Restricted O2 consumption in pea roots induced by hexanoic acid is linked to depletion of Krebs cycle substrates

Plant roots are exposed to hypoxia in waterlogged soils, and they are further challenged by specific phytotoxins produced by microorganisms in such conditions. One such toxin is hexanoic acid (HxA), which, at toxic levels, causes a strong decline in root O2 consumption. However, the mechanism underlying this process is still unknown. We treated pea (Pisum sativum L.) roots with 20 mM HxA at pH 5.0 and 6.0 for a short time (1 h) and measured leakage of key electrolytes such as metal cations, malate, citrate and nonstructural carbohydrates (NSC). After treatment, mitochondria were isolated to assess their functionality evaluated as electrical potential and O2 consumption rate. HxA treatment resulted in root tissue extrusion of K+, malate, citrate and NSC, but only the leakage of the organic acids and NSC increased at pH 5.0, concomitantly with the inhibition of O2 consumption. The activity of mitochondria isolated from treated roots was almost unaffected, showing just a slight decrease in oxygen consumption after treatment at pH 5.0. Similar results were obtained by treating the pea roots with another organic acid with a short carbon chain, that is, butyric acid. Based on these results, we propose a model in which HxA, in its undissociated form prevalent at acidic pH, stimulates the efflux of citrate, malate and NSC, which would, in turn, cause starvation of mitochondrial respiratory substrates of the Krebs cycle and a consequent decline in O2 consumption. Cation extrusion would be a compensatory mechanism in order to restore plasma membrane potential

Efeito da taxa de carregamento sobre a remoção de poluentes de esgoto em sistemas alagados construídos

Objetivou-se estudar o efeito da taxa de carregamento sobre a eficiência de sistemas alagados, construídos de escoamento horizontal subsuperficial (SAC-EHSS), em remover poluentes de esgoto sanitário. Os SAC-EHSS foram alimentados com efluente proveniente de tanque séptico, sob taxas de carregamento orgânico volumétrico (TCO V) de 53 a 231 g m-3d-1 de demanda química de oxigênio (DQO total) e as associadas taxas de carregamento (TC V) de demanda química de oxigênio solúvel, sólidos suspensos totais (SST), nitrogênio total (N-Total) e fósforo total (P-Total). Para avaliação de desempenho dos SAC-EHSS, as mesmas variáveis foram quantificadas em seu efluente. Relação linear e positiva foi obtida entre as taxas de remoção de DQO total, DQO solúvel e SST, e as TC V, nas faixas em que foram aplicadas, além de não terem sido observados efeitos negativos desta variável sobre a eficiência na remoção desses poluentes. As taxas de remoção de N-Total e P-Total não apresentaram, entretanto, tendência de aumento com a TC V aplicada nos SAC- EHSS, cultivados com taboa e utilizados no tratamento de efluente sanitário. As cargas aplicadas desses nutrientes devem ser consideradas referenciais no dimensionamento desses sistemas, caso se queira maximizar a remoção global de poluentes da água residuária

Tratamento de esgoto sanitário em sistemas alagados construídos cultivados com lírio-amarelo

Neste artigo, avaliou-se a eficiência de quatro sistemas alagados construídos (SACs) no tratamento de esgoto sanitário após ser submetido a tratamento preliminar e, no caso de alguns SACs, a tratamento primário (tanque séptico). Os SACs foram cultivados com lírio-amarelo (Hemerocallis flava), tendo a brita #0 como meio suporte, e submetidos às taxas de carregamento orgânico (TCO) de esgoto sanitário, em termos de DBO (kg ha-1 d-1), de 44; 98; 230 e 395 kg ha-1 d-1 e tempos de detenção hidráulica (TDH) de 3,9; 2,0; 1,0 e 0,75 dias, respectivamente. Para avaliar a eficiência dos sistemas, foram realizadas, no afluente e no efluente aos SACs, análises de DBO, DQO, SST, N-total, P-total, K e Na durante 6 meses de funcionamento do sistema. Nos SACs, houve predominância do ambiente anóxico/aeróbio, com remoção de SST, DBO e DQO, suficiente para atender aos padrões de lançamento de efluentes estabelecidos na legislação ambiental do Estado de Minas Gerais

Cinética de remoção de matéria orgânica em sistemas alagados construídos cultivados com lírio amarelo

Objetivou-se, com a realização deste trabalho, obter o ajuste do modelo matemático adaptado de cinética de primeira ordem e os respectivos parâmetros cinéticos para descrição da degradação da matéria orgânica em SACs cultivados com lírio amarelo (Hemerocallis flava), no tratamento de esgoto doméstico. Os SACs foram cultivados com lírio amarelo e submetidos a diferentes taxas de carregamento orgânico superficial (TCOs) de esgoto doméstico: 44; 98; 230 e 395 kg ha-1 d-1 de DBO. O modelo matemático adaptado de decaimento do material orgânico apresentou bom ajuste e descreveu adequadamente a cinética de remoção de matéria orgânica (DQO) nos sistemas avaliados apresentando, geralmente, R² superior a 75%. Em ordem crescente de TCO valores de coeficientes de degradação (Kv) foram, respectivamente, de 0,45; 0,69; 1,23 e 1,72 d-1, considerados baixos para os dois primeiros SACs e normais para os outros dois, e os valores de "n" de 0,448; 0,107; 0,327 e 0,461, na faixa normalmente encontrada na literatura.This work aimed to obtain the adjustment of the mathematical model adapted from the first order kinetics and its respective parameters for describing the organic matter degradation in constructed wetlands (CWs) planted with yellow lily (Hemerocallis flava) for the treatment of domestic sewage. The CWs were cultivated with yellow lily and subjected to different surface organic loading rates (TCOs) of domestic sewage: 44, 98, 230 and 395 kg ha-1 day-1 BOD. The mathematical model adapted from the decay of organic material showed a good fit and adequately described the kinetics of removal of organic matter (COD) in the evaluated systems, with generally more than 75% R². In ascending order of TCO values of degradation coefficients (Kv) were, respectively, of 0.45, 0.69, 1.23 and 1.72 d-1, considered low for the first two CWs and normal for the other two, and the values of "n" of 0.448, 0.107, 0.327 and 0.461 in the range normally found in the literature

Spatio-temporal relief from hypoxia and production of reactive oxygen species during bud burst in grapevine (Vitis vinifera L.)

Background and Aims: Plants regulate cellular oxygen partial pressures (pO2), together with reduction/ oxidation (redox) state to manage rapid developmental transitions such as bud burst after a period of quiescence. However, our understanding of pO2 regulation in complex meristematic organs such as buds is incomplete, and particularly lacks spatial resolution. Methods: The gradients in pO2 from the outer scales to the primary meristem complex were measured in grapevine (Vitis vinifera L.) buds, together with respiratory CO2 production rates and the accumulation of superoxide and hydrogen peroxide, from ecodormancy through the first 72 h preceding bud burst, triggered by the transition from low to ambient temperatures. Key Results: Steep internal pO2 gradients were measured in dormant buds with values as low as 2.5 kPa found in the core of the bud prior to bud burst. Respiratory CO2 production rates increased soon after the transition from low to ambient temperatures and the bud tissues gradually became oxygenated in a patterned process. Within 3 h of the transition to ambient temperatures, superoxide accumulation was observed in the cambial meristem, co-localising with lignified cellulose associated with pro-vascular tissues. Thereafter, superoxide accumulated in other areas subtending the apical meristem complex, in the absence of significant hydrogen peroxide accumulation, except in the cambial meristem. By 72 h, the internal pO2 gradient showed a biphasic profile, where the minimum pO2 was external to the core of the bud complex. Conclusions: Spatial and temporal control of the tissue oxygen environment occurs within quiescent buds, and the transition from quiescence to bud burst is accompanied by a regulated relaxation of the hypoxic state and accumulation of reactive oxygen species (ROS) within the developing cambium and vascular tissues of the heterotrophic grapevine buds

Evaluation of root porosity and radial oxygen loss of disomic addition lines of Hordeum marinum in wheat

Hordeum marinum Huds. is a waterlogging-tolerant wild relative of wheat (Triticum aestivum L.). Greater root porosity (gas volume per root volume) and formation of a barrier to reduce root radial O₂ loss (ROL) contribute to the waterlogging tolerance of H. marinum and these traits are evident in some H. marinum–wheat amphiploids. We evaluated root porosity, ROL patterns and tolerance to hypoxic stagnant conditions for 10 various H. marinum (two accessions) disomic chromosome addition (DA) lines in wheat (two varieties), produced from two H. marinum–wheat amphiploids and their recurrent wheat parents. None of the DA lines had a barrier to ROL or higher root porosity than the wheat parents. Lack of a root ROL barrier in the six DA lines for H. marinum accessionH21 in Chinese Spring (CS) wheat indicates that the gene(s) for this trait do not reside on one of these six chromosomes; unfortunately, chromosome 3 of H. marinum has not been isolated in CS. Unlike the H21–CS amphiploid, which formed a partial ROL barrier in roots, the H90–Westonia amphiploid and the four derived DA lines available did not. The unaltered root aeration traits in the available DA lines challenge the strategy of using H. marinum as a donor of these traits to wheat.Dennis Konnerup, A.I. Malik, A.K.M.R. Islam and Timothy David Colme

Sensitivity of chickpea and faba bean to root-zone hypoxia, elevated ethylene, and carbon dioxide

During soil waterlogging, plants experience O2 deficits, elevated ethylene, and high CO2 in the root-zone. The effects on chickpea (Cicer arietinum L.) and faba bean (Vicia faba L.) of ethylene (2 μL L−1), CO2 (2–20% v/v) or deoxygenated stagnant solution were evaluated. Ethylene and high CO2 reduced root growth of both species, but O2 deficiency had the most damaging effect and especially so for chickpea. Chickpea suffered root tip death when in deoxygenated stagnant solution. High CO2 inhibited root respiration and reduced growth, whereas sugars accumulated in root tips, of both species. Gas-filled porosity of the basal portion of the primary root of faba bean (23%, v/v) was greater than for chickpea (10%), and internal O2 movement was more prominent in faba bean when in an O2-free medium. Ethylene treatment increased the porosity of roots. The damaging effects of low O2, such as death of root tips, resulted in poor recovery of root growth upon reaeration. In conclusion, ethylene and high CO2 partially inhibited root extension in both species, but low O2 in deoxygenated stagnant solution had the most damaging effect, even causing death of root tips in chickpea, which was more sensitive to the low O2 condition than faba bean

Gas exchange and growth responses to nutrient enrichment in invasive Glyceria maxima and native New Zealand Carex species

We compared photosynthetic gas exchange, the photosynthesis-leaf nitrogen (N) relationship, and growth response to nutrient enrichment in the invasive wetland grass Glyceria maxima (Hartman) Holmburg with two native New Zealand Carex sedges (C. virgata Boott and C. secta Boott), to explore the ecophysiological traits contributing to invasive behaviour. The photosynthesis-nitrogen relationship was uniform across all three species, and the maximum light-saturated rate of photosynthesis expressed on a leaf area basis (A maxa) did not differ significantly between species. However, specific leaf area (SLA) in G. maxima (17±6m 2kg -1) was 1.3 times that of the sedges, leading to 1.4 times higher maximum rates of photosynthesis (350-400nmolCO 2g -1 dry masss -1) expressed on a leaf mass basis (A maxm) when N supply was unlimited, compared to the sedges (<300nmolCO 2g -1 dry masss -1). Analysis of Covariance (ANCOVA) revealed significant positive relationships between leaf N content and chlorophyll a:b ratios, stomatal conductance (g s), dark respiration rate (R d), and the photosynthetic light saturation point (I k) in G. maxima, but not in the sedges. ANCOVA also identified that, compared to G. maxima, the sedges had 2.4 times higher intrinsic water use efficiency (A/g s: range 20-70 cf. 8-30μmolCO 2mol -1 H 2O) and 1.6 times higher nitrogen use efficiency (NUE: 25-30 cf. 20-23gdry massg -1N) under excess N supply. Relative growth rates (RGR) were not significantly higher in G. maxima than the sedges, but correlations between leaf N, gas exchange parameters (A maxa, A maxm, R d and g s) and RGR were all highly significant in G. maxima, whereas they were weak or absent in the sedges. Allocation of biomass (root:shoot ratio, leaf mass ratio, root mass ratio), plant N and P content, and allocation of N to leaves all showed significantly greater phenotypic plasticity and stronger correlation to final biomass in G. maxima than in the sedges. We therefore conclude that photosynthesis and growth rates are not intrinsically higher in this invader than in the native species with which it competes, but that its success under nutrient enrichment is a consequence of greater physiological responsiveness and growth plasticity, and stronger integration between gas exchange and growth, coupled with indifference to resource wastage (i.e. low WUE and NUE) at high nutrient supply. The poorer performance of G. maxima than the sedges under low nutrient supply supports the importance of nutrient management, especially N, as a strategy to minimise the invasive behaviour of fast-growing herbaceous species in wetlands. © 2012 Elsevier B.V