RESUMO
Maize root responds to nitrate by modulating its development through the coordinated action of many interacting players. Nitric oxide is produced in primary root early after the nitrate provision, thus inducing root elongation. In this study, RNA sequencing was applied to discover the main molecular signatures distinguishing the response of maize root to nitrate according to their dependency on, or independency of, nitric oxide, thus discriminating the signaling pathways regulated by nitrate through nitric oxide from those regulated by nitrate itself of by further downstream factors. A set of subsequent detailed functional annotation tools (Gene Ontology enrichment, MapMan, KEGG reconstruction pathway, transcription factors detection) were used to gain further information and the lateral root density was measured both in the presence of nitrate and in the presence of nitrate plus cPTIO, a specific NO scavenger, and compared to that observed for N-depleted roots. Our results led us to identify six clusters of transcripts according to their responsiveness to nitric oxide and to their regulation by nitrate provision. In general, shared and specific features for the six clusters were identified, allowing us to determine the overall root response to nitrate according to its dependency on nitric oxide.
Assuntos
Regulação da Expressão Gênica de Plantas , Nitratos/metabolismo , Raízes de Plantas/metabolismo , Transcriptoma , Zea mays/metabolismo , Benzoatos , Fertilizantes , Imidazóis , Óxido Nítrico/metabolismoRESUMO
Nitrogen (N) is an essential macronutrient for crops. Plants have developed several responses to N fluctuations, thus optimizing the root architecture in response to N availability. Nitrate and ammonium are the main inorganic N forms taken up by plants, and act as both nutrients and signals, affecting gene expression and plant development. In this study, RNA-sequencing was applied to gain comprehensive information on the pathways underlying the response of maize root, pre-treated in an N-deprived solution, to the provision of nitrate or ammonium. The analysis of the transcriptome shows that nitrate and ammonium regulate overlapping and distinct pathways, thus leading to different responses. Ammonium activates the response to stress, while nitrate acts as a negative regulator of transmembrane transport. Both the N-source repress genes related to the cytoskeleton and reactive oxygen species detoxification. Moreover, the presence of ammonium induces the accumulation of anthocyanins, while also reducing biomass and chlorophyll and flavonoids accumulation. Furthermore, the later physiological effects of these nutrients were evaluated through the assessment of shoot and root growth, leaf pigment content and the amino acid concentrations in root and shoot, confirming the existence of common and distinct features in response to the two nitrogen forms.
Assuntos
Compostos de Amônio/farmacologia , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Nitratos/farmacologia , Nitrogênio/metabolismo , Transcriptoma , Zea mays/fisiologia , Aminoácidos , Análise por Conglomerados , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Raízes de Plantas/genética , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/fisiologia , Análise de Sequência de RNA , Zea mays/genética , Zea mays/crescimento & desenvolvimentoRESUMO
Nitrate acts as a signal in regulating plant development in response to environment. In particular nitric oxide, auxin and strigolactones (SLs) were supposed to cooperate to regulate the maize root response to this anion. In this study, a combined approach based on liquid chromatography-quadrupole/time-of-flight tandem mass spectrometry and on physiological and molecular analyses was adopted to specify the involvement of SLs in the maize response to N. Our results showed that N deficiency strongly induces SL exudation, likely through stimulating their biosynthesis. Nitrate provision early counteracts and also ammonium lowers SL exudation, but less markedly. Exudates obtained from N-starved and ammonium-provided seedlings stimulated Phelipanche germination, whereas when seeds were treated with exudates harvested from nitrate-provided plants no germination was observed. Furthermore, our findings support the idea that the inhibition of SL production observed in response to nitrate and ammonium would contribute to the regulation of lateral root development. Moreover, the transcriptional regulation of a gene encoding a putative maize WBC transporter, in response to various nitrogen supplies, together with its mRNA tissue localization, supported its role in SL allocation. Our results highlight the dual role of SLs as molecules able to signal outwards a nutritional need and as endogenous regulators of root architecture adjustments to N, thus synchronizing plant growth with nitrogen acquisition.
Assuntos
Lactonas/metabolismo , Nitratos/metabolismo , Nitrogênio/metabolismo , Zea mays/fisiologia , Compostos de Amônio/metabolismo , Transporte Biológico , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Germinação/efeitos dos fármacos , Ácidos Indolacéticos/metabolismo , Óxido Nítrico/metabolismo , Reguladores de Crescimento de Plantas , Sementes , Zea mays/genéticaRESUMO
Nitrogen (N) is an indispensable nutrient for crops but its availability in agricultural soils is subject to considerable fluctuation. Plants have developed plastic responses to external N fluctuations in order to optimise their development. The coordinated action of nitric oxide and auxin seems to allow the cells of the root apex transition zone (TZ) of N-deprived maize to rapidly sense nitrate (NO3 - ). Preliminary results support the hypothesis that reactive oxygen species (ROS) signalling might also have a role in this pathway, probably through a putative maize orthologue of UPBEAT1 (UPB1). To expand on this hypothesis and better understand the different roles played by different root portions, we investigated the dynamics of ROS production, and the molecular and biochemical regulation of the main components of ROS production and scavenging in tissues of the meristem, transition zone, elongation zone and maturation zone of maize roots. The results suggest that the inverse regulation of ZmUPB1 and ZmPRX112 transcription observed in cells of the TZ in response to nitrogen depletion or NO3 - supply affects the balance between superoxide (O2 â¢- ) and hydrogen peroxide (H2 O2 ) in the root apex and consequently triggers differential root growth. This explanation is supported by additional results on the overall metabolic and transcriptional regulation of ROS homeostasis.
Assuntos
Nitratos/metabolismo , Regulação da Expressão Gênica de Plantas/genética , Peróxido de Hidrogênio , Proteínas de Plantas/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Transdução de Sinais/genética , Transdução de Sinais/fisiologia , Superóxidos/metabolismo , Zea mays/metabolismoRESUMO
Nitrate is an essential nutrient for plants, and crops depend on its availability for growth and development, but its presence in agricultural soils is far from stable. In order to overcome nitrate fluctuations in soil, plants have developed adaptive mechanisms allowing them to grow despite changes in external nitrate availability. Nitrate can act as both nutrient and signal, regulating global gene expression in plants, and the root tip has been proposed as the sensory organ. A set of genome-wide studies has demonstrated several nitrate-regulated genes in the roots of many plants, although only a few studies have been carried out on distinct root zones. To unravel new details of the transcriptomic and proteomic responses to nitrate availability in a major food crop, a double untargeted approach was conducted on a transition zone-enriched root portion of maize seedlings subjected to differing nitrate supplies. The results highlighted a complex transcriptomic and proteomic reprogramming that occurs in response to nitrate, emphasizing the role of this root zone in sensing and transducing nitrate signal. Our findings indicated a relationship of nitrate with biosynthesis and signalling of several phytohormones, such as auxin, strigolactones, and brassinosteroids. Moreover, the already hypothesized involvement of nitric oxide in the early response to nitrate was confirmed with the use of nitric oxide inhibitors. Our results also suggested that cytoskeleton activation and cell wall modification occurred in response to nitrate provision in the transition zone.
Assuntos
Nitratos/farmacologia , Raízes de Plantas/genética , Raízes de Plantas/metabolismo , Proteômica/métodos , Transcriptoma/genética , Zea mays/genética , Zea mays/metabolismo , Benzoatos/farmacologia , Cromossomos de Plantas/genética , Perfilação da Expressão Gênica , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Ontologia Genética , Genes de Plantas , Imidazóis/farmacologia , Marcação por Isótopo , Modelos Biológicos , Anotação de Sequência Molecular , Raízes de Plantas/efeitos dos fármacos , Regiões Promotoras Genéticas/genética , Proteoma/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Reação em Cadeia da Polimerase em Tempo Real , Reprodutibilidade dos Testes , Análise de Sequência de RNA , Transcriptoma/efeitos dos fármacos , Zea mays/efeitos dos fármacosRESUMO
Crop plant development is strongly dependent on nitrogen availability in the soil and on the efficiency of its recruitment by roots. For this reason, the understanding of the molecular events underlying root adaptation to nitrogen fluctuations is a primary goal to develop biotechnological tools for sustainable agriculture. However, knowledge about molecular responses to nitrogen availability is derived mainly from the study of model species. Nitric oxide (NO) has been recently proposed to be implicated in plant responses to environmental stresses, but its exact role in the response of plants to nutritional stress is still under evaluation. In this work, the role of NO production by maize roots after nitrate perception was investigated by focusing on the regulation of transcription of genes involved in NO homeostasis and by measuring NO production in roots. Moreover, its involvement in the root growth response to nitrate was also investigated. The results provide evidence that NO is produced by nitrate reductase as an early response to nitrate supply and that the coordinated induction of non-symbiotic haemoglobins (nsHbs) could finely regulate the NO steady state. This mechanism seems to be implicated on the modulation of the root elongation in response to nitrate perception. Moreover, an improved agar-plate system for growing maize seedlings was developed. This system, which allows localized treatments to be performed on specific root portions, gave the opportunity to discern between localized and systemic effects of nitrate supply to roots.
Assuntos
Regulação da Expressão Gênica de Plantas , Nitrato Redutase/genética , Nitratos/farmacologia , Óxido Nítrico/metabolismo , Zea mays/fisiologia , Compostos de Amônio/farmacologia , Hemoglobinas/genética , Homeostase , Modelos Biológicos , Nitrogênio/farmacologia , Proteínas de Plantas/genética , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/genética , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/fisiologia , Plântula/efeitos dos fármacos , Plântula/genética , Plântula/crescimento & desenvolvimento , Plântula/fisiologia , Transdução de Sinais , Solo/química , Zea mays/efeitos dos fármacos , Zea mays/genética , Zea mays/crescimento & desenvolvimentoRESUMO
Nitrogen availability seriously affects crop productivity and environment. The knowledge of post-transcriptional regulation of plant response to nutrients is important to improve nitrogen use efficiency of crop. This research was aimed at understanding the role of miRNAs in the molecular control of plant response to nitrate. The expression profiles of six mature miRNAs were deeply studied by quantitative real time polymerase chain reaction and in situ hybridization (ISH). To this aim, a novel optimized protocol was set up for the use of digoxygenin-labelled Zip Nucleic Acid-modified oligonucleotides as probes for ISH. Significant differences in miRNAs' transcripts accumulation were evidenced between nitrate-supplied and nitrate-depleted roots. Real-time PCR analyses and in situ detection of miRNA confirmed the array data and allowed us to evidence distinct miRNAs spatio-temporal expression patterns in maize roots. Our results suggest that a prolonged nitrate depletion may induce post-transcriptionally the expression of target genes by repressing the transcription of specific miRNAs. In particular, the repression of the transcription of miR528a/b, miR528a*/b*, miR169i/j/k, miR169i*/j*/k*, miR166j/k/n and miR408/b upon nitrate shortage could represent a crucial step integrating nitrate signals into developmental changes in maize roots.
Assuntos
MicroRNAs/metabolismo , Nitratos/metabolismo , Raízes de Plantas/metabolismo , Zea mays/metabolismo , Sondas de DNA , Perfilação da Expressão Gênica , Regulação da Expressão Gênica de Plantas , Hibridização In Situ , MicroRNAs/genética , Raízes de Plantas/genética , Regiões Promotoras Genéticas , RNA de Plantas/genética , RNA de Plantas/metabolismo , Reação em Cadeia da Polimerase em Tempo Real , Zea mays/genéticaRESUMO
Protein hydrolysate (PH)-based biostimulants offer a cost-effective and sustainable approach for the regulation of physiological processes in plants to stimulate growth and improve stress tolerance. Understanding the mode of action of PHs is challenging, but it is indispensable to improve existing candidates and to develop novel molecules with enhanced stimulatory effects. Hence, the present study aimed to understand the proteome level responses in the B73 maize roots treated with APR, a PH biostimulant, at two increasing concentrations and to compare and integrate it with the transcriptomic data obtained previously under identical experimental conditions. Results indicate that APR induced dose-dependent global changes in the transcriptome and proteome of maize roots. APR treatment altered the expression and abundance of several genes and proteins related to redox homeostasis, stress response, glycolysis, tricarboxylic acid cycle, pentose phosphate pathway, and other metabolic pathways of carbohydrates, amino acids, and lipids. Further, metabolic processes of phytohormone, secondary metabolites, especially phenylpropanoids, flavonoids, and terpenoids and transport, and cytoskeletal reorganization associated mechanisms were stimulated. Our results suggest that APR treatment altered the redox homeostasis and thus triggered an oxidative signal. This could be one of the key regulators of the cascade of downstream events involving multiple signaling, hormonal, and metabolic pathways, resulting in an altered physiological and metabolic state which consequently could lead to improved growth and stress adaptation observed in biostimulant-treated plants.
Assuntos
Proteínas de Plantas/genética , Hidrolisados de Proteína/farmacologia , Zea mays/efeitos dos fármacos , Zea mays/genética , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Proteínas de Plantas/química , Proteínas de Plantas/metabolismo , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/genética , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Hidrolisados de Proteína/química , Proteômica , Transcriptoma/efeitos dos fármacos , Zea mays/crescimento & desenvolvimento , Zea mays/metabolismoRESUMO
Studies on model plants have shown that temporary soil flooding exposes roots to a significant hypoxic stress resulting in metabolic re-programming, accumulation of toxic metabolites and hormonal imbalance. To date, physiological and transcriptional responses to flooding in grapevine are poorly characterized. To fill this gap, we aimed to gain insights into the transcriptional and metabolic changes induced by flooding on grapevine roots (K5BB rootstocks), on which cv Sauvignon blanc (Vitis vinifera L.) plants were grafted. A preliminary experiment under hydroponic conditions enabled the identification of transiently and steadily regulated hypoxia-responsive marker genes and drafting a model for response to oxygen deprivation in grapevine roots. Afterward, over two consecutive vegetative seasons, flooding was imposed to potted vines during the late dormancy period, to mimick the most frequent waterlogging events occurring in the field. Untargeted transcriptomic and metabolic profiling approaches were applied to investigate early responses of grapevine roots during exposure to hypoxia and subsequent recovery after stress removal. The initial hypoxic response was marked by a significant increase of the hypoxia-inducible metabolites ethanol, GABA, succinic acid and alanine which remained high also 1 week after recovery from flooding with the exception of ethanol that leveled off. Transcriptomic data supported the metabolic changes by indicating a substantial rearrangement of primary metabolic pathways through enhancement of the glycolytic and fermentative enzymes and of a subset of enzymes involved in the TCA cycle. GO and KEGG pathway analyses of differentially expressed genes showed a general down-regulation of brassinosteroid, auxin and gibberellin biosynthesis in waterlogged plants, suggesting a general inhibition of root growth and lateral expansion. During recovery, transcriptional activation of gibberellin biosynthetic genes and down-regulation of the metabolic ones may support a role for gibberellins in signaling grapevine rootstocks waterlogging metabolic and hormonal changes to the above ground plant. The significant internode elongation measured upon budbreak during recovery in plants that had experienced flooding supported this hypothesis. Overall integration of these data enabled us to draft a first comprehensive view of the molecular and metabolic pathways involved in grapevine's root responses highlighting a deep metabolic and transcriptomic reprogramming during and after exposure to waterlogging.
RESUMO
Background and Aim: Humic substances (HSs) influence the chemical and physical properties of the soil, and are also known to affect plant physiology and nutrient uptake. This study aimed to elucidate plant metabolic pathways and physiological processes influenced by HS activity. Methods: Arabidopsis roots were treated with HS for 8 h. Quantitative mass spectrometry-based proteomics analysis of root proteins was performed using the iTRAQ (Isobaric Tag for Relative and Absolute Quantification) technique. Out of 902 protein families identified and quantified for HS treated vs. untreated roots, 92 proteins had different relative content. Bioinformatic tools such as STRING, KEGG, IIS and Cytoscape were used to interpret the biological function, pathway analysis and visualization of network amongst the identified proteins. Results: From this analysis it was possible to evaluate that all of the identified proteins were functionally classified into several categories, mainly redox homeostasis, response to inorganic substances, energy metabolism, protein synthesis, cell trafficking, and division. Conclusion: In the present study an overview of the metabolic pathways most modified by HS biological activity is provided. Activation of enzymes of the glycolytic pathway and up regulation of ribosomal protein indicated a stimulation in energy metabolism and protein synthesis. Regulation of the enzymes involved in redox homeostasis suggest a pivotal role of reactive oxygen species in the signaling and modulation of HS-induced responses.
RESUMO
Biostimulants are a wide range of natural or synthetic products containing substances and/or microorganisms that can stimulate plant processes to improve nutrient uptake, nutrient efficiency, tolerance to abiotic stress, and crop quality ( http://www.biostimulants.eu/ , accessed September 27, 2017). The use of biostimulants is proposed as an advanced solution to face the demand for sustainable agriculture by ensuring optimal crop performances and better resilience to environment changes. The proposed approach is to predict and characterize the function of natural compounds as biostimulants. In this research, plant growth assessments and transcriptomic approaches are combined to investigate and understand the specific mode(s) of action of APR, a new product provided by the ILSA group (Arzignano, Vicenza). Maize seedlings (B73) were kept in a climatic chamber and grown in a solid medium to test the effects of two different combinations of the protein hydrolysate APR (A1 and A1/2). Data on root growth evidenced a significant enhancement of the dry weight of both roots and root/shoot ratio in response to APR. Transcriptomic profiles of lateral roots of maize seedlings treated with two increasing concentrations of APR were studied by mRNA-sequencing analysis (RNA-seq). Pairwise comparisons of the RNA-seq data identified a total of 1006 differentially expressed genes between treated and control plants. The two APR concentrations were demonstrated to affect the expression of genes involved in both common and specific pathways. On the basis of the putative function of the isolated differentially expressed genes, APR has been proposed to enhance plant response to adverse environmental conditions.
Assuntos
Colágeno/farmacologia , Raízes de Plantas/genética , Hidrolisados de Proteína/farmacologia , RNA Mensageiro/genética , Plântula/crescimento & desenvolvimento , Zea mays/genética , Colágeno/química , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Hidrolisados de Proteína/química , RNA Mensageiro/metabolismo , Plântula/efeitos dos fármacos , Plântula/genética , Plântula/metabolismo , Transcriptoma , Zea mays/efeitos dos fármacos , Zea mays/crescimento & desenvolvimento , Zea mays/metabolismoRESUMO
Nitrate (NO3 (-)) is a key element for crop production but its levels in agricultural soils are limited. Plants have developed mechanisms to cope with these NO3 (-) fluctuations based on sensing nitrate at the root apex. Particularly, the transition zone (TZ) of root apex has been suggested as a signaling-response zone. This study dissects cellular and molecular mechanisms underlying NO3 (-) resupply effects on primary root (PR) growth in maize, confirming nitric oxide (NO) as a putative modulator. Nitrate restoration induced PR elongation within the first 2 h, corresponding to a stimulation of cell elongation at the basal border of the TZ. Xyloglucans (XGs) immunolocalization together with Brefeldin A applications demonstrated that nitrate resupply induces XG accumulation. This effect was blocked by cPTIO (NO scavenger). Transcriptional analysis of ZmXET1 confirmed the stimulatory effect of nitrate on XGs accumulation in cells of the TZ. Immunolocalization analyses revealed a positive effect of nitrate resupply on auxin and PIN1 accumulation, but a transcriptional regulation of auxin biosynthesis/transport/signaling genes was excluded. Short-term nitrate treatment repressed the transcription of genes involved in strigolactones (SLs) biosynthesis and transport, mainly in the TZ. Enhancement of carotenoid cleavage dioxygenases (CCDs) transcription in presence of cPTIO indicated endogenous NO as a negative modulator of CCDs activity. Finally, treatment with the SLs-biosynthesis inhibitor (TIS108) restored the root growth in the nitrate-starved seedlings. Present report suggests that the NO-mediated root apex responses to nitrate are accomplished in cells of the TZ via integrative actions of auxin, NO and SLs.
RESUMO
Roots are considered to be a vital organ system of plants due to their involvement in water and nutrient uptake, anchorage, propagation, storage functions, secondary metabolite (including hormones) biosynthesis, and accumulation. Crops are strongly dependent on the availability of nitrogen in soil and on the efficiency of nitrogen utilization for biomass production and yield. However, knowledge about molecular responses to nitrogen fluctuations mainly derives from the study of model species. Nitric oxide (NO) has been proposed to be implicated in plant adaptation to environment, but its exact role in the response of plants to nutritional stress is still under evaluation. Recently a novel role for NO production and scavenging, thanks to the coordinate spatio-temporal expression of nitrate reductase and non-symbiotic hemoglobins, in the maize root response to nitrate has been postulated. This control of NO homeostasis is preferentially accomplished by the cells of the root transition zone (TZ) which seem to represent the most nitrate responsive portion of maize root. The TZ is already known to function as a sensory center able to gather information from the external environment and to re-elaborate them in an adequate response. These results indicate that it could play a central role also for nitrate sensing by roots. A lot of work is still needed to identify and characterize other upstream and downstream signals involved in the "nitrate-NO" pathway, leading to root architecture adjustments and finally to stress adaptation.
Assuntos
Nitratos/fisiologia , Óxido Nítrico/metabolismo , Raízes de Plantas/crescimento & desenvolvimento , Zea mays/metabolismo , Zea mays/crescimento & desenvolvimentoRESUMO
Quantitative real-time PCR (qPCR) is a powerful tool to measure gene expression levels. Accurate and reproducible results are dependent on the correct choice of the reference genes for data normalization. To date, screenings evaluating candidate reference gene stability for expression studies in maize have not been reported. In the present work, we analyzed the expression patterns of 12 genes in a set of 20 maize samples, obtained from different tissues of plants grown at various experimental conditions. Using genorm(PLUS), NormFinder and BestKeeper algorithms, the expression stability of three "classical" reference genes, such as ACT, TUB and 18S rRNA, and the newly identified candidates, was assessed. With respect to the algorithms, our results showed similar performance among genorm(PLUS), NormFinder and BestKeeper in evaluating the suitability of reference genes. Our data therefore showed that the currently and widely used reference genes for data normalization in maize were not the most stable expressed transcripts. Five of the new putative reference genes (CUL, FPGS, LUG, MEP and UBCP) exhibited the highest expression stability according to all algorithms. In conclusion, with this study, we provide a list of validated reference genes and their relative primer sequences to conduct reliable qPCR experiments in maize.
Assuntos
Perfilação da Expressão Gênica/métodos , Genes de Plantas , Zea mays/genética , Algoritmos , Primers do DNA/genética , Regulação da Expressão Gênica de Plantas , Folhas de Planta/genética , Raízes de Plantas/genética , Reação em Cadeia da Polimerase em Tempo Real , Padrões de ReferênciaRESUMO
Stress responses depend on the correct regulation of gene expression. The discovery that abiotic as well as biotic stresses can regulate miRNA levels, coupled with the identification and functional analyses of stress-associated genes as miRNA targets, provided clues about the vital role that several miRNAs may play in modulating plant resistance to stresses. Nitrogen availability seriously affects crops productivity and environment and the understanding of the miRNA-guided stress regulatory networks should provide new tools for the genetic improvement of nitrogen use efficiency of crops. A recent study revealed the potential role of a number of nitrate-responsive miRNAs in the maize adaptation to nitrate fluctuations. In particular, results obtained suggested that a nitrate depletion might regulate the expression of genes involved in the starvation adaptive response, by affecting the spatio-temporal expression patterns of specific miRNAs.
Assuntos
Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , MicroRNAs/metabolismo , Nitratos/farmacologia , Transcrição Gênica/efeitos dos fármacos , Zea mays/efeitos dos fármacos , Zea mays/genética , MicroRNAs/genética , Transporte de RNA/efeitos dos fármacos , Transporte de RNA/genética , Estresse Fisiológico/efeitos dos fármacos , Estresse Fisiológico/genéticaRESUMO
Humic substances (HS) represent the organic material mainly widespread in nature. HS have positive effects on plant physiology by improving soil structure and fertility and by influencing nutrient uptake and root architecture. The biochemical and molecular mechanisms underlying these events are only partially known. HS have been shown to contain auxin and an "auxin-like" activity of humic substances has been proposed, but support to this hypothesis is fragmentary. In this review article, we are giving an overview of available data concerning molecular structures and biological activities of humic substances, with special emphasis on their hormone-like activities.