Internal CO2 Research Articles

Salt stress on physiology, biometry and fruit quality of grafted Passiflora edulis

The production of grafted passion fruit is an alternative for plant adaptation to saline environments. The objective of this study was to evaluate the effect of salt stress on physiology, biometry and fruit quality of P. edulis grafted on Passiflora spp. The experiment was conducted in completely randomized design, in a 3 x 2 factorial scheme, corresponding to three species of Passiflora (P. edulis, P. gibertii and P. cincinnata) with P. edulis scion and two levels of irrigation water salinity (0.5 - control and 4.5 dS m-1), with four repetitions. Water salinity compromises gas exchanges (CO2 assimilation raste and transpiration) and physiological variables (total chlorophyll and total water consumption) in grafted P. edulis. The interaction between the factors (water salinity x species) compromised only the growth in plant height and number of leaves. In relation to the species, auto-grafted P. edulis stood out from the other species, with higher internal CO2 concentration, number of leaves, stem dry mass, peel thickness, total soluble solids (TSS) of the pulp and TSS/TA ratio (titratable acidity). Auto-grafted P. edulis under saline conditions develops vital mechanisms (TSS and TSS/TA), which attenuates the effects of salt stress on the physico-chemical quality of the fruits.

Investigation of the Energy Saving Efficiency of a Natural Ventilation Strategy in a Multistory School Building

Under-ventilation and high energy consumption are some of the problems associated with school classrooms. Thus, it is necessary to develop a ventilation strategy that is characterized by high energy-saving and ventilation efficiency. To this end, this study aims to investigate natural ventilation as a possible strategy to improve the indoor environment while reducing ventilation loads and maintaining energy costs during intermediate seasons. Ventilation and cooling load reductions based on the opening and closing of several windows were analyzed. Window flow coefficients and ventilation rates were measured and used for computational fluid dynamics (CFD) simulation to obtain pressure coefficients for 16 wind directions. The results obtained showed that the improved natural ventilation strategy could be used to effectively establish required indoor conditions (26 °C, 60% RH). Additionally, compared with the mechanical ventilation system with variable refrigerant flow, this natural strategy resulted in a decrease in energy consumption of approximately 30%. However, its application requires that internal heat gain and CO2 emissions, which depend on human population density, as well as the room usage schedule should be considered.

LEAF GAS EXCHANGE AND FLOWERING OF MANGO SPRAYED WITH BIOSTIMULANT IN SEMI-ARID REGION

ABSTRACT The aim of the present study was to evaluate the effect of biostimulant containing amino acids and yeast extract on the physiological and reproductive characteristics of mango cv. Tommy Atkins during the shoot maturation phase in tropical semi-arid region. The experimental design consisted of randomized blocks with five treatments, five replications and five plants per plot. Treatments consisted of: T1) two foliar sprays with [biostimulant + KCl] + two foliar sprays with K2SO4; T2) No biostimulant and four foliar sprays with K2SO4; T3) three individual foliar sprays with biostimulant and one foliar spray with K2SO4; T4) two foliar sprays with biostimulant and two foliar sprays with K2SO4; and T5) two foliar sprays with [biostimulant + K2SO4] + one foliar spray with K2SO4. There is a positive effect of the biostimulant containing amino acids and yeast extract on transpiration, internal CO2 concentration, water-use efficiency and number of reproductive and non-differentiated shoots of mango cv. Tommy Atkins cultivated under tropical semi-arid condition, with attenuating effect on plant abiotic stress. For shoot maturation of mango cv. Tommy Atkins, three foliar sprays with biostimulant containing amino acids and yeast extract (10 mL per plant) and one with K2SO4 (3%), starting at 45 days after paclobutrazol application (T3), can be recommended.

Gas exchanges and photosynthetic efficiency in sub-forest species from Atlantic Forest

The availability of light is one of the factors that most limits the photosynthesis of juvenile trees in the understory of the forest. The study was carried out in the Mata do Pau-Ferro State Park, located in the city of Areia, PB. The objective of this study was to evaluate how gas exchanges occur in individuals of Psychotria colorata (Willd. Ex Roem & Schult.), Senna georgica Irwin & Barneby, Himatanthus phagedaenicus (Mart.) Woodson, Solanum swartzianum Roem. & Schult, Psychotria carthagenensis Jacq.e Psychotria hoffmannseggiana (Willd. ex Schult.) in the understory of a remnant of Mata Atlântica. The rate of photosynthesis (A), transpiration (E), stomatal conductance (Gs), internal CO2 concentration (Ci) leaf temperature-air temperature (°C), and internal carbon (Ci), instantaneous efficiency of water use (EUA) (A/E), Intrinsic efficiency of water use (EiUC) (A/Gs) and the intrinsic efficiency of carboxylation (ratio A/Ci). The rates of maximum photosynthesis (A), photosynthesis (E) and stomatal conductance (Gs) were shown to be influenced by the time of day, as there was no interference of external factors in the diurnal patterns of gas exchange, variations are due to endogenous factors, probably due to the circadian rhythm. The parameter of the gas exchange of sub-forest species responds differently, in the small variations in the luminosity levels of the forest understory

Sensitivity and Uncertainty Analyses of Flux-based Ecosystem Model towards Improvement of Forest GPP Simulation

An ecosystem model serves as an important tool to understand the carbon cycle in the forest ecosystem. However, the sensitivities of parameters and uncertainties of the model outputs are not clearly understood. Parameter sensitivity analysis (SA) and uncertainty analysis (UA) play a crucial role in the improvement of forest gross primary productivity GPP simulation. This study presents a global SA based on an extended Fourier amplitude sensitivity test (EFAST) method to quantify the sensitivities of 16 parameters in the Flux-based ecosystem model (FBEM). To systematically evaluate the parameters’ sensitivities, various parameter ranges, different model outputs, temporal variations of parameters sensitivity index (SI) were comprehensively explored via three experiments. Based on the numerical experiments of SA, the UA experiments were designed and performed for parameter estimation based on a Markov chain Monte Carlo (MCMC) method. The ratio of internal CO2 to air CO2 ( f C i ) , canopy quantum efficiency of photon conversion ( α q ) , maximum carboxylation rate at 25 ° C ( V m 25 ) were the most sensitive parameters for the GPP. It was also indicated that α q , E V m and Q 10 were influenced by temperature throughout the entire growth stage. The result of parameter estimation of only using four sensitive parameters (RMSE = 1.657) is very close to that using all the parameters (RMSE = 1.496). The results of SA suggest that sensitive parameters, such as f c i , α q , E V m , V m 25 strongly influence on the forest GPP simulation, and the temporal characteristics of the parameters’ SI on GPP and NEE were changed in different growth. The sensitive parameters were a major source of uncertainty and parameter estimation based on the parameter SA could lead to desirable results without introducing too great uncertainties.

Ecophysiology of the Southern Highbush blueberry cv. Biloxi in response to nitrogen fertigation

In Brazil, the nutritional requirements of the blueberry are not sufficiently known, thus requiring further research on the management of mineral fertilization. In this perspective, this work aimed to evaluate physiological attributes of Southern Highbush blueberry plants cv. Biloxi as a function of nitrogen fertigation in Brasília-DF. The experiment was conducted from August 2018 to July 2019, in the Fruit Sector of the Experimental Biology Station of the University of Brasilia (UnB), Federal District. This experiment adopted a randomized block design, with four treatments: 10; 20; 30, and 40 g of N plant-1, 8 replications, and 5 plants per experimental plot. The following variables were measured: net photosynthesis rate (A), transpiration (E), stomatal conductance (gs), internal CO2 concentration (Ci), instantaneous water-use efficiency (WUE), carboxylation efficiency (CE), SPAD index (SPAD) and leaf nitrogen (N). There was an effect of the different nitrogen doses applied on the physiological attributes. The plants of the blueberry cultivar Biloxi increased their photosynthetic rates at doses up to 30 g of N plant-1. Nitrogen rates did not influence stomatal conductance nor did they provide improvements in the carboxylation efficiency of the blueberry plants. Under the conditions of the present work, the highest N leaf contents were obtained with the application of 30 g N plant-1, and values above this concentration did not correspond to higher net photosynthesis rates, transpiration, and CO2 concentration in the leaf mesophyll.

Photosynthetic activity and RAPD profile of polyethylene glycol treated B. juncea L. under nitric oxide and abscisic acid application

The involvement of two extremely important signalling molecules, nitric oxide (NO) and abscisic acid (ABA) has been employed by plants to facilitate the adaptive/tolerate response during stressful conditions. However, the interactive role of exogenously applied NO and ABA is very less studied at physiological, biochemical and molecular levels. The present study therefore, evaluated the effects of individual and simultaneous addition of exogenous NO donor SNP (100μM) and ABA (10μM) on photosynthesis, Calvin-Benson cycle enzymes, S-assimilation enzymes, oxidative stress components, and genotoxicity in Brassica juncea cv. Varuna, exposed to polyethylene glycol (PEG)-induced drought stress. Results showed that a loss induced by PEG was significantly surpassed by the application of NO or/and ABA with PEG for chlorophyll content, net photosynthestic rate (Pn), internal CO2 concentration (Ci), stomatal conductance (gs), transpiration rate (Tr), maximum photosystem II (PSII) efficiency (Fv/Fm), actual PSII efficiency (ΦPSII), intrinsic PSII efficiency (Fv´/ Fm´), photochemical quenching (qP), non-photochemical quenching (NPQ), electron transport chain (ETC), ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCo), glyceraldehyde-3-phosphate dehydrogenase (GapDH), phosphoribulokinase (PRK), ATP-sulfurylase (ATP-S), and serine acetyltransferase (SAT) activities. The genomic template stability (GTS) (measured as changes in RAPD profiles) was significantly affected and showed varying degrees of DNA polymorphism, highest in PEG and lowest in PEG + NO and PEG + NO + ABA. Furthermore, the changes in RAPD profiles showed consistent results when compared with various photosynthetic and oxidative parameters. Altogether, this study concluded that supplementation of individual NO and together with ABA was more effective than individual ABA in alleviating PEG-induced drought stress in B. juncea L. seedlings.

A physiological approach for pre-selection of Eucalyptus clones resistant to drought

Abstract: Water deficit is one of the abiotic stresses that most affects the growth and survival of Eucalyptus. Mechanisms used to tolerate water-limited environments influence the distribution of Eucalyptus species in their natural environment. Here, we take a physiological approach to pre-screen Eucalyptus plants for tolerance to drought. Ten different clones of E. urophylla and E. grandis × E. urophylla that are known to show contrasting responses to water deficit under field conditions, were grown in Clark’s nutrient solution (WW, well-watered) and with polyethylene glycol (-1.0 MPa) to simulate water deficit (WD). Clones responded differently to drought with differentiated photosynthetic limitations in drought-treated clones. Photosynthetic rates, stomatal conductance, transpiration and internal CO2 concentrations were reduced in all genotypes under stress conditions. Clone i144 had a smaller reduction in the evaluated physiological traits, also showing increased root growth in WD-treated plants. Clones 3367 and i224, thought to be moderately tolerant, also followed these patterns. Clones gg157, 1568 and 1641, all of which are moderately sensitive under field conditions, reduced most of the physiological characters evaluated. However, clone gg157 demonstrated increased root system growth, even during short periods of water stress. Clones i042 and i182 were deemed drought-susceptible, with large reductions in photosynthesis and growth, despite showing a high increase in abscisic acid content presumably as a defense mechanism. Interaction between A (photosyntetic rate), E (transpiration rate), ETR/A (electrons transport rate/photosynthetic rate) and SDM/ RDM (shoot dry matter/root dry matter) demonstrated the most significant differences between WD-treated clones and offer great potential for use as selection criterion for water deficit-tolerant genotypes.

Water status, cell damage and gas exchanges in West Indian cherry (Malpighia emarginata) under salt stress and nitrogen fertilization

This study was conducted to evaluate water status, cell damage and gas exchanges of West Indian cherry grown under saline water irrigation and nitrogen (N) fertilization in the post-grafting stage. The experiment was carried out in drainage lysimeters under greenhouse conditions in Regolithic Neosol with sandy loam texture. Treatments consisted of two levels of electrical conductivity of water (ECw) (0.8 and 4.5 dS m-1) and four N doses (70; 85; 100 and 115% of the N recommendation), arranged in randomized blocks, with three replicates. The dose relative to 100% corresponded to 200 g of N per plant per year. Irrigation with 4.5 dS m-1 electrical conductivity water resulted in a reduction in stomatal conductance, transpiration, CO2 assimilation rate and instantaneous carboxylation efficiency but increased cell damage percentage and internal CO2 concentration in West Indian cherry plants. Inhibition of CO2 assimilation rate in West Indian cherry plants is related to non-stomatal effects. Irrigation with 4.5 dS m-1 water and fertilization with 115% of N recommendation intensified leaf water saturation deficit in the West Indian cherry crop. The BRS Jaburu West Indian cherry was sensitive to 4.5 dS m-1 water salinity.

Genetic diversity of under-utilized indigenous finger millet genotypes from Koraput, India for crop improvement

Phenotyping and genetic assessment of germplasm provide information about trait variability, which helps for effective breeding programs. In the present study, 12 indigenous finger millet genotypes from Koraput, India and three high-yielding improved genotypes were used for elucidation of genotypic variability of photosynthetic traits and genetic diversity using 36 SCoT (Start codon targeted polymorphism) markers. Significant variations were noticed in the CO2 photosynthetic rate (PN), stomatal conductance (gs), transpiration rate (E), internal CO2 concentration (Ci), water use efficiency and carboxylation efficiency among the genotypes. Significant variations of stomatal traits, pigment content, PS II activity and dry matter accumulation were also observed. The major morpho-physiological traits such as stomatal conductance, dry matter accumulation, shoot length and stomata per leaf area are played a pivotal role and are the major determinants of phenotypic diversity. The positive association of photosynthesis with dry matter accumulation indicates that some of the genotypes remarkably have more photosynthetic rate along with better plant biomass accumulation and can be used in future crop improvement program. Further, SCoT markers were polymorphic and revealed moderately high level of genetic diversity and provided information on population structure among the finger millet genotypes. The SCoT primers, SCoT-14, SCoT-18 SCoT-20 and SCoT-23 showed the higher PIC value and marker index, and potentiality for exploring the genetic diversity of studied millet genotypes. Based on the genetic similarity analysis it is revealed that some of the indigenous finger millet genotypes such as Jhana, Lala, Kurkuti, Ladu, Bhadi and Taya showed highest genetic disimilarity with modern high yielding genotype and can be considered as the potential genetic resources for breeding program.

Internal Structure and CO2 Reservoirs of Habitable Water Worlds

Abstract Water worlds are water-rich (>1 wt% H2O) exoplanets. The classical models of water worlds considered layered structures determined by the phase boundaries of pure water. However, water worlds are likely to possess comet-like compositions, with between ∼3 and 30 mol% CO2 relative to water. In this study, we build an interior structure model of habitable (i.e., surface liquid ocean–bearing) water worlds using the latest results from experimental data on the CO2–H2O system to explore the CO2 budget and localize the main CO2 reservoirs inside of these planets. We show that CO2 dissolved in the ocean and trapped inside of a clathrate layer cannot accommodate a cometary amount of CO2 if the planet accretes more than 11 wt% of volatiles (CO2 + H2O) during its formation. If the atmosphere holds more than a negligible amount of the CO2 (>0.01% of the planet mass), the planet will not have a habitable surface temperature. We propose a new, potentially dominant, CO2 reservoir for water worlds: CO2 buried inside of the high-pressure water ice mantle as CO2 ices or (H2CO3 · H2O), the monohydrate of carbonic acid. If insufficient amounts of CO2 are sequestered in either this reservoir or the planet’s iron core, habitable-zone water worlds could generically be stalled in their cooling before liquid oceans have a chance to condense.

Technological and Construction Concept Algae Reactor with Internal CO2 Supply

Technological and Construction Concept Algae Reactor with Internal CO2 Supply

PYRACLOSTROBIN PRESERVES PHOTOSYNTHESIS IN ARABICA COFFEE PLANTS SUBJECTED TO WATER DEFICIT

The objective of this study was to investigate the effect of pyraclostrobin on the photosynthetic performance of rabica coffee plants subjected or not to a water deficit, using the parameter of gas exchange (net CO2 assimilation, stomatal conductance, transpiration rate, and internal CO2 concentration and nocturnal respiration), chlorophyll fluorescence a parameters (minimum fluorescence, maximum fluorescence, maximum quantum yield of photosystem II, effective quantum yield of PSII, quantum yield of regulated energy dissipation and quantum yield dissipation non-regulated) as well as the concentrations of chloroplast pigments. In the plants maintained without water deficit, pyraclostrobin did not cause any alteration on the parameters of chlorophyll a fluorescence; however, it contributed to an increase in the level of chlorophyll a + b, CO2 assimilation and CO2 influx for the carboxylation sites of the stroma. Decreases in nocturnal respiration in plants treated with pyraclostrobin, submitted or not to water deficit seems to be a common strategy in reducing energy waste in the maintenance metabolism. Under water deficit, pyraclostrobin contributed to increase the photochemical yield, enabling plants to effectively prevent the capture, use and dissipation of light energy.

Role of Zinc Oxide Nanoparticles in Countering Negative Effects Generated by Cadmium in Lycopersicon esculentum

Nanotechnology now plays a revolutionary role in many applications; nanomaterials have experienced significant importance in both basic and applied sciences as well as in bio-nanotechnology. Zinc oxide nanoparticles (ZnO-NPs) have become one of the most important metal oxide NPs in biological applications due to their beneficial impacts. The purpose of this study was to explore the effects of ZnO-NPs in reducing Cd toxicity by studying the growth, photosynthesis reactions, antioxidant system, oxidative stress, and protein content in Lycopersicon esculentum (tomato). ZnO-NPs induced an upregulation of antioxidative enzymes which protect the photosynthetic apparatus in plants. Seeds of tomato were sown to create nursery. At 20 days after sowing (DAS), seedlings were transferred to soil pots. Varied concentrations (0.4, 0.6 or 0.8 mM) of Cd were applied to the soil after 24 and 25 DAS. Zinc (Zn; 50 mg/L) and ZnO-NPs (50 mg/L) treatments were given continuously for 5 days from 31 to 35 DAS and sampling took place at 45 DAS. The results indicate that a Cd-generated oxidative burst in the form of elevated hydrogen peroxide (H2O2) levels resulted in a decline in cell viability through enhanced activity of the antioxidant system and proline content; the data increased on follow-up treatment with ZnO-NPs. Foliar application of ZnO-NPs significantly enhanced plant height, fresh, and dry weight of plant, leaf area, SPAD chlorophyll, photosynthetic attributes, i.e., net photosynthetic rate (PN), transpiration rate (E), internal CO2 concentration (Ci), and stomatal conductance (gs). Application of ZnO-NPs reduced the adverse effects generated by Cd and increased protein content, activities of nitrate reductase and carbonic anhydrase over the control in both stressed and non-stressed plants. Additionally, microscopic studies showed a marked increase in stomatal aperture after ZnO-NPs treatment in the presence or absence of Cd. This was associated with decrease in malondialdehyde and superoxide radical (O2−) levels. The present study suggests that ZnO-NPs can be effectively used to reduce the toxicity of Cd in tomato plants and may also be suitable for testing on other crop species.

Diurnal modulation of PEPCK decarboxylation activity impacts photosystem II light-energy use in a drought-induced CAM species

Crassulacean acid metabolism (CAM) is a photosynthetic pathway characterized by nocturnal CO2 fixation into organic acids followed by their diurnal decarboxylation. Decarboxylation activity is time regulated, usually presenting higher activity in the middle of the day. This process can be performed by phosphoenolpyruvate carboxykinase (PEPCK) and/or by malic enzyme, resulting in an increase in internal CO2 concentration which may act to suppress photorespiration. It is suggested that the CO2 provided by the decarboxylation can improve the photochemical use of energy in CAM plants. This photosynthetic pathway also contributes to improve water use efficiency, and, in an interesting way, some species can engage this photosynthesis when subjected to water deficit. Guzmania monostachia is a bromeliad that occupies habitats with intermittent water availability and CAM can be induced by water deficit. To test the light-time modulation of decarboxylation activity and light-energy use in G. monostachia, we analyzed the activity of PEPCK, the main decarboxylating enzyme for this bromeliad, as well as the photochemical and non-photochemical quenching and organic acids contents at three times of the day. Results showed a diurnal modulation where the highest PEPCK decarboxylation activity coincided with an increase in the photochemical quenching and a decrease in the non-photochemical quenching. In addition, a reduction in acid content was observed, strongly indicating the interface between CO2 generation through acid decarboxylation and its effect on PSII photochemical activity and photorespiration in CAM-induced plants. The same was not observed for well-watered plants. Also, PEPCK activity modulation may be related to transcriptional and post-translational regulation, since an increase in transcript abundance and a modulation in the dephosphorylated enzyme activity was noted. Moreover, we suggest that the time modulation of PEPCK plays an important role in regulating PSII energy use in CAM plants.

Impact of high throughput green synthesized silver nanoparticles on agronomic traits of onion

Onion (Allium cepa L.) which is belonging to the family Liliaceae, is one of the greatest vital crops field worldwide. In this current work, Stored, high throughput and green synthesized silver nanoparticles; AgNPs (2000 ppm) were used as an eco-friendly nano fertilizer for onion in field conditions. All state of art analysis (Uv–vis, TEM, SEM, particle size analyzer and zeta potential) were used to characterize the formed AgNPs. Twelve concentrations (from 5 to 100 ppm) of AgNPs, were applied to onion, in addition to, two commercial nano products as control; iron nanoparticles (FeNPs) and zinc nanoparticles (ZnNPs) (2000 and 2500 ppm, as recommended by the markets). All concentrations were prepared under optical conditions and were applied three times in open field in a randomized complete block design (RCBD) during both seasons 2017/2018 and 2018/2019 as foliar application for onion plants after 25, 40 and 55 days, directly after the first irrigation of the plant. To this end, the physio-biochemical parameters such as CO2 concentration, stomatal conductance and internal CO2 were calculated via steady-state porometer 11 (LICOR, LI-1600, Lincoln, NE, USA). After 120 days of growth sowing (DAS), yield components and quality were evaluated. Just after harvesting, onion was subjected to extraction using dichloromethane for further analysis. All extracts were analyzed using GC–MS under the optimum operational condition to calculate the different constituents. The obtained results designated that, foliar application using 20 ppm of AgNPs displayed the highest mean values of all morphological, yield, yield components and quality characters compared with other concentrations and also to the commercial products, that used very high doses ranged from 2000 to 2500 ppm that can lead to genotoxicity in term of mutations in future, for human health. In conclusion, AgNPs can be used as an eco-friendly nano fertilizer with a recommended dose of 20 ppm which is considered a safe dose to the environment and human health too, compared with the crazy doses of the available commercial products.

Productive and physiological performance of lettuce cultivars under hydroponic cultivation in the semi-arid region of the Northeast

Lettuce is the most-produced leafy vegetable in Brazil; however, to achieve satisfactory production in the different regions, it is necessary to choose the correct cultivar. The aim of this work was to evaluate the productive and physiological performance of lettuce cultivars in a hydroponic system located in Caucaia, in the state of Ceará. A completely randomised design was used, with four cultivars (Isabela, Vanda, Elba and Summer Crisp) and four replications. The following were evaluated: plant height and diameter (PH and PD), total fresh and dry weight (TFW and TDW), commercial fresh weight (CFW), internal CO2 concentration (Ci), stomatal conductance (gs), photosynthesis (A), ratio between internal and external CO2 concentration (Ci/Ca), and transpiration (E). Differences were seen between cultivars in the production and physiological characteristics, except for Ci and Ci/Ca. The ‘Elba’ and ‘Summer Crisp’ cultivars were the first to show signs of bolting (32 and 36 days) and greater height, 38.7 and 31.8 cm respectively. The ‘Isabela’ and ‘Vanda’ cultivars obtained the greatest values for CFW (43.5 and 41.13 g) and TFW (49.38 and 46.46 g). In relation to physiological performance, the ‘Isabela’ and ‘Summer Crisp’ cultivars presented the most photosynthesis. The ‘Isabela’ cultivar had the best productive and physiological performance, in addition to being the only cultivar that presented no signs of bolting, and is therefore strongly suggested for hydroponic production under the conditions of this study.

Beneficial role of acetylcholine in chlorophyll metabolism and photosynthetic gas exchange in Nicotiana benthamiana seedlings under salinity stress.

Acetylcholine (ACh) is believed to improve plant growth. However, regulation at biochemical and molecular levels is largely unknown. The present study investigated the impact of exogenously applied ACh (10µm) on growth and chlorophyll metabolism in hydroponically grown Nicotiana benthamiana under salt stress (150mm NaCl). Salinity reduced root hydraulic conductivity while ACh-treated seedlings exhibited a significant increase, resulting in increased relative water content. Salinity induced a reduction in chlorophyll biosynthetic intermediates, such as protoporphyrin-IX, Mg-photoporphyrin-IX and protochlorophyllide, which were significantly ameliorated in the presence of ACh. This influence of ACh on chlorophyll synthesis was confirmed by up-regulation of HEMA1, CHLH, CAO and POR genes. Gas exchange parameters, i.e. stomatal conductance, internal CO2 concentration and transpiration rate, increased with ACh, thereby alleviating the salinity effects on photosynthesis. In addition, the salinity-induced enhancement of lipid peroxidation declined after ACh treatment through modulation of the activity of the assayed antioxidant enzymes (superoxide dismutase and peroxidase). Importantly, ACh significantly reduced the uptake of Na and increased uptake of K, resulting in a decline in the Na/K ratio. Results of the present study indicate that ACh can be effective in ameliorating NaCl-induced osmotic stress, altering chlorophyll metabolism and thus photosynthesis by maintaining ion homeostasis, hydraulic conductivity and water balance.

Effect of glutamate on Pyricularia oryzae infection of rice monitored by changes in photosynthetic parameters and antioxidant metabolism.

Considering the importance of blast caused by Pyricularia oryzae in the decrease of rice yield worldwide, this study aimed to assess the photosynthetic performance [leaf gas exchange and chlorophyll (Chl) a fluorescence parameters as well as the photosynthetic pigments concentration], the activities of antioxidant enzymes [ascorbate peroxidase, catalase (CAT), peroxidase (POX), superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione-S-transferase] and concentrations of hydrogen peroxide (H2 O2 ) and malondialdehyde (MDA) in the leaves of rice plants non-supplied (-Glu) or supplied (+Glu) with glutamate (Glu) and non-infected or infected by P. oryzae. Blast severity was reduced in the leaves of +Glu plants. On the infected leaves of +Glu plants, the values for internal CO2 concentration were lower while the values for net carbon assimilation rate, stomatal conductance as well as for the concentrations of Chl a, Chl b and carotenoids were higher in comparison to infected leaves of -Glu plants. The functionality of the photosynthetic apparatus was preserved in the infected leaves of +Glu plants. The activities of CAT, GPX, GR, POX and SOD increased in the infected leaves of both -Glu and +Glu plants compared to their non-inoculated counterparts, but their activities were lower for +Glu plants. The lower activity of these antioxidative enzymes was triggered by the reduced hydrogen peroxide concentration in the infected leaves of +Glu plants resulting in lower MDA concentration. It can be concluded that photosynthesis was less impaired in infected plants supplied with glutamate due to the lower biochemical constraints for CO2 fixation. Moreover, there was a need for lower activity of reactive oxygen species scavenging enzymes in infected leaves of plants supplied with glutamate due to the lower oxidative stress imposed by P. oryzae infection.

Photosynthesis and gas exchanges of forage cactus varieties (Opuntia and Nopalea) grown under screen and irrigation

Forage cactus is a CAM-optional plant according to its water status. The objective of this study was to characterize the net photosynthesis rate (Pn), transpiration rate (E), stomatal conductance (C), internal CO 2 concentration(CO 2int. ), water use efficiency (WUE) and instantaneous carboxylation efficiency ( CEi ) of forage cactus varieties of the genus Opuntia and Nopalea grown in the Brazilian semiarid region under screen conditions and periodic irrigation. The varieties IPA-200016 ( O. stricta ), IPA-100003 ( O. ficus indica ), IPA-200008 ( O. atropes ), IPA-200149 ( O. larreri ) and IPA-100004 ( N. cochenillifera ) were grown under screen conditions, with 50% light reduction, and irrigated every seven days using 1/3 of total weekly evapotranspiration. Measurements were made in all cladodes, on two-year-old plants, at 6:00 a.m., 12:00 p.m., 6:00 p.m. and 0:00 a.m. with the aid of CIDBio-Science Ultra-Light CI-340®. All variables analyzed vary between genotypes and times. The varieties had the same pattern for Pn , E , C , CO 2int. , WUE and CEi . Gas exchange takes place at day time (optional-CAM). Assimilation of CO 2 predominates at night (CAM). The loss of H 2 O is most evident during the day (C3). Stomatal conductance is identical to those reported for C3 and C4 plants. The IPA-200149 variety stands out in relatin to WUE and CEi in relatin to the others.