Chitosan Coating as a Strategy to Increase Postemergent Herbicidal Efficiency and Alter the Interaction of Nanoatrazine with Bidens pilosa Plants.

The atrazine nanodelivery system, composed of poly(ε-caprolactone) (PCL+ATZ) nanocapsules (NCs), has demonstrated efficient delivery of the active ingredient to target plants in previous studies, leading to greater herbicide effectiveness than conventional formulations. Established nanosystems can be enhanced or modified to generate new biological activity patterns. Therefore, this study aimed to evaluate the effect of chitosan coating of PCL+ATZ NCs on herbicidal activity and interaction mechanisms with Bidens pilosa plants. Chitosan-coated NCs (PCL/CS+ATZ) were synthesized and characterized for size, zeta potential, polydispersity, and encapsulation efficiency. Herbicidal efficiency was assessed in postemergence greenhouse trials, comparing the effects of PCL/CS+ATZ NCs (coated), PCL+ATZ NCs (uncoated), and conventional atrazine (ATZ) on photosystem II (PSII) activity and weed control. Using a hydroponic system, we evaluated the root absorption and shoot translocation of fluorescently labeled NCs. PCL/CS+ATZ presented a positive zeta potential (25 mV), a size of 200 nm, and an efficiency of atrazine encapsulation higher than 90%. The postemergent herbicidal activity assay showed an efficiency gain of PSII activity inhibition of up to 58% compared to ATZ and PCL+ATZ at 96 h postapplication. The evaluation of weed control 14 days after application ratified the positive effect of chitosan coating on herbicidal activity, as the application of PCL/CS+ATZ at 1000 g of a.i. ha-1 resulted in better control than ATZ at 2000 g of a.i. ha-1 and PCL+ATZ at 1000 g of a.i. ha-1. In the hydroponic experiment, chitosan-coated NCs labeled with a fluorescent probe accumulated in the root cortex, with a small quantity reaching the vascular cylinder and leaves up to 72 h after exposure. This behavior resulted in lower leaf atrazine levels and PSII inhibition than ATZ. In summary, chitosan coating of nanoatrazine improved the herbicidal activity against B. pilosa plants when applied to the leaves but negatively affected the root-to-shoot translocation of the herbicide. This study opens avenues for further investigations to improve and modify established nanosystems, paving the way for developing novel biological activity patterns.

Influence of plant growth-promoting bacteria on leaf carbon and nitrogen metabolism of two drought-stressed neotropical tree species: a metabolomic approach.

Deforestation of Atlantic Forest has caused prolonged drought events in the last decades. The need for reforestation is growing, and the development of native seedlings that are more tolerant to drought stress is necessary. A biotechnological tool that improves plant tolerance is the use of plant growth-promoting bacteria (PGPB) as inoculants. Two species of PGPB were inoculated in drought-stressed seedlings of two neotropical tree species that have been used in environmental restoration programs: Cecropia pachystachya and Cariniana estrellensis. Biometrical, physiological, and metabolomic parameters from carbon and nitrogen pathways were evaluated. We found that the PGPB positively influenced photosynthesis and growth parameters in both trees under drought. The enzymes activities, the tricarboxylic acid cycle intermediates, the amino acids, and protein contents were also influenced by the PGPB treatments. The results allowed us to find the specific composition of secondary metabolites of each plant species. This study provides evidence that there is not a single mechanism involved in drought tolerance and that the inoculation with PGPB promotes a broad-spectrum tolerance response in Neotropical trees. The inoculation with PGPB appears as an important strategy to improve drought tolerance in Atlantic Forest native trees and enhance environmental restoration programs' success. MAIN CONCLUSION: The association with plant growth-promoting bacteria improved the tolerance to drought in Neotropical trees through biochemical, physiological, and biometrical parameters. This can enhance the success of forest restoration programs.

Associative Bacteria and Arbuscular Mycorrhizal Fungus Increase Drought Tolerance in Maize (Zea mays L.) through Morphoanatomical, Physiological, and Biochemical Changes.

Water deficiency has been recognized as a major abiotic stress that causes losses in maize crops around the world. The maize crop is very important due to the range of products that are derived from this plant. A potential way to reduce the damages caused by water deficiency in maize crops is through the association with plant growth-promoting bacteria (PGPB) and arbuscular mycorrhizal fungi (AMF). To define the mechanisms developed by associative PGPB and AMF in maize that are involved in protection against moderate drought (MD), this study evaluated the biometrical, anatomical, biochemical, and physiological parameters of maize grown under MD and inoculated with different PGPB (Azospirillum brasilense strain Ab-V5 and Bacillus sp. strain ZK) and with AMF. The relative water content did not change in the treatments. The association with ZK increased the shoot:total ratio, total dry weight, maximum quantum yield of photosystem II, vascular cylinder thickness, and vascular cylinder area. The Ab-V5 inoculation led to an increment in root dry weight, the area of metaxylem vessel elements, and nitrate reductase activity. The AMF association did not lead to changes in the measured parameters. The results indicate that the association with PGPB is a relevant alternative to contribute to reducing losses in maize crops under drought. However, AMF is not indicated for this crop under drought.

Teaching and mental health in medical students.

OBJECTIVE: The objective of this study was to evaluate the relationship between quality of life, perceived stress, anxiety, and depression in medical students and the university teaching method: traditional method versus active methodology. METHODS: Four questionnaires were administered to volunteer students (n=361) enrolled in two institutions that employ active (Universidade Tiradentes) or traditional (Faculdade de Medicina do ABC) teaching methodology: socioeconomic level; brief quality of life (World Health Organization Quality of Life-Bref); perceived stress scale (PSS10); and depression and anxiety scale (hospital anxiety and depression scale). RESULTS: Of the students who responded to the questionnaires (226 UNIT and 135 FMABC), 70% were female and 67% were White. The majority did not use medication for depression (90%), anxiety (81%), and stress management (91%). Regarding anxiety, it was found: absence in the traditional method and moderate anxiety in the active methodology (26% UNIT×13% FMABC) (p<0.001). Regarding quality of life, it was found to be better quality of life in the environment domain at FMABC (78.12%) versus 71.88% at the UNIT (p<0.001). There was no difference between the institutions in relation to depression and perceived stress, and in quality of lifethere was only a difference in the environmental domain (p<0.001). In relation to gender, stress was higher in females (93.7%) than males (79.6%) with p<0.001. CONCLUSION: Differences were recorded between the groups regarding anxiety, with a predominance in UNIT students (active methodology), and no differences were recorded in relation to depression, perceived stress, and quality of life in all domains, except for the environment domain, which was higher in the traditional methodology, although about one-third of participants used medication for anxiety/depression.

Interplay between nitric oxide and inorganic nitrogen sources in root development and abiotic stress responses.

Nitrogen (N) is an essential nutrient for plants, and the sources from which it is obtained can differently affect their entire development as well as stress responses. Distinct inorganic N sources (nitrate and ammonium) can lead to fluctuations in the nitric oxide (NO) levels and thus interfere with nitric oxide (NO)-mediated responses. These could lead to changes in reactive oxygen species (ROS) homeostasis, hormone synthesis and signaling, and post-translational modifications of key proteins. As the consensus suggests that NO is primarily synthesized in the reductive pathways involving nitrate and nitrite reduction, it is expected that plants grown in a nitrate-enriched environment will produce more NO than those exposed to ammonium. Although the interplay between NO and different N sources in plants has been investigated, there are still many unanswered questions that require further elucidation. By building on previous knowledge regarding NO and N nutrition, this review expands the field by examining in more detail how NO responses are influenced by different N sources, focusing mainly on root development and abiotic stress responses.

Teaching and mental health in medical students

SUMMARY OBJECTIVE: The objective of this study was to evaluate the relationship between quality of life, perceived stress, anxiety, and depression in medical students and the university teaching method: traditional method versus active methodology. METHODS: Four questionnaires were administered to volunteer students (n=361) enrolled in two institutions that employ active (Universidade Tiradentes) or traditional (Faculdade de Medicina do ABC) teaching methodology: socioeconomic level; brief quality of life (World Health Organization Quality of Life-Bref); perceived stress scale (PSS10); and depression and anxiety scale (hospital anxiety and depression scale). RESULTS: Of the students who responded to the questionnaires (226 UNIT and 135 FMABC), 70% were female and 67% were White. The majority did not use medication for depression (90%), anxiety (81%), and stress management (91%). Regarding anxiety, it was found: absence in the traditional method and moderate anxiety in the active methodology (26% UNIT×13% FMABC) (p<0.001). Regarding quality of life, it was found to be better quality of life in the environment domain at FMABC (78.12%) versus 71.88% at the UNIT (p<0.001). There was no difference between the institutions in relation to depression and perceived stress, and in quality of lifethere was only a difference in the environmental domain (p<0.001). In relation to gender, stress was higher in females (93.7%) than males (79.6%) with p<0.001. CONCLUSION: Differences were recorded between the groups regarding anxiety, with a predominance in UNIT students (active methodology), and no differences were recorded in relation to depression, perceived stress, and quality of life in all domains, except for the environment domain, which was higher in the traditional methodology, although about one-third of participants used medication for anxiety/depression.

The efficient activity of plant essential oils for inhibiting Botrytis cinerea and Penicillium expansum: Mechanistic insights into antifungal activity.

Botrytis cinerea and Penicillium expansum produce deterioration in fruit quality, causing losses to the food industry. Thus, plant essential oils (EOs) have been proposed as a sustainable alternative for minimizing the application of synthetic fungicides due to their broad-spectrum antifungal properties. This study investigated the efficacy of five EOs in suppressing the growth of B. cinerea and P. expansum and their potential antifungal mechanisms. EOs of Mentha × piperita L., Origanum vulgare L., Thymus vulgaris L., Eucalyptus globules Labill., and Lavandula angustifolia Mill., were screened for both fungi. The results showed that the EO of T. vulgaris and O. vulgare were the most efficient in inhibiting the growth of B. cinerea and P. expansum. The concentration increase of all EO tested increased fungi growth inhibition. Exposure of fungi to EOs of T. vulgaris and O. vulgare increased the pH and the release of constituents absorbing 260 nm and soluble proteins, reflecting membrane permeability alterations. Fluorescence microscopic examination revealed that tested EOs produce structural alteration in cell wall component deposition, decreasing the hypha width. Moreover, propidium iodide and Calcein-AM stains evidenced the loss of membrane integrity and reduced cell viability of fungi treated with EOs. Fungi treated with EOs decreased the mitochondria activity and the respiratory process. Therefore, these EOs are effective antifungal agents against B. cinerea and P. expansum, which is attributed to changes in the cell wall structure, the breakdown of the cell membrane, and the alteration of the mitochondrial activity.

Titanium biogenic nanoparticles to help the growth of Trichoderma harzianum to be used in biological control.

BACKGROUND: The biogenic synthesis of metallic nanoparticles is a green alternative that reduces the toxicity of this nanomaterials and may enable a synergy between the metallic core and the biomolecules employed in the process enhancing biological activity. The aim of this study was to synthesize biogenic titanium nanoparticles using the filtrate of the fungus Trichoderma harzianum as a stabilizing agent, to obtain a potential biological activity against phytopathogens and mainly stimulate the growth of T. harzianum, enhancing its efficacy for biological control. RESULTS: The synthesis was successful and reproductive structures remained in the suspension, showing faster and larger mycelial growth compared to commercial T. harzianum and filtrate. The nanoparticles with residual T. harzianum growth showed inhibitory potential against Sclerotinia sclerotiorum mycelial growth and the formation of new resistant structures. A great chitinolytic activity of the nanoparticles was observed in comparison with T. harzianum. In regard to toxicity evaluation, an absence of cytotoxicity and a protective effect of the nanoparticles was observed through MTT and Trypan blue assay. No genotoxicity was observed on V79-4 and 3T3 cell lines while HaCat showed higher sensitivity. Microorganisms of agricultural importance were not affected by the exposure to the nanoparticles, however a decrease in the number of nitrogen cycling bacteria was observed. In regard to phytotoxicity, the nanoparticles did not cause morphological and biochemical changes on soybean plants. CONCLUSION: The production of biogenic nanoparticles was an essential factor in stimulating or maintaining structures that are important for biological control, showing that this may be an essential strategy to stimulate the growth of biocontrol organisms to promote more sustainable agriculture.

Multilevel approach to plant-nanomaterial relationships: from cells to living ecosystems.

Due to their unique properties, nanomaterials behave peculiarly in biosystems. Regarding plants, the interactions of nanomaterials can be interpreted on a spatial scale: from local interactions in cells to systemic effects on whole plants and on ecosystems. Interpreted on a time scale, the effects of nanomaterials on plants may be immediate or subsequent. At the cellular level, the composition and structure of the cell wall and membranes are modified by nanomaterials, promoting internalization. The effects of nanomaterials on germination and seedling physiology and on the primary and secondary metabolism in the shoot are realized at organ and organism levels. Nanomaterials interact with the beneficial ecological partners of plants. The effects of nanomaterials on plant growth-promoting rhizobacteria and legume-rhizobia symbiosis can be stimulating or inhibitory, depending on the concentration and type of nanomaterial. Nanomaterials exert a negative effect on arbuscular mycorrhiza, and vice versa. Pollinators are exposed to nanomaterials, which may affect plant reproduction. The substances released by the roots influence the availability of nanomaterials in the rhizosphere, and components of plant cells trigger internalization, translocation, and transformation of nanomaterials. Understanding of the multilevel and bidirectional relationship between plants and nanomaterials is of great relevance.

Encapsulated plant growth regulators and associative microorganisms: Nature-based solutions to mitigate the effects of climate change on plants.

Over the past decades, the atmospheric CO2 concentration and global average temperature have been increasing, and this trend is projected to soon become more severe. This scenario of climate change intensifies abiotic stress factors (such as drought, flooding, salinity, and ultraviolet radiation) that threaten forest and associated ecosystems as well as crop production. These factors can negatively affect plant growth and development with a consequent reduction in plant biomass accumulation and yield, in addition to increasing plant susceptibility to biotic stresses. Recently, biostimulants have become a hotspot as an effective and sustainable alternative to alleviate the negative effects of stresses on plants. However, the majority of biostimulants have poor stability under environmental conditions, which leads to premature degradation, shortening their biological activity. To solve these bottlenecks, micro- and nano-based formulations containing biostimulant molecules and/or microorganisms are gaining attention, as they demonstrate several advantages over their conventional formulations. In this review, we focus on the encapsulation of plant growth regulators and plant associative microorganisms as a strategy to boost their application for plant protection against abiotic stresses. We also address the potential limitations and challenges faced for the implementation of this technology, as well as possibilities regarding future research.

Nanoencapsulation Boosts the Copper-Induced Defense Responses of a Susceptible Coffea arabica Cultivar against Hemileia vastatrix.

Due to the environmental risks of conventional Cu-based fungicides, Cu-loaded chitosan nanoparticles have been developed as nano-pesticides, aiming to protect plants against different diseases. In this sense, the objective was to verify the effects of chitosan nanoparticles containing Cu2+ ions on leaf discs of Coffea arabica cv. IPR 100 infected with Hemileia vastatrix. The treatments were water as a control (CONT), unloaded chitosan nanoparticles (NP), chitosan nanoparticles containing Cu2+ ions (NPCu), and free Cu2+ ions (Cu). Different concentrations of NP (0.25; 0.5; 1 g L-1) and Cu2+ ions (1.25; 2.5; 5 mmol L-1) were tested. The severity of the coffee rust was 42% in the CONT treatment, 22% in NP, and 2% in NPCu and Cu. The treatments protected coffee leaves; however, NPCu stood out for initial stress reduction, decreasing Cu phytotoxicity, promoting photosynthetic activity maintenance, and increasing antioxidant responses, conferring significant protection against coffee rust. At low concentrations (1.25 mmol L-1), NPCu showed higher bioactivity than Cu. These results suggest that Cu-loaded chitosan nanoparticles can induce a more significant plant defense response to the infection of Hemileia vastatrix than conventional Cu, avoiding the toxic effects of high Cu concentrations. Thus, this nanomaterial has great potential to be used as nano-pesticides for disease management.

Cardiotoxicity in cancer patients treated with chemotherapy: A systematic review.

Objective: The objective of the study was to assess the incidence of chemotherapy cardiotoxicity. Methods: This is a systematic review carried out through the PubMed, VHL and Scientific Electronic Library Online databases, using the descriptors "Cardiotoxicity" and "Chemotherapy" associated with the Boolean operator "AND." Initially, 15,090 articles were found between 2015 and 2021. After applying the defined inclusion and exclusion criteria, 80 studies remained, of which 27 underwent complete reading, after which all were included in the study. Results: In total, 32,009 cancer patients were analyzed, of which 27,270 (85.2%) were female. Breast cancer was the most frequent neoplasm, with 11,145 (34.8%) cases. Regarding the type of chemotherapy, anthracycline was the most prevalent, analyzed in 18 (66.7%) studies, followed by trastuzumab, in 9 (33.3%) studies. Of the studies evaluated, five did not present any case of cardiotoxicity, a total of 2255 (8.3%) cases were recorded, in addition other outcomes mentioned in patients after chemotherapy were arrhythmia (n = 522), acute coronary syndrome (n = 185), diastolic dysfunction (n = 184), cardiomyopathy (n = 161), and arterial hypertension (n = 89). Conclusion: Post-chemotherapeutic cardiotoxicity was mentioned in most studies, being present in a relevant percentage of the sample. Furthermore, these patients may develop other cardiovascular events.

Soil Treatment with Nitric Oxide-Releasing Chitosan Nanoparticles Protects the Root System and Promotes the Growth of Soybean Plants under Copper Stress.

The nanoencapsulation of nitric oxide (NO) donors is an attractive technique to protect these molecules from rapid degradation, expanding, and enabling their use in agriculture. Here, we evaluated the effect of the soil application of chitosan nanoparticles containing S-nitroso-MSA (a S-nitrosothiol) on the protection of soybeans (Glycine max cv. BRS 257) against copper (Cu) stress. Soybeans were grown in a greenhouse in soil supplemented with 164 and 244 mg kg-1 Cu and treated with a free or nanoencapsulated NO donor at 1 mM, as well as with nanoparticles without NO. There were also soybean plants treated with distilled water and maintained in soil without Cu addition (control), and with Cu addition (water). The exogenous application of the nanoencapsulated and free S-nitroso-MSA improved the growth and promoted the maintenance of the photosynthetic activity in Cu-stressed plants. However, only the nanoencapsulated S-nitroso-MSA increased the bioavailability of NO in the roots, providing a more significant induction of the antioxidant activity, the attenuation of oxidative damage, and a greater capacity to mitigate the root nutritional imbalance triggered by Cu stress. The results suggest that the nanoencapsulation of the NO donors enables a more efficient delivery of NO for the protection of soybean plants under Cu stress.

Post-emergence herbicidal activity of nanoatrazine against Alternanthera tenella Colla plants compared to other weed species.

The encapsulation of atrazine into poly(epsilon-caprolactone) nanocapsules has been shown to improve the efficiency of the herbicide and decrease its environmental impacts. In the current work, we evaluated the efficiency of nanoatrazine in the post-emergence control of Alternanthera tenella Colla plants and performed a meta-analysis to compare the results with studies already published with other weeds. The first experiment was carried out in the field, where we observed that nanoatrazine (at 200 g a. i. ha-1) induced higher inhibition of the maximum quantum efficiency of photosystem II (up to 39%) than conventional atrazine at the same concentration. However, nanoencapsulation did not improve the visually-determined weed control by atrazine. To better understand the response of A. tenella plants to nanoatrazine, a second experiment was carried out in a greenhouse with four-leaf stage plants treated with nano and conventional atrazine at 200, 500, 1000, and 2000 g a. i. ha-1. Nanoatrazine showed higher efficiency (up to 33%) than commercial atrazine in inhibiting photosystem II activity at all doses until 48 h after application. Again, weed control and plant dry mass did not differ between formulations. From the meta-analysis, it was observed that A. tenella plants showed a response to nanoatrazine that differs from other target species, as the gain in efficiency resulting from the nanoencapsulation was restricted to the short-term analysis, and did not result in better weed control. These results reinforce that the efficiency of nanoatrazine is dependent on the studied species.

Interaction of Nanoatrazine and Target Organism: Evaluation of Fate and Photosystem II Inhibition in Hydroponically Grown Mustard (Brassica juncea) Plants.

Poly(epsilon-caprolactone) nanoparticles are an efficient carrier system for atrazine. However, there is a gap regarding the effects of nanoencapsulation on herbicide-plant interactions. Here, we evaluate the fate and photosystem II inhibition of nano and commercial atrazine in hydroponically grown mustard (Brassica juncea) plants whose roots were exposed to the formulations. In addition, to quantify the endogenous levels of atrazine in plant organs, we measured the inhibition of photosystem II activity by both formulations. Moreover, the fluorescently labeled nanoatrazine was tracked in plant tissues using confocal microscopy. The nanoencapsulation induced greater inhibition of photosystem II activity as well as higher accumulation of atrazine in roots and leaves. The nanoparticles were quickly absorbed by the roots, being detected in the vascular tissues and the leaves. Overall, these results provide insights into the mechanisms involved in the enhanced preemergent herbicidal activity of nanoatrazine against target plants.

Effects of biogenic silver and iron nanoparticles on soybean seedlings (Glycine max).

BACKGROUND: Biogenic metallic nanoparticles have been emerging as a promising alternative for the control of phytopathogens and as nanofertilizers. In this way, it is essential to investigate the possible impacts of these new nanomaterials on plants. In this study, the effects of soil contamination with biogenic silver (AgNPs) and iron (FeNPs) with known antifungal potential were investigated on morphological, physiological and biochemical parameters of soybean seedlings. RESULTS: The exposure of plants/seedlings to AgNPs induced the reduction of root dry weight followed by oxidative stress in this organ, however, adaptive responses such as a decrease in stomatal conductance without impacts on photosynthesis and an increase in intrinsic water use efficiency were also observed. The seedlings exposed to FeNPs had shown an increase in the levels of oxygen peroxide in the leaves not accompanied by lipid peroxidation, and an increase in the expression of POD2 and POD7 genes, indicating a defense mechanism by root lignification. CONCLUSION: Our results demonstrated that different metal biogenic nanoparticles cause different effects on soybean seedlings and these findings highlight the importance of investigating possible phytotoxic effects of these nanomaterials for the control of phytopathogens or as nanofertilizers.

Nitric oxide-releasing nanomaterials: from basic research to potential biotechnological applications in agriculture.

Nitric oxide (NO) is a multifunctional gaseous signal that modulates the growth, development and stress tolerance of higher plants. NO donors have been used to boost plant endogenous NO levels and to activate NO-related responses, but this strategy is often hindered by the relative instability of donors. Alternatively, nanoscience offers a new, promising way to enhance NO delivery to plants, as NO-releasing nanomaterials (e.g. S-nitrosothiol-containing chitosan nanoparticles) have many beneficial physicochemical and biochemical properties compared to non-encapsulated NO donors. Nano NO donors are effective in increasing tissue NO levels and enhancing NO effects both in animal and human systems. The authors believe, and would like to emphasize, that new trends and technologies are essential for advancing plant NO research and nanotechnology may represent a breakthrough in traditional agriculture and environmental science. Herein, we aim to draw the attention of the scientific community to the potential of NO-releasing nanomaterials in both basic and applied plant research as alternatives to conventional NO donors, providing a brief overview of the current knowledge and identifying future research directions. We also express our opinion about the challenges for the application of nano NO donors, such as the environmental footprint and stakeholder's acceptance of these materials.

Development of a Preemergent Nanoherbicide: From Efficiency Evaluation to the Assessment of Environmental Fate and Risks to Soil Microorganisms.

Nanoparticles based on biodegradable polymers have been shown to be excellent herbicide carriers, improving weed control and protecting the active ingredient in the crop fields. Metribuzin is often found in natural waters, which raises environmental concerns. Nanoencapsulation of this herbicide could be an alternative to reduce its losses to the environment and improve gains in its efficiency. However, there is a paucity of information about the behavior of nanoformulations of herbicides in environmental matrices. In this study, the stability of nanoencapsulated metribuzin in polymeric nanoparticles (nanoMTZ) was verified over time, as well as its dissipation in different soils, followed by the effects on soil enzymatic activity. The physiological parameters and control effects of nanoMTZ on Ipomoea grandifolia plants were investigated. No differences were verified in the half-life of nanoencapsulated metribuzin compared to a commercial formulation of the herbicide. Moreover, no suppressive effects on soil enzymatic activities were observed. The retention of nanoMTZ in the tested soils was lower compared to its commercial analogue. However, the mobility of nanoencapsulated metribuzin was not greatly increased, reflecting a low risk of groundwater contamination. Weed control was effective even at the lowest dose of nanoMTZ (48 g a.i. ha-1), which was consistent with the higher efficiency of nanoMTZ compared to the conventional herbicide in inhibiting PSII activity and decreasing pigment levels. Overall, we verified that nanoMTZ presented a low environmental risk, with increased weed control.

Nanoencapsulation improves the protective effects of a nitric oxide donor on drought-stressed Heliocarpus popayanensis seedlings.

Despite the important role played by nitric oxide (NO) in plants subjected to abiotic stress, NO donors application to induce drought tolerance in neotropical tree seedlings has not yet been tested. It is also worth investigating whether NO bioactivity in drought-stressed seedlings could be potentiated by NO donors nanoencapsulation. The aim of the current study is to evaluate the effects of chitosan nanoparticles (NPs) containing S-nitroso-mercaptosuccinic acid (S-nitroso-MSA) on drought-stressed seedlings of neotropical tree species Heliocarpus popayanensis Kunth in comparison to free NO donor and NPs loaded with non-nitrosated MSA. Nanoencapsulation slowed down NO release from S-nitroso-MSA, and nanoencapsulated S-nitroso-MSA yielded 2- and 1.6-fold higher S-nitrosothiol levels in H. popayanensis roots and leaves, respectively, than the free NO donor. S-nitroso-MSA has prevented drought-induced CO2 assimilation inhibition, regardless of nanoencapsulation, but the nanoencapsulated NO donor has induced earlier ameliorative effect. Both NO and MSA have decreased oxidative stress in H. popayanensis roots, but this effect was not associated with antioxidant enzyme induction, with higher seedling biomass, or with proline and glycine betaine accumulation. Nanoencapsulated S-nitroso-MSA was the only formulation capable of increasing leaf relative water content in drought-stressed plants (from 32.3% to 60.5%). In addition, it induced root hair formation (increase by 36.6% in comparison to well-hydrated plants). Overall, results have evidenced that nanoencapsulation was capable of improving the protective effect of S-nitroso-MSA on H. popayanensis seedlings subjected to drought stress, a fact that highlighted the potential application of NO-releasing NPs to obtain drought-tolerant tree seedlings for reforestation programs.

Nitrogen use plasticity in response to light intensity in neotropical tree species of distinct functional groups.

Environmental conditions influence the use of different nitrogen (N) sources by plants. We hypothesized that an increase in light intensity favors the use of nitrate (NO3 - ) relative to ammonium (NH4 + ) by seedlings of neotropical tree species from different functional groups, that is, Cecropia pachystachya (a shade-intolerant species), Cariniana estrellensis (a shade-tolerant canopy species), and Guarea kunthiana (a shade-tolerant understory species). We analyzed the growth and N metabolism in seedlings simultaneously provided with NH4 + and NO3 - , under lower (LL) and higher (HL) light intensity. 15 N incorporation into amino acids was monitored after incubation with 15 N-labeled NH4 + or NO3 - . Under HL, all species showed decreased leaf area ratio, and increased growth, nitrate reductase activity and assimilated N content. Cecropia pachystachya increased the use of both N sources under HL, with substantial increases in 15 N-amino acids derived from 15 NO3 - (12.5- and 4.0-fold in roots and leaves, respectively) and 15 NH4 + (4.5- and 3.0-fold in roots and leaves, respectively). Guarea kunthiana showed the greatest plasticity in N use, as the assimilation of 15 NO3 - in roots and leaves increased substantially under HL (11.2- and 17.0-fold, respectively). Cariniana estrellensis increased the assimilation of 15 NH4 + in roots and 15 NO3 - in leaves under HL. Therefore, the responses of N use strategies to light intensity varied with the species according to their ecological characteristics.