Seed and Foliar Application of Amino Acids Improve Variables of Nitrogen Metabolism and Productivity in Soybean Crop

The effects of foliar amino acid and Zn applications on agronomic traits and Zn biofortification in soybean (Glycine max L.)

The production and consumption of soybeans are widespread due to their nutritional and industrial value. Nutrient enrichment is vital for improving the nutritional quality of soybeans. This study aimed to evaluate the effect of foliar application of amino acids (AA) and zinc (Zn) on agronomic traits and the accumulation of grain Zn in soybeans. The experimental design comprised 16 treatment combinations involving four levels of amino acid application (0, 50, 100, and 150 ml 100 L-1) and Zn (0, 2, 4, and 6 mg L-1) following a randomized complete block design with three replications in field conditions. The results demonstrated that the application of foliar Zn and AA did not affect the yield, whereas that of AA50*Zn2 and AA150*Zn2 affected the number of pods and branches. The effects of AA application on N and the protein content in grains were determined to be significant. The application of AA100*Zn6 emerged as the most effective treatment for the enhancement of Zn biofortification in soybean grains. The combined foliar application of AA and Zn contributed to enhanced Zn accumulation in the grains.

Liquid fertilizers produced by microwave-assisted acid hydrolysis of livestock and poultry wastes and their effects on hot pepper cultivation

Liquid fertilizers (LFs) produced by microwave-assisted acid hydrolysis of livestock and poultry wastes were applied to potted hot pepper (Capsicum annuum L.) to evaluate their potential to be used as amino acid LFs. A preliminary experiment was conducted to determine the optimum acid-hydrolysis conditions for producing LFs from a mixture of pig hair and faeces (P) and another mixture of chicken feathers and faeces (C). Two LFs were produced under the optimum acid-hydrolysis conditions (acidification by sulphuric acid (7.5 mol L-1) in a microwave (200 W) for 90 minutes), and a commercial amino acid LF (Guo Guang (GG)) was used for comparison. P, C and GG fertilizers were tested in potted hot pepper cultivation at two doses, whereas no fertilizer application served as the control (CK). P and C fertilizers significantly increased the fruit yield compared with GG fertilizer, particularly at the higher dose. Moreover, the treatments improved the fruit vitamin C and soluble sugar contents in the order of C > P > GG compared with CK. These results could be attributed to more types of amino acids in C fertilizer than in P and GG fertilizers. The results also indicated that the prepared fertilizers could significantly increase the shoot and root dry weight, soil available nitrogen and phosphorus contents and nitrogen, phosphorus, and potassium (NPK) uptake by plants compared with CK. In conclusion, microwave-assisted acid hydrolysis could effectively convert unusable wastes into valuable fertilizers comparable or even superior to commercial fertilizers.

Amino Acids Biostimulants and Protein Hydrolysates in Agricultural Sciences

The effects of different types of biostimulants on crops include improving the visual quality of the final products, stimulating the immune systems of plants, inducing the biosynthesis of plant defensive biomolecules, removing heavy metals from contaminated soil, improving crop performance, reducing leaching, improving root development and seed germination, inducing tolerance to abiotic and biotic stressors, promoting crop establishment and increasing nutrient-use efficiency. Protein hydrolysates are mixtures of polypeptides and free amino acids resulting from enzymatic and chemical hydrolysis of agro-industrial protein by-products obtained from animal or plant origins, and they are able to alleviate environmental stress effects, improve growth, and promote crop productivity. Amino acids involve various advantages such as increased yield and yield components, increased nutrient assimilation and stress tolerance, and improved yield components and quality characteristics. They are generally achieved through chemical or enzymatic protein hydrolysis, with significant capabilities to influence the synthesis and activity of some enzymes, gene expression, and redox-homeostasis. Increased yield, yield components, and crop quality; improved and regulated oxidation-reduction process, photosynthesis, and physiological activities; decreased negative effects of toxic components; and improved anti-fungal activities of plants are just some of the more important benefits of the application of phenols and phenolic biostimulants. The aim of this manuscript is to survey the impacts of amino acids, different types of protein hydrolysates, phenols, and phenolic biostimulants on different plants by presenting case studies and successful paradigms in several horticultural and agricultural crops.

Nitrogen balance and gap of a high yield tropical soybean crop under irrigation

Nitrogen (N) is the most extracted and exported element by the soybean crop. In high yield tropical environments with irrigation, little is known about N accumulation in different soybean plant organs as well as the N balance. The objective of this study was to characterize soybean growth, N accumulation in plant organs, N balance, and N gap in a high yield tropical environment. This study was performed in a homogeneous field, in a soil with low organic matter, with 20 kg ha-1 of N, under furrow fertilization. Evaluations were performed ten times, temporally distributed from emergence to senescence. The soybean cultivar used was 'RK7518 IPRO' and was sown with row spacing of 0.45 m and a seeding rate of 300,000 plants ha-1. Plant N partition, N from the biological N fixation (BNF), grain yield, crop harvest index (HI), N harvest index (NHI) with and without root contribution were evaluated. Also, at the grain filling stage the N gap was evaluated from the soil by difference between whole plant accumulated N and the amount of N from BNF. The average grain yield was 6,470 kg ha-1 and leads to a negative partial balance of N of -33.4 and -42.8 kg[N] ha-1 with and without roots, respectively. The N gap from the soil was 231.7 kg[N] ha-1. It is recommended to adopt techniques that increase the efficiency of BNF and the soil N accumulation to balance these production systems in the medium to long term.

Commercial Initiation of Feather Hydrolysate as Supreme Fertilizer: A Smart Bio-Cleaning Strategy of Poultry Waste

Purpose

Economic development of India mainly depends on agricultural sectors. The Indian traditional agricultural system is mainly based on chemical fertilizer to get better yield. The main motto of this research work is to change the traditional faith of Indian farmers and rural Indian economy.

Methods

Bioprocessing of feather prepared from an efficient newly isolated bacterial strain, identified as Bacillus wiedmanni SAB10 is used to produce a nitrogen rich liquid fertilizer. The cell-free hydrolysate was prepared from submerged fermentation of poultry litter (1.25%, w/v) as sole media with supplemented as chicken feather (1%, w/v) in 79.41 h with pH 10.6.

Results

Fermented hydrolysate contains a significant quantity of total amino acid (503.02 mg/L) with diversity (Cystine, Phenylalanine, Tyrosine, lysine, Valine, Proline and Alanine), total oligopeptides (4.65 mg/ml) and thiol content (58.09 µg/ml) which influence growth and yield (1.02 fold) of moong beans (Vigna radiata) plant in pot trials and as well as successfully scale up in field trials by the farmers. This liquid fertilizer not only makes plant healthy and has drought tolerance (proline content- 0.023 mg/g) capacity but also increases the grain quality by spraying the fertilizer on foliage with a ratio of 2:1 (Water: Feather hydrolysate) for two times (before the 1st flash and 2nd flash of flowering).

Conclusion

Fermented feather hydrolysate is used full as a foliage fertilizer for the cultivation of moong beans. Some commercial properties and its eco-friendly, cost-effectiveness will make it a smart liquid fertilizer in near future.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12649-022-01982-9.

Comparative analysis of pumpkin rootstocks mediated impact on melon sensory fruit quality through integration of non-targeted metabolomics and sensory evaluation

Melon fruits are popular because of sweet taste and pleasant aroma. Grafting has been extensively used for melons to alleviate abiotic stresses and control soil borne diseases. However, use of grafting for vegetable fruit quality improvement is less studies. In modern age fruit quality particularly sensory quality characteristics have key importance from consumer eye lens. We performed liquid chromatography-mass spectrometry and metabonomic analysis to examine sensory fruit quality of melon grafted onto ten different pumpkin rootstocks. Bases on the result of our study, 478 metabolites were detected and 184 metabolites consisting of lipids, amino acids and organic oxygen compounds were differentially expressed in grafted melon fruits. The results from metabolomic, physiochemical and sensory analysis explain the differences in melon fruit flavor from two contrasting rootstocks. In conclusion the fruits from Tianzhen No. 1 rootstock exhibited better organoleptic characteristics and higher soluble sugars content [glucose (19.87 mg/g), fructose (19.68 mg/g) and sucrose (169.45 mg/g)] compared with other rootstocks used in this study. Moreover, the contents of bitterness causing amino acids such as L-arginine, L-asparagine, Histidinyl-histidine and Acetyl-DL-valine were found lower in Tianzhen No. 1-grafted melon fruits compared with Sizhuang No. 12-grafted melon fruits. These fruit quality characteristics made Tianzhen No. 1 rootstock suitable for commercial cultivation of Yuniang melon.

Combined application of asparagine and thiourea improves tolerance to lead stress in wheat by modulating AsA-GSH cycle, lead detoxification and nitrogen metabolism

Lead (Pb), like other heavy metals, is not essentially required for optimal plant growth; however, plants uptake it from the soil, which poses an adverse effect on growth and yield. Asparagine (Asp) and thiourea (Thi) are known to assuage the negative impacts of heavy metal pollution on plant growth; however, combined application of Asp and Thi has rarely been tested to discern if it could improve wheat yield under Pb stress. Thus, this experimentation tested the role of individual and combined applications of Asp (40 mM) and Thi (400 mg/L) in improving wheat growth under lead (Pb as PbCl₂, 0.1 mM) stress. Lead stress significantly reduced plant growth, chlorophyll contents and photosystem system II (PSII) efficiency, whereas it increased Pb accumulation in the leaves and roots, leaf proline contents, phytochelatins, and oxidative stress related attributes. The sole or combined application of Asp and Thi increased the vital antioxidant biomolecules/enzymes, including reduced glutathione (GSH), ascorbic acid (AsA), ascorbate peroxsidase (APX), catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Furthermore, the sole or the combined application of Asp and Thi modulated nitrogen metabolism by stimulating the activities of nitrate and nitrite reductase, glutamate synthase (GOGAT) and glutamine synthetase (GS). Asp and Thi together led to improve plant growth and vital physiological processes, but lowered down Pb accumulation compared to those by their sole application. The results suggest that Asp and Thi synergistically can improve wheat growth under Pb-toxicity.

Effects of Exogenous L-Asparagine on Poplar Biomass Partitioning and Root Morphology

L-Asparagine (Asn) has been regarded as one of the most economical molecules for nitrogen (N) storage and transport in plants due to its relatively high N-to-carbon (C) ratio (2:4) and stability. Although its internal function has been addressed, the biological role of exogenous Asn in plants remains elusive. In this study, different concentrations (0.5, 1, 2, or 5 mM) of Asn were added to the N-deficient hydroponic solution for poplar ‘Nanlin895’. Morphometric analyses showed that poplar height, biomass, and photosynthesis activities were significantly promoted by Asn treatment compared with the N-free control. Moreover, the amino acid content, total N and C content, and nitrate and ammonia content were dramatically altered by Asn treatment. Moreover, exogenous Asn elicited root growth inhibition, accompanied by complex changes in the transcriptional pattern of genes and activities of enzymes associated with N and C metabolism. Combined with the plant phenotype and the physiological and biochemical indexes, our data suggest that poplar is competent to take up and utilize exogenous Asn dose-dependently. It provides valuable information and insight on how different forms of N and concentrations of Asn influence poplar root and shoot growth and function, and roles of Asn engaged in protein homeostasis regulation.

The Interaction Effect of Laser Irradiation and 6-Benzylaminopurine Improves the Chemical Composition and Biological Activities of Linseed (Linum usitatissimum) Sprouts

Even though laser light (LL) and 6-benzylaminopurine (BAP) priming are well-known as promising strategies for increasing the growth and nutritional value of several plants, no previous studies have investigated their synergistic effect. Herein, we investigated the effects of laser light, 6-benzylaminopurine (BAP) priming, and combined LL-BAP treatment on the nutritional value, chemical composition, and the biological activity of Linum usitatissimum sprouts. The fresh weight, leaf pigments, primary and secondary metabolites, enzymes, and antimicrobial activities were determined. A substantial enhancement was observed in the growth characteristics and leaf pigments of laser-irradiated and BAP-primed sprouts. Furthermore, the combined treatments improved the accumulation of minerals, vitamins, and amino acids, and also enhanced the N-metabolism more than LL or BAP alone. Furthermore, the combined priming boosted the antioxidant capacity by increasing the contents of fatty acids, phenols, and flavonoids. Antimicrobial activity and the highest increase in bioactive compounds were recorded in linseed sprouts simultaneously treated with LL and BAP. This work suggests that priming L. usitatissimum sprouts with laser light and BAP is a promising approach that can improve the nutritional value and health-promoting impacts of L. usitatissimum sprouts.

Fertilizers and Fertilization Strategies Mitigating Soil Factors Constraining Efficiency of Nitrogen in Plant Production

Fertilizer Use Efficiency (FUE) is a measure of the potential of an applied fertilizer to increase its impact on the uptake and utilization of nitrogen (N) present in the soil/plant system. The productivity of N depends on the supply of those nutrients in a well-defined stage of yield formation that are decisive for its uptake and utilization. Traditionally, plant nutritional status is evaluated by using chemical methods. However, nowadays, to correct fertilizer doses, the absorption and reflection of solar radiation is used. Fertilization efficiency can be increased not only by adjusting the fertilizer dose to the plant's requirements, but also by removing all of the soil factors that constrain nutrient uptake and their transport from soil to root surface. Among them, soil compaction and pH are relatively easy to correct. The goal of new the formulas of N fertilizers is to increase the availability of N by synchronization of its release with the plant demand. The aim of non-nitrogenous fertilizers is to increase the availability of nutrients that control the effectiveness of N present in the soil/plant system. A wide range of actions is required to reduce the amount of N which can pollute ecosystems adjacent to fields.

Interactive effect of glycine, alanine, and calcium nitrate Ca(NO3)2 on wheat (Triticum aestivum L.) under lead (Pb) stress

Aim of this study was to evaluate the interactive effects of glycine, alanine, calcium nitrate [Ca(NO₃)₂], and their mixture on the growth of two wheat (Triticum aestivum L.) varieties, i.e., var. Punjab-2011 and var. Anaj-2017 under lead [0.5 mM Pb(NO₃)₂] stress. A pot experiment was conducted for this purpose. Pre-sowing seed treatment with 1 mM glycine, alanine, and calcium nitrate [Ca(NO₃)₂] was applied under two levels of lead nitrate [Pb(NO₃)₂] stress, i.e., control and 0.5 mM Pb(NO₃)₂. Lead (0.5 mM) stress significantly decreased root and shoot lengths, fresh and dry weights of root and shoot, and chlorophyll contents, while it increased activities of antioxidant enzymes such as catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and peroxidase (POD) in both wheat varieties. Lead (0.5 mM) stress increased the accumulation of free proline, glycinebetaine, total free amino acids, and total soluble protein contents. Although var. Punjab-2011 was higher in root fresh and dry weights, shoot length, and total leaf area per plant, however, var. Anaj-2017 showed less reduction in shoot dry weight, root fresh weight, and shoot length under lead stress. Under lead stress, Punjab-2011 was higher in grain yield and number of grain plant^-1, chlorophyll a contents, membrane permeability (%), POD activity, total free amino acids, and glycinebetaine (GB) contents as compared to Anaj-2017. Pre-sowing seed treatments with glycine, alanine, calcium nitrate, and their mixture (1 mM of each) increased shoot dry weight, number of grains per plants, 100-grain weight, number of spikes, and chlorophyll a contents under normal and lead-stressed conditions. Wheat var. Anaj-2017 showed higher growth and yield attributes as compared to var. Punjab-2011. Results of the current study have shown that pre-sowing seed treatments with glycine, alanine, calcium nitrate, and their mixture (1 mM of each) can overcome the harmful effects of lead (Pb) stress in wheat plants.

Effects of Pymetrozine and Tebuconazole with Foliar Fertilizer Through Mixed Application on Plant Growth and Pesticide Residues in Cucumber

The mixed application of pesticides and foliar fertilizer has been widely used in the production of cucumber, however, their effects on plant growth and pesticide dissipation are still unclear. In this study, the effects of mixed application of pymetrozine, tebuconazole and foliar fertilizer on the cucumber plant growth and pesticide dissipation were investigated simultaneously. The results show that the mixed use of pymetrozine, tebuconazole, especially adding foliar fertilizer, improved the physiological indexes (i.e., area, nitrogen content and chlorophyll content of the leaves, and root growth) of cucumber plants compared to those with the application of single pesticide. Meanwhile, it can significantly affect the dissipation of pymetrozine even in the slower growth matrices (lower leaves, stems, and plants). The residue of tebuconazole in cucumber plants was affected by the combination of formulation type and foliar fertilizer. This study can provide data for scientifically guiding the mixed application of pesticide and fertilizer.

Metabolomics analysis of cucumber fruit in response to foliar fertilizer and pesticides using UHPLC-Q-Orbitrap-HRMS

Pesticides and fertilizers are often used to improve the yield and quality of cucumber fruit. In this study, the effect of pesticide applied with or without foliar fertilizer on the cucumber fruit metabolism was investigated. The results showed that the mixed use of pesticides and foliar fertilizer could significantly increase the contents of organic acids and the antioxidant level. When pesticide was used without foliar fertilizer, cucumber fruit up-regulated (1.3 times) shikimate-phenylpropanoid pathway and improved the antioxidant capacity to deal with the pesticide stress. However, the tricarboxylic acid cycle was up-regulated 1.1 times and the antioxidant capacity was improved to promote the pesticide dissipation when pesticide was applied with foliar fertilizer. These observations indicate that the mixed application of foliar fertilizer and pesticides can regulate related metabolites and metabolic pathways, improve the quality and antioxidant capacity of cucumber fruit, and promote the dissipation of pesticides.

Transcriptomics Analysis of Wheat Tassel Response to Tilletia laevis Kühn, Which Causes Common Bunt of Wheat

Tilletia laevis Kühn [synonym T. foetida (Wallr.) Liro] can lead to a wheat common bunt, which is one of the most serious diseases affecting kernels, a serious reduction in grain yield, and losses can reach up to 80% in favorable environments. To understand how wheat tassels respond to T. laevis, based on an RNA-Seq technology, we analyzed a host transcript accumulation on healthy wheat tassels and on tassels infected by the pathogen. Our results showed that 7,767 out of 15,658 genes were upregulated and 7,891 out of 15,658 genes were downregulated in wheat tassels. Subsequent gene ontology (GO) showed that differentially expressed genes (DEGs) are predominantly involved in biological processes, cellular components, and molecular functions. Additionally, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that 20 pathways were expressed significantly during the infection of wheat with T. laevis, while biosynthesis of amino acids, carbon metabolism, and starch and sucrose metabolism pathways were more highly expressed. Our findings also demonstrated that genes involved in defense mechanisms and myeloblastosis (MYB) transcription factor families were mostly upregulated, and the RNA-seq results were validated by quantitative real-time polymerase chain reaction (qRT-PCR). This is the first report on transcriptomics analysis of wheat tassels in response to T. laevis, which will contribute to understanding the interaction of T. laevis and wheat, and may provide higher efficiency control strategies, including developing new methods to increase the resistance of wheat crops to T. laevis-caused wheat common bunt.

The Exogenous Application of Micro-Nutrient Elements and Amino Acids Improved the Yield, Nutritional Status and Quality of Mango in Arid Regions

The mango is one of the most valuable and appealing tropical fruits due to its color, aroma, tasteful remarkable flavor, and nutritive value; however, improving the yield and quality of mango is an urgent goal in order to combat global population growth. The application of amino acids and a micronutrient mixture might improve the yield and quality features but further research is still required in arid regions. To study the combined effect of a micronutrient mixture (MM) and amino acids (AA) at different rates, twenty-seven Fagri Kalan mango trees (15 years old) were carefully selected. The foliar application effect of MM and AA on vegetative growth, total chlorophyll, leaf chemical constituents, productivity, and the fruit quality of mango trees (cv. Fagri Kalan) was investigated. The findings revealed that the investigated growth measurements and leaf chemical contents, as well as the fruiting aspects and the fruit quality improved significantly due to the application of MM and AA. A higher application rate of the micronutrient mixture (2 g L⁻¹) in combination with the highest amino acid concentration (2 mg L⁻¹) was the most effective combination that increased the yield, total soluble solids (TSS), total sugars (TS), and total carbohydrates by 28.0%, 3.0%, 5.8% and 15.0%, respectively, relative to untreated plants. The relationship between such characteristics revealed a strong positive correlation (0.80–0.95), confirming the importance of these materials in increasing the yield and quality of mangoes. Thus, using doses of MM and AA as a foliar spray four times during each growing season is recommended under similar environmental conditions and horticulture practices used in the current experiment.

Profiling of Plant Growth-Promoting Metabolites by Phosphate-Solubilizing Bacteria in Maize Rhizosphere

Microbial treatment has recently been attracting attention as a sustainable agricultural strategy addressing the current problems caused by unreasonable agricultural practices. However, the mechanism through which microbial inoculants promote plant growth is not well understood. In this study, two phosphate-solubilizing bacteria (PSB) were screened, and their growth-promoting abilities were explored. At day 7 (D7), the lengths of the root and sprout with three microbial treatments, M16, M44, and the combination of M16 and M44 (Com), were significantly greater than those with the non-microbial control, with mean values of 9.08 and 4.73, 7.15 and 4.83, and 13.98 and 5.68 cm, respectively. At day 14 (D14), M16, M44, and Com significantly increased not only the length of the root and sprout but also the underground and aboveground biomass. Differential metabolites were identified, and various amino acids, amino acid derivatives, and other plant growth-regulating molecules were significantly enhanced by the three microbial treatments. The profiling of key metabolites associated with plant growth in different microbial treatments showed consistent results with their performances in the germination experiment, which revealed the metabolic mechanism of plant growth-promoting processes mediated by screened PSB. This study provides a theoretical basis for the application of PSB in sustainable agriculture.

Evaluation of the foliar nutrition influence on selected quantitative and qualitative paprameters of sugar mayze (Zea mays SK saccharata)

We evaluated the effect of foliar application of fertilizer Tecnokel amino Zn on selected quantitative (weight of one corn cob, average length of corn cob, number of grains per row and number of rows per cob) and qualitative (total yield, total carotenoid content, total sugar content) parameters of sweetcorn. The small trail experiment was founded in 2016 in the Botanical Garden of the Slovak University of Agriculture. We observed 7 selected varieties of sweetcorn and two variants: control and with leaf nutrition. 15 plants we revaluated for each variety under both variants. The corn was grown in three repetitions for each variant. Based on the obtained results, we found that both the qualitative and quantitative parameters were mainly dependent on the genotype. Statistically significant was effect of the variety on the total sugar content in maize grains. Influence of foliar nutrition was not confirmed as statistically significant, but Tecnokel amino Zn has a positive impact on several quantitative parameters as weight of one maize ear or average length of corncobs. Content of total carotenoid doesn´t depend on genotype or variant.

Signaling Role of Glutamate in Plants

It is well known that glutamate (Glu), a neurotransmitter in human body, is a protein amino acid. It plays a very important role in plant growth and development. Nowadays, Glu has been found to emerge as signaling role. Under normal conditions, Glu takes part in seed germination, root architecture, pollen germination, and pollen tube growth. Under stress conditions, Glu participates in wound response, pathogen resistance, response and adaptation to abiotic stress (such as salt, cold, heat, and drought), and local stimulation (abiotic or biotic stress)-triggered long distance signaling transduction. In this review, in the light of the current opinion on Glu signaling in plants, the following knowledge was updated and discussed. 1) Glu metabolism; 2) signaling role of Glu in plant growth, development, and response and adaptation to environmental stress; as well as 3) the underlying research directions in the future. The purpose of this review was to look forward to inspiring the rapid development of Glu signaling research in plant biology, particularly in the field of stress biology of plants.

Melatonin promotes plant growth by maintaining integration and coordination between carbon and nitrogen metabolisms

Melatonin-induced growth promotion of maize seedlings is associated with maintaining coordination between gene expressions and activities of key enzymes involved in carbon and nitrogen metabolisms. Melatonin is a pleiotropic molecule that influences many diverse actions to enhance plant growth. The effect of melatonin on maintaining a necessary balance between carbon and nitrogen metabolisms that underpins the growth process in higher plants remains unclear. In this study, the influence of melatonin on nitrogen assimilation, mitochondrial respiration, and photosynthesis, which are major pathways related with carbon and nitrogen metabolism, was investigated on the basis of the seedling growth of maize. Melatonin applications (10, 100, and 1000 μmol L^-1) significantly increased the growth parameters assessed by root elongation, plant height, leaf surface area, and the contents of protein, carbohydrate, and chlorophyll in comparison to the control seedlings. They also had a strong encouraging effect on the activities and gene expressions of enzymes (nitrate reductase, nitrite reductase, glutamine synthase, glutamate 2-oxoglutarate transferase, and NADH-glutamate dehydrogenase) involved in the nitrogen assimilation process. While melatonin applications elevated nitrate and nitrite concentrations, they markedly lowered ammonium content compared to control. Similarly, the activity of citrate synthase, the first enzyme of citric acid cycle providing carbon skeleton for nitrogen assimilation, was significantly augmented by melatonin applications. Moreover, melatonin considerably upregulated the gene expressions of citrate synthase and cytochrome oxidase, an enzyme responsible for ATP production. Remarkable increments were recorded at Rubisco activity and gene expressions of Rubisco and Rubisco activase in melatonin-treated seedlings. In conclusion, all these data put together reveal that melatonin-induced growth promotion of maize seedlings resulted from its coordinating effect on carbon and nitrogen metabolisms.

Comparative effect of elicitors on the physiology and secondary metabolites in broccoli plants

Elicitation is an economic and sustainable technique for increasing the content of secondary metabolites, mainly bioactive compounds, in plants grown for better human nutrition. The aim of this study was to compare the physiological responses (water relations and mineral nutrition) and the enrichment in glucosinolates (GLSs) and phenolic compounds of broccoli plants (Brassica oleracea L. var. italica) receiving different elicitation treatments. The treatments involved the priming of seeds with KCl and the exposure of plants to elicitors, including K₂SO₄ and NaCl solutions and foliar sprays of methyl jasmonate (MeJA), salicylic acid (SA), and methionine (Met). The physiological response of the plants in terms of root hydraulic conductance was improved by priming with KCl and elicitation with MeJA or Met. Foliar application of Met significantly increased the plant biomass and enhanced mineral nutrition. In general, all treatments increased the accumulation of indole GLSs, but K₂SO₄ and MeJA gave the best response and MeJA also favored the formation of a newly described compound, cinnamic-GLS, in the plants. Also, the use of Met and SA as elicitors and the supply of K₂SO₄ increased the abundance of phenolic compounds; K₂SO₄ also enhanced growth but did not alter the water relations or the accumulation of mineral nutrients. Therefore, although the response to elicitation was positive, with an increased content of bioactive compounds, regulation of the water relations and of the mineral status of the broccoli plants was critical to maintain the yield.