Dissecting the Roles of Phosphorus Use Efficiency, Organic Acid Anions, and Aluminum-Responsive Genes under Aluminum Toxicity and Phosphorus Deficiency in Ryegrass Plants.

Aluminum (Al) toxicity and phosphorus (P) deficiency are widely recognized as major constraints to agricultural productivity in acidic soils. Under this scenario, the development of ryegrass plants with enhanced P use efficiency and Al resistance is a promising approach by which to maintain pasture production. In this study, we assessed the contribution of growth traits, P efficiency, organic acid anion (OA) exudation, and the expression of Al-responsive genes in improving tolerance to concurrent low-P and Al stress in ryegrass (Lolium perenne L.). Ryegrass plants were hydroponically grown under optimal (0.1 mM) or low-P (0.01 mM) conditions for 21 days, and further supplied with Al (0 and 0.2 mM) for 3 h, 24 h and 7 days. Accordingly, higher Al accumulation in the roots and lower Al translocation to the shoots were found in ryegrass exposed to both stresses. Aluminum toxicity and P limitation did not change the OA exudation pattern exhibited by roots. However, an improvement in the root growth traits and P accumulation was found, suggesting an enhancement in Al tolerance and P efficiency under combined Al and low-P stress. Al-responsive genes were highly upregulated by Al stress and P limitation, and also closely related to P utilization efficiency. Overall, our results provide evidence of the specific strategies used by ryegrass to co-adapt to multiple stresses in acid soils.

Tolerance of cultivars and clonal selections of peach rootstocks to excess aluminum / Tolerância de cultivares e seleções clonais de porta-enxertos de pessegueiro ao excesso de alumínio

Forms of aluminum (Al) present in the solution of tropical and subtropical soils can cause toxicity in rootstocks and peach cultivars, impairing growth and productivity. This can be minimized by growing Al-tolerant rootstocks and cultivars. However, this is not sufficiently known, especially because plant breeding programs do not always consider tolerance as a selection variable for genetic materials. The study aimed to (a) select cultivars and clonal selections of Al-tolerant peach rootstocks, (b) identify variables that confer Al tolerance for use in genetic improvement programs, and (c) propose critical levels (NC) and ranges of toxicity (TF) of Al in relation to morphological variables of the root system. The experimental design was completely randomized, comprising a factorial of 13 (cultivars and clonal selections) x 2 (with and without Al) with three replications. Own-rooted 'BRS Mandinho' peach seedlings (without rootstock) and grafted seedlings of 'BRS Mandinho' on different cultivars and clonal rootstock selections were cultivated in a hydroponic system, composing two levels for the Al factor (absence and presence at 100 mg L−1). The morphological variables of the canopy and root system, Al accumulation in tissues, translocation factor, and the critical level (NC) and toxicity range (TF) of Al in the roots were evaluated. Rootstocks FB-SM-09-43, JB-ESM-09-13, SAS-SAU-09-71, SS-CHI-09-40, 'Sharpe' and VEH-GRA-09-55 were tolerant at high Al concentrations. The NC of Al in the roots in relation to the root surface area of peach rootstocks was 1400 mg Al kg−1, and the FT was between 1200 and 1500 mg Al kg−1.(AU)

Formas de alumínio (Al) presentes na solução de solos tropicais e subtropicais podem causar toxicidade em porta-enxertos e cultivares de pessegueiro, prejudicando o crescimento e a produtividade. Isso pode ser minimizado pelo cultivo de porta-enxertos e cultivares tolerantes ao Al. Porém, isso não é suficientemente conhecido, principalmente porque os programas de melhoramento vegetal nem sempre consideram a tolerância como uma variável de seleção de materiais genéticos. O estudo teve como objetivo (a) selecionar cultivares e seleções clonais de porta-enxertos de pessegueiro tolerantes ao Al, (b) identificar variáveis que confiram tolerância ao Al para uso em programas de melhoramento genético e (c) propor níveis críticos (NC) e faixas de toxicidade (FT) do Al em relação às variáveis morfológicas do sistema radicular. O delineamento experimental foi inteiramente casualizado, compreendendo fatorial 13 (cultivares e seleções clonais) x 2 (com e sem Al) com três repetições. Mudas de pessegueiro 'BRS Mandinho' autoenraizadas (sem porta-enxerto) e mudas enxertadas de 'BRS Mandinho' em diferentes cultivares e seleções de porta-enxertos clonais foram cultivadas em sistema hidropônico, compondo dois níveis para o fator Al (ausência e presença a 100 mg L−1). Foram avaliadas as variáveis morfológicas da parte aérea e do sistema radicular, acúmulo de Al nos tecidos, fator de translocação, NC e FT do Al nas raízes. Os porta-enxertos FB-SM-09-43, JB-ESM-09-13, SAS-SAU-09-71, SS-CHI-09-40, 'Sharpe' e VEH-GRA-09-55 foram tolerantes a altas concentrações de Al. O NC do Al nas raízes em relação à área radicular dos porta-enxertos de pessegueiro foi de 1400 mg Al kg−1, e o FT ficou entre 1200 e 1500 mg Al kg−1.(AU)

Cloning, Expression Analysis, and Functional Characterization of Candidate Oxalate Transporter Genes of HbOT1 and HbOT2 from Rubber Tree (Hevea brasiliensis).

Secretion of oxalic acid from roots is an important aluminum detoxification mechanism for many plants such as Hevea brasiliensis (rubber tree). However, the underlying molecular mechanism and oxalate transporter genes in plants have not yet been reported. In this study, the oxalate transporter candidate genes HbOT1 and HbOT2 from the rubber tree were cloned and preliminarily identified. It was found that HbOT1 had a full length of 1163 bp with CDS size of 792 bp, encoding 263 amino acids, and HbOT2 had a full length of 1647 bp with a CDS region length of 840 bp, encoding 279 amino acid residues. HbOT1 and HbOT2 were both stable hydrophobic proteins with transmembrane structure and SNARE_assoc domains, possibly belonging to the SNARE_assoc subfamily proteins of the SNARE superfamily. qRT-PCR assays revealed that HbOT1 and HbOT2 were constitutively expressed in different tissues, with HbOT1 highly expressed in roots, stems, barks, and latex, while HbOT2 was highly expressed in latex. In addition, the expressions of HbOT1 and HbOT2 were up-regulated in response to aluminum stress, and they were inducible by metals, such as copper and manganese. Heterologous expression of HbOT1 and HbOT2 in the yeast mutant AD12345678 enhanced the tolerance to oxalic acid and high concentration aluminum stress, which was closely correlated with the secretion of oxalic acid. This study is the first report on oxalate transporter genes in plants, which provides a theoretical reference for the study on the molecular mechanism of oxalic acid secretion to relieve aluminum toxicity and on aluminum-tolerance genetic engineering breeding.

Amelioration of aluminum phytotoxicity in Solanum lycopersicum by co-inoculation of plant growth promoting Kosakonia radicincitans strain CABV2 and Streptomyces corchorusii strain CASL5.

Aluminum (Al) toxicity is the main constraint for crop cultivation in acidic soils. In this study, Al-tolerant rhizobacteria Kosakonia radicincitans (CABV2) and actinobacteria Streptomyces corchorusii (CASL5) were isolated from Beta vulgaris rhizosphere in acidic soil. Both isolates displayed high tolerance to Al (10 mM), produce siderophores, indole-3-acetic acid, 1-aminocyclopropane-1-carboxylate and solubilize phosphate. Co-inoculation of CABV2 and CASL5 strains were significantly increased the root length (312.90%), shoot length (183.19%), fresh weight (224.82%), dry weight (309.25%) and photosynthetic pigments (chlorophyll a 279.69%, chlorophyll b 188.23% and carotenoids 158.20%) of Solanum lycopersicum plants under 300 mg Al kg-1 soil conditions as compared to uninoculated Al stressed plants. Similarly, the co-inoculation treated plants subjected to Al stress condition enhanced the uptake of essential nutrients (N 229%, P 252%, K 115%, Fe 185%, Mg 345% and Ca 202%) by plants as compared to Al stressed uninoculated plants. Under Al stress (300 mg Al kg-1 soil), co-inoculation significantly decreased malondialdehyde content (66%), and increased catalase (83%), superoxide dismutase (82%), peroxidase (89%) activities and root exudates (organic acids 6.44-12.36 fold) in S. lycopersicum as compared to uninoculated plants, indicating that the CABV2 and CASL5 strains were reduced Al-induced oxidative stress. Moreover, co-inoculation significantly reduced Al accumulation in the root (89%), stem (95%) and leaves (94%) of S. lycopersicum under Al stress at 300 mg Al kg-1 soil, compared to the uninoculated plants. This is the first report of K. radicincitans strain CABV2 and S. corchorusii strain CASL5 potentially reducing Al uptake in S. lycopersicum.

Mass spectrometry-based quantification and spatial localization of small organic acid exudates in plant roots under phosphorus deficiency and aluminum toxicity.

Low-molecular-weight organic acid (OA) extrusion by plant roots is critical for plant nutrition, tolerance to cations toxicity, and plant-microbe interactions. Therefore, methodologies for the rapid and precise quantification of OAs are necessary to be incorporated in the analysis of roots and their exudates. The spatial location of root exudates is also important to understand the molecular mechanisms directing OA production and release into the rhizosphere. Here, we report the development of two complementary methodologies for OA determination, which were employed to evaluate the effect of inorganic ortho-phosphate (Pi) deficiency and aluminum toxicity on OA excretion by Arabidopsis roots. OA exudation by roots is considered a core response to different types of abiotic stress and for the interaction of roots with soil microbes, and for decades has been a target trait to produce plant varieties with increased capacities of Pi uptake and Al tolerance. Using targeted ultra-performance liquid chromatography coupled with high-resolution tandem mass spectrometry (UPLC-HRMS/MS), we achieved the quantification of six OAs in root exudates at sub-micromolar detection limits with an analysis time of less than 5 min per sample. We also employed targeted (MS/MS) matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) to detect the spatial location of citric and malic acid with high specificity in roots and exudates. Using these methods, we studied OA exudation in response to Al toxicity and Pi deficiency in Arabidopsis seedlings overexpressing genes involved in OA excretion. Finally, we show the transferability of the MALDI-MSI method by analyzing OA excretion in Marchantia polymorpha gemmalings subjected to Pi deficiency.

Root Adaptation via Common Genetic Factors Conditioning Tolerance to Multiple Stresses for Crops Cultivated on Acidic Tropical Soils.

Crop tolerance to multiple abiotic stresses has long been pursued as a Holy Grail in plant breeding efforts that target crop adaptation to tropical soils. On tropical, acidic soils, aluminum (Al) toxicity, low phosphorus (P) availability and drought stress are the major limitations to yield stability. Molecular breeding based on a small suite of pleiotropic genes, particularly those with moderate to major phenotypic effects, could help circumvent the need for complex breeding designs and large population sizes aimed at selecting transgressive progeny accumulating favorable alleles controlling polygenic traits. The underlying question is twofold: do common tolerance mechanisms to Al toxicity, P deficiency and drought exist? And if they do, will they be useful in a plant breeding program that targets stress-prone environments. The selective environments in tropical regions are such that multiple, co-existing regulatory networks may drive the fixation of either distinctly different or a smaller number of pleiotropic abiotic stress tolerance genes. Recent studies suggest that genes contributing to crop adaptation to acidic soils, such as the major Arabidopsis Al tolerance protein, AtALMT1, which encodes an aluminum-activated root malate transporter, may influence both Al tolerance and P acquisition via changes in root system morphology and architecture. However, trans-acting elements such as transcription factors (TFs) may be the best option for pleiotropic control of multiple abiotic stress genes, due to their small and often multiple binding sequences in the genome. One such example is the C2H2-type zinc finger, AtSTOP1, which is a transcriptional regulator of a number of Arabidopsis Al tolerance genes, including AtMATE and AtALMT1, and has been shown to activate AtALMT1, not only in response to Al but also low soil P. The large WRKY family of transcription factors are also known to affect a broad spectrum of phenotypes, some of which are related to acidic soil abiotic stress responses. Hence, we focus here on signaling proteins such as TFs and protein kinases to identify, from the literature, evidence for unifying regulatory networks controlling Al tolerance, P efficiency and, also possibly drought tolerance. Particular emphasis will be given to modification of root system morphology and architecture, which could be an important physiological "hub" leading to crop adaptation to multiple soil-based abiotic stress factors.

Loss of function of Arabidopsis NADP-malic enzyme 1 results in enhanced tolerance to aluminum stress.

In acidic soils, aluminum (Al) toxicity is a significant limitation to crop production worldwide. Given its Al-binding capacity, malate allows internal as well as external detoxification strategies to cope with Al stress, but little is known about the metabolic processes involved in this response. Here, we analyzed the relevance of NADP-dependent malic enzyme (NADP-ME), which catalyzes the oxidative decarboxylation of malate, in Al tolerance. Plants lacking NADP-ME1 (nadp-me1) display reduced inhibition of root elongation along Al treatment compared with the wild type (wt). Moreover, wt roots exposed to Al show a drastic decrease in NADP-ME1 transcript levels. Although malate levels in seedlings and root exudates are similar in nadp-me1 and wt, a significant increase in intracellular malate is observed in roots of nadp-me1 after long exposure to Al. The nadp-me1 plants also show a lower H2 O2 content in root apices treated with Al and no inhibition of root elongation when exposed to glutamate, an amino acid implicated in Al signaling. Proteomic studies showed several differentially expressed proteins involved in signal transduction, primary metabolism and protection against biotic and other abiotic stimuli and redox processes in nadp-me1, which may participate directly or indirectly in Al tolerance. The results indicate that NADP-ME1 is involved in adjusting the malate levels in the root apex, and its loss results in an increased content of this organic acid. Furthermore, the results suggest that NADP-ME1 affects signaling processes, such as the generation of reactive oxygen species and those that involve glutamate, which could lead to inhibition of root growth.

Aluminum, a Friend or Foe of Higher Plants in Acid Soils.

Aluminum (Al) is the most abundant metal in the earth's crust, but its availability depends on soil pH. Despite this abundance, Al is not considered an essential element and so far no experimental evidence has been put forward for a biological role. In plants and other organisms, Al can have a beneficial or toxic effect, depending on factors such as, metal concentration, the chemical form of Al, growth conditions and plant species. Here we review recent advances in the study of Al in plants at physiological, biochemical and molecular levels, focusing mainly on the beneficial effect of Al in plants (stimulation of root growth, increased nutrient uptake, the increase in enzyme activity, and others). In addition, we discuss the possible mechanisms involved in improving the growth of plants cultivated in soils with acid pH, as well as mechanisms of tolerance to the toxic effect of Al.

Responses of symbiotic nitrogen-fixing common bean to aluminum toxicity and delineation of nodule responsive microRNAs.

Aluminum (Al) toxicity is widespread in acidic soils where the common bean (Phaseolus vulgaris), the most important legume for human consumption, is produced and it is a limiting factor for crop production and symbiotic nitrogen fixation. We characterized the nodule responses of common bean plants inoculated with Rhizobioum tropici CIAT899 and the root responses of nitrate-fertilized plants exposed to excess Al in low pH, for long or short periods. A 43-50% reduction in nitrogenase activity indicates that Al toxicity (Alt) highly affected nitrogen fixation in common bean. Bean roots and nodules showed characteristic symptoms for Alt. In mature nodules Al accumulation and lipoperoxidation were observed in the infected zone, while callose deposition and cell death occurred mainly in the nodule cortex. Regulatory mechanisms of plant responses to metal toxicity involve microRNAs (miRNAs) along other regulators. Using a miRNA-macroarray hybridization approach we identified 28 (14 up-regulated) Alt nodule-responsive miRNAs. We validated (quantitative reverse transcriptase-PCR) the expression of eight nodule responsive miRNAs in roots and in nodules exposed to high Al for long or short periods. The inverse correlation between the target and miRNA expression ratio (stress:control) was observed in every case. Generally, miRNAs showed a higher earlier response in roots than in nodules. Some of the common bean Alt-responsive miRNAs identified has also been reported as differentially expressed in other plant species subjected to similar stress condition. miRNA/target nodes analyzed in this work are known to be involved in relevant signaling pathways, thus we propose that the participation of miR164/NAC1 (NAM/ATAF/CUC transcription factor) and miR393/TIR1 (TRANSPORT INHIBITOR RESPONSE 1-like protein) in auxin and of miR170/SCL (SCARECROW-like protein transcription factor) in gibberellin signaling is relevant for common bean response/adaptation to Al stress. Our data provide a foundation for evaluating the individual roles of miRNAs in the response of common bean nodules to Alt.

Effect of salicylic acid on the attenuation of aluminum toxicity in Coffea arabica L. suspension cells: A possible protein phosphorylation signaling pathway.

The protective effect of salicylic acid (SA) on aluminum (Al) toxicity was studied in suspension cells of Coffea arabica L. The results showed that SA does not produce any effect on cell growth and that the growth inhibition produced by aluminum is restored during simultaneous treatment of the cells with Al and SA. In addition, the cells exposed to both compounds, Al and SA, showed evident morphological signals of recovery from the toxic state produced in the presence of Al. The cells treated with SA showed a lower accumulation of Al, which was linked to restoration from Al toxicity because the concentration of Al(3+) outside the cells, measured as the Al(3+)-morin complex, was not modified by the presence of SA. Additionally, the inhibition of phospholipase C by Al treatment was restored during the exposure of the cells to SA and Al. The involvement of protein phosphorylation in the protective effect of SA on Al-toxicity was suggested because staurosporine, a protein kinase inhibitor, reverted the stimulatory effect of the combination of Al and SA on protein kinase activity. These results suggest that SA attenuates aluminum toxicity by affecting a signaling pathway linked to protein phosphorylation.

Tolerance of physic nut plants to aluminum activity in nutrient solution / Tolerância de plantas de pinhão-manso à atividade de alumínio, em solução nutritiva

Plants have different levels of tolerance to phytotoxic effects of aluminum and the exploitation of this characteristic is of significant importance to the use of acid soils. This research aimed to evaluate the effect of aluminum activity in nutrient solution on growth of physic nut young plant. After seven days of adaptation, plants were submitted to Al concentrations of 0; 200; 400; 600; 800 and 1,000 µmol L­1, corresponding to Al3+ activity solution, of: 14.5, 21.4; 46.6; 75.6; 108.3 e 144.8 µmol L­1, respectively. The increased activity of Al3+ decreased linearly the number of leaves, plant height, leaf area, shoot dry matter and root length of physic nut plant. Physic nut young plants are sensitive to high aluminum activity in solution. The root length, number of leaves, shoot dry matter and total dry matter were variables more affected by Al activity in solution, and can be used to discriminate the tolerance levels to aluminum in physic nut plants. The accumulation of aluminum increased in a activity-dependent manner; however, its translocation from root to shoot was low.

As plantas apresentam diferentes níveis de tolerância aos efeitos fitotóxicos do alumínio e a exploração dessa característica torna-se de relevante importância para a utilização dos solos ácidos. Objetivou-se com este trabalho avaliar o efeito da atividade de alumínio, em solução nutritiva, no crescimento inicial de plantas de pinhão-manso (Jatropha curcas L). As plantas foram cultivadas em vasos com capacidade para 1,5 L, contendo solução nutritiva. Após sete dias de adaptação, as plantas foram submetidas a concentrações de Al de 0, 200, 400, 600, 800 e 1.000 µmol L­1, que corresponderam a atividades de Al3+ em solução de: 14,5; 21,4; 46,6; 75,6; 108,3 e 144,8 µmol L­1, respectivamente. O aumento da atividade de Al3+ reduziu o número de folhas por planta, altura da planta, área foliar, matéria seca da parte aérea e comprimento da raiz principal das plantas de pinhão-manso. Plantas de pinhão-manso são sensíveis a elevada atividade de Al em solução. O comprimento da raiz, número de folhas e a produção de matéria seca da parte aérea e total foram as características mais afetadas pela atividade de Al em solução, e podem ser utilizadas para discriminar os níveis de tolerância ao alumínio em plantas de pinhão-manso. O acúmulo de alumínio aumentou de uma maneira dependente da atividade; no entanto, sua translocação das raízes para a parte aérea foi baixa.

Tolerance of arabica coffee cultivars for aluminum in nutritive solution

This work aimed to evaluate the Coffea arabica cultivars for aluminum toxicity tolerance, in modified Hoagland solution. A completely randomized design with five repetitions in a factorial 4 x 4 (cultivar x combinations of aluminum) was used. After 44 days of the sowing, were transferred ten seedlings each cultivar germinated in the absence of Al3+ to solution without Al3+, and ten for solution with Al3+; ten seedlings each cultivar germinated in presence of Al3+ to solution without Al3+, and ten for solution with Al3+. In the treatment with aluminum, the element was added to the nutritive solution in the concentration of 0.83 mmol L-1 as Al2(SO4)3.16H2O. The cultivars Catuaí Amarelo IAC 62 and Iapar 59 were tolerant to the aluminum; cultivar Oeiras presented intermediate tolerance, while cultivar Obatã IAC 1669-20 was sensitive. The tolerance of the coffee cultivars to the aluminum during the initial development of the seedlings did not depend on the presence of aluminum in the germination phase.

Rúcula em cultivo hidropônico submetida em diferentes concentrações de alumínio / Eruca in hydroponics posted in different concentrations of aluminum

Objetivou-se avaliar os efeitos do alumínio em solução nutritiva, no crescimento de plantas de rúcula (Eruca sativa Mill.) em condições controladas. Utilizou-se tricloreto de alumínio, AlCl3, sendo os tratamentos: 0,0; 15,0; 30,0; 45,0 e 60,0 mg Al3+ L-1 de solução. As sementes de rúcula foram distribuídas em espuma fenólica onde receberam água destilada durante 10 dias após a semeadura (DAS) e após esse período as plântulas foram transferidas para vasos plásticos de capacidade de 2 kg com areia lavada e peneirada. Na omissão de alumínio (0,0 mg Al3+ L-1) o pH foi ajustado para 6,0. O experimento foi dividido em três etapas: 1) do 11º ao 14º DAS, as plantas foram irrigadas com solução completa diluída a 50% (pH 6,0); 2) do 15º ao 28º DAS, as plantas foram irrigadas com solução completa, modificada, com fósforo na concentração de 3,1 mg L-1 (pH 6,0); 3) do 29º ao 45º DAS, as plantas foram submetidas aos tratamentos com alumínio na solução nutritiva completa, modificada com concentração de fósforo de 3,1 mg L-1 e pH ajustado para 4,2. Aos 45 DAS foram avaliados: número de folhas, comprimento da parte aérea, das raízes e total, massa seca das raízes, das hastes e total além da área foliar. O delineamento experimental foi inteiramente casualizado com cinco repetições e os dados submetidos à análise de variância e estudo de regressão polinomial. O crescimento das plantas de rúcula é significativamente reduzido na presença do alumínio (AlCl3 ) em condições de solução nutritiva.

Aimed to evaluate the effects of aluminum in nutrient solution on growth of Eruca plants (Eruca sativa Mill.) under controlled conditions. We used aluminum trichloride, AlCl3, and the treatments: 0.0, 15.0, 30.0, 45.0 and 60.0 mg Al3 + L-1 solution. Eruca seeds were distributed phenolic foam which received distilled water for 10 days after sowing (DAS) and after this period the seedlings were transferred to plastic pots capacity of 2 kg washed sand and sieved. The omission of aluminum (Al3+ 0.0 mg L-1) the pH was adjusted to 6.0. The experiment was divided into three stages: 1) from 11 to the 14 DAS, the plants were irrigated with a solution diluted 50% (pH 6.0), 2) from 15 to 28 DAS, plants were irrigated with complete solution modified with phosphorus at a concentration of 3.1 mg L-1 (pH 6.0), 3) from 29 to the 45 DAS, the plants were treated with aluminum in the complete nutrient solution, modified with phosphorus concentration of 3,1 mg L-1 and pH adjusted to 4.2. At 45 DAS were evaluated: number of leaves, shoot length, root and total, dry mass of roots, stems and total leaf area as well. A completely randomized design with five replicates and the data submitted to analysis of variance and polynomial regression study. Plant growth rocket is significantly reduced in the presence of aluminum (AlCl3) under conditions.of.nutrient.solution

HERANÇA DA TOLERÂNCIA AO ALUMÍNIO EM TRIGO

Crosses and backcrosses were performed between the semi-dwarf cultivars IAC-24 and Anahuac, tolerant and sensitive to aluminum toxicity, respectively. Seedlings from the parents, F1 generation of the cross between them as well as from the backcrosses to both parents were evaluated in nutrient solutions containing 2 mg/l of Al3+. Progenies of F2 and F3 generations from the cross and progenies of F2 generation from the backcrosses were also studied. Plants that were able to show root regrowth of the central primary root in the complete nutrient solution after a treatment of 48 hours in solution containing 2 mg/l of Al3+ were considered tolerant. The cultivar IAC-24 differed from Anahuac by one pair of dominant genes for the tolerance to the presence of this aluminum concentration into the nutrient solution.

Cruzamentos e retrocruzamentos foram efetuados entre os cultivares de porte semi-anão IAC-24 e Anahuac, tolerante e sensível à toxicidade de alumínio, respectivamente. Plântulas dos parentais e da geração F1 do cruzamento entre eles bem como dos retrocruzamentos para ambos os parentais foram avaliadas em soluções nutritivas de tratamento contendo 2 mg/litro de Al3+. Progênies de gerações F2 e F3 do cruzamento e progênies F2 dos retrocruzamentos foram também avaliadas . A tolerância à toxicidade de alumínio foi medida pela capacidade de crescimento da raiz primária central em solução nutritiva completa, após um tratamento de 48 horas em solução contendo 2 mg/litro de Al3+. O cultivar IAC-24 diferiu do Anahuac por um par de genes dominantes para tolerância à presença dessa concentração de alumínio nas soluções nutritivas.

Herança da tolerância ao alumínio em trigo

Crosses and backcrosses were performed between the semi-dwarf cultivars IAC-24 and Anahuac, tolerant and sensitive to aluminum toxicity, respectively. Seedlings from the parents, F1 generation of the cross between them as well as from the backcrosses to both parents were evaluated in nutrient solutions containing 2 mg/l of Al3+. Progenies of F2 and F3 generations from the cross and progenies of F2 generation from the backcrosses were also studied. Plants that were able to show root regrowth of the central primary root in the complete nutrient solution after a treatment of 48 hours in solution containing 2 mg/l of Al3+ were considered tolerant. The cultivar IAC-24 differed from Anahuac by one pair of dominant genes for the tolerance to the presence of this aluminum concentration into the nutrient solution.

Cruzamentos e retrocruzamentos foram efetuados entre os cultivares de porte semi-anão IAC-24 e Anahuac, tolerante e sensível à toxicidade de alumínio, respectivamente. Plântulas dos parentais e da geração F1 do cruzamento entre eles bem como dos retrocruzamentos para ambos os parentais foram avaliadas em soluções nutritivas de tratamento contendo 2 mg/litro de Al3+. Progênies de gerações F2 e F3 do cruzamento e progênies F2 dos retrocruzamentos foram também avaliadas . A tolerância à toxicidade de alumínio foi medida pela capacidade de crescimento da raiz primária central em solução nutritiva completa, após um tratamento de 48 horas em solução contendo 2 mg/litro de Al3+. O cultivar IAC-24 diferiu do Anahuac por um par de genes dominantes para tolerância à presença dessa concentração de alumínio nas soluções nutritivas.

Efeitos do alumínio em pimenteiras do reino (Piper nigrum, L.)cultivadas em solução nutritiva

Black pepper (Piper nigrum, L.) is usually grown in soils of low natural fertility and high aluminum saturation. An experiment using young plants of the Guajarina cultivar grown in nutrient solution was carried out in order to verify the effects of aluminum on the growth and chemical composition and determine the concentration in the substrate which causes toxicity symptoms. Aluminum was added to the nutrient solution at the rates of 0, 5, 10, 15, 20 and 40 mg/L. The initial symptom of Al toxicity was a slower development of the roots, which were thicker than those of the control. Dry weight increased when aluminum supply increased from 0 to 15 ppm Al; correspondingly there was a higher uptake of P, K, Ca, Mg, Mn, Fe and AL It appears that black pepper is tolerant to Al concentrations as high as 20 mg/L. Higher rates cause nutritional disturbances and reduction in growth.

A pimenteira do reino (Piper nigrum, L.) vem sendo cultivada, em sua maior parte, em áreas com solos de baixa fertilidade natural, caracterizadas por baixa saturação por bases, alta saturação de alumínio e acidez elevada. Visando estudar os efeitos do alumínio sobre a cultura foi conduzido um experimento com a cultivar Guajarina em solução nutritiva. As doses de alumínio estudadas foram: 0; 5; 10; 15; 20 e 40 mg/L. O sintoma inicial de toxidez de alumínio foi caracterizado por um retardamento no crescimento radicular, com aumento no diâmetro das raízes. Observou-se efeito positivo do alumínio na produção de matéria seca com adição de até 15 mg/L na solução, o que correspondeu a maior absorção de P, K, Ca, Mg, Mn, Fe e AL Concluiu-se que a pimenteira é tolerante à presença de concentrações de Al inferiores a 20 mg/L no substrato. Doses superiores provocam distúrbios nutricionais com redução no crescimento da planta.

Efeitos do alumínio em pimenteiras do reino (Piper nigrum, L.)cultivadas em solução nutritiva

Black pepper (Piper nigrum, L.) is usually grown in soils of low natural fertility and high aluminum saturation. An experiment using young plants of the Guajarina cultivar grown in nutrient solution was carried out in order to verify the effects of aluminum on the growth and chemical composition and determine the concentration in the substrate which causes toxicity symptoms. Aluminum was added to the nutrient solution at the rates of 0, 5, 10, 15, 20 and 40 mg/L. The initial symptom of Al toxicity was a slower development of the roots, which were thicker than those of the control. Dry weight increased when aluminum supply increased from 0 to 15 ppm Al; correspondingly there was a higher uptake of P, K, Ca, Mg, Mn, Fe and AL It appears that black pepper is tolerant to Al concentrations as high as 20 mg/L. Higher rates cause nutritional disturbances and reduction in growth.

A pimenteira do reino (Piper nigrum, L.) vem sendo cultivada, em sua maior parte, em áreas com solos de baixa fertilidade natural, caracterizadas por baixa saturação por bases, alta saturação de alumínio e acidez elevada. Visando estudar os efeitos do alumínio sobre a cultura foi conduzido um experimento com a cultivar Guajarina em solução nutritiva. As doses de alumínio estudadas foram: 0; 5; 10; 15; 20 e 40 mg/L. O sintoma inicial de toxidez de alumínio foi caracterizado por um retardamento no crescimento radicular, com aumento no diâmetro das raízes. Observou-se efeito positivo do alumínio na produção de matéria seca com adição de até 15 mg/L na solução, o que correspondeu a maior absorção de P, K, Ca, Mg, Mn, Fe e AL Concluiu-se que a pimenteira é tolerante à presença de concentrações de Al inferiores a 20 mg/L no substrato. Doses superiores provocam distúrbios nutricionais com redução no crescimento da planta.