>AtSnRK2.1</i>, AED91326.1; <i>AtSnRK2.9</i>, AEC07398.1; <i>AtSnRK2.10</i>, AEE33751.1; <i>AtSnRK2.4</i>, AEE28666.1; <i>AtSnRK2.5</i>, AED97781.1; <i>AtSnRK2.7</i>, AEE87152.1; <i>Populus tremula</i> (<i>PtreSnRK2.6a</i>), AGW51610.1; <i>Zea mays</i> (<i>ZmSnRK2.2</i>), NM_001137717.1; <i>Solanum tuberosum</i> (<i>StSnRK2.8</i>), AFR68945.1; <i>Oryza sativa</i> (<i>RK1</i>), ABB89146.1; <i>Oryza sativa</i> (<i>SAPK4)</i>, BAD18000.1; <i>Sorghum bicolor</i> (<i>SAPK4</i>), AGM39623.1; and <i>Zea mays</i> (<i>SAPK5</i>), ACG42286.1. The bootstrap values are shown on the tree branches. (B) Subcellular localization of the <i>GhSnRK2-GFP</i> protein. (2 and 5) GFP alone; (4 and 6) <i>GhSnRK2-GFP</i> in onion epidermal cells; (1 and 3) corresponding bright-field images. (C) The expression pattern of the <i>GhSnRK2</i> gene in cotton plants subjected to 10% PEG stress. The gene expression data were normalized to that of the cotton histone 3 gene. The values are presented as the means of three experimental replicates. The vertical axis represents the relative expression level. The values from1 to 6 indicate the time (h) of PEG treatment. Asterisk denotes a significant difference (P<0.05) compared with the control (0 h). (D) Relative expression levels of the <i>GhSnRK2</i> gene in various cotton plant tissues. Samples from root (RT) stem (ST), cauline leaves (CL), rosettes leaves (RL) and flowers (FL) were analyzed. The vertical axis represents the relative expression level. The letters denote significant differences (P<0.05) based on Duncan's multiple range tests. The cotton histone 3 gene was used as an internal control for normalization of the gene expression data.</p

Functional Characterization of Cotton GaMYB62L, a Novel R2R3 TF in Transgenic Arabidopsis

<div><p>Drought stress can trigger the production of ABA in plants, in response to adverse conditions, which induces the transcript of stress-related marker genes. The R2R3 MYB TFs are implicated in regulation of various plants developmental, metabolic and multiple environmental stress responses. Here, a R2R3-MYB cloned gene, <i>GaMYB62L</i>, was transformed in Arabidopsis and was functionally characterized. The <i>GaMYB62L</i> protein contains two SANT domains with a conserved R2R3 imperfect repeats. The <i>GaMYB62L</i> cDNA is 1,017 bp with a CDS of 879, encodes a 292-residue polypeptide with MW of 38.78 kD and a pI value of 8.91. Overexpressed <i>GaMYB62L</i> transgenic Arabidopsis have increased proline and chlorophyll content, superior seed germination rate under salt and osmotic stress, less water loss rate with reduced stomatal apertures, high drought avoidance as compared to WT on water deprivation and also significant plant survival rates at low temperature. In addition, overexpressed <i>GaMYB62L</i> lines were more sensitive to ABA mediated germination and root elongation assay. Moreover, ABA induced <i>GaMYB62L</i> overexpression, enhanced the expression of ABA stress related marker genes like <i>RD22</i>, <i>COR15A</i>, <i>ADH1</i>, and <i>RD29A</i>. Together, overexpression of <i>GaMYB62L</i> suggested having developed better drought, salt and cold tolerance in transgenic Arabidopsis and thus presented it as a prospective candidate gene to achieve better abiotic stress tolerance in cotton crop.</p></div

Cloning of <i>Gossypium hirsutum</i> Sucrose Non-Fermenting 1-Related Protein Kinase 2 Gene (<i>GhSnRK2</i>) and Its Overexpression in Transgenic <i>Arabidopsis</i> Escalates Drought and Low Temperature Tolerance

<div><p>The molecular mechanisms of stress tolerance and the use of modern genetics approaches for the improvement of drought stress tolerance have been major focuses of plant molecular biologists. In the present study, we cloned the <i>Gossypium hirsutum</i> sucrose non-fermenting 1-related protein kinase 2 (<i>GhSnRK2</i>) gene and investigated its functions in transgenic Arabidopsis. We further elucidated the function of this gene in transgenic cotton using virus-induced gene silencing (VIGS) techniques. We hypothesized that <i>GhSnRK2</i> participates in the stress signaling pathway and elucidated its role in enhancing stress tolerance in plants via various stress-related pathways and stress-responsive genes. We determined that the subcellular localization of the <i>GhSnRK2</i>-green fluorescent protein (GFP) was localized in the nuclei and cytoplasm. In contrast to wild-type plants, transgenic plants overexpressing <i>GhSnRK2</i> exhibited increased tolerance to drought, cold, abscisic acid and salt stresses, suggesting that <i>GhSnRK2</i> acts as a positive regulator in response to cold and drought stresses. Plants overexpressing <i>GhSnRK2</i> displayed evidence of reduced water loss, turgor regulation, elevated relative water content, biomass, and proline accumulation. qRT-PCR analysis of <i>GhSnRK2</i> expression suggested that this gene may function in diverse tissues. Under normal and stress conditions, the expression levels of stress-inducible genes, such as <i>AtRD29A, AtRD29B, AtP5CS1, AtABI3, AtCBF1</i>, and <i>AtABI5</i>, were increased in the <i>GhSnRK2</i>-overexpressing plants compared to the wild-type plants. <i>GhSnRK2</i> gene silencing alleviated drought tolerance in cotton plants, indicating that VIGS technique can certainly be used as an effective means to examine gene function by knocking down the expression of distinctly expressed genes. The results of this study suggested that the <i>GhSnRK2</i> gene, when incorporated into Arabidopsis, functions in positive responses to drought stress and in low temperature tolerance.</p></div

Plant transformation vector and the expression pattern of the <i>GhSnRK2</i> gene in the transgenic lines.

<p>(A) Schematic representation of the T-DNA region of the binary vector <i>pCAMBIA2301-GhSnRK2</i>. (B) Expression pattern of the <i>GhSnRK2</i> gene in the transgenic plants. Various upregulated expression patterns of the <i>GhSnRK2</i> gene in transgenic lines were detected, as indicated by the vertical axis. The values are presented as the means of three experimental replicates; the error bars indicate the standard deviations. The <i>AtACT2</i> gene was used as an internal control for normalization of gene expression.</p

Expression analysis of stress-responsive marker genes.

<p>The relative transcript levels of the stress-responsive genes <i>AtABI5, AtABI3, AtP5CS1, AtRD29A, AtCBF1</i>, and <i>AtRD29B</i> in the <i>GhSnRK2</i>-overexpressing and WT lines. qRTPCR was performed for gene expression analysis. The vertical axis displays the expression pattern. Three biological replicates produced similar results.</p

Silencing efficiency and transcript level of the <i>GhSnRK2</i> gene silenced plants.

<p>(A) Phenotype of gene silenced and non-silenced plants; 14 dpi. Wild-type (WT), negative control Empty vector (pTRV), positive control (pTRV-GrCLA1), gene silenced CRI409 cotton cultivars [pTRV-GhSnRk2 (09)], and gene silenced CRI99668 cotton cultivars [pTRV-<i>GhSnRK2</i> (68)]. (B) The silencing efficiency as determined by the expression pattern of WT, vector control (pTRV) and <i>GhSnRK2</i> gene silenced plants based on qRT-PCR. (C) The distribution of the TRV- construct in the gene silenced plants. Samples from the root, the stem and the leaves of gene silenced and non-silenced plants were analyzed via qRT-PCR. The values are presented as the means of three biological replicates. Asterisk denotes a significant difference (P<0.05).</p

Transcript levels of stress-responsive genes in <i>35S</i>: <i>GaMYB62L</i> in response to ABA.

<p><b>(A)</b> Transcript level of stress-responsive markers in <i>GaMYB62L</i> overexpressed and WT treated by 100μM ABA using qRT-PCR. Test and control samples (2 week old) were treated with and without 100μM ABA for 6 hr. Transcript levels of <i>RD22</i>, <i>ABI1</i>, <i>ABI2</i>, <i>ADH</i>, <i>COR15A</i>, <i>RD29A</i>, <i>RD29B</i>, <i>EM6</i>, <i>RD26</i> and <i>P5CS</i> stress marker genes were analyzed by qRT-PCR. Arabidopsis <i>ubiquitin 10</i> used as control gene, means value with ±SD. * <i>p</i> < 0.05; ** <i>p</i> <0.01 and *** <i>p</i> <0.001 calculated by student t-test.</p