Friend or foe? Reactive oxygen species production, scavenging and signaling in plant response to environmental stresses

γ-Aminobutyric acid plays a key role in plant acclimation to a combination of high light and heat stress

Plants are frequently subjected to different combinations of abiotic stresses, such as high light (HL) intensity, and elevated temperatures. These environmental conditions pose a threat to agriculture production, affecting photosynthesis, and decreasing yield. Metabolic responses of plants, such as alterations in carbohydrates and amino acid fluxes, play a key role in the successful acclimation of plants to different abiotic stresses, directing resources toward stress responses, and suppressing growth. Here we show that the primary metabolic response of Arabidopsis (Arabidopsis thaliana) plants to HL or heat stress (HS) is different from that of plants subjected to a combination of HL and HS (HL+HS). We further demonstrate that the combined stress results in a unique metabolic response that includes increased accumulation of sugars and amino acids coupled with decreased levels of metabolites participating in the tricarboxylic acid cycle. Among the amino acids exclusively accumulated during HL+HS, we identified the nonproteinogenic amino acid γ-aminobutyric acid (GABA). Analysis of different mutants deficient in GABA biosynthesis (GLUTAMATE DESCARBOXYLASE 3 [gad3]) as well as mutants impaired in autophagy (autophagy-related proteins 5 and 9 [atg5 and atg9]), revealed that GABA plays a key role in the acclimation of plants to HL+HS, potentially by promoting autophagy. Taken together, our findings identify a role for GABA in regulating plant responses to combined stress.

Redox and Hormonal Changes in the Transcriptome of Grape (Vitis vinifera) Berries during Natural Noble Rot Development

Noble rot is a favorable form of the interaction between grape (Vitis spp.) berries and the phytopathogenic fungus Botrytis cinerea. The transcriptome pattern of grapevine cells subject to natural noble rot development in the historic Hungarian Tokaj wine region has not been previously published. Furmint, a traditional white Tokaj variety suited to develop great quality noble rot was used in the experiments. Exploring a subset of the Furmint transcriptome redox and hormonal changes distinguishing between noble rot and bunch rot was revealed. Noble rot is defined by an early spike in abscisic acid (ABA) accumulation and a pronounced remodeling of ABA-related gene expression. Transcription of glutathione S-transferase isoforms is uniquely upregulated, whereas gene expression of some sectors of the antioxidative apparatus (e.g., catalases, carotenoid biosynthesis) is downregulated. These mRNA responses are lacking in berries exposed to bunch rot. Our results help to explain molecular details behind the fine and dynamic balance between noble rot and bunch rot development.

The Reactions of Photosynthetic Capacity and Plant Metabolites of Sedum hybridum L. in Response to Mild and Moderate Abiotic Stresses

In this article, for the first time, an experimental study of the effect of mild and moderate osmotic stress, NaCl content and the effect of low positive temperature on photosynthetic activity and composition of metabolites of immature plants Sedum hybridum L. is reported. In this representative of the genus Sedum adapted to arid conditions and having the properties of a succulent, a change in photosynthetic activity and an increase in the level of protective metabolites in the shoots were revealed when exposed to mild and moderate stress factors. The results of this study can be used in work on the adaptation of succulent plants to arid conditions, environmental monitoring and work on the directed induction of valuable secondary metabolites in succulents to obtain new herbal medicines.

Oligosaccharides production from coprophilous fungi: An emerging functional food with potential health-promoting properties

Functional foods are essential food products that possess health-promoting properties for the treatment of infectious diseases. In addition, they provide energy and nutrients, which are required for growth and survival. They occur as prebiotics or dietary supplements, including oligosaccharides, processed foods, and herbal products. However, oligosaccharides are more efficiently recognized and utilized, as they play a fundamental role as functional ingredients with great potential to improve health in comparison to other dietary supplements. They are low molecular weight carbohydrates with a low degree of polymerization. They occur as fructooligosaccharide (FOS), inulooligosaccharadie (IOS), and xylooligosaccahride (XOS), depending on their monosaccharide units. Oligosaccharides are produced by acid or chemical hydrolysis. However, this technique is liable to several drawbacks, including inulin precipitation, high processing temperature, low yields, and high production costs. As a consequence, the application of microbial enzymes for oligosaccharide production is recognized as a promising strategy. Microbial enzymatic production of FOS and IOS occurs by submerged or solid-state fermentation in the presence of suitable substrates (sucrose, inulin) and catalyzed by fructosyltransferases and inulinases. Incorporation of FOS and IOS enriches the rheological and physiological characteristics of foods. They are used as low cariogenic sugar substitutes, suitable for diabetics, and as prebiotics, probiotics and nutraceutical compounds. In addition, these oligosaccharides are employed as anticancer, antioxidant agents and aid in mineral absorption, lipid metabolism, immune regulation etc. This review, therefore, focuses on the occurrence, physico-chemical characteristics, and microbial enzymatic synthesis of FOS and IOS from coprophilous fungi. In addition, the potential health benefits of these oligosaccharides were discussed in detail.

Unravelling the treasure trove of drought-responsive genes in wild-type peanut through transcriptomics and physiological analyses of root

Peanut is one of the most valuable legumes, grown mainly in arid and semi-arid regions, where its production may be hindered by the lack of water. Therefore, breeding drought tolerant varieties is of great importance for peanut breeding programs around the world. Unlike cultivated peanuts, wild peanuts have greater genetic diversity and are an important source of alleles conferring tolerance/resistance to abiotic and biotic stresses. To decipher the transcriptome changes under drought stress, transcriptomics of roots of highly tolerant Arachis duranensis (ADU) and moderately susceptible A. stenosperma (AST) genotypes were performed. Transcriptome analysis revealed an aggregate of 1465 differentially expressed genes (DEGs), and among the identified DEGs, there were 366 single nucleotide polymorphisms (SNPs). Gene ontology and Mapman analyses revealed that the ADU genotype had a higher number of transcripts related to DNA methylation or demethylation, phytohormone signal transduction and flavonoid production, transcription factors, and responses to ethylene. The transcriptome analysis was endorsed by qRT-PCR, which showed a strong correlation value (R² = 0.96). Physio-biochemical analysis showed that the drought-tolerant plants produced more osmolytes, ROS phagocytes, and sugars, but less MDA, thus attenuating the effects of drought stress. In addition, three SNPs of the gene encoding transcription factor NFAY (Aradu.YE2F8), expansin alpha (Aradu.78HGD), and cytokinin dehydrogenase 1-like (Aradu.U999X) exhibited polymorphism in selected different genotypes. Such SNPs could be useful for the selection of drought-tolerant genotypes.

Uptake of a plasticizer (di-n-butyl phthalate) impacts the biochemical and physiological responses of barley

BACKGROUND

DBP is one of the most commonly used plasticizers for imparting desirable properties to polymers. The introduction of phthalates is reported to have occurred in the late 1920s, and there has been a significant rise in their release into the environment in past decades due to a lack of covalent bonding with the parent matrix. Because of their numerous applications in day-to-day life, phthalates have become ubiquitous and also classified as endocrine disruptors. Hence, several studies have been conducted to investigate the phthalate-mediated toxicities in animals; however, plants have not been explored to the same amount.

METHODS

Therefore, in the present study, the accumulation and translocation along with morpho-physiological perturbations in barley plants after 15, 30, 60, and 120 days of exposure to di-n-butyl phthalate (DBP) are investigated using standard protocols.

RESULTS

The maximal accumulation and translocation of DBP in the roots and shoots of barley plants was observed after 60 days of exposure. The exposure of DBP from 15 to 120 days was recorded to decline all the morphological indices (i.e., dry weight, net primary productivity, seed number per spike, and seed weight) of barley plants. The pigments content declined under DBP treatment for all exposure durations except 120 days exposure. Carbohydrate content increased after 15-30 days of exposure afterward it was observed to be decreased under 60 and 120 days of exposure. The protein content was declined in DBP stressed plants for 15-120 days. Proline content was increased in all exposure durations and maximal percent increase was recorded in 120 days of exposure. MDA content showed an increase at earlier exposure durations then followed by a decline in long-term exposure. Hydrogen peroxide content increased at all exposure durations. There were significant alterations observed in the activities of all antioxidative enzymes in comparison to the control. Furthermore, DBP stressed plants after 60 days were analyzed for the macromolecular variations using Fourier transform infrared spectroscopy (FTIR).

CONCLUSION

Thus, the outcomes of the current work provide an appraisal of phthalates' uptake and translocation mediated phytotoxic responses in barley plants. These observations can help in developing genetically modified edible plants that are resistant to phthalates uptake, thereby ensuring food security.

Unrevealing arsenic and lead toxicity and antioxidant response in spinach: a human health perspective

Arsenic (As) and lead (Pb) are highly toxic and carcinogenic metal(loid)s. The present study evaluated the human exposure risk via estimating As and Pb uptake and physiological/biochemical modifications inside spinach plant grown under metal(loid)-contaminated growth medium. Plants were treated with three levels of each metal(loid) (0, 25 and 125 µM) for four weeks. The spinach plants accumulated high concentration of metal(loid)s in roots (0-18.9 ug g^-1 Pb and 0.2-22.7 ug g^-1 As) and less were translocated towards shoot (0-0.3 ug g^-1 Pb and 0.2-8.8 ug g^-1 As). Metal(loid) accumulation in plants decreased plant biomass and pigment contents and provoked oxidative stress by increased hydrogen peroxide (H₂O₂) production in roots up to 65% and 22%, respectively, for As and Pb. The production of H₂O₂ in leaves was decreased up to 59% and 45%, respectively, for As and Pb than control. Moreover, the antioxidant system (superoxide, catalase, guaiacol peroxidase, ascorbate peroxidase) gets activated under metal(loid) stress. The exposure assessment indices revealed high carcinogenic (CR > 10^-4) and non-carcinogenic (HQ > 1) risks owing to the consumption of As- and Pb-contaminated spinach leaves. Results revealed As is being more toxic to plants and humans than Pb. These findings suggest possible alarming consequences of As and Pb to spinach and their assimilation within the edible tissues.

Condensed tannins as antioxidants that protect poplar against oxidative stress from drought and UV-B

Condensed tannins (CTs, proanthocyanidins) are widespread polymeric flavan-3-ols known for their ability to bind proteins. In poplar (Populus spp.), leaf condensed tannins are induced by both biotic and abiotic stresses, suggesting diverse biological functions. Here we demonstrate the ability of CTs to function as physiological antioxidants, preventing oxidative and cellular damage in response to drought and UV-B irradiation. Chlorophyll fluorescence was used to monitor photosystem II performance, and both hydrogen peroxide and malondialdehyde content was assayed as a measure of oxidative damage. Transgenic MYB-overexpressing poplar (Populus tremula × P. tremuloides) with high CT content showed reduced photosystem damage and lower hydrogen peroxide and malondialdehyde content after drought and UV-B stress. This antioxidant effect of CT was observed using two different poplar MYB CT regulators, in multiple independent lines and different genetic backgrounds. Additionally, low-CT MYB134-RNAi transgenic poplars showed enhanced susceptibility to drought-induced oxidative stress. UV-B radiation had different impacts than drought on chlorophyll fluorescence, but all high-CT poplar lines displayed reduced sensitivity to both stresses. Our data indicate that CTs are significant defences against oxidative stress. The broad distribution of CTs in forest systems that are exposed to diverse abiotic stresses suggests that these compounds have wider functional roles than previously realized.

Nitric Oxide Signaling and Its Association with Ubiquitin-Mediated Proteasomal Degradation in Plants

Nitric oxide (NO) is a versatile signaling molecule with diverse roles in plant biology. The NO-mediated signaling mechanism includes post-translational modifications (PTMs) of target proteins. There exists a close link between NO-mediated PTMs and the proteasomal degradation of proteins via ubiquitylation. In some cases, ubiquitin-mediated proteasomal degradation of target proteins is followed by an NO-mediated post-translational modification on them, while in other cases NO-mediated PTMs can regulate the ubiquitylation of the components of ubiquitin-mediated proteasomal machinery for promoting their activity. Another pathway that links NO signaling with the ubiquitin-mediated degradation of proteins is the N-degron pathway. Overall, these mechanisms reflect an important mechanism of NO signal perception and transduction that reflect a close association of NO signaling with proteasomal degradation via ubiquitylation. Therefore, this review provides insight into those pathways that link NO-PTMs with ubiquitylation.

Potassium signaling in plant abiotic responses: Crosstalk with calcium and reactive oxygen species/reactive nitrogen species

Potassium ion (K⁺) has been regarded as an essential signaling in plant growth and development. K⁺ transporters and channels at transcription and protein levels have been made great progress. K⁺ can enhance plant abiotic stress resistance. Meanwhile, it is now clear that calcium (Ca²⁺), reactive oxygen species (ROS), and reactive nitrogen species (RNS) act as signaling molecules in plants. They regulate plant growth and development and mediate K⁺ transport. However, the interaction of K⁺ with these signaling molecules remains unclear. K⁺ may crosstalk with Ca²⁺ and ROS/RNS in abiotic stress responses in plants. Also, there are interactions among K⁺, Ca²⁺, and ROS/RNS signaling pathways in plant growth, development, and abiotic stress responses. They regulate ion homeostasis, antioxidant system, and stress resistance-related gene expression in plants. Future work needs to focus on the deeper understanding of molecular mechanism of crosstalk among K⁺, Ca²⁺, and ROS/RNS under abiotic stress.

Root hair growth from the pH point of view

Root hairs are tubular outgrowths of epidermal cells that increase the root surface area and thereby make the root more efficient at absorbing water and nutrients. Their expansion is limited to the root hair apex, where growth is reported to take place in a pulsating manner. These growth pulses coincide with oscillations of the apoplastic and cytosolic pH in a similar way as has been reported for pollen tubes. Likewise, the concentrations of apoplastic reactive oxygen species (ROS) and cytoplasmic Ca²⁺ oscillate with the same periodicity as growth. Whereas ROS appear to control cell wall extensibility and opening of Ca²⁺ channels, the role of protons as a growth signal in root hairs is less clear and may differ from that in pollen tubes where plasma membrane H⁺-ATPases have been shown to sustain growth. In this review, we outline our current understanding of how pH contributes to root hair development.

High antioxidant activity of phenolic compounds dampens oxidative stress in Espinosa nothofagi galls induced on Nothofagus obliqua buds

Reactive oxygen species (ROS) are considered the first signaling molecules involved in gall development, linked to the establishment of cyto-histological gradients leading to gall tissue redifferentiation. ROS overproduction induces the failure of gall establishment or its premature senescence. Galls could therefore have efficient mechanisms of ROS dissipation and maintenance of homeostasis, such as polyphenol synthesis. The co-occurrence of ROS and polyphenols in the Espinosa nothofagi galls induced on Nothofagus obliqua buds was explored and was related to the antioxidant capacity of the inner (IC) and outer (OC) gall compartments. We hypothesize that: (i) ROS are produced and accumulated in both tissue compartments of E. nothofagi galls in co-occurrence with polyphenolic, flavonols, and lignin, conferring high antioxidant activity to inner and outer gall tissue compartment; (ii) antioxidant activity is higher in IC related to a higher polyphenol concentration in this compartment. The results show that ROS and polyphenols, mainly flavonols, are produced and accumulated in IC and OC, while lignin accumulated mainly in the IC. In both gall compartments, polyphenols mediate ROS elimination, confirmed by histochemical and spectrophotometry techniques. The IC extract has the highest antioxidant capacity, probably due to lignin deposition and a higher polyphenol concentration in this compartment.

Root Metabolite Differences in Two Maize Varieties Under Lead (Pb) Stress

To assess root metabolic differences of maize varieties in their response to lead (Pb) stress, the lead-tolerant variety Huidan No. 4 and the lead-sensitive variety Ludan No. 8 were tested under Pb-free and Pb-stressed conditions. Changes in metabolites were measured using ultra-performance liquid chromatography-mass spectrometry. Pb stress changed the levels of the amino acids proline, glutamine, lysine, and arginine in both varieties, whereas glutamate and phenylalanine levels changed only in Huidan No. 4. Pb stress altered cystine, valine, methionine, and tryptophan levels only in Ludan No. 8. Therefore, the synthesis and decomposition of amino acids may affect the response of maize to Pb stress. The degree of change in differential metabolites for Huidan No. 4 was greater than that for Ludan No. 8. In cell wall subcellular components, increases in superoxide dismutase (SOD), peroxidases (PODs), and Pb concentrations were greater in Huidan No. 4 than in Ludan No. 8. Therefore, the greater Pb tolerance of Huidan No. 4 could be due to better sequestration of Pb in cell walls and more effective removal of reactive oxygen species (ROS) from the plant. The levels of certain metabolites only increased in Ludan No. 8, indicating that Pb-sensitive varieties may use different metabolic pathways to cope with Pb stress. Both varieties showed increased levels of some metabolites related to antioxidant protection and osmotic regulation. This study provides an understanding of maize Pb tolerance mechanisms and a basis for further development of tools for use in maize breeding.

Inter-Genera Colonization of Ocimum tenuiflorum Endophytes in Tomato and Their Complementary Effects on Na+/K+ Balance, Oxidative Stress Regulation, and Root Architecture Under Elevated Soil Salinity

Endophytic bacilli of ethano-botanical plant Ocimum tenuiflorum were screened for salt stress-alleviating traits in tomato. Four promising O. tenuiflorum endophytes (Bacillus safensis BTL5, Bacillus haynesii GTR8, Bacillus paralicheniformis GTR11, and Bacillus altitudinis GTS16) were used in this study. Confocal scanning laser microscopic studies revealed the inter-genera colonization of O. tenuiflorum endophytes in tomato plants, giving insights for widening the applicability of potential endophytes to other crops. Furthermore, in a pot trial under 150 mM NaCl concentration, the inoculated endophytes contributed in reducing salt toxicity and improving recovery from salt-induced oxidative stress by different mechanisms. Reduction in reactive oxygen species (ROS) (sub-cellular H₂O₂ and superoxide) accumulation was observed besides lowering programmed cell death and increasing chlorophyll content. Endophyte inoculation supplemented the plant antioxidant enzyme system via the modulation of enzymatic antioxidants, viz., peroxidase, ascorbate peroxidase, superoxide dismutase, and catalase, apart from increasing proline and total phenolics. Antioxidants like proline have dual roles of antioxidants and osmoregulation, which might also have contributed to improved water relation under elevated salinity. Root architecture, viz., root length, projection area, surface area, average diameter, tips, forks, crossings, and the number of links, was improved upon inoculation, indicating healthy root growth and enhanced nutrient flow and water homeostasis. Regulation of Na⁺/K⁺ balance and water homeostasis in the plants were also evident from the modulation in the expression of abiotic stress-responsive genes, viz., LKT1, NHX1, SOS1, LePIP2, SlERF16, and SlWRKY39. Shoot tissues staining with light-excitable Na⁺ indicator Sodium Green^TM Tetra (tetramethylammonium) salt showed low sodium transport and accumulation in endophyte-inoculated plants. All four endophytes exhibited different mechanisms for stress alleviation and indicated complementary effects on plant growth. Furthermore, this could be harnessed in the form of a consortium for salt stress alleviation. The present study established inter-genera colonization of O. tenuiflorum endophytes in tomato and revealed its potential in maintaining Na⁺/K⁺ balance, reducing ROS, and improving root architecture under elevated salinity.

Serendipita indica alleviates drought stress responses in walnut (Juglans regia L.) seedlings by stimulating osmotic adjustment and antioxidant defense system

Juglans regia L. is a good host for Serendipita indica. Under drought condition, seedlings colonized with S. indica showed higher values in plant height, total fresh biomass, root/shoot ratio, relative growth rate, leaf relative water content and chlorophyll content, gas exchange parameters, maximal photochemical efficiency, photochemical quenching, and effective photosystem II quantum yield than the uncolonized seedlings. It suggested beneficial effects of S. indica on host plants' growth and physiological parameters in response to drought. In comparison with the uncolonized seedlings, S. indica-colonized seedlings showed lower levels in hydrogen peroxide, superoxide anion, malondialdehyde, and relative electrical conductivity under drought condition, suggesting the ability of S. indica to prevent or retard the accumulation of reactive oxygen species and to diminish the oxidative injure. Furthermore, walnut seedlings responded to drought by actively accumulating osmotic regulation substances including soluble protein, soluble sugar, and proline. Root colonization with S. indica was more conductive to the accumulation. Moreover, in response to drought stress, walnut seedlings, regardless of colonization, increased activities of superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and glutathione reductase, levels of ascorbate and glutathione, and ratios of reduced ascorbate/dehydroascorbic acid and reduced glutathione/oxidized glutathione in leaves and roots. S. indica colonization induced much more increase in the abovementioned indicators as compared to the uncolonized seedlings. Overall, S. indica colonization alleviated the detrimental effects of drought stress by altering root system, enhancing osmotic adjustment, and repressing the accumulation of reactive oxygen species via stimulating antioxidant system including enzymatic and nonenzymatic components. KEY POINTS: • S. indica stimulated root growth of walnut seedlings under drought condition. • S. indica accelerated osmotic adjustment under drought condition. • S. indica activated antioxidant defense mechanism under drought condition.

Stress memory gene FaHSP17.8-CII controls thermotolerance via remodeling PSII and ROS signaling in tall fescue

High temperature is the most limiting factor in the growth of cool-season turfgrass. To cope with high-temperature stress, grass often adopt a memory response by remembering one past recurring stress and preparing a quicker and more robust reaction to the next stress exposure. However, little is known about how stress memory genes regulate the thermomemory response in cool-season turfgrass. Here, we characterized a transcriptional memory gene, Fa-heat shock protein 17.8 Class II (FaHSP17.8-CII) in a cool-season turfgrass species, tall fescue (Festuca arundinacea Schreb.). The thermomemory of FaHSP17.8-CII continued for more than 4 d and was associated with a high H3K4me3 level in tall fescue under heat stress (HS). Furthermore, heat acclimation or priming (ACC)-induced reactive oxygen species (ROS) accumulation and photosystem II (PSII) electron transport were memorable, and this memory response was controlled by FaHSP17.8-CII. In the fahsp17.8-CII mutant generated using CRISPR/Cas9, ACC+HS did not substantially block the ROS accumulation, the degeneration of chloroplast ultra-structure, and the inhibition of PSII activity compared with HS alone. However, overexpression of FaHSP17.8-CII in tall fescue reduced ROS accumulation and chloroplast ultra-structure damage, and improved chlorophyll content and PSII activity under ACC+HS compared with that HS alone. These findings unveil a FaHSP17.8-CII-PSII-ROS module regulating transcriptional memory to enhance thermotolerance in cool-season turfgrass.

Low-Phytotoxic Deep Eutectic Systems as Alternative Extraction Media for the Recovery of Chitin from Brown Crab Shells

The versatility of chitin and its derivatives has allowed their utilization in a wide range of applications, from wastewater treatment to pharmaceutical or biomedical industries. However, even though the extraction method used industrially is extremely efficient, it involves the use of strong acids and bases and results in the disposal of large quantities of toxic effluents. Deep eutectic systems (DESs) have emerged as a promising new class of alternative solvents, including for chitin recovery. Yet, the assessment of their toxicity has often been neglected. Therefore, in this work, the phytotoxicity of choline chloride (ChCl)/organic acid-based DESs toward wheat seeds was evaluated by measuring different growth parameters and stress biomarkers. DESs were then explored for the efficient recovery of chitin contained in brown crab shell residues at varying conditions of temperature and processing time as well as with and without water addition. The obtained chitin was then characterized through different analytical techniques and compared to a standard as well as to chitin obtained by a conventional acid/alkaline hydrolysis. Results have shown that by applying a ChCl/lactic acid-based DES (which was the system that showed the least phytotoxic effects on wheat; EC50 ≥ 1.6 mg/mL) at 130 °C, it was possible to obtain pure chitin (up to 98%) with characteristics similar to those presented by commercial chitin or chitin recovered by conventional hydrolysis in a shorter time (more than 8-fold faster), thus suggesting that ChCl/organic acid-based DESs can truly represent a low-phytotoxic alternative extraction media for the recovery of chitin from the crab shell biomass.

Antioxidative Responses of Duckweed (Lemna minor L.) to Phenol and Rhizosphere-Associated Bacterial Strain Hafnia paralvei C32-106/3

Duckweed (L. minor) is a cosmopolitan aquatic plant of simplified morphology and rapid vegetative reproduction. In this study, an H. paralvei bacterial strain and its influence on the antioxidative response of the duckweeds to phenol, a recalcitrant environmental pollutant, were investigated. Sterile duckweed cultures were inoculated with H. paralvei in vitro and cultivated in the presence or absence of phenol (500 mg L⁻¹), in order to investigate bacterial effects on plant oxidative stress during 5 days. Total soluble proteins, guaiacol peroxidase expression, concentration of hydrogen peroxide and malondialdehyde as well as the total ascorbic acid of the plants were monitored. Moreover, bacterial production of indole-3-acetic acid (IAA) was measured in order to investigate H. paralvei’s influence on plant growth. In general, the addition of phenol elevated all biochemical parameters in L. minor except AsA and total soluble proteins. Phenol as well as bacteria influenced the expression of guaiacol peroxidase. Different isoforms were associated with phenol compared to isoforms expressed in phenol-free medium. Considering that duckweeds showed increased antioxidative parameters in the presence of phenol, it can be assumed that the measured parameters might be involved in the plant’s defense system. H. paralvei is an IAA producer and its presence in the rhizosphere of duckweeds decreased the oxidative stress of the plants, which can be taken as evidence that this bacterial strain acts protectively on the plants during phenol exposure.

Soil Salinity, a Serious Environmental Issue and Plant Responses: A Metabolomics Perspective

The effects of global warming have increasingly led to devastating environmental stresses, such as heat, salinity, and drought. Soil salinization is a serious environmental issue and results in detrimental abiotic stress, affecting 7% of land area and 33% of irrigated lands worldwide. The proportion of arable land facing salinity is expected to rise due to increasing climate change fuelled by anthropogenic activities, exacerbating the threat to global food security for the exponentially growing populace. As sessile organisms, plants have evolutionarily developed mechanisms that allow ad hoc responses to salinity stress. The orchestrated mechanisms include signalling cascades involving phytohormones, kinases, reactive oxygen species (ROS), and calcium regulatory networks. As a pillar in a systems biology approach, metabolomics allows for comprehensive interrogation of the biochemistry and a deconvolution of molecular mechanisms involved in plant responses to salinity. Thus, this review highlights soil salinization as a serious environmental issue and points to the negative impacts of salinity on plants. Furthermore, the review summarises mechanisms regulating salinity tolerance on molecular, cellular, and biochemical levels with a focus on metabolomics perspectives. This critical synthesis of current literature is an opportunity to revisit the current models regarding plant responses to salinity, with an invitation to further fundamental research for novel and actionable insights.

Harnessing Chlorophyll Fluorescence for Phenotyping Analysis of Wild and Cultivated Tomato for High Photochemical Efficiency under Water Deficit for Climate Change Resilience

Fluctuations of the weather conditions, due to global climate change, greatly influence plant growth and development, eventually affecting crop yield and quality, but also plant survival. Since water shortage is one of the key risks for the future of agriculture, exploring the capability of crop species to grow with limited water is therefore fundamental. By using chlorophyll fluorescence analysis, we evaluated the responses of wild tomato accession Solanum pennellii LA0716, Solanum lycopersicum cv. Μ82, the introgression line IL12-4 (from cv. M82 Χ LA0716), and the Greek tomato cultivars cv. Santorini and cv. Zakinthos, to moderate drought stress (MoDS) and severe drought stress (SDS), in order to identify the minimum irrigation level for efficient photosynthetic performance. Agronomic traits (plant height, number of leaves and root/shoot biomass), relative water content (RWC), and lipid peroxidation, were also measured. Under almost 50% deficit irrigation, S. pennellii exhibited an enhanced photosynthetic function by displaying a hormetic response of electron transport rate (ETR), due to an increased fraction of open reaction centers, it is suggested to be activated by the low increase of reactive oxygen species (ROS). A low increase of ROS is regarded to be beneficial by stimulating defense responses and also triggering a more oxidized redox state of quinone A (QA), corresponding in S. pennellii under 50% deficit irrigation, to the lowest stomatal opening, resulting in reduction of water loss. Solanumpennellii was the most tolerant to drought, as it was expected, and could manage to have an adequate photochemical function with almost 30% water regime of well-watered plants. With 50% deficit irrigation, cv. Μ82 and cv. Santorini did not show any difference in photochemical efficiency to control plants and are recommended to be cultivated under deficit irrigation as an effective strategy to enhance agricultural sustainability under a global climate change. We conclude that instead of the previously used Fv/Fm ratio, the redox state of QA, as it can be estimated by the chlorophyll fluorescence parameter 1 - qL, is a better indicator to evaluate photosynthetic efficiency and select drought tolerant cultivars under deficit irrigation.

FaHSP17.8-CII orchestrates lead tolerance and accumulation in shoots via enhancing antioxidant enzymatic response and PSII activity in tall fescue

Tall fescue (Festuca arundinacea Schreb.) shows huge potential for lead (Pb) phytoremediation, while little is known on the molecular mechanisms involved in Pb tolerance and accumulation. Here, genetic engineering strategy was firstly used to investigate Pb tolerance and accumulation in tall fescue. The transgenic tall fescue overexpressing a class II (CII) sHSP gene FaHSP17.8-CII was generated. After exposure to 1000 mg/L Pb(NO₃)₂, two FaHSP17.8-CII overexpressing lines, OE#3 and OE#7, showed higher tolerance to Pb as illustrated by the reduced levels of electrolyte leakage (EL) and malondialdehyde (MDA) as compared to the wild-type (WT) plants under Pb stress. Moreover, the FaHSP17.8-CII overexpression lines, OE#3 and OE#7, exhibited 36.3% and 46.6% higher shoot Pb accumulation relative to the WT grasses. When the grasses were exposed to Pb stress, the two OE lines had higher CAT, POD and SOD activities as compared to WT. Additionally, overexpression of FaHSP17.8-CII improved the synthesis of chlorophyll and transcript abundance of FapsbC, FapsbD and FapsbE, and alleviated the photoinhibition of PSII in tall fescue under Pb stress. This study provides an initial genetic engineering strategy to improve Pb phytoremediation efficiency in tall fescue by FaHSP17.8-CII overexpression.

Cross-Talks Between Macro- and Micronutrient Uptake and Signaling in Plants

In nature, land plants as sessile organisms are faced with multiple nutrient stresses that often occur simultaneously in soil. Nitrogen (N), phosphorus (P), sulfur (S), zinc (Zn), and iron (Fe) are five of the essential nutrients that affect plant growth and health. Although these minerals are relatively inaccessible to plants due to their low solubility and relative immobilization, plants have adopted coping mechanisms for survival under multiple nutrient stress conditions. The double interactions between N, Pi, S, Zn, and Fe have long been recognized in plants at the physiological level. However, the molecular mechanisms and signaling pathways underlying these cross-talks in plants remain poorly understood. This review preliminarily examined recent progress and current knowledge of the biochemical and physiological interactions between macro- and micro-mineral nutrients in plants and aimed to focus on the cross-talks between N, Pi, S, Zn, and Fe uptake and homeostasis in plants. More importantly, we further reviewed current studies on the molecular mechanisms underlying the cross-talks between N, Pi, S, Zn, and Fe homeostasis to better understand how these nutrient interactions affect the mineral uptake and signaling in plants. This review serves as a basis for further studies on multiple nutrient stress signaling in plants. Overall, the development of an integrative study of multiple nutrient signaling cross-talks in plants will be of important biological significance and crucial to sustainable agriculture.

Selenium restores mitochondrial dysfunction to reduce Cr-induced cell apoptosis in Chinese cabbage (Brassica campestris L. ssp. Pekinensis) root tips

Chromium (Cr) disrupts the growth and physiology of plants. Selenium (Se) is considered as a promising option to help plants ameliorate Cr toxicity. To investigate the effects of exogenous Se on reactive oxygen species (ROS) burst and programmed cell death (PCD) in root tip cells under Cr stress, hydroponic experiments were carried out with Chinese cabbage seedlings grown in Hoagland solution containing 1 mg L^-1 Cr and 0.1 mg L^-1 Se. Results showed that Se scavenged the overproduction of H₂O₂ and O₂^－·, and alleviated the level of lipid peroxidation in root tips stressed by Cr. Moreover, Se effectively prevented DNA degradation and reduced the number of apoptotic cells in root tips. Compared with Cr treatment, Se supplementation reduced the content of ROS and malondialdehyde in mitochondria by 38.23% and 17.52%, respectively. Se application decreased the opening degree of mitochondrial permeability transition pores by 32.30%, increased mitochondrial membrane potential by 40.91%, alleviated the release of cyt c from mitochondria into cytosol by 18.42% and caused 57.40% decrease of caspase 3-like protease activity, and thus restored mitochondrial dysfunction caused by Cr stress. In addition, the alteration of Se on mitochondrial physiological properties maintained calcium homeostasis between mitochondria and cytosol, which further contributed to reducing the appearance of Cr-induced PCD. Findings suggested that Se restored mitochondrial dysfunction, which further rescued root tip cells from PCD, consequently activating defense strategies to protect plants from Cr toxicity and maintaining plant growth.

Adaptive Mechanisms of Halophytes and Their Potential in Improving Salinity Tolerance in Plants

Soil salinization, which is aggravated by climate change and inappropriate anthropogenic activities, has emerged as a serious environmental problem, threatening sustainable agriculture and future food security. Although there has been considerable progress in developing crop varieties by introducing salt tolerance-associated traits, most crop cultivars grown in saline soils still exhibit a decline in yield, necessitating the search for alternatives. Halophytes, with their intrinsic salt tolerance characteristics, are known to have great potential in rehabilitating salt-contaminated soils to support plant growth in saline soils by employing various strategies, including phytoremediation. In addition, the recent identification and characterization of salt tolerance-related genes encoding signaling components from halophytes, which are naturally grown under high salinity, have paved the way for the development of transgenic crops with improved salt tolerance. In this review, we aim to provide a comprehensive update on salinity-induced negative effects on soils and plants, including alterations of physicochemical properties in soils, and changes in physiological and biochemical processes and ion disparities in plants. We also review the physiological and biochemical adaptation strategies that help halophytes grow and survive in salinity-affected areas. Furthermore, we illustrate the halophyte-mediated phytoremediation process in salinity-affected areas, as well as their potential impacts on soil properties. Importantly, based on the recent findings on salt tolerance mechanisms in halophytes, we also comprehensively discuss the potential of improving salt tolerance in crop plants by introducing candidate genes related to antiporters, ion transporters, antioxidants, and defense proteins from halophytes for conserving sustainable agriculture in salinity-prone areas.

Pest and disease management by red light

Light is essential for plant life. It provides a source of energy through photosynthesis and regulates plant growth and development and other cellular processes, such as by controlling the endogenous circadian clock. Light intensity, quality, duration and timing are all important determinants of plant responses, especially to biotic stress. Red light can positively influence plant defence mechanisms against different pathogens, but the molecular mechanism behind this phenomenon is not fully understood. Therefore, we reviewed the impact of red light on plant biotic stress responses against viruses, bacteria, fungi and nematodes, with a focus on the physiological effects of red light treatment and hormonal crosstalk under biotic stress in plants. We found evidence suggesting that exposing plants to red light increases levels of salicylic acid (SA) and induces SA signalling mediating the production of reactive oxygen species, with substantial differences between species and plant organs. Such changes in SA levels could be vital for plants to survive infections. Therefore, the application of red light provides a multidimensional aspect to developing innovative and environmentally friendly approaches to plant and crop disease management.

Fe acquisition at the crossroad of calcium and reactive oxygen species signaling

Due to its redox properties, iron is both essential and toxic. Therefore, soil iron availability variations pose a significant problem for plants. Recent evidence suggests that calcium and reactive oxygen species coordinate signaling events related to soil iron acquisition. Calcium was found to affect directly IRT1-mediated iron import through the lipid-binding protein EHB1 and to trigger a CBL-CIPK-mediated signaling influencing the activity of the key iron-acquisition transcription factor FIT. In parallel, under prolonged iron deficiency, reactive oxygen species both inhibit FIT function and depend on FIT through the function of the catalase CAT2. We discuss the role of calcium and reactive oxygen species signaling in iron acquisition, with post-translational mechanisms influencing the localization and activity of iron-acquisition regulators and effectors.

In the tripartite combination ozone-poplar-Chrysomela populi, the pollutant alters the plant-insect interaction via primary metabolites of foliage

Ozone (O₃)-induced metabolic changes in leaves are relevant and may have several ecological significances. Here, variations in foliar chemistry of two poplar clones (Populus deltoides × maximowiczii, Eridano, and P. × euramericana, I-214) under a chronic O₃ treatment (80 ppb, 5 h d^-1 for 10 consecutive days) were investigated. The aim was to elucidate if leaf age and/or O₃-sensitivity (considering Eridano and I-214 as O₃-sensitive and O₃-resistant, respectively) can affect suitability of poplar foliage for Chrysomela populi L. (Coleoptera Chrysomelidae), in terms of palatability. Comparing controls, only low amino acid (AA) contents were reported in Eridano [about 3- and 4-fold in mature and young leaves (ML and YL, respectively)], and all the investigated primary metabolites [i.e. water soluble carbohydrates (WSC), proteins (Prot) and AA] were higher in YL than in ML of I-214 (+23, +54 and + 20%, respectively). Ozone increased WSC only in YL of Eridano (+24%, i.e. highest values among samples; O₃ effects are always reported comparing O₃-treated plants with the related controls). A concomitant decrease of Prot was observed in both ML and YL of Eridano, while only in YL of I-214 (-41, -45 and -51%, respectively). In addition, O₃ decreased AA in YL of Eridano and in ML of I-214 (-40 and -14%, respectively). Comparing plants maintained under charcoal-filtered air, total ascorbate (Asc) was lower in Eridano in both ML and YL (around -22%), and abscisic acid (ABA) was similar between clones; furthermore, higher levels of Asc were reported in YL than in ML of Eridano (+19%). Ozone increased Asc and ABA (about 2- and 3-fold, respectively) in both ML and YL of Eridano, as well as ABA in YL of I-214 (about 2-fold). Comparing leaves maintained under charcoal-filtered air, the choice feeding test showed that the 2nd instar larvae preferred YL, and the quantity of YL consumed was 9 and 4-fold higher than ML in Eridano and I-214, respectively. Comparing leaves exposed to O₃-treatment, a significant feeding preference for YL disks was also observed, regardless of the clone. The no-choice feeding test showed that larval growth was slightly higher on untreated YL than on untreated ML (+19 and + 10% in Eridano and I-214, respectively). The body mass of larvae fed with O₃-treated YL was also significantly higher than that of larvae fed with untreated YL (3- and 2-fold in Eridano and I-214). This study highlights that realistic O₃ concentrations can significantly impact the host/insect interactions, a phenomenon dependent on leaf age and O₃-sensitivity of the host.

Genome-wide identification of ascorbate-glutathione cycle gene families in soybean (Glycine max) reveals gene duplication events and specificity of gene members linked to development and stress conditions

Ascorbate-glutathione (AsA-GSH) cycle plays an important role in tuning beneficial ROS accumulation for intracellular signals and imparts plant tolerance to oxidative stress by detoxifying excess of ROS. Here, we present genome-wide identification of AsA-GSH cycle genes (APX, MDHAR, DHAR, and GR) in several leguminous species and expression analyses in G. max during stress, germination and tissue development. Our data revealed 24 genes in Glycine genus against the maximum of 15 in other leguminous species, which was due to 9 pars of duplicated genes mostly originated from sub/neofunctionalization. Cytosolic APX and MDHAR genes were highly expressed in different tissues and physiological conditions. Germination induced genes encoding AsA-GSH proteins from different cell compartments, whereas vegetative phase (leaves) stimulated predominantly genes related to chloroplast/mitochondria proteins. Moreover, cytosolic APX-1, 2, MDHAR-1a, 1b and GR genes were the primary genes linked to senescence and biotic stresses, while stAPX-a, b and GR (from organelles) were the most abiotic stress related genes. Biotic and abiotic stress tolerant genotypes generally showed increased MDHAR, DHAR and/or GR mRNA levels compared to susceptible genotypes. Overall, these data clarified evolutionary events in leguminous plants and point to the functional specificity of duplicated genes of the AsA-GSH cycle in G. max.

Differential Regulation of NAPDH Oxidases in Salt-Tolerant Eutrema salsugineum and Salt-Sensitive Arabidopsis thaliana

Reactive oxygen species (ROS) signalling is crucial in modulating stress responses in plants, and NADPH oxidases (NOXs) are an important component of signal transduction under salt stress. The goal of this research was to investigate whether the regulation of NOX-dependent signalling during mild and severe salinity differs between the halophyte Eutrema salsugineum and the glycophyte Arabidopsis thaliana. Gene expression analyses showed that salt-induced expression patterns of two NOX genes, RBOHD and RBOHF, varied between the halophyte and the glycophyte. Five days of salinity stimulated the expression of both genes in E. salsugineum leaves, while their expression in A. thaliana decreased. This was not accompanied by changes in the total NOX activity in E. salsugineum, while the activity in A. thaliana was reduced. The expression of the RBOHD and RBOHF genes in E. salsugineum leaves was induced by abscisic acid (ABA) and ethephon spraying. The in silico analyses of promoter sequences of RBOHD and RBOHF revealed multiple cis-acting elements related to hormone responses, and their distribution varied between E. salsugineum and A. thaliana. Our results indicate that, in the halophyte E. salsugineum, the maintenance of the basal activity of NOXs in leaves plays a role during acclimation responses to salt stress. The different expression patterns of the RBOHD and RBOHF genes under salinity in E. salsugineum and A. thaliana point to a modified regulation of these genes in the halophyte, possibly through ABA- and/or ethylene-dependent pathways.

The effects of base station as an electromagnetic radiation source on flower and cone yield and germination percentage in Pinus brutia Ten

Electromagnetic radiation is a substantial pollution factor that most of the living things found almost everywhere are constantly exposed to with current technology. The number of studies conducted on the effects of this exposed radiation on the living things constantly is limited; and almost all of the studies conducted are aimed at measuring the effects of short-term exposure. In addition to this, most of the studies conducted on plants focus on herbaceous plant species. In this study, the effects of distance to base station on flower and cone yield and germination percentage were investigated in Pinus brutia individuals, one of the critical forest tree species. The study results revealed that being close to the base station significantly reduced the number of flowers and cones in P. brutia individuals, and that the values obtained in individuals at a distance of 800 m from the base station were 11 times more than the number of flowers and 7 times more than the number of cones compared to the individuals at a distance of 100 m. In the seeds subject to the study, there is a three-times difference in terms of the germination percentage among the individuals located at the furthest and closest distance to the base station. These results show that P. brutia individuals are considerably affected by the base station.

Heat shock treatment maintains the quality attributes of postharvest jujube fruits and delays their senescence process during cold storage

The effects of heat shock (HT), 1-methylcyclopropene (1-MCP), or their combination (HT + 1-MCP) on the quality of fresh jujube fruits during cold storage were studied. Among them, HT showed the best preservation effect on jujube fruits, which was more effective than others in inhibiting the increase of red index, decay incidence, and weight loss and delaying the decrease of firmness, soluble solids content (SSC), titratable acidity (TA), and ascorbic acid (AsA) content. Besides, it could delay the degradation rate of the cell wall to maintain the integrity of cell membrane, and keep the high activity of active oxygen scavenging enzymes. During cold storage, malondialdehyde (MDA) content and relative electrolyte leakage (REL) of the HT group were significantly lower than those of the control group, 1-MCP, and HT + 1-MCP group (p < .05), while superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities were significantly higher than those of other groups (p < .05). It was concluded that the postharvest HT treatment could effectively delay the senescence and decay of jujube fruits. PRACTICAL APPLICATIONS: Jujube fruits have high nutritional value used for food and medicine. However, they are not tolerant to storage after harvest, resulting in high economic losses. Therefore, it is of great significance to find a suitable method to maintain the quality of jujube fruits. Our results revealed the effect of HT, 1-MCP, and their combination on the quality maintenance of jujube fruits, and found that HT could effectively maintain the quality of them, which could be used as an effective method for keeping jujube fruits fresh.

Changes in Antioxidative Compounds and Enzymes in Small-Leaved Linden (Tilia cordata Mill.) in Response to Mistletoe (Viscum album L.) Infestation

Mistletoe infestation leads to a decrease in the growth of woody plants, their longevity, and partial or complete drying of the top, as well as premature death. Various environmental stress factors, both abiotic and biotic, stimulate the formation of reactive oxygen species and the development of oxidative stress in plant tissues. This study aimed to investigate the effect of mistletoe (Viscum album L.) infestation on the response of the antioxidative defense system in leaves of small-leaved linden (Tilia cordata Mill.). Leaves from infested trees were taken from branches (i) without mistletoe, (ii) with 1–2 mistletoe bushes (low degree of infestation), and (iii) with 5–7 mistletoe bushes (high degree of infestation). The relative water content and the chlorophyll a and b contents in leaves from linden branches affected by mistletoe were significantly lower than those in leaves from non-infested trees and from host-tree branches with no mistletoe. At the same time, leaves from branches with low and high degrees of infestation had significantly higher electrolyte leakage, malondialdehyde and hydrogen peroxide content, oxidized forms of ascorbic acid (dehydroascorbic and 2,3-diketogulonic acids), and oxidized glutathione. The results of principal component analysis show that the development of oxidative stress was accompanied by an increase in proline content and in superoxide dismutase, ascorbate peroxidase, glutathione peroxidase, and glutathione reductase activity. Several biochemical parameters (proline, ascorbic acid, dehydroascorbic acid, glutathione, glutathione peroxidase, ascorbate peroxidase, and dehydroascorbate reductase) were found to be altered in leaves from host-tree branches with no mistletoe. This result indicates that the mistletoe infestation of trees not only causes local changes in the locations of hemiparasite attachment, but also affects the redox metabolism in leaves from other parts of the infested tree.

Overexpression of FaHSP17.8-CII improves cadmium accumulation and tolerance in tall fescue shoots by promoting chloroplast stability and photosynthetic electron transfer of PSII

Genetic improvement could play a significant role in enhancing the Cd accumulation, translocation and tolerance in plants. In this study, for the first time, we constructed transgenic tall fescue overexpressing a class II (CII) sHSP gene FaHSP17.8-CII, which enhanced Cd tolerance and the root-to-shoot Cd translocation. After exposed to 400 μM CdCl₂, two FaHSP17.8-CII overexpressing lines (OE#3 and OE#7) exhibited 30% and 40% more shoot fresh weight, respectively, relative to the wild-type (WT). Both transgenic lines showed higher tolerance to Cd, as evidenced by lower levels of electrolyte leakage and malondialdehyde compared to the WT plants under Cd stress. FaHSP17.8-CII overexpression increased shoot Cd contents 49-59% over the WT plants. The Cd translocation factor of root-to-shoot in OE grasses was 69-85% greater than WT under Cd stress. Furthermore, overexpression of FaHSP17.8-CII reduced Cd-induced damages of chloroplast ultra-structure and chlorophyll synthesis, and then improved photosystem II (PSII) function under Cd stress, which resulted in less reactive oxygen species (ROS) accumulation in OE grasses than that in WT exposed to Cd stress. The study suggests a novel FaHSP17.8-CII-PSII-ROS module to understand the mechanisms of Cd detoxification and tolerance, which provides a new strategy to improve phytoremediation efficiency in Cd-stressed grasses.

The Alkali Tolerance of Broomcorn Millet (Panicum miliaceum L.) at the Germination and Seedling Stage: The Case of 296 Broomcorn Millet Genotypes

Broomcorn millet (BM), one of the earliest domesticated cereal crops originating in northern China, can tolerate extreme conditions, such as drought and high temperatures, which are prevalent in saline-alkali, arid, and barren landscapes. However, its adaptive mechanism to alkali stress is yet to be comprehensively understood. In this study, 80 and 40 mM standard alkali stress concentrations were used to, respectively, evaluate the alkali tolerance at the germination and seedling stages of 296 BM genotypes. Principal component analysis (PCA), Pearson's correlation analysis, and F-value comprehensive analysis were performed on the germination parameters (germination potential, germination index, germination rate, vigor index, root length/weight, sprout length/weight, and alkali damage rate). Based on their respective F-values, the BM genotypes were divided into five categories ranging from highly alkali resistant to alkali sensitive. To study the response of seedlings to alkaline stress, we investigated the phenotypic parameters (plant height, green leaf area, biomass, and root structure) of 111 genotypes from the above five categories. Combining the parameters of alkali tolerance at the germination and seedling stages, these 111 genotypes were further subdivided into three groups with different alkali tolerances. Variations in physiological responses of the different alkali-tolerant genotypes were further investigated for antioxidant enzyme activity, soluble substances, malondialdehyde (MDA) content, electrolyte leakage rate, and leaf structure. Compared with alkali-sensitive genotypes, alkali-tolerant genotypes had high antioxidant enzyme activity and soluble osmolyte content, low MDA content and electrolyte leakage rate, and a more complete stomata structure. Taken together, this study provides a comprehensive and reliable method for evaluating alkali tolerance and will contribute to the improvement and restoration of saline-alkaline soils by BM.

Role of Reactive Oxygen Species and Hormones in Plant Responses to Temperature Changes

Temperature stress is one of the major abiotic stresses that adversely affect agricultural productivity worldwide. Temperatures beyond a plant's physiological optimum can trigger significant physiological and biochemical perturbations, reducing plant growth and tolerance to stress. Improving a plant's tolerance to these temperature fluctuations requires a deep understanding of its responses to environmental change. To adapt to temperature fluctuations, plants tailor their acclimatory signal transduction events, and specifically, cellular redox state, that are governed by plant hormones, reactive oxygen species (ROS) regulatory systems, and other molecular components. The role of ROS in plants as important signaling molecules during stress acclimation has recently been established. Here, hormone-triggered ROS produced by NADPH oxidases, feedback regulation, and integrated signaling events during temperature stress activate stress-response pathways and induce acclimation or defense mechanisms. At the other extreme, excess ROS accumulation, following temperature-induced oxidative stress, can have negative consequences on plant growth and stress acclimation. The excessive ROS is regulated by the ROS scavenging system, which subsequently promotes plant tolerance. All these signaling events, including crosstalk between hormones and ROS, modify the plant's transcriptomic, metabolomic, and biochemical states and promote plant acclimation, tolerance, and survival. Here, we provide a comprehensive review of the ROS, hormones, and their joint role in shaping a plant's responses to high and low temperatures, and we conclude by outlining hormone/ROS-regulated plant responsive strategies for developing stress-tolerant crops to combat temperature changes.

Characterization of Dynamic Regulatory Gene and Protein Networks in Wheat Roots Upon Perceiving Water Deficit Through Comparative Transcriptomics Survey

A well-developed root system benefits host plants by optimizing water absorption and nutrient uptake and thereby increases plant productivity. In this study we have characterized the root transcriptome using RNA-seq and subsequential functional analysis in a set of drought tolerant and susceptible genotypes. The goal of the study was to elucidate and characterize water deficit-responsive genes in wheat landraces that had been through long-term field and biochemical screening for drought tolerance. The results confirm genotype differences in water-deficit tolerance in line with earlier results from field trials. The transcriptomics survey highlighted a total of 14,187 differentially expressed genes (DEGs) that responded to water deficit. The characterization of these genes shows that all chromosomes contribute to water-deficit tolerance, but to different degrees, and the B genome showed higher involvement than the A and D genomes. The DEGs were mainly mapped to flavonoid, phenylpropanoid, and diterpenoid biosynthesis pathways, as well as glutathione metabolism and hormone signaling. Furthermore, extracellular region, apoplast, cell periphery, and external encapsulating structure were the main water deficit-responsive cellular components in roots. A total of 1,377 DEGs were also predicted to function as transcription factors (TFs) from different families regulating downstream cascades. TFs from the AP2/ERF-ERF, MYB-related, B3, WRKY, Tify, and NAC families were the main genotype-specific regulatory factors. To further characterize the dynamic biosynthetic pathways, protein-protein interaction (PPI) networks were constructed using significant KEGG proteins and putative TFs. In PPIs, enzymes from the CYP450, TaABA8OH2, PAL, and GST families play important roles in water-deficit tolerance in connection with MYB13-1, MADS-box, and NAC transcription factors.

Strigolactones regulate arsenate uptake, vacuolar-sequestration and antioxidant defense responses to resist arsenic toxicity in rice roots

We explored genetic evidence for strigolactones' role in rice tolerance to arsenate-stress. Comparative analyses of roots of wild-type (WT) and strigolactone-deficient mutants d10 and d17 in response to sodium arsenate (Na₂AsO₄) revealed differential growth inhibition [WT (11.28%) vs. d10 (19.76%) and d17 (18.03%)], biomass reduction [(WT (33.65%) vs. d10 (74.86%) and d17 (60.65%)] and membrane damage (WT < d10 and d17) at 250 μM Na₂AsO₄. Microscopic and biochemical analyses showed that roots of WT accumulated lower levels of arsenic and oxidative stress indicators like reactive oxygen species and malondialdehyde than those of strigolactone-deficient mutants. qRT-PCR data indicated lower expression levels of genes (OsPT1, OsPT2, OsPT4 and OsPT8) encoding phosphate-transporters in WT roots than mutant roots, explaining the decreased arsenate and phosphate uptake by WT roots. Increased levels of glutathione and OsPCS1 and OsABCC1 transcripts indicated an efficient vacuolar-sequestration of arsenic in WT roots. Furthermore, higher activities (transcript levels) of SOD (OsCuZnSOD1 and OsCuZnSOD2), APX (OsAPX1 and OsAPX2) and CAT (OsCATA) corresponded to lower oxidative damage in WT roots compared with strigolactone-mutant roots. Collectively, these results highlight that strigolactones are involved in arsenic-stress mitigation by regulating arsenate-uptake, glutathione-biosynthesis, vacuolar-sequestration of arsenic and antioxidant defense responses in rice roots.

Role of ethylene and light in chitosan-induced local and systemic defence responses of tomato plants

Plant defence responses can be triggered by the application of elicitors for example chitosan (β-1,4-linked glucosamine; CHT). It is well-known that CHT induces rapid, local production of reactive oxygen species (ROS) and nitric oxide (NO) resulting in fast stomatal closure. Systemic defence responses are based primarily on phytohormones such as ethylene (ET) and salicylic acid (SA), moreover on the expression of hormone-mediated defence genes and proteins. At the same time, these responses can be dependent also on external factors, such as light but its role was less-investigated. Based on our result in intact tomato plants (Solanum lycopersicum L.), CHT treatment not only induced significant ET emission and stomatal closure locally but also promoted significant production of superoxide which was also detectable in the distal, systemic leaves. However, these changes in ET and superoxide accumulation were detected only in wild type (WT) plants kept in light and were inhibited under darkness as well as in ET receptor Never ripe (Nr) mutants suggesting pivotal importance of ET and light in inducing resistance both locally and systemically upon CHT. Interestingly, CHT-induced NO production was mostly independent of ET or light. At the same time, expression of Pathogenesis-related 3 (PR3) was increased locally in both genotypes in the light and in WT leaves under darkness. This was also observed in distal leaves of WT plants. The CHT-induced endoplasmic reticulum (ER) stress, as well as unfolded protein response (UPR) were examined for the first time, via analysis of the lumenal binding protein (BiP). Whereas local expression of BiP was not dependent on the availability of light or ET, systemically it was mediated by ET.

Evaluation of physiological and biochemical responses of pistachio plants (Pistacia vera L.) exposed to pesticides

Pesticides may manipulate plant physiology as non-target organisms. In this study, we examined biochemical responses of pistachio plants (Pistacia vera L.) to imidacloprid and phosalone as common pesticides used to control pistachio psyllids. Enzymatic characterization in treated plants with pesticides showed greater specific activities of superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, phenylalanine ammonia-lyase, glutathione reductase, and glutathione S-transferase compared with untreated plants during 14 days after treatment. Further experiments displayed elevated levels of total phenols and total proteins coupled with significant increases in proline and total soluble carbohydrate contents in treated plants in comparison to untreated plants. Moreover, pesticide treatment leads to a significant decrease in polyphenol oxidase activity. Nevertheless, no significant changes in contents of hydrogen peroxide, malondialdehyde, total chlorophyll, and electrolyte leakage index were obtained in treated plants. Pesticides' impacts on host plant physiology resulted in similar responses between two pesticides with differences in peak days. Overall, the findings of this study provide an insight into the side effects of phosalone and imidacloprid, chemicals with no specific target site in plants, on the physiology and biochemistry of pistachio plants at recommended rates.

Engineering Climate-Change-Resilient Crops: New Tools and Approaches

Environmental adversities, particularly drought and nutrient limitation, are among the major causes of crop losses worldwide. Due to the rapid increase of the world's population, there is an urgent need to combine knowledge of plant science with innovative applications in agriculture to protect plant growth and thus enhance crop yield. In recent decades, engineering strategies have been successfully developed with the aim to improve growth and stress tolerance in plants. Most strategies applied so far have relied on transgenic approaches and/or chemical treatments. However, to cope with rapid climate change and the need to secure sustainable agriculture and biomass production, innovative approaches need to be developed to effectively meet these challenges and demands. In this review, we summarize recent and advanced strategies that involve the use of plant-related cyanobacterial proteins, macro- and micronutrient management, nutrient-coated nanoparticles, and phytopathogenic organisms, all of which offer promise as protective resources to shield plants from climate challenges and to boost stress tolerance in crops.

Leaf Age-Dependent Photosystem II Photochemistry and Oxidative Stress Responses to Drought Stress in Arabidopsis thaliana Are Modulated by Flavonoid Accumulation

We investigated flavonoid accumulation and lipid peroxidation in young leaves (YL) and mature leaves (ML) of Arabidopsis thaliana plants, whose watering stopped 24 h before sampling, characterized as onset of drought stress (OnDS), six days before sampling, characterized as mild drought stress (MiDS), and ten days before sampling, characterized as moderate drought stress (MoDS). The response to drought stress (DS) of photosystem II (PSII) photochemistry, in both leaf types, was evaluated by estimating the allocation of absorbed light to photochemistry (Φ_PSII), to heat dissipation by regulated non-photochemical energy loss (Φ_NPQ) and to non-regulated energy dissipated in PSII (Φ_NO). Young leaves were better protected at MoDS than ML leaves, by having higher concentration of flavonoids that promote acclimation of YL PSII photochemistry to MoDS, showing lower lipid peroxidation and excitation pressure (1 - q_p). Young leaves at MoDS possessed lower 1 - q_p values and lower excess excitation energy (EXC), not only compared to MoDS ML, but even to MiDS YL. They also possessed a higher capacity to maintain low Φ_NO, suggesting a lower singlet oxygen (¹O₂) generation. Our results highlight that leaves of different developmental stage may display different responses to DS, due to differential accumulation of metabolites, and imply that PSII photochemistry in Arabidopsis thaliana may not show a dose dependent DS response.

Polystyrene microplastics induce apoptosis via ROS-mediated p53 signaling pathway in zebrafish

Microplastic (MP) pollution is ubiquitous and has become an emerging threat to aquatic biota. Recent scientific reports have recorded their toxic impacts at the cellular and organism levels, but the underlying molecular mechanism of their toxicity remains unclear. The present study elucidates an array of molecular events underlying apoptosis in the gills of polystyrene microplastics (PS-MPs) exposed zebrafish (Danio rerio). PS-MPs at different concentrations (10 and 100 μg L^-1) induced the reactive oxygen species (ROS) generation, in turn affecting the oxidative and immune defense mechanism. The expression profile of antioxidant genes cat, sod1, gpx1a and gstp1 were altered significantly. PS-MPs also significantly inhibited the neurotransmission in zebrafish. In addition, the PS-MPs exposure upregulated the expression of p53, gadd45ba, and casp3b resulting in apoptosis. We demonstrate that PS-MPs significantly upregulate the transcriptional pattern of tnfa and ptgs2a which are essential gene markers in inflammatory mechanism. Further, the oxidative damage induced by PS-MPs exposure could lead to cytological damage resulting in altered lamellar structures, capillary dilation, and necrosis in gill histomaps. In conclusion, the findings of this work strongly suggest that PS-MPs induce dose-and time-dependent ROS mediated apoptotic responses in zebrafish. Furthermore, the physiological responses observed in the gills correlate with the above observations and helps in unravelling the potential molecular mechanism underpinning the PS-MPs toxicity in zebrafish.

Effect of Oxidative Stress on Physicochemical Quality of Taiwanese Seagrape (Caulerpa lentillifera) with the Application of Alternating Current Electric Field (ACEF) during Post-Harvest Storage

This study aims to determine the physicochemical quality of seagrape (Caulerpa lentillifera) as a freshness label for products cultivated in different seasons. The applied post-harvest storage experiments compared between, within and without seawater that led to oxidative stress conditions. Water content, malondialdehyde (MDA) compound, total phenolic content (TPC), and chlorophyll content were observed at 0, 3, 6, and 9 days of storage. The storage without seawater showed sharper quality reductions by reaching 20–40% of water loss, 70–90% of MDA production, 15–25% of TPC reduction, and 40–60% of total chlorophyll degradation. The storage within seawater showed lower quality reductions due to the specific growth rates still reaching 5–10%. This study found that the greater the physicochemical quality, the slower the decomposition rates of the stored seagrape during storage. Therefore, the seagrapes’ obvious discoloration occurred earlier in winter, followed by summer and spring. Kinetics of chlorophyll degradation on seagrape in different seasons meet different order-reactions during storage. Furthermore, alternating current electric field (ACEF) treatment with 125 kV/m of intensity for 60 min can lower the spring seagrapes’ physicochemical quality by reaching 10–30% of inhibition, resulting in the shelf-life extension for up to 12 days of post-harvest storage.

Acetic acid improves drought acclimation in soybean: an integrative response of photosynthesis, osmoregulation, mineral uptake and antioxidant defense

Exposure to drought stress negatively affects plant productivity and consequently threatens global food security. As global climates change, identifying solutions to increase the resilience of plants to drought is increasingly important. Several chemical treatments have recently emerged as promising techniques for various individual and combined abiotic stresses. This study shows compelling evidence on how acetic acid application promotes drought acclimation responses in soybean by investigating several morphological, physiological and biochemical attributes. Foliar applications of acetic acid to drought-exposed soybean resulted in improvements in root biomass, leaf area, photosynthetic rate and water use efficiency; leading to improved growth performance. Drought-induced accumulation of reactive oxygen species, and the resultant increased levels of malondialdehyde and electrolyte leakage, were considerably reverted by acetic acid treatment. Acetic acid-sprayed plants suffered less oxidative stress due to the enhancement of antioxidant defense mechanisms, as evidenced by the increased activities of superoxide dismutase, ascorbate peroxidase, catalase, glutathione peroxidase and glutathione S-transferase. Improved shoot relative water content was also linked to the increased levels of soluble sugars and free amino acids, indicating a better osmotic adjustment following acetic acid treatment in drought-exposed plants. Acetic acid also increased stem/root, leaf/stem and leaf/root mineral ratios and improved overall mineral status in drought-stressed plants. Taken together, our results demonstrated that acetic acid treatment enabled soybean plants to positively regulate photosynthetic ability, water balance, mineral homeostasis and antioxidant responses; thereby suggesting acetic acid as a cost-effective and easily accessible chemical for the management of soybean growth and productivity in drought-prone areas.

Mitochondrial redox systems as central hubs in plant metabolism and signaling

Plant mitochondria are indispensable for plant metabolism and are tightly integrated into cellular homeostasis. This review provides an update on the latest research concerning the organization and operation of plant mitochondrial redox systems, and how they affect cellular metabolism and signaling, plant development, and stress responses. New insights into the organization and operation of mitochondrial energy systems such as the tricarboxylic acid cycle and mitochondrial electron transport chain (mtETC) are discussed. The mtETC produces reactive oxygen and nitrogen species, which can act as signals or lead to cellular damage, and are thus efficiently removed by mitochondrial antioxidant systems, including Mn-superoxide dismutase, ascorbate-glutathione cycle, and thioredoxin-dependent peroxidases. Plant mitochondria are tightly connected with photosynthesis, photorespiration, and cytosolic metabolism, thereby providing redox-balancing. Mitochondrial proteins are targets of extensive post-translational modifications, but their functional significance and how they are added or removed remains unclear. To operate in sync with the whole cell, mitochondria can communicate their functional status via mitochondrial retrograde signaling to change nuclear gene expression, and several recent breakthroughs here are discussed. At a whole organism level, plant mitochondria thus play crucial roles from the first minutes after seed imbibition, supporting meristem activity, growth, and fertility, until senescence of darkened and aged tissue. Finally, plant mitochondria are tightly integrated with cellular and organismal responses to environmental challenges such as drought, salinity, heat, and submergence, but also threats posed by pathogens. Both the major recent advances and outstanding questions are reviewed, which may help future research efforts on plant mitochondria.