How exogenous nitric oxide regulates nitrogen assimilation in wheat seedlings under different nitrogen sources and levels

Nitrogen (N) is one of the most important nutrients for plants and nitric oxide (NO) as a signaling plant growth regulator involved in nitrogen assimilation. Understanding the influence of exogenous NO on nitrogen metabolism at the gene expression and enzyme activity levels under different sources of nitrogen is vitally important for increasing nitrogen use efficiency (NUE). This study investigated the expression of key genes and enzymes in relation to nitrogen assimilation in two Australian wheat cultivars, a popular high NUE cv. Spitfire and a normal NUE cv. Westonia, under different combinations of nitrogen and sodium nitroprusside (SNP) as the NO donor. Application of NO increased the gene expressions and activities of nitrogen assimilation pathway enzymes in both cultivars at low levels of nitrogen. At high nitrogen supplies, the expressions and activities of N assimilation genes increased in response to exogenous NO only in cv. Spitfire but not in cv. Westonia. Exogenous NO caused an increase in leaf NO content at low N supplies in both cultivars, while under high nitrogen treatments, cv. Spitfire showed an increase under ammonium nitrate (NH4NO3) treatment but cv. Westonia was not affected. N assimilation gene expression and enzyme activity showed a clear relationship between exogenous NO, N concentration and N forms in primary plant nitrogen assimilation. Results reveal the possible role of NO and different nitrogen sources on nitrogen assimilation in Triticum aestivum plants

Differential impact of LPG-and PG-deficient Leishmania major mutants on the immune response of human dendritic cells

<div><p>Background</p><p><i>Leishmania major</i> infection induces robust interleukin-12 (IL12) production in human dendritic cells (hDC), ultimately resulting in Th1-mediated immunity and clinical resolution. The surface of <i>Leishmania</i> parasites is covered in a dense glycocalyx consisting of primarily lipophosphoglycan (LPG) and other phosphoglycan-containing molecules (PGs), making these glycoconjugates the likely pathogen-associated molecular patterns (PAMPS) responsible for IL12 induction.</p><p>Methodology/Principal Findings</p><p>Here we explored the role of parasite glycoconjugates on the hDC IL12 response by generating <i>L</i>. <i>major</i> Friedlin V1 mutants defective in LPG alone, (FV1 <i>lpg1-</i>), or generally deficient for all PGs, (FV1 <i>lpg2-</i>). Infection with metacyclic, infective stage, <i>L</i>. <i>major</i> or purified LPG induced high levels of <i>IL12B</i> subunit gene transcripts in hDCs, which was abrogated with FV1 <i>lpg1-</i> infections. In contrast, hDC infections with FV1 <i>lpg2-</i> displayed increased <i>IL12B</i> expression, suggesting other PG-related/<i>LPG2</i> dependent molecules may act to dampen the immune response. Global transcriptional profiling comparing WT, FV1 <i>lpg1-</i>, FV1 <i>lpg2-</i> infections revealed that FV1 <i>lpg1-</i> mutants entered hDCs in a silent fashion as indicated by repression of gene expression. Transcription factor binding site analysis suggests that LPG recognition by hDCs induces IL-12 in a signaling cascade resulting in Nuclear Factor κ B (NFκB) and Interferon Regulatory Factor (IRF) mediated transcription.</p><p>Conclusions/Significance</p><p>These data suggest that <i>L</i>. <i>major</i> LPG is a major PAMP recognized by hDC to induce IL12-mediated protective immunity and that there is a complex interplay between PG-baring <i>Leishmania</i> surface glycoconjugates that result in modulation of host cellular IL12.</p></div

How exogenous nitric oxide regulates nitrogen assimilation in wheat seedlings under different nitrogen sources and levels

<div><p>Nitrogen (N) is one of the most important nutrients for plants and nitric oxide (NO) as a signaling plant growth regulator involved in nitrogen assimilation. Understanding the influence of exogenous NO on nitrogen metabolism at the gene expression and enzyme activity levels under different sources of nitrogen is vitally important for increasing nitrogen use efficiency (NUE). This study investigated the expression of key genes and enzymes in relation to nitrogen assimilation in two Australian wheat cultivars, a popular high NUE cv. Spitfire and a normal NUE cv. Westonia, under different combinations of nitrogen and sodium nitroprusside (SNP) as the NO donor. Application of NO increased the gene expressions and activities of nitrogen assimilation pathway enzymes in both cultivars at low levels of nitrogen. At high nitrogen supplies, the expressions and activities of N assimilation genes increased in response to exogenous NO only in cv. Spitfire but not in cv. Westonia. Exogenous NO caused an increase in leaf NO content at low N supplies in both cultivars, while under high nitrogen treatments, cv. Spitfire showed an increase under ammonium nitrate (NH₄NO₃) treatment but cv. Westonia was not affected. N assimilation gene expression and enzyme activity showed a clear relationship between exogenous NO, N concentration and N forms in primary plant nitrogen assimilation. Results reveal the possible role of NO and different nitrogen sources on nitrogen assimilation in <i>Triticum aestivum</i> plants.</p></div

Effects of NO and nitrogen sources on NR activity.

<p>Wheat seedlings (cvs Spitfire and Westonia) were grown in glasshouse for two weeks. Then, plants were irrigated with nitrogen-free nutrient solution for a week. Plants treated with different concentrations (left = 4mM and right = 40 mM) and different chemical forms of nitrogen (A = NHCl, B = KNO₃ and C = NH₄NO₃) with 0 (as a control), 20 or 100 μM of SNP for 3 days. Leaf tissues were harvested 24 hours after nitrogen treatments. NR activity was measured on three biological repeats. Different letters mean significantly different at 5% levels as calculated by Duncan multiple test.</p

Effects of NO and nitrogen sources on GS activity.

<p>Wheat seedlings (cvs Spitfire and Westonia) were grown in glasshouse for two weeks. Then, plants were irrigated with nitrogen-free nutrient solution for a week. Plants treated with different concentrations (left = 4mM and right = 40 mM) and different chemical forms of nitrogen (A = NHCl, B = KNO₃ and C = NH₄NO₃) with 0 (as a control), 20 or 100 μM of SNP for 3 days. Leaf tissues were harvested 24 hours after nitrogen treatments. GS activity was measured on three biological repeats. Different letters meaning significantly different at 5% levels as calculated by Duncan multiple test.</p

Effects of NO and nitrogen sources on NO content.

<p>Wheat seedlings (cvs Spitfire and Westonia) were grown in glasshouse for two weeks. Then, plants were irrigated with nitrogen-free nutrient solution for a week. Plants treated with different concentrations (left = 4mM and right = 40 mM) and different chemical forms of nitrogen (A = NHCl, B = KNO₃ and C = NH₄NO₃) with 0 (as a control), 20 or 100 μM of SNP for 3 days. Leaf tissues were harvested 24 hours after nitrogen treatments. NO content was measured on three biological repeats. Different letters meaning significantly different at 5% levels as calculated by Duncan multiple test.</p

Effects of high nitrogen (40 mM) on mRNA expression.

<p>Effects of high nitrogen (40 mM) on mRNA expression.</p

List of primers.

<p>List of primers.</p