Gabriela Cordon

Re-absorption of chlorophyll fluorescence in leaves revisited. A comparison of correction models

The application of correction methods to account for re-absorption of chlorophyll fluorescence emission in leaves is subject to a number of controversies in the literature. These uncertainties lead to high discrepancies in the corrected spectral distribution of fluorescence and consequently in the interpretation of related physiological features of plants, according to the chosen method used in the process of correction. In this research, three correction methods, based on transmittance and/or reflectance measurements on leaves, were analysed comparatively. One method gave high values for the corrected fluorescence ratio between 685 nm and 737 nm (F685/F737 approximately 7 to 20 according to the different species of leaves). The two other methods were found to give similar results with corrected fluorescence ratios around a value of two (F685/F737 approximately 2). While the first method was developed in the light of empirical considerations, the latter two models are based upon defined physical approaches depicting interaction between light and matter. The theoretical basis of these methods, the validation methodologies used to support them and the similarity in the spectra corrected by light re-absorption for both models, all showed that they should be treated as confident and suitable approximations to solve the problem of light re-absorption in leaves.

Atrazine and Methyl Viologen Effects on Chlorophyll-a Fluorescence Revisited-Implications in Photosystems Emission and Ecotoxicity Assessment.

In this work, we use the effect of herbicides that affect the photosynthetic chain at defined sites in the photosynthetic reaction steps to derive information about the fluorescence emission of photosystems. The interpretation of spectral data from treated and control plants, after correction for light reabsorption processes, allowed us to elucidate current controversies in the subject. Results were compatible with the fact that a nonnegligible Photosystem I contribution to chlorophyll fluorescence in plants at room temperature does exist. In another aspect, variable and nonvariable chlorophyll fluorescence were comparatively tested as bioindicators for detection of both herbicides in aquatic environment. Both methodologies were appropriate tools for this purpose. However, they showed better sensitivity for pollutants disconnecting Photosystem II–Photosystem I by blocking the electron transport between them as Atrazine. Specifically, changes in the (experimental and corrected by light reabsorption) red to far red fluorescence ratio, in the maximum photochemical quantum yield and in the quantum efficiency of Photosytem II for increasing concentrations of herbicides have been measured and compared. The most sensitive bioindicator for both herbicides was the quantum efficiency of Photosystem II.

Optical properties of the adaxial and abaxial faces of leaves. Chlorophyll fluorescence, absorption and scattering coefficients.

Emission fluorescence spectra were obtained for the adaxial and abaxial faces of dicotyledonous (Ficus benjamina L., Ficus elastica, Gardenia jasminoides and Hedera helix) and monocotyledonous leaves (Gladiolus spp. and Dracaena cincta bicolor). After correction by light-re-absorption processes, using a previously published physical model, the adaxial faces of dicotyledons showed a fluorescence ratio Fred/Ffar-red rather lower than the respective values for the abaxial faces. Monocotyledons and shade-adapted-plants showed similar values for the corrected fluorescence ratio for both faces. Even when differences in experimental fluorescence emission from adaxial and abaxial leaves in dicotyledons are mostly due to light re-absorption processes, the residual dissimilarity found after application of the correction model would point to the fact that fluorescence re-absorption is not the only responsible for the observed disparity. It was concluded that light re-absorption processes does not account entirely for the differences in the experimental emission spectra between adaxial and abaxial leaves. Differences that remains still present after correction might be interpreted in terms of a different photosystem ratio (PSII/PSI). Experiments at low temperature sustained this hypothesis. In dicotyledons, light reflectance for adaxial leaves was found to be lower than for the abaxial ones. It was mainly due to an increase in the scattering coefficient for the lower leaf-side. The absorption coefficient values were slightly higher for the upper leaf-side. During senescence of Ficus benjamina leaves, the scattering coefficient increased for both the upper and lower leaf-sides. With senescence time the absorption coefficient spectra broadened while the corrected fluorescence ratio (Fred/Ffar-red) decreased for both faces. The results pointed to a preferential destruction of photosystem II relative to photosystem I during senescence.

Chlorophyll fluorescence, photochemical reflective index and normalized difference vegetative index during plant senescence.

The relationship between the Photochemical Reflectance Index (PRI), Normalized Difference Vegetation Index (NDVI) and chlorophyll fluorescence along senescence was investigated in this work. Reflectance and radiance measurements were performed at canopy level in grass species presenting different photosynthetic metabolism: Avena sativa (C3) and Setaria italica (C4), at different stages of the natural senescence process. Sun induced-chlorophyll fluorescence at 760nm (SIF760) and the apparent fluorescence yield (SIF760/a, with a=irradiance at time of measurement) were extracted from the radiance spectra of canopies using the Fraunhofer Line Discrimination-method. The photosynthetic parameters derived from Kautsky kinetics and pigment content were also calculated at leaf level. Whilst stand level NDVI patterns were related to changes in the structure of canopies and not in pigment content, stand level PRI patterns suggested changes both in terms of canopy and of pigment content in leaves. Both SIF760/a and ΦPSII decreased progressively along senescence in both species. A strong increment in NPQ was evident in A. sativa while in S. italica NPQ values were lower. Our most important finding was that two chlorophyll fluorescence signals, ΦPSII and SIF760/a, correlated with the canopy PRI values in the two grasses assessed, even when tissues at different ontogenic stages were present. Even though significant changes occurred in the Total Chlr/Car ratio along senescence in both studied species, significant correlations between PRI and chlorophyll fluorescence signals might indicate the usefulness of this reflectance index as a proxy of photosynthetic RUE, at least under the conditions of this study. The relationships between stand level PRI and the fluorescence estimators (ΦPSII and SIF760/a) were positive in both cases. Therefore, an increase in PRI values as in the fluorescence parameters would indicate higher RUE.

ASSESSMENT OF THE ROLE OF FLUORESCENT ROOT AND SEED EXUDATES IN CROP PLANTS

Fluorescent compounds have been reported in plant leaves, having an important biological role in the protection towards UV irradiation. It is also known that stress conditions in plants stimulate the production of some of these compounds in their aerial portion. However, less is known about their production by roots or seeds and their presence in the soil surrounding them. We report here that, soybean, sunflowers and rapeseed produced fluorescent seed and root exudates. Phosphorus deficiency in rapeseed stimulates the excretion of fluorescent compounds by roots, mainly chlorogenic acid and scopoletin. When the effect of the fluorescent fraction from soybean seed exudates on Macrophomina phaseolina was tested, an enhanced induction of sclerotia formation, hyphal squeezing and lysis in the mycelium was observed. The fluorescent compounds and perhaps other chemical molecules also present in exudates might constitute a transitory defense barrier against early attack by pathogens.

Arsenic effects on some photophysical parameters of Cichorium intybus under different radiation and water irrigation regimes

The presence of arsenic (As) in groundwater is a major problem in several parts of Latin America. In the present work, non-destructive approaches to monitor the effects of As on plants of Cichorium intybus, an herbaceous Asteraceae, were explored. In this sense, the effects of As at different levels of water and radiation were evaluated on these crops. Plants were grown in a greenhouse, watered daily with As solutions and exposed to different water and/or light conditions for four months, using a three-factor (As, water, radiation) and two-level resource (As vs non As, field capacity vs half-field capacity condition, light vs shade condition) factorial design. The parameters most affected by this treatment were the area under the first derivative of the reflectance spectrum in the blue region, chlorophyll concentration, the Fred/Ffar-red fluorescence ratio and the quantum yield for the photophysical decay. These changes indicated the ability of this plant species to be a biomonitor for the presence of arsenic in irrigation water. Interestingly, it was further proved in this work that the biomonitoring capacity was enhanced in the presence of sunlight.

Las elusivas ciencias ambientales: aspectos epistemológicos y socio-históricos

El presente articulo completo esta referido al Sistema Nacional de Ciencia, Tecnologia e Innovacion en Cuba desde 1959 hasta el ano 2012. Se selecciono esta etapa debido a que anteriormente no habia actividades cientificas en el pais. Tambien se enuncian las interrelaciones principales en los temas de ambiente y sostenibilidad en dicho sistema y se exponene ejemplos relevantes de la ciencia cubana.La continuidad, seguimiento y evaluacion de los planes ambientales o de sustentabilidad de las Instituciones de Educacion Superior, presentan una serie de procesos de mayor o menor incertidumbre para que trascienda, en a mediano y largo plazo, los cambios de sus autoridades universitarias. Por lo tanto es necesario planear una estrategia que le de mayor certidumbre, buscando hacer cambios en la estructura universitaria, en su legislacion y el uso de bases de datos inteligentes. Desde nuestras vivencias en la Universidad Veracruzana, se desarrolla tres procesos articulados que nos dan mayor certidumbre en la aplicacion de los planes de sustentabilidad o ambientales, estos son: 1) La certidumbre del proceso de la sustentabilidad a mediano y largo plazo (Reglamento); 2) La apropiacion del proceso por la comunidad universitaria (Red Universitaria) y; 3) El seguimiento y la planeacion (Sistema de Informacion Geografica).O presente artigo e uma reflexao acerca do processo de formacao universitaria encontram-se possibilidades de incorporar a cultura da sustentabilidade por meio de acoes que ampliam o olhar dos atores sociais. O presente artigo relata acoes empreendidas pela UNIVALI-SC- BRASIL e explicita alguns resultados que podem ser evidenciados pelas mudancas de atitudes dos sujeitos fazem parte deste contexto. Nesse processo, e relevante introduzir indicadores sociais e ambientais que orientem diferentes projetos rumo a uma transicao socio-ecologica. As mudancas de tratamento do espaco fisico imprimem mudancas sutis na comunidade academica em geral, na revisao curricular, no processo de formacao continuada de professores, no processo de gestao da instituicao. Na integracao dos espacos fisicos e intelectuais da academia, cria-se e se constroi concepcoes que podem mobilizar as transformacoes necessarias ao caminho da busca de um mundo melhor, de valores eticos e de respeito as diferentes dimensoes entre natureza e cultura.Este trabajo presenta una revision sobre la dimension ambiental en materia institucional que intenta plasmar los avances y desafios en el sistema de ciencia y tecnologia en Argentina. El problema ambiental es un problema politico. El poder economico se ha globalizado mientras las instituciones politicas siguen ancladas al territorio y deben dar respuesta a sus sociedades. El caso de Argentina presenta singularidades que se pretenden revisar desde las formas en que se genera el conocimiento y la estructura de la produccion cientifica en el sistema. Lejos de dar respuestas o posturas rigidas o cripticas, este articulo intenta abrir el debate y generar interrogantes con vistas a un futuro sustentable con equidad social. Esta propuesta se organiza con una breve descripcion del sistema, su organizacion y estructura institucional, para dar lugar a una lectura sobre la dimension ambiental, y finalmente unas conclusiones provisorias sobre su complejidad.La infraestructura vial incide en el desarrollo economico pero la sostenibilidad de esta relacion depende de la gestion del territorio. El objetivo de este trabajo es hacer un diagnostico de la gestion territorial del proyecto de conexion vial Aburra-Cauca, mediante el analisis cualitativo de politicas publicas y el analisis cuantitativo de informacion espacial, para construir una linea base sobre el manejo del impacto ambiental, economico y social de la via. Los resultados muestran que con esta nueva via se busca soportar las apuestas productivas articulando los centros subregionales y comunicando el departamento de Antioquia y la ciudad de Medellin con el futuro puerto de Turbo en el caribe colombiano. La gestion territorial identificada privilegia el corto plazo, reduciendo el riesgo ambiental mediante la reubicacion de la poblacion afectada durante la fase de construccion de la via.RESUMEN Este articulo tiene como objetivo reflexionar sobre la formidable complejidad epistemologica de las ciencias ambientales, que no remiten formalmente solo al conjunto de ciencias naturales, sino tambien al de las ciencias sociales y humanas, asi como a otros saberes y practicas sociales. Esta complejidad presenta un desafio a sus investigadores, desde el planteo mismo del paradigma de conocimiento que los guia hasta las preguntas que orientan la pesquisa, el momento metodologico, el diseno seleccionado, las tecnicas y procedimientos utilizados y el dialogo interdisciplinario que estas ciencias concitan. Analiza como las cuestiones sociales moldearon el surgimiento de las ciencias ambientales y le dieron algunas caracteristicas propias, como ciencias orientadas a problemas. Asimismo, reflexiona sobre el objeto material de estas ciencias –el ambiente–. Por ultimo, el articulo plantea la cuestion de las escalas en el tratamiento del ambiente como herramientas necesarias para el abordaje de los estudios ambientales y su caracter sistemico e interdisciplinario. Todas estas dimensiones agregan densidad a la trama de lo ambiental y lo tornan un objeto de conocimiento complejo, con una naturaleza elusiva, indocil a las recetas y dificil de capturar en la investigacion desde un abordaje monodisciplinario.Esta comunicacion tiene como proposito expresar en pocas palabras la experiencia recogida en esta ultima decada entre la problematica de los residuos y la vinculacion social de la Universidad, en contextos de pobreza estructural. Escenarios de exclusion social donde el problema ambiental urbano adquiere nuevas formas territoriales, es decir, comunitarias. La universidad se encontro entonces con la necesidad de dar respuesta tanto en materia ambiental frente al tratamiento de los propios residuos como tambien interpelar la realidad social de los trabajadores urbanos del conurbano metropolitanos de Buenos Aires. El camino no ha sido sencillo, pero la experiencia ha sido mas que valiosa. En este sentido, se comparte algunos resultados y se ponen a discusion el caso de UBA VERDE.En este trabajo se analiza el Sistema Nacional de Ciencia, Tecnologia e Innovacion (SNCTI) y la forma en que influye en el desarrollo sustentable en Mexico. Se aborda un aspecto historico que data del ano 1950, momento en el que se crea el Instituto Nacional de la Investigacion Cientifica. Se reporta la evolucion del SNCTI que incluye su organizacion, los fondos de operacion, la formacion de recursos humanos y su relacion con el sector privado. Se examina la forma en que el sistema ha influido en el desarrollo del conocimiento y de la tecnologia en materia ambiental, asi como las capacidades con que cuenta el pais para la formacion de recursos humanos en el tema. Tambien se relaciona a este Sistema con diferentes programas que cada administracion del Gobierno Federal crea para fortaleces al desarrollo sustentable en Mexico.Este articulo presenta un analisis de la actual crisis de sustentabilidad que vive el planeta y a partir de ello aborda sus causas y la necesidad de cambiar la educacion superior, proponiendo algunas ideas rspecto a como debe ser la educacion que entregue la universidad en el futuroIntroducir una propuesta teorica como la economia ecologica (EE), alimentada por las leyes de la termodinamica y la ecologia, aspectos lejanos a las teorias economicas clasicas, en una facultad de economia tradicional no resulta facil. El articulo de reflexion propone senalar la necesidad de un pensamiento ambiental, que posibilite una educacion ambiental superior que a su vez evidencia la importancia de la EE en la formacion de los futuros profesionales. Para lograrlo, resulta preciso revisar primero el contexto de la teoria de la economia, para comprender, o no, la complejidad ambiental. Segundo, senalar algunas vertientes y potencialidades del pensamiento ambiental latinoamericano. Y finalmente, presento como ejemplo, la aplicacion del pensamiento ambiental como base de una educacion ambiental superior y estrategia de acercamiento preliminar a la EE, en un seminario electivo dictado durante varios semestres en la Facultad de Ciencias Economicas de la Universidad Nacional de Colombia