Leaf Internal CO2 Concentration Research Articles

Long-term CO2 Enrichment Increases Biomass but Results in Rapid Physiological Acclimation of Petunia and Pansy

Although crops often respond immediately to enriched CO2 concentrations (e.g., increased photosynthesis), this initial response is often not sustained throughout production, thus reducing the benefit of this input. For horticulture species, the timing and extent of these acclimation responses are still widely uncertain. Therefore, the objective of this research was to determine species-specific acclimation responses to elevated CO2 concentrations for pansy (Viola ×wittrockiana ‘Matrix Blue Blotch Improved’) and petunia (Petunia ×hybrida ‘Dreams Midnight’). Seedlings were transplanted to 11.5-cm pots and placed in growth chambers with air temperature, relative humidity, and radiation intensity setpoints of 21 °C, 55%, and 250 μmol⋅m−2⋅s−1, respectively. Carbon dioxide treatments were established using the two growth chambers with setpoints of either 400 (ambient) or 1000 μmol⋅mol−1 (elevated) maintained during a 16-hour photoperiod. In addition to data collected through destructive harvest, the rate of photosynthesis (A) in response to increasing internal leaf CO2 concentration (A-Ci) and at the operating CO2 concentration (A-Ca) were measured weekly with a portable leaf photosynthesis system at saturating [A-Ci (1000 μmol⋅m−2⋅s−1)] or production [A-Ca (250 μmol⋅m−2⋅s−1)] radiation intensities. For both pansy and petunia, elevated CO2 produced greater total shoot dry mass than ambient CO2 after 4 weeks. However, the decreased maximum rate of photosynthetic electron transport, maximum rate of Rubisco carboxylase, and triose phosphate utilization rate of both species were also observed under elevated CO2. Similarly, A measured at 400 and 1000 μmol⋅mol−1 was reduced for both pansy and petunia grown under the elevated compared with ambient CO2 concentration based on A-Ca responses after 7 days, indicating quick physiological acclimation to this input. These results provide information regarding the timing and extent of physiological acclimation in response to elevated CO2 concentrations. However, because of physiological acclimation potentially occurring within 7 days of treatment initiation, additional research is necessary to develop species-specific recommendations for controlled environment production.

Responses to elevated daytime air and canopy temperature during panicle development in four rice genotypes under paddy conditions in large field chambers

Rising air temperatures have the capacity to impact rice yields in future climates. Studies in large temperature-controlled field chambers were established to examine the responses of four contrasting rice genotypes to elevated daytime temperatures (ET) during reproductive development under paddy conditions. Field chambers were effective in raising mean above-canopy maximum daytime temperatures from 29.9 to 41.1°C during 12 d of ET treatment (68–80 d after emergence, DAE), while increased transpiration under ET resulted in lowering of mean lower-canopy maximum temperature to 33.2°C. Nevertheless, the earliest genotype Vandana encountered a hot spell of 37.0°C at 68–74 DAE in the lower canopy at its late reproductive stage, which exceeded the spikelet sterility threshold of 33.7°C, so its spikelet fertility, grain number and grain yield were reduced under ET. Genotypes differed in the extent of canopy cooling, with less reduction in Vandana and IR64 than in N22 and Takanari. For canopy cooling to be effective, stratification of air layers must occur within the canopy, which was more effective under the shorter and denser canopy of N22 and Takanari (plant height of 70–80 ​cm) than under IR64 (90–110 ​cm) and Vandana (115–130 ​cm). Genotypes with appropriate canopy structures should be chosen for high vapour pressure deficit (VPD) conditions. Both maximum canopy temperature and VPD need to be specified to define the critical threshold for heat tolerance. Takanari was notable for greater leaf area retention and greater leaf photosynthetic capacity due to the maintenance of a higher internal leaf CO2 concentration, which led to higher spikelet and grain numbers and higher yield potential under ET conditions.

Parâmetros fisiológicos e produtivos de trigo afetados pela remoção de perfilhos e pela desfolha

Abstract The objective of this work was to evaluate the photosynthetic parameters, yield potential, and response to defoliation of wheat (Triticum aestivum) plants subjected to tiller removal. Two experiments were conducted under greenhouse conditions. In the first, the two following cultivars were evaluated for complete tiller removal: TBIO Audaz and BRS 394, with a high and low tillering capacity, respectively. In the second, only 'TBIO Audaz' was subjected to detillering and defoliation at post-anthesis. Tiller removal increased the yield potential of the main stem of both tested cultivars and the CO2 assimilation potential of the flag leaf, which was possibly a strategy to meet the demands for an increased sink strength, as evidenced by the response curves to irradiance and leaf internal CO2 concentration. The partial defoliation of 'TBIO Audaz' increased daily CO2 assimilation, both in intact and detillered plants. Detillered plants show a higher photosynthetic and yield potential of the main stem, but also a greater sensitivity to defoliation in the post-anthesis period.

Morpho-physiological growth performance and phytoremediation capabilities of selected xerophyte grass species toward Cr and Pb stress

Being sessile organisms, plants cannot escape unwanted changes in the environment. The rapid human population explosion caused significant environmental problems. Heavy metals produced through various sources can cause severe damage to living organisms. The study was planned to evaluate four grass species’ morpho-physiological growth characteristics and phytoremediation capabilities under chromium (Cr) and lead stress (Pb) in the arid climate. Typha angustifolia, Tragus roxburghii, Aeluropus logopoides, and Cenchrus ciliaris grass species were used for the study. One-year-old stubbles from the Cholistan desert were used for the experiment. Cr treatments in the form of K2Cr2O7 were applied at 0, 20, 40, and 80 mg L–1, whereas Pb was applied as PbCl2 at 0, 50, 200, and 500 mg L–1 as control, low, moderate and high-stress, respectively. After 6 weeks of heavy metals treatments, plants were harvested and analyzed for growth performance and phytoremediation capabilities. Results depicted that, regarding morphological attributes, T. angustifolia performed better, followed by C. ciliaris; no clear pattern was observed for T. roxburghii and A. logopoides. The CO2 assimilation rate (Co2d) and water use efficiency (WUE) increased as the heavy metal stress increased in all species under both metals. In contrast, total chlorophyll content was higher under low stress. Other physiological parameters, such as relative humidity (RHd), net photosynthetic rate (A), transpiration rate (E), stomatal conductance (Gs), leaf internal CO2 concentration (Ci) and membrane stability index (MSI) gradually decreased as the Cr, and Pb stress levels increased among all the species. Moreover, Cr and Pb absorption contents of T. angustifolia were higher than the other three species at each stress level. Overall, T. angustifolia thrived against heavy metals stress and showed higher biomass, maximum photosynthetic measurements, WUE and higher metal absorption among all the selected species. Results concluded that although all the selected species behaved fine under stress conditions, T. angustifolia performance was better; thus, it can be used to remediate the soil near industrial estates.

Growth and photosynthetic responses of Chinese cabbage (Brassica rapa L. cv. Tokyo Bekana) to continuously elevated carbon dioxide in a simulated Space Station “Veggie” crop-production environment

Among candidate leafy vegetable species initially considered for astronauts to pick and eat from the Veggie plant-growth unit on the International Space Station (ISS), Chinese cabbage (Brassica rapa L. cv. Tokyo Bekana) ranked high in ground-based screening studies. However, subsequent attempts to optimize growth within rigorous ISS-like growth environments on the ground were frustrated by development of leaf chlorosis, necrosis, and uneven growth. ‘Tokyo Bekana’ (‘TB’) grown on ISS during the VEG-03B and C flights developed similar stress symptoms. After lengthy troubleshooting efforts to identify causes of sub-par growth in highly controlled environments, the super-elevated CO2 concentrations that plants on ISS are exposed to continuously (average of 2,800 µmol/mol) emerged as a candidate environmental condition responsible for the observed plant-stress symptoms. Subsequent ground-based studies found continuous exposure to ISS levels of CO2 under Veggie environmental and cultural conditions to significantly inhibit growth of ‘TB’ compared to near-Earth-normal CO2 controls. The present study investigated growth and gas-exchange responses of ‘TB’ to sub-ISS but still elevated CO2 levels (900 or 1,350 µmol/mol) in combination with other potential stressors related to ISS/Veggie compared to 450 µmol/mol CO2 controls. Shoot dry mass of plants grown at 450 µmol•mol−1 CO2 for 28 days was 96% and 80% higher than that of plants grown at 900 µmol•mol−1 CO2 and 1,350 µmol•mol−1 CO2, respectively. Leaf number and leaf area of controls were significantly higher than those of plants grown at 1,350 µmol•mol−1 CO2. Photosynthetic rate measured using a leaf cuvette was significantly lower for plants grown at 900 µmol•mol−1 CO2 than for controls. The ratio of leaf internal CO2 concentration (Ci) to cuvette ambient CO2 concentration (Ca) was significantly lower for plants grown at 450 µmol•mol−1 CO2 than for plants grown at elevated CO2. Thus, continuously elevated CO2 in combination with a Veggie cultivation system decreased growth, leaf area, and photosynthetic efficiency of Chinese cabbage ‘Tokyo Bekana’. The results of this study suggest that ‘Tokyo Bekana’ is very sensitive to continuously elevated CO2 in such a growth environment, and indicate the need for improved environmental control of CO2 and possibly root-zone factors for successful crop production in the ISS spaceflight environment. Differential sensitivity of other salad crops to an ISS/Veggie growth environment also is possible, so it is important to mimic controllable ISS-like environmental conditions as precisely as possible during ground-based screening.

On geologic timescales, plant carbon isotope fractionation responds to precipitation similarly to modern plants and has a small negative correlation with pCO2

Leaf carbon isotope fractionation (Δleaf) is sensitive to environmental conditions and can provide insights into the state and evolution of leaf gas-exchange in response to climate and environment factors. In modern plants, water availability is the strongest environmental predictor of Δleaf across sites that experience relatively uniform and low concentrations of CO2 in the atmosphere (pCO2). Growth chamber experiments show Δleaf of modern plants can also be sensitive to changing pCO2. However, over geologic time, it is uncertain how Δleaf has responded to shifts in pCO2 and precipitation. To address this problem, we collected sediment (rock) samples from fossil leaf sites that represent a range of pCO2 values from ∼200 to 900 ppmV, over 40 degrees of latitude from New Mexico to the High Arctic, and 40 million years spanning the Late Cretaceous to the Oligocene. For each site, the carbon isotope composition of atmospheric CO2 (δ13Catm), pCO2, mean annual precipitation, and mean annual temperature were constrained from independent proxies. From sediment samples, we extracted long-chain n-alkanes (biomarkers derived from plant wax). We then measured the carbon isotope ratios of sediment-derived n-C29 and n-C31 alkanes to calculate Δleaf. Results show a negative correlation between Δleaf and pCO2 even after controlling for mean annual precipitation. The Δleaf response to pCO2 is small (−0.3 ± 0.09‰/100 ppmV), suggesting plants are adjusting internal leaf CO2 concentrations to atmospheric pCO2 concentrations, likely by optimizing leaf gas-exchange to maximize carbon intake and minimize water loss in response to environmental conditions. Similar to previous studies of geologic sediments and living plants, Δleaf was also positively correlated with water availability and, to a lesser extent, sensitive to plant type and possibly altitude. As a result, the Δleaf – pCO2 relationship in the geologic past may be more complex than observed in modern studies and therefore, precludes its use as a pCO2 proxy.

Evaluation of photosynthesis, physiological, and biochemical responses of chickpea (Cicer arietinum L. cv. Pirouz) under water deficit stress and use of vermicompost fertilizer

One goal in the face of drought stress conditions is to increase growth and yield through the reduction of negative effects of stress. Vermicompost can play an effective role in plant growth and development and in reducing harmful effects of various environmental stresses on plants due to its porous structure, high water storage capacity, having hormone-like substances, plant growth regulators, and high levels of macro and micro nutrients. This study considered the physiological, biochemical, and photosynthetic responses of the chickpea to different combinations of vermicompost and water stress in a greenhouse environment. Two factors were involved, addition of vermicompost to soil at four ratios: control (100 wt% (weight percentage) soil); 10 wt% vermicompost+90% soil; 20 wt% vermicompost+80 wt% soil; 30 wt% vermicompost+70 wt% soil weight percentage, and treatment of water stress at three levels including 75, 50, and 25% of field capacity. The results showed that vermicompost had a significant effect on all traits under stress and non-stress conditions. Application of vermicompost in soil, especially at the levels of 20 and 30 wt% significantly increased all studied traits under non-stress conditions. Under moderate stress conditions, vermicompost at 30 wt% treatment resulted in a significant increase in the photosynthetic pigments, CO2 assimilation rate, internal leaf CO2 concentration, transpiration, the maximal quantum yield of photosystem II (PSII) photochemistry (Fv/Fm), concentrations of Ca and K in root and leaf tissues, proline and soluble protein contents in root tissues. Peroxidase (POX) and catalase (CAT) enzyme activities decreased significantly with increasing proportions of vermicompost, but the activity of superoxide dismutase was not significantly different. In conclusion, the above results showed that vermicompost fertilizer had a positive effect on physiological, biochemical, and photosynthetic responses of chickpea under non-stress and moderate stress conditions, but no positive effect was determined under severe water stress.

Light intensity-regulated stomatal development in three generations of Lepidium sativum

Stomata are of crucial importance for CO2 uptake and the water economy of terrestrial plants. They evolve during the early phases of leaf development according to genetically conserved information modulated in its expression by environmental conditions. Mature leaves experience the environment, e.g. light intensity, and signal to younger developing leaves, modifying stomatal density (SD) and probably other leaf traits as well. In addition, the parental environment can affect the offspring’s phenotypes in an adaptive manner. However, the transgenerational effect of light on SD and interactions with the offspring’s light environment have not been studied so far. Here we compare transgenerational (parental) and growth-light (environmental) effects on SD. We grew three generations of garden cress (Lepidium sativum) in two contrasting light environments in a full factorial design. Stomatal and pavement cell densities (SD, PCD), 13C abundance as a proxy of leaf internal CO2 concentration (Ci), and leaf area were analysed in cotyledons and first true leaves of parental plants and two generations of offspring. Our results indicate that SD of offspring reflects both current and maternal light intensities. The transgenerational effect of light on SD was much smaller than the influence of current growth light and the former’s manifestation was dependent on light experienced by offspring. The cotyledons’ SD was unresponsive to variations in Ci but retained its light sensitivity, though it was smaller than in true leaves. High light reduced amphistomy in favour of the lower (abaxial) leaf side. SD and PCD were linearly proportional irrespective of light level, indicating invariant portions of spacing and amplifying cell divisions, and causing lower sensitivity of stomatal index at high SD. We show that light-stimulated stomatal development in garden cress differs in cotyledons and true leaves, varies between adaxial and abaxial leaf sides, and retains transgenerational information about environmental clues.

Gas exchange and photosynthetic light response curves in nematode-infected tomato plants treated with Thuya occidentalis

The use of homeopathic formulations on plants may cause changes in plant metabolism and result in disease control by inducing resistance. This work aimed to study the physiological responses of tomato plants infected with nematode (Meloidogyne incognita) and treated with highly diluted preparations of Thuya occidentalis, a homeopathic remedy. The different treatments included T. occidentalis 6CH, 24CH, and 50CH (Centesimal Hahnemanian), a water control (with nematode and without treatment), and an absolute control (no treatment and no nematode). The assay was conducted in a greenhouse using a randomized block design with four replications. Gas exchange parameters were measured at specific times before and after nematode inoculation. Photosynthetic rate, stomatal conductance, transpiration, leaf internal CO2 concentration, and leaf temperature were measured at various photosynthetic photon flux densities. No significant difference was found in the different gas exchange specific measure parameters between the treatments. Untreated infected plants showed an increase in net photosynthesis and in the carboxylation capacity, as shown by the light response curve. Treatment with T. occidentalis 24CH inhibited the increase in CO2 fixation in tomato plants inoculated with M. incognita, leading to a similar behavior as healthy plants, independently of the photon density.

Evaluation of Municipal Solid Waste Compost and/or Fertigation as Peat Substituent for Pepper Seedlings Production

Pepper (Capsicum annuum L.) seed germination and seedling growth using municipal solid waste compost (MSWC) in various proportions was examined. MSWC extracts (10− 0 up to 10− 6 dilutions) were evaluated for seed priming/germination in Petri dishes. The MSWC extracts at 10− 1–10− 6 showed similar seedling germination, whereas extracts at 10− 1–10− 3 accelerated root radical length compared to the control treatment. However, pure extracts (at 10− 0) almost failed seed germination. Under nursery conditions, six substrates were prepared from commercial peat and MSWC and were further assessed in conjunction with the nutrient application as basic fertilizer (BF) or hydro fertilizer (HF). The addition of MSWC into peat inhibited seed emergence and increased the mean germination time, while fertigation accelerated seed emergence at 15% addition of MSWC. Addition of > 30% MSWC reduced seedling height, leaf number and fresh weight. BF and HF increased fresh weight in seedlings grown in 15% MSWC. Leaf chlorophyll and total carotenoids content decreased in > 60% MSWC into the peat. The greatest leaf photosynthetic rate was found with the application of HF, while higher leaf stomatal conductance and leaf internal CO2 concentration were found in plants grown without fertilizers for both 15 and 45% of MSWC addition. The K content decreased, Na content increased, while P content did not differ with MSWC addition. Fertigation improved seedlings’ nutritive status. No visual phytotoxicity was observed macroscopically. Low content (15–30%) of MSWC may act as alternative substitute to peat with more positive effects observed, if nutrients are provided through HF rather than BF.

Effect of Leaf Water Potential on Internal Humidity and CO2 Dissolution: Reverse Transpiration and Improved Water Use Efficiency under Negative Pressure.

The pull of water from the soil to the leaves causes water in the transpiration stream to be under negative pressure decreasing the water potential below zero. The osmotic concentration also contributes to the decrease in leaf water potential but with much lesser extent. Thus, the surface tension force is approximately balanced by a force induced by negative water potential resulting in concavely curved water-air interfaces in leaves. The lowered water potential causes a reduction in the equilibrium water vapor pressure in internal (sub-stomatal/intercellular) cavities in relation to that over water with the potential of zero, i.e., over the flat surface. The curved surface causes a reduction also in the equilibrium vapor pressure of dissolved CO2, thus enhancing its physical solubility to water. Although the water vapor reduction is acknowledged by plant physiologists its consequences for water vapor exchange at low water potential values have received very little attention. Consequences of the enhanced CO2 solubility to a leaf water-carbon budget have not been considered at all before this study. We use theoretical calculations and modeling to show how the reduction in the vapor pressures affects transpiration and carbon assimilation rates. Our results indicate that the reduction in vapor pressures of water and CO2 could enhance plant water use efficiency up to about 10% at a leaf water potential of −2 MPa, and much more when water potential decreases further. The low water potential allows for a direct stomatal water vapor uptake from the ambient air even at sub-100% relative humidity values. This alone could explain the observed rates of foliar water uptake by e.g., the coastal redwood in the fog belt region of coastal California provided the stomata are sufficiently open. The omission of the reduction in the water vapor pressure causes a bias in the estimates of the stomatal conductance and leaf internal CO2 concentration based on leaf gas exchange measurements. Manufactures of leaf gas exchange measurement systems should incorporate leaf water potentials in measurement set-ups.

Constraining ecosystem model with adaptive Metropolis algorithm using boreal forest site eddy covariance measurements

Abstract. We examined parameter optimisation in the JSBACH (Kaminski et al., 2013; Knorr and Kattge, 2005; Reick et al., 2013) ecosystem model, applied to two boreal forest sites (Hyytiälä and Sodankylä) in Finland. We identified and tested key parameters in soil hydrology and forest water and carbon-exchange-related formulations, and optimised them using the adaptive Metropolis (AM) algorithm for Hyytiälä with a 5-year calibration period (2000–2004) followed by a 4-year validation period (2005–2008). Sodankylä acted as an independent validation site, where optimisations were not made. The tuning provided estimates for full distribution of possible parameters, along with information about correlation, sensitivity and identifiability. Some parameters were correlated with each other due to a phenomenological connection between carbon uptake and water stress or other connections due to the set-up of the model formulations. The latter holds especially for vegetation phenology parameters. The least identifiable parameters include phenology parameters, parameters connecting relative humidity and soil dryness, and the field capacity of the skin reservoir. These soil parameters were masked by the large contribution from vegetation transpiration. In addition to leaf area index and the maximum carboxylation rate, the most effective parameters adjusting the gross primary production (GPP) and evapotranspiration (ET) fluxes in seasonal tuning were related to soil wilting point, drainage and moisture stress imposed on vegetation. For daily and half-hourly tunings the most important parameters were the ratio of leaf internal CO2 concentration to external CO2 and the parameter connecting relative humidity and soil dryness. Effectively the seasonal tuning transferred water from soil moisture into ET, and daily and half-hourly tunings reversed this process. The seasonal tuning improved the month-to-month development of GPP and ET, and produced the most stable estimates of water use efficiency. When compared to the seasonal tuning, the daily tuning is worse on the seasonal scale. However, daily parametrisation reproduced the observations for average diurnal cycle best, except for the GPP for Sodankylä validation period, where half-hourly tuned parameters were better. In general, the daily tuning provided the largest reduction in model–data mismatch. The models response to drought was unaffected by our parametrisations and further studies are needed into enhancing the dry response in JSBACH.

Genetic engineering of polyamine metabolism changes Medicago truncatula responses to water deficit

In the current scenario of climate change and increasing water scarcity there is an increased need to combine research efforts for the development of abiotic stress resistant crops, specifically plants able to support water deficit (WD). Polyamines (PAs) have been described as being involved in the regulation of many physiological processes and a variety of stress responses in plants. Arginine decarboxylase (ADC) is considered a key enzyme of the polyamine (PA) biosynthetic pathway. In this study, a T2 transgenic homozygous line of Medicago truncatula expressing the oat Adc under the control of CaMV 35S was obtained and was shown to have higher leaf accumulation of putrescine, spermidine and norspermidine compared to wild type plants. The photosynthetic parameters, leaf internal CO2 concentration (Ci), net CO2 assimilation rate (A), transpiration (E) and stomatal conductance (gs) of transformed and untransformed lines during WD and water deficit recovery experiments were measured by IRGA (infrared gas analyzer) and compared over time. Two light intensities were used, growth light intensity (391 μmol m−2 s−1) and saturating light intensity (1044 μmol m−2 s−1). Independently of the light intensity, and under WD, the transgenic line stood out with increased Ci, A, E and gs; suggesting a possible benefit of the augmented PAs under such disturbing environmental conditions. We showed that the constitutive expression of the oat Adc gene improve the physiological responses to WD and that WD recovered transgenic plants had higher seed yield, suggesting a possible benefit of PA metabolism manipulation in legumes.

Diffusion limitations and metabolic factors associated with inhibition and recovery of photosynthesis following cold stress in Elymus nutans Griseb.

We studied the effects of cold stress (5°C) and re-warming (25°C) on gas exchange, photosystem II, key photosynthetic enzyme activities, gene expression, and carbohydrate metabolite concentrations in two Elymus nutans genotypes differing in cold resistance (DX, cold-tolerant and ZD, cold-sensitive). Cold stress led to irreversible reductions in photosynthetic rate. This reduction was accompanied by declining stomatal and mesophyll conductance (gs and gm), transpiration rate (Tr) and photochemical efficiency in both genotypes, however there were smaller decreases in DX than in ZD. Cold-tolerant DX maintained higher photosynthetic enzyme activities and transcript levels, as well as higher reducing sugar concentrations and sucrose accumulation. The relationship between Pn and internal leaf CO2 concentration (Pn/Ci curve) during cold and re-warming was analyzed to estimate the relative influence of stomatal and non-stomatal components on photosynthesis. Stomatal limitation, non-stomatal limitation, and CO2 compensation point (CP) increased in both genotypes under cold stress, but to a lesser extent in DX. Maximum CO2 assimilation rate (Pmax), and carboxylation efficiency (CE) declined, but DX had significantly higher levels of Pmax and CE than ZD. Following cold-stress recovery, the maximum quantum yield of PSII (Fv/Fm), apparent electron transport rate (ETR), Rubisco activity, Rubisco activation state and CE in DX resumed to the control levels. In contrast, Pn, Pmax, gs, gm, and Tr recovered only partially for DX, suggesting that incomplete recovery of photosynthesis in DX may be mainly related to diffusion limitations. Higher Rubisco large subunit (RbcL) and Rubisco activase (RCA) transcript levels, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity, and carbohydrate accumulation contributed to higher photosynthetic recovery in DX. These results indicate that the maintenance of higher Pn and Pmax under cold stress and recovery in cold-tolerant DX could be attributed to reduced diffusion limitations and rapid recuperation of metabolic factors.

Influence of arbuscular mycorrhizal fungi and treated wastewater on water relations and leaf structure alterations of Viburnum tinus L. plants during both saline and recovery periods

Nowadays, irrigation with low quality water is becoming an alternative to satisfy the needs of crops. However, some plant species have to deal with high salinity of reclaimed water, by adapting their physiological behaviour during both saline and recovery periods and developing morphological changes in their leaves. The application of arbuscular mycorrhizal fungi (AMF) could also be a suitable option to mitigate the negative effects of this kind of water, although the effectiveness of plant-AMF association is influenced by many factors. In this work, during forty weeks, the combined effect of Glomus iranicum var. tenuihypharum and two types of water: control, C, EC<0.9dSm−1 and reclaimed water, RW (with EC: 4dSm−1 during a first saline period and EC: 6dSm−1 during a second saline period) was evaluated for laurustinus plants (Viburnum tinus L.) transplanted in soil. This was followed by a recovery period of eight weeks, when all the plants were irrigated in the control irrigation conditions. Seasonal and daily changes in stem water potential (Ψstem), stomatal conductance (gs), photosynthesis (Pn) and leaf internal CO2 concentration (Ci) of laurustinus plants were evaluated. Leaf structure alterations, nutrient imbalance, height and leaf hydraulic conductivity (Kleaf) were also determined. Due to the high difficulty of absorbing water from the soil, RW plants showed a high volumetric water content (θv) in soil. The stem water potential and the stomatal conductance (gs) values were reduced in RW plants throughout the second saline period. These decreases were also found during the day. Leaf Ca2+/Na+ and K+/Na+ ratios diminished in RW plants respect to the C plants due to the Na+ accumulation, although height and chlorophyll content values did not show statistical differences. Leaves from RW plants showed a significantly thicker mesophyll than Control leaves as a consequence of high EC. The area of palisade parenchyma (PP) increased while the area of spongy parenchyma (SP) decreased in RW leaves with respect to the C leaves. These structural changes could be considered as a strategy to maximize photosynthesis potential in saline conditions. Mycorrhizal inoculation improved the water status of both C and RW plants by increasing their Ψstem and gs values. As regards leaf structure, AMF showed an opposite effect to salinity for PP and SP. At the end of the recovery period, hardly any statistical differences of physiological parameters were found between treatments, although a tendency to improve them was observed in inoculated plants. In any case, the leaf structural changes and the great reduction in Kleaf observed at Ψleaf below −1.5MPa would constitute an important mechanism for laurustinus plants to reduce the water loses produced by salinity.

Magnesium-induced alterations in the photosynthetic performance and resistance of rice plants infected with Bipolaris oryzae

Brown spot (BS), caused by the fungus Bipolaris oryzae, is one of the most important diseases contracted by rice. We investigated the effect of magnesium (Mg) on the development of BS, caused by Bipolaris oryzae, and the effects of disease development on the photosynthetic performance of rice (Oryza sativa L.) plants (cv. Metica-1) grown in nutrient solutions containing 0.25 or 4.0 mM of Mg. Assessments of BS severity, leaf Mg and pigment concentrations (total chlorophylls and carotenoids), were carried out at 120 h after inoculation, in addition to gas exchange parameters,. Higher leaf concentration of Mg was observed in plants supplied with 4.0 mM Mg than in those supplied with 0.25 mM. The increase in leaf Mg was accompanied by a decrease in BS severity, higher concentration of total chlorophyll and better photosynthetic performance. Plants supplied with 4.0 mM Mg had higher average values for carbon assimilation, stomatal conductance and internal leaf CO2 concentration when compared with plants supplied with 0.25 mM Mg. Conversely, the concentration of carotenoids was lower in plants supplied with the higher Mg rate. These results suggest that Mg suppresses disease severity and preserves photosynthetic performance by allowing for better stomatal conductance and, consequently, greater availability of CO2 at the carboxylation sites.

Characterization and functional analysis of a B3 domain factor from Zea mays.

In this study, we isolated a full-length cDNA and named ZmBDF from zea mays. ZmBDF encoded a protein of 356 amino acids and phylogenetic analysis showed that it belongs to a closely related subgroup with B3 domain factors in plants. The transcript level of ZmBDF could be induced by ABA, MeJA, salt or drought treatments. To further investigated the function of ZmBDF, ZmBDF over-expression transgenic lines were got by transforming it into Arabidopsis thaliana. ZmBDF over-expression transgenic plants in Arabidopsis could increase drought and salt tolerant in germination assay. Under drought condition, net photosynthetic rates (PN), stomatal conductance (gs), and internal leaf CO2 concentration (Ci) were less affected in transgenic plants compared with wild type. Besides, the chlorophyll a and chlorophyll b (chl a/chl b) ratio decreased in WT plants than the transgenic plants and total carotenoid content show opposite trends. Moreover, transgenic plants could also reduce the stomatal density and changed the stomatal shape. Taken together, our data suggested that ZmBDF could improve stress tolerance to drought and salt in maize.

Simultaneous overexpression of cyanidase and formate dehydrogenase in Arabidopsis thaliana chloroplasts enhanced cyanide metabolism and cyanide tolerance

Cyanide is a strong inhibitor of diverse metabolic reactions and easily absorbed by organisms. However, cyanide is also a byproduct of plant and microbial metabolism. This is why these groups of organisms contain pathways for cyanide detoxification. Large amounts of cyanides are also produced by industries and are today mostly removed by physical and chemical methods. Phytoremediation can provide an alternative to these techniques, but existing cyanide concentrations at contaminated sites often exceed the capacities of plant metabolism. In this study, we overexpressed a bacterial cyanidase together with a plant formate dehydrogenase in Arabidopsis thaliana in order to establish a synthetic pathway for cyanide degradation. Simultaneous overexpression of both enzymes would ultimately result in the formation of CO2 and NH3 from cyanide. Both enzymes were targeted to chloroplasts and shown to be active in planta. When plants were spray-inoculated with cyanide, overexpressors of the synthetic cyanide degradation pathway showed less reduction in leaf pigment contents, lower induction of antioxidant enzymes, and reduced growth retardation compared to controls. Growth on cyanide was also tested for seedlings germinating on agar, plants in hydroponics, and plants growing in sand. In all three assays, plants overexpressing the synthetic pathway for cyanide degradation showed enhanced growth and biomass accumulation compared to controls. Gas exchange measurements confirmed enhanced stress resistance of transgenic plants and suggested that cyanide degradation to CO2 increased the leaf internal CO2 concentration. Results are discussed in comparison to other approaches for cyanide phytoremediation.

A model of plant isoprene emission based on available reducing power captures responses to atmospheric CO2

We present a unifying model for isoprene emission by photosynthesizing leaves based on the hypothesis that isoprene biosynthesis depends on a balance between the supply of photosynthetic reducing power and the demands of carbon fixation. We compared the predictions from our model, as well as from two other widely used models, with measurements of isoprene emission from leaves of Populus nigra and hybrid aspen (Populus tremula × P. tremuloides) in response to changes in leaf internal CO2 concentration (C(i)) and photosynthetic photon flux density (PPFD) under diverse ambient CO2 concentrations (C(a)). Our model reproduces the observed changes in isoprene emissions with C(i) and PPFD, and also reproduces the tendency for the fraction of fixed carbon allocated to isoprene to increase with increasing PPFD. It also provides a simple mechanism for the previously unexplained decrease in the quantum efficiency of isoprene emission with increasing C(a). Experimental and modelled results support our hypothesis. Our model can reproduce the key features of the observations and has the potential to improve process-based modelling of isoprene emissions by land vegetation at the ecosystem and global scales.

A novel stress-induced sugarcane gene confers tolerance to drought, salt and oxidative stress in transgenic tobacco plants.

BackgroundDrought is a major abiotic stress that affects crop productivity worldwide. Sugarcane can withstand periods of water scarcity during the final stage of culm maturation, during which sucrose accumulation occurs. Meanwhile, prolonged periods of drought can cause severe plant losses.Methodology/Principal FindingsIn a previous study, we evaluated the transcriptome of drought-stressed plants to better understand sugarcane responses to drought. Among the up-regulated genes was Scdr1 (sugarcane drought-responsive 1). The aim of the research reported here was to characterize this gene. Scdr1 encodes a putative protein containing 248 amino acids with a large number of proline (19%) and cysteine (13%) residues. Phylogenetic analysis showed that ScDR1is in a clade with homologs from other monocotyledonous plants, separate from those of dicotyledonous plants. The expression of Scdr1 in different varieties of sugarcane plants has not shown a clear association with drought tolerance.Conclusions/SignificanceThe overexpression of Scdr1 in transgenic tobacco plants increased their tolerance to drought, salinity and oxidative stress, as demonstrated by increased photosynthesis, water content, biomass, germination rate, chlorophyll content and reduced accumulation of ROS. Physiological parameters, such as transpiration rate (E), net photosynthesis (A), stomatal conductance (gs) and internal leaf CO2 concentration, were less affected by abiotic stresses in transgenic Scdr1 plants compared with wild-type plants. Overall, our results indicated that Scdr1 conferred tolerance to multiple abiotic stresses, highlighting the potential of this gene for biotechnological applications.