Estresse hídrico durante a fase reprodutiva de duas linhagens de soja

The objective of this work was to evaluate the effects of drought stress in the reproductive stage (R3) on the physiological parameters and grain yield of two soybean (Glycine max) lines. The Vx-08-10819 and Vx-08-11614 soybean lines were grown in a greenhouse, where they were irrigated until they reached the R3 development stage. During three days, the weight of the pots was monitored daily in order to maintain 100, 60, and 40% field capacity (control and moderate and severe stress, respectively). The parameters gas exchange and chlorophyll a fluorescence, as well as chloroplast pigments, osmoregulatory solutes and antioxidant enzymes, were determined. After stress, the plants were rehydrated until the end of the reproductive stage (R8), to evaluate grain yield. Vx-08-10819 showed traits that contributed to drought tolerance, such as better water-use efficiency, modulation of leaf area, and enzymatic activity, as well as a more efficient photosynthetic apparatus and a lower lipid peroxidation rate than Vx-08-11614. In addition, Vx-08-10819 maintained its productivity even after the severe water deficit. By contrast, water limitations affected negatively the productivity of Vx-08-11614. The Vx-08-10819 soybean line can efficiently withstand drought periods during the reproductive stage, without any interferences on final grain yield.O objetivo deste trabalho foi avaliar os efeitos do estresse hídrico no estádio reprodutivo (R3) sobre os parâmetros fisiológicos e o rendimento de grãos de duas linhagens de soja (Glycine max). As linhagens de soja Vx-08-10819 e Vx-08-11614 foram cultivadas em casa de vegetação, onde foram irrigadas até atingirem o estágio de desenvolvimento R3. Durante três dias, o peso dos vasos foi monitorado diariamente para manter 100, 60 e 40% da capacidade de campo (controle e estresses moderado e severo, respectivamente). Foram determinados os parâmetros trocas gasosas e fluorescência da clorofila a, além dos pigmentos cloroplastídicos, solutos osmorregulatórios e enzimas antioxidantes. Após o estresse, as plantas foram reidratadas até o final do estádio reprodutivo (R8) para avaliar o rendimento de grãos. Vx-08-10819 apresentou características que contribuíram para a tolerância à seca, como melhor eficiência no uso da água, modulação da área foliar e atividade enzimática, bem como aparato fotossintético mais eficiente e menor peroxidação lipídica que Vx-08-11614. Além disso, Vx-08-10819 manteve sua produtividade mesmo após deficiência hídrica severa. Em contraste, as limitações hídricas afetaram negativamente a produtividade de Vx-08-11614. A linhagem de soja Vx-08-10819 pode suportar eficientemente períodos de seca durante o estádio reprodutivo, sem que haja interferência no rendimento final de grãos

GROWTH, DEVELOPMENT, AND PHOTOSYNTHETIC PERFORMANCE OF TWO SOYBEAN LINEAGES IN RESPONSE TO DROUGHT

Drought stress is a common environmental factor that constrains plants from expressing their ecophysiological potential, disrupting various physiological and biochemical processes. Hence, the objective of this work was to evaluate the growth, development and photosynthetic performance under drought in the vegetative phenological stage of soybean in two lineages with potential difference tolerance to this abiotic stress, lineages (‘Vx-08-10819’ and ‘Vx-08-11614’. For this purpose, biometric traits of development, relative water content in leaves, photosynthetic pigments, gas exchange, and chlorophyll a fluorescence were evaluated. The experimental design was a randomized block design with 4 replications and arranged in a 2 × 3 factorial scheme, comprising of two soybean lineages (Vx-08-10819 and Vx-08-11614) in combination with three water availability [100% (control), 60%, and 40% of field capacity]. Relative water content in leaves, total leaf area, and shoot dry weight of lineage Vx-08-10819 were not changed after exposure to drought. Besides that, photosynthetic capacity of lineage Vx-08-10819 was less affected than lineage Vx-08-11614 to drought, showing that this lineage is tolerant to this abiotic stress in at vegetative stage V4. Keywords: chlorophylls; gas exchange; Glycine max (L.) Merr; water relations.   Crescimento, desenvolvimento e desempenho fotossintético de duas linhagens de soja em resposta à seca   RESUMO: O estresse hídrico é um fator ambiental comum que impede as plantas de expressarem seu potencial ecofisiológico, interrompendo vários processos fisiológicos e bioquímicos. Portanto, o objetivo deste trabalho foi avaliar o crescimento, o desenvolvimento e o desempenho fotossintético sob seca na fase fenológica vegetativa da soja em duas linhagens com potencial diferença na tolerância a este estresse abiótico, as linhagens Vx-08-10819 e Vx-08-11614. Para tanto, foram avaliadas características biométricas de desenvolvimento, teor relativo de água nas folhas, pigmentos fotossintéticos, trocas gasosas e fluorescência da clorofila a. O delineamento experimental foi em blocos casualizados com 4 repetições e dispostos em esquema fatorial 2 × 3, composto por duas linhagens de soja (Vx-08-10819 e Vx-08-11614) em combinação com três disponibilidades hídricas [100% (controle), 60% e 40% da capacidade de campo]. O conteúdo relativo de água nas folhas, a área foliar total e o peso seco da parte aérea da linhagem Vx-08-10819 não foram alterados após a exposição à seca. Além disso, a capacidade fotossintética da linhagem Vx-08-10819 foi menos afetada do que a linhagem Vx-08-11614 à seca, mostrando que esta linhagem é tolerante à este estresse abiótico no estágio vegetativo V4. Palavras-chave: clorofilas; troca gasosa; Glycine max (L.) Merr; relações hídricas.Drought stress is a common environmental factor that constrains plants from expressing their ecophysiological potential, disrupting various physiological and biochemical processes. Hence, the objective of this work was to evaluate the growth, development and photosynthetic performance under drought in the vegetative phenological stage of soybean in two lineages with potential difference tolerance to this abiotic stress, lineages (‘Vx-08-10819’ and ‘Vx-08-11614’. For this purpose, biometric traits of development, relative water content in leaves, photosynthetic pigments, gas exchange, and chlorophyll a fluorescence were evaluated. The experimental design was a randomized block design with 4 replications and arranged in a 2 × 3 factorial scheme, comprising of two soybean lineages (Vx-08-10819 and Vx-08-11614) in combination with three water availability [100% (control), 60%, and 40% of field capacity]. Relative water content in leaves, total leaf area, and shoot dry weight of lineage Vx-08-10819 were not changed after exposure to drought. Besides that, photosynthetic capacity of lineage Vx-08-10819 was less affected than lineage Vx-08-11614 to drought, showing that this lineage is tolerant to this abiotic stress in at vegetative stage V4. Keywords: chlorophylls; gas exchange; Glycine max (L.) Merr; water relations.   Crescimento, desenvolvimento e desempenho fotossintético de duas linhagens de soja em resposta à seca   RESUMO: O estresse hídrico é um fator ambiental comum que impede as plantas de expressarem seu potencial ecofisiológico, interrompendo vários processos fisiológicos e bioquímicos. Portanto, o objetivo deste trabalho foi avaliar o crescimento, o desenvolvimento e o desempenho fotossintético sob seca na fase fenológica vegetativa da soja em duas linhagens com potencial diferença na tolerância a este estresse abiótico, as linhagens Vx-08-10819 e Vx-08-11614. Para tanto, foram avaliadas características biométricas de desenvolvimento, teor relativo de água nas folhas, pigmentos fotossintéticos, trocas gasosas e fluorescência da clorofila a. O delineamento experimental foi em blocos casualizados com 4 repetições e dispostos em esquema fatorial 2 × 3, composto por duas linhagens de soja (Vx-08-10819 e Vx-08-11614) em combinação com três disponibilidades hídricas [100% (controle), 60% e 40% da capacidade de campo]. O conteúdo relativo de água nas folhas, a área foliar total e o peso seco da parte aérea da linhagem Vx-08-10819 não foram alterados após a exposição à seca. Além disso, a capacidade fotossintética da linhagem Vx-08-10819 foi menos afetada do que a linhagem Vx-08-11614 à seca, mostrando que esta linhagem é tolerante à este estresse abiótico no estágio vegetativo V4. Palavras-chave: clorofilas; troca gasosa; Glycine max (L.) Merr; relações hídricas

Study of drought resistance in soybean: physiological, metabolic and molecular evaluations

A soja é a principal planta leguminosa cultivada no mundo. A elevada demanda pela soja se justifica na importância do seu grão para a alimentação humana e animal. Entretanto, o seu rendimento pode ser afetado pelos estresses abióticos, sendo a seca o fator ambiental mais impactante na sua produtividade. Assim, o objetivo deste trabalho foi identificar e caracterizar linhagens de soja contrastantes para a resistência à seca, mediante avaliações fisiológicas, bioquímicas e moleculares. Quatro genótipos de soja foram utilizados nos experimentos: cultivar Embrapa 48 (E48), referencial de tolerância ao déficit hídrico e 3 linhagens provenientes do Programa de Melhoramento da Soja da Universidade Federal de Viçosa, previamente caracterizadas como sensível (11644) e tolerantes (11377 e 13241) ao déficit hídrico. As plantas foram avaliadas em três condições: 1) plena irrigação (controle), 2) déficit hídrico (DH) após suspensão da irrigação do solo até atingir potencial hídrico foliar na antemanhã de -1,5 MPa, e 3) reidratação por 3 dias (RH), posterior ao déficit hídrico. Os genótipos 11644, 11377 e E48 alcançaram o potencial hídrico de -1,5 MPa após 8 dias de suspensão da irrigação, contra 10 dias na linhagem 13241. Menor área foliar constitutiva e maior incremento na concentração de ácido abscísico (ABA) foliar permitiram a linhagem 13241 exibir a menor redução no Teor Relativo de Água (TRA), após o déficit hídrico. De maneira inversa, a linhagem 11644 apresentou as maiores reduções no TRA e suculência foliar. O processo fotossintético foi igualmente inibido pelo déficit hídrico em todos os genótipos. Porém, o cultivar tolerante E48 exibiu maior incremento na eficiência no uso da água (EUA). O acúmulo de osmolitos foi mais expressivo nas linhagens 11377 e 13241. Nas análises dos componentes antioxidativos, a linhagem 11644 obteve maiores incrementos na concentração de espécies reativas de oxigênio (ROS), maior nível de peroxidação de lipídios e menor atividade das enzimas antioxidantes catalase (CAT) e dismutase do superóxido (SOD). Adicionalmente nessa linhagem, a glutationa teve limitada atuação contra o estresse oxidativo induzido pelo déficit hídrico. Na linhagem 13241, maiores incrementos na atividade da CAT, SOD, peroxidase do ascorbato (APX) e peroxidase da glutationa (GPX) indicam a participação efetiva dessas enzimas antioxidantes na defesa contra o estresse. No cultivar E48, metabólitos antioxidantes, como a glutationa e ascorbato, demonstraram papel mais importante. A partir desses resultados, pôde-se corroborar que dentre as linhagens, a 11644 foi a mais sensível ao déficit hídrico, enquanto a 13241 foi a mais tolerante. Por essa razão, a linhagem 11377 foi excluída das análises de perfil metabólico e expressão gênica. A avaliação do perfil metabólico demonstrou que a resposta dos genótipos ao déficit hídrico foi direcionada para o ajustamento osmótico, pelo aumento dos aminoácidos, carboidratos e poliaminas. Contudo, não foi possível por meio do perfil metabólico discernir níveis de tolerância ao déficit hídrico entre os genótipos. A análise da expressão gênica via PCR real time foi realizada somente com as linhagens 11644 e 13241. Os resultados não apresentaram diferenças significativas para a maioria dos genes avaliados, mas foi possível identificar um padrão evidente de resposta ao se observar as médias dos resultados. Genes diretamente envolvidos com: mecanismos de resistência à seca, biossíntese do ABA, defesas antioxidantes e fatores de transcrição responsivos a estresses, apresentaram aumento na expressão na linhagem 13241. Em conclusão, a linhagem 13241 apresenta maior tolerância ao déficit hídrico em comparação a 11377, e ainda, se equipara na maioria das respostas com aquelas apresentadas pelo cultivar E48. Por outro lado, os resultados evidenciam que a linhagem 11644 se mostra sensível ao déficit hídrico. Conclui-se também que a reidratação das plantas por 72 horas propiciou a recuperação da maioria dos parâmetros fisiológicos e bioquímicos para os mesmos níveis do tratamento controle. Todos esses resultados são importantes para a identificação e caracterização de mecanismos de tolerância de plantas cultivadas, que posteriormente poderão ser utilizados em Programas de Melhoramento da Qualidade da Soja, visando à geração de genótipos mais resistentes à seca.Soybean is the main oilseed crop grown in the world. The high demand for soybeans is justified by the importance of their grain in human and animal nutrition. However, its yield can be affected by the abiotic stresses, being the drought the most impacting environmental factor in its productivity. However, its yield can be affected by the abiotic stresses, being the drought the most impacting environmental factor in its productivity. Therefore, the goal of this work was to identify and characterize contrasting soybean lines for drought resistance, through physiological, biochemical and molecular evaluations. Four soybean genotypes were used in the experiments: cultivar Embrapa 48 (E48), reference for tolerance to water deficit and 3 lines from the Programa de Melhoramento da Soja da Universidade Federal de Viçosa, one previously characterized as sensitive (11644) and two tolerant (11377 and 13241) to the water deficit. Plants were evaluated under three conditions: 1) full irrigation (control), 2) water deficit (DH) after suspension of soil irrigation until reaching leaf water potential in the morning of -1.5 MPa, and 3) Rehydration for 3 days (RH), after the water deficit. The genotypes 11644, 11377 and E48 reached the water potential of -1.5 MPa after 8 days of irrigation suspension, versus 10 days in the line 13241. Lower constitutive leaf area and greater increase in abscissic acid (ABA) foliar concentration allowed the line 13241 exhibits the lowest reduction in Relative Water Content (TRA), after water deficit. Conversely, the line 11644 presented the greatest reductions in TRA and foliar succulence. The photosynthetic process was similarly inhibited by water deficit in all genotypes, through intense diffusive restriction. However E48 tolerant genotype exhibited a greater increase in water use efficiency (WUE). The accumulation of osmolytes was more expressive in lines 11377 and 13241. In the analysis of the antioxidative components line 11644 showed higher increases in the concentration of reactive oxygen species (ROS), higher level of lipid peroxidation and lower activity of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). Additionally, glutathione had limited action against the oxidative stress induced by the water déficit in line11644. In line 13241, greater increases in the activity of CAT, SOD, ascorbate peroxidase (APX) and glutathione peroxidase (GPX) indicate the effective participation of antioxidative enzymes in defense against stress. In E48 antioxidant metabolites, such as glutathione and ascorbate have been shown to play a more important role. From these results it was possible to corroborate that 11644 is the most sensitive line to the water deficit, whereas the 13241 is the most tolerant. Therefore, line11377 was excluded from metabolic profile and gene expression analyzes. Metabolic adjustment demonstrated that plants responses to the water deficit was directed to the osmotic adjustment by the increase of amino acids, carbohydrates and polyamines. However, it was not possible through the metabolic profile to discern levels of tolerance to water deficit among genotypes. Gene expression analysis via real time PCR was performed only with the lines 11644 and 13241. The results did not showed significant differences for most evaluated genes, but it was possible to identify an obvious response pattern when observing the results. Genes directly involved in drought resistance mechanisms, such as ABA biosynthesis, antioxidant defenses and stress-responsive transcription factors, apparently have most strongly induced expression in line 13241. In conclusion, line 13241 is more tolerant to water deficit than 11377, and most of its responses match those of tolerant reference genotype E48. Line 11644 is a soybean genotype sensitive to water deficit. It was also concluded that the plants rehydration for 72 hours provided the recovery of physiological and biochemical parameters for the same levels of control treatment. All these results are important for the identification and characterization of tolerance mechanisms of cultivated plants, which can later be used in Soybean Quality Improvement Programs, aiming at the generation of more drought resistant genotypes.Conselho Nacional de Desenvolvimento Científico e Tecnológic

Answers the antioxidant system and the glutathione metabolism in Salvinia molesta DS Mitchell (Salviniaceae) submitted to arsenite

Com o objetivo de avaliar os efeitos do AsIII no metabolismo antioxidativo de Salvinia molesta, indivíduos dessa espécie foram expostos às concentrações de 0, 5, 10 e 20 μM desse elemento em solução nutritiva, permanecendo sob tratamento por 24 h para as análises bioquímicas e 96 h para verificar a absorção de As, a taxa de crescimento relativo (TCR) e a sintomatologia visual. Plantas de S. molesta acumularam As nas folhas submersas e nas flutuantes, resultando em redução na TCR desses órgãos. Sintomas visuais, como clorose e necrose aumentaram com o incremento na concentração do poluente e tempo de exposição aos tratamentos. As respostas antioxidativas diferiram entre folhas flutuantes e folhas submersas, havendo nestas últimas, redução na atividade das enzimas dismutase do superóxido e catalase em plantas expostas a maior concentração de AsIII. Com isso, houve aumento na produção de espécies reativas de oxigênio nas folhas submersas e consequentes danos em membranas celulares. Nas folhas flutuantes, verificou-se atividade absoluta mais elevada das enzimas antioxidativas (catalase, peroxidase total, peroxidase do ascorbato e dismutase do superóxido) e menor acúmulo de As, em comparação com as folhas submersas. Em conjunto, esses fatores podem ser os responsáveis pela ausência de danos significativos em membranas celulares e de alterações no conteúdo de pigmentos cloroplastídicos nas folhas flutuantes. O teor de glutationa total e a atividade de algumas enzimas envolvidas no seu metabolismo, também foram alterados em resposta ao As III em S. molesta. A presença do poluente estimulou, tanto em folhas flutuantes, quanto nas folhas submersas, incrementos nas concentrações de glutationa total e na atividade da sintetase da ɣ-glutamilcisteína. As enzimas peroxidase da glutationa e sulfotransferase da glutationa, também apresentaram incrementos em suas atividades em ambos os órgãos avaliados, enquanto a redutase da glutationa aumentou somente nas folhas submersas. De modo geral, as folhas flutuantes demonstraram maior tolerância ao As do que as folhas submersas. No entanto, essa resposta diferenciada entre os órgãos necessita de estudos adicionais para ser esclarecida. O tempo de exposição aos tratamentos e a concentração de AsIII influenciaram nas respostas das plantas e indicam a necessidade de novas pesquisas, no sentido de caracterizar os efeitos desses fatores no metabolismo antioxidativo de S. molesta e definir o seu potencial como espécie fitorremediadora de As.In order to evaluate the effects of AsIII in antioxidant metabolism of Salvinia molesta, individuals of this specie were exposed to concentrations of 0, 5, 10 and 20 μM of this element in nutrient solution, remaining under treatment for 24 h to biochemical analyzes and 96 h to verify As absorption, relative growth rate (RGR), and visual symptoms. S. molesta plants accumulated As in the submerged and on the floating leaves, resulting in reduction in the RGR of this organs. Visual symptoms, such as chlorosis and necrosis increased with the increase in pollutant concentration and duration of exposure to treatments. Antioxidative responses differ between floating leaves and submerged leaves, having is this last, reduction in the activity of the enzymes superoxide dismutase and catalase in higher concentrations of As III. This led to increased production of reactive oxygen species and consequent damage to cell membranes in the submerged leaves. In the floating leaves, it was found the highest absolute activity of antioxidant enzymes (catalase, total peroxidase, ascorbate peroxidase and superoxide dismutase) and less accumulation of As, as compared to the submerged leaves. Together, these factors may be responsible for the absence of significant cell membranes damage and changes in the content of chloroplastidic pigments in floating leaves. The glutathione content and the activity of some enzymes involved in its metabolism were also changes in response to As III in S. molesta. The presence of pollutant stimulated both in floating leaves and in the submerged leaves, increases in concentrations of total glutathione and the ɣ-glutamylcysteine synthetase activity. The glutathione peroxidase and glutathione sulfotransferase also showed increases in their activities, while glutathione reductase showed no change in the floating leaves, but increased significantly in the submerged leaves. In general, the floating leaves showed greater tolerance than the submerged leaves. However, this differential response between the organs needs further studies to be clarified. The exposure time and the concentration of AsIII influenced in plant responses and indicate the need for further research, in order to characterize the effects of these factors in antioxidative metabolism of S. molesta and define its potential as As phytoremediation species.Fundação de Amparo a Pesquisa do Estado de Minas Gerai

Role of glutathione in tolerance to arsenite in Salvinia molesta, an aquatic fern

ABSTRACT In many plant species, tolerance to toxic metals is highly dependent on glutathione, an essential metabolite for cellular detoxification. We evaluated the responses of glutathione metabolism to arsenite (AsIII) in Salvinia molesta, an aquatic fern that has unexplored phytoremediation potential. Plants were exposed to different AsIII concentrations in nutrient solution for 24 h. AsIII caused cell membrane damage to submerged leaves, indicating oxidative stress. There was an increase in the glutathione content and ϒ-glutamylcysteine synthetase enzyme activity in the submerged and floating leaves. The glutathione peroxidase and glutathione sulfotransferase enzymes also showed increased activity in both plant parts, whereas glutathione reductase only showed increased activity in the submerged leaves. These findings suggest an important role for glutathione in the protection of S. molesta against the toxic effects of AsIII, with more effective tolerance responses in the floating leaves

Potassium Phosphite Induces Tolerance to Water Deficit Combined with High Irradiance in Soybean Plants

Changes in plant metabolism due to water deficit combined with other stresses, such as high irradiance and high temperatures, cause damage to the physiology and development of crops, which can lead to significant yield losses. The aim of this study was to determine the potential of potassium phosphite (PP) to induce tolerance to water deficit combined with high irradiance in soybean plants. The experiment was carried out in an acclimatized growth chamber. Soybean plants, upon reaching the R1 developmental stage, received the following treatments: PP application (0 L ha−1–control; 0.6 L ha−1 PP; and 1.2 L ha−1 PP), two levels of PAR irradiance (650 µmol m−2 s−1–control; and 1500 µmol m−2 s−1–high irradiance (HI)), and three water availability levels (90% of field capacity (FC), and water deficit at 40% FC and 50% FC). The treatments were maintained for 12 days. The PP increased the photosynthetic rate of plants submitted to a dosage of 1.2 L ha−1 and stresses of 50% FC + HI. PP also decreased the intensity of lipid peroxidation, and rate of electrolyte leakage, which suggests stability of cell membranes. These responses may have occurred due to the activation of the antioxidant enzymes superoxide dismutase and peroxidase. Furthermore, the application of PP increased the proline concentrations, suggesting osmotic adjustment in response to stress. These results provide the first record of PP-induced tolerance in plants under combined water and HI stresses. PP proves to be a potential alternative method to reduce the harmful effects caused by the combined stresses of water deficit and high irradiance in soybean

Morpho-Physiological Traits and Oil Quality in Drought-Tolerant <i>Raphanus sativus</i> L. Used for Biofuel Production

Raphanus sativus L. is a potential source of raw material for biodiesel fuel due to the high oil content in its grains. In Brazil, this species is cultivated in the low rainfall off-season, which limits the productivity of the crop. The present study investigated the effects of water restriction on the physiological and biochemical responses, production components, and oil quality of R. sativus at different development stages. The treatments consisted of 100% water replacement (control), 66%, and 33% of field capacity during the phenological stages of vegetative growth, flowering, and grain filling. We evaluated characteristics of water relations, gas exchange, chlorophyll a fluorescence, chloroplast pigment, proline, and sugar content. The production components and chemical properties of the oil were also determined at the end of the harvest cycle. Drought tolerance of R. sativus was found to be mediated primarily during the vegetative growth stage by changes in photosynthetic metabolism, stability of photochemical efficiency, increased proline concentrations, and maintenance of tissue hydration. Grain filling was most sensitive to water limitation and showed a reduction in yield and oil content. However, the chemical composition of the oil was not altered by the water deficit. Our data suggest that R. sativus is a drought-tolerant species

Morphoanatomical, Physiological, and Biochemical Indicators in <i>Lactuca sativa</i> L. Germination and Growth in Response to Fluoride

Fluoride is one of the main phytotoxic environmental pollutants, and high concentrations (10–30 mg L−1) are commonly detected in surface and groundwater. Little, however, is known about the effects of this pollutant on crops that require irrigation during their development, which, in addition to phytotoxicity, may cause negative human health effects. Thus, the aim of this study was to characterize the effects of potassium fluoride (KF) on the germination of lettuce seeds and identify the physiological and anatomical markers of this pollutant’s action on plants exposed to it during growth. Initially, lettuce seeds were sown in gerboxes and soaked in solutions containing 0 mg L−1, 10 mg L−1, 20 mg L−1, and 30 mg L−1 KF. Plants grown in a greenhouse were treated daily with KF irrigation at the same KF concentrations for 40 days. KF exposure reduced the germination rate and germination speed index of lettuce seeds at 20 mg L−1 and 30 mg L−1, resulting in compromised root development at the highest KF concentration. Lettuce plants displayed a slight photosynthesis reduction and a significant photochemical efficiency decrease after exposures to all KF concentrations. Lower chlorophyll contents and nitrogen balance indices were observed in plants exposed to 30 mg L−1 KF. On the other hand, increases in phenolic compounds and malondialdehyde were noted with increasing KF concentrations. Lettuce plants can, therefore, accumulate fluoride in leaves when irrigated with KF-rich water. The investigated physiological and biochemical variables were proven to be adequate fluoride action biomarkers in lettuce plants and may become an important tool in the study of olericulture contaminants

Tolerance of Eugenia dysenterica to Aluminum: Germination and Plant Growth

Native Cerrado plants are exposed to soils with low pH and high availability of Al. In this study, we measured the Al content in adult plants, and investigated the effects of various Al doses on germination and early development of Eugenia dysenterica plants. For germination tests, the seeds were soaked in Al solution and evaluated for twenty days in growth chambers. In a second experiment, young plants were cultivated in hydroponic systems with various Al concentrations to evaluate the morphological, anatomical and physiological characteristics of E. dysenterica. Anatomical changes and low germinative vigor were observed in seeds germinated in 600 and 800 &mu;mol Al3+ L&minus;1. In the hydroponic system, 200 &mu;mol Al3+ L&minus;1 stimulated root growth in young plants. The activity of antioxidant enzymes and the accumulation of phenolic compounds were greatest at the highest Al doses, preventing changes in gas exchange and chlorophyll a fluorescence. Starch grain accumulation was noted in plant cells exposed to 200 and 400 &mu;mol Al3+ L&minus;1. Adult E. dysenterica trees also accumulated Al in leaves, bark and seeds. These data suggest that E. dysenterica is tolerant to Al