Resumo em Português:
Plantas respondem ao ataque de herbívoros e patógenos com liberação de compostos orgânicos voláteis. Essas moléculas funcionam como defesas indiretas quando atraem inimigos naturais dos herbívoros e assim beneficiam a planta emissora. Uma questão controversa é se plantas vizinhas não-atacadas captam esses voláteis e respondem aumentando suas barreiras defensivas contra um ataque iminente. Apesar do seu forte apelo popular e da Talking Trees Hypothesis estar completando 25 anos, só recentemente os mais céticos estão sendo convencidos. Tem-se aceitado que respostas induzidas pela trasnferência de informação entre plantas ocorrem em pelo menos dois sistemas planta-herbívoro. No entanto, o grau de generalização do fenômeno e a dimensão da sua importância ecológica e evolutiva permanecem desconhecidos. Uma recente abordagem multidisciplinar, integrando Biologia Molecular, Bioquímica e Fisiologia à Ecologia, acena com novas e mais poderosas ferramentas metodológicas para esclarecer os processos de biossíntese, emissão, transporte e recepção dos sinais pelas plantas. Essa abordagem tem fornecido o suporte mecanicista adicional às evidências ecológicas da defesa induzida da planta, manifestada e mensurada mediante respostas ecofisiológicas e comportamentais dos insetos herbívoros.Resumo em Inglês:
Plants respond to herbivores and pathogens attack with increased emission of volatile organic compounds. These molecules act as indirect defences when attracting natural enemies of herbivores and thus benefit the plant. It remains controversial whether undamaged plants capture chemicals released by damaged neighbouring plants and respond to them by increasing their defensive barriers against an imminent attack. In spite of public appeal and of this being the 25th year of the Talking Trees Hypothesis, only recently have the most sceptical scientists been convinced. The induced response to herbivory by interplant information transfer has been found in two plant-herbivore systems. However, the universality of the phenomenon and its ecological and evolutionary relevance remain unclear. The integration of Molecular Biology, Biochemistry, Physiology, and Ecology begin to shed light on the mechanisms of the signal transfer. This integrative approach has developed new and more sensitive tools for identification of complex volatile mixtures and for understanding the process of biosynthesis, emission, transportation and reception of signals.Resumo em Inglês:
Yellow vein mosaic disease of mesta (kenaf, Hibiscus cannabinus L.; and roselle, H. sabdariffa L.) is a new entrant to the disease scenario and it is associated with a novel monopartite Begomovirus. Changes in different biochemical parameters in diseased mesta plants were observed as compared to healthy ones. Isozyme pattern and assays of different enzymes, namely catalase, acid phosphatase, peroxidase, esterase, polyphenol oxidase and superoxide dismutase, revealed lower activities of catalase, acid phosphatase and peroxidase enzymes and enhanced activities of esterase, polyphenol oxidase and superoxide dismutase in diseased plants as compared to healthy ones. Due to the infection, chlorophyll content, phenolics and total soluble protein decreased whereas free amino acid, proline and disease-related proteins increased in the host plants. Differential responses of polyacetylene and isoflavone content as well as SDS-PAGE band profiling of total soluble proteins were also observed in plants due to the infection.Resumo em Inglês:
Water uptake kinetics of axes and cotyledons of Vigna radiata seeds has been studied during incubation at chilling temperature (4°C) and under cycloheximide treatment. Germination rate of scarified seeds was faster than intact seeds, which can be correlated with their comparative water uptake kinetics. Chilling temperature during incubation significantly slowed down water uptake by both intact and scarified seeds. Treatment with cycloheximide was also somewhat effective in retarding water uptake, but only in scarified seeds. Water uptake by axes isolated from intact seeds (attached or detached from the cotyledons) was inhibited completely by chilling temperature as well as by cycloheximide treatment while these treatments were ineffective in preventing water uptake by cotyledons. In the case of scarified seeds, such treatments again inhibited water uptake by axes only, the effect being more prominent in attached ones. Preincubation of intact seeds with cycloheximide for 6 h also inhibited water uptake by isolated axes, but not by cotyledons, during subsequent incubation in water.Resumo em Português:
Plântulas de Pfaffia glomerata (Spreng.) Pedersen foram cultivadas em cinco níveis (0, 20, 40, 60 e 80 μM) de cádmio (Cd) em um sistema hidropônico durante 7 d, visando-se analisar o crescimento, as concentrações de micronutrientes, clorofilas e carotenóides, bem como as atividades da desidratase do ácido δ-aminolevulínico (ALA-D; E.C.4.2.1.24) e fosfatase ácida (AP; E.C.3.1.3.2) nas plantas. A concentração de Cd, na parte aérea e raízes, aumentou com o incremento dos níveis de Cd. A concentração de Cd nas raízes foi, em média, 12 vezes maior do que na parte aérea. O comprimento das raízes não foi afetado pelos tratamentos de Cd. Em contraste, a biomassa seca da parte aérea e raízes aumentou significativamente pela adição de 20 e 40 μM Cd. Além disso, a biomassa seca total das plantas somente diminuiu no nível de 80 μM Cd em relação à das plantas-controle. Por outro lado, a biomassa radicular diminuiu significativamente pela adição de Cd a níveis superiores a 40 μM. Constatou-se resposta dependente do órgão e do micronutriente à toxicidade de Cd. As concentrações de Zn e Cu na parte aérea e raízes não foram alteradas pela presença de Cd. A absorção de Mn foi diminuída pelo estresse de Cd, porém sua translocação não foi alterada. Um efeito sinergístico do Cd na concentração de Fe nas raízes foi observado nos níveis de 20 e 80 μM Cd. As atividades da ALA-D e AP foram diminuídas com o incremento dos níveis de Cd, porém a ALA-D foi mais afetada. Naquelas concentrações de Cd, a concentração de clorofila também foi diminuída. Houve uma correlação positiva entre as concentrações de carotenóides e clorofila. Os resultados indicam que a P. glomerata parece ter algum grau de tolerância ao Cd.Resumo em Inglês:
Pfaffia glomerata (Spreng.) Pedersen plantlets were grown under different cadmium (Cd) concentrations (0, 20, 40, 60 and 80 μM) in a hydroponic system during 7 d. Plant growth, micronutrient, chlorophyll and carotenoid concentrations, as well as δ-aminolevulinic acid dehydratase (ALA-D; E.C.4.2.1.24) and acid phosphatase (AP; E.C.3.1.3.2) activities were then analysed. Cadmium concentration in both shoots and roots increased with increasing external Cd levels. Metal concentration was on average 12-fold greater in root than in shoot tissues. Root length was unaffected by Cd treatments. In contrast, dry weight of both shoot and roots increased significantly upon addition of 20 and 40 μM Cd. Moreover, shoot and total plant dry weight was only reduced in plants treated with 80 μM Cd. Conversely, root dry weight decreased significantly upon addition of Cd concentrations above 40 μM. A micronutrient- and organ-dependent response to Cd toxicity was observed. Zinc and Cu concentrations in both shoot and roots did not alter upon treatment with Cd. Cadmium stress reduced Mn uptake but not its translocation within the plant. A synergistic effect of Cd on Fe concentration in root at 20 μM and 80 μM Cd levels was observed. The activity of AP, and especially that of ALA-D, was reduced with increasing Cd levels. At those these Cd levels, chlorophyll concentration was also reduced. There was a positive correlation between concentrations of carotenoids and chlorophylls. Our results indicate that P. glomerata seems to have some degree of Cd tolerance.Resumo em Português:
O planalto sul-brasileiro apresenta um mosaico de duas comunidades vegetais contrastantes, florestas com Araucaria e campos, que diferem em suas abundâncias relativas e nos padrões espaciais de nitrato e amônio no solo. Entretanto, ainda não se conhecem as preferências quanto ao N inorgânico de uma espécie-chave neste mosaico, Araucaria angustifolia, a espécie arbórea dominante nas florestas com Araucaria e uma importante espécie florestal que invade os campos adjacentes. Respostas de crescimento medidas em um estudo em casa de vegetação demonstraram que a espécie o prefere o NH4+ ao NO3-, como fonte de N inorgânico. Quando fornecido isoladamente, o NO3- induziu sintomas de deficiência de N: aumentos na razão raiz:parte aérea, ramificação radicular e massa foliar por área, espessamento dos ápices caulinares e redução nas concentrações por unidade de massa de clorofila e N, nas folhas jovens. Uma nutrição baseada em nitrato também afetou a distribuição de N e C na planta como um todo: as folhas jovens acumularam menos N e mostraram uma maior razão C:N do que as folhas maduras. A atividade da redutase do nitrato (ARN) seguiu o padrão de partição entre raiz e parte aérea esperado para coníferas de clima temperado (atividade concentrada nas raízes). No entanto, a presença de ARN mesmo sob nutrição exclusivamente com NH4+ indica que as plantas devem ter níveis constitutivos da enzima ou que baixos níveis de NO3- (possivelmente gerado pela contaminação do meio de cultivo) podem induzir ARN. Sugere-se que A. angustifolia tem no amônio sua forma preferencial de N inorgânico e que esta preferência pode favorecer um melhor estabelecimento nos campos do que nas florestas.Resumo em Inglês:
The southern Brazilian highland plateau is a mosaic of two contrasting plant communities, Araucaria forests and grasslands, which differ in the relative abundances and spatial patterns of soil nitrate and ammonium. However, we still do not know the inorganic N preferences of one key species in this mosaic, Araucaria angustifolia, the dominant tree species in the Araucaria forests and an important tree species invading the adjacent grasslands. Growth responses measured in a greenhouse study demonstrated that the species prefers NH4+ over NO3- as an inorganic N source. When provided alone, NO3- induced N deficiency symptoms: increases in root: shoot ratio, root branching and leaf mass per area, thickening of the shoot apexes and decreased mass-based chlorophyll and N concentrations of the young leaves. Nitrate-based nutrition also affected the whole plant N and carbon (C) distribution: young leaves accumulated less N and showed a larger C:N ratio than mature leaves. The nitrate reductase activity (NRA) followed the pattern of root: shoot partitioning expected for temperate climate conifers (activity concentrated in roots). However, the presence of NRA even under sole NH4+ nutrition indicates that plants may show constitutive levels of the enzyme, or that low levels of NO3- (possibly formed by contamination of the growth media) can induce leaf NRA. We suggest that A. angustifolia has ammonium as a preferential inorganic N source, and that this preference may favor a more successful establishment in grassland than in forest areas.Resumo em Inglês:
The ecdysteroid 20-hydroxyecdysone (20E) is a steroid hormone found in insects and few plants. To analyze its temporal and spatial distribution in Pfaffia glomerata (Amaranthaceae), we selected among 71 accessions, the accession 13 which showed the highest root 20E total quantity (1.48 g/plant root). The 20E was constantly detected in flowers, leaves, stems, and roots, but its percentage was variable throughout its development. The highest 20E percentage was found in flowers (0.82%), roots (0.66%), leaves (0.60%), and stems (0.24%). While stems showed the least variable 20E percentage (0.13% - 0.24%), followed by roots (0.42% - 0.66%), and flowers (0.47% - 0.82%). Leaves showed the greatest 20E percentage variation (0.21% - 0.60%). The stem and leaves 20E total amount remained constant, showing a little variation while root 20E total amount increased over time, suggesting that 20E may be accumulated in roots. These findings suggest that 20E has tissue specific functions in plant and may have ecological significance since uncoordinated pulses of 20E are often lethal to insects.Resumo em Inglês:
Protease inhibitors in legumes are one of the most promising weapons that confer resistance against insects by inhibiting proteases present in the gut of insect larvae. In the present study, trypsin inhibitor activity was detected in the seed flour extracts of 10 selected varieties of chickpea. The presence of inhibitor was confirmed by dot blot analysis. All the varieties showed inhibitory activity in vitro against the gut protease of Helicoverpa armigera (HGP). Trypsin inhibitor has been purified to near homogeneity to 60.46 fold and 29.20% recovery from chickpea seeds using heat denaturation, ammonium sulphate fractionation, DEAE-Sephadex A-25 and Sephadex G-75. The purified inhibitor showed a single band on SDS-PAGE corresponding to molecular mass of 30,000 Da. The purified inhibitor was active over a wide pH range although it retained maximum activity between pH 6 and 10. The inhibitor protein was stable up to 80°C but retained only 40% of activity when heated at 100°C for 20 min. The inhibitor lost its activity completely at 121°C. The chickpea trypsin inhibitor exhibited inhibitory activity against Helicoverpa armigera both in vitro and in vivo. In insect bioassay, a progressive decline in larval weight, growth and survival as well as temporal extension of larval growth was observed after feeding H. armigera larvae on diet supplemented with increasing concentrations of chickpea trypsin inhibitor. The adult emergence was also adversely affected by the inhibitor. It may be concluded that chickpea trypsin inhibitor has insecticidal potential against H. armigera.Resumo em Português:
A produção e a qualidade do grão (incluindo alguns aspectos da qualidade tecnológica) sob estresse térmico, durante o enchimento do grão, foram avaliadas em dois genótipos de trigo mole (Triticum aestivum L.) e trigo rijo (Triticum turgidum subsp. durum) com diferentes tolerâncias às temperaturas elevadas após a antese. O estresse térmico, após a antese, induziu o desenvolvimento de grãos enrugados e com peso reduzido. Observaram-se ainda modificações ultraestruturais em nível da camada de aleurona e nas células do endosperma. Os grãos submetidos a temperaturas mais elevadas mostraram índices de sedimentação SDS menores, tendo estado este efeito associado a um aumento nos teores em proteína do grão e ainda a um decréscimo nos níveis de aminoácidos essenciais. Apesar das respostas às temperaturas elevadas não terem sido diferenciadas entre os genótipos de trigo, os resultados sugerem que o estresse térmico, durante o período de enchimento do grão, pode afectar a força do gluten, diminuindo a qualidade da farinha de trigo.Resumo em Inglês:
The yield and grain quality (as well as technological traits) of two heat-stressed genotypes of bread (Triticum aestivum L.) and durum wheat (Triticum turgidum subsp. durum) having different tolerance to high temperatures after anthesis were investigated. Heat stress, during grain filling, triggered grain shrinkage with a reduced weight and ultrastructural changes in the aleurone layer and in the endosperm cells. Heat stress also decreased the sedimentation index SDS, an effect associated with increased protein content in the grain but with decreased levels of essential amino acids. Although the responses to heat stress were similar among the Triticum genotypes, it is further suggested that during grain filling, high temperatures might affect gluten strength, diminishing the wheat flour quality.