RESUMO
MAIN CONCLUSION: NH4+ is necessary for full functionality of reduction-based Fe deficiency response in plants. Nitrogen (N) is present in soil mainly as nitrate (NO3-) or ammonium (NH4+). Although the significance of a balanced supply of NO3- and NH4+ for optimal growth has been generally accepted, its importance for iron (Fe) acquisition has not been sufficiently investigated. In this work, hydroponically grown cucumber (Cucumis sativus L. cv. Maximus) plants were supplied with NO3- as the sole N source under -Fe conditions. Upon the appearance of chlorosis, plants were supplemented with 2 mM NH4Cl by roots or leaves. The NH4+ treatment increased leaf SPAD and the HCl-extractable Fe concentration while decreased root apoplastic Fe. A concomitant increase in the root concentration of nitric oxide and activity of FRO and its abolishment by an ethylene action inhibitor, indicated activation of the components of Strategy I in NH4+-treated plants. Ammonium-pretreated plants showed higher utilization capacity of sparingly soluble Fe(OH)3 and higher root release of H+, phenolics, and organic acids. The expression of the master regulator of Fe deficiency response (FIT) and its downstream genes (AHA1, FRO2, and IRT1) along with EIN3 and STOP1 was increased by NH4+ application. Temporal analyses and the employment of a split-root system enabled us to suggest that a permanent presence of NH4+ at concentrations lower than 2 mM is adequate to produce an unknown signal and causes a sustained upregulation of Fe deficiency-related genes, thus augmenting the Fe-acquisition machinery. The results indicate that NH4+ appears to be a widespread and previously underappreciated component of plant reduction-based Fe deficiency response.
Assuntos
Compostos de Amônio , Cucumis sativus , Regulação da Expressão Gênica de Plantas , Ferro , Raízes de Plantas , Cucumis sativus/genética , Cucumis sativus/metabolismo , Cucumis sativus/fisiologia , Compostos de Amônio/metabolismo , Raízes de Plantas/genética , Raízes de Plantas/metabolismo , Ferro/metabolismo , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Transdução de Sinais , Deficiências de Ferro , Folhas de Planta/metabolismo , Folhas de Planta/genética , Folhas de Planta/efeitos dos fármacos , Nitratos/metabolismo , Nitratos/farmacologia , Óxido Nítrico/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Nitrogênio/metabolismoRESUMO
Carbonate-rich soils limit plant performance and crop production. Previously, local adaptation to carbonated soils was detected in wild Arabidopsis thaliana accessions, allowing the selection of two demes with contrasting phenotypes: A1 (carbonate tolerant, c+) and T6 (carbonate sensitive, c-). Here, A1(c+) and T6(c - ) seedlings were grown hydroponically under control (pH 5.9) and bicarbonate conditions (10 mM NaHCO3 , pH 8.3) to obtain ionomic profiles and conduct transcriptomic analysis. In parallel, A1(c+) and T6(c - ) parental lines and their progeny were cultivated on carbonated soil to evaluate fitness and segregation patterns. To understand the genetic architecture beyond the contrasted phenotypes, a bulk segregant analysis sequencing (BSA-Seq) was performed. Transcriptomics revealed 208 root and 2503 leaf differentially expressed genes in A1(c+) versus T6(c - ) comparison under bicarbonate stress, mainly involved in iron, nitrogen and carbon metabolism, hormones and glycosylates biosynthesis. Based on A1(c+) and T6(c - ) genome contrasts and BSA-Seq analysis, 69 genes were associated with carbonate tolerance. Comparative analysis of genomics and transcriptomics discovered a final set of 18 genes involved in bicarbonate stress responses that may have relevant roles in soil carbonate tolerance.
Assuntos
Bicarbonatos , Solo , Bicarbonatos/metabolismo , Carbonatos/metabolismo , Perfilação da Expressão Gênica , Genômica , Regulação da Expressão Gênica de PlantasRESUMO
Increased availability of toxic Al3+ is the main constraint limiting plant growth on acid soils. Plants adapted to acid soils, however, tolerate toxic Al3+, and some can accumulate Al in their aerial parts to a significant degree. Studies on Al-tolerant and Al-accumulating species have mainly focused on the vegetation of acid soils distributed as two global belts in the northern and southern hemispheres, while acid soils formed outside these regions have been largely neglected. The acid soils (pH 3.4-4.2) of the tea plantations in the south Caspian region of Northern Iran were surveyed over three seasons at two main locations. Aluminum and other mineral elements (including nutrients) were measured in 499 plant specimens representing 86 species from 43 families. Al accumulation exceeding the criterion for accumulator species (>1000 µg g-1 DW) was found in 36 species belonging to 23 families of herbaceous annual or perennial angiosperms, in addition to three bryophyte species. Besides Al, Fe accumulation (1026-5155 µg g-1 DW) was also observed in the accumulator species that exceeded the critical toxicity concentration, whereas no such accumulation was observed for Mn. The majority of analyzed accumulator plants (64%) were cosmopolitan or pluriregional species, with a considerable rate of Euro-Siberian elements (37%). Our findings, which may contribute to phylogenetic studies of Al accumulators, also suggest suitable accumulator and excluder species for the rehabilitation of acid-eroded soils and introduce new model species for investigating Al accumulation and exclusion mechanisms.
RESUMO
The present study aims to evaluate the response of the three Mediterranean local grapevines 'Garnacha Blanca', 'Garnacha Tinta', and 'Macabeo' to treatments with biocontrol products, namely a botanical extract (Akivi, Dittrichia viscosa extract) and a beneficial microorganism (Bacillus UdG, Bacillus velezensis). A combination of transcriptomics and metabolomics approaches were chosen in order to study grapevine gene expression and to identify gene marker candidates, as well as, to determine differentially concentrated grapevine metabolites in response to biocontrol product treatments. Grapevine plants were cultivated in greenhouse under controlled conditions and submitted to the treatments. Thereafter, leaves were sampled 24h after treatment to carry out the gene expression study by RT-qPCR for the three cultivars and by RNA-sequencing for 'Garnacha Blanca'. Differentially expressed genes (DEGs) were investigated for both treatments and highly influenced DEGs were selected to be tested in the three cultivars as treatment gene markers. In addition, the extraction of leaf components was performed to quantify metabolites, such as phytohormones, organic acids, and phenols. Considering the upregulated and downregulated genes and the enhanced metabolites concentrations, the treatments had an effect on jasmonic acid, ethylene, and phenylpropanoids defense pathways. In addition, several DEG markers were identified presenting a stable overexpression after the treatments in the three grapevine cultivars. These gene markers could be used to monitor the activity of the products in field treatments. Further research will be necessary to confirm these primary results under field conditions.
RESUMO
High bicarbonate concentrations of calcareous soils with high pH can affect crop performance due to different constraints. Among these, Fe deficiency has mostly been studied. The ability to mobilize sparingly soluble Fe is a key factor for tolerance. Here, a comparative transcriptomic analysis was performed with two naturally selected Arabidopsis thaliana demes, the carbonate-tolerant A1(c+) and the sensitive T6(c-). Analyses of plants exposed to either pH stress alone (pH 5.9 vs. pH 8.3) or to alkalinity caused by 10 mM NaHCO3 (pH 8.3) confirmed better growth and nutrient homeostasis of A1(c+) under alkaline conditions. RNA-sequencing (RNA-seq) revealed that bicarbonate quickly (3 h) induced Fe deficiency-related genes in T6(c-) leaves. Contrastingly, in A1(c+), initial changes concerned receptor-like proteins (RLP), jasmonate (JA) and salicylate (SA) pathways, methionine-derived glucosinolates (GS), sulfur starvation, starch degradation, and cell cycle. Our results suggest that leaves of carbonate-tolerant plants do not sense iron deficiency as fast as sensitive ones. This is in line with a more efficient Fe translocation to aerial parts. In A1(c+) leaves, the activation of other genes related to stress perception, signal transduction, GS, sulfur acquisition, and cell cycle precedes the induction of iron homeostasis mechanisms yielding an efficient response to bicarbonate stress.
Assuntos
Arabidopsis/metabolismo , Bicarbonatos/toxicidade , Ciclopentanos/metabolismo , Oxilipinas/metabolismo , Brotos de Planta/efeitos dos fármacos , Salicilatos/metabolismo , Estresse Fisiológico/genética , Transcriptoma/genética , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/fisiologia , Bicarbonatos/farmacologia , Calmodulina/metabolismo , Ciclo Celular/efeitos dos fármacos , Ciclo Celular/genética , Perfilação da Expressão Gênica , Regulação da Expressão Gênica de Plantas/genética , Ontologia Genética , Glucosinolatos/metabolismo , Glutationa/metabolismo , Homeostase , Concentração de Íons de Hidrogênio , Ferro/metabolismo , Peroxidases/metabolismo , Brotos de Planta/genética , Brotos de Planta/metabolismo , Brotos de Planta/fisiologia , Mapas de Interação de Proteínas , RNA-Seq , Transdução de Sinais/efeitos dos fármacos , Amido/metabolismo , Enxofre/metabolismo , Fatores de TranscriçãoRESUMO
Tea plants (Camellia sinensis) can hyperaccumulate and tolerate high leaf concentrations of aluminium (Al). The quality of tealeaves and the positive health effects of their infusion depend on the leaf concentrations of both polyphenolic substances and mineral elements. This study explored the influence of Al supply on these leaf components under low and optimal phosphorus (P) availability. After 8â¯weeks exposure in hydroponics, multifactorial analysis revealed a negative influence of leaf Al on magnesium (Mg), P, boron (B), and manganese (Mn) leaf concentrations. Contrastingly, these essential mineral nutrients were positively related to leaf epigallocatechin. Galloylated catechins were positively related to leaf iron (Fe). After short-term exposure (24 and 96â¯h), RT-qPCR (Reverse Transcription-quantitative Polymerase Chain Reaction) analysis revealed upregulation of galloylation-related genes by substrate acidification both in old and young leaves. Only the extremely high Al accumulation in old leaves activated genes involved in biosynthesis of galloylated catechins, while in young leaves the lower Al leaf concentrations activated genes involved in anthocyanin accumulation. In conclusion, low pH and enhanced Al availability to tea plants have a strong influence on the polyphenolic pattern of tealeaves and therefore may alter both the leaves' antioxidant properties and their ability to bind Al and Fe in non-toxic form.
Assuntos
Alumínio/farmacologia , Camellia sinensis/metabolismo , Minerais/metabolismo , Proteínas de Plantas/metabolismo , Polifenóis/metabolismo , Camellia sinensis/efeitos dos fármacos , Camellia sinensis/genética , Perfilação da Expressão Gênica , Minerais/análise , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/genética , Folhas de Planta/metabolismo , Proteínas de Plantas/genética , Polifenóis/análise , Transdução de Sinais , Transcriptoma/efeitos dos fármacosRESUMO
During tea preparation mineral elements are extracted from the dried leaves of tea (Camellia sinensis (L.) Kuntze) plants into the solution. Micro-particle induced X-ray emission was employed to investigate the spatial distribution of magnesium (Mg), calcium (Ca) and manganese (Mn) in the young and old leaves of tea plants grown in the absence and presence of aluminium (Al) in the substrate. Results revealed that in tea leaves the largest concentrations of Mg occurred in the epidermis, of Ca in oxalate crystals and of Mn in epidermis and oxalate crystals; there was a leaf-age effect on tissue-specific concentrations of Mg, Ca and Mn with all tissues of old leaves containing larger concentrations of Mg, Ca and Mn than young leaves; supplementation of substrate with Al reduced concentrations of Mg, Ca and Mn in the old leaves, and a link between the distribution of Mg, Ca and Mn in the tea leaves with the extraction efficiencies of these elements into the tea was possible. We conclude that old leaves of tea plants cultivated under conditions of low Al availability will have the largest concentrations of Mg, Ca and Mn and may represent most acceptable ingredient for the preparation of tea.
Assuntos
Cálcio/metabolismo , Camellia sinensis/química , Magnésio/metabolismo , Manganês/metabolismo , Folhas de Planta/química , Chá/química , Alumínio/metabolismo , Cálcio/análise , Magnésio/análise , Manganês/análise , Extração em Fase Sólida , Espectrometria por Raios X , Distribuição TecidualRESUMO
Pests and diseases pose a threat to food security, which is nowadays aggravated by climate change and globalization. In this context, agricultural policies demand innovative approaches to more effectively manage resources and overcome the ecological issues raised by intensive farming. Optimization of plant mineral nutrition is a sustainable approach to ameliorate crop health and yield. Zinc is a micronutrient essential for all living organisms with a key role in growth, development, and defense. Competition for Zn affects the outcome of the host-attacker interaction in both plant and animal systems. In this review, we provide a clear framework of the different strategies involving low and high Zn concentrations launched by plants to fight their enemies. After briefly introducing the most relevant macro- and micronutrients for plant defense, the functions of Zn in plant protection are summarized with special emphasis on superoxide dismutases (SODs) and zinc finger proteins. Following, we cover recent meaningful studies identifying Zn-related passive and active mechanisms for plant protection. Finally, Zn-based strategies evolved by pathogens and pests to counteract plant defenses are discussed.
RESUMO
High soil carbonate limits crop performance especially in semiarid or arid climates. To understand how plants adapt to such soils, we explored natural variation in tolerance to soil carbonate in small local populations (demes) of Arabidopsis thaliana growing on soils differing in carbonate content. Reciprocal field-based transplants on soils with elevated carbonate (+C) and without carbonate (-C) over several years revealed that demes native to (+C) soils showed higher fitness than those native to (-C) soils when both were grown together on carbonate-rich soil. This supports the role of soil carbonate as a driving factor for local adaptation. Analyses of contrasting demes revealed key mechanisms associated with these fitness differences. Under controlled conditions, plants from the tolerant deme A1(+C) native to (+C) soil were more resistant to both elevated carbonate and iron deficiency than plants from the sensitive T6(-C) deme native to (-C) soil. Resistance of A1(+C) to elevated carbonate was associated with higher root extrusion of both protons and coumarin-type phenolics. Tolerant A1(+C) also had better Ca-exclusion than sensitive T6(-C) . We conclude that Arabidopsis demes are locally adapted in their native habitat to soils with moderately elevated carbonate. This adaptation is associated with both enhanced iron acquisition and calcium exclusion.
Assuntos
Adaptação Fisiológica , Arabidopsis/fisiologia , Carbonatos/metabolismo , Solo/química , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Cálcio/metabolismo , Clorofila/metabolismo , Cumarínicos/farmacologia , Ferro/metabolismo , Fenóis/metabolismo , Extratos Vegetais/química , Folhas de Planta/metabolismo , Estresse FisiológicoRESUMO
Metal defence against insect herbivory in hyperaccumulator plants is well documented. However, there are contradictory results regarding protection against snails. According to the joint effects hypothesis, inorganic and organic defences cooperate in plant protection. To test this hypothesis, we explored the relationships between snail (Cantareus aspersus) feeding and multiple inorganic and organic leaf components in the Cd hyperaccumulator plant Noccaea praecox. Plants grouped by rosette size growing in nutrient solution supplemented or not with 50 µM Cd were offered to the snails. After 3 days of snail feeding, the plants and snails were analysed. In addition to Cd concentrations, we analysed leaves for nutritional factors (sugar and protein), defence-related compounds (glucosinolates, phenolics, tannins, salicylic acid and jasmonate) and essential mineral nutrients. Cadmium concentrations in the snails and in snail excrements were also analysed. Snails preferentially fed on plants grown without Cd. Medium-sized plants exposed to Cd were the least consumed. Snail excrements from this trial weighed less and had higher Cd concentrations than those from other treatments. Cadmium increased salicylate and jasmonate production. A positive relationship between jasmonate levels and the number of attacked leaves was found. Principal component analysis revealed that leaf sugar concentration was the main factor positively affecting snails' leaf consumption, while leaf Cd had a negative but weaker influence. In conclusion, leaf sugar concentration mainly governs snails' feeding preferences. High leaf Cd concentrations do not deter herbivores from attacking leaves, but they do reduce leaf consumption. Our results clearly support the joint effects hypothesis.
Assuntos
Metais/toxicidade , Caramujos/fisiologia , Açúcares/metabolismo , Animais , Biomassa , Brassicaceae/metabolismo , Herbivoria/efeitos dos fármacos , Folhas de Planta/metabolismo , Análise de Componente Principal , Caramujos/efeitos dos fármacosRESUMO
Mechanisms to detoxify aluminium (Al) is a hot topic for cultivated plants. However, little information is known about the mechanisms used by native plants to deal with Al-toxicity. In Cerrado, some generalist mistletoe species, such as Passovia ovata (Pohl ex DC.) Kuijt and Struthanthus polyanthus Mart. can parasitize Al-accumulating and Al-excluding plant species without any clear symptoms of toxicity and mineral deficiency, while Psittacanthus robustus (Mart.) Marloth, a more specialist mistletoe, seems to be an Al-dependent species, parasitizing only Al-accumulating hosts. Here we (i) characterized the forms and compartmentalization of Al in leaves of P. robustus; (ii) compared Ca and Al leaf concentration, and leaf concentration of organic acids and polyphenols between facultative Al-accumulating (P. ovata and S. polyanthus) and Al-dependent (P. robustus) mistletoe species infecting Miconia albicans (Sw.) Steud. (Al-accumulating species). P. robustus chelated Al3+ with oxalate and stored it in the phloematic and epidermic leaf tissues. Leaf Ca and Al concentration did not differ among species. Leaf oxalate concentration was higher in the Al-dependent species. Concentrations of citrate and phenolic compounds were higher in the leaves of the facultative Al-accumulating species. These results show that facultative Al-accumulating and Al-dependent species use different mechanisms to detoxify Al. Moreover, this is the first report on a mistletoes species (P. robustus) with a potential calcifuge behaviour in Cerrado.
Assuntos
Alumínio/química , Loranthaceae/química , Alumínio/toxicidade , Brasil , Folhas de Planta/química , Especificidade da EspécieRESUMO
The mechanisms of extreme Al-resistance in Urochloa decumbens are not established. Full resistance expression requires a lag time of 72-96h and is preceded by a sensitive phase (24-48h) with Al-induced root growth inhibition. The aim here was to identify key processes of the activation phase of Al-resistance analysing both root exudates and comparative root proteome. Samples were taken after 0, 24 and 96h exposure to 0 or 200µM Al. Al-induced stimulation of citrate and oxalate efflux was limited to the sensitive phase. Only 11 proteins revealed Al-induced abundance differences; six were identified. After 24h, phenylalanine ammonium lyase (PAL), methionine synthase (MS), and deoxymugineic acid synthase (DMAS) decreased, while acid phosphatase (APase) abundance increased. Coincident with growth recovering, PAL and MS, but not DMAS, returned to initial levels. After 96h, γcarbonic anhydrase (γCA) and adenylate kinase (AK) along with two unidentified proteins were more abundant. In conclusion, few protein changes characterize the initial response to Al in signalgrass. During the alarm phase, changes are related to P-mobilization, downregulation of Fe-acquisition, reduction of phenolic biosynthesis, and small stimulation of organic acid exudation. After recovering (resistant phase), biosynthesis of phenolics and methionine, but not Fe-mobilization are re-established. Full expression of Al-resistance is characterized by enhanced γCA mediating mitochondrial complex I assembly and increased AK abundance indicating higher root respiration and better provision of ADP and Mg2+ to ATP synthase, respectively. The unidentified proteins and the specific role of γCA in Al resistance of U. decumbens will centre future research.
Assuntos
Alumínio/toxicidade , Resistência a Medicamentos , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Proteínas de Plantas/metabolismo , Raízes de Plantas/efeitos dos fármacos , Poaceae/efeitos dos fármacos , Poluentes do Solo/toxicidade , 5-Metiltetra-Hidrofolato-Homocisteína S-Metiltransferase/antagonistas & inibidores , 5-Metiltetra-Hidrofolato-Homocisteína S-Metiltransferase/química , 5-Metiltetra-Hidrofolato-Homocisteína S-Metiltransferase/genética , 5-Metiltetra-Hidrofolato-Homocisteína S-Metiltransferase/metabolismo , Anidrases Carbônicas/química , Anidrases Carbônicas/genética , Anidrases Carbônicas/metabolismo , Bases de Dados de Proteínas , Perfilação da Expressão Gênica , Mapeamento de Peptídeos , Fenilalanina Amônia-Liase/antagonistas & inibidores , Fenilalanina Amônia-Liase/química , Fenilalanina Amônia-Liase/genética , Fenilalanina Amônia-Liase/metabolismo , Proteínas de Plantas/antagonistas & inibidores , Proteínas de Plantas/química , Proteínas de Plantas/genética , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Poaceae/crescimento & desenvolvimento , Poaceae/metabolismo , Proteômica/métodos , Plântula/efeitos dos fármacos , Plântula/crescimento & desenvolvimento , Plântula/metabolismoRESUMO
In bread wheat, besides malate, the importance of citrate efflux for Al tolerance has also been reported. For better understanding the Al tolerance mechanism in bread wheat, here, we performed both a molecular characterization of the citrate transporter gene TaMATE1 and an investigation on the upstream variations in citrate and malate transporter genes. TaMATE1 belong to multidrug transporter protein family, which are located on the long arm of homoeologous group 4 chromosomes (TaMATE1-4A, TaMATE1-4B TaMATE1-4D). TaMATE1 homoeologues transcript expression study exhibited the preponderance of homoeologue TaMATE1-4B followed by TaMATE1-4D whereas homoeologue TaMATE1-4A seemed to be silenced. TaMATE1, particularly homoeologue TaMATE1-4B and TaALMT1 transcripts were much more expressed in the root apices than in shoots of Al tolerant genotype Barbela 7/72/92 under both control and Al stress conditions. In addition, in both tissues of Barbela 7/72/92, higher basal levels of these gene transcripts were observed than in Anahuac (Al sensitive). Noticeably, the presence of a transposon in the upstream of TaMATE1-4B in Barbela 7/72/92 seems to be responsible for its higher transcript expression where it may confer citrate efflux. Thus, promoter variations (transposon in TaMATE1-4B upstream and type VI promoter in TaALMT1) associated with higher basal transcript expression of TaMATE1-4B and TaALMT1 clearly show how different mechanisms for Al tolerance operate simultaneously in a single genotype. In conclusion, our results demonstrate that Barbela 7/72/92 has favorable alleles for these organic acids transporter genes which could be utilized through genomic assisted selection to develop improved cultivars for acidic soils.
Assuntos
Proteínas de Transporte/genética , Ácido Cítrico/metabolismo , Regiões Promotoras Genéticas/genética , Triticum/genética , Alelos , Alumínio/toxicidade , Sequência de Bases , Transporte Biológico , Ácidos Carboxílicos/metabolismo , Proteínas de Transporte/metabolismo , Genótipo , Dados de Sequência Molecular , Filogenia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/genética , Raízes de Plantas/metabolismo , Brotos de Planta/efeitos dos fármacos , Brotos de Planta/genética , Brotos de Planta/metabolismo , Análise de Sequência de DNA , Estresse Fisiológico , Triticum/efeitos dos fármacos , Triticum/metabolismoRESUMO
Tea plants (Camellia sinensis) are well adapted to acid soils with high Al availability. These plants not only accumulate high leaf Al concentrations, but also respond to Al with growth stimulation. Decreased oxidative stress has been associated with this effect. Why tea plants not exposed to Al suffer from oxidative stress has not been clarified. In this study, hydroponically grown tea plants treated with 0 to 300 µM Al were analyzed for growth, Al and Fe accumulation, and Al distribution by means of morin and hematoxylin staining. Roots of control plants stained black with hematoxylin. This indicates the formation of a Fe-hematoxylin complex. Young leaves of controls accumulated more than 1000 mg Fe kg(-1) dry weight. This concentration is above the Fe-toxicity threshold in most species. Supply of Al stimulated growth and reduced Fe uptake and transport. These results indicate that Al-induced growth stimulation might be due to alleviation of a latent Fe toxicity occurring in tea plants without Al supply.
Assuntos
Alumínio/metabolismo , Camellia sinensis/metabolismo , Ferro/metabolismo , Folhas de Planta/metabolismo , Adaptação Fisiológica/efeitos dos fármacos , Alumínio/farmacologia , Transporte Biológico/efeitos dos fármacos , Camellia sinensis/efeitos dos fármacos , Camellia sinensis/crescimento & desenvolvimento , Relação Dose-Resposta a Droga , Hidroponia , Estresse Oxidativo/efeitos dos fármacos , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/crescimento & desenvolvimento , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismoRESUMO
Brachiaria, a genus of forage grasses of African origin, is gaining considerable importance because of both its nutritional value and its high stress resistance. An extraordinary resistance to Al toxicity has been reported in B. decumbens. The mechanisms of this hyperresistance are still unknown. This study explores the localization of Al in two contrasting Brachiaria species, the hyperresistant B. decumbens and the less resistant B. brizantha. Scanning Electron Microscope/Energy Dispersive Spectrometry, confocal fluorescence microscopy and optical microscopy of lumogallion or morin-stained roots was performed. Species differences in Al resistance were evident at 32 µM Al(3+) activity in low ionic strength full nutrient solution containing Si. Roots of B. decumbens accumulated less Al than those of B. brizantha. Moreover, location and Al form seemed different. In B. decumbens Al accumulation was localized in hot spots of high Al concentrations. These sites with high Al accumulation mainly correspond to root hairs. B. brizantha exhibited a more even distribution of Al in cell walls of the root tip. Analysis of soluble phenolic substances in roots revealed species differences in response to Al. An Al-induced increase of chlorogenic acid concentrations was found in B. decumbens but not in B. brizantha. Taken together the results suggest a possible role for chlorogenic acid as a primer for changes in root epidermal cell patterning that may contribute to the Al hyperresistance in B. decumbens.
Assuntos
Compostos de Alumínio/farmacologia , Brachiaria/citologia , Cloretos/farmacologia , Epiderme Vegetal/efeitos dos fármacos , Raízes de Plantas/citologia , Cloreto de Alumínio , Compostos de Alumínio/metabolismo , Brachiaria/efeitos dos fármacos , Brachiaria/crescimento & desenvolvimento , Brachiaria/metabolismo , Cloretos/metabolismo , Cinamatos/metabolismo , Microscopia Confocal , Microscopia Eletrônica de Varredura , Epiderme Vegetal/metabolismo , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismoRESUMO
Information on localization of Al in tea leaf tissues is required in order to better understand Al tolerance mechanism in this Al-accumulating plant species. Here, we have used low-energy X-ray fluorescence spectro-microscopy (LEXRF) to study localization of Al and other low Z-elements, namely C, O, Mg, Si and P, in fully developed leaves of the tea plant [Camellia sinensis (L.) O. Kuntze]. Plants were grown from seeds for 3 months in a hydroponic solution, and then exposed to 200 microM AlCl(3) for 2 weeks. Epidermal-mesophyll and xylem phloem regions of 20 microm thick cryo-fixed freeze-dried tea-leaf cross-sections were raster scanned with 1.7 and 2.2 keV excitation energies to reach the Al-K and P-K absorption edges. Al was mainly localized in the cell walls of the leaf epidermal cells, while almost no Al signal was obtained from the leaf symplast. The results suggest that the retention of Al in epidermal leaf apoplast represent the main tolerance mechanism to Al in tea plants. In addition LEXRF proved to be a powerful tool for localization of Al in plant tissues, which can help in our understanding of the processes of Al uptake, transport and tolerance in plants.
Assuntos
Alumínio/metabolismo , Camellia sinensis/metabolismo , Microscopia de Fluorescência/métodos , Folhas de Planta/metabolismo , Espectrometria por Raios X/métodos , Camellia sinensis/citologia , Floema/citologia , Epiderme Vegetal/citologia , Epiderme Vegetal/metabolismo , Folhas de Planta/citologia , Xilema/citologiaRESUMO
Aluminium tolerance in maize is mainly due to more efficient Al exclusion. Nonetheless, even in tolerant varieties Al can gain access into the cells. Detoxification by binding to strong organic ligands should therefore play a role also in plants with high Al exclusion capacity. To test this hypothesis in this study the concentrations of soluble, free and bound, phenolics were analyzed in roots of two maize varieties differing in Al tolerance. Exposure for 24 h to 50 microM Al in nutrient solution strongly inhibited root elongation in the sensitive variety 16 x 36, but not in the Al-tolerant variety Cateto. Cateto accumulated about half the concentration of Al in roots than 16 x 36 (analysis performed after root desorption with citrate). Roots of Al-tolerant Cateto contained higher concentrations of caffeic acid, catechol and catechin than roots of the sensitive variety. Exposure to Al induced the accumulation of taxifolin in roots of both varieties. However, Al-tolerant Cateto accumulated about twice the concentration than Al-sensitive 16 x 36 of this pentahydroxyfavonol. The molar ratio for phenolics with catecholate groups to Al was about unity in roots of Cateto, while in those of 16 x 36 the ratio was ten times lower. Both the fact that these phenolics are strong ligands for Al and their high antioxidant and antiradical activity suggest that these compounds may provide protection against the Al fraction that is able to surpass the exclusion mechanisms operating in the tolerant maize variety.
Assuntos
Alumínio/metabolismo , Fenóis/análise , Raízes de Plantas/metabolismo , Zea mays/metabolismo , Alumínio/farmacologia , Ácidos Cafeicos/metabolismo , Catequina/metabolismo , Catecóis/metabolismo , Malondialdeído/metabolismo , Raízes de Plantas/efeitos dos fármacos , Quercetina/agonistas , Quercetina/análogos & derivados , Quercetina/metabolismo , Zea mays/efeitos dos fármacosRESUMO
Thlaspi praecox Wulfen (Brassicaceae) is a perennial Cd/Zn hyperaccumulating plant species that forms functional arbuscular mycorrhizal (AM) symbiosis. Glucosinolates (GS) were studied in different organs of field-collected T. praecox at differing plant developmental stages. Additionally, AM colonization was recorded. Total GS concentrations and profiles of nine individual GS varied during the plant life cycle. Novel individual GS that were related to specific developmental phases, mainly to flowering and seed production, were identified. The highest total GS and sinalbin concentrations in rosette leaves were found in the vegetative phase, possibly contributing to protection of young, palatable leaves. The lowest were found in roots during the flowering and the seeding phases. Increased total GS concentrations in roots and enhanced aliphatic GS, especially glucobrassicanapin, in the senescence phase may protect roots from herbivory during winter and early spring. The presence of glucotropaeolin and the absence of glucobrassicanapin in the flowering phase coincided with peak AM colonization. This is the first report on GS profiles in an AM and metal-hyperaccumulating plant.
Assuntos
Brassicaceae/crescimento & desenvolvimento , Brassicaceae/metabolismo , Cádmio/metabolismo , Glucosinolatos/metabolismo , Micorrizas/fisiologia , Zinco/metabolismo , Animais , Brassicaceae/fisiologia , Micorrizas/metabolismoRESUMO
Elemental uptake and arbuscular mycorrhizal (AM) colonisation were studied during the life cycle of field collected Cd/Zn hyperaccumulating Thlaspi praecox (Brassicaceae). Plant biomass and tissue concentrations of Cd, Pb, Zn, Fe and Ni were found to vary during development, while no variation in P, K, Ca, Mn and Cu tissue concentrations were observed. The lowest Cd bioaccumulation in rosette leaves (BAF(RL)) observed during seeding was partially attributed to lower translocation from roots to rosette leaves and partially to high translocation to stalks, indicating a high Cd mobility to reproductive tissues, in line with our previous studies. The highest intensity of AM colonisation (M%) was observed in the flowering phase and was accompanied by increased root Cd, Zn, Pb and Fe contents. In addition, a positive correlation between AM colonisation and Fe contents in rosette leaves was found. The results indicate developmental dependence of AM formation, accompanied by selective changes in nutrient acquisition in T. praecox that are related to increased plant needs, and the protective role of AM colonisation on metal polluted sites during the reproductive period.
Assuntos
Metais Pesados/análise , Micorrizas/fisiologia , Poluentes do Solo/análise , Thlaspi , Biodegradação Ambiental , Biomassa , Micorrizas/isolamento & purificação , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/metabolismo , Folhas de Planta/microbiologia , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Raízes de Plantas/microbiologia , Brotos de Planta/crescimento & desenvolvimento , Brotos de Planta/metabolismo , Brotos de Planta/microbiologia , Simbiose , Thlaspi/crescimento & desenvolvimento , Thlaspi/metabolismo , Thlaspi/microbiologiaRESUMO
Farmers have used metal compounds in phytosanitary treatments for more than a century; however, it has recently been suggested that plants absorb high concentrations of metals from the substrate as a self-defense mechanism against pathogens and herbivores. This metal defense hypothesis is among the most attractive proposals for the 'reason to be' of metal hyperaccumulator species. On a molecular basis, metal defense against biotic stress seems to imply common and/or complementary pathways of signal perception, signal transduction and metabolism. This does not imply a broad band of co-resistance to different stress types but reflects a continuous cross talk during the coevolution of plants, pathogens and herbivores competing in an environment where efficient metal ion acquisition and ion homeostasis are essential for survival.