Resumo em Inglês:
In the present study the physiological response of water hyacinth (Eichhornia crassipes [Mart.] Solms) to the combined exposure of excess nutrients and Hg was examined. Young water hyacinth plants were exposed to a range of HgCl2 and KNO3 concentrations. After eight weeks, submerged plant tissues reached an Hg concentration of 4 mg g-1. The accumulation of P and S was reduced by the addition of HgCl2, and also the P and K concentrations in emerged and submerged parts decreased. In contrast, the addition of HgCl2 increased Ca and Mg concentrations in submerged parts. Furthermore, the concentration ratios of submerged/emerged parts for Ca, Mg and P were also reduced by the addition of HgCl2. The interaction of HgCl2 and KNO3 was synergistic and decreased Fv/Fm, total chlorophyll content and P and Mn concentrations in emerged parts. In submerged plant parts Ca concentration increased and K content stabilized as a result of the above interaction. However, the total accumulation of Hg per plant was not reduced, thereby confirming the water hyacinth as a promising candidate for the heavy metal phytoremediation of eutrophic waters.Resumo em Português:
É conhecido que o nitrato melhora a tolerância de plantas à deficiência de oxigênio provocada pela inundação do sistema radicular. Porém, pouco se sabe sobre as causas deste fenômeno. Realizamos um estudo do metabolismo do nitrato em raízes de soja sob hipóxia, empregando plantas cultivadas em sistema hidropônico, após suspender a aeração e cobrir a superfície da solução nutritiva com óleo mineral. O consumo de nitrato no meio foi maior sob hipóxia do que normóxia. Porém, na presença de cloranfenicol o consumo em hipóxia foi reduzido de forma significativa. Houve acúmulo do nitrito no meio sob hipóxia e este acúmulo foi parcialmente eliminado por cloranfenicol. A redução do consumo de nitrato na presença de cloranfenicol foi atribuída à atividade bacteriana. O nitrato endógeno da raiz foi bastante reduzido sob hipóxia, indicando mobilização do mesmo. Apesar do transporte do nitrato até a parte aérea, via xilema, ter sido também reduzido sob hipóxia, a intensidade dessa redução foi dependente da concentração de nitrato no meio, o que indica que pelo menos uma porção do nitrato encontrado no xilema teve origem no meio. A atividade da redutase do nitrato da raiz também foi fortemente reduzida sob hipóxia, porém recuperou-se rapidamente com o retorno à normóxia. De modo geral, os dados estão de acordo com o envolvimento de duas rotas metabólicas para explicar o consumo do nitrato que não foi inibido pelo cloranfenicol: a redução de parte do nitrato em nitrito (apesar da menor atividade de redutase do nitrato), seguida pela sua liberação no meio (pelo menos um terço do nitrato consumido seguiu esta rota), e o transporte de nitrato à parte aérea Contudo, é muito pouco provável que estas duas rotas metabólicas expliquem o consumo de todo nitrato.Resumo em Inglês:
Nitrate is reported to improve tolerance of plants towards oxygen deficiency enabled by waterlogging of the root system, but the mechanism underlying the phenomenon remains poorly understood. We studied the metabolism of nitrate in roots exposed to hypoxia, using soybean plants growing in a hydroponic system after suspending aeration and covering the surface of the nutrient solution with mineral oil. Nitrate depletion from the medium was more intense under hypoxia than normoxia, but in the presence of chloramphenicol, consumption under hypoxia was significantly reduced. Nitrite accumulated in the medium in the state of hypoxia and this effect was partially eliminated by chloramphenicol. Nitrate consumption sensitive to chloramphenicol was attributed to bacterial activity. Endogenous root nitrate was strongly reduced under hypoxia indicating mobilization. Although the transport of nitrate to the shoot via the xylem was also reduced under hypoxia, the severity of this reduction was dependent on the concentration of nitrate in the medium, suggesting that at least some of the nitrate in the xylem came from the medium. Root nitrate reductase was also strongly reduced under hypoxia, but recovered rapidly on return to normoxia. Overall, the data are consistent with two main metabolic fates for chloramphenicol-insensitive nitrate depletion under hypoxia: the reduction of some nitrate to nitrite (despite the reduced nitrate reductase activity) followed by its release to the medium (at least one-third of the nitrate consumed followed this route), and the transport of nitrate to the shoot. Nevertheless, it is highly unlikely that these metabolic routes account for all the nitrate consumed.Resumo em Inglês:
The effects of various conc of (10-11, 10-9 and 10-7 M) 24-epibrassinolide (24-epiBL) on polyamines and auxins contents was analyzed in 7days old seedlings of Raphanus sativus L. cv. Pusa chetki under copper metal stress. Cu metal (0.2mM) treatment significantly increased endogenous levels of putrescine, spermidine and spermine when compared with control values. Cadaverine content got decreased under metal stress. Endogenous polyamines showed varying levels in seedlings when applying 24-epiBL treatment only. Maximum increase was found in putrescine, cadaverine and spermidine in 10-11, 10-9 and 10-7 M conc of 24-epiBL respectively when applied alone to R. sativus seedlings. However, metal treatment supplemented with 24-epiBL revealed small increase in polyamines. Putrescine and cadaverine got enhanced in combination of Cu metal and 10-7 M (24-epiBL) in comparison to metal treatment alone, whereas decrease in spermidine and spermine levels were recorded in combinations of Cu metal and 10-9 and 10-7 M 24-epiBL respectively. Endogenous contents of Indole-3-acetic acid (IAA) and Naphthalene acetic acid (NAA) were significantly affected by 24-epiBL when applied alone or along with Cu metal. Both free and bound forms of NAA were not detected in untreated seedlings, but were recorded in seedlings treated with metal stress. Decreased IAA contents observed in metal treatment got enhanced significantly in seedlings with 24-epiBL supplementation. To the best of our knowledge the present investigation is the first one to explain the effects of 24-epiBL on endogenous contents of polyamines, indole acetic acid and naphthalene acetic acid under copper metal stress.Resumo em Português:
A transpiração (E), a resistência difusiva (r s) e parâmetros anatômicos foram medidos em mudas enxertadas de quarto genótipos de umbuzeiro (BGU s 44, 48, 50 and 68) com o objetivo de avaliar alterações e possíveis variações genotípicas induzidas pela seca intermitente. As medidas de transpiração foram tomadas diariamente até ocorrer o fechamento estomático das plantas sob suspensão da irrigação, e após a reirrigação e suspensão da rega novamente, repetindo-se este ciclo por um período de 31 dias (período de estresse). As plantas controle foram irrigadas diariamente. Foi observado um padrão regular no mecanismo de abertura e fechamento estomático ao longo dos períodos de rega, exibindo diferenças entre os genótipos. O comportamento estomático dos genótipos BGU 44 e BGU 68 se correlacionaram com a temperatura do ar (Tar), umidade relativa (RH) e déficit de pressão de vapor (VPD), enquanto que o BGU 50 apresentou correlação com a radiação fotossinteticamente ativa (PAR). BGU 48 não apresentou correlação com os fatores ambientais. Foram observadas alterações anatômicas em resposta à seca na densidade estomática (SD), reduções no índice estomático (SI) e abertura do ostíolo (SA). As características anatômicas do genótipo BGU 48 permaneceram inalteradas. Houve uma inversão na proporção dos tecidos do BGU 44 sob condições de estresse, reduzindo a espessura do parênquima esponjoso e aumentando a do parênquima paliçádico. O inverso ocorreu com o BGU 68, enquanto que os demais genótipos permaneceram inalterados. Os resultados encontrados neste estudo sugerem que o BGU 68 é o genótipo mais sensível à seca e que as mudanças anatômicas induzidas pela seca intermitente não são suficientes para explicar as diferenças fisiológicas entre os genótipos.Resumo em Inglês:
Transpiration (E), diffusive resistance (r s) and anatomical parameters were measured in plants of four grafted umbu tree genotypes (GBUs 44, 48, 50 and 68) in order to evaluate alterations induced by intermittent drought and possible genotypic variations. Transpiration measurements were taken daily until stomatal closure by withholding water. Measurements were also taken, when the plants were re-watered and the watering was interrupted again. This cycle was repeated for a period of 31 days (stress period). The control plants were also irrigated daily. A regular pattern in the stomatal opening/closing mechanism was observed throughout the watering period, exhibiting intra-specific differences. Stomatal behavior of GBU 44 and GBU 68 were influenced by air temperature (Tar), relative humidity (RH) and vapor pressure deficit (VPD), whereas GBU 50 was influenced by photosynthetically active radiation (PAR). GBU 48 was not influenced by these environmental factors. Anatomical alterations in response to drought were observed in stomatal density (SD), reductions in the stomatal index (SI) and stomatal aperture size (SA). The anatomical features of the GBU 48 genotype remained unaltered. There was an inversion in tissue proportion in GBU 44 under stress conditions, reducing the spongy parenchyma and increasing palisade parenchyma thickness. The inverse occurred with GBU 68, while the remaining genotypes were unaltered. The results found in this study suggest that GBU 68 is the most drought-sensitive genotype and anatomical changes induced by intermittent drought are not enough to explain the physiological differences between genotypes.Resumo em Português:
Com o objetivo de avaliar as alterações no potencial hídrico foliar e o acúmulo de solutos compatíveis induzidos pela seca intermitente, foi desenvolvido um experimento em casa de vegetação utilizando-se quatro genótipos de umbuzeiro (GBU 44, GBU 48, GBU 50 e GBU 68) e dois regimes hídricos (controle e estresse com suspensão da irrigação), com quatro repetições. O potencial hídrico foliar (ψw) foi medido em intervalos de quatro horas durante 24 horas no momento do primeiro fechamento estomático e no final do período experimental. Também foram avaliados os teores de carboidratos solúveis totais, aminoácidos, proteína e prolina nas folhas e nas raízes. Houve diferença significativa entre os acessos estudados para a maioria dos parâmetros avaliados. O horário de menor ψw foi entre 8h e 12h. O ψw das plantas estressadas do GBU 50 reduziu significativamente às 8h, enquanto que as plantas controle reduziram às 12 h. O acesso GBU 68 apresentou os valores mais elevados de ψw. O prolongamento do estresse provocou reduções nos teores de carboidratos nas folhas de todos os acessos. Houve aumento no teor de aminoácidos nas folhas dos GBUs 44 e 48 e reduções de 40% e 43% para GBUs 50 e 68, respectivamente. Também foram observadas alterações nos teores de prolina. Nas raízes, houve aumento nos teores de carboidratos apenas no GBU 48. Foram verificadas alterações nos teores de aminoácidos, proteína e prolina. O umbuzeiro apresenta comportamento isoídrico, mantendo altos valores de potencial hídrico foliar e uma grande variação no acúmulo de solutos em resposta à seca, com marcada diferença genotípica.Resumo em Inglês:
In order to evaluate changes in leaf water potential (ψw) and solute accumulation induced by intermittent drought, an research was performed under greenhouse conditions using four umbu tree genotypes (GBU 44, GBU 48, GBU 50 and GBU 68) and two water treatments (control and stressed by withholding water), with four replicates. The ψw was measured in four-hour intervals during a 24-hour period at the first stomatal closure and at the end of the experimental period. Carbohydrates, amino acids, protein and proline contents were also evaluated in leaves and roots. Significant differences were found in most of the studied parameters. The lower ψw hour was between 800 h and 1200 h. GBU 50 reduced significantly ψw in stressed plants at 800 h, while control plants reduced at 1200 h . GBU 68 presented the higher ψw. The extending of the stress induced reductions to carbohydrates in the leaves of all genotypes, increases in amino acids to GBU 44 and 48, and reductions of 40% and 43% to GBU 50 and 68, respectively; results also showed alterations in proline content. In the roots, increases in carbohydrates were observed only in GBU 48. Alterations in amino acids, protein, and proline were verified. Umbu trees presented isohydric behavior maintaining high leaf water potential and a great variability in organic solutes accumulation in response to drought with marked differences among the genotypes.Resumo em Inglês:
The ecophysiological behavior of brazilwood (Caesalpinia echinata Lam.) plants was evaluated as affected by light quantity and quality. Nine-month-old plants were cultivated under 0%, 50%, and 80% artificial shading, and natural shading imposed by a closed canopy for a period of 392 days. At the end of that period growth parameters were measured, including relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), specific leaf mass (SLM) and root:shoot ratio (R:S). Higher leaf area, dry mass and RGR were obtained under 50% artificial shade. Under full sunlight (0% shade), growth was satisfactory showing higher R:S and SLM. Growth was inhibited under 80% artificial and natural shading indicating that C. echinata is not pioneer-succession or climax specie. Simulating a gap, plants cultivated under artificial shade (50%) were transferred to full sunlight for an interval of 192 h, during which net photosynthesis (A), transpiration (E), stomatic conductance (gs), deficit of pressure vapor (VPDleaf-to-air) and the efficiency quantum potential of photosystem II (Fv/Fm) were analyzed. Plants transferred to full sunlight presented severe burning and abscission of the leaflets, as well as inhibition of A and of the photochemical efficiency of PSII (Fv/Fm). This observation associated with the reduced growth under full sunlight and better performance under moderate shade suggests characteristics of intermediate species.Resumo em Inglês:
Leaf gas exchange, water potential, and specific leaf area of two tropical semi-deciduous tree species, Brosimum lactescens S. Moore and Tovomita schomburgkii Planch & Triana, were quantified to establish how these properties were affected by seasonal variations in rainfall and leaf canopy position. The study was conducted at a site near Sinop Mato Grosso, Brazil, which is located within the ecotone of savanna and tropical rain forest. Both species exhibited significant declines in leaf water potential (ΨL), specific leaf area, area- and mass-based light saturated photosynthesis and dark respiration, and maximum stomatal conductance during the dry-season, suggesting that leaf structural properties and gas exchange are significantly altered by drought that develops during the 4-month dry season. Internal leaf CO2 concentrations (Ci) were consistently lower during the dry season suggesting that the decline in maximum photosynthesis was due in part to a decline in stomatal conductance. However, seasonal variations in leaf gas exchange were larger for upper-canopy leaves, indicating an important interaction between drought stress and canopy position. The seasonal variation in leaf gas exchange and morphology was presumably due to a combination of drought stress and leaf lifespan. The results of this study suggest that drought has important implications for the leaf physiology and morphology of semi-deciduous Amazonian forest trees.Resumo em Português:
Variações na morfologia e alocação de biomassa em folhas e ramos foram investigadas em 15 espécies arbóreas de Cerrado com distintas fenologias foliares e crescendo em condições naturais. As espécies decíduas apresentaram maiores valores que as sempreverdes para razão entre massa de folhas e do ramo, área foliar individual, área foliar por ramo, índice de exposição foliar e número de folhas pelo comprimento do ramo. As diferenças acerca das relações ramo-folhagem entre os grupos fenológicos poderia ser explicada pelos ramos plagiotrópicos nas decíduas e pelos ramos eretos nas semidecíduas e sempre verdes. Ramos plagiotrópicos propiciam similar irradiância incidente ao longo do ramo e alta alocação de biomassa em favor das folhas sem auto-sombreamento da folhagem nas decíduas. A variação estrutural entre ramos curtos e longos foi indicada por uma relação exponencial entre o índice de exposição foliar com o comprimento do ramo em todas decíduas, em três semidecíduas e duas sempreverdes. Assim, especialmente nas decíduas, ramos curtos apresentam maior área foliar por comprimento de ramo do que ramos longos. A diferenciação entre ramos curtos e longos depende do comprimento do ramo nas decíduas em função do número de folhas no ramo ser pré-determinado nas gemas. Diferentemente, a neo-formação de folhas nas semidecíduas e sempreverdes mantêm mais constante a relação ramo-folhagem por comprimento de ramo, em função da folhagem ser produzida de acordo com o crescimento do ramo durante o ano. Em conclusão, a persistência da folhagem, inclinação de ramo, tipo de produção foliar, e alocação de recursos entre os componentes autotróficos e heterotróficos da copa são características interdependentes nas espécies arbóreas de Cerrado ao longo dos distintos grupos fenológicos foliares.Resumo em Inglês:
The morphology and the biomass allocation in shoots and leaves were investigated in 15 cerrado tree species with distinct leaf phenology growing under natural conditions. Higher values of leaf/shoot ratio on mass base, individual leaf area, leaf area per shoot, leaf display index, and leaf number per shoot length were found in deciduous than in evergreen species. The differences about shoot-foliage relationship across leaf phenological groups could be explained by plagiotropic shoots on deciduous and by erect shoots in semideciduous and evergreen species. Plagiotropic shoots allow similar irradiance along shoots and high biomass allocation in favor of leaves without foliage self-shading in deciduous tree species. The structural differentiation between short and long shoots was indicated by an exponential relationship between leaf display index and shoot length in all deciduous, in three semideciduous, and in two evergreen species. Therefore, especially in deciduous, the short shoots had higher leaf area per unit of length than the long shoots. The differentiation between short and long shoots depends on the shoot length in deciduous because of the leaf number on shoot is predetermined in buds. Contrastingly, the leaf neo-formation in semideciduous and in evergreen tree species keeps the shoot-leaf relationship per shoot length more constant, because of the foliage being produced according to the shoot growth during the year. In conclusion, the foliage persistence, the shoot inclination, the type of leaf production and the resources allocation between autotrophic and heterotrophic vegetative canopy parts are interdependent in cerrado tree species across different leaf phenological groups.