Implications of the mesophyll conductance to CO2 for photosynthesis and water-use efficiency during long-term water stress and recovery in two contrasting Eucalyptu species

Water stress (WS) slows growth and photosynthesis (An), but most knowledge comes from short-time studies that do not account for longer term acclimation processes that are especially relevant in tree species. Using two Eucalyptus species that contrast in drought tolerance, we induced moderate and severe water deficits by withholding water until stomatal conductance (gsw) decreased to two pre-defined values for 24 d, WS was maintained at the target gsw for 29 d and then plants were re-watered. Additionally, we developed new equations to simulate the effect on mesophyll conductance (gm) of accounting for the resistance to refixation of CO2. The diffusive limitations to CO2, dominated by the stomata, were the most important constraints to An. Full recovery of An was reached after re-watering, characterized by quick recovery of gm and even higher biochemical capacity, in contrast to the slower recovery of gsw. The acclimation to long-term WS led to decreased mesophyll and biochemical limitations, in contrast to studies in which stress was imposed more rapidly. Finally, we provide evidence that higher gm under WS contributes to higher intrinsic water-use efficiency (iWUE) and reduces the leaf oxidative stress, highlighting the importance of gm as a target for breeding/genetic engineering.

Estudio de los efectos en el vi��edo de la modificaci��n del d��ficit h��drico continuo en los periodos anterior y posterior al envero (cv. Cabernet Sauvignon; Vitis vinifera L.)

En regiones semi��ridas, con veranos c��lidos, evapotranspiraciones elevadas, humedades relativas bajas, adem��s de precipitaciones intermitentes y escasas (400 mm al a��o) que reducen la recarga del perfil en invierno, se puede ver afectada la productividad y sostenibilidad de los vi��edos. Por eso en estas zonas puede ser necesario utilizar el riego suplementario para mantener la calidad y aumentar la productividad. En este marco de circunstancias es en el que se desarrolla la mayor��a de la viticultura espa��ola, y en concreto en la zona centro donde se realiz�� el estudio. Con este trabajo se pretende estudiar la influencia del agua del riego, con distintas dosis y aplicada en diferentes fases de crecimiento y maduraci��n de la baya, en la producci��n y calidad de la uva. Se estudi�� la influencia del d��ficit moderado continuo aplicado antes y despu��s de envero, en el aprovechamiento de los recursos ambientales y en la respuesta del cv. Cabernet Sauvignon. El ensayo se desarroll�� en 2010 y 2011 en la finca ���La Alcoholera���, perteneciente a bodegas LICINIA S.L., ubicada en la localidad de Chinch��n, Comunidad de Madrid, Espa��a. Durante 2010 y 2011 se realizaron estudios en cepas del cv. Cabernet Sauvignon (clon 15), injertadas sobre 41B y plantadas en 2005. Con poda corta en Cord��n Royat unilateral de 80 cm de altura, y cuya vegetaci��n alcanz�� una altura de 97 cm. Las cepas del ensayo fueron conducidas verticalmente en espaldera (VSP), con 10 yemas por metro lineal. Las plantas dentro de la fila fueron separadas 1 m y la distancia de la calle fue de 3 m. La orientaci��n de las filas norte ��� sur. Se plantearon cuatro tratamientos experimentales con diferentes dosis y momento de aplicaci��n del riego. - T: Testigo. D��ficit ligero, con un aporte continuado de agua desde floraci��n (420 mm). - DMc: D��ficit moderado continuo. Manejo del riego convencional, empezando en pre-envero (154 mm) - DM1: D��ficit moderado a partir de pre-envero. Aporte de riego continuado desde floraci��n reduci��ndose la dosis de riego en pre-envero (312 mm). - DM2: D��ficit moderado hasta pre-envero. Se empez�� a regar a partir de preenvero (230 mm). Se observ�� que bajo condiciones de estr��s h��drico leve, el crecimiento se reduce disminuyendo la migraci��n de fotoasimilados hacia los ��rganos vegetativos. Generando menor ��rea foliar en las plantas sometidas a d��ficit h��drico moderado entre floraci��n y cuajado. Disminuyendo su consumo. En maduraci��n la humedad del suelo dependi�� principalmente del riego aplicado y del consumo de la planta; dicho consumo dependi�� a la vez del desarrollo foliar del canopy y de la necesidad h��drica de la vid. El aumento del d��ficit h��drico disminuy�� el contenido de agua en el suelo, lo que provoc�� diferencias en el estado h��drico y en el intercambio gaseoso de las hojas. En condiciones de d��ficit moderado, la fotos��ntesis se encontr�� altamente correlacionada con el potencial h��drico foliar medido a mediod��a solar. Adem��s en condiciones de d��ficit moderado continuo la disponibilidad h��drica, la demanda atmosf��rica y el nivel de hidrataci��n de las hojas, interaccionaron de forma compleja en la regulaci��n estom��tica de las hojas, condicionando el intercambio gaseoso y la eficiencia en el uso del agua. Al aumentar el volumen de agua aplicado el peso de madera de poda por metro de fila fue superior. Las diferencias encontradas en el rendimiento fueron debidas a las diferencias en el peso de baya. El cual estuvo condicionado por la estrategia de riego, ya que, el d��ficit h��drico moderado antes de envero fue m��s cr��tico para el rendimiento que el d��ficit impuesto durante la madurez. Por otro lado, la biomasa dependi�� de la actividad fisiol��gica de la planta, la cual fue altamente dependiente de la disponibilidad h��drica. D��ficit h��drico moderado aplicado de cuajado a envero, gener�� bayas m��s peque��as y aument�� la relaci��n hollejo:pulpa. El d��ficit moderado aplicado despu��s de envero favoreci�� la acumulaci��n de IPT y antocianos extra��bles, mejorando la calidad de la uva, pero disminuy�� la acidez de la baya. El riego aplicado de envero a vendimia desaceler�� la concentraci��n de az��cares en bayas que fueron sometidas a d��ficit antes de pre-envero. ABSTRACT Mediterranean climate is characterized by hot summers, high evapotranspiration rates, and scarce precipitations (400 mm per year) during grapevine cycle. These extremely dry conditions affect vineyard productivity and sustainability. Supplementary irrigation is needed practice in order to maintain yield and quality. Almost all Spanish grape growing regions are characterized by these conditions, especially in the center region, where this trial was performed. The main objective of this work is to study the influence of water irrigation on yield and quality. For this aim, different levels of irrigation (mm of water applied) were applied during different stages of growth and berry maturity of Caberent Sauvignon grapevines. The work was conducted from 2010 to 2011 and located in Licinia (40�� 12�� N, 3�� 28�� W), Madrid, Spain. The cultivar utilized was Cabernet Sauvignon, clone 15 grafted onto rootstock 41B, planted in 2005. The vineyard was oriented north-south, with spacing on 3 meters between rows and 1 meter between plants. Vines were spurpruned to 10 buds per meter and trained in unilateral cordon with a height of 80 cm. Shoots were positioned vertically (VSP). Considering the amount of water and the moment of the application, four experimental treatments were applied: - T: Control sample. Slight deficit (420 mm) applied from bloom to maturity. - DMc: Continuous moderate deficit. Traditional irrigation: application of 154 mm of water from pre-veraison to maturity. - DM1: Deficit moderate from pre-veraison. Irrigation of 312 mm of water from bloom to pre-veraison. - DM2: Deficit moderate to pre-veraison. Irrigation of 230 mm of water from preveraison to maturity Under moderated water stress conditions it was seen than leaf growth decreases due to the reduction of migration of photo-assimilates to vegetative organs. Vines with moderate water deficit between flowering and ripening develop less leaf area and decrease its water consumption. During maturation of berries, soil moisture depends on irrigation and plant consumption. This consumption further depends on vegetation development and on the vine needs for water. By increasing water deficit, the water content in the soil decreases. This causes differences in leaf water status and in the gases exchange. Under moderate deficit conditions, photosynthesis was found highly correlated with midday leaf water potential. Further, atmospheric demand and the level of leaves hydration interact in complex ways in the stomatal regulation, which affects leaf gas exchange and the efficiency of water use. The amount of water applied is directly proportional to pruning weight. Changes in berry weight cause differences in yield ratios. The differences in berry weights are conditioned by the irrigation strategy, the moderate water deficit before veraison influences more than the deficit applied from veraison. Biomass generated for the plant depends on its physiological activity, which is highly related to the water availability. Moderate water deficit applied from fruit set to ripening generates smaller berries, increasing the pulp/skin ratio. Moderate deficit applied after veraison promotes the accumulation of extractables anthocyans and TPI. Despite this treatment improves color parameters of the grapes, it decreases its total acidity. Irrigation applied from veraison to harvest slows down sugar accumulation in berries compared to those under deficit before veraison conditions.

A study on the inclusion of forest canopy morphology data in numerical simulations for the purpose of wind resource assessment

A series of numerical simulations of the flow over a forest stand have been conducted using two different turbulence closure models along with various levels of canopy morphology data. Simulations have been validated against Stereoscopic Particle Image Velocimetry measurements from a wind tunnel study using one hundred architectural model trees, the porosities of which have been assessed using a photographic technique. It has been found that an accurate assessment of the porosity of the canopy, and specifically the variability with height, improves simulation quality regardless of the turbulence closure model used or the level of canopy geometry included. The observed flow field and recovery of the wake is in line with characteristic canopy flows published in the literature and it was found that the shear stress transport turbulence model was best able to capture this detail numerically.

A photosystem I reaction center driven by chlorophyll d in oxygenic photosynthesis

A far-red type of oxygenic photosynthesis was discovered in Acaryochloris marina, a recently found marine prokaryote that produces an atypical pigment chlorophyll d (Chl d). The purified photosystem I reaction center complex of A. marina contained 180 Chl d per 1 Chl a with PsaA���F, -L, -K, and two extra polypeptides. Laser excitation induced absorption changes of reaction center Chl d that was named P740 after its peak wavelength. A midpoint oxidation reduction potential of P740 was determined to be +335 mV. P740 uses light of significantly low quantum energy (740 nm = 1.68 eV) but generates a reducing power almost equivalent to that produced by a special pair of Chl a (P700) that absorbs red light at 700 nm (1.77 eV) in photosystem I of plants and cyanobacteria. The oxygenic photosynthesis based on Chl d might either be an acclimation to the far-red light environments or an evolutionary intermediate between the red-absorbing oxygenic and the far-red absorbing anoxygenic photosynthesis that uses bacteriochlorophylls.

Evolution of plastid gene rps2 in a lineage of hemiparasitic and holoparasitic plants: Many losses of photosynthesis and complex patterns of rate���variation

The plastid genomes of some nonphotosynthetic parasitic plants have experienced an extreme reduction in gene content and an increase in evolutionary rate of remaining genes. Nothing is known of the dynamics of these events or whether either is a direct outcome of the loss of photosynthesis. The parasitic Scrophulariaceae and Orobanchaceae, representing a continuum of heterotrophic ability ranging from photosynthetic hemiparasites to nonphotosynthetic holoparasites, are used to investigate these issues. We present a phylogenetic hypothesis for parasitic Scrophulariaceae and Orobanchaceae based on sequences of the plastid gene rps2, encoding the S2 subunit of the plastid ribosome. Parasitic Scrophulariaceae and Orobanchaceae form a monophyletic group in which parasitism can be inferred to have evolved once. Holoparasitism has evolved independently at least five times, with certain holoparasitic lineages representing single species, genera, and collections of nonphotosynthetic genera. Evolutionary loss of the photosynthetic gene rbcL is limited to a subset of holoparasitic lineages, with several holoparasites retaining a full length rbcL sequence. In contrast, the translational gene rps2 is retained in all plants investigated but has experienced rate accelerations in several hemi- as well as holoparasitic lineages, suggesting that there may be substantial molecular evolutionary changes to the plastid genome of parasites before the loss of photosynthesis. Independent patterns of synonymous and nonsynonymous rate acceleration in rps2 point to distinct mechanisms underlying rate variation in different lineages. Parasitic Scrophulariaceae (including the traditional Orobanchaceae) provide a rich platform for the investigation of molecular evolutionary process, gene function, and the evolution of parasitism.

Tracking molecular evolution of photosynthesis by characterization of a major photosynthesis gene cluster from Heliobacillus mobilis

A DNA sequence has been obtained for a 35.6-kb genomic segment from Heliobacillus mobilis that contains a major cluster of photosynthesis genes. A total of 30 ORFs were identified, 20 of which encode enzymes for bacteriochlorophyll and carotenoid biosynthesis, reaction-center (RC) apoprotein, and cytochromes for cyclic electron transport. Donor side electron-transfer components to the RC include a putative RC-associated cytochrome c553 and a unique four-large-subunit cytochrome bc complex consisting of Rieske Fe-S protein (encoded by petC), cytochrome b6 (petB), subunit IV (petD), and a diheme cytochrome c (petX). Phylogenetic analysis of various photosynthesis gene products indicates a consistent grouping of oxygenic lineages that are distinct and descendent from anoxygenic lineages. In addition, H. mobilis was placed as the closest relative to cyanobacteria, which form a monophyletic origin to chloroplast-based photosynthetic lineages. The consensus of the photosynthesis gene trees also indicates that purple bacteria are the earliest emerging photosynthetic lineage. Our analysis also indicates that an ancient gene-duplication event giving rise to the paralogous bchI and bchD genes predates the divergence of all photosynthetic groups. In addition, our analysis of gene duplication of the photosystem I and photosystem II core polypeptides supports a ���heterologous fusion model��� for the origin and evolution of oxygenic photosynthesis.

A global two component signal transduction system that integrates the control of photosynthesis, carbon dioxide assimilation, and nitrogen���fixation

Photosynthesis, biological nitrogen fixation, and carbon dioxide assimilation are three fundamental biological processes catalyzed by photosynthetic bacteria. In the present study, it is shown that mutant strains of the nonsulfur purple photosynthetic bacteria Rhodospirillum rubrum and Rhodobacter sphaeroides, containing a blockage in the primary CO2 assimilatory pathway, derepress the synthesis of components of the nitrogen fixation enzyme complex and abrogate normal control mechanisms. The absence of the Calvin���Benson���Bassham (CBB) reductive pentose phosphate CO2 fixation pathway removes an important route for the dissipation of excess reducing power. Thus, the mutant strains develop alternative means to remove these reducing equivalents, resulting in the synthesis of large amounts of nitrogenase even in the presence of ammonia. This response is under the control of a global two-component signal transduction system previously found to regulate photosystem biosynthesis and the transcription of genes required for CO2 fixation through the CBB pathway and alternative routes. In addition, this two-component system directly controls the ability of these bacteria to grow under nitrogen-fixing conditions. These results indicate that there is a molecular link between the CBB and nitrogen fixation process, allowing the cell to overcome powerful control mechanisms to remove excess reducing power generated by photosynthesis and carbon metabolism. Furthermore, these results suggest that the two-component system integrates the expression of genes required for the three processes of photosynthesis, nitrogen fixation, and carbon dioxide fixation.

The origin of atmospheric oxygen on Earth: The innovation of oxygenic photosynthesis

The evolution of O2-producing cyanobacteria that use water as terminal reductant transformed Earth's atmosphere to one suitable for the evolution of aerobic metabolism and complex life. The innovation of water oxidation freed photosynthesis to invade new environments and visibly changed the face of the Earth. We offer a new hypothesis for how this process evolved, which identifies two critical roles for carbon dioxide in the Archean period. First, we present a thermodynamic analysis showing that bicarbonate (formed by dissolution of CO2) is a more efficient alternative substrate than water for O2 production by oxygenic phototrophs. This analysis clarifies the origin of the long debated ���bicarbonate effect��� on photosynthetic O2 production. We propose that bicarbonate was the thermodynamically preferred reductant before water in the evolution of oxygenic photosynthesis. Second, we have examined the speciation of manganese(II) and bicarbonate in water, and find that they form Mn-bicarbonate clusters as the major species under conditions that model the chemistry of the Archean sea. These clusters have been found to be highly efficient precursors for the assembly of the tetramanganese-oxide core of the water-oxidizing enzyme during biogenesis. We show that these clusters can be oxidized at electrochemical potentials that are accessible to anoxygenic phototrophs and thus the most likely building blocks for assembly of the first O2 evolving photoreaction center, most likely originating from green nonsulfur bacteria before the evolution of cyanobacteria.

The Relationship between Photosynthesis and a Mastoparan-Induced Hypersensitive Response in Isolated Mesophyll Cells1

The G-protein activator mastoparan (MP) was found to elicit the hypersensitive response (HR) in isolated Asparagus sprengeri mesophyll cells at micromolar concentrations. The HR was characterized by cell death, extracellular alkalinization, and an oxidative burst, indicated by the reduction of molecular O2 to O2������. To our knowledge, this study was the first to monitor photosynthesis during the HR. MP had rapid and dramatic effects on photosynthetic electron transport and excitation energy transfer as determined by variable chlorophyll a fluorescence measurements. A large increase in nonphotochemical quenching of chlorophyll a fluorescence accompanied the initial stages of the oxidative burst. The minimal level of fluorescence was also quenched, which suggests the origin of this nonphotochemical quenching to be a decrease in the antenna size of photosystem II. In contrast, photochemical quenching of fluorescence decreased dramatically during the latter stages of the oxidative burst, indicating a somewhat slower inhibition of photosystem II electron transport. The net consumption of O2 and the initial rate of O2 uptake, elicited by MP, were higher in the light than in the dark. These data indicate that light enhances the oxidative burst and suggest a complex relationship between photosynthesis and the HR.

Protective Function of Chloroplast 2-Cysteine Peroxiredoxin in Photosynthesis. Evidence from Transgenic Arabidopsis1

2-Cysteine peroxiredoxins (2-CPs) constitute a ubiquitous group of peroxidases that reduce cell-toxic alkyl hydroperoxides to their corresponding alcohols. Recently, we cloned 2-CP cDNAs from plants and characterized them as chloroplast proteins. To elucidate the physiological function of the 2-CP in plant metabolism, we generated antisense mutants in Arabidopsis. In the mutant lines a 2-CP deficiency developed during early leaf and plant development and eventually the protein accumulated to wild-type levels. In young mutants with reduced amounts of 2-CP, photosynthesis was impaired and the levels of D1 protein, the light-harvesting protein complex associated with photosystem II, chloroplast ATP synthase, and ribulose-1,5-bisphosphate carboxylase/oxygenase were decreased. Photoinhibition was particularly pronounced after the application of the protein synthesis inhibitor, lincomycin. We concluded that the photosynthetic machinery needs high levels of 2-CP during leaf development to protect it from oxidative damage and that the damage is reduced by the accumulation of 2-CP protein, by the de novo synthesis and replacement of damaged proteins, and by the induction of other antioxidant defenses in 2-CP mutants.

Restrictions to Carbon Dioxide Conductance and Photosynthesis in Spinach Leaves Recovering from Salt Stress

Salt accumulation in spinach (Spinacia oleracea L.) leaves first inhibits photosynthesis by decreasing stomatal and mesophyll conductances to CO2 diffusion and then impairs ribulose-1,5-bisphosphate carboxylase/oxygenase (S. Delfine, A. Alvino, M. Zacchini, F. Loreto [1998] Aust J Plant Physiol 25: 395���402). We measured gas exchange and fluorescence in spinach recovering from salt accumulation. When a 21-d salt accumulation was reversed by 2 weeks of salt-free irrigation (rewatering), stomatal and mesophyll conductances and photosynthesis partially recovered. For the first time, to our knowledge, it is shown that a reduction of mesophyll conductance can be reversed and that this may influence photosynthesis. Photosynthesis and conductances did not recover when salt drainage was restricted and Na content in the leaves was greater than 3% of the dry matter. Incomplete recovery of photosynthesis in rewatered and control leaves may be attributed to an age-related reduction of conductances. Biochemical properties were not affected by the 21-d salt accumulation. However, ribulose-1,5-bisphosphate carboxylase/oxygenase activity and content were reduced by a 36- to 50-d salt accumulation. Photochemical efficiency was reduced only in 50-d salt-stressed leaves because of a decrease in the fraction of open photosystem II centers. A reduction in chlorophyll content and an increase in the chlorophyll a/b ratio were observed in 43- and 50-d salt-stressed leaves. Low chlorophyll affects light absorptance but is unlikely to change light partitioning between photosystems.

Decrease in Phosphoribulokinase Activity by Antisense RNA in Transgenic Tobacco. Relationship between Photosynthesis, Growth, and Allocation at Different Nitrogen Levels1

To study the direct effects of photosynthesis on allocation of biomass by altering photosynthesis without altering leaf N or nitrate content, phosphoribulokinase (PRK) activity was decreased in transgenic tobacco (Nicotiana tabacum L.) with an inverted tobacco PRK cDNA and plants were grown at different N levels (0.4 and 5 mm NH4NO3). The activation state of PRK increased as the amount of enzyme was decreased genetically at both levels of N. At high N a 94% decrease in PRK activity had only a small effect (20%) on photosynthesis and growth. At low N a 94% decrease in PRK activity had a greater effect on leaf photosynthesis (decreased by up to 50%) and whole-plant photosynthesis (decreased by up to 35%) than at high N. These plants were up to 35% smaller than plants with higher PRK activities because they had less structural dry matter and less starch, which was decreased by 3- to 4-fold, but still accumulated to 24% to 31% of dry weight; young leaves contained more starch than older leaves in older plants. Leaves had a higher ion and water content, and specific leaf area was higher, but allocation between shoot and root was unaltered. In conclusion, low N in addition to a 94% decrease in PRK by antisense reduces the activity of PRK sufficient to diminish photosynthesis, which limits biomass production under conditions normally considered sink limited.

Interactions between Senescence and Leaf Orientation Determine in Situ Patterns of Photosynthesis and Photoinhibition in Field-Grown Rice1

Photosynthesis and photoinhibition in field-grown rice (Oryza sativa L.) were examined in relation to leaf age and orientation. Two varieties (IR72 and IR65598-112-2 [BSI206]) were grown in the field in the Philippines during the dry season under highly irrigated, well-fertilized conditions. Flag leaves were examined 60 and 100 d after transplanting. Because of the upright nature of 60-d-old rice leaves, patterns of photosynthesis were determined by solar movements: light falling on the exposed surface in the morning, a low incident angle of irradiance at midday, and light striking the opposite side of the leaf blade in the afternoon. There was an early morning burst of CO2 assimilation and high levels of saturation of photosystem II electron transfer as incident irradiance reached a maximum level. However, by midday the photochemical efficiency increased again almost to maximum. Leaves that were 100 d old possessed a more horizontal orientation and were found to suffer greater levels of photoinhibition than younger leaves, and this was accompanied by increases in the de-epoxidation state of the xanthophyll cycle. Older leaves had significantly lower chlorophyll content but only slightly diminished photosynthesis capacity.