Botánica

The effects of red/far red (R/FR) ratios on leaf ascorbate (AA) and glutathione (GSH) accumulation were examined in common bean (Phaseolus vulgaris L.). Growth under low R/FR ratios resulted in a "shade" phenotype and much lower leaf AA and GSH contents than high (R/FR) ratios. Photosyn thesis rates were unaffected by changes in the R/FR ratio but leaf respiration rates, pyridine nucle otide pools and antioxidant enzyme activities were decreased under the low R/FR regime. The GSH Edited by Ulf-Ingo Flügge pool changed slowly in response to altered R/FR ratios but leaf ascorbate acclimated over a single photoperiod. We conclude that light quality signals, particularly R/FR ratios, are important regula

Barley is one of the most widely cultivated crops in rainfed areas of the Mediterranean, where drought is the main factor that limits yield. Knowledge of the physiological traits responsible for adaptation of barley cultivars to Mediterranean environments may be relevant for future breeding strategies. Yield potential versus drought tolerance is an open debate. Here, we studied two barley cultivars (Graphic and Kym), of similar time to anthesis and crop duration, that are widely cultivated in the western Mediterranean. Grain yield was evaluated in 41 field trials and ranged (averaged for the 16-32 cultivars assayed in each trial) from 0.7 to 9.1 Mg ha À1. Yield components and carbon isotope discrimination (D 13 C) of grains was analysed in another two trials. Graphic production was greater than Kym in all conditions. This greater yield was sustained mainly by more ears per unit ground area, which may be attributable to higher growth potential during tillering. Moreover, Graphic showed greater D 13 C of kernels, indicating improved water status even at the end of the crop cycle. To examine differences in early growth, these cultivars were grown in optimal conditions and then photosynthetic activity and biomass analysed at the end of tillering. Graphic showed greater above-ground and root biomass as well as total leaf area per plant and per tiller than Kym, and also tended to have more tillers per plant, but its shoot-to-root biomass ratio was lower. Nitrogen content per unit leaf area was correlated negatively with plant and with tiller leaf area and positively with the shoot-to-root biomass ratio. Photosynthetic rate per unit leaf area was lower in Graphic and positively related to a lower nitrogen content, whereas stomatal limitation of photosynthesis and water use www.elsevier.com/locate/fcr Field Crops Research 91 (2005) 149-160 Abbreviations: A, net CO 2 assimilation rate; A max , CO 2-saturated net CO 2 assimilation rate; A sat , light-saturated net CO 2 assimilation rate; c a , c i , ambient and intercellular CO 2 concentration, respectively; DW, dry weight; D 13 C, carbon isotope discrimination; F m and F 0 m , maximum fluorescence in dark-adapted and light-adapted leaves, respectively; F v /F m , maximum efficiency of PSII photochemistry after dark-adaptation; F 0 v =F 0 m , efficiency of energy capture by open PSII centers; F 0 o , minimum fluorescence yield in light-adapted state; f PSII , quantum yield of PSII electron transport; g s , stomatal conductance; J max,RuBP , maximum potential rate of electron transport contributing to ribulose 1,5-biphosphate regeneration; J max,PSII , the rate of PSII electron transport in saturating light and CO 2 ; l, stomatal limitation to A sat ; PPFD, photosynthetic active photon flux density; PSII, photosystem II; q P , photochemical quenching of chlorophyll fluorescence; R d , dark respiration; RuBP, ribulose 1,5bisphosphate; RWC, relative leaf water content; TR, transpiration rate; V c,max , maximum carboxylation velocity of Rubisco; WUE, water use efficiency; c w , leaf water potential.

The contribution of ear photosynthesis to grain filling in wheat (Triticum aestivum L.) is not well known. The main objective of this work was to evaluate this contribution through three different experimental approaches: (1) ear photosynthesis was reduced by removing awns or shading the ears (in combination with a defoliation treatment), (2) grain weight per ear was compared in an 'all shaded' crop versus plants where only the vegetative parts were shaded ('ear emerging'), and (3) ear photosynthesis was reduced with DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea), a specific inhibitor of photosystem II. In field experiments in La Plata (Argentina), cultivars Klein Escudo and BioINTA 3000 were subjected to awn removal and ear shading treatments, with or without severe defoliation, and to 'all canopy shaded' versus 'ear emerging' treatments. Although the estimated contribution of ear photosynthesis to grain yield differed depending on the experimental approach used (from about 12-42%), in general cv. Klein Escudo (with the largest awns) showed a greater contribution of ear photosynthesis. In both cultivars, the percentage contribution of ear photosynthesis was larger for defoliated plants. The magnitude of this contribution was positively associated with the length of awns of each cultivar. Awn removal had a nonsignificant (p ≤ 0.05) effect on grain weight per ear (GW ear) in the short-awned cv. BioINTA 3000. In cv. Klein Escudo, the effects of de-awning were larger, reaching values of ca. 15 and 19% decrease of GW ear in non-defoliated and defoliated plants respectively. In both cultivars, grains in a distal position within the spikelet (G3) were most affected by the decrease of the photosynthetic source. The photosynthetic rate of the ear was higher in cv. Klein Escudo than in cv. BioINTA 3000. We analyzed the contribution of remobilization of pre anthesis assimilates (stem plus sheaths). Comparing both cultivars, dry matter translocation from the stem showed the opposite pattern to the contribution of ear photosynthesis, i.e. it was higher in cv. BioINTA 3000 than in Klein Escudo. In Bordenave, Argentina, ear shading treatments revealed an important contribution of ear photosynthesis to grain yield in cv. Huenpan (a long awned, water-deficit tolerant genotype), either under water deficit or irrigation, whereas in cv. Baguette Premiun 11 (short awns) there was apparently no effect of ear photosynthesis on yield. Finally, inhibition of ear photosynthesis with DCMU reduced grain weight per ear to a similar extent as ear shading. Ear photosynthesis might represent a "buffer" to maintain grain yield under source limitations (e.g. defoliation, water stress conditions), and could have an important role even without stress, because an incipient 'source' limitation might be emerging in modern cultivars of bread wheat.

b-carotene. Moreover, a coordinated response involving glutathione reductase activity, thiols and ascorbic The purpose of the present work was to evaluate both acid is triggered to limit free radical dependent effects. oxidative stress and the antioxidant response system in leaves from wheat (Triticum aestivum cv. Buck Key words: Antioxidants, lipid radicals, oxygen radicals, Poncho) subjected sequentially to drought and waterwater stress, wheat. ing. Drought was imposed by withholding water until soil water potential reached −2.0 MPa and maintained under those conditions for 24 h. DCFDA oxidation by

The production of reactive oxygen species in the chloroplast decrease in photosynthetic electron transport activity and photosystem II (PSII) efficiency (F v /F m). Treatment of stressed may increase under water deficit. To determine if this causes oxidative damage to the photosynthetic apparatus, we analyzed leaves with L-galactono-1,4-lactone (GL) increased their ascorbic acid content and enhanced photochemical and non-photo-the accumulation of oxidatively damaged proteins in thylakoids chemical quenching of chlorophyll fluorescence. GL reduced of water-stressed wheat (Triticum aesti7um L.) leaves. Water stress was imposed on 4-week-old plants by withholding water-oxidative damage to photosynthetic proteins of droughted plants, but it reverted the decrease in electron transport activity ing for 10 days to reach a soil water potential of about − 2.0 MPa. In thylakoids of water-stressed leaves there was an and PSII efficiency only partially, suggesting that other factors increase in oxidative damage, particularly in polypeptides of 68, also contributed to loss of photosystem activity in droughted plants. Increasing the ascorbic acid content of leaves might be 54, 41 and 24 kDa. High molecular mass oxidized (probably cross-linked) proteins accumulated in chloroplasts of droughted an effective strategy to protect thylakoid membranes from leaves. Oxidative damage was associated with a substantial oxidative damage in water-stressed leaves. limitations to CO 2 have a minimal impact (Cornic and Masacci 1996). Photosystem activity and photophosphorylation have been shown to decrease in droughted plants (Hanson and Hitz 1983, He et al. 1995). Non-stomatal limitations to photosynthesis in droughted plants might be related to oxidative damage to chloroplast lipids, pigments and proteins. In droughted wheat, sunflower and pea leaves (

The photosynthetic characteristics of the ear and flag leaf of well-watered (WW) and water-stressed (WS) durum wheat (Triticum turgidum L. var. durum) were studied in plants grown under greenhouse and Mediterranean field conditions. Gas exchange measurements simultaneously with modulated chlorophyll fluorescence were used to study the response of the ear and flag leaf to CO 2 and O 2 during photosynthesis. C 4 metabolism was identified by assessing the sensitivity of photosynthetic rate and electron transport to oxygen. The presence of CAM metabolism was assessed by measuring daily patterns of stomatal conductance and net CO 2 assimilation. In addition, the histological distribution of Rubisco protein in the ear parts was studied by immunocytochemical localisation. Relative water content (RWC) and osmotic adjustment (osmotic potential at full turgor) were also measured in these organs. Oxygen sensitivity of the assimilation rate and electron transport, the lack of Rubisco compartmentalisation in the mesophyll tissues and the gas-exchange pattern at night indicated that neither C 4 nor CAM metabolism occurs in the ear of WW or WS plants. Nevertheless, photosynthetic activity of the flag leaf was more affected by WS conditions than that of the ear, under both growing conditions. The lower sensitivity under water stress of the ear than of the flag leaf was linked to higher RWC and osmotic adjustment in the ear bracts and awns. We demonstrate that the better performance of the ear under water stress (compared to the flag leaf) is not related to C 4 or CAM photosynthesis. Rather, drought tolerance of the ear is explained by its higher RWC in drought. Osmotic adjustment and xeromorphic traits of ear parts may be responsible. Abbreviations A sat : Light-saturated net CO 2 assimilation rate AE A* sat : Corrected light-saturated net CO 2 assimilation rate of the ear (i.e. A sat +R d) AE F m and F m ¢: Maximum fluorescence in dark-adapted and light-adapted organs respectively AE F v /F m : Maximum efficiency of PSII photochemistry after darkadaptation AE F v ¢/F m ¢: Efficiency of energy capture by open PSII centres AE F o ¢: Minimum fluorescence yield in light-adapted state AE / PSII :

The aim of this educational review is to provide practical information on the hardware, methodology, and the hands on application of chlorophyll (Chl) a fluorescence technology. We present the paper in a question and answer format like frequently asked questions. Although nearly all information on the application of Chl a fluorescence can be found in the literature, it is not always easily

La realización de viajes de campaña constituye un aporte fundamental para los estudios de grado de algunas carreras. Específicamente para alumnos del área biológica es la oportunidad de aprender en ambientes informales, realizar actividades que no podrían ser desarrolladas en el laboratorio y permite construir conocimiento a través de interacciones con el ambiente que invitan a observar, identificar, medir y comparar. En esta presentación se describen las características del viaje de campaña al Palmar de Colón del curso de Fisiología Vegetal de la Facultad de Ciencias Naturales y Museo, con el propósito de evaluar la experiencia piloto que el equipo docente viene desarrollando y definir algunas orientaciones para mejorar su aprovechamiento. El propósito de la actividad es que los alumnos integren contenidos previos de su carrera con los específicos del curso de Fisiología Vegetal para analizar, interpretar y explicar el comportamiento adaptativo de especies en ambientes naturales. Los alumnos deben completar una guía de actividades, en la registran parámetros descriptivos de cada ambiente, rasgos morfo-fisiológicos de las especies, miden procesos vinculados con el balance de agua y carbono y discuten su posible importancia en cada ambiente. Se realiza una puesta en común sobre cada ítem fomentando la discusión e intercambio de ideas. Con el fin de que los estudiantes tengan acceso a algunos equipos utilizados en la disciplina, la cátedra aporta aquellos que permitan efectuar mediciones morfológicas y fisiológicas de caracteres y procesos vinculados con los balances de agua y carbono. Se evalúa la experiencia a través de una encuesta.

Using chlorophyll (Chl) a fluorescence many aspects of the photosynthetic apparatus can be studied, both in vitro and, noninvasively, in vivo. Complementary techniques can help to interpret changes in the Chl a fluorescence kinetics. Kalaji et al. (Photosynth Res 122:121-158, 2014a) addressed several questions about instruments, methods and applications based on Chl a fluorescence. Here, additional Chl a fluorescence-related topics are discussed again in a question and answer format. Examples are the effect of connectivity on photochemical quenching, the correction of F V /F M values for PSI fluorescence, the energy partitioning concept, the interpretation of the complementary area, probing the donor side of PSII, the assignment of bands of 77 K fluorescence emission spectra to fluorescence emitters, the relationship between prompt and delayed fluorescence, potential problems when sampling tree canopies, the use of fluorescence parameters in QTL studies, the use of Chl a fluorescence in biosensor Hazem M. Kalaji and Gert Schansker have contributed equally to this paper.

Las partes verdes de la espiga (e.g. brácteas, aristas) son fuente de asimilados en cereales C3. Sin embargo, la contribución de la fotosíntesis de la espiga en trigo pan (Triticum aestivum L.) es menos conocida que el resto de las fuentes de asimilados (v.g. fotosíntesis de la hoja bandera, retranslocados del tallo). En trigo es ampliamente aceptado que la limitación por fuente no está presente en cultivares antiguos (Kruk et al. 1997; Borrás et al. 2004). Sin embargo, en germoplasma moderno, la limitación por fuente podría estar emergiendo (e.g. Álvaro 2008a). En este contexto los asimilados fijados por los órganos verdes de la espiga (v.g. glumas y aristas) podrían ser más relevante para sostener el llenado de granos. Capítulo 2: El principal objetivo de este capítulo fue evaluar la contribución de la espiga mediante tres aproximaciones experimentales diferentes: (1) reduciendo la fotosíntesis de la espiga por remoción de las aristas o sombreo de las espigas (combinados con un tr...

los viajes de campaña no son sólo una tradición sino que además, se insertan curricularmente como requisito para obtener el título de Licenciatura. De hecho, la FCNyM es la unidad académica de la UNLP que cuenta con mayores recursos asignados a este rubro. No es difícil imaginar el lugar reservado para los viajes de campaña en la formación de los naturalistas del siglo XVIII, vinculado a la descripción y clasificación del mundo natural, pero ¿cuál sería ser el rol de los viajes de campaña en la formación de Biólogos del siglo XXI? Si bien existe un consenso implícito entre docentes y alumnos respecto de la importancia de las salidas de campo en la formación de los futuros graduados, los argumentos detrás de brought to you by CORE View metadata, citation and similar papers at core.ac.uk

INTRODUCCIÓN Las temperaturas elevadas durante el llenado de granos producen una disminución en el peso de los granos (con el concomitante deterioro del rendimiento) (Porter et al., 1999). Esta disminución puede oscilar entre un 3 a un 5 % por cada grado por encima de una temperatura media de 25 C (Wardlaw y Wrigley 1994; Savin, 2007; Savin, 2010). La relación entre la temperatura y el rendimiento ha sido ampliamente estudiada, analizando la depresión de la temperatura del canopeo (diferencia entre la temperatura del canopeo y la ambiental). Sin embargo, el llenado de granos se produce específicamente en la espiga, órgano con características particulares (Tambussi et al., 2005; Tambussi et al., 2007) (v.g. presencia de aristas) que podrían tener un balance térmico diferencial al resto del canopeo. El objetivo de este trabajo fue analizar la variabilidad en la temperatura de espigas de diferentes cultivares de trigo pan y su relación con características morfo-fisiológicas.

In crop studies, shading is a common approach for reducing source activity (i.e. assimilates produced by photosynthesis); however, if source reduction is not directly proportional to the degree of light attenuation, estimations could be flawed. We analysed the effects of shading at three levels on light transmittance, air and canopy temperatures, and actual photosynthetic activity at different times of day, and on grain weight in a modern genotype of bread wheat (Triticum aestivum L.). The treatments were imposed 10 days after anthesis and comprised three levels of shading with meshes: 80%, 50% and 10% transmittance during midday. The decrease in midday photosynthetic activity (electron transport rate, ETR; and CO2 assimilation, An) in the shading treatments compared with control plants did not fit a 1:1 relationship with light transmittance of the meshes; for example, the reduction in ETR and An was <50% under the mesh with 50% light transmittance. The decrease in light transmit...