High Antioxidant Activity Facilitates Maintenance of Cell Division in Leaves of Drought Tolerant Maize Hybrids

Comparative transcriptomic data confirm the findings of dehydration stress-induced redox biology of indigenous aromatic rice cultivars

The present work compares the transcriptome data sets of post-imbibitional dehydration stress-raised seedlings of two contrasting indigenous aromatic rice cultivars (Oryza sativa L., Cultivars Jamainadu and Badshabhog) for unfolding genetic regulation of dehydration stress. The result of RNA-seq analysis in Illumina platform in general revealed significant cultivar-specific expression of genes under dehydration stress that substantiate the data of redox metabolic fingerprints (assessed in terms of differential efficacy of ascorbate-glutathione pathway, ROS-antioxidant interaction dynamics and sensitive biomarkers of oxidative stress). Both the cultivars showed a diverse global transcriptomic response under water-deficit condition. Transcripts selected for heatmap generation with proper annotation revealed genes that are significantly expressed and mainly involved in redox functions, signaling, membrane trafficking, replication, protein synthesis, etc. Gene ontology (GO) analysis proposed that dehydration stress in the drought-tolerant cultivar Badshabhog was attributable to the enhanced expression of genes associated with carbon dioxide-concentrating mechanism, peroxysomal biogenesis, protein modification, protein synthesis, mitochondrial electron transport chain functioning, intercellular protein transport, histone demethylation associated with developmental process, regulation of apoptosis, etc. The redox genes that got significantly over-expressed in the IARC Badshabhog vis-à-vis Jamainadu include l-ascorbate oxidase/peroxidase, monothiol glutaredoxin-S1, thioredoxin-like protein AAED1 (chloroplastic), thioredoxin-like protein CXXS1, NADH-dehydrogenase (ubiquinone)-1-beta subcomplex subunit 3-B, NADH-dehydrogenase subunit 6 and K, lipoxygenase 6 isoform-XI, etc. Overall, the results of the RNA-seq analysis led to the identification of cultivar-specific genes, with the cultivar Badshabhog exhibiting significantly greater molecular reprogramming for redox regulation and signaling necessary for combating dehydration stress.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03829-z.

Genetic diversity Analysis using molecular markers of some rice varieties for Physiological, biochemical and yield Traits under water deficit condition.. [DOI: 10.21203/rs.3.rs-3111398/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Rice is a major staple food crop all over the world. Recent climate change trends forecast an increase in drought severity, necessitating the creation of novel drought-tolerant rice cultivars in order to continue rice production in this ecosystem. This study was carried out at the experimental farm of the rice research and training center (RRTC) using the randomized complete block design (RCBD) to assess the impact of water scarcity on eight rice varieties by identifying differences in physiological and biochemical responses among drought-sensitive and resistant rice varieties, in addition applying two PCR-based molecular marker systems ISSR and SCoT to assess the genetic diversity among the studied rice varieties. The results revealed that, Water shortage stress significantly reduced relative water content, total chlorophyll content, grain yield, and yield characteristics. while, it significantly raised proline content and antioxidant enzyme activity (CAT, APX, and SOD). The combined analysis of variance demonstrated that the mean squares for environments, varieties, and their interaction were highly significant for all investigated traits, suggesting that the germplasm used in the study had significant genetic diversity from one environment (normal irrigation) to another (water deficit) and could rank differently in both of them. Mean performance data showed that, Puebla and Hispagran varieties were selected as the most favourable varieties for most physiological and biochemical parameters studied, as well as yield traits which recorded the highest desirable values under both irrigation treatments. They were recommended for use in rice hybrid breeding programmes for water scarcity tolerance. Genetic Similarity and Cluster Analysis revealed that, the both molecular markers exhibited comparable genetic diversity values but a higher level of polymorphism was represented by ISSR. This indicates the high efficiency of both markers in discriminating the tested varieties. The dendrogram generated by ISSR and SCoT markers combined data divided the varieties into two major clusters. Cluster I consisted of the genotype Sakha 106. Cluster II retained seven varieties, which were further divided into two sub-clusters; Sakha 101, Sakha 105, Sakha 106, Sakha 107 constituted the first subgroup, while Giza 177, Hispagran, and Puebla formed the second one.

Condiciones óptimas de extracción de compuestos antioxidante del alga roja Acanthophora spicifera

La Acanthophora spicifera un alga roja de fácil adaptación a diferentes condiciones ambientales, por su capacidad de regenerarse por fragmentación, convirtiéndola en una especie invasora en áreas tropicales y subtropicales. Además, es conocida por sus componentes bioactivos (antioxidantes, fitohormonas, fitopigmentos). En este estudio se plantea determinar las condiciones óptimas de extracción de compuestos antioxidantes de la macroalga que crece en la zona intermareal de la playa de San Pedro de la provincia de Santa Elena, en dos procesos de secado (horno y liofilización) y extracción etanólica (digestión y ultrasonido) a diferentes concentraciones de etanol (50% y 70%) en rangos de tiempo y temperatura para su posterior determinación de actividad antioxidante por los métodos DPPH, ABTS, fenoles, flavonoides y auxinas totales en microplacas. Los datos se analizaron mediante análisis de varianza (ANOVA) usando el software estadístico R.4.2.0 e InfoStat, observan que los mejores resultados se dieron por digestión con una concentración de etanol al 50% y se obtuvieron valores para: la actividad captadora de radicales DPPH 3.65±0.011 µmol ET/g ps, mayor actividad inhibidora del radical catiónico ABTS 14.06±0.03 µmol ET/g ps, para flavonoides 1278.58±2.94 µg EQ/g ps, para fenoles 900±0.129 µg GEA/g ps. Las condiciones óptimas para la extracción etanolica de la macroalga A. spicifera., fueron 47 °C y 47 minutos para la actividad captadora de radicales DPPH y 47 °C y 39 minutos para la actividad inhibidora del radical catiónico ABTS, 45 °C y 37 minutos para Fenoles totales y 43 °C y 38 minutos para Flavonoides totales. Palabras clave: actividad antioxidante, Acanthophora spicifera, optimización

Estudio de la variabilidad en el tiempo y espacio de la actividad antioxidante y composición bioquímica de Kappaphycus alvarezii en diferentes densidades de siembra

Kappaphycus alvarezii es una de las especies de algas más cultivadas en el mundo, debido a su alto contenido de compuestos bioactivos con reportes antioxidantes y bioestimulantes. El presente estudio evaluó el efecto de las densidades de plantación sobre la composición bioquímica y antioxidante de K. alvarezii cultivada en un sistema de línea larga durante las estaciones seca y húmeda, con el fin de proporcionar una base científica para una cosecha óptima. Se midieron el contenido de humedad, cenizas, grasa, fibra, auxinas, fenoles, flavonoides, DPPH y ABTS. Los datos se analizaron mediante pruebas t, Wilcoxon, Kruskal-Wallis y ANOVA unidireccional. Los resultados mostraron un mayor contenido de grasa (2,01 % P.s), fibra bruta (5,21% P.s), contenido total de fenoles (324,09 μg GAE/g P.s) y ABTS (9,32 μg GAE/g P.s) durante la estación seca. Con respecto a la densidad de plantación, se produjo un aumento significativo del contenido en cenizas, fenoles totales y ABTS con una densidad de 10 líneas.célula-1 al mismo tiempo. Los contenidos de flavonoides, DPPH y auxina mostraron una tendencia estacional opuesta, alcanzando los niveles máximos en la estación húmeda. Este estudio aporta nueva información sobre las condiciones ambientales que pueden provocar cambios en la actividad antioxidante y la composición bioquímica de esta especie con vistas al desarrollo de bioproductos para diferentes sectores industriales como el alimentario, el farmacéutico y el de los fertilizantes en Ecuador. Palabras claves: Alga roja; Fenoles; Flavonoides; Antioxidante; Composición bioquímica; Variación estacional; densidad de siembra.

Sugar beet extract rich in glycine betaine modulates oxidative defense system and key physiological characteristics of maize under water-deficit stress

Now-a-days, plant-based extracts, as a cheap source of growth activators, are being widely used to treat plants grown under extreme climatic conditions. So, a trial was conducted to assess the response of two maize (Zea mays L.) varieties, Sadaf (drought tolerant) and Sultan (drought sensitive) to foliar-applied sugar beet extract (SBE) under varying water-deficit conditions. Different SBE (control, 1%, 2%, 3% & 4%) levels were used in this study, and plants were exposed to water-deficit [(75% and 60% of field capacity (FC)] and control (100% FC) conditions. It was observed that root and shoot dry weights (growth), total soluble proteins, RWC-relative water contents, total phenolics, chlorophyll pigments and leaf area per plant decreased under different water stress regimes. While, proline, malondialdehyde (MDA), RMP-relative membrane permeability, H2O2-hydrogen peroxide and the activities of antioxidant enzymes [CAT-catalase, POD-peroxidase and SOD-superoxide dismutase] were found to be improved in water stress affected maize plants. Exogenous application of varying levels of SBE ameliorated the negative effects of water-deficit stress by enhancing the growth attributes, photosynthetic pigments, RWC, proline, glycinebetaine (GB), activities of POD and CAT enzymes and levels of total phenolics, whereas it reduced the lipid peroxidation in both maize varieties under varying water stress levels. It was noted that 3% and 4% levels of SBE were more effective than the other levels used in enhancing the growth as well as other characteristics of the maize varieties. Overall, the sugar beet extract proved to be beneficial for improving growth and metabolism of maize plants exposed to water stress.

Drought affects the rate and duration of organ growth but not inter-organ growth coordination

Drought at flowering and grain filling greatly reduces maize (Zea mays) yield. Climate change is causing earlier and longer-lasting periods of drought, which affect the growth of multiple maize organs throughout development. To study how long periods of water deficit impact the dynamic nature of growth, and to determine how these relate to reproductive drought, we employed a high-throughput phenotyping platform featuring precise irrigation, imaging systems, and image-based biomass estimations. Prolonged drought resulted in a reduction of growth rate of individual organs-though an extension of growth duration partially compensated for this-culminating in lower biomass and delayed flowering. However, long periods of drought did not affect the highly organized succession of maximal growth rates of the distinct organs, i.e. leaves, stems, and ears. Two drought treatments negatively affected distinct seed yield components: Prolonged drought mainly reduced the number of spikelets, and drought during the reproductive period increased the anthesis-silking interval. The identification of these divergent biomass and yield components, which were affected by the shift in duration and intensity of drought, will facilitate trait-specific breeding toward future climate-resilient crops.

Turgor-time controls grass leaf elongation rate and duration under drought stress

The process of leaf elongation in grasses is characterized by the creation and transformation of distinct cell zones. The prevailing turgor pressure within these cells is one of the key drivers for the rate at which these cells divide, expand and differentiate, processes that are heavily impacted by drought stress. In this article, a turgor-driven growth model for grass leaf elongation is presented, which combines mechanistic growth from the basis of turgor pressure with the ontogeny of the leaf. Drought-induced reductions in leaf turgor pressure result in a simultaneous inhibition of both cell expansion and differentiation, lowering elongation rate but increasing elongation duration due to the slower transitioning of cells from the dividing and elongating zone to mature cells. Leaf elongation is, therefore, governed by the magnitude of, and time spent under, growth-enabling turgor pressure, a metric which we introduce as turgor-time. Turgor-time is able to normalize growth patterns in terms of varying water availability, similar to how thermal time is used to do so under varying temperatures. Moreover, additional inclusion of temperature dependencies within our model pioneers a novel concept enabling the general expression of growth regardless of water availability or temperature.

Dissipation of pyridaphenthion by cyanobacteria: Insights into cellular degradation, detoxification and metabolic regulation

Excessive use of organophosphorus pesticides such as pyridaphenthion (PY) to constrain insects induced crop loss, results in soil and water sources contamination. Cyanobacteria are sensitive biological indicators and promising tools for bioremediation of soil and water pollutants. To understand PY toxicity, detoxification and degradation in cyanobacteria, we performed a comparative study in the two diazotrophic cyanobacteria; Anabaena laxa and Nostoc muscorum. They were exposed to mild (5 mg/L) and high (10 mg/L) concentrations of PY for 7 days. Compared to A. laxa, N. muscorum efficiently showed high PY accumulation and degradation to a safe environmentally product; 6-hydroxy-2-phenylpyridazin-3(2 H)-one. PY inhibited cell growth and reduced Chl a content and photosynthesis related enzymes (PEPC and RuBisCo) activities in both species, but to less extend in N. muscorum. It also induced oxidative damage, particularly in A. laxa, as indicated by high H₂O₂, lipid peroxidation and protein oxidation levels and increased NADPH oxidase enzyme activity. N. muscorum invested more in antioxidants induction, i.e., induced ascorbate and glutathione cycle, however, these antioxidants increments in A. laxa were less pronounced. Overall, this study provides more in-deep insights into the PY toxicity and the role of N. muscorum as a promising PY remediator.

Cadmium inhibits cell cycle progression and specifically accumulates in the maize leaf meristem

It is well known that cadmium (Cd) pollution inhibits plant growth, but how this metal impacts leaf growth processes at the cellular and molecular level is still largely unknown. In the current study, we show that Cd specifically accumulates in the meristematic tissue of the growing maize leaf, while Cd concentration in the elongation zone rapidly declines as the deposition rates diminish and cell volumes increase due to cell expansion. A kinematic analysis shows that, at the cellular level, a lower number of meristematic cells together with a significantly longer cell cycle duration explain the inhibition of leaf growth by Cd. Flow cytometry analysis suggests an inhibition of the G1/S transition, resulting in a lower proportion of cells in the S phase and reduced endoreduplication in expanding cells under Cd stress. Lower cell cycle activity is also reflected by lower expression levels of key cell cycle genes (putative wee1, cyclin-B2-4, and minichromosome maintenance4). Cell elongation rates are also inhibited by Cd, which is possibly linked to the inhibited endoreduplication. Taken together, our results complement studies on Cd-induced growth inhibition in roots and link inhibited cell cycle progression to Cd deposition in the leaf meristem.

Salinity Stress Enhances the Antioxidant Capacity of Bacillus and Planococcus Species Isolated From Saline Lake Environment

This study aims at exploiting salinity stress as an innovative, simple, and cheap method to enhance the production of antioxidant metabolites and enzymes from bacteria for potential application as functional additives to foods and pharmaceuticals. We investigated the physiological and biochemical responses of four bacterial isolates, which exhibited high tolerance to 20% NaCl (wt/vol), out of 27 bacterial strains isolated from Aushazia Lake, Qassim region, Saudi Arabia. The phylogenetic analysis of the 16S rRNA genes of these four isolates indicated that strains ST1 and ST2 belong to genus Bacillus, whereas strains ST3 and ST4 belong to genus Planococcus. Salinity stress differentially induced oxidative damage, where strains ST3 and ST4 showed increased lipid peroxidation, lipoxygenase, and xanthine oxidase levels. Consequently, high antioxidant contents were produced to control oxidative stress, particularly in ST3 and ST4. These two Planococcus strains showed increased glutathione cycle, phenols, flavonoids, antioxidant capacity, catalase, and/or superoxide dismutase (SOD). Interestingly, the production of glutathione by Planococcus strains was some thousand folds greater than by higher plants. On the other hand, the induction of antioxidants in ST1 and ST2 was restricted to phenols, flavonoids, peroxidase, glutaredoxin, and/or SOD. The hierarchical analysis also supported strain-specific responses. This is the first report that exploited salinity stress for promoting the production of antioxidants from bacterial isolates, which can be utilized as postbiotics for promising applications in foods and pharmaceuticals.

Starch biosynthesis contributes to the maintenance of photosynthesis and leaf growth under drought stress in maize

To understand the growth response to drought, we performed a proteomics study in the leaf growth zone of maize (Zea mays L.) seedlings and functionally characterized the role of starch biosynthesis in the regulation of growth, photosynthesis and antioxidant capacity, using the shrunken-2 mutant (sh2), defective in ADP-glucose pyrophosphorylase. Drought altered the abundance of 284 proteins overrepresented for photosynthesis, amino acid, sugar and starch metabolism, and redox-regulation. Changes in protein levels correlated with enzyme activities (increased ATP synthase, cysteine synthase, starch synthase, RuBisCo, peroxiredoxin, glutaredoxin, thioredoxin and decreased triosephosphate isomerase, ferredoxin, cellulose synthase activities, respectively) and metabolite concentrations (increased ATP, cysteine, glycine, serine, starch, proline and decreased cellulose levels). The sh2 mutant showed a reduced increase of starch levels under drought conditions, leading to soluble sugar starvation at the end of the night and correlating with an inhibition of leaf growth rates. Increased RuBisCo activity and pigment concentrations observed in WT, in response to drought, were lacking in the mutant, which suffered more oxidative damage and recovered more slowly after re-watering. These results demonstrate that starch biosynthesis contributes to maintaining leaf growth under drought stress and facilitates enhanced carbon acquisition upon recovery.

Two Festuca Species-F. arundinacea and F. glaucescens-Differ in the Molecular Response to Drought, While Their Physiological Response Is Similar

Impact of photosynthetic and antioxidant capacities on drought tolerance of two closely related forage grasses, Festuca arundinacea and Festuca glaucescens, was deciphered. Within each species, two genotypes distinct in drought tolerance were subjected to a short-term drought, followed by a subsequent re-watering. The studies were focused on: (i) analysis of plant physiological performance, including: water uptake, abscisic acid (ABA) content, membrane integrity, gas exchange, and relative water content in leaf tissue; (ii) analysis of plant photosynthetic capacity (chlorophyll fluorescence; gene expression, protein accumulation, and activity of selected enzymes of the Calvin cycle); and (iii) analysis of plant antioxidant capacity (reactive oxygen species (ROS) generation; gene expression, protein accumulation and activity of selected enzymes). Though, F. arundinacea and F. glaucescens revealed different strategies in water uptake, and partially also in ABA signaling, their physiological reactions to drought and further re-watering, were similar. On the other hand, performance of the Calvin cycle and antioxidant system differed between the analyzed species under drought and re-watering periods. A stable efficiency of the Calvin cycle in F. arundinacea was crucial to maintain a balanced network of ROS/redox signaling, and consequently drought tolerance. The antioxidant capacity influenced mostly tolerance to stress in F. glaucescens.

Plant growth-promoting bacteria improve leaf antioxidant metabolism of drought-stressed Neotropical trees

Plant growth-promoting bacteria association improved the enzymatic and non-enzymatic antioxidant pathways in Neotropical trees under drought, which led to lower oxidative damage and enhanced drought tolerance in these trees. Water deficit is associated with oxidative stress in plant cells and may, thus, negatively affect the establishment of tree seedlings in reforestation areas. The association with plant growth-promoting bacteria (PGPB) is known to enhance the antioxidant response of crops, but this strategy has not been tested in seedlings of Neotropical trees. We evaluated the effects of inoculation with two PGPB (Azospirillum brasilense and Bacillus sp.) on the antioxidant metabolism of Cecropia pachystachya and Cariniana estrellensis seedlings submitted to drought. We measured the activity of antioxidant enzymes and the content of non-enzymatic antioxidants in leaves, and biometrical parameters of the seedlings. In both tree species, drought decreased the activity of antioxidant enzymes and the content of non-enzymatic antioxidant compounds. For C. pachystachya, the enzymatic and non-enzymatic pathways were mostly influenced by A. brasilense inoculation, which enhanced ascorbate peroxidase (APX) and superoxide dismutase activities and positively affected the level of non-enzymatic antioxidant compounds. In C. estrellensis, A. brasilense inoculation enhanced APX activity. However, A. brasilense and Bacillus sp. inoculation had more influence on the non-enzymatic pathway, as both bacteria induced a greater accumulation of secondary compounds (such as chlorogenic acid, gallic acid, rutin and synapic acid) compared to that in non-inoculated plants under drought. For both species, PGPB improved biometrical parameters related to drought tolerance, as specific leaf area and leaf-area ratio. Our results demonstrate that PGPB induced antioxidant mechanisms in drought-stressed Neotropical trees, increasing drought tolerance. Thus, PGPB inoculation provides a biotechnological alternative to improve the success of reforestation programmes.

Redox homeostasis in the growth zone of the rice leaf plays a key role in cold tolerance

We analysed the cellular and molecular changes in the leaf growth zone of tolerant and sensitive rice varieties in response to suboptimal temperatures. Cold reduced the final leaf length by 35% and 51% in tolerant and sensitive varieties, respectively. Tolerant lines exhibited a smaller reduction of the leaf elongation rate and greater compensation by an increased duration of leaf growth. Kinematic analysis showed that cold reduced cell production in the meristem and the expansion rate in the elongation zone, but the latter was compensated for by a doubling of the duration of cell expansion. We performed iTRAQ proteome analysis on proliferating and expanding parts of the leaf growth zone. We identified 559 and 542 proteins, of which 163 and 210 were differentially expressed between zones, and 96 and 68 between treatments, in the tolerant and sensitive lines, respectively. The categories protein biosynthesis and redox homeostasis were significantly overrepresented in the up-regulated proteins. We therefore measured redox metabolites and enzyme activities in the leaf growth zone, demonstrating that tolerance of rice lines to suboptimal temperatures correlates with the ability to up-regulate enzymatic antioxidants in the meristem and non-enzymatic antioxidants in the elongation zone.

Biomarkers for grain yield stability in rice under drought stress

Crop yield stability requires an attenuation of the reduction of yield losses caused by environmental stresses such as drought. Using a combination of metabolomics and high-throughput colorimetric assays, we analysed central metabolism and oxidative stress status in the flag leaf of 292 indica rice (Oryza sativa) accessions. Plants were grown in the field and were, at the reproductive stage, exposed to either well-watered or drought conditions to identify the metabolic processes associated with drought-induced grain yield loss. Photorespiration, protein degradation, and nitrogen recycling were the main processes involved in the drought-induced leaf metabolic reprogramming. Molecular markers of drought tolerance and sensitivity in terms of grain yield were identified using a multivariate model based on the values of the metabolites and enzyme activities across the population. The model highlights the central role of the ascorbate-glutathione cycle, particularly dehydroascorbate reductase, in minimizing drought-induced grain yield loss. In contrast, malondialdehyde was an accurate biomarker for grain yield loss, suggesting that drought-induced lipid peroxidation is the major constraint under these conditions. These findings highlight new breeding targets for improved rice grain yield stability under drought.

Chitosan Upregulates the Genes of the ROS Pathway and Enhances the Antioxidant Potential of Grape (Vitis vinifera L. 'Touriga Franca' and 'Tinto Cão') Tissues

Chitosan is an environmentally-friendly active molecule that has been explored for numerous agricultural uses. Its use in crop protection is well-known, however, other properties, such as bioactivity, deserve attention. Moreover, the modes of actions of chitosan remain to be elucidated. The present study assessed the levels of total phenolic compounds, the antioxidant potential, and the expression of reactive oxygen species (ROS) scavenging genes in the berries (skins and seeds), leaves, cluster stems, and shoots upon chitosan application on two red grapevine varieties (Touriga Franca and Tinto Cão). The application of chitosan on the whole vine before and after veraison led to the increased levels of polyphenols, anthocyanins, and tannins in Tinto Cão berries, and polyphenols and tannins in Touriga Franca berries, respectively. CUPric Reducing Antioxidant Capacity (CUPRAC) and Ferric Reducing Antioxidant Power (FRAP) assays indicated an increase in the antioxidant potential of berries. With the exception of ascorbate peroxidase (APX), all the ROS pathway genes tested, i.e., iron-superoxide dismutase (Fe-SOD), copper-zinc-superoxide dismutase (Cu/Zn-SOD), catalase (CAT), glutathione reductase (GR), glutaredoxin (Grx), respiratory burst oxidase (Rboh), amine oxidase (AO), peroxidase (POD) and polyphenol oxidase (PPO), were found up-regulated in chitosan-treated berries. Results from the analyses of leaves, stems, and shoots revealed that chitosan not only induced the synthesis of phenolic compounds but also acted as a facilitator for the transfer of polyphenols from the leaves to the berries.

Leaf Production and Expansion: A Generalized Response to Drought Stresses from Cells to Whole Leaf Biomass-A Case Study in the Tomato Compound Leaf

It is clearly established that there is not a unique response to soil water deficit but that there are as many responses as soil water deficit characteristics: Drought intensity, drought duration, and drought position during plant cycle. For a same soil water deficit, responses can also differ on plant genotype within a same species. In spite of this variability, at least for leaf production and expansion processes, robust tendencies can be extracted from the literature when similar watering regimes are compared. Here, we present response curves and multi-scale dynamics analyses established on tomato plants exposed to different soil water deficit treatments. Results reinforce the trends already observed for other species: Reduction in plant leaf biomass under water stress was due to reduction in individual leaf biomass and areas whereas leaf production and specific leaf area were not affected. The dynamics of leaf expansion was modified both at the leaf and cell scales. Cell division and expansion were reduced by drought treatments as well as the endoreduplication process. Combining response curves analyses together with dynamic analyses of tomato compound leaf growth at different scales not only corroborate results on simple leaf responses to drought but also increases our knowledge on the cellular mechanisms behind leaf growth plasticity.

The foliar application of a mixture of semisynthetic chitosan derivatives induces tolerance to water deficit in maize, improving the antioxidant system and increasing photosynthesis and grain yield

Research has shown that chitosan induces plant stress tolerance and protection, but few studies have explored chemical modifications of chitosan and their effects on plants under water stress. Chitosan and its derivatives were applied (isolated or in mixture) to maize hybrids sensitive to water deficit under greenhouse conditions through foliar spraying at the pre-flowering stage. After the application, water deficit was induced for 15 days. Analyses of leaves and biochemical gas exchange in the ear leaf were performed on the first and fifteenth days of the stress period. Production attributes were also analysed at the end of the experiment. In general, the application of the two chitosan derivatives or their mixture potentiated the activities of the antioxidant enzymes superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and guaiacol peroxidase at the beginning of the stress period, in addition to reducing lipid peroxidation (malonaldehyde content) and increasing gas exchange and proline contents at the end of the stress period. The derivatives also increased the content of phenolic compounds and the activity of enzymes involved in their production (phenylalanine ammonia lyase and tyrosine ammonia lyase). Dehydroascorbate reductase and compounds such as total soluble sugars, total amino acids, starch, grain yield and harvest index increased for both the derivatives and chitosan. However, the mixture of derivatives was the treatment that led to the higher increase in grain yield and harvest index compared to the other treatments. The application of semisynthetic molecules derived from chitosan yielded greater leaf gas exchange and a higher incidence of the biochemical conditions that relieve plant stress.

ZmNF-YB16 Overexpression Improves Drought Resistance and Yield by Enhancing Photosynthesis and the Antioxidant Capacity of Maize Plants

ZmNF-YB16 is a basic NF-YB superfamily member and a member of a transcription factor complex composed of NF-YA, NF-YB, and NF-YC in maize. ZmNF-YB16 was transformed into the inbred maize line B104 to produce homozygous overexpression lines. ZmNF-YB16 overexpression improves dehydration and drought stress resistance in maize plants during vegetative and reproductive stages by maintaining higher photosynthesis and increases the maize grain yield under normal and drought stress conditions. Based on the examination of differentially expressed genes between the wild-type (WT) and transgenic lines by quantitative real time PCR (qRT-PCR), ZmNF-YB16 overexpression increased the expression of genes encoding antioxidant enzymes, the antioxidant synthase, and molecular chaperones associated with the endoplasmic reticulum (ER) stress response, and improved protection mechanism for photosynthesis system II. Plants that overexpression ZmNF-YB16 showed a higher rate of photosynthesis and antioxidant enzyme activity, better membrane stability and lower electrolyte leakage under control and drought stress conditions. These results suggested that ZmNF-YB16 played an important role in drought resistance in maize by regulating the expression of a number of genes involved in photosynthesis, the cellular antioxidant capacity and the ER stress response.

Dynamics of metabolic responses to periods of combined heat and drought in Arabidopsis thaliana under ambient and elevated atmospheric CO2

As a consequence of global change processes, plants will increasingly be challenged by extreme climatic events, against a background of elevated atmospheric CO2. We analysed responses of Arabidopsis thaliana to periods of a combination of elevated heat and water deficit at ambient and elevated CO2 in order to gain mechanistic insights regarding changes in primary metabolism. Metabolic changes induced by extremes of climate are dynamic and specific to different classes of molecules. Concentrations of soluble sugars and amino acids increased transiently after short (4-d) exposure to heat and drought, and readjusted to control levels under prolonged (8-d) stress. In contrast, fatty acids showed persistent changes during the stress period. Elevated CO2 reduced the impact of stress on sugar and amino acid metabolism, but not on fatty acids. Integrating metabolite data with transcriptome results revealed that some of the metabolic changes were regulated at the transcriptional level. Multivariate analyses grouped metabolites on the basis of stress exposure time, indicating specificity in metabolic responses to short and prolonged stress. Taken together, the results indicate that dynamic metabolic reprograming plays an important role in plant acclimation to climatic extremes. The extent of such metabolic adjustments is less under high CO2, further pointing towards the role of high CO2 in stress mitigation.

The reduction in maize leaf growth under mild drought affects the transition between cell division and cell expansion and cannot be restored by elevated gibberellic acid levels

Growth is characterized by the interplay between cell division and cell expansion, two processes that occur separated along the growth zone at the maize leaf. To gain further insight into the transition between cell division and cell expansion, conditions were investigated in which the position of this transition zone was positively or negatively affected. High levels of gibberellic acid (GA) in plants overexpressing the GA biosynthesis gene GA20-OXIDASE (GA20OX-1^OE ) shifted the transition zone more distally, whereas mild drought, which is associated with lowered GA biosynthesis, resulted in a more basal positioning. However, the increased levels of GA in the GA20OX-1^OE line were insufficient to convey tolerance to the mild drought treatment, indicating that another mechanism in addition to lowered GA levels is restricting growth during drought. Transcriptome analysis with high spatial resolution indicated that mild drought specifically induces a reprogramming of transcriptional regulation in the division zone. 'Leaf Growth Viewer' was developed as an online searchable tool containing the high-resolution data.

Structure Annotation and Quantification of Wheat Seed Oxidized Lipids by High-Resolution LC-MS/MS

Lipid oxidation is a process ubiquitous in life, but the direct and comprehensive analysis of oxidized lipids has been limited by available analytical methods. We applied high-resolution liquid chromatography-mass spectrometry (LC-MS) and tandem mass spectrometry (MS/MS) to quantify oxidized lipids (glycerides, fatty acids, phospholipids, lysophospholipids, and galactolipids) and implemented a platform-independent high-throughput-amenable analysis pipeline for the high-confidence annotation and acyl composition analysis of oxidized lipids. Lipid contents of 90 different naturally aged wheat (Triticum aestivum) seed stocks were quantified in an untargeted high-resolution LC-MS experiment, resulting in 18,556 quantitative mass-to-charge ratio features. In a posthoc liquid chromatography-tandem mass spectrometry experiment, high-resolution MS/MS spectra (5 mD accuracy) were recorded for 8,957 out of 12,080 putatively monoisotopic features of the LC-MS data set. A total of 353 nonoxidized and 559 oxidized lipids with up to four additional oxygen atoms were annotated based on the accurate mass recordings (1.5 ppm tolerance) of the LC-MS data set and filtering procedures. MS/MS spectra available for 828 of these annotations were analyzed by translating experimentally known fragmentation rules of lipids into the fragmentation of oxidized lipids. This led to the identification of 259 nonoxidized and 365 oxidized lipids by both accurate mass and MS/MS spectra and to the determination of acyl compositions for 221 nonoxidized and 295 oxidized lipids. Analysis of 15-year aged wheat seeds revealed increased lipid oxidation and hydrolysis in seeds stored in ambient versus cold conditions.

Perturbation of Auxin Homeostasis and Signaling by PINOID Overexpression Induces Stress Responses in Arabidopsis

Under normal and stress conditions plant growth require a complex interplay between phytohormones and reactive oxygen species (ROS). However, details of the nature of this crosstalk remain elusive. Here, we demonstrate that PINOID (PID), a serine threonine kinase of the AGC kinase family, perturbs auxin homeostasis, which in turn modulates rosette growth and induces stress responses in Arabidopsis plants. Arabidopsis mutants and transgenic plants with altered PID expression were used to study the effect on auxin levels and stress-related responses. In the leaves of plants with ectopic PID expression an accumulation of auxin, oxidative burst and disruption of hormonal balance was apparent. Furthermore, PID overexpression led to the accumulation of antioxidant metabolites, while pid knockout mutants showed only moderate changes in stress-related metabolites. These physiological changes in the plants overexpressing PID modulated their response toward external drought and osmotic stress treatments when compared to the wild type. Based on the morphological, transcriptome, and metabolite results, we propose that perturbations in the auxin hormone levels caused by PID overexpression, along with other hormones and ROS downstream, cause antioxidant accumulation and modify growth and stress responses in Arabidopsis. Our data provide further proof for a strong correlation between auxin and stress biology.