Effects of Exogenous Dopamine on the Uptake, Transport, and Resorption of Apple Ionome Under Moderate Drought

Potassium silica nanostructure improved growth and nutrient uptake of sorghum plants subjected to drought stress

Introduction

Recent advancements in nanotechnology present promising opportunities for enhancing crop resilience in adverse environmental conditions.

Methods

In this study, we conducted a factorial experiment to investigate the influence of potassium nanosilicate (PNS) on sorghum plants exposed to varying degrees of drought stress A randomized complete block design with three replications was employed to subject the sorghum plants to different drought conditions. The three levels of stress were designated as non-stress (NS at -0.03 MPa), moderate stress (MD at -0.6 MPa), and severe stress (SD at -1.2 MPa). The plants were administered PNS at concentrations of 0 mM (control), 3.6 mM Si, and 7.2 mM Si.

Results and discussion

As drought stress intensified, we observed significant reductions in multiple plant parameters, including height, fresh weight, dry weight, leaf number, stem diameter, cluster length, seed weight, and nutrient uptake, with the most pronounced effects observed under SD conditions. Interestingly, nitrogen (N) and potassium (K) levels exhibited an increase under drought stress and PNS application, peaking at MD, alongside Si concentrations. Notably, PNS application facilitated enhanced nutrient uptake, particularly evident in the significant increase in nitrogen concentration observed at 3.6 mM PNS. Furthermore, the application of PNS significantly enhanced the fresh weight and nutrient concentrations (notably K and Si) in sorghum seeds under drought stress, despite varying statistical significance for other nutrients. These findings shed light on the mechanisms through which PNS exerts beneficial effects on plant performance under drought stress. By elucidating the complex interactions between PNS application, drought stress, and plant physiology, this study contributes significantly to the development of sustainable agricultural practices aimed at bolstering crop resilience and productivity in water-limited environments.

Development of a Nanomarker for In Vivo Monitoring of Dopamine in Plants

Dopamine, alongside norepinephrine and epinephrine, belongs to the catecholamine group, widely distributed across both plant and animal kingdoms. In mammals, these compounds serve as neurotransmitters with roles in glycogen mobilization. In plants, their synthesis is modulated in response to stress conditions aiding plant survival by emitting these chemicals, especially dopamine that relieves their resilience against stress caused by both abiotic and biotic factors. In present studies, there is a lack of robust methods to monitor the operations of dopamine under stress conditions or any adverse situations across the plant's developmental stages from cell to cell. In our study, we have introduced a groundbreaking approach to track dopamine generation and activity in various metabolic pathways by using the simple nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs). These CQDs exhibit dominant biocompatibility, negligible toxicity, and environmentally friendly characteristics using a quenching process for fluorometric dopamine detection. This innovative nanomarker can detect even small amounts of dopamine within plant cells, providing insights into plant responses to strain and anxiety. Confocal microscopy has been used to corroborate this occurrence and to provide visual proof of the process of binding dopamine with these N, S-CQDs inside the cells.

Novel nucleus-localized GRAM protein encoding OsGRAM57 gene enhances salt tolerance through ABA-dependent pathway and modulated carbohydrate metabolism

GRAM (Glucosyltransferases-like GTPase activators and Myotubularin) domain-encoding proteins play pivotal roles in plant growth and responses to biotic stresses. Yet, their influence on abiotic stress responses has remained enigmatic. This study unveils a novel nucleus-localized OsGRAM57, a GRAM protein-encoding gene and its profound regulatory functions in enhancing salt stress tolerance using Arabidopsis thaliana as a model plant. OsGRAM57-OEX (OsGRAM57-OEX) lines displayed significant enhancement in salt tolerance, modulated physiological, biochemical, K+/Na+ ratios, and enzymatic indices as compared to their wild-type (WT). Furthermore, OsGRAM57-OEX seedlings demonstrate increased levels of endogenous abscisic acid (ABA) and other phytohormones, while metabolic profiling revealed enhanced carbohydrate metabolism. Delving into the ABA signaling pathway, OsGRAM57 emerged as a central regulator, orchestrating the expression of genes crucial for salt stress responses, carbohydrate metabolism, and ABA signaling. The observed interactions with target genes and transactivation assays provided additional support for OsGRAM57's pivotal role. These findings underscore OsGRAM57's positive influence on the ABA pathway and affirm its capacity to enhance salt tolerance through an ABA-dependent pathway and fine-tuned carbohydrate metabolism. In summary, this new study reveals the previously undiscovered regulatory roles of OsGRAM57 in Arabidopsis abiotic stress responses, offering promising ways for strengthening plant resilience in the face of adverse environmental conditions.

Dopamine Alleviates Phloridzin Toxicity in Apple by Modifying Rhizosphere Bacterial Community Structure and Function

Phloridzin significantly influences apple plant growth, development, and resistance to environmental stresses by engaging in various metabolic processes. Its excessive accumulation in soil, attributed to continuous monoculture practices, not only inhibits plant growth but also disrupts the rhizosphere microbial community. This study aims to explore the remedial effects of dopamine, a known antioxidant and stress resistance modulator in plants, on the adverse impacts of phloridzin stress in apple. Through hydroponic and pot experiments, it was demonstrated that dopamine significantly mitigates the growth inhibition caused by phloridzin stress in apple by reducing reactive oxygen species levels and enhancing photosynthesis and nitrogen transport. Additionally, dopamine reduced phloridzin concentrations in both the rhizosphere and roots. Furthermore, dopamine positively influences the structure of the rhizosphere microbial community, enriching beneficial microbes associated with nitrogen cycling. It increases the potential for soil nitrogen degradation and fixation by upregulating the abundance of ureC, GDH, and nifH, as revealed by metagenomic analysis. This aids in alleviating phloridzin stress. The study reveals dopamine's pivotal roles in modulating rhizosphere ecology under phloridzin stress and suggests its potential in sustainable apple cultivation practices to counter ARD and enhance productivity.

Exogenous melatonin improves germination rate in buckwheat under high temperature stress by regulating seed physiological and biochemical characteristics

The germinations of three common buckwheat (Fagopyrum esculentum) varieties and two Tartary buckwheat (Fagopyrum tataricum) varieties seeds are known to be affected by high temperature. However, little is known about the physiological mechanism affecting germination and the effect of melatonin (MT) on buckwheat seed germination under high temperature. This work studied the effects of exogenous MT on buckwheat seed germination under high temperature. MT was sprayed. The parameters, including growth, and physiological factors, were examined. The results showed that exogenous MT significantly increased the germination rate (GR), germination potential (GP), radicle length (RL), and fresh weight (FW) of these buckwheat seeds under high-temperature stress and enhanced the content of osmotic adjustment substances and enzyme activity. Comprehensive analysis revealed that under high-temperature stress during germination, antioxidant enzymes play a predominant role, while osmotic adjustment substances work synergistically to reduce the extent of damage to the membrane structure, serving as the primary key indicators for studying high-temperature resistance. Consequently, our results showed that MT had a positive protective effect on buckwheat seeds exposed to high temperature stress, providing a theoretical basis for improving the ability to adapt to high temperature environments.

Regulatory mechanisms of dopamine metabolism in a marine Meyerozyma guilliermondii GXDK6 under NaCl stress as revealed by integrative multi-omics analysis

Dopamine can be used to treat depression, myocardial infarction, and other diseases. However, few reports are available on the de novo microbial synthesis of dopamine from low-cost substrate. In this study, integrated omics technology was used to explore the dopamine metabolism of a novel marine multi-stress-tolerant aromatic yeast Meyerozyma guilliermondii GXDK6. GXDK6 was found to have the ability to biosynthesize dopamine when using glucose as the substrate. 14 key genes for the biosynthesis of dopamine were identified by whole genome-wide analysis. Transcriptomic and proteomic data showed that the expression levels of gene AAT2 encoding aspartate aminotransferase (regulating dopamine anabolism) were upregulated, while gene AO-I encoding copper amine oxidase (involved in dopamine catabolism) were downregulated under 10 % NaCl stress compared with non-NaCl stress, thereby contributing to biosynthesis of dopamine. Further, the amount of dopamine under 10 % NaCl stress was 2.51-fold higher than that of zero NaCl, which was consistent with the multi-omics results. Real-time fluorescence quantitative PCR (RT-qPCR) and high-performance liquid chromatography (HPLC) results confirmed the metabolic model of dopamine. Furthermore, by overexpressing AAT2, AST enzyme activity was increased by 24.89 %, the expression of genes related to dopamine metabolism was enhanced, and dopamine production was increased by 56.36 % in recombinant GXDK6AAT2. In conclusion, Meyerozyma guilliermondii GXDK6 could utilize low-cost carbon source to synthesize dopamine, and NaCl stress promoted the biosynthesis of dopamine.

MdHB7-like positively modulates apple salt tolerance by promoting autophagic activity and Na+ efflux

Salt stress adversely affects the yield and quality of crops and limits their geographical distribution. Studying the functions and regulatory mechanisms of key genes in the salt stress response is important for breeding crops with enhanced stress resistance. Autophagy plays an important role in modulating the tolerance of plants to various types of abiotic stressors. However, the mechanisms underlying salt-induced autophagy are largely unknown. Cation/Ca2+ exchanger proteins enhance apple salt tolerance by inhibiting Na+ accumulation but the mechanism underlying the response to salt stress remains unclear. Here, we show that the autophagy-related gene MdATG18a modulated apple salt tolerance. Under salt stress, the autophagic activity, proline content, and antioxidant enzyme activities were higher and Na+ accumulation was lower in MdATG18a-overexpressing transgenic plants than in control plants. The use of an autophagy inhibitor during the salt treatment demonstrated that the regulatory function of MdATG18a depended on autophagy. The yeast-one-hybrid assay revealed that the homeodomain-leucine zipper (HD-Zip) transcription factor MdHB7-like directly bound to the MdATG18a promoter. Transcriptional regulation and genetic analyses showed that MdHB7-like enhanced salt-induced autophagic activity by promoting MdATG18a expression. The analysis of Na+ efflux rate in transgenic yeast indicated that MdCCX1 expression significantly promoted Na+ efflux. Promoter binding, transcriptional regulation, and genetic analyses showed that MdHB7-like promoted Na+ efflux and apple salt tolerance by directly promoting MdCCX1 expression, which was independent of the autophagy pathway. Overall, our findings provide insight into the mechanism underlying MdHB7-like-mediated salt tolerance in apple through the MdHB7-like-MdATG18a and MdHB7-like-MdCCX1 modules. These results will aid future studies on the mechanisms underlying stress-induced autophagy and the regulation of stress tolerance in plants.

Fruit crops combating drought: Physiological responses and regulatory pathways

Drought is a common stress in agricultural production. Thus, it is imperative to understand how fruit crops respond to drought and to develop drought-tolerant varieties. This paper provides an overview of the effects of drought on the vegetative and reproductive growth of fruits. We summarize the empirical studies that have assessed the physiological and molecular mechanisms of the drought response in fruit crops. This review focuses on the roles of calcium (Ca2+) signaling, abscisic acid (ABA), reactive oxygen species signaling, and protein phosphorylation underlying the early drought response in plants. We review the resulting downstream ABA-dependent and ABA-independent transcriptional regulation in fruit crops under drought stress. Moreover, we highlight the positive and negative regulatory mechanisms of microRNAs in the drought response of fruit crops. Lastly, strategies (including breeding and agricultural practices) to improve the drought resistance of fruit crops are outlined.

Comparative Assessment of Antioxidant Activity and Functional Components of Chionanthus virginicus and Chionanthus pubescens from the Andean Region of Ecuador

The present study aims to provide information about the antioxidant capacity and secondary metabolites from different plant parts of two species that are grown in Ecuador: Chionanthus pubescens (the Ecuadorian national tree), and Chionanthus virginicus (the fringe tree-endemic to the United States of America and adapted to Ecuador's physiographical and ecological conditions). These two species have still not been investigated for these characteristics. A comparative estimation of the antioxidant activities between the leaf, fruit, and inflorescence extracts was performed. In the quest for new medicines, the extracts were analyzed for phenolic, anthocyanin, and flavonoid content. A slight difference was observed between C. pubescens and C. virginicus flowers, the highest antioxidant activity being found in the C. pubescens leaf (DPPH IC₅₀ = 62.8866 mg/mL, ABTS IC₅₀ = 55.852 mg/mL, and FRAP IC₅₀ = 2.8466 g/mL). Our results showed correlations between antioxidant activity, total phenolic content, and flavonoids. This study confirmed that the C. pubescens leaves and fruits from the Andean region of Ecuador represent a good source of antioxidants, especially due to the presence of a high content of phenolic compounds (homovanillic acid, 3,4 dimethoxyphenylacetic acid, vanillic acid, gallic acid, etc.) as determined by the HPLC-DAD method.

New Insight into the Function of Dopamine (DA) during Cd Stress in Duckweed (Lemna turionifera 5511)

Dopamine (DA), a kind of neurotransmitter in animals, has been proven to cause a positive influence on plants during abiotic stress. In the present study, the function of DA on plants under cadmium (Cd) stress was revealed. The yellowing of duckweed leaves under Cd stress could be alleviated by an exogenous DA (10/20/50/100/200 μM) supplement, and 50 μM was the optimal concentration to resist Cd stress by reducing root breakage, restoring photosynthesis and chlorophyll content. In addition, 24 h DA treatment increased Cd content by 1.3 times in duckweed under Cd stress through promoting the influx of Cd2+. Furthermore, the gene expression changes study showed that photosynthesis-related genes were up-regulated by DA addition under Cd stress. Additionally, the mechanisms of DA-induced Cd detoxification and accumulation were also investigated; some critical genes, such as vacuolar iron transporter 1 (VIT1), multidrug resistance-associated protein (MRP) and Rubisco, were significantly up-regulated with DA addition under Cd stress. An increase in intracellular Ca2+ content and a decrease in Ca2+ efflux induced by DA under Cd stress were observed, as well as synchrony with changes in the expression of cyclic nucleotide-gated ion channel 2 (CNGC2), predicting that, in plants, CNGC2 may be an upstream target for DA action and trigger the change of intracellular Ca2+ signal. Our results demonstrate that DA supplementation can improve Cd resistance by enhancing duckweed photosynthesis, changing intracellular Ca2+ signaling, and enhancing Cd detoxification and accumulation. Interestingly, we found that exposure to Cd reduced endogenous DA content, which is the result of a blocked shikimate acid pathway and decreased expression of the tyrosine aminotransferase (TAT) gene. The function of DA in Cd stress offers a new insight into the application and study of DA to Cd phytoremediation in aquatic systems.

Exogenous melatonin alleviates apple replant disease by regulating rhizosphere soil microbial community structure and nitrogen metabolism

Apple replant disease (ARD) is a common soil-borne disease afflicting apple plants. Melatonin is a broad-spectrum oxygen scavenger that plays a key role in alleviating stress-induced damage in plants. In this study, we aimed to determine whether adding melatonin to replant soil can promote plant growth by improving the rhizosphere soil environment and nitrogen metabolism. In replant soil, chlorophyll synthesis was blocked, reactive oxygen species (ROS) accumulated in large quantities, and membrane lipid peroxidation was aggravated; this eventually resulted in slow plant growth. However, the application of 200 μM exogenous melatonin enhanced the tolerance of plants to ARD by up-regulating the expression of antioxidant enzyme-related genes and increasing ROS scavenging enzyme activity. Exogenous melatonin also increased the absorption and utilization of ¹⁵N by increasing the expression of nitrogen absorption genes and the activity of nitrogen metabolism enzymes. Exogenous melatonin enhanced the soil microbial environment by promoting soil enzyme activity and bacterial richness and decreasing the abundance of several harmful fungi in rhizosphere soil. Mantel test results showed that soil properties (except for AP) and growth indexes were positively correlated with the rate of ¹⁵N absorption and utilization. Spearman correlation analysis showed that the above factors were closely related to the richness and diversity of bacteria and fungi, indicating that the composition of microbial communities might play a key role in mediating change in the soil environment and thus affect nutrient absorption and growth. These findings provide new insights into how melatonin enhances ARD tolerance.

Elemental Profile, General Phytochemical Composition and Bioaccumulation Abilities of Selected Allium Species Biofortified with Selenium under Open Field Conditions

Allium species are known as a rich source of many compounds with potential healing effects. Biofortification is recognized as an effective agrotechnical measure for raising the level of biogenic elements-especially microelements in the edible parts of these species, so Allium can be considered as a 'natural dietary supplement'. The aim of this research was to test the effects of foliar application of Se fertilizer (Na₂SeO₄) in different doses (control-0, 10, 20 and 30 g per ha) on the content of macro, microelements and secondary metabolites (SMs)-free phenolics, flavonoids and hydroxycinnamic acid derivatives in the edible parts, i.e., leaves of two selected Allium species in Serbia (A. odorum and A. schoenoprasum), which grew in open field conditions over the course of two growing seasons. The bioaccumulation factor (BAF), as an indicator of the ability of plants to accumulate biogenic elements, was also determined. Although with no full regularity, the dose of 10 g of Se per ha yielded the highest content for the most biogenic elements for both alliums in the first growing season, i.e., a dose of 20 g of Se per ha for A. schoenoprasum, and a dose of 30 g of Se per ha for A. odorum in the second growing season. The obtained results justified the Se-biofortification of different alliums. The BAF values indicated the ability of both Allium species to accumulate S, K and P in their leaves during both growing seasons. The accumulation of potentially toxic elements was not recorded for either species, emphasizing the safety of the produced plant material for human consumption. Additionally, Se-treated plants had higher SM contents compared to control plants. The growing season also showed an impact on SM content; i.e., in the second season, characterized as drought-stressed, the synthesis of SMs was significantly higher compared to that in the first season. Further research should be directed towards finding the appropriate dose of Se, expanded in the sense of conducting research in controlled conditions, as well as different ways of applying Se fertilizer. The idea of this study was also to popularize the examined Allium species, which are rarely grown in the territory of Serbia.

Pre-treatment of melatonin enhances the seed germination responses and physiological mechanisms of soybean (Glycine max L.) under abiotic stresses

The germination of soybean (Glycine max L.) seeds is critically affected by abiotic stresses which resulting in decreasing crop growth and yield. However; little is known about the physiological mechanisms of germination and the potential role of melatonin on soybean seed germination under drought, salt, cold, and heat stresses. Therefore, the current study investigated the possible effects of melatonin to enhance germination indices and other physiological attributes by alleviating the harmful impacts of these stresses during germination. Seeds of soybean were pre-treated (seed priming) with melatonin at MT1 (20 μmol L^-1), MT2 (50 μmol L^-1), MT3 (100 μmol L^-1), MT4 (200 μmol L^-1), and MT5 (300 μmol L^-1) and exposed to the four stresses (drought at PEG 15%, salt at 150mM, cold at 10 °C, and heat at 30 °C) . It was noted that MT1 (20 μmol L^-1), MT2 (50 μmol L^-1), and MT3 (100 μmol L^-1) remarkably improved the germination potential, germination rate, radical length, and biomass under given stresses. Furthermore, MT1, MT2, and MT3 progressively increased the proline to minimize the impact of drought, salt, cold, and heat stresses. In addition, all stresses significantly induced oxidative damage however, salt (150 mM NaCl) and heat (30 °C) stresses highly increased the malondialdehyde content (MDA) and hydrogen peroxide (H2O2) as compared to drought (PEG 15%) and cold (10 °C) stresses. Moreover, MT2 and MT3 significantly enhanced the activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) to reduce the oxidative damage in soybean seeds during the germination. Overall, melatonin at 50 μmol L^-1 and 100 μmol L^-1 considerably mitigated the harmful impacts of drought, salt, cold, and heat stress by enhancing germination and other physiological mechanisms of soybean. This study could provide bases to enhance the melatonin-mediated tolerance of soybean and other related crops at early growth stages when exposed to abiotic stresses.

Exogenous Dopamine and MdTyDC Overexpression Enhance Apple Resistance to Fusarium solani

Fusarium solani, one of the main pathogenic fungi involved in apple replant disease (ARD), is a serious threat to apple growth and development. Dopamine and tyrosine decarboxylase (TyDC), a key enzyme in the dopamine synthesis pathway, have been reported to play an active role in plant responses to biotic and abiotic stresses, but little is known about the functions of dopamine and Malus domestica TyDC (MdTyDC) in the interaction between F. solani and apple roots. In this study, seedlings treated with exogenous dopamine and apple plants overexpressing MdTyDC were inoculated with F. solani; both treatments reduced the root system damage caused by F. solani. After inoculation with F. solani, exogenous dopamine increased dopamine content in the seedlings; alleviated the inhibition of biomass accumulation; increased root metabolic activity, photosynthetic efficiency, and antioxidant enzyme activities; reduced reactive oxygen species accumulation; and upregulated the expression of genes encoding chitinase, β-1,3-glucanase, and pathogenesis-related proteins. Similar results were observed in MdTyDC-overexpressing apple plants. In addition, the overexpression of MdTyDC increased tyramine content and the deposition of cell wall-bound amines in roots. Overall, our results reveal that exogenous dopamine and overexpression of MdTyDC enhance apple resistance to F. solani, which is an important application for the prevention of ARD.

Extensive cross-talk among stress-regulated protective metabolites, biogenic-amines and phytohormone-signalling, co-ordinated by dopamine-mediated seed-priming, governs tolerance against fluoride stress in rice

Seed priming with dopamine reduced fluoride bioaccumulation, induced endogenous dopamine level, thereby orchestrating phytohormone homeostasis and biogenic amine metabolism, and modulating osmolyte and antioxidant machinery to enhance fluoride tolerance in rice. The aim of this study was to decipher the efficacy of seed priming with dopamine in curtailing the adverse impacts of fluoride toxicity in rice seedlings. Fluoride-stressed seedlings exhibited severe growth retardation, high fluoride bioaccumulation, electrolyte leakage and marked cellular injuries. Dopamine priming stimulated the overall physiological growth parameters during stress, via reduced formation of H₂O₂, malondialdehyde and methylglyoxal, due to lesser fluoride-accumulation. Fluoride stress-induced endogenous dopamine level was further induced upon dopamine priming, marked by the up regulated DOPA decarboxylase expression. Additionally, dopamine treatment led to escalated activity of catalase, superoxide dismutase and glutathione peroxidase in the stressed seedlings, concomitant with altered CAT, SOD and GPX expression. The higher accumulation of protective osmolytes (proline and total amino acids) and non-enzymatic antioxidants (phenolics, flavonoids, anthocyanins, glutathione and carotenoids), upon dopamine priming, during fluoride stress, could be linked with the altered expression pattern of the respective genes. Dopamine promoted active utilization of the biogenic amine (polyamines and ϒ-amino butyric acid) pools for toxicity mitigation, correlated with the modulation of the concerned enzyme activity and gene expression. Dopamine stimulated the accumulation of phytohormones like gibberellin and salicylic acid, via inducing the biosynthetic genes like gibberellin-3-oxidase (GA3ox) and isochorismate synthase (ICS), respectively, while depreciating the abscisic acid and melatonin level during fluoride stress. To our knowledge, this is the first documented report for the remedial role of dopamine priming against fluoride stress in any plant species. This study will open new arenas in sustainable agriculture for the exploitation of this pulsating biomolecule against fluoride stress.

Simultaneous Action of Silymarin and Dopamine Enhances Defense Mechanisms Related to Antioxidants, Polyamine Metabolic Enzymes, and Tolerance to Cadmium Stress in Phaseolus vulgaris

Silymarin (Sm) and dopamine (DA) act synergistically as potential antioxidants, mediating many physiological and biochemical processes. As a first report, we investigated the synergistic effect of Sm and DA in mitigating cadmium stress in Phaseolus vulgaris plants. Three experiments were conducted simultaneously using 40 cm diameter pots to elucidate how Sm and DA affect cadmium tolerance traits at morphological, physiological, and biochemical levels. Cadmium stress triggered a marked reduction in growth, productivity, and physio-biochemical characteristics of common bean plants compared to unstressed plants. Seed priming (SP) and foliar spraying (FS) with silymarin (Sm) or dopamine (DA) ((DA (SP) + Sm (FS) and Sm (SP) + DA (FS)) ameliorated the damaging effects of cadmium stress. Sm seed priming + DA foliar spraying (Sm (SP) + DA (FS)) was more efficient. The treated stressed common bean plants showed greater tolerance to cadmium stress by diminishing oxidative stress biomarkers (i.e., O₂^•-, H₂O₂, and MDA) levels through enhanced enzymatic (SOD, CAT, POD, APX) and non-enzymatic (ascorbic acid, glutathione, α-tocopherol, choline, phenolics, flavonoids) antioxidant activities and osmoprotectants (proline, glycine betaine, and soluble sugars) contents, as well as through improved photosynthetic efficiency (total chlorophyll and carotenoids contents, photochemical activity, and efficiencies of carboxylation (iCE) and PSII (Fv/Fm)), polyamines (Put, Spd, and Spm), and polyamine metabolic enzymes (ADC and ODC) accumulation. These findings signify that Sm and DA have remarkable anti-stress effects, which can help regulate plant self-defense systems, reflecting satisfactory plant growth and productivity. Thus, realizing the synergistic effect of Sm and DA in cadmium tolerance confers potential new capabilities for these compounds to function in sustainable agriculture.

Improved tolerance of apple plants to drought stress and nitrogen utilization by modulating the rhizosphere microbiome via melatonin and dopamine

This study explored the contributions of melatonin and dopamine to the uptake and utilization of nitrogen and the formation of rhizosphere microbial communities in ‘Tianhong 2’/M. hupehensis, with the goal improving plant resistance to drought stress. Drought stress was formed by artificially controlling soil moisture content. And melatonin or dopamine solutions were applied to the soil at regular intervals for experimental treatment. After 60 days of treatment, plant indices were determined and the structure of the rhizosphere microbial community was evaluated using high-throughput sequencing technology. The findings revealed two ways through which melatonin and dopamine alleviate the inhibition of growth and development caused by drought stress by promoting nitrogen uptake and utilization in plants. First, melatonin and dopamine promote the absorption and utilization of nitrogen under drought stress by directly activating nitrogen transporters and nitrogen metabolism-related enzymes in the plant. Second, they promote the absorption of nitrogen by regulating the abundances of specific microbial populations, thereby accelerating the transformation of the soil nitrogen pool to available nitrogen that can be absorbed directly by plant roots and utilized by plants. These findings provide a new framework for understanding how melatonin and dopamine regulate the uptake and utilization of nitrogen in plants and improve their ability to cope with environmental disturbances.

Exogenous 5-aminolevulinic acid alleviates low-temperature damage by modulating the xanthophyll cycle and nutrient uptake in tomato seedlings

5-Aminolevulinic acid (ALA), an antioxidant existing in plants, has been widely reported to participate in the process of coping with cold stress of plants. In this study, exogenous ALA promoted the growth of tomato plants and alleviated the appearance of purple tomato leaves under low-temperature stress. At the same time, exogenous ALA improved antioxidant enzyme activities, SlSOD gene expression, Fv/Fm, and proline contents and reduced H₂O₂ contents, SlRBOH gene expression, relative electrical conductivity, and malondialdehyde contents to alleviate the damage caused by low temperature to tomato seedlings. Compared with low-temperature stress, spraying exogenous ALA before low-temperature stress could restore the indicators of photochemical quenching, actual photochemical efficiency, electron transport rate, and nonphotochemical quenching to normal. Exogenous ALA could increase the total contents of the xanthophyll cycle pool, the positive de-epoxidation rate of the xanthophyll cycle and improved the expression levels of key genes in the xanthophyll cycle under low-temperature stress. In addition, we found that exogenous ALA significantly enhanced the absorption of mineral nutrients, promoted the transfer and distribution of mineral nutrients to the leaves, and improved the expression levels of mineral nutrient absorption-related genes, which were all conducive to the improved adaptation of tomato seedlings under low-temperature stress. In summary, the application of exogenous ALA can increase tomato seedlings' tolerance to low-temperature stress by improving the xanthophyll cycle and the ability of the absorption of mineral nutrients in tomato seedlings.

Induction of polyploid Malus prunifolia and analysis of its salt tolerance

The apple rootstock Malus prunifolia (Willd.) Borkh. is widely used for apple production. Because polyploid plants are often more tolerant to abiotic stress than diploids, we wondered whether polyploidy induction in M. prunifolia might improve its stress tolerance, particularly to high salinity. We used a combination of colchicine and dimethyl sulfoxide (DMSO) to induce chromosome doubling in M. prunifolia and identified the resulting polyploids by stomatal observations and flow cytometry. We found the best way to induce polyploidy in M. prunifolia was to use 2% DMSO and 0.05% colchicine for 2 days for leaves or 0.02% colchicine for stem segments. The results of hydroponic salt treatment showed that polyploid plants were more salt tolerant and had greater photosynthetic efficiency, thicker leaf epidermis and palisade tissues, and shorter but denser root systems than diploids. During salt stress, the polyploid leaves and roots accumulated less Na+, showed upregulated expression of three salt overly sensitive (SOS) pathway genes, and produced fewer reactive oxygen species. The polyploid plants also had considerably higher ABA and jasmonic acid levels than diploid plants under salt stress. Under normal growth conditions, gibberellins (GAs) levels were much lower in polyploid leaves than in diploid leaves; however, after salt treatment, polyploid leaves showed upregulation of essential GAs synthesis genes. In summary, we developed a system for the induction of polyploidy in M. prunifolia and response to salt stress of the resulting polyploids, as reflected in leaf and root morphology, changes in Na+ accumulation, antioxidant capacity and plant hormone levels.

Plant hormones and neurotransmitter interactions mediate antioxidant defenses under induced oxidative stress in plants

Due to global climate change, abiotic stresses are affecting plant growth, productivity, and the quality of cultivated crops. Stressful conditions disrupt physiological activities and suppress defensive mechanisms, resulting in stress-sensitive plants. Consequently, plants implement various endogenous strategies, including plant hormone biosynthesis (e.g., abscisic acid, jasmonic acid, salicylic acid, brassinosteroids, indole-3-acetic acid, cytokinins, ethylene, gibberellic acid, and strigolactones) to withstand stress conditions. Combined or single abiotic stress disrupts the normal transportation of solutes, causes electron leakage, and triggers reactive oxygen species (ROS) production, creating oxidative stress in plants. Several enzymatic and non-enzymatic defense systems marshal a plant's antioxidant defenses. While stress responses and the protective role of the antioxidant defense system have been well-documented in recent investigations, the interrelationships among plant hormones, plant neurotransmitters (NTs, such as serotonin, melatonin, dopamine, acetylcholine, and γ-aminobutyric acid), and antioxidant defenses are not well explained. Thus, this review discusses recent advances in plant hormones, transgenic and metabolic developments, and the potential interaction of plant hormones with NTs in plant stress response and tolerance mechanisms. Furthermore, we discuss current challenges and future directions (transgenic breeding and genome editing) for metabolic improvement in plants using modern molecular tools. The interaction of plant hormones and NTs involved in regulating antioxidant defense systems, molecular hormone networks, and abiotic-induced oxidative stress tolerance in plants are also discussed.

Ionomic Combined with Transcriptomic and Metabolomic Analyses to Explore the Mechanism Underlying the Effect of Melatonin in Relieving Nutrient Stress in Apple

Nutrient stress harms plant growth and yield. Melatonin is a biologically active, multifunctional hormone that relieves abiotic stress in plants. Although previous studies have shown that melatonin plays an important role in improving nutrient-use efficiency, the mechanism of its regulation of nutrient stress remains unclear. In this study, melatonin was applied to apple plants under nutrient stress, and morphological indices, physiological and biochemical indices, and stomatal morphology were evaluated. The response of apple plants to nutrient deficiency and the melatonin mechanism to alleviate nutrient stress were analyzed by combining ionome, transcriptome, and metabolome. The results showed that exogenous melatonin significantly alleviated the inhibitory effect of nutritional stress on the growth of apple plants by regulating stomatal morphology, improving antioxidant enzyme activity, promoting ion absorption, and utilizing and changing the absorption and distribution of minerals throughout the plant. The transcriptome results showed that melatonin alleviated nutrient stress and promoted nutrient absorption and utilization by regulating glutathione metabolism and upregulating some metal ion transport genes. The metabolome results indicated that levels of oxalic acid, L-ascorbic acid, anthocyanins (cyanidin-3-O-galactoside), lignans (lirioresinol A and syringaresinol), and melatonin significantly increased after exogenous melatonin was applied to plants under nutrient stress. These differentially expressed genes and the increase in beneficial metabolites may explain how melatonin alleviates nutrient stress in plants.

Trehalose alleviates salt tolerance by improving photosynthetic performance and maintaining mineral ion homeostasis in tomato plants

Trehalose (Tre), which was an osmoprotective or stabilizing molecule, played a protective role against different abiotic stresses in plants and showed remarkable perspectives in salt stress. In this study, the potential role of Tre in improving the resistance to salt stress in tomato plants was investigated. Tomato plants (Micro Tom) were treated with Hoagland nutrient solution (CK), 10 mM Tre (T), 150 mM sodium chloride (NaCl, S), and 10 mM Tre+150 mM NaCl (S+T) for 5 days. Our results showed that foliar application of Tre alleviated the inhibition of tomato plant growth under salt stress. In addition, salt stress decreased the values of net photosynthetic rate (Pn, 85.99%), stomata conductance (gs, 57.3%), and transpiration rate (Tr, 47.97%), but increased that of intercellular carbon dioxide concentration (Ci, 26.25%). However, exogenous application of Tre significantly increased photosynthetic efficiency, increased the activity of Calvin cycle enzymes [ribulose diphosphate carboxylase/oxygenase (Rubisco), fructose-1,6-bisphosphate aldolase (FBA), fructose-1, 6-bisphosphatase (FBPase), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and transketolase (TK)], up-regulated the expression of genes encoding enzymes, induced stomatal opening, and alleviated salt-induced damage to the chloroplast membrane and structure. In the saline environment, photosynthetic electron transport was restricted, resulting the J-I-P phase to decrease. At the same time, the absorption, capture, and transport energies per excited cross-section and per active reaction center decreased, and the dissipation energy increased. Conversely, Tre reversed these values and enhanced the photosystem response to salt stress by protecting the photosynthetic electron transport system. In addition, foliage application with Tre significantly increased the potassium to sodium transport selectivity ratio (S _K-Na ) by 16.08%, and increased the levels of other ions to varying degrees. Principal component analysis (PCA) analysis showed that exogenous Tre could change the distribution of elements in different organs and affect the expressions of SlSOS1, SlNHX, SlHKT1.1, SlVHA, and SlHA-A at the transcriptional level under salt stress, thereby maintaining ion homeostasis. This study demonstrated that Tre was involved in the process of mitigating salt stress toxicity in tomato plants and provided specific insights into the effectiveness of Tre in mediating salt tolerance.

Plants' Physio-Biochemical and Phyto-Hormonal Responses to Alleviate the Adverse Effects of Drought Stress: A Comprehensive Review

Water, a necessary component of cell protoplasm, plays an essential role in supporting life on Earth; nevertheless, extreme changes in climatic conditions limit water availability, causing numerous issues, such as the current water-scarce regimes in many regions of the biome. This review aims to collect data from various published studies in the literature to understand and critically analyze plants' morphological, growth, yield, and physio-biochemical responses to drought stress and their potential to modulate and nullify the damaging effects of drought stress via activating natural physiological and biochemical mechanisms. In addition, the review described current breakthroughs in understanding how plant hormones influence drought stress responses and phytohormonal interaction through signaling under water stress regimes. The information for this review was systematically gathered from different global search engines and the scientific literature databases Science Direct, including Google Scholar, Web of Science, related studies, published books, and articles. Drought stress is a significant obstacle to meeting food demand for the world's constantly growing population. Plants cope with stress regimes through changes to cellular osmotic potential, water potential, and activation of natural defense systems in the form of antioxidant enzymes and accumulation of osmolytes including proteins, proline, glycine betaine, phenolic compounds, and soluble sugars. Phytohormones modulate developmental processes and signaling networks, which aid in acclimating plants to biotic and abiotic challenges and, consequently, their survival. Significant progress has been made for jasmonates, salicylic acid, and ethylene in identifying important components and understanding their roles in plant responses to abiotic stress. Other plant hormones, such as abscisic acid, auxin, gibberellic acid, brassinosteroids, and peptide hormones, have been linked to plant defense signaling pathways in various ways.

Cytokinin and abscisic acid alleviate drought stress through changing organic acids profile, ion immolation, and fatty acid profile to improve yield of wheat (Triticum aestivum L.) cultivars

There is an increasing interest for plant hormones to modulate the harmful effects of drought on crops. The present study was conducted to assess the effect of foliar-applied cytokin (CK) and abscisic acid (ABA) on yield, organic acids, minerals, and fatty acid profile of wheat (Triticum aestivum L.) cultivars (MV17 and Pishgam) in response to drought stress. The results showed drought significantly decreased grain yield and biomass, but they were enhanced by CK and ABA application. Acetic acid increased under drought stress conditions, and the remarkable increase (~ twofold) in succinic acid content was observed with ABA application under drought stress in MV17 cultivar. In general, drought stress decreased malic acid, pyruvic acid, and citric acid, but CK enhanced them. The leaf accumulations of potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), iron (Fe²⁺), and zinc (Zn²⁺) decreased by drought, where its reduction in MV17 was greater than Pishgam. However, an increased sodium (Na⁺) content was observed in plants experiencing drought with non-foliar application of ABA and CK. The plant growth hormones especially CK increased K⁺, Ca²⁺, Mg²⁺, Fe²⁺, and Zn²⁺, but decreased Na⁺. Fatty acid profile showed increased polyunsaturated fatty acids and monounsaturated fatty acids upon the drought stress. According to heat map, organic acids represented the maximum variations but fatty acids showed the minimum change during the treatments. The present study recommended foliar-applied CK to alleviate drought stress on wheat yield.

Phytotoxicity mechanism of the natural radionuclide thorium in Vicia faba

Elucidation of the phytotoxic mechanisms of thorium (Th) is important for controlling Th accumulation in crops and improving the efficiency of phytoremediation. Here, we analyzed the subcellular distribution of Th in Vicia faba seedlings and the toxic reaction of seedlings to Th (5-40 μmol·L^-1) at the subcellular and cellular levels. Increasing the phosphate level in the culture medium from 0.01 to 0.1 mmol·L^-1 decreased the Th accumulation by the roots by 47-57%. Th was mainly distributed in the root cell walls (94-96%) and existed mainly in the form of residue (92-94%). Th accumulation in the root was similar to the changes observed for P, Ni, Cu, and Fe. High concentrations of Th (40 μmol·L^-1) induced abnormal root growth and leaf photosynthetic metabolism. At the cellular level, Th (40 μmol·L^-1) induced root edge cell death and inhibited root respiration and cell mitosis. SOD, POD and CAT activities were involved in the regulation of reactive oxygen species accumulation in the roots. Untargeted metabolomics identified 580 and 262 differentially expressed metabolites in roots and leaves. At the metabolic level, its toxicological mechanism involved a severe inhibition of the expression of nucleotides in roots and leaves.

Melatonin and dopamine mediate the regulation of nitrogen uptake and metabolism at low ammonium levels in Malus hupehensis

In plants, ammonium (NH₄⁺) is the main nitrogen source and acts as a physiological and morphological response signaling molecule. Melatonin and dopamine are associated with plant responses to abiotic stress. However, previous studies have rarely focused on nutrient stress, and the roles of melatonin and dopamine in the uptake and metabolism of nitrogen in plants remain unclear. In this study, we investigated the regulatory effects of melatonin and dopamine on nitrogen utilization efficiency in apple seedlings under two NH₄⁺ concentrations (2 and 0.1 mM) by measuring plant growth, root system architecture, ¹⁵NH₄⁺ content, and related enzyme activity and gene expression. Under low nitrogen supply, apple seedling growth slowed and showed marked reductions in biomass accumulation, chlorophyll content, and nutrient uptake. However, both melatonin and dopamine significantly improved plant growth, chlorophyll content, and root development and enhanced antioxidant enzyme activity. Exogenous application of melatonin or dopamine also promoted the absorption and accumulation of ¹⁵NH₄⁺ and enhanced nitrogen metabolism-related enzyme activity. At the molecular level, melatonin and dopamine significantly increased the expression levels of nitrogen metabolism genes and transporter genes. Overall, these results suggest that melatonin and dopamine can relieve nutrient stress caused by low concentrations of NH₄⁺ through regulating the absorption and metabolism of nitrogen.

Overexpression of the tyrosine decarboxylase gene MdTyDC in apple enhances long-term moderate drought tolerance and WUE

Drought stress affects the apple yield and quality. Tyrosine decarboxylase (TyDC) plays a fundamental role in many secondary metabolite reactions in higher plants (including those involving dopamine). Our aims of this study are: 1) to identify the role of TyDC in dopamine derivative biosynthesis and its function in long-term moderate drought conditions; and 2) to explore the role of MdTyDC in plant growth and development as well as the drought stress response. Wild type and three independently apple plants overexpression of MdTyDC were treated for long-term moderate drought stress. The growth and physiological parameters of apple plant, photosynthetic capacity, antioxidant enzymes activity, water use efficiency (WUE), stomatal behavior, amino acid content and dopamine content were detected under long-term moderate drought stress. Overexpression of MdTyDC (OE) in apple showed better growth performance, higher photosynthetic capacity and higher capacity for photochemical reactions than wild type lines (WT). Under long-term moderate drought stress, OE lines showed higher WUE, increased ABA content, decreased stomatal aperture, higher antioxidant activity, lower accumulation of ROS and increases in amino acids, such as proline, phenylalanine and lysine. In addition, qRT-PCR revealed higher gene expression of MdTyDC and dopamine content in OE compared with WT lines under long-term moderate drought stress. These results indicate that MdTyDC confers long-term moderate drought tolerance by improving photosynthetic capacity, WUE, antioxidant activity, dopamine content and changing the contents of amino acids (such as proline accumulation).

Heterologous Expression of the Melatonin-Related Gene HIOMT Improves Salt Tolerance in Malus domestica

Melatonin, a widely known indoleamine molecule that mediates various animal and plant physiological processes, is formed from N-acetyl serotonin via N-acetylserotonin methyltransferase (ASMT). ASMT is an enzyme that catalyzes melatonin synthesis in plants in the rate-determining step and is homologous to hydroxyindole-O-methyltransferase (HIOMT) melatonin synthase in animals. To date, little is known about the effect of HIOMT on salinity in apple plants. Here, we explored the melatonin physiological function in the salinity condition response by heterologous expressing the homologous human HIOMT gene in apple plants. We discovered that the expression of melatonin-related gene (MdASMT) in apple plants was induced by salinity. Most notably, compared with the wild type, three transgenic lines indicated higher melatonin levels, and the heterologous expression of HIOMT enhanced the expression of melatonin synthesis genes. The transgenic lines showed reduced salt damage symptoms, lower relative electrolyte leakage, and less total chlorophyll loss from leaves under salt stress. Meanwhile, through enhanced activity of antioxidant enzymes, transgenic lines decreased the reactive oxygen species accumulation, downregulated the expression of the abscisic acid synthesis gene (MdNCED3), accordingly reducing the accumulation of abscisic acid under salt stress. Both mechanisms regulated morphological changes in the stomata synergistically, thereby mitigating damage to the plants' photosynthetic ability. In addition, transgenic plants also effectively stabilized their ion balance, raised the expression of salt stress-related genes, as well as alleviated osmotic stress through changes in amino acid metabolism. In summary, heterologous expression of HIOMT improved the adaptation of apple leaves to salt stress, primarily by increasing melatonin concentration, maintaining a high photosynthetic capacity, reducing reactive oxygen species accumulation, and maintaining normal ion homeostasis.

Enhanced Autophagic Activity Improved the Root Growth and Nitrogen Utilization Ability of Apple Plants under Nitrogen Starvation

Autophagy is a conserved degradation pathway for recycling damaged organelles and aberrant proteins, and its important roles in plant adaptation to nutrient starvation have been generally reported. Previous studies found that overexpression of autophagy-related (ATG) gene MdATG10 enhanced the autophagic activity in apple roots and promoted their salt tolerance. The MdATG10 expression was induced by nitrogen depletion condition in both leaves and roots of apple plants. This study aimed to investigate the differences in the growth and physiological status between wild type and MdATG10-overexpressing apple plants in response to nitrogen starvation. A hydroponic system containing different nitrogen levels was used. The study found that the reduction in growth and nitrogen concentrations in different tissues caused by nitrogen starvation was relieved by MdATG10 overexpression. Further studies demonstrated the increased root growth and the higher nitrogen absorption and assimilation ability of transgenic plants. These characteristics contributed to the increased uptake of limited nitrogen nutrients by transgenic plants, which also reduced the starvation damage to the chloroplasts. Therefore, the MdATG10-overexpressing apple plants could maintain higher photosynthetic ability and possess better growth under nitrogen starvation stress.

Plant Growth Promoting and Stress Mitigating Abilities of Soil Born Microorganisms

Abiotic stresses affect the plant growth in different ways and at different developmental stages that reduce the crop yields. The increasing world population continually demands more crop yields; therefore it is important to use low-cost technologies against abiotic stresses to increase crop productivity. Soil microorganisms survive in the soil associated with plants in extreme condition. It was demonstrated that these beneficial microorganisms promote plant growth and development under various stresses. The soil microbes interact with the plant through rhizospheric or endophytic association and promote the plant growth through different processes such as nutrients mobilization, disease suppression, and hormone secretions. The microorganisms colonized in the rhizospheric region and imparted the abiotic stress tolerance by producing 1-aminocyclopropane-1- carboxylate (ACC) deaminase, antioxidant, and volatile compounds, inducing the accumulation of osmolytes, production of exopolysaccharide, upregulation or downregulation of stress genes, phytohormones and change the root morphology. A large number of these rhizosphere microorganisms are now patented. In the present review, an attempt was made to throw light on the mechanism of micro-organism that operates during abiotic stresses and promotes plant survival and productivity.

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.

Dopamine Alleviates Hydrocarbon Stress in Brassica oleracea through Modulation of Physio-Biochemical Attributes and Antioxidant Defense Systems

Hydrocarbon stress has become one of the most restrictive factors for crop choice and productivity in most parts of the world. Dopamine (DA) has positively influenced the metabolic, physiological and biochemical activities besides the growth of plants under numerous abiotic stress conditions. The current study was performed to analyze the potential of DA to alleviate hydrocarbon stress and improve growth of Brassica oleracea plants. Hydrocarbon stress in plants was induced by growing in 5% and 10% crude oil contaminated soil. Crude oil stressed plants exhibited reduced growth besides decreased level of photosynthetic pigments and gas exchange attributes. Moreover, oil stressed plants showed elevated level of hydrogen peroxide (H₂O₂), electrolyte leakage (EL), malondialdehyde (MDA) and superoxide radical (O^2-). However, exogenous application of 50, 100 and 200 μmol L^-1 DA improved photosynthesis, shoot and root dry weight of B. oleracea seedlings growing in hydrocarbon amended soil. Additionally, DA100 treatments improved non-enzymatic and enzymatic antioxidants of treated seedlings. Our results demonstrate that increased gas exchange attributes, modulation of osmoregulators and improved activity of the antioxidative enzymes alleviated hydrocarbon stress in DA supplemented B. oleracea plants. Consequently, the first time observed ameliorative role of DA in hydrocarbon stress opens a new arena for application of this dynamic biomolecule for sustainable crop production.

Overexpression of MdATG8i improves water use efficiency in transgenic apple by modulating photosynthesis, osmotic balance, and autophagic activity under moderate water deficit

Water deficit is one of the major limiting factors for apple (Malus domestica) production on the Loess Plateau, a major apple cultivation area in China. The identification of genes related to the regulation of water use efficiency (WUE) is a crucial aspect of crop breeding programs. As a conserved degradation and recycling mechanism in eukaryotes, autophagy has been reported to participate in various stress responses. However, the relationship between autophagy and WUE regulation has not been explored. We have shown that a crucial autophagy protein in apple, MdATG8i, plays a role in improving salt tolerance. Here, we explored its biological function in response to long-term moderate drought stress. The results showed that MdATG8i-overexpressing (MdATG8i-OE) apple plants exhibited higher WUE than wild-type (WT) plants under long-term moderate drought conditions. Plant WUE can be increased by improving photosynthetic efficiency. Osmoregulation plays a critical role in plant stress resistance and adaptation. Under long-term drought conditions, the photosynthetic capacity and accumulation of sugar and amino acids were higher in MdATG8i-OE plants than in WT plants. The increased photosynthetic capacity in the OE plants could be attributed to their ability to maintain optimal stomatal aperture, organized chloroplasts, and strong antioxidant activity. MdATG8i overexpression also promoted autophagic activity, which was likely related to the changes described above. In summary, our results demonstrate that MdATG8i-OE apple lines exhibited higher WUE than WT under long-term moderate drought conditions because they maintained robust photosynthesis, effective osmotic adjustment processes, and strong autophagic activity.

Magnaporthe oryzae systemic defense trigger 1 (MoSDT1)-mediated metabolites regulate defense response in Rice

BACKGROUND

Some of the pathogenic effector proteins play an active role in stimulating the plant defense system to strengthen plant resistance.

RESULTS

In this study, ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC/Q-TOF-MS) was implemented to identify altered metabolites in transgenic rice containing over-expressed M. oryzae Systemic Defense Trigger 1 (MoSDT1) that was infected at three-time points. The characterized dominating metabolites were organic acids and their derivatives, organic oxygen compounds, lipids, and lipid-like molecules. Among the identified metabolites, shikimate, galactinol, trehalose, D-mannose, linolenic acid, dopamine, tyramine, and L-glutamine are precursors for the synthesis of many secondary defense metabolites Carbohydrate, as well as amino acid metabolic, pathways were revealed to be involved in plant defense responses and resistance strengthening.

CONCLUSION

The increasing salicylic acid (SA) and jasmonic acid (JA) content enhanced interactions between JA synthesis/signaling gene, SA synthesis/receptor gene, raffinose/fructose/sucrose synthase gene, and cell wall-related genes all contribute to defense response in rice. The symptoms of rice after M. oryzae infection were significantly alleviated when treated with six identified metabolites, i.e., galactol, tyramine, L-glutamine, L-tryptophan, α-terpinene, and dopamine for 72 h exogenously. Therefore, these metabolites could be utilized as an optimal metabolic marker for M. oryzae defense.

Beneficial Effects of Exogenous Melatonin and Dopamine on Low Nitrate Stress in Malus hupehensis

Malus hupehensis, as an apple rootstock, is an economically important tree species popular due to its excellent fruit yield and stress resistance. Nitrogen is one of the critical limiting factors of plant growth and fruit yield, so it is crucial to explore new methods to improve nitrogen use efficiency. Melatonin and dopamine, as multifunctional metabolites, play numerous physiological roles in plants. We analyzed the effects of exogenous melatonin and dopamine treatments on the growth, root system architecture, nitrogen absorption, and metabolism of M. hupehensis when seedlings were exposed to nitrate-deficient conditions. Under low nitrate stress, plant growth slowed, and chlorophyll contents and ¹⁵NO₃ ^- accumulation decreased significantly. However, the application of 0.1 μmol/L melatonin or 100 μmol/L exogenous dopamine significantly reduced the inhibition attributable to low nitrate levels during the ensuing period of stress treatment, and the effect of dopamine was more obvious. In addition to modifying the root system architecture of nitrate-deficient plants, exogenous melatonin and dopamine also changed the uptake, transport, and distribution of ¹⁵NO₃ ^-. Furthermore, both exogenous melatonin and dopamine enhanced tolerance to low nitrate stress by maintaining the activity of enzymes (NR, NiR, GS, Fd-GOGAT, and NADH-GOGAT) and the transcription levels of related genes involved in leaf and root nitrogen metabolism. We also found that exogenous melatonin and dopamine promoted the expression of nitrate transporter genes (NRT1.1, NRT2.4, NRT2.5, and NRT2.7) in nitrate-deficient plant leaves and roots. Our results suggest that both exogenous melatonin and dopamine can mitigate low nitrate stress by changing the root system architecture, promoting the absorption of nitrate, and regulating the expression of genes related to nitrogen transport and metabolism. However, according to a comprehensive analysis of the results, exogenous dopamine plays a more significant role than melatonin in improving plant nitrogen use efficiency.

MdHB-7 Regulates Water Use Efficiency in Transgenic Apple (Malus domestica) Under Long-Term Moderate Water Deficit

Improved water use efficiency (WUE) promotes plant survival and crop yield under water deficit conditions. Although the plant-specific HD-Zip I transcription factors have important roles in plant adaptation to various abiotic stresses, including water deficit, their functions in regulating WUE of apple (Malus domestica) are poorly understood. We characterized the role of MdHB-7 in WUE regulation by subjecting MdHB-7 transgenic plants to long-term moderate soil water deficit. The long-term WUE (WUE_L) of transgenic apple plants with MdHB-7 overexpression or MdHB-7 RNA interference (RNAi) differed significantly from that of control plants. Upregulation of MdHB-7 caused reduced stomatal density, whereas the suppression of MdHB-7 increased stomatal density under both normal and long-term moderate soil water deficit conditions. Moderate reduction in stomatal density helped to improve the WUE of MdHB-7 overexpression transgenic plants, especially under water deficit conditions. MdHB-7 overexpression plants maintained high rates of photosynthesis that were conducive to the accumulation of biomass and the improvement of WUE_L. MdHB-7 overexpression also alleviated the inhibition of root growth caused by long-term moderate soil water deficit and improved root vitality and hydraulic conductivity, which were essential for improving plant WUE_L. By contrast, MdHB-7 RNA interference reduced the WUE_L of transgenic plants by inhibiting these factors under normal and long-term moderate soil water deficit conditions. Taken together, our results provide solid evidence for a crucial role of MdHB-7 in the regulation of apple WUE_L and provide new insights for improving the WUE of apple plants under moderate soil water deficit.

Functions of dopamine in plants: a review

Dopamine (3-hydroxytyramine or 3,4-dihydroxyphenethylamine) has many functions in animals, but also shows several other functions in plants. Since the discovery of dopamine in plants in 1968, many studies have provided insight into physiological and biochemical functions, and stress responses of this molecule. In this review, we describe the biosynthesis of dopamine, as well as its role in plant growth and development. In addition, endogenous or exogenously applied dopamine improved the tolerance against several abiotic stresses, such as drought, salt, and nutrient stress. There are also several studies that dopamine contributes to the plant immune response against plant disease. Dopamine affects the expression of many abiotic stresses related genes, which highlights its role as a multi-regulatory molecule and can coordinate many aspects of plant development. Our review emphasized the effects of dopamine against environmental stresses along with future research directions, which will help improve the yield of eco-friendly crops and ensure food security.

Potassium deficiency reconfigures sugar export and induces catecholamine accumulation in oil palm leaves

Metabolic effects of potassium (K) deficiency have been described for nearly 70 years but specific effects of low K availability on sugar composition, sugar export rate and its relationship with other leaf metabolites are not very well documented. Having such pieces of information is nevertheless essential to identify metabolic signatures to monitor K fertilization. This is particularly true in oil-producing crop species such as oil palm (Elaeis guineensis), which is strongly K-demanding and involves high sugar dependence for fruit formation because of low carbon use efficiency in lipid synthesis. Here, we used metabolic analyses, measured sugar export rates with ¹³C isotopic labeling and examined the effects of K availability on both leaflet and rachis sugar metabolism in oil palm seedlings. We show that low K leads to a modification of sugar composition mostly in rachis and decreased sucrose and hexose export rates from leaflets. As a result, leaflets contained more starch and induced alternative pathways such as raffinose synthesis, although metabolites of the raffinose pathway remained quantitatively minor. The alteration of glycolysis by low K was compensated for by an increase in alternative sugar phosphate utilization by tyrosine metabolism, resulting in considerable amounts of tyramine and dopamine.

Melatonin improves the germination rate of cotton seeds under drought stress by opening pores in the seed coat

The germination of cotton (Gossypium hirsutum L.) seeds is affected by drought stress; however, little is known about the physiological mechanism affecting germination and the effect of melatonin (MT) on cotton seed germination under drought stress. Therefore, we studied the effects of exogenous MT on the antioxidant capacity and epidermal microstructure of cotton under drought stress. The results demonstrated a retarded water absorption capacity of testa under drought stress, significantly inhibiting germination and growth in cotton seeds. Drought stress led to the accumulation of reactive oxygen species (ROS), malondialdehyde (MDA), and osmoregulatory substances (e.g., proline, soluble protein, and soluble sugars); it also decreased the activity of antioxidant enzymes and α-amylase. Drought stress inhibited gibberellin acid (GA3) synthesis and increased abscisic acid (ABA) content, seriously affecting seed germination. However, seeds pre-soaked with MT (100 µM) showed a positive regulation in the number and opening of stomata in cotton testa. The exogenous application of MT increased the germination rate, germination potential, radical length, and fresh weight, as well as the activities of superoxide dismutase (SOD), peroxidase (POD), and α-amylase. In addition, MT application increased the contents of organic osmotic substances by decreasing the hydrogen peroxide (H2O2), superoxide anion (O2 -), and MDA levels under drought stress. Further analysis demonstrated that seeds pre-soaked with MT alleviated drought stress by affecting the ABA and GA3 contents. Our findings show that MT plays a positive role in protecting cotton seeds from drought stress.

New insights on neurotransmitters signaling mechanisms in plants

Neurotransmitters (NTs) such as acetylcholine, biogenic amines (dopamine, noradrenaline, adrenaline, histamine), indoleamines [(melatonin (MEL) & serotonin (SER)] have been found not only in mammalians, but also in diverse living organisms-microorganisms to plants. These NTs have emerged as potential signaling molecules in the last decade of investigations in various plant systems. NTs have been found to play important roles in plant life including-organogenesis, flowering, ion permeability, photosynthesis, circadian rhythm, reproduction, fruit ripening, photomorphogenesis, adaptation to environmental changes. This review will provide an overview of recent advancements on the physiological and molecular mechanism of NTs in plants. Moreover, molecular crosstalk of SER and MEL with various biomolecules is also discussed. The study of these NTs may serve as new understanding of the mechanisms of signal transmission and cell sensing in plants subjected to various environmental stimulus.

Physiological and transcriptome analyses of the effects of exogenous dopamine on drought tolerance in apple

Water shortage is one of the main limiting factors in apple (Malus domestica Borkh.) production. Although dopamine is produced in plants and has been linked with response to abiotic stress, the underlying mechanism remains unknown. In this study, physiological analyses revealed that pretreatment with 100 μM dopamine alleviated drought stress in apple seedlings. Dopamine inhibited the degradation of photosynthetic pigments and increased net photosynthetic rate under drought stress. Dopamine also reduced H₂O₂ content, possibly through direct scavenging and by mediating the antioxidant enzyme activity. Seedlings pretreated with dopamine had higher sucrose and malic acid contents but lower starch accumulation in their leaves. RNA-Seq analysis identified 1052 differentially expressed genes (DEGs) between non-treated and dopamine-pretreated plants under drought. An in-depth analysis of these DEGs revealed that dopamine regulated the expression of genes related to metabolism of nitrogen, secondary compounds, and amino acids under drought stress. In addition, dopamine may improve apple drought tolerance by activating Ca²⁺ signaling pathways through increased expression of CNGC and CAM/CML family genes. Moreover, analysis of transcription factor expression suggested that dopamine affected drought tolerance mainly through the regulation of WRKY, ERF, and NAC transcription factors.

Comparing the growth-promoting potential of Paenibacillus lentimorbus and Bacillus amyloliquefaciens in Oryza sativa L. var. Sarju-52 under suboptimal nutrient conditions

An adequate supply of mineral nutrients is crucial to obtain optimum productivity in agriculture. The present investigation was carried to find the inoculation effect of plant growth-promoting rhizobacteria (PGPR), i.e., Paenibacillus lentimorbus B-30488 (B-30488), Bacillus amyloliquefaciens SN13 (SN13) and their consortium for the growth of rice var. Sarju-52, grown under suboptimal nutrient conditions. The study revealed that the individual PGPR treatments showed comparatively better performance than consortia in morphological, physiological, biochemical, and nutrient analysis. Towards understanding the complex mechanism(s), untargeted metabolite profiling was performed using GC-MS, showed alteration of metabolites in rice seedlings facing suboptimal nutrient conditions and inoculated with PGPR. Metabolites such as oleic acid, mannitol, and ethyl iso-allocol were accumulated significantly under starved conditions. Under suboptimal nutrient conditions, sugars such as ribose, glucose, fructose, trehalose, palmitic acid, and myristic acid were accumulated significantly in PGPR inoculated seedlings. The significantly altered pathways due to PGPR inoculation under suboptimal nutrient conditions mainly belongs to carbohydrate and fatty acid metabolism. Interestingly, it was observed that among all the treatments, inoculation with SN13 performed comparatively better than other treatments. Further, in SN13 inoculated samples the qRT-PCR analysis of transcription factors and metabolism-related genes were validated that indicates PGPR deploy metabolic re-programming in rice var. Sarju-52 to enhance its nutrient use efficiency, tolerance, and growth under suboptimum nutrient conditions.

Exogenous Dopamine Application Promotes Alkali Tolerance of Apple Seedlings

Arid and semiarid apple producing areas suffer from severe alkalinity of soil, which strongly affects the yield and quality of apples. Dopamine (DA) is involved in metabolic activities in response to abiotic stress in plants. To detect the effects of exogenous DA application on the adaption of apple (Malus hupehensis) seedlings to alkali stress and as a protection from oxidative stress, 0.1 mM DA was identified as the most suitable concentration by hydroponic culture. Further experimentation showed that the growth and photosynthesis of apple seedlings were significantly inhibited under alkali stress, and more reactive oxygen species accumulated, compared with control. However, exogenous DA application suppressed the loss of the plant height, root length, chlorophyll levels, and photosynthetic capacity of apple seedlings that were caused by alkali stress. In the leaves of alkali stressed seedlings, the catalase, superoxide dismutase, and peroxidase activities were lower and hydrogen peroxide and malondialdehyde levels were higher than in the untreated plants. The presence of DA significantly alleviated such effects of alkali stress. In addition, exogenous DA application increased the antioxidant capacity of apple seedlings under alkali stress by increasing the level of chlorogenic acid. These results are significant for improving the alkali tolerance of apple in apple-producing areas with alkalized soil.

The Role of the Plant Antioxidant System in Drought Tolerance

Water deficiency compromises plant performance and yield in many habitats and in agriculture. In addition to survival of the acute drought stress period which depends on plant-genotype-specific characteristics, stress intensity and duration, also the speed and efficiency of recovery determine plant performance. Drought-induced deregulation of metabolism enhances generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) which in turn affect the redox regulatory state of the cell. Strong correlative and analytical evidence assigns a major role in drought tolerance to the redox regulatory and antioxidant system. This review compiles current knowledge on the response and function of superoxide, hydrogen peroxide and nitric oxide under drought stress in various species and drought stress regimes. The meta-analysis of reported changes in transcript and protein amounts, and activities of components of the antioxidant and redox network support the tentative conclusion that drought tolerance is more tightly linked to up-regulated ascorbate-dependent antioxidant activity than to the response of the thiol-redox regulatory network. The significance of the antioxidant system in surviving severe phases of dehydration is further supported by the strong antioxidant system usually encountered in resurrection plants.