Ileana Echevarría-Machado

Melatonin has been recognized as a regulator of plant growth and stress responses; however, its role in nitrogen metabolism, particularly in Capsicum chinense Jacq., remains poorly understood. In this study, we evaluated the effect of melatonin priming alone (chemopriming, CP) or in combination with substrate reinforcement (soil drench, SD) (CP + SD), at different doses, on physiological, biochemical, and molecular parameters in habanero pepper plants growing in non-stressed conditions. Growth traits, nitrogen-related metabolites, total carbohydrates, the expression of key genes involved in nitrogen metabolism, and glutamate dehydrogenase (GDH) activity were analyzed. The results showed that priming increased biomass mainly at 25 and 50 µM, whereas the combined treatment promoted improvements from early doses (5 µM). Additionally, the evaluated genes exhibited tissue-specific expression patterns. Most genes were downregulated in leaves, whereas proline and total carbohydrate levels correlated with fresh and dry weight. Our results provide new insights into the regulation of nitrogen metabolism according to the application method and dosage, establishing an application strategy to optimize nitrogen metabolism and growth in habanero peppers. The mechanism of melatonin in regulating the balance of C and N metabolites and its impact on the response of chili plants to growth and environmental signals should be addressed later.

Introduction: The present work reports the production and characterization of chitosan microspheres (QUI) and chitosan/palygorskite hybrid microspheres (QUI/Pal) and investigates their performance for the controlled delivery of the biostimulants glycine (Gly) and glutamic acid (Glu) and their potential application in plants. Methods: Three groups of microspheres were obtained using the water-in-oil emulsion method and characterized by Scanning Electron Microscopy (SEM), swelling degree (H), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). The captured amino acids were quantified by UV-Visible spectrophotometry, and their potential biological activity was assessed. Results: The incorporation of palygorskite into hybrid microspheres (QUI/Pal) significantly improved amino acid capture efficiency and modulated delivery kinetics, resulting in slower and more gradual release profiles compared to QUI microspheres. Discussion: Mathematical modeling revealed a two-stage diffusion process: an initial Fickian phase followed by a non-Fickian phase associated with polymer matrix relaxation. Biological studies demonstrated that QUI/Pal microspheres loaded with amino acids did not generate adverse toxic effects in plants. Conclusion: Biological assays with Capsicum chinense (habanero pepper) showed that QUI/Pal microspheres improved germination percentage, biomass production, and root elongation in a dose-dependent manner. These results confirm the potential of QUI/Pal microspheres as effective systems for the controlled delivery of biostimulants in agricultural applications.

Although the role of proline (Pro) as an important osmolyte has been extensively studied, there are few comprehensive studies on their metabolism under salinity conditions. We investigated Pro metabolism in two habanero pepper varieties with contrasting salinity responses: Mayan Chan (tolerant) and Mayan Ba’alche (sensitive). First, a phylogenetic analysis of enzymes participating in their biosynthesis, P5CS and P5CR, and in its degradation, PDH, was performed. Additionally, the levels of their transcripts, the enzymatic activity, and Pro content were determined in plants subjected to 150 mM NaCl by short (0, 24, 48 and 72 h) and long (seven days) periods. Potassium flux in roots exposed to NaCl, in the absence or presence of Pro, was also measured. Phylogenetic analysis showed that the sequences were grouped according to their taxonomic family and not by salt tolerance of the species. Molecular and biochemical analyses showed significant differences between organs and varieties; the tolerant variety showed highest levels of transcripts, biosynthesis enzymes activities and accumulation of Pro. The results suggested that Pro metabolism in habanero pepper is a complex process, that is regulated at different levels and differentially between organs and varieties. Exogenous Pro only reduced potassium efflux in the sensitive variety exposed to NaCl, suggesting that a precise threshold of this amino acid is required to perform this function.

Aspectos como la sostenibilidad, la eficiencia, el cuidado del ambiente y la salud de los seres vivos son de relevancia actual dentro de la nutrición mineral, la cual permite la producción de cultivos que brinda alimentos a la población mundial. Sin embargo, en este estudio se resalta la importancia del nitrógeno debido a que es el elemento mineral que más impacto tiene en los rendimientos de los cultivos. Se aborda su importancia en la nutrición mineral, en las bioestructuras celulares, en los rendimientos y, finalmente, su papel como molécula señal en la interacción planta-patógeno. En este trabajo se hace énfasis en el por qué es importante una nutrición nitrogenada adecuada para las plantas tanto en cantidad como en calidad, ya que ésta es un indicativo de la forma química en la que se suministra el nitrógeno dentro de los esquemas de fertilización agrícola. Este enfoque es un campo reciente de estudio que podría contribuir, en el futuro, al diseño de estrategias de nutrición nitrogenada adecuadas para mejorar los rendimientos agrícolas y la tolerancia de los cultivos a las plagas y enfermedades, con un uso reducido de contaminantes químicos.

Introduction: Currently, the literature on amino acid delivery through microspheres is almost nonexistent. The present study was based on the development and characterization of hybrid microspheres of a polymeric matrix structured with palygorskite nanoclays. These microspheres are proposed to be used as controlled delivery systems of amino acids for agricultural applications. Methods: Hybrid microspheres of Poly(lactic acid) (PLA) and Palygorskite (Pal) were prepared via the double emulsion method with solvent evaporation. Likewise, the amino acids Glycine (Gly) and Glutamic acid (Glu) were integrated in situ during the preparation of the microspheres, all of which were characterized through Scanning Electron Microscopy (SEM), Particle Size (TP) and X-ray Diffraction (XRD); the amino acids were detected through Ultraviolet (UV) spectrophotometry. Results and Discusssion: Microspheres with spherical morphology were obtained, and as the Pal content increased, they displayed irregular surfaces with particle sizes between 101 and 152 μm. Pal in the microspheres was detected with XRD. The microspheres that trapped a greater amount of amino acids were those containing 2.5% Pal, which presented longer delivery times compared to those microspheres with only the PLA matrix. Conclusion: The mathematical modeling of the delivery kinetics demonstrated that the amino acid release depends on the diffusion mechanism through the microspheres; the study also demonstrated that the presence of nanoclays influences the diffusion speed.

Recently, it has been proposed that plant melatonin receptors belong to the superfamily of G protein-coupled receptors (GPCRs). However, a detailed description of the phylogeny, protein structure, and binding properties of melatonin, which is still lacking, can help determine the signaling and function of this compound. Melatonin receptor homologs (PMTRs) were identified in 90 Viridiplantae sensu lato proteomes using profile Hidden Markov Models (HMM), which yielded 174 receptors across 87 species. Phylogenetic analysis revealed an expansion of PMTR sequences in angiosperms, which were grouped into three clades. Docking studies uncovered a conserved internal melatonin-binding site in PMTRs, which was analogous to the site in human MT1 receptors. Binding affinity simulations indicated this internal site exhibits stronger melatonin binding compared to a previously reported superficial pocket. Ligand–receptor interaction analysis and alanine scanning highlighted a major role of hydrophobic interactions, with hydrogen bonds contributing predominantly at the internal site, while non-interacting charged residues stabilize the binding pocket. Tunnel and ligand transport simulations suggested melatonin moves favorably through the internal cavity to access the binding site. Also, we presented for the first time details of these pockets in a non-model species, Capsicum chinense. Taken together, the structural analyses presented here illustrate opportunities and theoretical evidence for performing structure–function studies via mutations in specific residues within the proposed new melatonin-binding site in PMTRs, shedding light on their role in plant melatonin signaling.

Scrub mangrove forests, dominated by Rhizophora mangle L., are characterized by high porewater salinity, which might compromise individual sap flow rates (SF) due to seasonal and diurnal microenvironmental variations. We tested the functional, anatomical, and SF responses of 12 individuals to microenvironmental variables such as solar radiation, photosynthetic photon flux, wind speed, evaporative demand, and porewater salinity, measured using an in situ weather station. Measurements were made in the dry and rainy seasons in the Yucatan Peninsula, using Granier heat dissipation sensors, installed on tree branches. During the rainy season, SF was twice as high as that during the dry season (0.22 ± 0.00 L h⁻¹ and 0.11 ± 0.00 L h⁻¹, respectively), despite lower evaporative demand. In both seasons, negative relationships between SF with vapor pressure deficit (VPD; dry τ = −0.54; rainy τ = −0.56) and with photosynthetic photon flux (PPF; dry τ = −0.97; rainy τ = −0.98) were found, indicating a strong hydraulic coupling to atmospheric conditions. Sap flow and transpiration rates of this R. mangle scrub mangrove forest exceeded those of some tropical dry deciduous forests, suggesting adaptations that support water transport in saline environments. The clustered xylem vessels of R. mangle ensure safe sap flow year-round. As an evergreen species, it contributes water to the atmosphere all year-round, underscoring its critical role in the tropical ecohydrological environment.

Proline (Pro) is a low-molecular-weight cyclic amino acid that plays an important role as a source of energy and reducing power and as a source of carbon and nitrogen compounds for plant development. In most plant species, Pro is considered a stress marker. It is also a common compatible solute and is used cumulatively by plants under osmotic stress. The pepper genus, which includes species of great economic importance distributed throughout the world, is the target of different types of stresses, both biotic and abiotic, and Pro plays an important role in tolerance to some of these stresses. In this work, we discuss the general aspects of the metabolism, transport, and different functions of Pro in the Capsicum genus. Special focus is given to critical investigations that should be conducted with respect to Pro accumulation under stress conditions, such as salinity and water deficit.

Plant glutamate receptors (GLRs) are integral membrane proteins that function as non-selective cation channels, involved in the regulation of developmental events crucial in plants. Knowledge of these proteins is restricted to a few species and their true agonists are still unknown in plants. Using tomato SlGLRs, a search was performed in the pepper database to identify GLR sequences in habanero pepper (Capsicum chinense Jacq.). Structural, phylogenetic, and orthology analysis of the CcGLRs, as well as molecular docking and protein interaction networks, were conducted. Seventeen CcGLRs were identified, which contained the characteristic domains of GLR. The variation of conserved residues in the M2 transmembrane domain between members suggests a difference in ion selectivity and/or conduction. Also, new conserved motifs in the ligand-binding regions are reported. Duplication events seem to drive the expansion of the species, and these were located in the evolution by using orthologs. Molecular docking analysis allowed us to identify differences in the agonist binding pocket between CcGLRs, which suggest the existence of different affinities for amino acids. The possible interaction of some CcGLRs with proteins leads to suggesting specific functions for them within the plant. These results offer important functional clues for CcGLR, probably extrapolated to other Solanaceae.

Cadmium (Cd) is one of the most toxic metals for the physiology of plants. Proper nutrient management through wastewater reuse can be an efficient strategy to mitigate its effects. In this research, the effects of cadmium were evaluated in the hydroponic cultivation of Solanum lycopersicum L. We conducted two experiments: one using mining wastewater with concentrations of 0, 5, 10, and 15 mg L-1 of Cd2+ (Experiment 1) and another using deionized water with concentrations of 0, 2.5, 5, 10, and 15 mg L-1 of Cd2+ (Experiment 2). Cadmium stress in plants reduced leaf area, chlorophyll content, and concentrations of potassium (K) and manganese (Mn), and increased concentrations of sulfur (S), phosphorus (P), iron (Fe), and copper (Cu). The employment of mining wastewater improved the plant’s response to Cd stress by reducing the translocation of Cd and increasing the contents of P, S, calcium (Ca) and magnesium (Mg) in leaves. At the same time, the use of deionized water decreased the contents of Cu in leaves. These nutrition-related effects influenced leaf area and chlorophyll content, as both indicators showed less impairment in the experiment with wastewater. These results provide additional value to the reuse of wastewater in agriculture.