Modulation of antioxidant defense and PSII components by exogenously applied acetate mitigates salinity stress in Avena sativa.

Salinity stress has detrimental effects on various aspects of plant development. However, our understanding of strategies to mitigate these effects in crop plants remains limited. Recent research has shed light on the potential of sodium acetate as a mitigating component against salinity stress in several plant species. Here, we show the role of acetate sodium in counteracting the adverse effects on oat (Avena sativa) plants subjected to NaCl-induced salinity stress, including its impact on plant morphology, photosynthetic parameters, and gene expression related to photosynthesis and antioxidant capacity, ultimately leading to osmoprotection. The five-week experiment involved subjecting oat plants to four different conditions: water, salt (NaCl), sodium acetate, and a combination of salt and sodium acetate. The presence of NaCl significantly inhibited plant growth and root elongation, disrupted chlorophylls and carotenoids content, impaired chlorophyll fluorescence, and down-regulated genes associated with the plant antioxidant defense system. Furthermore, our findings reveal that when stressed plants were treated with sodium acetate, it partially reversed these adverse effects across all analyzed parameters. This reversal was particularly evident in the increased content of proline, thereby ensuring osmoprotection for oat plants, even under stressful conditions. These results provide compelling evidence regarding the positive impact of sodium acetate on various plant development parameters, with a particular focus on the enhancement of photosynthetic activity.

Brassinosteroid Signaling Pathways: Insights into Plant Responses under Abiotic Stress.

With the growing global population, abiotic factors have emerged as a formidable threat to agricultural food production. If left unaddressed, these stress factors might reduce food yields by up to 25% by 2050. Plants utilize natural mechanisms, such as reactive oxygen species scavenging, to mitigate the adverse impacts of abiotic stressors. Diverse plants exhibit unique adaptations to abiotic stresses, which are regulated by phytohormones at various levels. Brassinosteroids (BRs) play a crucial role in controlling essential physiological processes in plants, including seed germination, xylem differentiation, and reproduction. The BR cascade serves as the mechanism through which plants respond to environmental stimuli, including drought and extreme temperatures. Despite two decades of research, the complex signaling of BRs under different stress conditions is still being elucidated. Manipulating BR signaling, biosynthesis, or perception holds promise for enhancing crop resilience. This review explores the role of BRs in signaling cascades and summarizes their substantial contribution to plants' ability to withstand abiotic stresses.

Integrated Action of Rhizobacteria with Aloe vera and Moringa Leaf Extracts Improves Defense Mechanisms in Hibiscus sabdariffa L. Cultivated in Saline Soil.

Osmotic stress is a serious physiological disorder that affects water movement within the cell membranes. Osmotic stress adversely affects agricultural production and sustainability and is largely caused by soil salinity and water stress. An integrated nitrogen-fixing bacteria (NFB) soil amendment and an exogenous foliar application of Aloe vera leaf extract (ALE), and moringa leaf extract (MLE) were evaluated on roselle (Hibiscus sabdariffa L.) growth, calyx yield, secondary metabolites, and tolerance to osmotic stress in salt-affected soil. The osmotic stress markedly decreased above- and below-ground development of the roselle plant, but integrated NFB soil amendment with ALE or MLE foliar application significantly alleviated its negative impacts. Broadly, an improvement was observed in chlorophyll, carbohydrates, and protein levels following NFB and extracts foliar application, as well as a significant enhancement in antioxidant production (total phenols, ascorbic acid, and FRAP), which decreased peroxide production and increased stress tolerance in plants. Under osmotic stress, the roselle calyx revealed the highest anthocyanin levels, which declined following NFB soil amendment and foliar extract application. Additionally, an enhancement in nitrogen (N), phosphorus (P), and potassium (K) contents and the K/Na ratio, along with a depression in sodium (Na) content, was noticed. The integrated application of Azospirillum lipoferum × ALE exhibited the best results in terms of enhancing above- and below-ground growth, calyx yield, secondary metabolites, and tolerance to osmotic stress of the roselle plants cultivated in the salt-affected soil.

Exploring the Effects of Selenium and Brassinosteroids on Photosynthesis and Protein Expression Patterns in Tomato Plants under Low Temperatures.

This study aimed to assess the effects of low-temperature stress on two tomato cultivars (S-22 and PKM-1) treated with 24-epibrassinolide (EBL) and selenium (Se) by determining the changes in the proteomics profiles, growth biomarkers, biochemical parameters, and physiological functions. The growth parameters, photosynthetic traits, and activity of nitrate reductase in the S-22 and PKM-1 plants were markedly reduced by exposure to low temperatures. However, the combined application of EBL and Se under different modes significantly enhanced the aforementioned parameters under stress and non-stress conditions. Exposure to low temperatures increased the activities of the antioxidant enzymes (catalase, peroxidase, and superoxide dismutase) and the proline content of leaves, which were further enhanced by treatment with Se and EBL in both varieties. This research sheds light on the potential for employing exogenous EBL and Se as crucial biochemical tactics to assist tomato plants in surviving low-temperature stress. Moreover, the differentially expressed proteins that were involved in plant metabolism following the combined application of EBL and Se under low-temperature stress were additionally identified. Functional analysis revealed that the Q54YH4 protein plays an active role against plant stressors. The conserved regions in the protein sequences were analyzed for assessing the reliability of plant responses against the external application of EBL and Se under low temperatures.

Photobiotechnology for abiotic stress resilient crops: Recent advances and prospects.

Massive crop failures worldwide are caused by abiotic stress. In plants, adverse environmental conditions cause extensive damage to the overall physiology and agronomic yield at various levels. Phytochromes are photosensory phosphoproteins that absorb red (R)/far red (FR) light and play critical roles in different physiological and biochemical responses to light. Considering the role of phytochrome in essential plant developmental processes, genetically manipulating its expression offers a promising approach to crop improvement. Through modulated phytochrome-mediated signalling pathways, plants can become more resistant to environmental stresses by increasing photosynthetic efficiency, antioxidant activity, and expression of genes associated with stress resistance. Plant growth and development in adverse environments can be improved by understanding the roles of phytochromes in stress tolerance characteristics. A comprehensive overview of recent findings regarding the role of phytochromes in modulating abiotic stress by discussing biochemical and molecular aspects of these mechanisms of photoreceptors is offered in this review.

Two Novel Plant-Growth-Promoting Lelliottia amnigena Isolates from Euphorbia prostrata Aiton Enhance the Overall Productivity of Wheat and Tomato.

Euphorbiaceae is a highly diverse family of plants ranging from trees to ground-dwelling minute plants. Many of these have multi-faceted attributes like ornamental, medicinal, industrial, and food-relevant values. In addition, they have been regarded as keystone resources for investigating plant-specific resilience mechanisms that grant them the dexterity to withstand harsh climates. In the present study, we isolated two co-culturable bacterial endophytes, EP1-AS and EP1-BM, from the stem internodal segments of the prostate spurge, Euphorbia prostrata, a plant member of the succulent family Euphorbiaceae. We characterized them using morphological, biochemical, and molecular techniques which revealed them as novel strains of Enterobacteriaceae, Lelliotia amnigena. Both the isolates significantly were qualified during the assaying of their plant growth promotion potentials. BM formed fast-growing swarms while AS showed growth as rounded colonies over nutrient agar. We validated the PGP effects of AS and BM isolates through in vitro and ex vitro seed-priming treatments with wheat and tomato, both of which resulted in significantly enhanced seed germination and morphometric and physiological plant growth profiles. In extended field trials, both AS and BM could remarkably also exhibit productive yields in wheat grain and tomato fruit harvests. This is probably the first-ever study in the context of PGPB endophytes in Euphorbia prostrata. We discuss our results in the context of promising agribiotechnology translations of the endophyte community associated with the otherwise neglected ground-dwelling spurges of Euphorbiaceae.

Impact of Exogenous Melatonin Application on Photosynthetic Machinery under Abiotic Stress Conditions.

Inhospitable conditions that hinder plant growth and development encompass a range of abiotic stresses, such as drought, extreme temperatures (both low and high), salinity, exposure to heavy metals, and irradiation. The cumulative impact of these stresses leads to a considerable reduction in agricultural productivity worldwide. The generation of reactive oxygen species (ROS) is a shared mechanism of toxicity induced by all these abiotic stimuli in plants, resulting in oxidative damage and membrane instability. Extensive research has shed light on the dual role of melatonin in plants, where it serves as both a growth regulator, fostering growth and development, and a potent protector against abiotic stresses. The inherent potential of melatonin to function as a natural antioxidant positions it as a promising biostimulant for agricultural use, bolstering plants' abilities to withstand a wide array of environmental challenges. Beyond its antioxidant properties, melatonin has demonstrated its capacity to regulate the expression of genes associated with the photosynthetic process. This additional characteristic enhances its appeal as a versatile chemical agent that can be exogenously applied to plants, particularly in adverse conditions, to improve their resilience and optimize photosynthetic efficiency in every phase of the plant life cycle. An examination of the molecular mechanisms underlying the stress-protective effects of exogenous melatonin on the photosynthetic machinery of plants under various abiotic stresses is presented in this paper. In addition, future prospects are discussed for developing stress-tolerant crops for sustainable agriculture in challenging environments.

Chrysanthemum: A Comprehensive Review on Recent Developments on In Vitro Regeneration.

Chrysanthemum is a flowering plant grown worldwide and is one of the most popular ornamental plants. Chrysanthemums are usually cultivated using root suckers and shoot cuttings. This conventional technique is relatively slow. In addition, as cuttings are gained regularly from mother plants, there is a chance of viral infection and degeneration, which raises the production cost. The hurdles mentioned above have been managed by applying in vitro propagation techniques, which can enhance reproduction rates through in vitro culture and use very small explants, which are impossible with the conventional approach. Usually, it is difficult to get true-to-type plants as the parents with good quality, but clonal propagation of a designated elite species makes it possible. Hence, this review highlights recent studies of the in vitro propagation of Chrysanthemum included; the appropriate explant sources, medium compositions, alternative disinfection of culture media, plant growth regulators (PGRs), different mutagenesis applications, acclimatization efficiency, and alternative light sources to overcome the shortcomings of conventional propagation techniques.

Melatonin Positively Influences the Photosynthetic Machinery and Antioxidant System of Avena sativa during Salinity Stress.

Recent studies have demonstrated melatonin protects various crops against abiotic stresses. However, the effects of melatonin on the photosynthetic apparatus of stressed plants is poorly characterized. We investigated the effects of melatonin pretreatment on photosynthesis and tolerance to salinity stress in Avena sativa (oat) plants. Oat plants were exposed to four treatments (three replicate pots per treatment): well-watered (WW; control); watered with 300 mM salt solution for 10 days (NaCl); pretreated with 100 µM melatonin solution for 7 days then watered normally for 10 days (Mel+W); or pretreated with 100 µM melatonin for 7 days then 300 mM salt for 10 days (Mel+NaCl). Considerable differences in growth parameters, chlorophyll content, stomatal conductance, proline accumulation, lipid peroxidation, electrolyte leakage, and growth parameters were observed between groups. Genes encoding three major antioxidant enzymes were upregulated in the Mel+NaCl group compared to the other groups. Chlorophyll-a fluorescence kinetic analyses revealed that almost all photosynthetic parameters were improved in Mel+NaCl plants compared to the other treatments. Analysis of genes encoding the major extrinsic proteins of photosystem II (PSII) revealed that PsbA, PsbB, PsbC, and PsbD (but not PsbO) were highly upregulated in Mel+NaCl plants compared to the other groups, indicating melatonin positively influenced photosynthesis under control conditions and salt stress. In addition, melatonin upregulated stress-responsive NAC transcription factor genes in plants exposed to salt stress. These findings suggest melatonin pretreatment improves photosynthesis and enhances salt tolerance in oat plants.

Photosystem II Extrinsic Proteins and Their Putative Role in Abiotic Stress Tolerance in Higher Plants.

Abiotic stress remains one of the major challenges in managing and preventing crop loss. Photosystem II (PSII), being the most susceptible component of the photosynthetic machinery, has been studied in great detail over many years. However, much of the emphasis has been placed on intrinsic proteins, particularly with respect to their involvement in the repair of PSII-associated damage. PSII extrinsic proteins include PsbO, PsbP, PsbQ, and PsbR in higher plants, and these are required for oxygen evolution under physiological conditions. Changes in extrinsic protein expression have been reported to either drastically change PSII efficiency or change the PSII repair system. This review discusses the functional role of these proteins in plants and indicates potential areas of further study concerning these proteins.

Positive regulatory role of sound vibration treatment in Arabidopsis thaliana against Botrytis cinerea infection.

Sound vibration (SV), a mechanical stimulus, can trigger various molecular and physiological changes in plants like gene expression, hormonal modulation, induced antioxidant activity and calcium spiking. It also alters the seed germination and growth of plants. In this study, we investigated the effects of SV on the resistance of Arabidopsis thaliana against Botrytis cinerea infection. The microarray analysis was performed on infected Arabidopsis plants pre-exposed to SV of 1000 Hertz with 100 decibels. Broadly, the transcriptomic analysis revealed up-regulation of several defense and SA-responsive and/or signaling genes. Quantitative real-time PCR (qRT-PCR) analysis of selected genes also validated the induction of SA-mediated response in the infected Arabidopsis plants pre-exposed to SV. Corroboratively, hormonal analysis identified the increased concentration of salicylic acid (SA) in the SV-treated plants after pathogen inoculation. In contrast, jasmonic acid (JA) level in the SV-treated plants remained stable but lower than control plants during the infection. Based on these findings, we propose that SV treatment invigorates the plant defense system by regulating the SA-mediated priming effect, consequently promoting the SV-induced resistance in Arabidopsis against B. cinerea.

Current Understanding of the Interplay between Phytohormones and Photosynthesis under Environmental Stress.

Abiotic stress accounts for huge crop losses every year across the globe. In plants, the photosynthetic machinery gets severely damaged at various levels due to adverse environmental conditions. Moreover, the reactive oxygen species (ROS) generated as a result of stress further promote the photosynthetic damage by inhibiting the repair system of photosystem II. Earlier studies have suggested that phytohormones are not only required for plant growth and development, but they also play a pivotal role in regulating plants' responses to different abiotic stress conditions. Although, phytohormones have been studied in great detail in the past, their influence on the photosynthetic machinery under abiotic stress has not been studied. One of the major factors that limits researchers from elucidating the precise roles of phytohormones is the highly complex nature of hormonal crosstalk in plants. Another factor that needs to be elucidated is the method used for assessing photosynthetic damage in plants that are subjected to abiotic stress. Here, we review the current understanding on the role of phytohormones in the photosynthetic machinery under various abiotic stress conditions and discuss the potential areas for further research.

Regulation of Photosynthesis during Abiotic Stress-Induced Photoinhibition.

Plants as sessile organisms are continuously exposed to abiotic stress conditions that impose numerous detrimental effects and cause tremendous loss of yield. Abiotic stresses, including high sunlight, confer serious damage on the photosynthetic machinery of plants. Photosystem II (PSII) is one of the most susceptible components of the photosynthetic machinery that bears the brunt of abiotic stress. In addition to the generation of reactive oxygen species (ROS) by abiotic stress, ROS can also result from the absorption of excessive sunlight by the light-harvesting complex. ROS can damage the photosynthetic apparatus, particularly PSII, resulting in photoinhibition due to an imbalance in the photosynthetic redox signaling pathways and the inhibition of PSII repair. Designing plants with improved abiotic stress tolerance will require a comprehensive understanding of ROS signaling and the regulatory functions of various components, including protein kinases, transcription factors, and phytohormones, in the responses of photosynthetic machinery to abiotic stress. Bioenergetics approaches, such as chlorophyll a transient kinetics analysis, have facilitated our understanding of plant vitality and the assessment of PSII efficiency under adverse environmental conditions. This review discusses the current understanding and indicates potential areas of further studies on the regulation of the photosynthetic machinery under abiotic stress.

In Vivo Assessment of Cold Tolerance through Chlorophyll-a Fluorescence in Transgenic Zoysiagrass Expressing Mutant Phytochrome A.

Chlorophyll-a fluorescence analysis provides relevant information about the physiology of plants growing under abiotic stress. In this study, we evaluated the influence of cold stress on the photosynthetic machinery of transgenic turfgrass, Zoysia japonica, expressing oat phytochrome A (PhyA) or a hyperactive mutant phytochrome A (S599A) with post-translational phosphorylation blocked. Biochemical analysis of zoysiagrass subjected to cold stress revealed reduced levels of hydrogen peroxide, increased proline accumulation, and enhanced specific activities of antioxidant enzymes compared to those of control plants. Detailed analyses of the chlorophyll-a fluorescence data through the so-called OJIP test exhibited a marked difference in the physiological status among transgenic and control plants. Overall, these findings suggest an enhanced level of cold tolerance in S599A zoysiagrass cultivars as reflected in the biochemical and physiological analyses. Further, we propose that chlorophyll-a fluorescence analysis using OJIP test is an efficient tool in determining the physiological status of plants under cold stress conditions.

Photo-biotechnology as a tool to improve agronomic traits in crops.

Phytochromes are photosensory phosphoproteins with crucial roles in plant developmental responses to light. Functional studies of individual phytochromes have revealed their distinct roles in the plant's life cycle. Given the importance of phytochromes in key plant developmental processes, genetically manipulating phytochrome expression offers a promising approach to crop improvement. Photo-biotechnology refers to the transgenic expression of phytochrome transgenes or variants of such transgenes. Several studies have indicated that crop cultivars can be improved by modulating the expression of phytochrome genes. The improved traits include enhanced yield, improved grass quality, shade-tolerance, and stress resistance. In this review, we discuss the transgenic expression of phytochrome A and its hyperactive mutant (Ser599Ala-PhyA) in selected crops, such as Zoysia japonica (Japanese lawn grass), Agrostis stolonifera (creeping bentgrass), Oryza sativa (rice), Solanum tuberosum (potato), and Ipomea batatas (sweet potato). The transgenic expression of PhyA and its mutant in various plant species imparts biotechnologically useful traits. Here, we highlight recent advances in the field of photo-biotechnology and review the results of studies in which phytochromes or variants of phytochromes were transgenically expressed in various plant species. We conclude that photo-biotechnology offers an excellent platform for developing crops with improved properties.

Expression analysis of rice pathogenesis-related proteins involved in stress response and endophytic colonization properties of gfp-tagged Bacillus subtilis CB-R05.

Bacillus subtilis CB-R05, possessing antagonistic effects against several fungal pathogens, is a diazotrophic plant growth-promoting bacteria marked with the green fluorescent protein (gfp) gene. To confirm the expression level of the pathogenesis-related (PR) proteins in rice inoculated with CB-R05, the expressions of four pathogenesis-related (PR) proteins (PR2, PR6, PR15, and PR16) were examined in the rice leaves treated with wounding stress over a time period. The PR proteins were generally more strongly expressed in the rice leaves inoculated with CB-R05 compared with the untreated control. The marked gfp-tagged B. subtilis CB-R05 strain was inoculated onto the rice seedlings under axenic conditions. Under the confocal laser scanning microscope (CLSM), the gfp-tagged CB-R05 bacterial cells were observed to penetrate the rhizoplane, especially in the elongation and differentiation zones of the rice roots, and colonize the root intracellularly. The bacteria, 24 h after the gfp-tagged CB-R05 inoculation, were seen to penetrate into the cell wall, cortex, xylem, and concentrate mainly in the vascular bundle. Numerous bacteria were observed within the intercellular spaces, root cortical cells, and xylem vessels. Over time, these bacteria dispersed to the lateral root junctions and propagated slowly from the roots to the stems and leaves. The B. subtilis CB-R05 population in the rice root rhizosphere was also monitored. These results show a very widespread colonization of the B. subtilis CB-R05 in the rice rhizosphere. Further attempts are under way to investigate the competition between the CB-R05 bacteria and the fungal pathogen in vivo.

Isolation and characterization of plant growth promoting endophytic diazotrophic bacteria from Korean rice cultivars.

We have isolated 576 endophytic bacteria from the leaves, stems, and roots of 10 rice cultivars and identified 12 of them as diazotrophic bacteria using a specific primer set of nif gene. Through 16S rDNA sequence analysis, nifH genes were confirmed in the two species of Penibacillus, three species of Microbacterium, three Bacillus species, and four species of Klebsiella. Rice seeds treated with these plant growth-promoting bacteria (PGPB) showed improved plant growth, increased height and dry weight and antagonistic effects against fungal pathogens. In addition, auxin and siderophore producing ability, and phosphate solubilizing activity were studied for the possible mechanisms of plant growth promotion. Among 12 isolates tested, 10 strains have shown higher auxin producing activity, 6 isolates were confirmed as strains with high siderophore producing activity while 4 isolates turned out to have high phosphate-solubilizing activity. These results strongly suggest that the endophytic diazotrophic bacteria characterized in this study could be successfully used to promote plant growth and inducing fungal resistance in plants.

A cell wall extract from Piriformospora indica promotes tuberization in potato (Solanum tuberosum L.) via enhanced expression of Ca(+2) signaling pathway and lipoxygenase gene.

Piriformospora indica is an axenically cultivable phytopromotional endosymbiont that mimics capabilities of arbuscular mycorrhizal fungi. This is a basidiomycete of the Sebacinaceae family, which promotes growth, development, and seed production in a variety of plant species. We report that the cell wall extract (CWE) from P. indica induces tuberization in vitro and promotes tuber growth and yield in potato. The CWE altered the calcium signaling pathway that regulates tuberization process. An increase in tuber number and size was correlated with increased transcript expression of the two Ca(2+)-dependant proteins (CaM1 and St-CDPK1) and the lipoxygenase (LOX) mRNA, which are known to play distinct roles in potato tuberization. External supplementation of Ca(2+) ions induced a similar set of tuberization pathway genes, indicating presence of an active Ca(2+) in the CWE of P. indica. Since potato tuberization is directly influenced by the presence of microflora in nature, the present study provides an insight into the novel mechanism of potato tuberization in relation to plant-microbe association. Ours is the first report on an in vitro tuber-inducing beneficial fungus.

Evaluation of abiotic stress tolerance in transgenic potato plants with reduced expression of PSII manganese stabilizing protein.

Manganese stabilizing protein (MSP) is an important component of the Photosystem II (PSII) oxygen evolving complex. In our previous work, transgenic potato plants with reduced expression of MSP (MSP-As) were developed and their physiological and biochemical responses were studied. In this report, we address the response of MSP-As plants toward salinity, heavy metal and osmotic stresses. MSP-As plants treated with NaCl, ZnCl(2) or mannitol solution showed significant level of tolerance under all the stress conditions. Specific enzyme activities of major ROS-scavenging enzymes were found significantly higher in MSP-As plants than the control plants. MSP-As plants accumulated increased levels of proline and low molecular weight metabolites such as ascorbate and α-tocopherol, which indicated that these plants were much more resistant to stress compared to the corresponding control plants. The primary photochemical efficiencies and the OJIP kinetics analyses further confirmed that MSP-As plants were in better optimal health under stress compared to the control plants. Although the exact reason behind the increased stress tolerance in stressed MSP-As plants is unclear, our results strongly indicate the role of MSP of unknown function in abiotic stress tolerance.

Engineering glucosinolates in plants: current knowledge and potential uses.

Glucosinolates (GSL) and their derivatives are well known for the characteristic roles they play in plant defense as signaling molecules and as bioactive compounds for human health. More than 130 GSLs have been reported so far, and most of them belong to the Brassicaceae family. Several enzymes and transcription factors involved in the GSL biosynthesis have been studied in the model plant, Arabidopsis, and in a few other Brassica crop species. Recent studies in GSL research have defined the regulation, distribution, and degradation of GSL biosynthetic pathways; however, the underlying mechanism behind transportation of GSLs in plants is still largely unknown. This review highlights the recent advances in the metabolic engineering of GSLs in plants and discusses their potential applications.