La fluorescence de la chlorophylle sur l'orge (Hordeum Vulgare L.): une possible voie pour le criblage de varietés tolerantes a la salinité et a la sécheresse

Preliminares de la publicación : Portada, Resúmenes, Índice (Obra completa: 122 Pags.). Tesis presentada y públicamente defendida en el I.A.M.Z. para la obtención del diploma de Altos Estudios del C.I.H.E.A.M. (Centro Internacional de Altos Estudios Agronómicos Mediterráneos).[FR] Dans ce travail on a testé des différentes méthodes basées sur la fluorescence de la chlorophylle in vivo pour l'évaluation de cultivars d'orge pour la tolérance a la salinité et a la sécheresse. Les feuilles d'orge coupées et incubées dans l'eau a l'obscurité, dans une solution saline a l'obscurité, ou dans l'eau a la lumiere, n'ont pas montré une variation apparente de la cinétique rapide de la fluorescence de la chlorophylle a température ambiante. Cependant, les feuilles d'orge coupées et incubées dans une solution saline a la lumiere ont montré une variation de la cinétique rapide de la fluorescence de la chlorophylle a température ambiante. Ce traitement induit une baisse du rapport Fv/Fp et une augmentation du rapport (Fi-Fo)/Fv. Dans ce travail on a trouvé une corrélation de (Fi-Fo)/Fv avec la CE50 pour germination-émergence sur 15 variétés d'orge. D'autre part, la cinétique de la fluorescence lente mesurée par les rapports (P-S)/S et le rapport de vitalité (P-T)/T semble difficile a utiliser pour le criblage des variétés résistantes a la salinité, si bien le rapport (P-S)/S peut jouer un role pour le criblage des variétés résistantes a la sécheresse. Aussi,on a obtenu des nouvelles informations sur l'effet de la salinité sur l'orge cultivée dans la TLA. En particulier, on a trouvé que l'efficience photochimique de PSII, mesuré sur feuilles non-détachées de la plante, ne semble pas changer en fonction de la salinité. Le fait illustré dans ce travail que la salinité et la sécheresse prédisposent la plante a etre affectée par des processus photoinhibitoires ou de régulation a la baisse de la photosynthese doit etre considérée pour établir des mét[ES] En este trabajo se han estudiado diferentes métodos de medida de la fluorescencia de clorofila, para su posible aplicación a la selección de cultivares de cebada tolerantes a salinidad y sequía. Las hojas de cebada cortadas e incubadas en la obscuridad, ya sea en agua 6 en una solución salina, así como las incubadas en agua a la luz no han mostrado cambios notables en la cinética rápida de la fluorescencia de clorofila a temperatura ambiente. Sin embargo, las hojas cortadas e incubadas en una solución salina a la luz han mostrado cambios en dicha cinética rápida. Estos cambios consisten en un descenso de la relación Fv/Fp y un aumento de la relación (Fi­Fo)/Fv. En este trabajo se ha encontrado una cierta correlación del parámetro (Fi-Fo)/Fv con la CE50 para germinación-emergencia en 15 variedades de cebada. Por otra parte, la cinética de fluorescencia lenta (medida por las relaciones (P-S)/S (P-T)/T) ha mostrado poca utilidad para la selección de variedades resistentes a la salinidad, aunque la relación (P-S)/S podria jugar un papel para la selección de variedades resistentes a la sequía. Además se han obtenido nuevas informaciones sobre el efecto de la salinidad en cebada cultivada en la TLA, ya que se ha encontrado que la eficencia fotoquimica de PSII medida en hojas todavía unidas a la planta no parece cambiar con la salinidad. Los datos obtenidos sugieren que la salinidad y la sequía predisponen la planta a procesos de fotoinhibición o regulación a la baja de fotosíntesis, lo que ha de ser tenido en cuenta para establecer métodos de selección para la tolerencia a estreses abióticos.[EN] Severa! parameters derived from the chlorophyll fluorescence induction curves have been evaluated for its possible application in the screening of barley cultivars for salinity and drought tolerance. Barley leaves incubated in the dark, in water or in saline solutions, and barley leaves incubated in water at high light intensities show no significant changes in the chlorophyll fluorescence rapid kinetics. However, the combination of the salt stress and high light intensities induces measurable changes in the chlorophyll fluorescence rapid kinetics. These changes consist in a decrease in the Fv/Fp ratio and an increase in the (Fi-Fo)/Fv ratio. Furthermore, we have found using fifteen barley cultivars a significant correlation between the (Fi-Fo)/Fv ratio after salt-light treatment and the CE50 for germination-emergence. The chlorophyll fluorescence slow kinetics, measured through the (P-S)/S and (P­T)!T ratios, seems of limited usefulness for salinity tolerance screening, although the (P-S)/S ratio may have sorne utility in the screening for drought tolerance. V-./e have also obtained new information in the effect of salinity on barley grown in the TLA, since we have found that the photochemical effeciency of PSI! measured in attached leaves does not change in response to salinity. The result found in this work that the salt stress may promote the down regulation of photosynthesis through photoinhibition or other causes, can be used in the practice to establish screening methods for tolerance to this abiotic stress.Peer reviewe

Evaluación de la tolerancia a estreses ambientales en plantas cultivadas mediante técnicas de fluorescencia de clorofila, análisis de pigmentos y contenido mineral

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Photosystem II efficiency and mechanisms of energy dissipation in iron-deficient, field-grown pear trees (Pyrus communis L.)

The dark-adapted Photosystem II efficiency of field-grown pear leaves, estimated by the variable to maximum chlorophyll fluorescence ratio, was little affected by moderate and severe iron deficiency. Only extremely iron-deficient leaves showed a decreased Photosystem II efficiency after dark adaptation. Midday depressions in Photosystem II efficiency were still found after short-term dark-adaptation in iron-deficient leaves, indicating that Photosystem II down-regulation occurred when the leaves were illuminated by excessive irradiance. The actual Photosystem II efficiency at steady-state photosynthesis was decreased by iron deficiency both early in the morning and at midday, due to closure of Photosystem II reaction centers and decreases of the intrinsic Photosystem II efficiency. Iron deficiency decreased the amount of light in excess of that which can be used in photosynthesis not only by decreasing absorptance, but also by increasing the relative amount of light dissipated thermally by the Photosystem II antenna. When compared to the controls, iron-deficient pear leaves dissipated thermally up to 20% more of the light absorbed by the Photosystem II, both early in the morning and at midday. At low light iron-deficient leaves with high violaxanthin cycle pigments to chlorophyll ratios had increases in pigment de-epoxidation, non-photochemical quenching and thermal dissipation. Our data suggest that ΔpH could be the major factor controlling thermal energy dissipation, and that large (more than 10-fold) changes in the zeaxanthin plus antheraxanthin to chlorophyll molar ratio caused by iron deficiency were associated only to moderate increases in the extent of photoprotection.This work was supported by grants AGF97-1177 from the Spanish Comisión Interministerial de Ciencia y Tecnología to A.A. and PB97-1176 from the Spanish Dirección General de Investigación Científica y Técnica and AIR3-CT94-1973 from the Commission of European Communities to J.A. Support to F.M. and R.B. was provided by a contract from the Spanish Ministry of Science and Culture and a fellowship from the Spanish Institute of International Cooperation.Peer Reviewe

Energy dissipation in the leaves of Fe‐deficient pear trees grown in the field

11 Pags.- 1 Tabl.Chlorophyll fluorescence has been used to investigate the degree of energy dissipation in leaves of pear trees affected by iron deficiency in the field. The experiments were carried out in the presence of moderate water stress in 1996, and in the absence of water stress in 1997. In both cases, high photosynthetic photon flux densities were present at midday. Sustained damage to photosystem II (photoinhibition) was not observed. However, chlorotic leaves showed photosynthesis down‐regulation processes that were enhanced by moderate water stress. These protective mechanisms were associated with decreases in the intrinsic efficiency of photosystem II and increases in non‐photochemical quenching. As a consequence of these protective processes, the amount of light absorbed by photosystem II that was thermally dissipated was larger in iron‐chlorotic leaves than in controls, both early in the morning and at midday. These data indicate that iron‐chlorotic leaves are protected against light excess not only by a decreased light absorption but also by photosynthesis down‐regulation processes.Supported by grants AGR97-1177 from the CICYT to A.A. and PB94-0086 from the DGICYT and AIR3-CT94-1973 from the Commission of European Communities to J.A.Supported for F.M. and R.B. was by a contract from the Spanish MEC and by a predoctoral fellowship from the Spanish ICMA, respectively.Peer reviewe

Effects of salinity on the photosynthetic pigment composition of barley (Hordeum vulgare L.) grown under a triple-line-source sprinkler system in the field

The effects of salinity on the flag leaf photosynthetic pigment contents and photosystem two efficiency have been studied in several cultivars of barley (Hordeum vulgare L.) in four growing seasons. Barley was grown in a triple-line-source sprinkler system, that maintains a linear soil salinity gradient. Salinity induced minor increases in the flag leaf total chlorophyll content, but did not cause significant changes in the relative pigment composition. The photosynthetic pigment stoichiometry of flag leaves was in the ranges 20-40: 100-200:110-180:90-150:230-290: 1000 (mol: mol) for neoxanthin: V+A+Z pigments: lutein: β-carotene:chlorophyll b:chlorophyll a. We observed changes in the pigment stoichiometry from year to year, indicating that the pigment composition of the flag barley leaf depends markedly on the environmental conditions. The actual efficiency of photosystem two, measured at full sun in the field with modulated chlorophyll fluorescence techniques, had small changes in response to salinity in the triple-line-source sprinkler system, whereas the non-photochemical fluorescence quenching increased in response to moderate salinity.Peer Reviewe

Remote and near-contact chlorophyll fluorescence during photosynthetic induction in iron-deficient sugar beet leaves

A comparison of time-resolved, laser-induced remote sensing and pulse amplitude modulation near-contact techniques has been carried out during photosynthetic induction in iron-deficient sugar beet leaves. Iron deficiency caused increases in the mean chlorophyll fluorescence lifetime. These increased chlorophyll fluorescence lifetimes occurred in dark-adapted leaves, during a sudden increase in light intensity and also at steady-state photosynthesis. Chlorophyll fluorescence lifetimes were correlated with the extent of nonphotochemical and/or photochemical quenching. During most of the photosynthetic induction period, Fe-deficient leaves showed lower actual PSII efficiencies than control leaves, due to decreases in photochemical quenching and intrinsic PSII efficiency. During photosynthetic induction Fe deficiency decreased the proportion of light absorbed by the PSII antenna that is used in photochemistry and increased the proportion dissipated thermally within the PSII antenna, the later being well correlated with nonphotochemical quenching. Laser instrumentation offers new perspectives for monitoring effects of stress conditions in plants at large spatial scales. | A comparison of time-resolved, laser-induced remote sensing and pulse amplitude modulation near-contact techniques has been carried out during photosynthetic induction in iron-deficient sugar beet leaves. Iron deficiency caused increases in the mean chlorophyll fluorescence lifetime. These increased chlorophyll fluorescence lifetimes occurred in dark-adapted leaves, during a sudden increase in light intensity and also at steady-state photosynthesis. Chlorophyll fluorescence lifetimes were correlated with the extent of nonphotochemical and/or photochemical quenching. During most of the photosynthetic induction period, Fe-deficient leaves showed lower actual PSII efficiencies than control leaves, due to decreases in photochemical quenching and intrinsic PSII efficiency. During photosynthetic induction Fe deficiency decreased the proportion of light absorbed by the PSII antenna that is used in photochemistry and increased the proportion dissipated thermally within the PSII antenna, the later being well correlated with nonphotochemical quenching. Laser instrumentation offers new perspectives for monitoring effects of stress conditions in plants at large spatial scales.Peer Reviewe

Chlorophyll Fluorescence as a Possible Tool for Salinity Tolerance Screening in Barley (Hordeum vulgare L.)

The application of chlorophyll fluorescence measurements to screening barley (Hordeum vulgare L.) genotypes for salinity tolerance has been investigated. Excised barley leaves were cut under water and incubated with the cut end immersed in water or in a 100-mM NaCl solution, either in the dark or in high light. Changes in rapid fluorescence kinetics occurred in excised barley leaves exposed to the saline solution only when the incubation was carried out in the presence of high light. Fluorescence changes consisted of decreases in the variable to maximum fluorescence ratio and in increases in the relative proportion of variable fluorescence leading to point I in the Kautsky fluorescence induction curve. These relative increases in fluorescence at point I appeared to arise from a delayed plastoquinone reoxidation in the dark, since they disappeared after short, far-red illumination, which is known to excite photosystem I preferentially. We show that a significant correlation existed between some fluorescence parameters, measured after a combined salt and high-light treatment, and other independent measurements of salinity tolerance. These results suggest that chlorophyll fluorescence, and especially the relative fluorescence at point I in the Kautsky fluorescence induction curve, could be used for the screening of barley genotypes for salinity tolerance.Supported by grants from DirecciÓn General de Investigación Científica y Técnica (PB91-0057) and European Community (Science and Technology for Development TS2*.0294.ES). R.B. was supported by a master's thesis fellowship from the Intemational Center for Advanced Agronomic Mediterranean Studies-Mediterranean Agronomic Institute of Zaragoza. F.M. was supported by a fellowship from Consejo Asesor de Investigación -Diputación General de Aragón.Peer reviewe

Iron deficiency in peach trees: Effects on leaf chlorophyll and nutrient concentrations in flowers and leaves

The effects of iron deficiency on the leaf chlorophyll concentrations and on the macro- (N, P, K, Ca and Mg) and micro-nutrient (Fe, Mn, Zn and Cu) composition of flowers (at full bloom) and leaves (60 and 120 days after full bloom) of field-grown peach (Prunus persica L. Batsch) trees were investigated. Flowers and leaves were taken and analysed from fifty individual trees. Our data indicate that large decreases in leaf chlorophyll concentration were found at the beginning of the season in control trees, possibly associated to a 'dilution' effect by leaf growth, that were later followed by leaf chlorophyll concentration increases. Leaf Fe chlorosis apparently results from two different processes, the dilution of leaf Chl caused by growth and the subsequent inability to produce and/or stabilize new Chl molecules in the thylakoid membrane. Iron chlorosis did not change the seasonal change patterns of any of the nutrients studied. In Fe-deficient trees the K concentration and the K/Ca ratio were high not only in leaves but also in flowers, indicating that this is a characteristic of Fe-deficient plant tissue in the whole fruit tree growing season. Flower Fe concentrations were well correlated with the degree of chlorosis developed later in the season by the trees, suggesting that flower analysis could be used for the prognosis of Fe deficiency in peach.Peer Reviewe

Effects of salinity on chlorophyll fluorescence and photosynthesis of barley (Hordeum vulgare L.) grown under a triple-line-source sprinkler system in the field

In flag leaves of four cultivars of barley (Hordeum vulgare L.) grown in the field under a triple-line-source sprinkler system, that produces a linear soil salinity gradient, a decrease in net carbon dioxide assimilation rate (P(N)) and stomatal conductance for water vapour (g(s)) was found. These changes were related to salinity tolerance at moderate salinity. With increasing salinity, P(N) was saturated at low irradiances and stomatal frequencies increased. A decrease in photosystem 2 (PS2) efficiency was not found in the field after dark adaptation even at high salinity. Salinity induced only small decreases in the actual PS2 efficiency at midday steady-state photosynthesis, indicating that the photosynthetic electron transport was little affected by salinity. Therefore, using PS2 efficiency estimates in attached leaves is probably not a useful tool to screen barley genotypes grown under saline conditions in the field for salinity tolerance. In contrast, excised flag leaves from high salinity plots, once in the laboratory, exhibited a decrease in the variable to maximum chlorophyll fluorescence ratio as compared to excised leaves from control plants. On the other hand, the P(N) rate might allow for a good discrimination between tolerant and non-tolerant cultivars.Peer Reviewe