Photosynthetic and ascorbate-glutathione metabolism in the flag leaves as compared to spikes under drought stress of winter wheat (<i>Triticum aestivum</i> L.)

<div><p>Ascorbate-glutathione (ASA-GSH) cycle is a major pathway of H₂O₂ scavenging and an effective mechanism of detoxification in plants. The differences in photosynthesis, chlorophyll content (Chl), relative water content (RWC), antioxidants and antioxidative enzyme activities involved in ASA-GSH metabolism were measured between the flag leaves and spike bracts (glumes and lemmas) during grain filling under drought stress. The expression of <i>APX1</i>, <i>GRC1</i>, <i>DHAR</i>, <i>MDHAR</i>, <i>GPX1</i>, and <i>GS3</i> in ASA-GSH cycle was also measured. Compared with the flag leaves, the spike bracts exhibited stable net photosynthetic rate (<i>P</i>_<i>N</i>) and chlorophyll content (Chl), a lower accumulation of reactive oxygen species (ROS), and more enhanced percentages of antioxidant enzyme activities and key enzymes gene transcription levels involved in ASA-GSH metabolism during the grain-filling stage under drought conditions. This could be the reasonable explanation for the more stable photosynthetic capacity in spikes, and the glumes and lemmas senesced later than the flag leaves at the late grain-filling stage. Also, the function of ASA-GSH cycle could not be ignored in alleviating oxidative damage by scavenging more excess ROS in spikes under drought stress.</p></div

Effects of drought on transcript levels of six genes encoding ASA-GSH cycle enzymes in the flag leaves, glumes, and lemmas of wheat at the grain-filling stage under well-watered (WW) and water-stressed (WS) conditions.

<p>Transcripts were analyzed by qRT-PCR using <i>Tubulin</i> gene as internal control. Each value is the mean ± standard deviation of three independent measurements. Values with different letters indicated the significant differences at <i>P < 0</i>.<i>05</i> level in each stress treatment through time according to Duncan’s multiple range test.</p

Effects of drought stress on the ratios of GSH/GSSG (A, B, and C) and ASA/DHA (D, E, and F) of the flag leaves, glumes, and lemmas at the grain-filling stage under well-watered (WW) and water-stressed (WS) conditions.

<p>All data represent means ± standard deviations (SD) of three replicates. Values with different letters indicated the significant differences at <i>P < 0</i>.<i>05</i> level in each stress treatment through time according to Duncan’s multiple range test.</p

DNA sequences of PCR primers were used for QRT-PCR determination of ASA-GSH biosynthesis-related genes in wheat.

<p>DNA sequences of PCR primers were used for QRT-PCR determination of ASA-GSH biosynthesis-related genes in wheat.</p

Effect of water deficit on antioxidant enzymes (APX, GR, DHAR, MDHAR, and GPX) activities involved in ASA-GSH metabolism in the flag leaves, glumes, and lemmas of wheat at the grain-filling stage under well-watered (WW) and water-stressed (WS) conditions.

<p>All data represent means ± standard deviations (SD) of three replicates. Values with different letters indicated the significant differences at <i>P < 0</i>.<i>05</i> level in each stress treatment through time according to Duncan’s multiple range test.</p

Chlorophyll content (Chl) and relative water content (RWC) of the flag leaves (A, D), glumes (B, E), and lemmas (C, F) at the grain-filling stage under well-watered (WW) and water-stressed (WS) conditions.

<p>All data represent means ± standard deviations (SD) of three replicates. Values with different letters indicated the significant differences at <i>P < 0</i>.<i>05</i> level in each stress treatment through time according to Duncan’s multiple range test.</p

Malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents of the flag leaves, glumes, and lemmas at the grain-filling stage under well-watered (WW) and water-stressed (WS) conditions.

<p>Malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents of the flag leaves, glumes, and lemmas at the grain-filling stage under well-watered (WW) and water-stressed (WS) conditions.</p

Unusual Activities of the Thioesterase Domain for the Biosynthesis of the Polycyclic Tetramate Macrolactam HSAF in <i>Lysobacter enzymogenes</i> C3

HSAF is an antifungal natural product with a new mode of action. A rare bacterial iterative PKS-NRPS assembles the HSAF skeleton. The biochemical characterization of the NRPS revealed that the thioesterase (TE) domain possesses the activities of both a protease and a peptide ligase. Active site mutagenesis, circular dichroism spectra, and homology modeling of the TE structure suggested that the TE may possess uncommon features that may lead to the unusual activities. The iterative PKS-NRPS is found in all polycyclic tetramate macrolactam gene clusters, and the unusual activities of the TE may be common to this type of hybrid PKS-NRPS