Efecto del glifosato sobre el crecimiento y acumulación de azúcares libres en dos biotipos de lolium perenne de distinta sensibilidad al herbicida

El movimiento sistémico del glifosato está determinado por el transporte de fotoasimilados. A su vez, la capacidad de un destino de consumir los asimilados está condicionada por su actividad metabólica. Pese a su importancia, la relación entre el glifosato y la síntesis de azúcares en hojas fuente ha sido poco abordada. El objetivo del presente trabajo fue evaluar los efectos del glifosato sobre el crecimiento y la acumulación de azúcares libres en dos biotipos de Lolium perenne de baja y alta sensibilidad al herbicida. Se trabajó con clones de ambos tipos de plantas, en macollaje, tratados con 1.440 g e.a. ha-1 de glifosato y sin tratamiento herbicida como controles. Se evaluó periódicamente el efecto del glifosato sobre el rebrote de hojas hasta las 50 horas post-aplicación y sobre los niveles de azúcares libres totales, reductores y no reductores en hojas a 1, 2, 3 y 5 días post-aplicación. A partir de las 25 horas post-aplicación, el glifosato provocó una disminución del crecimiento del 58% en el biotipo susceptible, con una acumulación de azúcares libres superior al 90% con relación al control, desde el primer día post-aplicación en adelante. La inhibición del crecimiento, inducida por el glifosato en plantas susceptibles, no depende de la limitación del traslado de fotoasimilados desde la parte aérea. Por tanto, la acumulación de azúcares libres en hojas podría explicarse por la caída en la tasa de crecimiento. En el biotipo de baja sensibilidad, en el que no se detectó inhibición del crecimiento, estos efectos fueron limitados.The systemic movement of glyphosate is determined by the transport of photoassimilates. In turn, the capacity of a destination to consume assimilates is conditioned by their metabolic activity. Despite its importance, the relationship between the glyphosate and the sugar synthesis from source leaves has been little studied. The aim of this work was to determine the effect of glyphosate on the growth and free sugar accumulation of two Lolium perenne biotypes of low and high glyphosate sensitivity. It was worked with clones of both types, in tillering, sprayed with 1,440 g a.e. ha-1 of glyphosate as treatments and without herbicide as controls. The glyphosate effects on the regrowth of leaves was studied until 50 hours post-application and on total free sugar, reducing free sugar and nonreducing free sugar from leaves to 1, 2, 3 and 5 days post-application were periodically evaluated. From 25 hours after glyphosate application, it caused on the susceptible biotype a growth decrease of 58% and an accumulation of free sugar above 90% compared to controls. In susceptible biotypes, growth inhibition does not depend on a reduced photoassimilate translocation from the overground part. Therefore, the free sugar accumulation in leaves could be explained by the fall in the rate of growth. These effects are limited in the low sensitivity biotype, where growth inhibition has not been detected

Regulation of Rubisco by inhibitors in the light

2-carboxy-D-arabinitol-1-phosphate (CA1P) bound to Rubisco either in leaf extracts or after purification can be displaced by SO42- ions. Thus, treatment of leaf extracts with a buffer containing 200 mol m-3 SO42- displaces any bound CA1P and enables measurement of maximum carboxylation potential. In tobacco leaves, the activity following treatment with SO42- ions ('maximal activity') is greater than the total Rubisco activity. The ratio of the two activities altered in a dynamic way with fluctuations in irradiance. Even in species which do not produce significant amounts of CA1P, the maximal activity greatly exceeded the total activity. Anion exchange separation of components in acid extracts confirmed the absence of CA1P in tobacco leaves harvested above an irradiance of 300 μmol quanta m-2 s-1, but the presence of another inhibitor of Rubisco. These results are consistent with the regulation of Rubisco activity by inhibitors other than CA1P which, like CA1P, can be displaced by SO42-ions

Universality of non-Ohmic shunt leakage in thin-film solar cells

We compare the dark current-voltage (IV) characteristics of three different thin-film solar cell types: hydrogenated amorphous silicon (a-Si:H) p-i-n cells, organic bulk heterojunction (BHJ) cells, and Cu(In, Ga)Se-2 (CIGS) cells. All three device types exhibit a significant shunt leakage current at low forward bias (V \u3c similar to 0.4) and reverse bias, which cannot be explained by the classical solar cell diode model. This parasitic shunt current exhibits non-Ohmic behavior, as opposed to the traditional constant shunt resistance model for photovoltaics. We show here that this shunt leakage (I-sh), across all three solar cell types considered, is characterized by the following common phenomenological features: (a) voltage symmetry about V = 0, (b) nonlinear (power law) voltage dependence, and (c) extremely weak temperature dependence. Based on this analysis, we provide a simple method of subtracting this shunt current component from the measured data and discuss its implications on dark IV parameter extraction. We propose a space charge limited (SCL) current model for capturing all these features of the shunt leakage in a consistent framework and discuss possible physical origin of the parasitic paths responsible for this shunt current mechanism. (C) 2010 American Institute of Physics. [doi:10.1063/1.3518509

Determination and significance of emerging algal toxins (cyanotoxins)

Cyanobacterial blooms have a long history and are widely recognized as sources of taste and odors in water supplies. There is an increasing concern for health effects in consumers with the identification of a number of toxic cyanobacterial metabolites. Cyanobacteria produce a range of toxins including peptide hepatotoxins (microcystins), neurotoxins (anatoxins and saxitoxins), cylindrospermopsin, and the lipopolysaccharide (LPS) endotoxins. Robust analytical methods must be available to monitor for toxins and assess their significance. An evaluation of isolated LPS endotoxins determined their toxicities to be very low. Methods were further developed for the determination of saxitoxins, anatoxin-a, and cylindrospermopsin. This included their determination in a single method. The neuroblastoma assay detected saxitoxins not determined by other methods. Gene probes for the detection of toxic cyanobacteria were applied to a number of field samples. Enzyme-linked immunosorbent assay (ELISA) methods, including commercially available test kits, were evaluated for determining microcystins with good results. A range of U.S. and Australian field samples were successfully analyzed using the above methods. Extraction methods for LPS endotoxins from cyanobacterial material were developed. Extracted LPS were then tested using temperature changes in injected mice. Deficiencies in existing analytical methods for specific toxins were used as the basis for selecting methods for further development. Kits based on ELISA procedures for determining microcystins have recently become available. Therefore, these were chosen for evaluation due to their simplicity and ease of use. The usefulness of the various methods was assessed by applying to them to a range of field samples