Plant growth regulators improve growth, photosynthesis, mineral nutrient and antioxidant system under cadmium stress in menthol mint (Mentha arvensis L.)

Exogenously applied nano-zinc oxide mitigates cadmium stress in Zea mays L. through modulation of physiochemical activities and nutrients homeostasis

The increasing levels of cadmium (Cd) pollution in agricultural soil reduces plant growth and yield. This study aims to determine the impact of green synthesized zinc oxide nanoparticles (ZnO-NPs) on the physiochemical activities, nutrition, growth, and yield of Zea mays L. under Cd stress conditions. For this purpose, ZnO-NPs (450 ppm and 600 ppm) synthesized from Syzygium aromaticum were applied through foliar spray to Z. mays and also used as seed priming agents. A significant decline in plant height (35.24%), biomass production (43.86%), mineral content, gas exchange attributes, and yield (37.62%) was observed in Cd-spiked plants compared to the control. While, 450 ppm ZnO-NPs primed seed increased plant height (18.46%), total chlorophyll (80.07%), improved ascorbic acid (25.10%), DPPH activity (26.66%), and soil mineral uptake (Mg+2 (38.86%), K+ (27.83%), and Zn+2 (43.68%) as compared to plants only spiked with Cd. On the contrary, the foliar-applied 450 ppm ZnO-NPs increased plant height (8.22%), total chlorophyll content (73.59%), ascorbic acid (21.39%), and DPPH activity (17.61%) and yield parameters; cob diameter (19.45%), and kernels numbers 6.35% enhanced compared to plants that were spiked only with Cd. The findings of the current study pave the way for safer and more cost-effective crop production in Cd-stressed soils by using green synthesized NPs and provide deep insights into the underlying mechanisms of NPs treatment at the molecular level to provide compelling evidence for the use of NPs in improving plant growth and yield.

The Exogenous Application of 24-Epibrassinolide (24-EBL) Increases the Cd and Pb Resilience in Zea mays (L.) by Regulating the Growth and Physiological Mechanism

Heavy metals (HMs) at a concentration above the threshold level act as environmental pollutants and very often threaten the agricultural productivity globally. Finding affordable and environmentally sustainable deliverables to address this issue is therefore a top focus. Phytohormones alleviate the HMs-induced toxicity and positively influence the plant growth. Considering the importance of phytohormones, the present study aimed to assess the effect of 24-epibrassinolide (24-EBL; 10 µM) as seed soaking treatment on growth performance of Zea mays (L.) contaminated separately with increasing concentrations (50-400 mg.kg-1) of lead (Pb) and cadmium (Cd). With increasing metal concentrations, growth and plant biometric criteria were reduced. For instance, Cd at 400 mg.kg-1 soil reduced the germination efficiency (56%), root (77%) and shoot (69%) dry weight, total chlorophyll (64%), and carotenoid content (45%). Contrarily, both HMs caused increase in stress biomarkers and antioxidant enzymes in seedling. However, exogenous administration of 24-EBL significantly enhanced the growth attributes, photosynthetic pigments, proline, MDA, and antioxidant enzyme activity while reducing the harmful effects of HMs stress on Z. mays. For instance, 24-EBL (10 µM) improved the germination percentage, root biomass, chl a, chl b, total chlorophyll, and carotenoid content by 16, 21, 17, 34, 18, and 15%, respectively, in 50 mg.Pb.kg-1 soil-treated Z. mays plants. Furthermore, the amounts of proline, MDA, and antioxidant enzymes in foliage of Z. mays were interestingly and dramatically lowered by 24-EBL application. Uptake of metals in plant organs was significantly reduced when 24-EBL was applied to Pb- and Cd-treated Z. mays. The recent findings help us better understand how 24-EBL regulates growth and development of Z. mays as well as how it boosts HMs' resilience, which could increase the possibility of employing 24-EBL to increase Z. mays productivity. Thus, the present findings confirmed the potentiality of pre-soaking the seed in 24-EBL solution that neutralizes the toxic effects of heavy metals in Z. mays plants. Therefore, it is suggested that applying phytohormones including 24-EBL in removal of heavy metal stress in plants is the best possible solution in sustainable agriculture.

Physiological and transcriptomic analyses reveal the cadmium tolerance mechanism of Miscanthus lutarioriparia

Miscanthus lutarioriparia is a promising energy crop that is used for abandoned mine soil phytoremediation because of its high biomass yield and strong tolerance to heavy metals. However, the biological mechanism of heavy metal resistance is limited, especially for applications in the soil restoration of mining areas. Here, through the investigation of soil cadmium(Cd) in different mining areas and soil potted under Cd stress, the adsorption capacity of Miscanthus lutarioriparia was analyzed. The physiological and transcriptional effects of Cd stress on M. lutarioriparia leaves and roots under hydroponic conditions were analyzed. The results showed that M. lutarioriparia could reduce the Cd content in mining soil by 29.82%. Moreover, different Cd varieties have different Cd adsorption capacities in soils with higher Cd concentration. The highest cadmium concentrations in the aboveground and belowground parts of the plants were 185.65 mg/kg and 186.8 mg/kg, respectively. The total chlorophyll content, superoxide dismutase and catalase activities all showed a trend of increasing first and then decreasing. In total, 24,372 differentially expressed genes were obtained, including 7735 unique to leaves, 7725 unique to roots, and 8912 unique to leaves and roots, which showed differences in gene expression between leaves and roots. These genes were predominantly involved in plant hormone signal transduction, glutathione metabolism, flavonoid biosynthesis, ABC transporters, photosynthesis and the metal ion transport pathway. In addition, the number of upregulated genes was greater than the number of downregulated genes at different stress intervals, which indicated that M. lutarioriparia adapted to Cd stress mainly through positive regulation. These results lay a solid foundation for breeding excellent Cd resistant M. lutarioriparia and other plants. The results also have an important theoretical significance for further understanding the detoxification mechanism of Cd stress and the remediation of heavy metal pollution in mining soil.

Identification and characterization of the critical genes encoding Cd-induced enhancement of SOD isozymes activities in Zhe-Maidong (Ophiopogon japonicus)

Superoxide dismutase (SOD) protects plants from abiotic stress-induced reactive oxygen species (ROS) damage. Here, the effects of cadmium (Cd) exposure on ROS accumulation and SOD isozymes, as well as the identification of significant SOD isozyme genes, were investigated under different Cd stress treatments to Zhe-Maidong (Ophiopogon japonicus). The exposure to Cd stress resulted in a notable elevation in the SOD activity in roots. Cu/ZnSODa and Cu/ZnSODb were the most critical SOD isozymes in response to Cd stress, as indicated by the detection results for SOD isozymes. A total of 22 OjSOD genes were identified and classified into three subgroups, including 10 OjCu/ZnSODs, 6 OjMnSODs, and 6 OjFeSODs, based on the analysis of conserved motif and phylogenetic tree. Cu/ZnSOD-15, Cu/ZnSOD-18, Cu/ZnSOD-20, and Cu/ZnSOD-22 were the main genes that control the increase in SOD activity under Cd stress, as revealed via quantitative PCR and transcriptome analysis. Additionally, under various heavy metal stress (Cu2+, Fe2+, Zn2+, Mn2+), Cu/ZnSOD-15, Cu/ZnSOD-18, and Cu/ZnSOD-22 gene expression were significantly upregulated, indicating that these three genes play a critical part in resisting heavy metal stress. The molecular docking experiments performed on the interaction between oxygen ion (O2•-) and OjSOD protein have revealed that the critical amino acid residues involved in the binding of Cu/ZnSOD-22 to the substrate were Pro135, Ile136, Ile140, and Arg144. Our findings provide a solid foundation for additional functional investigations on the OjSOD genes, as well as suggestions for improving genetic breeding and agricultural management strategies to increase Cd resistance in O. japonicus.

Efficient nanostructured materials to reduce nutrient leaching to overcome environmental contaminants

Nutrient leaching is a major reason for fresh and ground water contamination. Menthol is the major bioactive ingredient of Mentha arvensis L. and one of the most traded products of global essential oil market. The indigenous production of menthol crystals in developing countries of the world can prove to be the backbone for local growers and poor farmers. Therefore, present research was designed to check the effects of nano-structured plant growth regulators (PGRs) (28-homobrassinolide and ethephon) with reduced leaching potentials on the essential oil and menthol (%) of Mentha arvensis L. The prepared nano-formulations were characterized by Fourier transform infrared (FTIR) spectroscopy, Laser induced breakdown spectroscopy (LIBS), Differential scanning colorimetry-thermal gravimetric analysis (DSC-TGA), Scanning electron microscopy (SEM), Atomic absorption spectrometry (AAS) and Zeta potential and Zeta size analysis. The menthol (%) was determined by modified spectrophotometric and gas chromatographic (GC) method. The highest essential oil (%) was obtained by the application of 28-homobrassinolide-Zn-NPs-L-II (0.92 ± 0.09%) and ethephon-Ca-NPs-L-III (0.91 ± 0.05%) as compared to the control (0.65 ± 0.03%) and blank (0.62 ± 0.09%). The highest menthol (%) was obtained by applying 28-homobrassinolide-Ca-NPs-L-I (80.06 ± 0.07%), 28-homobrassinolide-Ca-NPs-L-II (80.48 ± 0.09%) and 28-homobrassinolide-Ca-NPs-L-III (80.84 ± 0.11%) and ethephon-Ca-NPs-L-III (81.53 ± 0.17%) and ethephon-Zn-NPs-L-II (81.93 ± 0.26%) as compared to control (67.19 ± 0.14%) and blank (63.93 ± 0.17%).

Effect of hesperidin on growth, photosynthesis, antioxidant systems and uptake of cadmium, copper, chromium and zinc by Celosia argentea plants

Rapid industrialization and extensive agricultural practices are the major causes of soil heavy metal contamination, which needs urgent attention to safeguard the soils from contamination. However, the phytotoxic effects of excessive metals in plants are the primary obstacle to efficient phytoextraction. The present study evaluated the effects of hesperidin (HSP) on metals (Cu, Cd, Cr, Zn) phytoextraction by hyperaccumulator (Celosia argentea L.) plants. For this purpose, HSP, a flavonoid compound with strong antioxidant potential to assist metal phytoextraction was used under metal stress in plants. Celosia argentea plants suffered significant (P ≤ 0.001) oxidative damage due to the colossal accumulation of metals (Cu, Cd, Cr, Zn). However, HSP supplementation notably (P ≤ 0.001) abated ROS generation (O2•‒, •OH, H2O2), lipoxygenase activity, methylglyoxal production, and relative membrane permeability that clearly indicated HSP-mediated decline in oxidative injury in plants. Exogenous HSP improved (P ≤ 0.001) the production of non-protein thiol, phytochelatins, osmolytes, and antioxidant compounds. Further, HSP enhanced (P ≤ 0.001) H2S and NO endogenous production, which might have improved the GSH: GSSG ratio. Consequently, HSP-treated C. argentea plants had higher biomass alongside elevated metal accumulation mirrored as profound modifications in translocation factor (TF), bioaccumulation coefficient (BAC), and bioconcentration factor (BCF). In this context, HSP significantly enhanced TF of Cr (P ≤ 0.001), Cd (P ≤ 0.001), and Zn (P ≤ 0.01), while BAC of Cr (P ≤ 0.001), Cd (P ≤ 0.001), and Zn (P ≤ 0.001). Further, BCF was significant (P ≤ 0.05) only in plants grown under Cr-spiked soil. Overall, HSP has the potential for phytoremediation of metals by C. argentea, which might be a suitable strategy for metal-polluted soils.

Effects of Cd treatment on morphology, chlorophyll content and antioxidant enzyme activity of Elymus nutans Griseb., a native plant in Qinghai-Tibet Plateau

Cd pollution is a global environmental problem. However, the response mechanism of the alpine plant Pelagia under Cd stress remains unclear. Therefore, in this study, a native plant(Elymus nutans Griseb.) of the Qinghai-Tibet Plateau was used as the material to quantify plant height, leaf number, length of leaf, crown width, root number, biomass, Dry weight malondialdehyde (MDA), free proline, superoxide dismutase (SOD), ascorbate enzyme (APX), catalase (CAT) and chlorophyll contents under different Cd concentrations. The results showed that the growth of Elymus nutans Griseb. was a phenomenon of "low concentration promotes growth, high concentration inhibited growth" under Cd treatment. It meant that 10 mg·L^-1 Cd promoted the growth of leaf number, plant height, crown width and tiller number, while 40 mg·L^-1 Cd inhibited the growth of root number and biomass of Elymus nutans Griseb. compare with the control. The MDA content, free proline content, SOD activity, APX activity and CAT activity of Elymus nutans Griseb. was increased with the increase of Cd treatment concentration to resist the oxidative damage caused by Cd to the body. At the same time, the accumulation of chlorophyll A, chlorophyll B and chlorophyll AB was decreased with the increase of Cd stress concentration. In addition, the carotenoid content did not change much between the control group and the treatment group, indicating that Cd treatment had little effect on it. The results could provide a reference for the mechanism of heavy metal resistance and the selection and improvement of Cd -resistant varieties of Elymus nutans Griseb.

Regulation of proline metabolism, AsA-GSH cycle, cadmium uptake and subcellular distribution in Brassica napus L. under the effect of nano-silicon

Cadmium (Cd) is known to have detrimental effects on plant growth and human health. Recent studies showed that silicon nanoparticles (SNPs) can decrease Cd toxicity in plants. Therefore, a study was conducted using 50 μM Cd and 1.50 mM SNPs to investigate Cd uptake, subcellular distribution, proline (Pro) metabolism, and the antioxidant defense system in rapeseed seedlings. In this study, results indicated that Cd stress negatively affected rapeseed growth, and high Cd contents accumulated in both shoots and roots. However, SNPs significantly decreased Cd contents in shoots and roots. Moreover, substantial increases were found in root fresh weight by 40.6% and dry weight by 46.6%, as well as shoot fresh weight by 60.1% and dry weight by 113.7% with the addition of SNPs. Furthermore, the addition of SNPs alleviated oxidative injury by maintaining the ascorbate-glutathione (AsA-GSH) cycle and increased Pro biosynthesis which could be due to high activities of Δ1-pyrroline-5-carboxylate synthase (P5CS) and reductase (P5CR) and decreased proline dehydrogenase (ProDH) activity. Furthermore, the addition of SNPs accumulated Cd in the soluble fraction (42%) and cell wall (45%). Results indicate that SNPs effectively reduce Cd toxicity in rapeseed seedlings which may be effective in promoting both rapeseed productivity and human health preservation.

Dynamic crosstalk between silicon nanomaterials and potentially toxic trace elements in plant-soil systems

Agricultural soil pollution with potentially toxic trace elements (PTEs) has emerged as a significant environmental concern, jeopardizing food safety and human health. Although, conventional remediation approaches have been used for PTEs-contaminated soils treatment; however, these techniques are toxic, expensive, harmful to human health, and can lead to environmental contamination. Nano-enabled agriculture has gained significant attention as a sustainable approach to improve crop production and food security. Silicon nanomaterials (SiNMs) have emerged as a promising alternative for PTEs-contaminated soils remediation. SiNMs have unique characteristics, such as higher chemical reactivity, higher stability, greater surface area to volume ratio and smaller size that make them effective in removing PTEs from the environment. The review discusses the recent advancements and developments in SiNMs for the sustainable remediation of PTEs in agricultural soils. The article covers various synthesis methods, characterization techniques, and the potential mechanisms of SiNMs to alleviate PTEs toxicity in plant-soil systems. Additionally, we highlight the potential benefits and limitations of SiNMs and discusses future directions for research and development. Overall, the use of SiNMs for PTEs remediation offers a sustainable platform for the protection of agricultural soils and the environment.

Exploring the Impact of Salicylic Acid and Farmyard Manure on Soil Rhizospheric Properties and Cadmium Stress Alleviation in Maize (Zea mays L.)

Cadmium (Cd) pollution is a growing environmental problem that negatively impacts plant growth and development, particularly in maize. In this research, the impact of farmyard manure (FYM) and salicylic acid (SA) on rhizospheric characteristics and the reduction of Cd stress in maize was examined at Government College (GC) University, Lahore, in 2022. The experiment was arranged with a randomized design, including three replications of 12 treatments (T1 = Control; T2 = Farmyard manure; T3 = Salicylic Acid; T4 = 100 mg/kg of soil Cd; T5 = 200 mg/kg of soil Cd; T6 = Farmyard manure + Salicylic acid; T7 = FYM + 100 mg/kg soil Cd; T8 = FYM + 200 mg/kg soil Cd; T9 = SA + 100 mg/kg soil Cd; T10 = SA + 200 mg/kg soil Cd; T11 = FYM + SA + 100 mg/kg soil Cd; T12 = FYM + SA + 200 mg/kg soil Cd). Results demonstrated that Cd stress negatively affected the maize plant and soil properties, but the application of SA and FYM was effective to mitigate the Cd stress up to a certain level. A reduction of 41.52%, 39.14%, and 39.94% in root length, length of the leaf, and crop growth rate was noticed, due to the Cd stress at 200 mg/kg soil, but this reduction was reduced to 18.83%, 10.35%, and 12.26%, respectively, when FYM and salicylic acid were applied as a combined application under the same stress level of Cd. The root biomass, leaf surface area, and length were all improved by SA and FYM, which enhanced the plant's capacity to absorb nutrients and improve growth under Cd stress. In conclusion, the use of salicylic acid together with farm manure can be an effective approach to mitigate Cd stress in maize crops.

Phosphorus and naphthalene acetic acid increased the seed yield by regulating carbon and nitrogen assimilation of flax

To evaluate the impact of phosphorus (P) combined with exogenous NAA on flax yield, enhance flax P utilization efficiency and productivity, minimize resource inputs and mitigate negative environmental and human effects. Therefore, it is crucial to comprehend the physiological and biochemical responses of flax to P and naphthylacetic acid (NAA) in order to guide future agronomic management strategies for increasing seed yield. A randomized complete block design trial was conducted under semi-arid conditions in Northwest China, using a factorial split-plot to investigate the effects of three P (0, 67.5, and 135.0 kg P2O5 ha-1) and three exogenous spray NAA levels (0, 20, and 40 mg NAA L-1) on sucrose phosphate synthase (SPS) and diphosphoribulose carboxylase (Rubisco) activities as well as nitrogen (N) and P accumulation and translocation in flax. Results indicated that the SPS and Rubisco activities, N and P accumulation at flowering and maturity along with assimilation and translocation post-flowering, fruiting branches per plant, tillers per plant, capsules per plant, and seed yield were 95, 105, 14, 27, 55, 15, 13, 110, 103, 82, 16, 61, 8, and 13% greater in the P treatments compared to those in the zero P treatment, respectively. Moreover, those characteristics were observed to be greater with exogenous spray NAA treatments compared to that no spray NAA treatment. Additionally, the maximum SPS and Rubisco activities, N and P accumulation, assimilation post-flowering and translocation, capsules per plant, and seed yield were achieved with the application of 67.5 kg P2O5 ha-1 with 20 mg NAA L-1. Therefore, these findings demonstrate that the appropriate combination of P fertilizer and spray NAA is an effective agronomic management strategy for regulating carbon and nitrogen assimilation by maintaining photosynthetic efficiency in plants to increase flax productivity.

Long-Chain Molecules with Agro-Bioactivities and Their Applications

Long-chain molecules play a vital role in agricultural production and find extensive use as fungicides, insecticides, acaricides, herbicides, and plant growth regulators. This review article specifically addresses the agricultural biological activities and applications of long-chain molecules. The utilization of long-chain molecules in the development of pesticides is an appealing avenue for designing novel pesticide compounds. By offering valuable insights, this article serves as a useful reference for the design of new long-chain molecules for pesticide applications.

Heavy Metals, Their Phytotoxicity, and the Role of Phenolic Antioxidants in Plant Stress Responses with Focus on Cadmium: Review

The current state of heavy metal (HM) environmental pollution problems was considered in the review: the effects of HMs on the vital activity of plants and the functioning of their antioxidant system, including phenolic antioxidants. The latter performs an important function in the distribution and binding of metals, as well as HM detoxification in the plant organism. Much attention was focused on cadmium (Cd) ions as one of the most toxic elements for plants. The data on the accumulation of HMs, including Cd in the soil, the entry into plants, and the effect on their various physiological and biochemical processes (photosynthesis, respiration, transpiration, and water regime) were analyzed. Some aspects of HMs, including Cd, inactivation in plant tissues, and cell compartments, are considered, as well as the functioning of various metabolic pathways at the stage of the stress reaction of plant cells under the action of pollutants. The data on the effect of HMs on the antioxidant system of plants, the accumulation of low molecular weight phenolic bioantioxidants, and their role as ligand inactivators were summarized. The issues of polyphenol biosynthesis regulation under cadmium stress were considered. Understanding the physiological and biochemical role of low molecular antioxidants of phenolic nature under metal-induced stress is important in assessing the effect/aftereffect of Cd on various plant objects-the producers of these secondary metabolites are widely used for the health saving of the world's population. This review reflects the latest achievements in the field of studying the influence of HMs, including Cd, on various physiological and biochemical processes of the plant organism and enriches our knowledge about the multifunctional role of polyphenols, as one of the most common secondary metabolites, in the formation of plant resistance and adaptation.

Seed Priming with Triacontanol Alleviates Lead Stress in Phaseolus vulgaris L. (Common Bean) through Improving Nutritional Orchestration and Morpho-Physiological Characteristics

Worldwide, crop productivity is highly influenced by heavy metal toxicity. Lead (Pb) the is second-most toxic heavy metal that has high persistence in soil. Lead is translocated in plants from rhizosphere soil and enters the food chain, where it poses a significant hazard to the health of humans. In the present investigation, seed priming with triacontanol (Tria) was used to mitigate Pb phytotoxicity in Phaseolus vulgaris L. (common bean). Seeds were primed with different concentrations of Tria (control, 10 µmol L^-1, 20 µmol L^-1, 30 µmol L^-1) solutions. The pot experiment was carried out by sowing Tria-primed seeds in contaminated soil with 400 mg kg^-1 Pb. Lead alone induced a decrease in the rate of germination and a significant reduction in biomass and growth of P. vulgaris as compared to the control. All these negative effects were reversed by Tria-primed seeds. Proliferation of photosynthetic pigments was observed 1.8-fold by Tria under Pb stress. Primed seeds with 20 µmol L^-1 Tria enhanced stomatal conductance (gs), photosynthetic rate (A), transpiration rate (Ei), and uptake of mineral contents (Mg⁺², Zn⁺², Na⁺, and K⁺) and reduced Pb accumulation in seedlings. Tria caused a 1.3-fold increase in osmotic regulator proline synthesis to alleviate Pb stress. Phenolics, soluble protein, and DPPH free radical scavenging activity were enhanced by Tria application, suggesting that exogenous Tria could be employed to improve plant tolerance to Pb stress.

Putrescine-functionalized carbon quantum dot (put-CQD) nanoparticle: A promising stress-protecting agent against cadmium stress in grapevine (Vitis vinifera cv. Sultana)

Due to their sessile nature, plant cannot escape from stress factors in their growing environment, in either biotic or abiotic nature. Amid the abiotic stress factors; high levels of soil cadmium (Cd) impose heavy metal stress on plants, resulting in critical injuries and reduced agronomic performance. In order to buffer the adverse effects of Cd stress, novel nanoparticles (NP) have been applied and notable improvements have been reported. According to the literature, the protective roles of polyamines (e.g., Putrescine; Put) and carbon quantum dots (CQD) have been reported with respect to the plant productivity under either stress or non-stress conditions. Those reports led us to hypothesize that the conjugation of Put and CQD (Put-CQD NPs) might lead to further augmented performance of plants under stress and non-stress conditions. In this regard, we successfully synthesized a novel nanomaterial Put-CQD NPs. In this respect, Put (50 mg L^-1), CQD (50 mg L^-1) and Put-CQD NPs (25 and 50 mg L^-1) were sprayed in 'Sultana' grapevines under Cd stress (10 mg kg^-1). As expected, upon stress, Cd content in leaf and root tissues increased by 103.40% and 65.15%, respectively (p < 0.05). The high uptake and accumulation of Cd in plant tissues were manifested in significant alterations of physiological and biochemical attributes of the plant. Concerning stress markers, Cd stress caused increases in content of induced MDA, H₂O₂, and proline as well as electrolyte leakage rate. As expected, Cd stress caused critical reductions in fresh and dry leaf weight by 21.31% and 42.34%, respectively (p < 0.05). On the other hand, both Put-CQD NPs increased fresh and dry leaf weigh up to approximately 30%. The Cd-mediated disturbances in photosynthetic pigments and chlorophyll fluorescence were buffered with Put-CQD NPs. Of the defence system, enzymatic (SOD, APX, GP) as well as anthocyanin and phenolics were induced by both Cd stress and Put-CQD NPs (p < 0.05). On the other hand, Cd stress reduced content of polyamines (putrescine (Put), spermine (Spm) and spermidine (Spd) by 39.28%, 53.36%, and 39.26%, respectively (p < 0.05). However, the reduction levels were buffered by the treatments. Considering the effectiveness of both NP concentrations, the lower dose (25 mg L^-1) could be considered as an optimal concentration. To our knowledge, this is the first report of its kind as a potential agent to reduce the adverse effects of Cd stress in grapevines.

Plant growth regulators mediated mitigation of salt-induced toxicities in mustard (Brassica juncea L.) by modifying the inherent defense system

Salt stress is one of the common environmental threats to crop growth, development, and productivity. Plant growth regulators (PGRs) are natural messengers and are known to play pivotal roles at different stages of the growth and development of plants under various environmental conditions. Keeping in mind the importance of PGRs in stress management, a factorial randomized pot experiment was conducted to evaluate the efficiency of three selected PGRs, namely gibberellic acid (GA₃), salicylic acid (SA) and triacontanol (Tria) for the amelioration of NaCl stress in mustard. Plants were subjected to four concentrations of NaCl (0, 50, 100 and 150 mM). Two foliar sprays of PGRs (GA₃, SA and Tria), each at 5 μM were applied to the foliage of plants using a hand sprayer. The increasing levels of NaCl decreased growth, physio-biochemical, histochemical and yield parameters in a dose-dependent manner while increasing activities of antioxidant enzymes, contents of osmolytes and oxidative stress biomarkers linearly with increasing levels of NaCl. The spray of GA₃, SA and Tria under stressed-free and stressed conditions improved the aforesaid attributes while decreasing the generation of stress biomarkers. Of sprayed PGRs, SA proved to be the best for alleviating the adverse effect of NaCl stress. Furthermore, it provides experimental data for its possible biotechnological applications in mustard crops exposed to high concentrations of salinity and possibly to other environmental stresses which have associated oxidative stress.

Nitrogen Supplementation Modulates Morphological, Biochemical, Yield and Quality Attributes of Peppermint

Due to the rising demand for essential oil in the world market, peppermint has gained an important status among aromatic and medicinal plants. It becomes imperative to optimize its performance in terms of the growth, physiological functioning and biosynthesis of specialized metabolites. A factorial randomized pot experiment was performed using three peppermint cultivars (Kukrail, Pranjal and Tushar) and five levels of leaf-applied nitrogen (N), viz. 0 (control), 0.5, 1.0, 1.5 and 2%. The phenological features, biochemical parameters, viability of root cells, stomatal and trichome behavior were assessed at 100 days after transplanting (DAT). The yield-related parameters, viz., herbage yield, essential oil content, menthol content and yield were studied at 120 DAT. The results revealed that increasing the N doses up to 1.5% enhanced all the studied parameters of peppermint, which thereafter (at the dose above 1.5% N) decreased. The variation pattern of the studied parameters was "low-high-low". Cultivar Kukrail surpassed the two other cultivars Tushar and Pranjal. Among the foliar sprays, the application of 1.5% N increased chlorophyll content and net photosynthetic rate in all three cultivars. Moreover, the essential oil (EO), EO yield and menthol yield of the plant were also increased linearly in all three cultivars as compared with their control plants. Nitrogen application enhanced the trichome size and density of the plants, as revealed through scanning electron microscopy. Furthermore, from the GC-MS studies, the EO content in the studied cultivars increased, particularly in the case of menthol, with the N application. It may be concluded that two sprays of N (1.5%) at appropriate growth stages could be beneficial for improving morphological, physio biochemical and yield attributes of peppermint.

Cadmium toxicity in medicinal plants: An overview of the tolerance strategies, biotechnological and omics approaches to alleviate metal stress

Medicinal plants, an important source of herbal medicine, are gaining more demand with the growing human needs in recent times. However, these medicinal plants have been recognized as one of the possible sources of heavy metal toxicity in humans as these medicinal plants are exposed to cadmium-rich soil and water because of extensive industrial and agricultural operations. Cadmium (Cd) is an extremely hazardous metal that has a deleterious impact on plant development and productivity. These plants uptake Cd by symplastic, apoplastic, or via specialized transporters such as HMA, MTPs, NRAMP, ZIP, and ZRT-IRT-like proteins. Cd exerts its effect by producing reactive oxygen species (ROS) and interfere with a range of metabolic and physiological pathways. Studies have shown that it has detrimental effects on various plant growth stages like germination, vegetative and reproductive stages by analyzing the anatomical, morphological and biochemical changes (changes in photosynthetic machinery and membrane permeability). Also, plants respond to Cd toxicity by using various enzymatic and non-enzymatic antioxidant systems. Furthermore, the ROS generated due to the heavy metal stress alters the genes that are actively involved in signal transduction. Thus, the biosynthetic pathway of the important secondary metabolite is altered thereby affecting the synthesis of secondary metabolites either by enhancing or suppressing the metabolite production. The present review discusses the abundance of Cd and its incorporation, accumulation and translocation by plants, phytotoxic implications, and morphological, physiological, biochemical and molecular responses of medicinal plants to Cd toxicity. It explains the Cd detoxification mechanisms exhibited by the medicinal plants and further discusses the omics and biotechnological strategies such as genetic engineering and gene editing CRISPR- Cas 9 approach to ameliorate the Cd stress.

Zinc oxide nanoparticles mediated biostimulant impact on cadmium detoxification and in silico analysis of zinc oxide-cadmium networks in Zea mays L. regulome

Cadmium (Cd) toxicity can significantly limit plant growth and development. To eliminate the toxic effects of Cd stress, we intended to evaluate the biochemical mediated physiological responses in maize treated with biostimulant and zinc oxide nanoparticles (ZnPs). In silico analysis exhibited that the maize treated with Cd stress (200 μM) had an adverse impact on CAT1, CAT2, CAT3 and gor1 proteins, which are influential in managing the machinery of redox homeostasis. While maize inoculated with bacteria-based biostimulant and ZnPs (10 ppm) showed prominently improved biomass, chlorophyll a, b and carotenoid content. We found a significant increase in the total sugar, protein, proline content and antioxidants under the effect of Cd stress. However, these parameters are further enhanced by applying biostimulants and ZnPs. Declined lipid peroxidation and membrane solubilization index under the effect of biostimulant and ZnPs was observed. Furthermore, these treatments improved maize's zinc, copper, sodium, magnesium, iron, potassium and calcium content. Based on these results, an antagonistic relationship between Zn and Cd uptake that triggered efficient Cd detoxification in maize shoot was found. Scanning electron micrography showed distorted leaf structure of the Cd stressed plants while the biostimulant and ZnPs reduced the structural cell damage of maize leaves. In silico study showed that ZnO positively regulates all protein interactors, including GRMZM2G317386_P01 (Metallo endo proteinase 1-MMP), GRMZM2G110220_P01 (Metallo endo proteinase 5-MMP), GRMZM2G103055_P01 (Alpha-amylase) and GRMZM2G006069_P01 (Zn-dependent exo peptidase superfamily) proteins which are involved in energy generating processes, channels formation, matrix re-localization and stress response. This suggests that ZnO offers an ideal role with protein interactors in maize. Our findings depict that these treatments, i.e., biostimulant and ZnPs alone, are efficient enough to exhibit Cd remediation potential in maize; however, their combination showed synergistic effects.

Mitigation of Negative Effects of Chromium (VI) Toxicity in Faba Bean (Vicia faba) Plants through the Supplementation of Kinetin (KN) and Gibberellic Acid (GA3)

The present study was carried out to explore the possible role of kinetin and gibberellic acid (GA3) on faba bean under chromium (Cr) stress. Cr treatment negatively affected growth and biomass production, reduced photosynthetic pigments, and inhibited photosynthesis, gas exchange parameters, antioxidant enzymes, and the glyoxylase cycle. Moreover, Cr stress enhanced the production of malondialdehyde (MDA, 216.11%) and hydrogen peroxide (H₂O₂, 230.16%), electrolyte leakage (EL, 293.30%), and the accumulation of proline and glycine betaine. Exogenous application of kinetin and GA3 increased growth and biomass, improved pigment contents and photosynthesis, as well as up-regulated the antioxidant system by improving the antioxidant enzyme activities and the content of nonenzymatic components, and the glyoxylase cycle. Additionally, kinetin and GA3 application displayed a considerable enhancement in proline (602.61%) and glycine betaine (423.72), which help the plants to maintain water balance under stress. Furthermore, a decline in Cr uptake was also observed due to kinetin and GA3 application. Exogenous application of kinetin and GA3 ameliorated the toxic effects of Cr in faba bean plants, up-shooting the tolerance mechanisms, including osmolyte metabolism and the antioxidant system.

Effects of Hydrogen Peroxide on In Vitro Cultures of Tea (Camellia sinensis L.) Grown in the Dark and in the Light: Morphology, Content of Malondialdehyde, and Accumulation of Various Polyphenols

Tea plants (Camellia sinensis L.) are phenol-accumulating crops that are widely used for public health. The healing effect of tea leaf products is due to the biosynthesis of such phenolic compounds (PCs) as flavans, which have P-vitamin capillary-strengthening activity. Due to their limited habitat and the value of their specialized metabolites of a phenolic nature, a promising approach is to establish in vitro cultures from them that retain the ability to form PCs, which is characteristic of ex vivo tea plants. The aim of this study was to investigate the effect of exogenic H₂O₂ (0.01 mM; 0.1 mM; 1 mM) on the growth, morphology, degree of stress response, and accumulation of various phenolic compounds in tea plant callus cultures of different ages (24 or 36 days) grown under different cultivation conditions (darkness or light). According to the results obtained, the H₂O₂ effect on tea callus cultures of different ages did not cause changes in their morphophysiological characteristics, both after 2 h of exposure (rapid response of callus culture, RRCC) and after 48 h (delayed response of callus culture, DRCC). The determination of the malondialdehyde (MDA) content, which serves as an indicator of changes in the level of lipid peroxidation (LPO) and the presence of stress responses in plant cells, indicated either its maintenance at the control level, a decrease, or an increase. All these effects depended on the growth conditions of the tea callus cultures (darkness or light), their age, the duration of exposure (rapid or delayed response), and the H₂O₂ concentration. Similar trends were noted for the total content of PCs as well as the amount of flavans, proanthocyanidins (soluble and insoluble forms), and lignin. The plant cell responses reflected changes in its adaptation programs, when specialized metabolites act as a target for the action of H₂O₂, thereby contributing to an increase in their resistance.

Evaluation of Trigonella foenum-graecum L. Plant Food Safety after Lead Exposure: Phytochemical Processes

Lead stands as a food contaminant through its accumulation in consumed plants. In this study, the effects of lead (II) chloride (PbCl2) and its levels of uptake on morphological and phytochemical responses of fenugreek were assessed to evaluate its tolerance and safety for human consumption. Results revealed that PbCl2 (50−2000 mg L−1) did not affect the germination rate, but it decreased the radicle length and amylase activity. After three months of Pb treatments, the elemental analysis showed that Pb accumulation was greater in roots than shoots, and it was not present in harvested seeds. The bioaccumulation factor > 1 and the translocation factor << 1 observed for 1000 mg L−1 PbCl2 suggested appropriateness of fenugreek as a phytostabilizer. Additionally, increased lipid peroxidation, hydrogen peroxide, flavonoid levels and catalase activity were observed in Pb-treated fenugreek. Meanwhile, decreased chlorophyll content was detected under these conditions. In turn, the total phenol was correlated with Pb treatment only in roots. HPLC analysis proved that under Pb stress, gallic acid was the most produced compound in treated roots compared to shoots, followed by quercetin. Syringic and chlorogenic acids were more produced in shoots. In conclusion, fenugreek can be used for Pb phytoremediation and is safe for consumption after Pb treatments in the traditional medicine system.

Unravelling the Effect of Triacontanol in Combating Drought Stress by Improving Growth, Productivity, and Physiological Performance in Strawberry Plants

To explore the effects of triacontanol (TR) on drought tolerance of strawberry plants (cv Fertona), two field experiments were carried out to study the effects of three supplementary foliar TR rates (0, 0.5, and 1 ppm) under the following three levels of water irrigation: 11 m³/hectare (40% of water holding capacity (WHC) severe as a drought treatment, 22 m³/hectare (80% of WHC) as moderate drought stress, and normal irrigation with 27 m³/hectare (100% of WHC) server as a control treatment. TR treatments were applied five times after 30 days from transplanting and with 15-day intervals. The results showed that drought stress (40% and 80%) markedly decreased the growth, fruit yield, and chlorophyll reading, as well as the gas exchange parameters (net photosynthetic rate, stomatal conductance, and transpiration rate). Meanwhile, drought stress at a high rate obviously increased antioxidant enzyme activities such as superoxide dismutase (SOD), peroxidase (POX), and catalase (CAT) contents in the leaves of the strawberry plants. The moderate and high drought stress rates enhanced some strawberry fruit quality parameters such as total soluble solids (TSS), vitamin C, and anthocyanin content compared to the control. Additionally, TR increased the activities of SOD, POX, and CAT. TR treatment significantly increased the chlorophyll contents, gas exchange parameters (photosynthetic rate and stomatal conductance), and water use efficiency (WUE). Plant height, fruit weight, and total biomass were increased also via TR application. Total yield per plant was increased 12.7% using 1 ppm of TR compared with the control. In conclusion, our results suggested that TR application could relieve the adverse effects of drought stress on the growth of strawberry plants by enhancing the antioxidant enzymes, photosynthesis rate, and WUE of the leaves.

Salicylic Acid Priming Regulates Stomatal Conductance, Trichome Density and Improves Cadmium Stress Tolerance in Mentha arvensis L

The application of phytohormones through seed priming could enhance quality of important medicinal and aromatic plants (MAPs) under heavy metal stress. We evaluated the potential of salicylic acid (SA) priming for overcoming the adverse effects of cadmium stress in Mentha arvensis L. plants. Suckers of plants were primed with SA before transplanting them into soil. At 30 days after transplanting, two doses (50 and 100 μm) of CdCl₂ were applied to the soil. Both Cd treatments altered plant growth, photosynthetic pigments, leaf gas exchange attributes, and mineral nutrient contents. The 50 and 100 μm Cd treatments increased endogenous Cd content by 97.95 and 98.03%, electrolyte leakage (EL) by 34.21 and 44.38%, hydrogen peroxide (H₂O₂) by 34.71 and 55.80%, malondialdehyde (MDA) by 53.08 and 63.15%, and superoxide content (O₂ ^-•) by 24.07 and 38.43%, respectively. Cd triggered the up-regulation of antioxidant enzyme activities (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; and glutathione reductase GR) and increased osmolyte biosynthesis and, interestingly, secondary metabolite (SM) accumulation. The presence of SA and Cd had an additive effect on these parameters. Nevertheless, plants primed with SA regulated stomatal conductance under Cd stress. SA priming to menthol mint plants under Cd stress overcome the effects of Cd stress while increasing SMs.

Alleviation of cadmium phytotoxicity in triacontanol treated Coriandrum sativum L. by modulation of physiochemical attributes, oxidative stress biomarkers and antioxidative system

Cadmium (Cd) is a hazardous metal that has a significant risk of transfer from soil to edible parts of food crops including shoots and seeds. Reduction of Cd accumulation is required to lower the risk of Cd exposure in humans and animals feeding on metal contaminated parts of such plants. Coriandrum sativum L. (coriander) exposed to Cd showed stress symptoms such as stunted growth, reduced photosynthetic activity and synthesis of chlorophyll pigments. Growth inhibition in Cd-treated plants was attributed to induction of oxidative stress as demonstrated by higher level of stress biomarkers such as electrolyte leakage, lipid peroxidation and hydrogen peroxide. Primary objective of the current study was to observe the ameliorative role of triacontanol (Tria) in Cd-stressed coriander seedlings. For this purpose, coriander seeds were primed with Tria concentrations of 5, 10, and 20 μmol L^-1. Seedlings developed from Tria treated seeds exhibited reduced loss of photosynthetic pigments; mitigated oxidative stress caused by Cd, through improved efficacy of antioxidant machinery comprising superoxide dismutase (SOD), peroxidase (POX), and catalase (CAT) enzymes besides non-enzymatic antioxidants including proline, phenolics and flavonoids. Triacontanol treated seedlings showed enhanced yield attributes suggesting that exogenous Tria could be employed to improve plant tolerance to Cd stress.

Exogenous Methyl Jasmonate Application Improved Physio-Biochemical Attributes, Yield, Quality, and Cadmium Tolerance in Fragrant Rice

Cadmium (Cd) has detrimental effects on crop plants, whereas, jasmonates (JAs) play a vital role in abiotic stress tolerance in plants. The present study investigated the effects of exogenous application of methyl jasmonate (MeJa) on the physio-biochemical attributes, yield, and quality of two fragrant rice cultivars, i.e., Xiangyaxiangzhan and Meixiangzhan-2 under Cd stress. The experiment was comprised of four treatments, i.e., CK, control (normal conditions); Cd: 100 mg Cd kg^-1 of soil; MeJa: exogenous application of MeJa at 20 mM; and Cd + MeJa: 100 mg Cd kg^-1 of soil + exogenous MeJa application at 20 mM. Results depicted that Cd toxicity resulted in a substantial reduction of enzymatic activities and non-enzymatic antioxidants, chlorophyll contents, while enhanced oxidative damage in the terms of lipid peroxidation (higher malondialdehyde (MDA) contents), H₂O₂, and electrolyte leakage. Proline contents were found higher whereas protein and soluble sugars were lower under Cd stress as compared with Ck and Cd + MeJa. Exogenous MeJa application further improved the panicles per pot, spikelets per panicle, seed setting (%), 1,000 grain weight, and yield per pot under Cd stress conditions as compared with non-MeJa applied plant under Cd stress. In addition, exogenous MeJa application enhanced the accumulation of macro (N, P, K, Mg, and Ca) and micronutrients (Mn, Zn, Fe, and Cr) in both cultivars under Cd stress, while reduced the Cd contents in different plant parts. Overall, the contents of Cd in different plant organs were recorded as: root > stem > leaves > grains for all treatments. Comparing both cultivars, the grain Cd contents were higher in Meixiangzhan 2 than Xiangyaxianzhan under Cd contaminated conditions. Conclusively, Cd toxicity impaired growth in rice by affecting physio-biochemical attributes, however, Xiangyaxiangzhan performed better than Meixiangzhan-2 cultivar.

Ecological performance of multifunctional pesticide tolerant strains of Mesorhizobium sp. in chickpea with recommended pendimethalin, ready-mix of pendimethalin and imazethpyr, carbendazim and chlorpyrifos application

The present study was designed to screen the Mesorhizobium strains (50) for tolerance with four recommended pesticides in chickpea. In-vitro, robust pesticide tolerant strains were developed in pesticides amended media over several generations. Further, verification of the multifunctional traits of pesticide tolerant mesorhizobia under pesticide stress was conducted in-vitro. Among different pesticides, significantly high tolerance in Mesorhizobium strains was observed with recommended doses of pendimethalin (37%) and ready-mix (36%) followed by chlorpyrifos (31%) and carbendazim (30%), on an overall basis. Based on multifunctional traits, Mesorhizobium strains viz. MR2, MR17 and recommended MR33 were the most promising. Ecological performance of the potential Mesorhizobium strains alone and in dual-inoculation with recommended PGP rhizobacterium strain RB-1 (Pseudomonas argenttinensis JX239745.1) was subsequently analyzed in field following standard pesticide application in PBG-7 and GPF-2 chickpea varieties for two consecutive rabi seasons (2015 and 2016). Dual-inoculant treatments; recommended RB-1 + MR33 (4.1%) and RB-1 + MR2 (3.8%) significantly increased the grain yield over Mesorhizobium alone treatments viz MR33 and MR2, respectively. Grain yield in PBG7 variety was significantly affected (7.3%) by the microbial inoculant treatments over GPF2 variety. Therefore, the potential pesticide tolerant strains MR2 and MR33 can be further explored as compatible dual-inoculants with recommended RB-1 for chickpea under environmentally stressed conditions (pesticide application) at multiple locations. Our approach using robust multifunctional pesticide tolerant Mesorhizobium for bio-augmentation of chickpea might be helpful in the formulation of effective bio-inoculants consortia in establishing successful chickpea-Mesorhizobium symbiosis.

Strategies and prospects for biostimulants to alleviate abiotic stress in plants

Global climate change-induced abiotic stresses (e.g., drought, salinity, extreme temperatures, heavy metals, and UV radiation) have destabilized the fragile agroecosystems and impaired plant performance and thereby reducing crop productivity and quality. Biostimulants, as a promising and eco-friendly approach, are widely used to address environmental concerns and fulfill the need for developing sustainable/modern agriculture. Current knowledge revealed that plant and animal derived stimulants (e.g., seaweeds and phytoextracts, humic substances, and protein hydrolysate) as well as microbial stimulants (e.g., plant beneficial bacteria or fungi) have great potential to elicit plant tolerance to various abiotic stresses and thus enhancing plant growth and performance-related parameters (such as root growth/diameter, flowering, nutrient use efficiency/translocation, soil water holding capacity, and microbial activity). However, to successfully implement biostimulant-based agriculture in the field under changing climate, the understanding of agricultural functions and action mechanism of biostimulants coping with various abiotic stresses at physicochemical, metabolic, and molecular levels is needed. Therefore, this review attempts to unravel the underlying mechanisms of action mediated by diverse biostimulants in relation to abiotic stress alleviation as well as to discuss the current challenges in their commercialization and implementation in agriculture under changing climate conditions.

Antioxidant enzymatic activities and profiling of gene expression associated with organophosphate stress tolerance in Solanum melongena L.cv. Longai

The tolerance mechanism of chemical pesticide is necessary to combat the pest infestation challenges. This study intended to analyze the responses of enzymatic activity and expression level of an antioxidant gene to organophosphate pesticide stress. The alteration of anti-oxidative correlated with pesticide treatment in eggplant (S. melongena L.cv. Longai) using varying concentrations (0, 50, 100, 150 and 200 ppm) of malathion (PM) and tatafen (PTF) each. The enzyme activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were observed to be elevated with pesticide treatment in eggplant seedling. FeSOD (iron SOD), CAT and APX genes associated in defense mechanisms were significantly expressed under PM and PTF stress which contributed to stress tolerance to the plant. The different concentration of both pesticide stresses altered the expression level of mRNA, FeSOD, CAT and APX genes in comparison to the non-treated plant. While mRNA level of three antioxidant genes were evaluated and found to be APX gene expression was more potent than the CAT and FeSOD gene subjected to different concentrations of PM and PTF in eggplant. The current experiment highlights the presence of minimum level of pesticide concentration impacted positively towards the plant growth and metabolism, while high level of pesticide concentration impacted negatively. In summary, antioxidant enzymes activity responded to both pesticide stresses at an early stage of exposure and their gene expression profiles provided more details about their complex interaction and effectively scavenge reactive oxygen species. This allows the plant to maintain growth under pesticide stress.

Transcriptome analysis and physiological indicators reveal the role of sulfur in cadmium accumulation and transportation in water spinach (Ipomoea aquatica Forsk.)

Cadmium (Cd) contamination of croplands has become a threat to crop food safety and human health. In this study, we investigated the effect of sulfur on the growth of water spinach under Cd stress and the amount of Cd accumulation by increasing the soil sulfate content. We found that the biomass of water spinach significantly increased after the application of sulfur while the shoot Cd concentration was considerably reduced (by 31%). The results revealed that sulfur could promote the expression of PME and LAC genes, accompanied by an increase in PME activity and lignin content. Also, the cell wall Cd content of water spinach roots was significantly increased under sulfur treatment. This finding suggests that sulfur could enhance the adsorption capacity of Cd by promoting the generation of cell wall components, thereby inhibiting the transportation of Cd via the apoplastic pathway. In addition, the higher expression of Nramp5 under the Cd1S0 (concentration of Cd and sulfur are 2.58 and 101.31 mg/kg respectively) treatment led to increased Cd uptake. The CAX3 and ABC transporters and GST were expressed at higher levels along with a higher cysteine content and GSH/GSSR value under Cd1S1 (concentration of Cd and sulfur are 2.60 and 198.36 mg/kg respectively) treatment, which contribute to the Cd detoxification and promotion of Cd compartmentalization in root vacuoles, thereby reducing the translocation of Cd to the shoot via the symplastic pathway.

Role of exogenously applied putrescine in amelioration of cadmium stress in Coriandrum sativum by modulating antioxidant system

Abiotic stress reduces the plant growth and biomass production. Putrescine (Put) may be applied to alleviate numerous types of abiotic stresses in plants. The present research was intended to evaluate the role of exogenously applied Put in extenuation of cadmium (Cd) stress in coriander plants. Coriander seeds primed with 0.25, 0.5, and1 mM Put were allowed to grow in 50 mg kg^-1 Cd contaminated soil for one month. Put treatment improved seed germination, gas exchange attributes, root growth and shoot growth of coriander. The improved activity of stress-responsive enzymes such as superoxide dismutase, catalase and peroxidase, besides amplification of proline was observed in Put treated seedlings under Cd stress. In addition, a reduced amount of total soluble protein and sugars content were noticed in Cd stressed seedlings. Nevertheless, Put reduced MDA level in treated plants. Our results demonstrated that Put mitigated Cd induced stress by modulating antioxidants and photosynthetic activity of coriander plants.Novelty statement Most of the researchers have studied the role of endogenous putrescine in alleviation of plant stress. However, during current study, we primed coriander seeds with putrescine. Our results elucidated very promising role of exogenously applied putrescine in stress mitigation and growth improvement of coriander seedlings under Cd stress. The findings of current study advocate the application of putrescine for stress alleviation in crop plants.

Jasmonic acid (JA) and gibberellic acid (GA3) mitigated Cd-toxicity in chickpea plants through restricted cd uptake and oxidative stress management

Cadmium stress is one of the chief environmental cues that can substantially reduce plant growth. In the present research, we studied the effect of jasmonic acid (JA) and gibberellic acid (GA₃) applied individually and/or in combination to chickpea (Cicer arietinum) plants exposed to 150 µM cadmium sulphate. Cadmium stress resulted in reduced plant growth and pigment contents. Moreover, chickpea plants under cadmium contamination displayed higher levels of electrolytic leakage, H₂O_2, and malonaldehyde, as well as lower relative water content. Plants primed with JA (1 nM) and those foliar-fed with GA₃ (10^-6 M) showed improved metal tolerance by reducing the accumulation of reactive oxygen species, malonaldehyde and electrolytic leakage, and increasing relative water content. . Osmoprotectants like proline and glycinebetaine increased under cadmium contamination. Additionally, the enzymatic activities and non-enzymatic antioxidant levels increased markedly under Cd stress, but application of JA as well as of GA₃ further improved these attributes. Enzymes pertaining to the ascorbate glutathione and glyoxylase systems increased significantly when the chickpea plants were exposed to Cd. However, JA and GA₃ applied singly or in combination showed improved enzymatic activities as well as nutrient uptake, whereas they reduced the metal accumulation in chickpea plants. Taken together, our findings demonstrated that JA and GA₃ are suitable agents for regulating Cd stress resistance in chickpea plants.

Triacontanol attenuates drought-induced oxidative stress in Brassica juncea L. by regulating lignification genes, calcium metabolism and the antioxidant system

Effect of triacontanol on drought-induced stress was studied in Brassica juncea L. Foliage of sixteen-days-old plants was sprayed with concentrations (0, 10, 20 and 30 μM) of triacontanol (TRIA) for 7 days. Subsequently, plants were subjected to drought stress (10% polyethylene glycol, PEG6000) for 7 days. Drought stress increased oxidative stress (TBARS, O₂^●- and H₂O₂), however, their contents were reduced by TRIA. Total soluble sugars, reduced glutathione, and proline content in stressed plants were increased by TRIA. Activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), catalase (CAT), and phenylalanine ammonia-lyase (PAL) activity were significantly increased in a dose-dependent manner with TRIA. Potassium (K⁺) level declined, while magnesium (Mg²⁺) and calcium (Ca²⁺) contents increased. The elevated level of lignin under drought with TRIA was significantly associated with MYB46 and PAL gene expression patterns. Altogether, our results suggest that foliar spray of 20 μM TRIA was more operative in reducing the negative impact of drought stress in B. juncea by regulating the antioxidant system, calcium, and lignification.

Targeting Cd coping mechanisms for stress tolerance in Brassica napus under spiked-substrate system: from physiology to remediation perspective

Cadmium (Cd) is a prevalent, non-essential, carcinogenic, and hazardous heavy metal that reduces plant productivity and capacity of arable land area around the globe. In the present substrate-based pot study, seedlings of Brassica napus 180015 were grown equidistantly in the spiked-substrate medium for 60 days under increasing concentrations of Cd (0, 10, 20, 30, 40, 50 mg kg^-1). Following harvest, the morpho-physio-biochemical, antioxidative, and Cd-induced tolerance responses were evaluated in B. napus under an increasing Cd stress regime. Additionally, these parameters were also investigated to select the plant's threshold tolerance limit for Cd under the spiked-substrate system. B. napus showed dynamic behavior regarding morpho-physio-biochemical attributes, including agronomic features, biomass, photosynthetic pigments, relative water content under increased Cd toxicity. Cd stress-induced hydrogen peroxide (H₂O₂) production with high MDA contents and passive EL, followed by the orchestration of both enzymatic (SOD, POD, APX, CAT, and GR) and non-enzymatic antioxidants (flavonoids, TPC, TPA, proline, and total soluble protein) up to a certain limit. In addition, Cd-induced stress upregulated transcriptional levels of antioxidative enzyme SOD, POD, APX, GR, and MT encoded genes in B. napus. The increasing trend of Cd accumulation in different tissues at the highest Cd concentration was as follows: root > leaf > stem. In spiked substrate system, B. napus demonstrated improved metal extractability performance and a high potential for phyto-management of low to moderate Cd contamination, implying that this study could be used for integrative breeding programs and decontaminating heavy metals in real contaminated scenarios.Novelty statementThis study provides an insight into Cd-coping mechanisms of oilseed rape involved in alleviating toxicity and simultaneous phyto-management of increasing Cd concentration under spiked substrate system. The current study is the first scientific evidence of using a Cd-spiked soilless substrate medium. The present study will further strengthen our understanding of Cd-instigated positive responses in B. napus. Furthermore, it will provide a useful basis for integrative breeding programs and decontaminating heavy metals in real contaminated scenarios.

Tolerance of Mentha crispa L. (garden mint) cultivated in cadmium-contaminated oxisol

The tolerance of Mentha crispa L. (garden mint) cultivated in cadmium-contaminated oxisol for 120 days was analyzed using plant growth variables such as height, the number of leaves and shoots in different Cd exposure periods, as well as assessing the metal concentration absorbed and accumulated in the plant parts (root, stem, and leaves). The maximum adsorption capacity was estimated at 9220 mg kg^-1 and used as a reference to establish the different Cd concentrations to be applied in the soil. M. crispa showed tolerance and revealed a reduction of height, the number of leaves and shoots, root development, and secondary toxicity signs such as chlorosis and leaf wilting. Comparing to the stems and leaves, Cd was retained mainly in the roots. PERMANOVA showed that plant growth variables and Cd concentrations in the plant's part were affected by the Cd exposure time. The canonical discriminant analysis demonstrated height as the most affected variable until 45 growing days, and different responses were observed after 75 days. However, the number of shoots was the variable most affected by higher Cd concentrations. The bioaccumulation and translocation factors for all treatments were lower than one, indicating that M. crispa can be considered as an excluder plant and applied for a phytostabilization strategy.

Salicylic acid-mediated alleviation of soil boron toxicity in Mentha arvensis and Cymbopogon flexuosus: Growth, antioxidant responses, essential oil contents and components

Boron (B) toxicity is a notable abiotic hindrance that restricts crop productivity by disturbing several physiological and biochemical processes in plants. This study was aimed to elucidate the role of salicylic acid (SA) in conferring tolerance to B stress in Mentha arvensis and Cymbopogon flexuosus. Boron toxicity led to a considerable decrease in shoot height and root length, fresh and dry mass of shoot and root, and physiological and biochemical parameters. However, exogenously applied SA relieved the adverse effects caused by B toxicity and led to an increase in growth parameters under B stress and non-stress conditions. The treatment of B resulted in its increased accumulation in roots and shoots of both the plants which, in turn, caused oxidative damage as evident by increased content of malondialdehyde and catalase, peroxidase, superoxide dismutase and glutathione reductase enzyme activities. However, exogenous SA supply significantly affected antioxidant enzyme activities and protected the plants from excess B. Moreover, the essential oil content of two selected plants declined under B toxicity and significantly enhanced in SA-treated stressed plants. The contents of menthol and menthyl acetate in M. arvensis were lowered in B stressed plants which significantly improved in SA treated B-stressed and in their respective SA alone treatment. Similarly, citral-A and citral-B content of C. flexuosus declined under B toxicity, however, SA reversed the negative effects of B toxicity on essential oil components. This assessment stipulated the promising role of exogenously applied SA in alleviating B toxicity in M. arvensis and C. flexuosus by improving antioxidant machinery and limiting B uptake which protects the structural integrity of leaves and also helps in increasing essential oil content.

Biochemical and Molecular Effects Induced by Triacontanol in Acquired Tolerance of Rice to Drought Stress

To assess the effect of triacontanol (TRIA) on rice plants grown under normal or drought conditions, rice seeds were presoaked in TRIA (35 ppm) for two hours. After 20 days of sowing, rice seedlings developed from TRIA-treated or untreated seeds were subjected to drought stress. After 10 days of plant exposure to drought stress, data of major growth attributes and the content of photosynthetic pigments were recorded. Moreover, the effect of drought stress on stomatal conductance and the photochemical efficiency of PSII (Fv/Fm) were followed. The data obtained indicated that the species of rice (Oryza sativa L.) cultivar Giza 177 under investigation was sensitive to drought stress where there were significant decreases in the fresh and dry weights of shoots and roots and in stomatal conductance, as well as in the content of chlorophyll a, chlorophyll b, and carotenoids. Seed priming with TRIA enhanced both growth and acquired plant tolerance to drought stress. Thus, TRIA via the enhancement of stomatal conductance through the regulation of stomatal closure, the rate of water loss, ABA metabolism, the accumulation of osmolytes, and the regulation of aquaporins genes improved the water status of plants grown under water scarcity. Moreover, TRIA via increasing the content of free amino acids and sugars under drought stress may increase the chance of plant tissues to retain more water under scarcity conditions.

Drought tolerance in Brassica napus is accompanied with enhanced antioxidative protection, photosynthetic and hormonal regulation at seedling stage

Climate change, food insecurity, water scarcity, and population growth are some of today's world's frightening problems. Drought stress exerts a constant threat to field crops and is often seen as a major constraint on global agricultural productivity; its intensity and frequency are expected to increase in the near future. The present study investigated the effects of drought stress (15% w/v polyethylene glycol PEG-6000) on physiological and biochemical changes in five Brassica napus cultivars (ZD630, ZD622, ZD619, GY605, and ZS11). For drought stress induction, 3-week-old rapeseed oil seedlings were treated with PEG-6000 in full strength Hoagland nutrient solution for 7 days. PEG treatment significantly decreased the plant growth and photosynthetic efficiency, including primary photochemistry (Fv/Fm) of PSII, intercellular CO₂ , net photosynthesis, chlorophyll contents, and water-use efficiency of all studied B. napus cultivars; however, pronounced growth retardations were observed in cultivar GY605. Drought-stressed B. napus cultivars also experienced a sharp rise in H₂ O₂ generation and malondialdehyde (MDA) content. Additionally, the accumulation of ROS was accompanied by increased activity of enzymatic antioxidants (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, glutathione reductase, and monodehydroascorbate reductase), although the increase was more obvious in ZD622 and ZS11. Drought stress also caused an increased endogenous hormonal biosynthesis (abscisic acid, jasmonic acid, salicylic acid) and accumulation of total soluble proteins and proline content, but the extent varies in B. napus cultivars. These results suggest that B. napus cultivars have an efficient drought stress tolerance mechanism, as shown by improved antioxidant enzyme activities, photosynthetic and hormonal regulation.

Hydrocotyle vulgaris L.: a new cadmium-tolerant landscape species and its physiological responses to cadmium exposure

Landscape plants have both ecological and aesthetic value and may also represent ideal candidates for phytoremediation. In the present study, one round of hydroponic culture for 14 days with different cadmium (Cd) concentrations (0, 0.5, 1, and 2 mg L^-1 Cd) was carried out to test whether Hydrocotyle vulgaris L. is a Cd-tolerant plant. Furthermore, physiological parameters, including pigment concentrations, photosynthesis, antioxidant enzyme activities (AEAs), and nutrient uptake, were also examined to determine the tolerance of H. vulgaris to Cd exposure. The results showed that H. vulgaris could grow normally under all Cd supply levels. The Cd removal efficiency reached 100% at Cd concentrations ≤1.0 mg L^-1. The concentrations of Cd in roots and shoots increased (P < 0.05) with Cd supplementation. The maximum concentrations of Cd reached 26.4 and 118 mg kg^-1 in shoots and roots, respectively. The translocation factor values were similar under all Cd treatments. The highest mean daily increase in biomass (MDIB) was obtained under 1 mg L^-1 Cd exposure, which increased by 69.86% compared to that in the control, which may be due to the increased photosynthetic pigments, photosynthetic rate, and the consistent nutrient concentrations under this Cd level, as there were positive relationships between these parameters and MDIB. Moreover, the activities of AEA also generally explicated highest among all Cd levels. All these results indicate that the above physiological parameters play a positive role in promoting plant growth and alleviating Cd stress. In summary, H. vulgaris was verified as a potential Cd-tolerant plant, providing new information for Cd phytoremediation. Furthermore, given its extensive habitat distribution, this species might be tested for phytoremediation of contaminated soils in future work.

Hemin-decreased cadmium uptake in pak choi (Brassica chinensis L.) seedlings is heme oxygenase-1 dependent and relies on its by-products ferrous iron and carbon monoxide

Cadmium (Cd) is a major pollutant in farmland, which not only greatly restricts crop production, but also brings a serious threat to human health through entering the food chain. Our previous study showed that hemin treatment could reduce the accumulation of Cd in pak choi seedlings. However, the underlying mechanism remains unclear. In this study, we used non-invasive micro-test technology (NMT) to detect the real-time Cd²⁺ flux from pak choi roots and demonstrated that hemin treatment decreased Cd uptake rather than its translocation within plants. Moreover, through comparing the responses of different chemical treatments in pak choi seedlings and Arabidopsis wild-type and heme oxygenase-1 (HO-1) mutant, we provided evidence that hemin-decreased Cd uptake was HO-1 dependent. Furthermore, analyses of hemin degradation products suggested that the hemin-derived suppression of Cd uptake suppression was probably relying on its degradation by-products, ferrous iron (Fe²⁺) and carbon monoxide (CO), via repressing the expression of a Fe²⁺/Cd²⁺ transporter BcIRT1 in pak choi roots.

Exogenous plant growth regulator alleviate the adverse effects of U and Cd stress in sunflower (Helianthus annuus L.) and improve the efficacy of U and Cd remediation

Plant growth regulators (PGRs) are widely used in agricultural activities and have the potential to improve plant growth and plant tolerance against metal stress. PGR-assisted phytoextraction is now an effective and inexpensive method for enhancing the plant removal of toxic metals from soil. In this study, we conducted experiments to determine the effects of PGR treatments on soil uranium (U) and cadmium (Cd) removal by sunflowers as well as their stress response to U and Cd contamination. We found that the plant growth was inhibited by combined U and Cd stress in sunflowers compared with that of the control; however, the application of exogenous PGR had reduced the combined U and Cd stress by stimulating photosynthesis, decreasing the levels of active oxygen and lipid peroxidation, and enhancing the activity of the antioxidant defence systems. Exogenous PGR also increased the uptake of U and Cd by sunflowers and therefore, improved their U and Cd remediation efficiency. Moreover, indoleacetic acid (IAA) was the most effective PGR at removing U and Cd in the soil; the U and Cd removal efficiency was 484.21% and 238.85% higher in the 500 mg L^-1 IAA application compared with that of the control without PGR application, respectively. Furthermore, none of the PGR treatments significantly influenced the available U and Cd contents in soil. Our results, therefore, may provide some detailed understanding on the technologies for the sustainable remediation of U and Cd contaminated soil by the combination of PGR treatments and phytoextraction.

Foliar Application of 24-Epibrassinolide Improves Growth, Ascorbate-Glutathione Cycle, and Glyoxalase System in Brown Mustard (Brassica juncea (L.) Czern.) under Cadmium Toxicity

Cadmium (Cd) metal toxicity is a crucial ecological matter that requires immediate efforts to mitigate it. Brassica juncea plants were exposed to Cd (0 and 200 µM as CdSO₄) and foliar application of 24-Epibrassinolide (EBR) (0, 10⁻⁷ and 10⁻⁵ M). The toxic effect of Cd was evident in terms of declined growth and biomass yield, lowered levels of pigment content and chlorophyll fluorescence, and reduction in gas exchange attributes. The levels of proline and glycinebetaine increased in response to Cd treatment. There was an imperative rise in the contents of H₂O₂ and malondialdehyde as well as electrolyte leakage in the Cd-stressed plants. With the application of EBR, there was a significant replenishment in growth attributes and photosynthetic efficacy. The contents of ROS (reactive oxygen species) and malondialdehyde as well as electrolyte leakage were reduced by the hormone supplementation. Enhancement in the contents of glutathione and ascorbic acid, and the activities of enzymes of the antioxidative defense system and glyoxalase system was recorded in response to Cd as well as hormone treatment. The in situ levels of Cd in roots and shoot were augmented in response to Cd treatment, but were found to be lowered by the EBR application.

Characterization of mechanisms involved in tolerance and accumulation of Cd in Biscutella auriculata L

Biscutella auriculata L. is one of the rare species that is able to grow in a very contaminated mining area in Villamayor de Calatrava (Ciudad Real, Spain). In an effort to understand the mechanisms involved in the tolerance of this plant to high metal concentrations, we grew B. auriculata in the presence of 125 μM Cd(NO₃)₂ for 15 days and analysed different parameters associated with plant growth, nitric oxide and reactive oxygen species metabolism, metal uptake and translocation, photosynthesis rate and biothiol (glutathione and phytochelatins) content. Treatment with Cd led to growth inhibition in both the leaves and the roots, as well as a reduction of photosynthetic parameters, transpiration and stomatal conductance. The metal was mainly accumulated in the roots and in the vascular tissue, although most Cd was detected in areas surrounding their epidermal cells, while in the leaves the metal accumulated mainly in spongy mesophyll, stomata and trichrome. Based on the Cd bioaccumulation (5.93) and translocation (0.15) factors, this species denoted enrichment of the metal in the roots and its low translocation to the upper tissues. Biothiol analysis showed a Cd-dependent increase of reduced glutathione (GSH) as well as the phytochelatins (PC2 and PC3) in both roots and leaves. Cd-promoted oxidative damage occurred mainly in the leaves due to disturbances in enzymatic and nonenzymatic antioxidants, while the roots did not show significant damage as a result of induction of antioxidant defences. It can be concluded that B. auriculata is a new Cd-tolerant plant with an ability to activate efficient metal-sequestering mechanisms in the root surface and leaves and to induce PCs, as well as antioxidative defences in roots.

Reactive Oxygen Species and Antioxidant Defense in Plants under Abiotic Stress: Revisiting the Crucial Role of a Universal Defense Regulator

Global climate change and associated adverse abiotic stress conditions, such as drought, salinity, heavy metals, waterlogging, extreme temperatures, oxygen deprivation, etc., greatly influence plant growth and development, ultimately affecting crop yield and quality, as well as agricultural sustainability in general. Plant cells produce oxygen radicals and their derivatives, so-called reactive oxygen species (ROS), during various processes associated with abiotic stress. Moreover, the generation of ROS is a fundamental process in higher plants and employs to transmit cellular signaling information in response to the changing environmental conditions. One of the most crucial consequences of abiotic stress is the disturbance of the equilibrium between the generation of ROS and antioxidant defense systems triggering the excessive accumulation of ROS and inducing oxidative stress in plants. Notably, the equilibrium between the detoxification and generation of ROS is maintained by both enzymatic and nonenzymatic antioxidant defense systems under harsh environmental stresses. Although this field of research has attracted massive interest, it largely remains unexplored, and our understanding of ROS signaling remains poorly understood. In this review, we have documented the recent advancement illustrating the harmful effects of ROS, antioxidant defense system involved in ROS detoxification under different abiotic stresses, and molecular cross-talk with other important signal molecules such as reactive nitrogen, sulfur, and carbonyl species. In addition, state-of-the-art molecular approaches of ROS-mediated improvement in plant antioxidant defense during the acclimation process against abiotic stresses have also been discussed.

The role of Fe-nano particles in scarlet sage responses to heavy metals stress

Despite the stabilized ornamental markets for scarlet sage (Salvia splendens), little is known about the stress resistance of heavy metals (HMs). Therefore, a hydroponic study was conducted to determine whether the addition of Fe nanoparticles (Fe NPs) at 0, 5, 10, 20 and 30 µM in Hoagland's nutrient solution reduce the toxicity caused by 100 μM of HMs (Cd, Cu, Ni, Cr and Pb). Exposure to HMs significantly reduced relative growth rate (RGR), chlorophyll content, chlorophyll fluorescence (Fv/Fm), total antioxidant activity (TAA), total phenol content (TPC) and antioxidant power assay (FRAP), while the malondialdehyde (MDA) accumulation, H₂O₂ generation and electrolyte leakage (EL) significantly increased. Fe NPs improved HMs toxicity by significant reduction in MDA content, H₂O₂ generation and EL while increase in the PGR, chlorophyll content, Fv/Fm, the TAA, TPC and FRAP. Exposure to HMs caused Fe deficiency-induced chlorosis while Fe NPs reduced the negative effects of HM by preventing further reduction of leaf Fe. The results highlighted that although using Fe NPs significantly improved plant growth and motivated the plant defense mechanisms in response to HMs toxicity, it had a negative effect on the phytoremediation properties of salvia splendens by reducing the accumulation of HMs in plant organs.

Triacontanol as a dynamic growth regulator for plants under diverse environmental conditions

Triacontanol (TRIA) being an endogenous plant growth regulator facilitates numerous plant metabolic activities leading to better growth and development. Moreover, TRIA plays essential roles in alleviating the stress-accrued alterations in crop plants via modulating the activation of the stress tolerance mechanisms. The present article critically focuses on the role of exogenously applied TRIA in morpho-physiology and biochemistry of plants for example, in terms of growth, photosynthesis, enzymatic activity, biofuel synthesis, yield and quality under normal and stressful conditions. This article also enlightens the mode of action of TRIA and its interaction with other phytohormones in regulating the physio-biochemical processes in counteracting the stress-induced damages in plants.