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Plant secondary metabolites (SMs) play important roles in plant survival and in creating ecological connections between other species. In addition to providing a variety of valuable natural products, secondary metabolites help protect plants against pathogenic attacks and environmental stresses. Given their sessile nature, plants must protect themselves from such situations through accumulation of these bioactive compounds. Indeed, secondary metabolites act as herbivore deterrents, barriers against pathogen invasion, and mitigators of oxidative stress. The accumulation of SMs are highly dependent on environmental factors such as light, temperature, soil water, soil fertility, and salinity. For most plants, a change in an individual environmental factor can alter the content of secondary metabolites even if other factors remain constant. In this review, we focus on how individual environmental factors affect the accumulation of secondary metabolites in plants during both biotic and abiotic stress conditions. Furthermore, we discuss the application of abiotic and biotic elicitors in culture systems as well as their stimulating effects on the accumulation of secondary metabolites. Specifically, we discuss the shikimate pathway and the aromatic amino acids produced in this pathway, which are the precursors of a range of secondary metabolites including terpenoids, alkaloids, and sulfur- and nitrogen-containing compounds. We also detail how the biosynthesis of important metabolites is altered by several genes related to secondary metabolite biosynthesis pathways. Genes responsible for secondary metabolite biosynthesis in various plant species during stress conditions are regulated by transcriptional factors such as WRKY, MYB, AP2/ERF, bZIP, bHLH, and NAC, which are also discussed here.

Background Incidences of heat stress due to the changing global climate can negatively affect the growth and yield of temperature-sensitive crops such as soybean variety, Pungsannamul. Increased temperatures decrease crop productivity by affecting biochemical, physiological, molecular, and morphological factors either individually or in combination with other abiotic stresses. The application of plant growth-promoting endophytic bacteria (PGPEB) offers an ecofriendly approach for improving agriculture crop production and counteracting the negative effects of heat stress. Results We isolated, screened and identified thermotolerant B. cereus SA1 as a bacterium that could produce biologically active metabolites, such as gibberellin, indole-3-acetic acid, and organic acids. SA1 inoculation improved the biomass, chlorophyll content, and chlorophyll fluorescence of soybean plants under normal and heat stress conditions for 5 and 10 days. Heat stress increased abscisic acid (ABA) and reduced salicylic acid (SA); however, SA1 inoculation markedly reduced ABA and increased SA. Antioxidant analysis results showed that SA1 increased the ascorbic acid peroxidase, superoxide dismutase, and glutathione contents in soybean plants. In addition, heat stress markedly decreased amino acid contents; however, they were increased with SA1 inoculation. Heat stress for 5 days increased heat shock protein (HSP) expression, and a decrease in GmHSP expression was observed after 10 days; however, SA1 inoculation augmented the heat stress response and increased HSP expression. The stress-responsive GmLAX3 and GmAKT2 were overexpressed in SA1-inoculated plants and may be associated with decreased reactive oxygen species generation, altered auxin and ABA stimuli, and enhanced potassium gradients, which are critical in plants under heat stress. Conclusion The current findings suggest that B. cereus SA1 could be used as a thermotolerant bacterium for the mitigation of heat stress damage in soybean plants and could be commercialized as a biofertilizer only in case found non-pathogenic.

Plant secondary metabolites, especially flavonoids, are major metabolites widely found in plants that play several key roles in plant defence and signalling in response to stress conditions. The most studied among these flavonoids are kaempferol and quercetin due to their anti-oxidative potential and their key roles in the defence system, making them more critical for plant adaptation in stress environments. Kaempferol and quercetin in plants have great therapeutic potential for human health. Despite being well-studied, some of their functional aspects regarding plants and human health need further evaluation. This review summarizes the emerging potential of kaempferol and quercetin in terms of antimicrobial activity, bioavailability and bioactivity in the human body as well as in the regulation of plant defence in response to stresses and as a signalling molecule in terms of hormonal modulation under stress conditions. We also evaluated the safe use of both metabolites in the pharmaceutical industry.

Background Salinity is a major threat to the agriculture industry due to the negative impact of salinity stress on crop productivity. In the present study, we isolated rhizobacteria and evaluated their capacities to promote crop growth under salt stress conditions. Results We isolated rhizospheric bacteria from sand dune flora of Pohang beach, Korea, and screened them for plant growth-promoting (PGP) traits. Among 55 bacterial isolates, 14 produced indole-3-acetic acid (IAA), 10 produced siderophores, and 12 produced extracellular polymeric and phosphate solubilization. Based on these PGP traits, we selected 11 isolates to assess for salinity tolerance. Among them, ALT29 and ALT43 showed the highest tolerance to salinity stress. Next, we tested the culture filtrate of isolates ALT29 and ALT43 for IAA and organic acids to confirm the presence of these PGP products. To investigate the effects of ALT29 and ALT43 on salt tolerance in soybean, we grew seedlings in 0 mM, 80 mM, 160 mM, and 240 mM NaCl treatments, inoculating half with the bacterial isolates. Inoculation with ALT29 and ALT43 significantly increased shoot length (13%), root length (21%), shoot fresh and dry weight (44 and 35%), root fresh and dry weight (9%), chlorophyll content (16–24%), Chl a (8–43%), Chl b (13–46%), and carotenoid (14–39%) content of soybean grown under salt stress. Inoculation with ALT29 and ALT43 also significantly decreased endogenous ABA levels (0.77-fold) and increased endogenous SA contents (6–16%), increased total protein (10–20%) and glutathione contents, and reduced lipid peroxidation (0.8–5-fold), superoxide anion (21–68%), peroxidase (12.14–17.97%), and polyphenol oxidase (11.76–27.06%) contents in soybean under salinity stress. In addition, soybean treated with ALT29 and ALT43 exhibited higher K + uptake (9.34–67.03%) and reduced Na + content (2–4.5-fold). Genes involved in salt tolerance, GmFLD19 and GmNARK , were upregulated under NaCl stress; however, significant decreases in GmFLD19 (3–12-fold) and GmNARK (1.8–3.7-fold) expression were observed in bacterial inoculated plants. Conclusion In conclusion, bacterial isolates ALT29 and ALT43 can mitigate salinity stress and increase plant growth, providing an eco-friendly approach for addressing saline conditions in agricultural production systems.

Abiotic stresses, such as salt and heat stress, coexist in some regions of the world and can have a significant impact on agricultural plant biomass and production. Rice is a valuable crop that is susceptible to salt and high temperatures. Here, we studied the role of flavanol 3-hydroxylase in response to combined salt and heat stress with the aim of better understanding the defensive mechanism of rice. We found that, compared with wild-type plants, the growth and development of transgenic plants were improved due to higher biosynthesis of kaempferol and quercetin. Furthermore, we observed that oxidative stress was decreased in transgenic plants compared with that in wild-type plants due to the reactive oxygen species scavenging activity of kaempferol and quercetin as well as the modulation of glutathione peroxidase and lipid peroxidase activity. The expression of high-affinity potassium transporter ( HKT ) and salt overly sensitive ( SOS ) genes was significantly increased in transgenic plants compared with in control plants after 12 and 24 h, whereas sodium-hydrogen exchanger ( NHX ) gene expression was significantly reduced in transgenic plants compared with in control plants. The expression of heat stress transcription factors (HSFs) and heat shock proteins (HSPs) in the transgenic line increased significantly after 6 and 12 h, although our understanding of the mechanisms by which the F3H gene regulates HKT , SOS , NHX , HSF , and HSP genes is limited. In addition, transgenic plants showed higher levels of abscisic acid (ABA) and lower levels of salicylic acid (SA) than were found in control plants. However, antagonistic cross talk was identified between these hormones when the duration of stress increased; SA accumulation increased, whereas ABA levels decreased. Although transgenic lines showed significantly increased Na+ ion accumulation, K+ ion accumulation was similar in transgenic and control plants, suggesting that increased flavonoid accumulation is crucial for balancing Na+/K+ ions. Overall, this study suggests that flavonoid accumulation increases the tolerance of rice plants to combined salt and heat stress by regulating physiological, biochemical, and molecular mechanisms.

Due to global climate change, crops are certainly confronted with a lot of abiotic and biotic stress factors during their growth that cause a serious threat to their development and overall productivity. Among different abiotic stresses, salt and drought are considered the most devastating stressors with serious impact on crop’s yield stability. Here, the current study aimed to elucidate how melatonin works in regulating plant biomass, oxidative stress, antioxidant defense system, as well as the expression of genes related to salt and drought stress in rice plants. Eight groups of rice plants (3 replicates, 5 plants each) underwent varied treatments: control, melatonin, salt, drought, salt + drought, salt + melatonin, drought + melatonin, and salt + drought + melatonin. Melatonin (100 µM) was alternately applied a week before stress exposure; salt stress received 100 mM NaCl every 3 days for 3 weeks, and drought stress involved 10% PEG. Young leaves were randomly sampled from each group. The results showed that melatonin treatment markedly reduces salt and drought stress damage by promoting root, shoot length, fresh and dry weight, increasing chlorophyll contents, and inhibiting excessive production of oxidative stress markers. Salt and drought stress significantly decreased the water balance, and damaged cell membrane by reducing relative water contents and increasing electrolyte leakage. However, melatonin treated rice plants showed high relative water contents and low electrolyte leakage. Under salt and drought stress conditions, exogenous application of melatonin boosted the expression level of salt and drought stress responsive genes like OsSOS , OsNHX , OsHSF and OsDREB in rice plants. Taken together, our results reveal that melatonin treatment significantly increases salt and drought tolerance of rice plants, by increasing plant biomass, suppressing ROS accumulation, elevating antioxidants defense efficiency, and up-regulating the expression of salt and drought stress responsive genes.

Heat stress is one of the major abiotic stresses that impair plant growth and crop productivity. Plant growth-promoting endophytic bacteria (PGPEB) and humic acid (HA) are used as bio-stimulants and ecofriendly approaches to improve agriculture crop production and counteract the negative effects of heat stress. Current study aimed to analyze the effect of thermotolerant SA1 an isolate of Bacillus cereus and HA on tomato seedlings. The results showed that combine application of SA1+HA significantly improved the biomass and chlorophyll fluorescence of tomato plants under normal and heat stress conditions. Heat stress increased abscisic acid (ABA) and reduced salicylic acid (SA) content; however, combined application of SA1+HA markedly reduced ABA and increased SA. Antioxidant enzymes activities revealed that SA1 and HA treated plants exhibited increased levels of ascorbate peroxidase (APX), superoxide dismutase (SOD), and reduced glutathione (GSH). In addition, heat stress markedly reduced the amino acid contents; however, the amino acids were increased with co-application of SA1+HA. Similarly, inductively-coupled plasma mass-spectrometry results showed that plants treated with SA1+HA exhibited significantly higher iron (Fe+), phosphorus (P), and potassium (K+) uptake during heat stress. Heat stress increased the relative expression of SlWRKY33b and autophagy-related (SlATG5) genes, whereas co-application of SA1+HA augmented the heat stress response and reduced SlWRKY33b and SlATG5 expression. The heat stress-responsive transcription factor (SlHsfA1a) and high-affinity potassium transporter (SlHKT1) were upregulated in SA1+HA-treated plants. In conclusion, current findings suggest that co-application with SA1+HA can be used for the mitigation of heat stress damage in tomato plants and can be commercialized as a biofertilizer.

Synthetic data generation addresses the challenges of obtaining extensive empirical datasets, offering benefits such as cost-effectiveness, time efficiency, and robust model development. Nonetheless, synthetic data-generation methodologies still encounter significant difficulties, including a lack of standardized metrics for modeling different data types and comparing generated results. This study introduces PVS-GEN, an automated, general-purpose process for synthetic data generation and verification. The PVS-GEN method parameterizes time-series data with minimal human intervention and verifies model construction using a specific metric derived from extracted parameters. For complex data, the process iteratively segments the empirical dataset until an extracted parameter can reproduce synthetic data that reflects the empirical characteristics, irrespective of the sensor data type. Moreover, we introduce the PoR metric to quantify the quality of the generated data by evaluating its time-series characteristics. Consequently, the proposed method can automatically generate diverse time-series data that covers a wide range of sensor types. We compared PVS-GEN with existing synthetic data-generation methodologies, and PVS-GEN demonstrated a superior performance. It generated data with a similarity of up to 37.1% across multiple data types and by 19.6% on average using the proposed metric, irrespective of the data type.

The intrinsic stochasticity of the memristor can be used to generate true random numbers, essential for non-decryptable hardware-based security devices. Here, we propose a novel and advanced method to generate true random numbers utilizing the stochastic oscillation behavior of a NbO x mott memristor, exhibiting self-clocking, fast and variation tolerant characteristics. The random number generation rate of the device can be at least 40 kb s −1 , which is the fastest record compared with previous volatile memristor-based TRNG devices. Also, its dimensionless operating principle provides high tolerance against both ambient temperature variation and device-to-device variation, enabling robust security hardware applicable in harsh environments. Obtaining true random numbers is of great importance for cryptography, however, it can be challenging to obtain a large bit rate. Here, the authors make use of the oscillating behaviour of a Mott memristor, which exhibit rapid oscillations, and therefore a large bit rate, alongside impressive endurance.

Insulin resistance is associated with the occurrence of stroke and atherosclerotic disease. However, the relationship between insulin resistance and the prognosis of acute ischemic stroke in non-diabetic patients is unclear. We hypothesized that insulin resistance might affect short-term functional recovery after acute ischemic stroke in non-diabetic patients. Between May 2014 and December 2016, 1377 consecutive patients with acute ischemic stroke were enrolled from a prospectively maintained stroke registry. After excluding patients with transient ischemic attacks (TIA), pre-stroke disabilities, diabetes mellitus, and patients with incomplete evaluations, 517 patients were included in the study. The homeostasis model assessment of insulin resistance (HOMA-IR) score was used to evaluate the degree of insulin resistance. The patients with the highest quartile of log HOMA-IR index scores were younger and had higher fasting blood glucose, total cholesterol, triglycerides, low-density lipoprotein, and HbA1c levels. Multivariable logistic regression analysis revealed that log HOMA-IR scores were independently associated with poor prognosis after adjusting for age and sex and p < 0.1 in univariable analysis. Insulin resistance was associated with the poor functional outcome of non-diabetic stroke patients. This evidence supports treating insulin resistance in acute ischemic stroke patients with blood glucose levels within the normal range.