Showing papers in "Brazilian Journal of Plant Physiology in 2005"

Lead toxicity in plants

Abstract: Contamination of soils by heavy metals is of widespread occurrence as a result of human, agricultural and industrial activities. Among heavy metals, lead is a potential pollutant that readily accumulates in soils and sediments. Although lead is not an essential element for plants, it gets easily absorbed and accumulated in different plant parts. Uptake of Pb in plants is regulated by pH, particle size and cation exchange capacity of the soils as well as by root exudation and other physico-chemical parameters. Excess Pb causes a number of toxicity symptoms in plants e.g. stunted growth, chlorosis and blackening of root system. Pb inhibits photosynthesis, upsets mineral nutrition and water balance, changes hormonal status and affects membrane structure and permeability. This review addresses various morphological, physiological and biochemical effects of Pb toxicity and also strategies adopted by plants for Pb-detoxification and developing tolerance to Pb. Mechanisms of Pb-detoxification include sequestration of Pb in the vacuole, phytochelatin synthesis and binding to glutathione and aminoacids etc. Pb tolerance is associated with the capacity of plants to restrict Pb to the cell walls, synthesis of osmolytes and activation of antioxidant defense system. Remediation of soils contaminated with Pb using phytoremediation and rhizofiltration technologies appear to have great potential for cleaning of Pb-contaminated soils.

Cadmium toxicity in plants

Abstract: Heavy metals are important environmental pollutants and their toxicity is a problem of increasing significance for ecological, evolutionary, nutritional, and environmental reasons. Plants posses homeostatic cellular mechanisms to regulate the concentration of metal ions inside the cell to minimize the potential damage that could result from the exposure to nonessential metal ions. This paper summarizes present knowledge in the field of higher plant responses to cadmium, an important environmental pollutant. Knowledge concerning metal toxicity, including mechanisms of cadmium homeostasis, uptake, transport and accumulation are evaluated. The role of the cell wall, the plasma membrane and the mycorrhizas, as the main barriers against cadmium entrance to the cell, as well as some aspects related to phytochelatin-based sequestration and compartmentalization processes are also reviewed. Cadmium-induced oxidative stress was also considered as one of the most studied topics of cadmium toxicity.

Copper in plants

Abstract: Copper is an essential metal for normal plant growth and development, although it is also potentially toxic. Copper participates in numerous physiological processes and is an essential cofactor for many metalloproteins, however, problems arise when excess copper is present in cells. Excess copper inhibits plant growth and impairs important cellular processes (i.e., photosynthetic electron transport). Since copper is both an essential cofactor and a toxic element, involving a complex network of metal trafficking pathways, different strategies have evolved in plants to appropriately regulate its homeostasis as a function of the environmental copper level. Such strategies must prevent accumulation of the metal in the freely reactive form (metal detoxification pathways) and ensure proper delivery of this element to target metalloproteins. The mechanisms involved in the acquisition of this essential micronutrient have not been clearly defined although a number of genes have recently been identified which encode potential copper transporters. This review gives a briefly overview of the current understanding of the more important features concerning copper toxicity and tolerance in plants, and brings information of recent findings on copper trafficking including copper detoxification factors, copper transporters and copper chaperones.

Chromium stress in plants

Abstract: The article presents an overview of the mechanism of chromium stress in plants. Chromium is known to be a toxic metal that can cause severe damage to plants and animals. Chromium-induced oxidative stress involves induction of lipid peroxidation in plants that causes severe damage to cell membranes. Oxidative stress induced by chromium initiates the degradation of photosynthetic pigments causing decline in growth. High chromium concentration can disturb the chloroplast ultrastructure thereby disturbing the photosynthetic process. Like copper and iron, chromium is also a redox metal and its redox behaviour exceeds that of other metals like Co, Fe, Zn, Ni, etc. The redox behaviour can thus be attributed to the direct involvement of chromium in inducing oxidative stress in plants. Chromium can affect antioxidant metabolism in plants. Antioxidant enzymes like SOD, CAT, POX and GR are found to be susceptible to chromium resulting in a decline in their catalytic activities. This decline in antioxidant efficiency is an important factor in generating oxidative stress in plants under chromium stress. However, both metallothioneins and organic acids are important in plants as components of tolerance mechanisms and are also involved in detoxification of this toxic metal.

Transport and detoxification of manganese and copper in plants

Abstract: Heavy metals like Mn and Cu, though essential for normal plant growth and development, can be toxic when present in excess in the environment. For normal plant growth maintenance of metal homeostasis is important. Excess uptake of redox active elements causes oxidative destruction. Thus, uptake, transport and distribution within the plant must be strongly controlled. Regulation includes precisely targeted transport from the macro-level of the tissue to the micro-level of the cell and organelles. Membrane transport systems play very important roles in metal trafficking. This review provides a broad overview of the long distance and cellular transport as well as detoxification and homeostasis mechanisms of Mn and Cu, which are essential micronutrients but extremely toxic at elevated concentrations.

Recent advances in aluminum toxicity and resistance in higher plants

Abstract: Aluminum toxicity is a major soil constraint to food and biomass production throughout the world. Considerable advances in the understanding of the mechanism of resistance involving exudation of organic acids have been made in recent years. However, despite intense research efforts, there are many aspects of Al toxicity that remain unclear. This article reviews the features of the chemistry of Al relevant to its toxicity followed by an examination of the mechanisms of toxicity and resistance. Emphasis, however, is given to the mechanisms of Al toxicity, since resistance has been covered recently by several reviews. Some topics which are specifically discussed in this review are: a) The possible role of cellular effects of low pH in Al toxicity, which has been largely ignored and needs to be addressed; b) The relevance of non-genotypic (cell-to-cell) variations in sensitivity to Al; c) Evidence indicating that although Al may well exert its toxic effects in the cell wall, it is highly unlikely that Al does so in a non-specific manner by mere exchangeable binding; and d) The hypothesis that the primary target of Al toxicity resides in the cell wall-plasma membrane-cytoskeleton (CW-PM-CSK) continuum has the potential to integrate and conciliate much of the apparently conflicting results in this field.

Phytoremediation: green technology for the clean up of toxic metals in the environment

Abstract: The contamination of the environment by toxic metals poses a threat for "Man and biosphere", reducing agricultural productivity and damaging the health of the ecosystem. In developed nations, this problem is being addressed and solved to some extent by using "green technology" involving metal tolerant plants, to clean up the polluted soils. The use of naturally occurring metal tolerant plants and the application of genetic manipulation, should hasten the process of transferring this technology from laboratory to field. Therefore, it is essential to investigate and understand how plants are able to tolerate toxic metals and to identify which metabolic pathways and genes are involved in such a process. Recent advances in knowledge derived from the "omics", have considerable potential in developing this green technology. However, strategies to produce genetically altered plants to remove, destroy or sequester toxic metals from the environment and the long-term implications, must be investigated carefully.

Cadmium-Zinc interactions in a hydroponic system using Ceratophyllum demersum L.: adaptive ecophysiology, biochemistry and molecular toxicology

Abstract: The interaction between an essential micronutrient, Zn and a toxic non-essential element, Cd has been comprehensively reviewed based on our experiments conducted with Ceratophyllum demersum L. in a hydroponic system. Since Cd and Zn belong to the group IIB transition elements and show similarities in chemistry, geochemistry and environmental properties, it would be one of the elemental pairs of choice to investigate metal-metal interactions. Evidence in support of the protective role of Zn against Cd toxicity in Ceratophyllum demersum L. is presented in this review. Based on our experimental results, we conclude that the antioxidant properties of Zn play an important role in counteracting Cd toxicity.

Dietary intake and health effects of selected toxic elements

Abstract: Anthropogenic activities have being contributing to the spread of toxic chemicals into the environment, including several toxic metals and metalloids, increasing the levels of human exposure to many of them. Contaminated food is an important route of human exposure and may represent a serious threat to human health. This mini review covers the health effects caused by toxic metals, especially Cd, Hg, Pb and As, the most relevant toxic elements from a human health point of view.

The influence of water management and environmental conditions on the chemical composition and beverage quality of coffee beans

Abstract: The influence of environmental conditions and irrigation on the chemical composition of green coffee beans and the relationship of these parameters to the quality of the beverage were investigated in coffee plantations in the regions of Adamantina, Mococa and Campinas, in the state of Sao Paulo, Brazil. The chemical composition and physical aspects of green coffee beans produced in the three regions were related through Principal Component Analyses (PCA) to the quality of beverage, as determined by sensorial and electronic analyses. The chemical composition was affected by the environmental conditions. Some differences in cup quality were detected by the electronic method but not by cup tasting. Irrigation was not a major factor affecting chemical composition, since there were few differences in relation to non-irrigated coffee plants. The production site appeared to be the main influencing factor on biochemical composition. A pronounced difference was observed in Adamantina, where annual average air temperature was 1.6-2.4oC warmer than in the other two areas and about 3.5oC above to the optimal limit for coffee cultivation.

Growth, photosynthesis and stress indicators in young rosewood plants (Aniba rosaeodora Ducke) under different light intensities

Abstract: Aniba rosaeodora is an Amazonian tree species that belongs to the family Lauraceae. Due to intense exploitation for extraction of essential oils (mainly linalol), A. rosaeodora is now considered an endangered species. On the other hand, there is little information about its ecophysiology which would be useful to support future forest planting programs. Hence, the effect of different light intensities on the growth and photosynthetic characteristics of young plants of A. rosaeodora was studied. Nine-month-old plants were subjected to four light treatments (T1= 10 a 250 µmol.m-2.s-1 / control; T2=500 to 800, T3=700 to 1000 and T4=1300 to 1800 µmol.m-2.s-1 / full sunlight). Allometric variables, gas exchange, contents of pigments and chlorophyll a fluorescence were analysed. As to the relative growth rates, it was found that plants of A. rosaeodora showed higher biomass accumulation when grown under intermediary irradiance conditions (T2). The best photosynthetic performance was achieved under conditions of T3. When growth was correlated with photosynthesis, it was found that plants under treatments T2 and T3 presented better responses in comparison with the lowest (T1) and highest (T4) light extremes. The highest pigment contents were obtained for plants in the shade (T1) and the lowest for those exposed to full sunlight (T4). The photochemical efficiency of photosystem II (Fv/Fm) was found that only plants in the shade treatment (T1) presented no stress from high irradiance. These findings suggest that both treatments (T1 and T4) altered the function of the A. rosaeodora plants, inhibiting photosynthesis and growth. Plants of A. rosaeodora developed photo-protection mechanisms under full sunlight. However, the species presented better photosynthetic response and biomass gain under intermediary irradiance conditions, displaying relative physiological plasticity, during the seedling phase.

Changes in nitrate reductase activity and oxidative stress response in the moss Polytrichum commune subjected to chromium, copper and zinc phytotoxicity

Abstract: The main aim of this paper was to investigate the effect of chromium (Cr), copper (Cu) and zinc (Zn) on nitrate reductase (NR) activity and oxidative stress responses in the moss Polytrichum commune. Cr, Cu and Zn resulted in the inhibition of NR activity. A decline in total chlorophyll content was observed after 24 and 48 h of metal treatment. Accumulation of the metals showed a dose and time dependent increase. High accumulation of Cu, Cr and Zn were seen in moss shoots after 24 and 48 h of treatment. Treatment of Cr, Cu and Zn for 24 or 48 h resulted in the increase of malondialdehyde (MDA) content in moss shoots. The highest increase was observed in shoots under Cu treatment followed by Cr and Zn. The MDA content was significantly higher after 48h. Antioxidant enzymes viz., catalase (CAT), guaiacol peroxidase (GPx), glutathione reductase (GR) and superoxide dismutase (SOD) were affected by elevated concentrations of the three metals. Increase in the activity of CAT, GR and SOD was seen after 24 and 48 h of treatment. GPx activity declined under Cr treatment. However, under Cu and Zn, an increase in GPx was seen after 24 h and 48 h of treatment. For Zn, the antioxidant efficiency was less affected as compared to Cr and Cu. The response of Polytrichum commune to toxic concentrations of Cr, Cu and Zn appears to induce oxidative damage as observed by the increase in MDA content and antioxidant metabolism.

Nickelophilous plants and their significance in phytotechnologies

Abstract: Nickeliferous soils are invaded predominantly by members of the Brassicaceae, Cyperaceae, Cunoniaceae, Caryophyllaceae, Fabaceae, Flacourtiaceae, Euphorbiaceous, Lamiaceae, Poaceae and Violaceae, and many of these plants are metal tolerant. About 300 Ni hyperaccumulating plants been identified. These members exhibit unusual appetite for toxic metals and elemental defense. Hyperaccumulators provide protection against fungal and insect attack. Investigations suggested that Ni-hyperaccumulation has a protective function against fungal and bacterial pathogens in Streptanthus polygaloides and Thlaspi montanum. Significance of nickelophilous plants and their significance in phytotechnologies are discussed in this paper.

Antioxidant-enzymatic system of two sorghum genotypes differing in salt tolerance

Abstract: Two forage sorghum genotypes were studied: CSF18 (salt-sensitive) and CSF20 (salt-tolerant). Shoot growth reduction as a result of salt stress was stronger in the salt sensitive genotype compared to the salt tolerant one. When the two genotypes were subjected to salt stress (75 mM NaCl) no significant change in lipid peroxidation was observed. However, salt stress induced increases in superoxide dismutase and catalase activities in both genotypes. These salt-induced increases were higher in the salt-tolerant genotype. Peroxidase activity was differentially affected by salt stress in the two genotypes. The activities of these peroxidases were decreased by salt stress in the salt-sensitive genotype and increased in the salt-tolerant genotype. In addition, the activity ratio between the superoxide dismutase and the H2O2-scavenging enzymes was higher in the salt-sensitive genotype. The results obtained support the hypothesis that the higher efficiency of the antioxidant-enzymatic system of the CSF20 genotype could be considered as one of the factors responsible for its tolerance to salt stress. Therefore, it is suggested that the ratio between superoxide dismutase and H2O2-scavenging enzyme activities could be used as a working hypothesis for a biochemical marker for salt tolerance in sorghum.

Ripening of "Pedro Sato" guava: study on its climacteric or non-climacteric nature

Abstract: Guava (Psidium guajava L.) is a tropical fruit exhibiting rapid post-harvest ripening. However, the physiological basis involved in the ripening process of guava is not totally clear, which makes it difficult to develop technologies to enhance fruit storability. Two experiments were carried out with the objective of determining the ripening behavior of 'Pedro Sato' guavas. In the first experiment, guava fruits at three maturity stages (I - dark green, II - light green and III - yellow-green) were stored at room temperature (23 ± 1°C and 85 ± 5 % RH). The respiratory rate, ethylene production, pulp and skin colours, and firmness were evaluated. In the second experiment, ethylene and 1-methylcyclopropene (1-MCP) were applied to guavas at the light green maturity stage and the ripening behaviour during storage at room temperature was studied. Fruits from all maturity stages showed a gradual increase in the respiratory rate and ethylene production. The intense changes in pulp and skin colours and in firmness preceded the maximum respiratory rate and ethylene production. 1-MCP reduced the rate of ripening, while the application of ethylene did not promote this process. These results do not permit the classification of 'Pedro Sato' guava as a traditional climacteric fruit.

Yield and composition of the essential oil of Mentha piperita L. (Lamiaceae) grown with biosolid

Abstract: This research evaluated the effects of biosolid levels on yield and chemical composition of Mentha piperita L. essential oil. Mint plants were grown in a greenhouse in pots containing the equivalent to 0, 28, 56, and 112 t.ha-1 biosolid. Three evaluations were made at 90, 110, and 120 days after planting (DAP). The oil was extracted from the dry matter of shoots by hydrodistillation, and composition was determined by GC/MS. Oil production was slightly affected by the biosolid, increasing when plants were grown with 28 t.ha-1, a condition which did not result in quality improvement. Menthyl acetate was the component obtained at the highest percentage in all treatments. At 90 DAP, plants showed a higher percentage of menthol, the second-highest oil constituent, with a content of 42.3% in plants grown without biosolid. The presence of biosolid favored menthofuran formation. As with menthol, menthone decreased with plant development. Under these conditions, plant harvesting is recommended at 90 DAP, period in which the menthol level was higher. Since the production of biosolid is on the rise, a suitable destination must be given to it, and restrictions exist for its use in relation to the environment and plants. Thus, although cultivation with 28 t.ha-1 is within the limits allowed by law, such a rate, which increased oil yield, did not improve oil quality. Therefore, biosolid from the Barueri Station is not recommended for cultivation of this specie.

Utilization of the chlorophyll a fluorescence technique as a tool for selecting tolerant species to environments of high irradiance

Abstract: We examine the hypothesis that the chlorophyll a fluorescence technique can be an efficient tool to support the selection of species adapted to high irradiance and therefore, suitable for use in initial rehabilitation projects of degraded areas. The experiment was conducted at the Pedro de Moura Operational Base, Amazonas, Brazil. The fluorescence transients were obtained using a portable fluorometer for leaves of Bombacopsis macrocalyx (Bm), Eugenia cumini (Ec), Iryanthera macrophyla (Im) and Senna reticulata (Sr), which were subjected to high irradiance between 12:00 am and 1:00 p.m. Using the OJIP test, the following were calculated: performance index (PIABS), density of reaction centres per cross section (RC/CS), maximum efficiency of photosystem II (fPo), and probability of energy excitation (yo) or that an absorbed photon (fEo) moves an electron beyond quinone A. The highest value of PIABS was found in Ec (0.40) while the lowest values were found in Bm (0.08) and Im (0.06). These low values of PIABS in Bm and Im were a result of the low values for RC/CS (121 for Bm; 142 for Im) and fPo (0.50 for Bm; 0.48 for Im) when compared to the values in Ec (RC/CS=303; fPo=0.72) and Sr (RC/CS=326; fPo=0.73). It was also observed that in Sr the decrease in PIABS when compared with Ec resulted from a low value of yo, which was 32 % lower than the value found in Ec. Regarding the PIABS per plant, Ec had the largest number of individuals with high performance while Im and Bm had the largest numbers of individuals with low performance. In conclusion, the chlorophyll a fluorescence technique enabled the evaluation of the photochemical performance of plants in the field, in turn permitting the selection of species most suitable for rehabilitation of degraded areas.

Metabolism and root exudation of organic acid anions under aluminium stress

Abstract: Numerous plant species can release organic acid anions (OA) from their roots in response to toxic aluminium (Al) ions present in the rooting medium. Hypothetically OA complex Al in the root apoplast and/or rhizosphere and thus avoid its interaction with root cellular components and its entry in the root symplast. Two temporal patterns of root OA exudation are observed. In pattern I, OA release is rapidly activated after the contact of the root with Al ions while in pattern II there is a lag phase between the addition of Al and the beginning of OA release. Compounds other than OA have been detected in root exudates and are also correlated with Al resistance in plants. Plant species like buckwheat and tea show mechanisms of Al tolerance, which confer them the capacity to inactivate and store Al internally in the leaves. Disturbances in metabolic pathways induced by Al are still obscure and their relation to the altered OA concentration observed in roots under Al stress is not yet established. High concentrations of OA in roots do not always lead to high rates of OA release even when the spatial distribution of these two characteristics along the root axis is taken into account. Al induces high permeability to OA in young root cells and anion channels located in the cell membrane have been proposed to mediate the transport of OA to outside the cell. Genetically modified plants that overexpress genes involved in the biosynthesis and transport of OA as well as in Al toxicity events at the cell level have been generated. In most cases the transformations resulted in an improved ability of the plant to cope with Al stress. These promising findings reinforce the possibility of engineering plants with superior resistance to Al-toxic acid soils. The environmental impact of the large amounts of root exudates possibly conferred by these genetically modified plants is discussed, with special emphasis on soil microbiota.

Ethylene production and acc oxidase gene expression during fruit ripening of Coffea arabica L.

Abstract: The phytohormone ethylene is involved in several physiological and developmental processes in higher plants, including ripening of fruits, abscission of organs and tissues, senescence, wound response as well as in other abiotic stresses. The enzyme 1-aminocyclopropane-1-carboxylate oxidase (ACO) catalyzes the last step of ethylene biosynthesis. The production of ethylene and the expression of a Coffea arabica ACO gene during the last stages of fruit maturation were investigated. A rapid increase of ethylene production at the green-yellow stage of fruit ripening, after the end of endosperm formation, and a decrease of ethylene production at the cherry stage indicates a climacteric phase during ripening. An ACC oxidase (Ca-ACO) from coffee fruit cDNA was cloned and characterized using primers previously reported. The cDNA is homologous to previously described ACC oxidase cDNA in Coffea. The nucleotide and amino acid deduced sequences of the clone showed high homology with ACO from climacteric fruits. Northern blots were performed to determine the Ca-ACO transcription pattern from different tissues and from fruits at different ripening stages. Coffee fruits at an early ripening stage (green) showed the lowest level of Ca-ACO transcript accumulation. The transcript levels of Ca-ACO did not change significantly during the later stages, suggesting the presence of post- transcriptional control mechanisms. These results, taken together, strongly suggest a climacteric nature of coffee fruit ripening.

Effects of the size of sown seed on growth and yield of common bean cultivars of different seed sizes

Abstract: A field experiment was conducted to evaluate the effects of planting different sizes of seed of the same cultivar on biomass accumulation and grain yield of common bean (Phaseolus vulgaris L.) cultivars of different seed sizes. A 6 X 2 split-plot factorial design with four replicates was employed, with six bean cultivars as main plots and two seed sizes (small and large, the latter twice as heavy as the former) of the same cultivar as subplots. Eight weekly samplings of biomass were performed, and yield components were measured at maturity. Large seeds increased the leaf area index and the shoot and root biomass of bean cultivars, particularly at the beginning of the growth cycle, but they did not affect the pod biomass. Improved growth associated with the large seed was more intense for erect than for prostrate cultivars. Plants originating from small seed presented a higher relative growth rate and net assimilation rate than plants from large seed. Large seed did not affect grain yield, but reduced the number of seeds per pod, increased the 100-seed mass, and reduced the harvest index. The results indicate that sowing larger seeds of a bean cultivar can improve early-season plant growth, which might be advantageous for crop establishment in stress environments. However, some compensatory effect, associated with delayed leaf senescence, higher net assimilation rate, or greater number of seeds per pod, allows plants originating from small seed to achieve similar grain yield. Lack of consistent effects of the seed size on grain yield indicate that the extra costs of sowing only the largest seed would not be profitable, but large seed resulted in larger grains at harvest which usually attain better market price.

Effect of temperature on polyunsaturated fatty acid accumulation in soybean seeds

Abstract: Soybean oil contains around 60 % of polyunsaturated fatty acids, which are responsible for the low oxidative stability of soy-derived products. Soybean lines with low linolenic acid content can be obtained by genetic manipulation; however, a high proportion of the variation in fatty acids content is due to environmental factors. This work aimed to determine the effect of temperature on oil composition and on the activity of the enzymes CDP-choline:1,2-diacylglycerolcholine phosphotransferase (CPT) and acyl-CoA:lysophosphatidylcholine acyltransferase (LPCAT), responsible for maintenance of polyunsaturated fatty acids in the cytoplasmic acyl-CoA pool, that is used for oil synthesis in the seeds. CAC-1, a soybean variety with linolenic acid content of about 8 % and CC4, a BC3F4 CAC-1 derived line, with about 4 % linolenic acid, were used. The lines were cultivated under two temperature: 34/28oC or 22/13oC - day/night. The seeds were collected along seven development stages, according to their fresh weight. Fatty acid analysis was carried out by gas chromatography and CPT and LPCAT activities were determined by measuring the radioactivity incorporated in their products, phosphatidyl-[14C]choline and phosphatidylcholine-[14C]oleoyl, respectively. Linolenic acid contents were 3.89 and 6.92 % for line CC4 and 7.39 and 12.49 % for variety CAC-1, when submitted to high and low temperature conditions, respectively. Both enzymes were more active, in the development stages analyzed, in seeds produced under low temperature. Kinetics characterization of CPT and LPCAT were conducted previously.

Glutamine enhances competence for organogenesis in pineapple leaves cultivated in vitro

Abstract: Leaf bases of pineapple cultured on a shoot induction medium (SIM) produced protuberances followed by shoot-buds via direct organogenesis at a frequency of 46 %. When 8 mM glutamine (gln) was a supplement to SIM (SIM8gln), the regeneration rate increased to 70 %, thus suggesting that 8mM gln increased explant competence for organogenesis. Besides this, shoot vigor was strongly enhanced in SIM8gln. Other gln concentrations (16 or 32 mM) evoked a lower frequency of shoot-bud induction and number of regenerated shoots per explant when compared to SIM8gln. In this study, it was defined that explant organogenic commitment to form shoot-buds occurred in the first 7 days of culture on SIM8gln. Thereafter, endogenous indole-3-acetic acid (IAA) and cytokinin (4 types) measurements were carried out during this period, that is, during the induction phase of shoot-bud formation. The IAA content increased greatly until the 5th day in the leaf bases cultured on SIM8gln. No such change in IAA concentration was observed in the explants cultivated on SIM or in the presence of the highest gln concentration (32 mM), this being inhibitory to the organogenic process. The only natural cytokinin detected was isopentenyladenine. An increase of 50 % in the level of this phytohormone occurred in leaf bases cultured on SIM8gln at the 5th day, when compared to SIM or of 170% compared to SIM32gln. These results suggest that 8 mM gln favorably influenced the organogenic process through changes in IAA and iP concentrations in pineapple leaves.

The complexity-stability hypothesis in plant gas exchange under water deficit

Abstract: We hypothesized that more complex, i.e. irregular, temporal dynamics and a more interconnected overall network supports greater stability to gas exchange parameters (herein, CO2 net assimilation and transpiration) in plants under water deficit. To test this hypothesis two genotypes of Phaseolus vulgaris were subjected to a period of absence of irrigation, and subsequent rewatering to achieve recovery. Gas exchanges parameters were measured each 10 s during 6 h to obtain time series to evaluate complexity by Approximate Entropy (ApEn) calculations, and network connectance in each water regime. Notably, the Jalo Precoce genotype showed significantly more stability than the Guarumbe genotype under system perturbation, coincident with greater irregularity in each gas exchange parameter and greater overall connectance for Jalo Precoce. This conclusion is consistent with other observations of greater homeostasis in more complex networks, seen in broad contexts such as cardiac rhythms and respiratory dynamics

Response of Crotalaria juncea to nickel exposure

Abstract: A presenca de metais pesados no ambiente e atualmente, um dos principais problemas de contaminacao ambiental, uma vez que, os metais liberados no ambiente contaminam o solo e entram na cadeia alimentar atraves das plantas, causando efeitos toxicos a curto e a longo prazo aos animais e seres humanos. No caso do metal pesado Niquel (Ni), foi constatado que a sua presenca nas plantas pode diminuir o crescimento, reduzir a taxa de fotossintese e provocar alteracoes, tanto nas atividades enzimaticas quanto metabolicas.Pouca informacao esta disponivel na literatura, com referencia a resposta antioxidante das plantas a expressao a esse metal. Neste sentido, os objetivos deste trabalho foram realizar diferentes ensaios para avaliar o efeito fitotoxico do Ni em plântulas de C. juncea. Neste estudo foram analisados parâmetros bioquimicos relativos a atividade das enzimas antioxidantes, Catalase (CAT), Superoxido Dismutase (SOD) e Glutationa Redutase (GR). Constatou-se que, nao houve alteracao da atividade GR e CAT nas raizes. Entretanto, atividades destas enzimas apresentaram aumento significativo na parte aerea. O aumento na atividade da GR, na parte aerea, pode ser explicado pelo fato de ser o ciclo Halliwell-Asada o principal mecanismo que age na desintoxicacao de Especies Ativas de Oxigenio. Quanto a atividade da SOD, quando comparados ambos tecidos, foi constatado que na parte aerea foi pouco alterada, entretanto, a atividade da SOD foi estimulada nas raizes na presenca do Ni. Para aumentar a precisao dos resultados, quantificou-se pela tecnica de Fluorescencia de Raios X, a concentracao de NiCl2 e o seu efeito na absorcao de nutrientes nas plântulas de crotalaria. Nesta analise, observou-se o acumulo do metal nas raizes e baixa translocacao para a parte aerea. Tambem foi analisada a concentracao de Malonaldeido (MDA) na parte aerea de plântulas de C. juncea, sendo constatada, a ocorrencia de peroxidacao lipidica na presenca do Ni. Finalmente, determinou-se o efeito do Ni sobre as concentracoes de aminoacidos soluveis em raizes e na parte aerea, como estrategia desta planta para superar o efeito do Ni , nao tendo sido observadas variacoes significativas nas concentracoes dos mesmos com os diferentes tratamentos com Ni. Palavra?Chave: Aminoacidos, Atividade Enzimatica, Crotalaria, Fitotoxicidade, Niquel, Poluicao Ambiental Abstract

Effects of different drying rates on the physiological quality of Coffea canephora Pierre seeds

Abstract: Desiccation tolerance in seeds depends on the species, development stage and drying conditions, especially the water removal rate. Coffea seeds are considered of intermediate performance, because they tolerate relative dehydration compared to orthodox seeds and are sensitive to low temperatures. The objective of this study was to verify the effect of different drying rates on the viability and storability of Coffea canephora seeds. A complete randomized experimental design was used, in a factorial 3 x 5 x 2 design, with three drying rates (fast, intermediate and slow), five final mean water contents after drying (51, 42, 33, 22 and 15 %) and two storage temperatures (10 and 20°C). The germination and seed vigor assessments, using radicle protrusion, cotyledon leaf opening, seedling emergence and emergence speed index, were performed shortly after drying and after two and four months storage. It was observed that with reduction in the water content there was reduction in the germination values and seed vigor, for all the drying rates. The greatest reductions in physiological quality occurred when the seeds were dried quickly and the best results were obtained at the intermediate drying rate. There was an effect of drying rate and storage temperature on the physiological quality of the seeds, and lower germination and vigor values were observed in seeds with lower water content stored at 20°C. C. canephora seeds were tolerant to desiccation down to 15 % water content and can be stored for four months at 10°C. A temperature of 20oC can be used to store C. canephora seeds, as long as the water content is not reduced to values below 22 % water content.

Induction and differentiation of reproductive buds in Coffea arabica L.

Abstract: The induction and differentiation phases of reproductive buds of Coffea arabica L. have not received much attention. In the present paper, axillary buds from five plagiotropic branches that developed in the same growing season without fruits (1st crop branches), and from green segments of five recently grown plagiotropic branches with fruits (2nd crop branches), were collected every two weeks during successive inductive months of the year. This study was carried out with adult arabica trees, Catuai Vermelho cv. IAC 81, cultivated under normal farming conditions in the region of Campinas, SP, Brazil (22o54' Lat. S). Slides of longitudinal-axial sections of 10-12 mm thickness were mounted for the characterization and quantification of histological stages of bud differentiation. The results indicate that the regulatory signals controlling the phases of induction and differentiation of floral buds are distinct, and that there are differences in the response between branches with and without fruits. In the case of 1st crop branches (no fruits present), induction of floral buds took place in January and February, whereas floral bud differentiation was observed during the months of March and April. In 2nd crop branches (fruits present), the induction of floral buds was observed during any month of the year provided that they had already overcome their juvenile state (October-July, in this study). In these 2nd crop branches, the flower bud differentiation was only observed after harvesting all pre-existing fruits of each branch (after May, in this study), which suggests that floral bud differentiation in Arabica coffee is influenced by the source-sink relationship, i.e. by the presence of developing fruits within each plagiotropic branch.

Identification of methyl jasmonate-responsive genes in sugarcane using cDNA arrays

Abstract: O acido jasmonico (JA) e seu ester metil-jasmonato (MeJA) sao moleculas sinalizadoras derivadas do acido linolenico e estao envolvidas no desenvolvimento da planta e na resposta aos estresses. MeJA regula a expressao genica ao nivel transcricional, do processamento do RNA e da traducao. Investigamos as mudancas na expressao genica em folhas de cana-de-acucar expostas ao MeJA usando arranjos de cDNA. O RNA total isolado a 0, 0,5, 1, 3, 6 e 12 horas apos o tratamento com MeJA foi utilizado para a sintese de sondas contendo a-33P-dCTP, as quais foram, posteriormente, hibridizadas em membranas de nailon contendo 1.536 clones de cDNA. Um aumento significativo na expressao genica em resposta ao MeJA foi detectado em genes que respondem a estresses e tambem em genes com funcao desconhecida, enquanto os genes que participam da fotossintese e da assimilacao de carboidrato foram reprimidos. A busca por dominios conservados em proteinas desconhecidas e a analise digital do perfil de expressao de mRNA revelaram possiveis proteinas novas relacionadas a estresses induzidas por MeJA e os tecidos onde os genes regulados por MeJA sao preferivelmente expressos.

Development of the nodulated soybean plant after flooding of the root system with different sources of nitrogen

Abstract: Flooding leads to hypoxia, a stress to which symbiotic N2 fixation is especially sensitive. The response of fully nodulated soybean plants to a 21-day period of flooding was studied by measurements of growth parameters and xylem transport of organic nitrogenous components to the shoot, in the presence and absence of NO3- and NH4+ in the medium. Flooding was found to seriously impair N2 fixation, irrespective of the N source, as indicated by strongly reduced xylem ureide levels. In the absence of a source of N, growth was strongly reduced during flooding while accumulation of N in the shoot was virtually abolished. Flooding in the presence of 5 mM NO3- or NH4+ led to the accumulation of total N in the shoot but only NO3- promoted increases in total dry matter, plant height and leaf area above that found in the absence of N. The accumulation of N, however, was lower than that of the non-flooded control for both NO3- and NH4+. The increases in total dry matter, plant height and leaf area with NO3- was as high as those of the non-flooded control. These data clearly show the beneficial effects of NO3- during a prolonged period of flooding of the nodulated root system of soybean.

Differential responses of ribulose-1,5-bisphosphate carboxylase/oxygenase activities of two Vigna unguiculata cultivars to salt stress

Abstract: Vita 3 and Vita 5 are two Vigna unguiculata cultivars that differ in their capacities for survival in saline environments; Vita 3 is more tolerant and Vita 5 more sensitive. Both cultivars were submitted to salt stress with 0.1 M NaCl. After 8 days, root and shoot growth from both cultivars was reduced but reduction was more pronounced in Vita 5. Furthermore, leaf area was also reduced in this cultivar. Chlorophyll content and chlorophyll fluorescence parameters were not affected by salt stress, but the specific activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) decreased in Vita 3 and increased in Vita 5. The use of immunological techniques also revealed that the Rubisco content from Vita 3 decreased while that of Vita 5 increased. The discussion of these results is aimed at reaching a better understanding of the differences between these cultivars in relation to salt stress.