Maize Seedlings Research Articles

Response of Maize (Zea mays L.) to Soil Contamination with Diclofenac, Ibuprofen and Ampicillin and Mixtures of These Drugs

Diclofenac (DIC) and ibuprofen (IBU) are popular non-steroidal anti-inflammatory drugs (NSAIDs), while ampicillin (AMP) is a relatively common antibiotic for treating bacterial infections. All of these drugs are only slightly retained in the human body, and therefore, their presence is found in the environment. In the present study, an attempt was made to determine the effects of diclofenac, ibuprofen and ampicillin on the growth and development of early stages of maize. The drugs were used both separately and in binary mixtures and a ternary mixture. The study found that NSAIDs exhibited the greatest phytotoxicity. Both diclofenac and ibuprofen, applied at the highest doses, reduced the fresh weight yield of maize seedlings relative to the control. Ampicillin, on the other hand, showed no adverse effect on the growth and development of maize seedlings. Analyzing the effect of selected drugs on changes in the content of photosynthetic pigments, it should be noted that they led to a systematic decrease in the content of chlorophylls and carotenoids in maize seedlings. Small changes in the values of the basic parameters of chlorophyll fluorescence may indicate the possibility of stress in maize seedlings.

Exogenous Application of Tyrosine Mitigated the Adversities of Drought Stress in Maize Seedlings through Modulation of Photosynthetic Performance and Antioxidants Defense Systems

Exogenous Application of Tyrosine Mitigated the Adversities of Drought Stress in Maize Seedlings through Modulation of Photosynthetic Performance and Antioxidants Defense Systems

Mechanistic insights of salicylic acid-mediated salt stress tolerance in Zea mays L. seedlings

Elevated sodium level (Na+) poses significant threat to crop plant physio-biochemical processes, leading to impaired growth followed by decline in productivity. Addressing this challenge, requires an eco-friendly and cost-effective strategy that enhances plant salt stress tolerance capacity. In this context, the exogenous source of plant growth regulators (PGRs) proved to be an efficient approach. Of various PGRs, salicylic acid (SA) is an emerging signaling molecule that boosts plant stress endurance mechanism. This study investigates SA-mediated salt stress tolerance in maize (Zea mays L.) seedlings, by examining morpho-physiological and biochemical traits. Maize seedlings were subjected to varying levels of salt stress (0, 25, 50, 75, 100, and 150 mM NaCl) for a period of 10-days. The results revealed that, a substantial decline in germination percentage, shoot and root length, plant biomass, vigour index, and various other physiological parameters under salt stress causing concentrations. Conversely, salt stress increased oxidative stress indicators, including hydrogen peroxide (H2O2) and malondialdehyde (MDA), osmolytes and elemental concentrations as well as antioxident enzymes (SOD, CAT, POX, APX, GR, AsA). However, the exogenous supplementation of SA at 0.1 mM significantly restored most morpho-physiological attributes in maize under salt stress conditions. This suggests that SA actively triggers the ascorbate-glutathione (AsA-GSH) pathway and other key enzymes, leading to sodium extrusion and improving antioxidant defense in maize seedlings. This finding provides valuable insights for maize farmers that employing SA could lead to improved maize production in saline soils.

Nitroreductase DnrA, Utilizing Strategies Secreted in Bacillus sp. Za and SCK6, Enhances the Detoxification of Acifluorfen.

The residues of acifluorfen present a serious threat to the agricultural environment and sensitive crops. DnrA, a nitroreductase, is an intracellular enzyme that restricts the application of wild-type Bacillus sp. Za in environmental remediation. In this study, two strategies were employed to successfully secrete DnrA in strains SCK6 and Za, and the secretion expression conditions were optimized to achieve rapid degradation of acifluorfen. Under the optimal conditions, the relative activities of the DnrA supernatant from strains SCK6-D and Za-W were 3.06-fold and 3.53-fold higher than that of strain Za, respectively. While all three strains exhibited similar tolerance to different concentrations of acifluorfen, strains SCK6-D and Za-W demonstrated significantly faster degradation efficiency compared to strain Za. Furthermore, the DnrA supernatant from strains SCK6-D and Za-W could effectively reduce the toxicity of acifluorfen on maize and cucumber seedlings. This study provides an effective technical approach for the rapid degradation of acifluorfen.

Maize insensitivity to culture filtrates from Exserohilum turcicum is related to quantitative resistance

AbstractTurcicum leaf blight (TLB) of maize is caused by Exserohilum turcicum. The TLB resistance is mainly associated with qualitative race‐specific resistance that is linked to several Ht genes namely Ht1, Ht2, Ht3, HtM, HtN, HtNB and HtP. However, quantitative TLB resistance also occurs, but its mechanisms are poorly understood. In this study, tolerance or insensitivity to chlorosis and necrosis of E. turcicum culture filtrate was associated with quantitative TLB resistance. A novel detached maize seedling assay was developed for E. turcicum culture filtrate using methanol‐treated modified Fries medium. Screening of E. turcicum isolates of races 2, 3, 23, 3 N, 23 N and 123 N against 61 maize inbred lines with diverse levels of resistance to TLB was conducted in the greenhouse by fungal inoculation and the detached seedling culture filtrate assay. Using an isolate of race 123 N, which can overcome all the qualitative resistance genes, a simple linear regression model (R2 = 0.68, p = .90) for the 61 inbred lines was established between disease severity from foliar inoculations and culture filtrate symptom rating of the detached seedling assay. Two maize lines CML474 and CML483 had relatively high culture filtrate symptom ratings but very low disease severity with foliar inoculation indicating that these sources of quantitative TLB resistance may be unrelated to tolerance to E. turcicum culture filtrates, whose effect on seedlings could be due to the toxin known as HT‐toxin or monocerin.

Larvicidal and feeding deterrent properties of extracts from Dieffenbachia maculata (Dumb cane) against Spodoptera frugiperda in maize (Zea mays)

This study examined the larvicidal and feeding deterrent properties of extracts from Dieffenbachia maculata against Spodoptera frugiperda (Fall army worm) in growing maize. A 9 m x 7 m space in the green house was divided into forty-two plots of 1 m by 0.75 m with 0.5 m discard between rows. This is to allow for a 2 x 3 x 4 factorial experiment replicated three times. Maize seeds were sown at two seeds per hole at a spacing of 90 cm by 60cm in each plot. Each plot was barricaded with wire mesh to prevent the migration of larvae from plot to plot. The irrigation system in the greenhouse supplied equal volume of water at the base of the maize seedlings every morning. Infested maize plants were treated with different Dumb cane plant extracts at the concentration of 25ml/l and30ml/l along with positive and negative controls. (The positive control was treated with Cypermethrine at 3l/ha) to compare the effect of concentrations on the fall army worm activity. In this experiment, the numbers of leaves affected was assessed every week and recorded. Leave perforation index was calculated. Dead armyworms were observed by prodding the larvae for movement and were recorded. Plant vigour was obtained by measuring plant height and the number of leaves formed. Effect of the worm on yield was determined by comparing total yield from sampled maize plants and this was compared to expected yield from the variety of maize used for the research. The positive control group exhibited a significantly lower level of infestation after treatment with a corresponding yield increase, (16.06% and 80.14%) respectively when compared to the treated groups. Similarly, leave extract using acetone at 30ml record significantly better results with 17.73% level of infestation after treatment application and 66.44% yield increase. This was closely followed by leaf extract using methanol at 30ml with significantly lower level of infestation and increased yield respectively. (21.35% and 60.42%). Conversely, the lowest value was recorded for the negative control. Among the extract treatments, the leaf extract using acetone at 30ml showed the highest efficacy in reducing infestation levels and demonstrated the most significant increase in maize yield. In this study, it was observed that application of the 30ml leaf extract of Dumb cane using acetone was effective and significantly increased army worm larval mortality, reduced leaf damage, and increased maize grain yield compared to the untreated control. The results indicated that the extracts from dumb cane leaves and stems exhibited promising capacity in the control of Fall army worm in maize. Further research is warranted to optimize the application protocols and evaluate any residual effects of the extracts on maize grain and ecosystem dynamics

Raffinose catabolism enhances maize waterlogging tolerance by stimulating adventitious root growth and development.

Raffinose mitigates plant heat, drought, and cold stresses; however, whether raffinose contributes to plant waterlogging tolerance is unknown. The maize raffinose synthase mutant zmrafs-1 had seedlings that lack raffinose, generated fewer and shorter adventitious roots, and were more sensitive to waterlogging stress, while overexpression of the raffinose synthase gene, ZmRAFS, increased raffinose content, stimulated adventitious root formation, and enhanced waterlogging tolerance of maize seedlings. Transcriptome analysis of null segregant seedlings compared with zmrafs-1, particularly when waterlogged, revealed that the expression of genes related to galactose metabolism and the auxin biosynthetic pathway were up-regulated by raffinose. Additionally, indole-3-acetic acid content was significantly decreased in zmrafs-1 seedlings and increased in ZmRAFS-overexpressing seedlings. Inhibition of the hydrolysis of raffinose by 1-deoxygalactonojirimycin decreased the waterlogging tolerance of maize seedlings, the expression of genes encoding proteins related to auxin transport-related genes, and the indole-3-acetic acid level in the seedlings, indicating that the hydrolysis of raffinose is necessary for maize waterlogging tolerance. These data demonstrate that raffinose catabolism stimulates adventitious root formation via the auxin signaling pathway to enhance maize waterlogging tolerance.

Fabrication of dual responsive microcapsules based on starch with enhanced foliar adhesion and photostability for improving control efficacy and reducing environmental risks

Stimuli-responsive controlled release formulations offer a promising avenue for enhancing effective utilization and mitigating environmental risks of pesticides. Herein, pH and enzyme-responsive pesticide microcapsules (AVE@CPS-Fe-TA) were constructed by encapsulating carboxylated porous starch (CPS) loaded with avermectin (AVE) within tannic acid-iron complexes (Fe-TA) to improve the insecticidal efficacy and reduce toxicity to non-targets of AVE. The results showed that the loading content of AVE in the modified starch-based microcapsules could be precisely adjusted by the enzymatic hydrolysis time of starch. The prepared AVE@CPS-Fe-TA had pH and α-amylase dual responsive release properties and exhibited superior photostability, and its photolysis half-life was extended by 15.57-fold compared to AVE technical. Additionally, the leaf retention rate of AVE@CPS-Fe-TA after being rinsed by simulated rainwater was 6.08 times higher than that of commercial formulation AVE EC. In greenhouse insecticidal activity experiment, AVE@CPS-Fe-TA demonstrated a high control efficacy against Ostrinia furnacalis and had a prolonged effective duration. Moreover, AVE@CPS-Fe-TA significantly reduced the acute toxicity of AVE to zebrafish and promoted the growth of maize seedlings. Therefore, this work would provide eco-friendly stimuli-responsive microcapsules of pesticides for improving the efficiency of utilization and reducing environmental risks.

Metabolic and Functional Interactions of H2S and Sucrose in Maize Thermotolerance through Redox Homeodynamics.

Hydrogen sulfide (H2S) is a novel gasotransmitter. Sucrose (SUC) is a source of cellular energy and a signaling molecule. Maize is the third most common food crop worldwide. However, the interaction of H2S and SUC in maize thermotolerance is not widely known. In this study, using maize seedlings as materials, the metabolic and functional interactions of H2S and SUC in maize thermotolerance were investigated. The data show that under heat stress, the survival rate and tissue viability were increased by exogenous SUC, while the malondialdehyde content and electrolyte leakage were reduced by SUC, indicating SUC could increase maize thermotolerance. Also, SUC-promoted thermotolerance was enhanced by H2S, while separately weakened by an inhibitor (propargylglycine) and a scavenger (hypotaurine) of H2S and a SUC-transport inhibitor (N-ethylmaleimide), suggesting the interaction of H2S and SUC in the development of maize thermotolerance. To establish the underlying mechanism of H2S-SUC interaction-promoted thermotolerance, redox parameters in mesocotyls of maize seedlings were measured before and after heat stress. The data indicate that the activity and gene expression of H2S-metabolizing enzymes were up-regulated by SUC, whereas H2S had no significant effect on the activity and gene expression of SUC-metabolizing enzymes. In addition, the activity and gene expression of catalase, glutathione reductase, ascorbate peroxidase, peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and superoxide dismutase were reinforced by H2S, SUC, and their combination under non-heat and heat conditions to varying degrees. Similarly, the content of ascorbic acid, flavone, carotenoid, and polyphenol was increased by H2S, SUC, and their combination, whereas the production of superoxide radicals and the hydrogen peroxide level were impaired by these treatments to different extents. These results imply that the metabolic and functional interactions of H2S and sucrose signaling exist in the formation of maize thermotolerance through redox homeodynamics. This finding lays the theoretical basis for developing climate-resistant maize crops and improving food security.

Reshaping the root endophytic microbiota in plants to combat mercury-induced stress

Emerging evidence suggests that plants experiencing abiotic stress actively seek help from soil microbes. However, the empirical evidence supporting this strategy is limited, especially in response to heavy metal stress. We used integrated microbial community profiling and culture-based methods to investigate the interaction between mercury (Hg) stress, the entophytic root microbiome, and maize seedlings. The results of the pot experiment showed that soil Hg (20 mg/kg) strongly inhibited maize growth, indicating its strong phytotoxicity. Furthermore, Hg stress significantly altered the structure of the bacterial and fungal communities and enriched the potentially pathogenic Fusarium sp., suggesting that soil Hg stress may enhance the bio-stress induced by Fusarium species in maize. Additionally, soil Hg also led to the enrichment of beneficial bacterial members of Streptomyces, Lysobacter, and Sphingomonas (defined as differential species), which were also identified as keystone species in the Hg treatment by the analysis of co-occurrence networks. Therefore, it can be postulated that the members of Streptomyces, Lysobacter, and Sphingomonas function as stress-alleviating microbes. We successfully isolated the representatives of these stress-alleviating microbes. As expected, these strains mitigated the detrimental effects of Hg stess for the maize seedlings, suggesting that plants recruit the stress-alleviated microbiota to combat Hg stress. This study provides insights into the potential of manipulating the root microbiome to enhance plant growth in polluted environments.

Investigating the Efficacy of Dry Region Zinc Solubilizing Bacteria for Growth Promotion of Maize and Wheat under Axenic Conditions

Zinc (Zn) plays a crucial role as a micronutrient, essential for the growth, development, and proper functioning of plants. Pakistani soils are deficient of micronutrient especially zinc. Supplementation of Zn fertilizers cannot do the job because only a small fraction of Zn is available to plants and rest is fixed in soil. To enhance the Zn availability different methods are being used which are expensive. Zinc solubilizing bacteria (ZSB) can be a potential candidate for solubilization of Zn and growth promoting activities in cereals. The present study aimed to evaluate the potential of dry region bacterial strains of Bahawalpur for improving Zn uptake and growth improvement in wheat and maize. Rhizosphere samples of wheat and maize were taken from the dry regions of Bahawalpur and bacterial strains were isolated and tested for their Zn solubilizing ability and screened for urease, siderophore activity, exopolysaccharide production, phosphorus solubilization and plant growth promoting abilities. Under axenic conditions selected isolates were further screened to assessed for improving the growth of wheat and maize seedlings. The rhizobacterial isolates IUB-34, IUB-80, IUB-93 and IUB-96 performed best to improve growth, physiology, biochemical attributes and root colonization. The maximum increase in root and shoot lengths were recorded 32.2 and 35.7% in wheat under IUB-34 application and in maize 43.8 and 39.9%, respectively, under IUB-96 application as compared to uninoculated control. Furthermore, maximum root colonization was also recorded under IUB-34 in wheat and IUB-96 in maize seedlings. Moreover, the biochemical characterization of selected isolates showed IAA (Auxins) production, protease, catalase, cellulose degradation, HCN and ACC-deaminase activities by these strains. However, only IUB-34 and IUB-96 were found positive for oxidase activity. Therefore, study concluded that use of dry region ZSB can solubilize Zn and make it available for plant to improve growth of wheat and maize. So, these isolates may be utilized for coating urea as a biofertilizer to increase the biofortification in cereals.

Enhancing maize resilience to microplastics and cadmium through nanoparticles intervention

Microplastic (MPs) and heavy metals (HMs) pollution present significant ecological and environmental threats due to their widespread production and release into natural ecosystems. This study aimed to investigate the individual effects of polyvinyl chloride microplastics (PVC-MPs) and cadmium (Cd) on various aspects of plant growth, as well as the potential ameliorative role of titanium dioxide nanoparticles (TiO2 NPs) in mitigating their adverse impacts. The experiment involved exposing maize seedlings to different concentrations of PVC-MPs (0, 2, and 4 mg L−1) and Cd (0, 50, and 100 mg kg−1), along with varying levels of TiO2NPs (50 µg mL−1). Our findings showed that Cd toxicity in the soil significantly reduced growth, gas exchange properties, sugar content, ascorbate-glutathione (ASA-GSH) cycle activity, cellular composition, and proline metabolism in maize. In contrast, Cd contaminating greatly boosted oxidative stress indicators, enzymatic and non-enzymatic antioxidants, and gene expression in maize. Stimulatingly, the use of TiO2NPs caused in a significant development in growth of plant, plant biomass, gas exchange parameters, enzymatic antioxidants and non-enzymatic antioxidant activity, and gene expressions of antioxidants enzymes, lowering oxidative stress (MDA and H2O2) and Cd absorption in maize plants. Furthermore, TiO2NPs increased cellular fractionation (cellulose and hemicellulose), altering proline metabolism and ASA-GSH cycle activity in maize plants. Overall, this work emphasizes the intricate interactions between MPs and Cd, and nanoparticles in plant systems, highlighting TiO2NPs as a possible strategy for increasing plant flexibility and minimizing the negative effects of environmental pollutants. These findings have crucial implications regarding the development of long-term agricultural management approaches in polluted areas.

Agricultural waste-based modified biochars differentially affected the soil properties, growth, and nutrient accumulation by maize (Zea mays L.) plants

Biochar (BC) is an organic compound formed by the pyrolysis of organic wastes. Application of BCs as soil amendments has many benefits including carbon sequestration, enhanced soil fertility and sustainable agriculture production. In the present study, we acidified the different BCs prepared from rice straw, rice husk, wheat straw, cotton stalk, poultry manure, sugarcane press mud and vegetable waste; following which, we applied them in a series of pot experiments. Comparisons were made between acidified and non- acidified BCs for their effects on seed germination, soil properties (EC, pH) nutrient contents (P, K, Na) and organic matter. The treatments comprised of a control, and all above-described BCs (acidified as well as non-acidified) applied to soil at the rate of 1% (w/w). The maize crop was selected as a test crop. The results showed that acidified poultry manure BC significantly improved germination percentage, shoot length, and biomass of maize seedlings as compared to other BCs and their respective control plants. However, acidified BCs caused a significant decrease in nutrient contents (P, K, Na) of soil,maize seedlings, and the soil organic matter contents as compared to non- acidified BCs. But when compared with control treatments, all BCs treatments (acidified and non-acidified) delivered higher levels of nutrients and organic matter contents. It was concluded that none of the BCs (acidified and non-acidified) had caused negative effect on soil conditions and growth of maize. In addition, the acidification of BC prior to its application to alkaline soils might had altered soil chemistry and delivered better maize growth. Moving forward, more research is needed to understand the long-term effects of modified BCs on nutrient dynamics in different soils. In addition, the possible effects of BC application timings, application rates, particle size, and crop species have to be evaluated systemtically.

The negative mycorrhizal growth response of host plants to Acaulospora cf. morrowiae irrespective of soil P availability

Acaulospora is one of the dominant genera of AMF associated with waterlogged vegetation, and its dominance was also revealed in the roots of a lowland rice variety indigenous to Southern Thailand. In a preliminary finding, the isolated Acaulospora showed growth suppression of lowland japonica Nipponbare rice, even in high phosphorus (P) soil. The isolated Acaulospora was identified to species level and assigned as Acaulospora cf. morrowiae Phattalung 1. The mycorrhizal growth response (MGR) of an upland indica rice and maize to A. cf. morrowiae was further tested under low and high P conditions. AMF colonization rates were high, over 70%, in both cases, with perfect arbuscule and vesicle formation; however, growth depression of the host plants was markedly observed. Reduced nutrient accumulation in both shoots and roots of host plants was noted, as depicted by nutrient profiling. To further substantiate the negative MGR to inoculation of A. cf. morrowiae, a standardized in vivo bioassay was performed using maize seedlings in a sand and perlite mixture, ensuring low P with 20 mg kg−1 P in the form of insoluble CaH2PO4. Shoot and root growth of maize seedlings were reduced at 23.7 and 36.1%, respectively, by the inoculation of AMF. The nutrient-parasitic nature of this AMF results from unproportioned drainage of photosynthates, indicating an unbalanced primary/nutrient trade-off system between symbionts. The overall associative merits or demerits of A. cf. morrowiae cannot be ruled out without thorough investigations considering several ecological perspectives and its fitter survival and dominance in waterlogged soils.

Exogenously applied putrescine regulates aluminium [al (III)] stress in maize (Zea mays L.): Physiological and metabolic implications

In this study, we investigated the role of exogenous application of putrescine (Put) for alleviation of Al (III) stress responses in maize seedlings. In presence of Put, the growth and biomass improved substantially in Al (III) stressed seedlings as compared to Al (III) alone. The production of hydrogen peroxide (H2O2) and superoxide radical (O2•-) were significantly restrained in during Al (III) stress in Put supplemented seedlings. The malondialdehyde (MDA) production was significantly controlled during Al (III) stress by Put supplementation as compared to the seedlings under Al (III) stress alone. The histochemical analysis showed variation in staining intensities of diaminobenzidine (DAB) and nitoroblue tetrazolium (NBT) salt to detect the presence of H2O2 and O2•- respectively, reflected strong role of Put in regulation of reactive oxygen species (ROS) production. The staining of roots with Schiff's reagent and Evans blue dye to detect lipid peroxidation and loss of plasma membrane integrity showed that Put controls the lipid peroxidation and maintains the integrity of the plasma membrane during Al (III) stress. The proton (1H) nuclear magnetic resonance (NMR) analysis of methanolic extracts of root and shoot of maize seedlings under Al (III) stress in presence or absence of Put showed considerable disparity in terms of metabolic profiles, which include amino acids, sugars, carbohydrates, organic acids and several aliphatic and aromatic compounds. The present study exhibited the potential role of Put for mitigation of Al (III) stress by enhancing growth, regulating ROS production, reducing oxidative stress, improving antioxidant metabolism and maintaining the metabolic pool.

Exploring the dynamics of ISR signaling in maize upon seed priming with plant growth promoting actinobacteria isolated from tea rhizosphere of Darjeeling.

Plant growth-promoting rhizobacteria (PGPR) offer an eco-friendly alternative to agrochemicals for better plant growth and development. Here, we evaluated the plant growth promotion abilities of actinobacteria isolated from the tea (Camellia sinensis) rhizosphere of Darjeeling, India. 16S rRNA gene ribotyping of 28 isolates demonstrated the presence of nine different culturable actinobacterial genera. Assessment of the in vitro PGP traits revealed that Micrococcus sp. AB420 exhibited the highest level of phosphate solubilization (i.e., 445 ± 2.1µg/ml), whereas Kocuria sp. AB429 and Brachybacterium sp. AB440 showed the highest level of siderophore (25.8 ± 0.1%) and IAA production (101.4 ± 0.5µg/ml), respectively. Biopriming of maize seeds with the individual actinobacterial isolate revealed statistically significant growth in the treated plants compared to controls. Among them, treatment with Paenarthrobacter sp. AB416 and Brachybacterium sp. AB439 exhibited the highest shoot and root length. Biopriming has also triggered significant enzymatic and non-enzymatic antioxidative defense reactions in maize seedlings both locally and systematically, providing a critical insight into their possible role in the reduction of reactive oxygen species (ROS) burden. To better understand the role of actinobacterial isolates in the modulation of plant defense, three selected actinobacterial isolates, AB426 (Brevibacterium sp.), AB427 (Streptomyces sp.), and AB440 (Brachybacterium sp.) were employed to evaluate the dynamics of induced systemic resistance (ISR) in maize. The expression profile of five key genes involved in SA and JA pathways revealed that bio-priming with actinobacteria (Brevibacterium sp. AB426 and Brachybacterium sp. AB440) preferably modulates the JA pathway rather than the SA pathway. The infection studies in bio-primed maize plants resulted in a delay in disease progression by the biotrophic pathogen Ustilago maydis in infected maize plants, suggesting the positive efficacy of bio-priming in aiding plants to cope with biotic stress. Conclusively, this study unravels the intrinsic mechanisms of PGPR-mediated ISR dynamics in bio-primed plants, offering a futuristic application of these microorganisms in the agricultural fields as an eco-friendly alternative.

Exogenous application of 5-NGS increased osmotic stress resistance by improving leaf photosynthetic physiology and antioxidant capacity in maize.

Drought is a critical limiting factor affecting the growth and development of spring maize (Zea mays L.) seedlings in northeastern China. Sodium 5-nitroguaiacol (5-NGS) has been found to enhance plant cell metabolism and promote seedling growth, which may increase drought tolerance. In the present study, we investigated the response of maize seedlings to foliar application of a 5-NGS solution under osmotic stress induced by polyethylene glycol (PEG-6000). Four treatment groups were established: foliar application of distilled water (CK), foliar application of 5-NGS (NS), osmotic stress + foliar application of distilled water (D), and osmotic stress + foliar application of 5-NGS (DN). Plant characteristics including growth and photosynthetic and antioxidant capacities under the four treatments were evaluated. The results showed that under osmotic stress, the growth of maize seedlings was inhibited, and both the photosynthetic and antioxidant capacities were weakened. Additionally, there were significant increases in the proline and soluble sugar contents and a decrease in seedling relative water content (RWC). However, applying 5-NGS alleviated the impact of osmotic stress on maize seedling growth parameters, particularly the belowground biomass, with a dry mass change of less than 5% and increased relative water content (RWC). Moreover, treatment with 5-NGS mitigated the inhibition of photosynthesis caused by osmotic stress by restoring the net photosynthetic rate (Pn) through an increase in chlorophyll content, photosynthetic electron transport, and intercellular CO2 concentration (Ci). Furthermore, the activity of antioxidant enzymes in the aboveground parts recovered, resulting in an approximately 25% decrease in both malondialdehyde (MDA) and H2O2. Remarkably, the activity of enzymes in the underground parts exhibited more significant changes, with the contents of MDA and H2O2 decreasing by more than 50%. Finally, 5-NGS stimulated the dual roles of soluble sugars as osmoprotectants and energy sources for metabolism under osmotic stress, and the proline content increased by more than 30%. We found that 5-NGS played a role in the accumulation of photosynthates and the effective distribution of resources in maize seedlings. Based on these results, we determined that foliar application of 5-NGS may improve osmotic stress tolerance in maize seedlings. This study serves as a valuable reference for increasing maize yield under drought conditions.

Zinc oxide nanoparticles alleviated vanadium-induced inhibition by regulating plant hormone signal transduction and phenylpropanoid biosynthesis in maize seedlings (Zea may L.)

Our efforts were to identify the role of zinc oxide nanoparticles (ZnO-NPs) on the growth of maize (Zea may L.) under vanadium (V) stress. Transcriptome analysis was performed on maize leaves subjected to CK, V, and V+ZnO treatments. It was found that the application of ZnO-NPs significantly reduces V accumulation and toxicity in maize. A total of 5441 and 3003 differentially expressed genes (DEGs) were identified in the CK vs. V and V+ZnO vs. V comparisons, respectively. Of these detected genes, 3016 DEGs were specific to CV vs. V, and 608 DEGs were specific to V+ZnO vs V, respectively. These genes were primarily involved in plant hormone signal transduction and phenylpropanoid biosynthesis pathways. Under V treatment, ZnO-NPs caused an up-regulation of SAUR, AUX/IAA, ARRs, GID1, and BRIIs, which resulted in high levels of IAA, CTK, GA, BRs, and JAs in maize seedlings compared to those without ZnO-NPs. The addition of ZnO-NPs also leads to a significant decrease in total phenolics and lignin contents in maize seedlings by down-regulating CCR, HCT, CAD, 4CL, and C4H genes compared to those without ZnO-NPs. Overall, the findings suggest that ZnO-NPs can improve V-induced growth suppression by changing the expression of selected genes and constitute a simple and efficient strategy for alleviating V toxicity in high-V soils.

Changes in Amino Acids Profile and Uptake on Maize Seedlings Treated with Protein Hydrolysates and Humic Substances

Protein hydrolysates (PH) and humic substances (HS) are biostimulants that promote crop growth. Despite the widening of knowledge and insights provided by research activities over the past thirty years, there are still uncertainties concerning the possible direct absorption by plants of organic nitrogen as amino acids (AA) delivered as PH and the role of HS. This study aimed to assess the impact of PH treatment on the amino acid profile of maize seedlings and the influence of HS on amino acid uptake. Maize seedlings were treated with either PH from the yeast of the sugarcane fermentation process or a synthetic mixture of amino acids mimicking the PH composition using dual-labeled amino acids (13C, 15N glutamic acid) combined with commercially available humic substances. The amino acid profile was analyzed using HPLC, and plant tissues were examined for 15N using nuclear magnetic resonance (NMR) and mass spectrometry. The application of PH stimulated maize growth, with a more significant effect observed in the presence of humic substances. The treatments significantly altered the plants’ total amino acid content and composition profile. Maize seedlings actively uptake amino acids, representing 21% of the total nitrogen composition. The ascertained improvement of amino acid uptake stimulated by humic substances is associated with their effect on the differential expression of amino permease transporters and plasma membrane H+-ATPase. PH and amino acids enhance maize growth by significantly increasing amino acid uptake. The addition of humic substances further improved the biostimulant effects.

Overexpression of the peroxidase gene ZmPRX1 increases maize seedling drought tolerance by promoting root development and lignification

Drought is a main abiotic stress factor hindering plant growth, development, and crop productivity. Therefore, it is crucial to understand the mechanisms by which plants cope with drought stress. Here, the function of the maize peroxidase gene ZmPRX1 in drought stress tolerance was investigated by measurement of its expression in response to drought treatment both in a ZmPRX1 overexpression line and a mutant line. The higher root lignin accumulation and seedling survival rate of the overexpression line than that of the wild type or mutant support a role for ZmPRX1 in maize drought tolerance by regulating root development and lignification. Additionally, yeast one-hybrid, Dule luciferase and ChIP-qPCR assays showed that ZmPRX1 is negatively regulated by a nuclear-localized ZmWRKY86 transcription factor. The gene could potentially be used for breeding of drought-tolerant cultivars.