Ascorbic acid metabolism and functions.

This Special Issue was assembled to mark the 25th anniversary of the proposal of the d -mannose/ l -galactose (Smirnoff-Wheeler) ascorbate biosynthesis pathway in plants ( Wheeler et al., 1998 ). The issue aims to assess the current state of knowledge and to identify outstanding questions about ascorbate metabolism and functions in plants.

WHIRLY1 functions in the nucleus to regulate barley leaf development and associated metabolite profiles.

The WHIRLY (WHY) DNA/RNA binding proteins fulfil multiple but poorly characterised functions in leaf development. Here, we show that WHY1 transcript levels were highest in the bases of 7-day old barley leaves. Immunogold labelling revealed that the WHY1 protein was more abundant in the nuclei than the proplastids of the leaf bases. To identify transcripts associated with leaf development we conducted hierarchical clustering of differentially abundant transcripts along the developmental gradient of wild-type leaves. Similarly, metabolite profiling was employed to identify metabolites exhibiting a developmental gradient. A comparative analysis of transcripts and metabolites in barley lines (W1-1 and W1-7) lacking WHY1, which show delayed greening compared with the wild type revealed that the transcript profile of leaf development was largely unchanged in W1-1 and W1-7 leaves. However, there were differences in levels of several transcripts encoding transcription factors associated with chloroplast development. These include a barley homologue of the Arabidopsis GATA transcription factor that regulates stomatal development, greening and chloroplast development, NAC1; two transcripts with similarity to Arabidopsis GLK1 and two transcripts encoding ARF transcriptions factors with functions in leaf morphogenesis and development. Chloroplast proteins were less abundant in the W1-1 and W1-7 leaves than the wild type. The levels of tricarboxylic acid cycle metabolites and GABA were significantly lower in WHY1 knockdown leaves than the wild type. This study provides evidence that WHY1 is localised in the nuclei of leaf bases, contributing the regulation of nuclear-encoded transcripts that regulate chloroplast development.

Evidence for Participation of 4f and 5d Orbitals in Lanthanide Metal-Ligand Bonding and That Y(III) Has Less of This Complex-Stabilizing Ability. A Thermodynamic, Spectroscopic, and DFT Study of Their Complexation by the Nitrogen Donor Ligand TPEN.

The formation constants (log K1) of lanthanide(III) (Ln) ions [except for Pm(III)] and the Y(III) cation have been measured with the ligand TPEN (N,N,N',N'-tetra-2-picolylethylenediamine). These log K1 values show a typical variation with ionic radius, with a local maximum at Sm(III) and a local minimum at Gd(III), with an overall increase in log K1 from La(III) to Lu(III) as the ionic radius decreases. The log K1 for the Y(III)/TPEN complex is much lower than expected from its ionic radius, while the literature log K1 for Am(III) is much higher. The latter effect is thought to be due to greater covalence in the M-L (metal-ligand) bond than for Ln(III) ions: the low log K1 for Y(III) is interpreted as being due to lower covalence. The f → f transitions in the Nd(III) and Pr(III) complexes were examined for effects that might indicate the participation of f orbitals in M-L bonding. The intensity of the f → f transitions in the Nd(III)/TPEN complex was greatly increased compared to that of the Nd3+ aqua ion, which appeared to be due to additional sharp peaks, possibly parity forbidden transitions where parity rules were broken by covalence in the M-L bond. The Pr(III)/TPEN complex showed that all of the f → f transitions shifted to longer wavelengths by some 5 nm, with modest increases in intensity. The effects seen in the f → f transitions of Nd(III) and Pr(III) with TPEN with its six nitrogen donors were present to a much smaller extent in the EDTA and other complexes with fewer nitrogen donors. The changes in the f → f transitions of the TPEN complexes of Er(III) and Ho(III) were small, suggesting a smaller contribution of f orbitals to M-L bonding in these heavier Ln(III) ions. The intense Laporte allowed f → d transitions in Ce(III) complexes show large shifts to longer wavelengths as complexes of, for example, EDTA with increasing numbers of nitrogen donors, suggesting the participation of both f and d orbitals, or either, in M-L bonding. The nature of M-L bonding in M(III)/TPEN complexes was further investigated via density functional theory calculations.

Two Ligands of Interest in Recovering Uranium from the Oceans: The Correct Formation Constants of the Uranyl(VI) Cation with 2,2'-Bipyridyl-6,6'-dicarboxylic Acid and 1,10-Phenanthroline-2,9-dicarboxylic Acid.

The ligands BDA (2,2'-bipyridyl-6,6'-dicarboxylic acid) and PDA (1,10-phenanthroline-2,9-dicarboxylic acid) are of interest as functional group types for ion-exchange materials for extracting uranium from the oceans, reported in a previous paper for PDA Lashley, M. A. ( Inorg. Chem. 2016 55 10818 10829). Yang, Y. ( Inorg. Chem. 2019, 58, 6064 6074) have published what they claim to be a more accurate result for the formation of the UO22+/PDA complex of log K1 = 22.84 compared with our reported value of log K1 = 16.5, as well as log K1 = 21.52 for the BDA complex. The determination of log K1 for the PDA and BDA complexes with the UO22+ cation was carried out by Yang et al. using a competition reaction between DTPA (diethylenetriamine pentaacetic acid) and BDA or PDA, monitoring the absorbance due to the BDA and PDA ligands. This competition method using absorbance versus pH titrations was developed for determining the formation constants of the complexes of several polypyridyl ligands plus PDA complexes of metal ions, which were too stable for log K determination by competition with protons. A key feature of such titrations is that in the competition reaction, the displacement of the pyridyl donor ligand (e.g., PDA) by the competing ligand (e.g., DTPA), the absorbance spectrum of the displaced pyridyl donor ligand should be observed. Competing ligands used to date have been EDTA (ethylenediamine tetraacetic acid), DTPA, or the hydroxide ion. In the study of Yang et al., no such displaced PDA or BDA was apparent in the absorbance spectra in their titrations so that their reported log K1 values have no validity. Their log K1 values are so much higher than log K1 for the uranyl DTPA complex (∼13.6) that DTPA could not possibly displace BDA or PDA from the uranyl cation, and a competition reaction could not possibly occur. We report the correct value of log K1 = 15.4 (ionic strength = zero) for the uranyl BDA complex, to illustrate the correct determination of such a constant by a competition reaction between BDA and hydroxide, showing how the characteristic absorbance spectrum for a BDA complex, here the UO22+ complex, disappears, and the distinctive absorbance spectrum of the free nonprotonated BDA ligand appears as the pH is increased, and BDA is displaced by the hydroxide ion.

Reflective mulch increases fruit yield of highbush blueberry (Vaccinium corymbosum L. cv. Darrow) grown in a northern maritime environment while maintaining key fruit quality traits.

BACKGROUND: In maritime growing environments, blueberry yield often exhibits excessive season-to-season variation, associated with poorly adapted photosynthetic responses to low light conditions. It is therefore necessary to develop methods that stabilise yield while maintaining or improving fruit quality. Here, we placed reflective mulch alongside plants at the early green fruit stage, to test the hypothesis that increasing the available seasonal light integral could enhance blueberry yield. We further determined several quality characteristics to ensure fruit marketability. RESULTS: Placement of mulch alongside plants reflected up to five times more light compared with bare ground, enhancing the amount of light reaching the canopy. This led to an adaptive increase of light saturated maximal photosynthetic rate of mulch-treated plants, resulting in a twofold increase in yield compared with control plants. Analysis of fruit quality characteristics showed that total soluble solids, sugars and organic acids were similar between treatments. Likewise, antioxidant capacity, total anthocyanin content and the content of individual anthocyanins did not change in response to reflective mulch treatment. CONCLUSIONS: The use of reflective mulch should be explored by industry as a cost-effective method for enhancing blueberry yield while maintaining fruit quality in maritime environments. © 2020 Society of Chemical Industry.

An aldo-keto reductase with 2-keto-l-gulonate reductase activity functions in l-tartaric acid biosynthesis from vitamin C in Vitis vinifera.

Tartaric acid has high economic value as an antioxidant and flavorant in food and wine industries. l-Tartaric acid biosynthesis in wine grape (Vitis vinifera) uses ascorbic acid (vitamin C) as precursor, representing an unusual metabolic fate for ascorbic acid degradation. Reduction of the ascorbate breakdown product 2-keto-l-gulonic acid to l-idonic acid constitutes a critical step in this l-tartaric acid biosynthetic pathway. However, the underlying enzymatic mechanisms remain obscure. Here, we identified a V. vinifera aldo-keto reductase, Vv2KGR, with 2-keto-l-gulonic acid reductase activity. Vv2KGR belongs to the d-isomer-specific 2-hydroxyacid dehydrogenase superfamily and displayed the highest similarity to the hydroxyl pyruvate reductase isoform 2 in Arabidopsis thaliana Enzymatic analyses revealed that Vv2KGR efficiently reduces 2-keto-l-gulonic acid to l-idonic acid and uses NADPH as preferred coenzyme. Moreover, Vv2KGR exhibited broad substrate specificity toward glyoxylate, pyruvate, and hydroxypyruvate, having the highest catalytic efficiency for glyoxylate. We further determined the X-ray crystal structure of Vv2KGR at 1.58 Å resolution. Comparison of the Vv2KGR structure with those of d-isomer-specific 2-hydroxyacid dehydrogenases from animals and microorganisms revealed several unique structural features of this plant hydroxyl pyruvate reductase. Substrate structural analysis indicated that Vv2KGR uses two modes (A and B) to bind different substrates. 2-Keto-l-gulonic acid displayed the lowest predicted free-energy binding to Vv2KGR among all docked substrates. Hence, we propose that Vv2KGR functions in l-tartaric acid biosynthesis. To the best of our knowledge, this is the first report of a d-isomer-specific 2-hydroxyacid dehydrogenase that reduces 2-keto-l-gulonic acid to l-idonic acid in plants.

Effect of phosphorus supply on root traits of two Brassica oleracea L. genotypes.

BACKGROUND: Phosphorus (P) deficiency limits crop production worldwide. Crops differ in their ability to acquire and utilise the P available. The aim of this study was to determine root traits (root exudates, root system architecture (RSA), tissue-specific allocation of P, and gene expression in roots) that (a) play a role in P-use efficiency and (b) contribute to large shoot zinc (Zn) concentration in Brassica oleracea. RESULTS: Two B. oleracea accessions (var. sabellica C6, a kale, and var. italica F103, a broccoli) were grown in a hydroponic system or in a high-throughput-root phenotyping (HTRP) system where they received Low P (0.025 mM) or High P (0.25 mM) supply for 2 weeks. In hydroponics, root and shoot P and Zn concentrations were measured, root exudates were profiled using both Fourier-Transform-Infrared spectroscopy and gas-chromatography-mass spectrometry and previously published RNAseq data from roots was re-examined. In HTRP experiments, RSA (main and lateral root number and lateral root length) was assessed and the tissue-specific distribution of P was determined using micro-particle-induced-X-ray emission. The C6 accession had greater root and shoot biomass than the F103 accession, but the latter had a larger shoot P concentration than the C6 accession, regardless of the P supply in the hydroponic system. The F103 accession had a larger shoot Zn concentration than the C6 accession in the High P treatment. Although the F103 accession had a larger number of lateral roots, which were also longer than in the C6 accession, the C6 accession released a larger quantity and number of polar compounds than the F103 accession. A larger number of P-responsive genes were found in the Low P treatment in roots of the F103 accession than in roots of the C6 accession. Expression of genes linked with "phosphate starvation" was up-regulated, while those linked with iron homeostasis were down-regulated in the Low P treatment. CONCLUSIONS: The results illustrate large within-species variability in root acclimatory responses to P supply in the composition of root exudates, RSA and gene expression, but not in P distribution in root cross sections, enabling P sufficiency in the two B. oleracea accessions studied.

Quantitative trait loci mapping of polyphenol metabolites in blackcurrant (Ribes nigrum L.).

INTRODUCTION: Commercially, blackcurrants (Ribes nigrum L.) are grown mainly for processing, especially for juice production. They are valued for their high levels of polyphenols, especially anthocyanins, which contribute to their characteristic deep colour, but also as a good source of vitamin C. Recently, evidence has accrued that polyphenols, such as anthocyanins, may have specific human health benefits. OBJECTIVE: The aims of this study were to investigate the genetic control of polyphenols and other key juice processing traits in blackcurrants. METHODS: The levels, over 2 years, of vitamin C, citrate, malate, succinate, total organic acids, total anthocyanins and total phenolics together with 46 mainly polyphenol metabolites were measured in a blackcurrant biparental mapping population. Quantitative trait loci (QTLs) for these traits were mapped onto a high-density SNP linkage map. RESULTS: At least one QTL was detected for each trait, with good consistency between the 2 years. Clusters of QTLs were found on each of the eight linkage groups (LG). For example, QTLs for the major anthocyanidin glucosides, delphinidin-3-O-glucoside and cyanidin-3-O-glucoside, co-localised with a QTL for total anthocyanin content on LG3 whereas the major anthocyanidin rutinosides, delphinidin-3-O-rutinoside and cyanidin-3-O-rutinoside, had QTLs on LG1 and LG2. Many of the QTLs explained a high proportion of the trait variation, with the most significant region, on LG3 at ~ 35 cM, explaining more than 60% of the variation in the coumaroylated metabolites, Cyanidin-coumaroyl-glucose, Delphinidin-coumaroyl-glucose, Kaempferol-coumaroyl-glucose and Myricetin-coumaroyl-glucose. CONCLUSION: The identification of robust QTLs for key polyphenol classes and individual polyphenols in blackcurrant provides great potential for marker-assisted breeding for improved levels of key components.

Fluorescence and Metal-Binding Properties of the Highly Preorganized Tetradentate Ligand 2,2'-Bi-1,10-phenanthroline and Its Remarkable Affinity for Cadmium(II).

The metal-ion-complexing properties of the tetradentate ligand 2,2'-bi-1,10-phenanthroline (BIPHEN) in 50% CH3OH/H2O are reported for a variety of metal ions. BIPHEN (with two reinforcing benzo groups in the backbone) was compared to other tetrapyridyls, 2,9-di(pyrid-2-yl)-1,10-phenanthroline (DPP; with one benzo group) and 2,2':6',2″:6″,2‴- quaterpyridine (QPY; with no benzo groups), with levels of preorganization BIPHEN > DPP > QPY. Formation constants were determined by following the variation of the intense π → π* transitions in the absorbance spectra of BIPHEN in the presence of metal ion as a function of the pH. The log K1 values show that the increased level of preorganization produced by the two benzo groups, reinforcing the backbone of the BIPHEN ligand, leads to increased complex stability with large metal ions (an ionic radius greater than 0.9 Å) compared to the less preorganized tetrapyridines DPP and QPY. In particular, the large CdII ion [log K1(BIPHEN) = 12.7] shows unusual selectivity over the small ZnII ion [log K1(BIPHEN) = 7.78]. The order of levels of preorganization BIPHEN > DPP > QPY leads to enhanced selectivity for SmIII over GdIII with increased preorganization, which is of interest in relation to separating AmIII from GdIII in the treatment of radioactive waste. AmIII is very close in ionic radius to SmIII, so that the size-based selectivity produced by the enhanced preorganization of BIPHEN should translate into enhanced AmIII/GdIII selectivity. The chelation-enhanced fluorescence (CHEF) effect in BIPHEN complexes is discussed. The CHEF effect in the ZnII complex is somewhat smaller than that for CdII, which is discussed in terms of decreased overlap in the Zn-N bonds formed by the too small ZnII, leading to a partial photoinduced-electron-transfer quenching of fluorescence. The structure of the complex [Cd(BIPHEN)2](ClO4)2 is reported and shows that the Cd-N bonds are largely normal for the unusual 8-coordination observed, except that steric clashes between the terminal pyridyl groups of each of the BIPHEN ligands, and the rest of the orthogonal BIPHEN ligand, lead to some stretching of the outer Cd-N bonds.

A reversible light- and genotype-dependent acquired thermotolerance response protects the potato plant from damage due to excessive temperature.

MAIN CONCLUSION: A powerful acquired thermotolerance response in potato was demonstrated and characterised in detail, showing the time course required for tolerance, the reversibility of the process and requirement for light. Potato is particularly vulnerable to increased temperature, considered to be the most important uncontrollable factor affecting growth and yield of this globally significant crop. Here, we describe an acquired thermotolerance response in potato, whereby treatment at a mildly elevated temperature primes the plant for more severe heat stress. We define the time course for acquiring thermotolerance and demonstrate that light is essential for the process. In all four commercial tetraploid cultivars that were tested, acquisition of thermotolerance by priming was required for tolerance at elevated temperature. Accessions from several wild-type species and diploid genotypes did not require priming for heat tolerance under the test conditions employed, suggesting that useful variation for this trait exists. Physiological, transcriptomic and metabolomic approaches were employed to elucidate potential mechanisms that underpin the acquisition of heat tolerance. This analysis indicated a role for cell wall modification, auxin and ethylene signalling, and chromatin remodelling in acclimatory priming resulting in reduced metabolic perturbation and delayed stress responses in acclimated plants following transfer to 40 °C.

Correction to: A reversible light- and genotype-dependent acquired thermotolerance response protects the potato plant from damage due to excessive temperature.

The article A reversible light- and genotype-dependent acquired thermotolerance response protects the potato plant from damage due to excessive temperature, written by Almudena Trapero-Mozos, Laurence J. M. Ducreux, Craita E. Bita, Wayne Morris, Cosima Wiese, Jenny A. Morris, Christy Paterson, Peter E. Hedley, Robert D. Hancock, and Mark Taylor, was originally published electronically on the publisher's internet portal (currently SpringerLink) on 8 March 2018 without open access. With the author(s)' decision to opt for Open Choice the copyright of the article changed on 30 April 2018 to © The Author(s) 2018 and the article is forthwith distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/ ), which permits use, duplication, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.The â€‹original â€‹article â€‹has â€‹been â€‹corrected.

Engineering heat tolerance in potato by temperature-dependent expression of a specific allele of HEAT-SHOCK COGNATE 70.

For many commercial potato cultivars, tuber yield is optimal at average daytime temperatures in the range of 14-22 °C. Further rises in ambient temperature can reduce or completely inhibit potato tuber production, with damaging consequences for both producer and consumer. The aim of this study was to use a genetic screen based on a model tuberization assay to identify quantitative trait loci (QTL) associated with enhanced tuber yield. A candidate gene encoding HSc70 was identified within one of the three QTL intervals associated with elevated yield in a Phureja-Tuberosum hybrid diploid potato population (06H1). A particular HSc70 allelic variant was linked to elevated yield in the 06H1 progeny. Expression of this allelic variant was much higher than other alleles, particularly on exposure to moderately elevated temperature. Transient expression of this allele in Nicotiana benthamiana resulted in significantly enhanced tolerance to elevated temperature. An TA repeat element was present in the promoter of this allele, but not in other HSc70 alleles identified in the population. Expression of the HSc70 allelic variant under its native promoter in the potato cultivar Desiree resulted in enhanced HSc70 expression at elevated temperature. This was reflected in greater tolerance to heat stress as determined by improved yield under moderately elevated temperature in a model nodal cutting tuberization system and in plants grown from stem cuttings. Our results identify HSc70 expression level as a significant factor influencing yield stability under moderately elevated temperature and identify specific allelic variants of HSc70 for the induction of thermotolerance via conventional introgression or molecular breeding approaches.

Redox Control of Aphid Resistance through Altered Cell Wall Composition and Nutritional Quality.

The mechanisms underpinning plant perception of phloem-feeding insects, particularly aphids, remain poorly characterized. Therefore, the role of apoplastic redox state in controlling aphid infestation was explored using transgenic tobacco (Nicotiana tabacum) plants that have either high (PAO) or low (TAO) ascorbate oxidase (AO) activities relative to the wild type. Only a small number of leaf transcripts and metabolites were changed in response to genotype, and cell wall composition was largely unaffected. Aphid fecundity was decreased significantly in TAO plants compared with other lines. Leaf sugar levels were increased and maximum extractable AO activities were decreased in response to aphids in all genotypes. Transcripts encoding the Respiratory Burst Oxidase Homolog F, signaling components involved in ethylene and other hormone-mediated pathways, photosynthetic electron transport components, sugar, amino acid, and cell wall metabolism, were increased significantly in the TAO plants in response to aphid perception relative to other lines. The levels of galactosylated xyloglucan were decreased significantly in response to aphid feeding in all the lines, the effect being the least in the TAO plants. Similarly, all lines exhibited increases in tightly bound (1→4)-ß-galactan. Taken together, these findings identify AO-dependent mechanisms that limit aphid infestation.

The redox state of the apoplast influences the acclimation of photosynthesis and leaf metabolism to changing irradiance.

The redox state of the apoplast is largely determined by ascorbate oxidase (AO) activity. The influence of AO activity on leaf acclimation to changing irradiance was explored in wild-type (WT) and transgenic tobacco (Nicotiana tobaccum) lines containing either high [pumpkin AO (PAO)] or low [tobacco AO (TAO)] AO activity at low [low light (LL); 250 µmol m-2  s-1 ] and high [high light (HL); 1600 µmol m-2  s-1 ] irradiance and following the transition from HL to LL. AO activities changed over the photoperiod, particularly in the PAO plants. AO activity had little effect on leaf ascorbate, which was significantly higher under HL than under LL. Apoplastic ascorbate/dehydroascorbate (DHA) ratios and threonate levels were modified by AO activity. Despite decreased levels of transcripts encoding ascorbate synthesis enzymes, leaf ascorbate increased over the first photoperiod following the transition from HL to LL, to much higher levels than LL-grown plants. Photosynthesis rates were significantly higher in the TAO leaves than in WT or PAO plants grown under HL but not under LL. Sub-sets of amino acids and fatty acids were lower in TAO and WT leaves than in the PAO plants under HL, and following the transition to LL. Light acclimation processes are therefore influenced by the apoplastic as well as chloroplastic redox state.

Photosynthetic limitation as a factor influencing yield in highbush blueberries (Vaccinium corymbosum) grown in a northern European environment.

Published evidence indicates that nearly 60% of blueberry-producing countries experience yield instability. Yield is a complex trait determined by genetic and environmental factors. Here, using physiological and biochemical approaches, we tested the hypothesis that yield instability results from year-to-year environmental variation that limits carbon assimilation, storage and partitioning. The data indicate that fruit development depends primarily on the daily production of non-structural carbohydrates by leaves, and there is no accumulation of a starch buffer to allow continuous ripening under conditions limiting for photosynthesis. Photosynthesis was saturated at moderate light irradiance and this was mainly due to stomatal and biochemical limitations. In a dynamic light environment, photosynthesis was further limited by slow stomatal response to increasing light. Finally, labelling with 13CO2 at specific stages of fruit development revealed a relatively even distribution of newly assimilated carbon between stems, roots and fruits, suggesting that the fruit is not a strong sink. We conclude that a significant component of yield variability results from limitations in photosynthetic efficiency that are compounded by an inability to accumulate starch reserves in blueberry storage tissues in a typical northern European environment. This work informs techniques for improving agronomic management and indicates key traits required for yield stability in such environments.

Characterization of the watercress (Nasturtium officinale R. Br.; Brassicaceae) transcriptome using RNASeq and identification of candidate genes for important phytonutrient traits linked to human health.

BACKGROUND: Consuming watercress is thought to provide health benefits as a consequence of its phytonutrient composition. However, for watercress there are currently limited genetic resources underpinning breeding efforts for either yield or phytonutritional traits. In this paper, we use RNASeq data from twelve watercress accessions to characterize the transcriptome, perform candidate gene mining and conduct differential expression analysis for two key phytonutritional traits: antioxidant (AO) capacity and glucosinolate (GLS) content. RESULTS: The watercress transcriptome was assembled to 80,800 transcripts (48,732 unigenes); 71 % of which were annotated based on orthology to Arabidopsis. Differential expression analysis comparing watercress accessions with 'high' and 'low' AO and GLS resulted in 145 and 94 differentially expressed loci for AO capacity and GLS respectively. Differentially expressed loci between high and low AO watercress were significantly enriched for genes involved in plant defence and response to stimuli, in line with the observation that AO are involved in plant stress-response. Differential expression between the high and low GLS watercress identified links to GLS regulation and also novel transcripts warranting further investigation. Additionally, we successfully identified watercress orthologs for Arabidopsis phenylpropanoid, GLS and shikimate biosynthesis pathway genes, and compiled a catalogue of polymorphic markers for future applications. CONCLUSIONS: Our work describes the first transcriptome of watercress and establishes the foundation for further molecular study by providing valuable resources, including sequence data, annotated transcripts, candidate genes and markers.

WHIRLY1 Functions in the Control of Responses to Nitrogen Deficiency But Not Aphid Infestation in Barley.

WHIRLY1 is largely targeted to plastids, where it is a major constituent of the nucleoids. To explore WHIRLY1 functions in barley (Hordeum vulgare), RNA interference-knockdown lines (W1-1, W1-7, and W1-9) that have very low levels of HvWHIRLY1 transcripts were characterized in plants grown under optimal and stress conditions. The WHIRLY1-1 (W1-1), W1-7, and W1-9 plants were phenotypically similar to the wild type but produced fewer tillers and seeds. Photosynthesis rates were similar in all lines, but W1-1, W1-7, and W1-9 leaves had significantly more chlorophyll and less sucrose than the wild type. Transcripts encoding specific subsets of chloroplast-localized proteins, such as ribosomal proteins, subunits of the RNA polymerase, and thylakoid nicotinamide adenine dinucleotide (reduced) and cytochrome b6/f complexes, were much more abundant in the W1-7 leaves than the wild type. Although susceptibility of aphid (Myzus persicae) infestation was similar in all lines, the WHIRLY1-deficient plants showed altered responses to nitrogen deficiency, maintaining higher photosynthetic CO2 assimilation rates than the wild type under limiting nitrogen. Although all lines showed globally similar low nitrogen-dependent changes in transcripts and metabolites, the increased abundance of FAR-RED IMPAIRED RESPONSE1-like transcripts in nitrogen-deficient W1-7 leaves infers that WHIRLY1 has a role in communication between plastid and nuclear genes encoding photosynthetic proteins during abiotic stress.

Cross-tolerance to biotic and abiotic stresses in plants: a focus on resistance to aphid infestation.

Plants co-evolved with an enormous variety of microbial pathogens and insect herbivores under daily and seasonal variations in abiotic environmental conditions. Hence, plant cells display a high capacity to respond to diverse stresses through a flexible and finely balanced response network that involves components such as reduction-oxidation (redox) signalling pathways, stress hormones and growth regulators, as well as calcium and protein kinase cascades. Biotic and abiotic stress responses use common signals, pathways and triggers leading to cross-tolerance phenomena, whereby exposure to one type of stress can activate plant responses that facilitate tolerance to several different types of stress. While the acclimation mechanisms and adaptive responses that facilitate responses to single biotic and abiotic stresses have been extensively characterized, relatively little information is available on the dynamic aspects of combined biotic/abiotic stress response. In this review, we consider how the abiotic environment influences plant responses to attack by phloem-feeding aphids. Unravelling the signalling cascades that underpin cross-tolerance to biotic and abiotic stresses will allow the identification of new targets for increasing environmental resilience in crops.

Highly Preorganized Ligand 1,10-Phenanthroline-2,9-dicarboxylic Acid for the Selective Recovery of Uranium from Seawater in the Presence of Competing Vanadium Species.

Studies of the complexation of new promising ligands with uranyl (UO22+) and other seawater cations can aid the development of more efficient, selective, and robust sorbents for the recovery of uranium from seawater. In this work, we propose that the ligand design principles based on structural preorganization can be successfully applied to obtain a dramatic enhancement in UO22+ ion binding affinity and selectivity. This concept is exemplified through the investigation of the complexes of UO22+, VO2+, and VO2+ with the highly preorganized ligand 1,10-phenanthroline-2,9-dicarboxylic acid (PDA) using a combination of fluorescence and absorbance techniques, along with density functional theory (DFT) calculations. The measured stability constant value, log K1, of 16.5 for the UO22+/PDA complex is very high compared to uranyl complexes with other dicarboxylic ligands. Moreover, PDA exhibits strong selectivity for uranyl over vanadium ions, since the determined stability constant values of the PDA complexes of the vanadium ions are quite low (V(IV) log K1 = 7.4, V(V) = 7.3). The structures of the corresponding UO22+, VO2+, and VO2+ complexes with PDA were identified by systematic DFT calculations and helped to interpret the stronger binding affinity for uranium over the vanadium ions. Because of its high chemical stability, selectivity, and structural preorganization for UO22+ complexation, PDA is a very promising candidate that can be potentially used in the development of novel adsorbent materials for the selective extraction of uranium from seawater.