Amaia Mena-Petite

The oxidative stress caused by salinity in two barley cultivars is mitigated by elevated CO2.

Changes in antioxidant metabolism because of the effect of salinity stress (0, 80, 160 or 240 mM NaCl) on protective enzyme activities under ambient (350 micromol mol(-1)) and elevated (700 micromol mol(-1)) CO(2) concentrations were investigated in two barley cultivars (Hordeum vulgare L., cvs Alpha and Iranis). Electrolyte leakage, peroxidation, antioxidant enzyme activities [superoxide dismutase (SOD), EC 1.15.1.1; ascorbate peroxidase (APX), EC 1.11.1.11; catalase (CAT), EC 1.11.1.6; dehydroascorbate reductase (DHAR), EC 1.8.5.1; monodehydroascorbate reductase (MDHAR), EC 1.6.5.4; glutathione reductase (GR), EC 1.6.4.2] and their isoenzymatic profiles were determined. Under salinity and ambient CO(2), upregulation of antioxidant enzymes such as SOD, APX, CAT, DHAR and GR occurred. However, this upregulation was not enough to counteract all ROS formation as both ion leakage and lipid peroxidation came into play. The higher constitutive SOD and CAT activities together with a higher contribution of Cu,Zn-SOD 1 detected in Iranis might possibly contribute and make this cultivar more salt-tolerant than Alpha. Elevated CO(2) alone had no effect on the constitutive levels of antioxidant enzymes in Iranis, whereas in Alpha it induced an increase in SOD, CAT and MDHAR together with a decrease of DHAR and GR. Under combined conditions of elevated CO(2) and salinity the oxidative damage recorded was lower, above all in Alpha, together with a lower upregulation of the antioxidant system. So it can be concluded that elevated CO(2) mitigates the oxidative stress caused by salinity, involving lower ROS generation and a better maintenance of redox homeostasis as a consequence of higher assimilation rates and lower photorespiration, being the response dependent on the cultivar analysed.

Lipoic acid and redox status in barley plants subjected to salinity and elevated CO2

Future environmental conditions will include elevated concentrations of salt in the soil and an elevated concentration of CO(2) in the atmosphere. Because these environmental changes will likely affect reactive oxygen species (ROS) formation and cellular antioxidant metabolism in opposite ways, we analyzed changes in cellular H(2)O(2) and non-enzymatic antioxidant metabolite [lipoic acid (LA), ascorbate (ASA), glutathione (GSH)] content induced by salt stress (0, 80, 160 or 240 mM NaCl) under ambient (350 micromol mol(-1)) or elevated (700 micromol mol(-1)) CO(2) concentrations in two barley cultivars (Hordeum vulgare L.) that differ in sensitivity to salinity (cv. Alpha is more sensitive than cv. Iranis). Under non-salinized conditions, elevated CO(2) increased LA content, while ASA and GSH content decreased. Under salinized conditions and ambient CO(2), ASA increased, while GSH and LA decreased. At 240 mM NaCl, H(2)O(2) increased in Alpha and decreased in Iranis. When salt stress was imposed at elevated CO(2), less oxidative stress and lower increases in ASA were detected, while LA was constitutively higher. The decrease in oxidative stress could have been because of less ROS formation or to a higher constitutive LA level, which might have improved regulation of ASA and GSH reductions. Iranis had a greater capacity to synthesize ASA de novo and had higher constitutive LA content than did Alpha. Therefore, we conclude that elevated CO(2) protects barley cultivars against oxidative damage. However, the magnitude of the positive effect is cultivar specific.

Atmospheric CO2 concentration influences the contributions of osmolyte accumulation and cell wall elasticity to salt tolerance in barley cultivars.

Future environmental conditions will include elevated concentrations of salt in the soils and elevated concentrations of CO(2) in the atmosphere. Soil salinization inhibits crop growth due to osmotic and ionic stress. However, plants possess salt tolerance mechanisms, such as osmotic and elastic adjustment, to maintain water status. These mechanisms, which enhance the uptake and accumulation of ions and the synthesis of compatible solutes, require substantial energy expenditure. Under elevated CO(2), the carbon and energy supplies are usually higher, which could facilitate the energetically expensive salt tolerance mechanisms. To test this hypothesis, the factors involved in osmotic and elastic adjustments in two barley cultivars (Hordeum vulgare cv. Alpha and cv. Iranis) grown under several salt concentrations and at ambient or elevated [CO(2)] were evaluated. Under ambient [CO(2)] and salt stress, both cultivars (1) decreased the volumetric elasticity modulus (epsilon) of their cell walls, and (2) adjusted osmotically by accumulating ions (Na(+) and Cl(-)) from the soil, confirming barley as an includer species. The contributions of sugars and other unidentified osmolytes also increased, while the contribution of organic acids decreased. Under elevated [CO(2)] and salt stress, epsilon decreased less and osmotic adjustment (OA) was greater than at ambient [CO(2)]. In fact, the greater OA under elevated [CO(2)] was positively correlated with the contributions of sugars and other unidentified compounds. These results indicate that barley is likely to be successful in more salinized soils due to its capacity for OA under elevated [CO(2)].

Influence of water stress on photosynthetic characteristics in barley plants under ambient and elevated CO2 concentrations

We evaluated the combined effects of elevated CO2 and water availability on photosynthesis in barley. Soil and plant water content decreased with water stress, but less under elevated CO2 concentration (EC) compared with ambient CO2 concentration (AC). During water stress, stomatal conductance, carboxylation rate, RuBP regeneration, and the rate of triose phosphate utilisation (TPU) were decreased but less when plants grew under EC. Drought treatments caused only a slight effect on maximum photochemical efficiency (variable to maximum fluorescence ratio, Fv/Fm), whereas the actual quantum yield (ΦPS2), maximum electron transport rate (Jmax) and photochemical quenching (qP) were decreased and the non photochemical quenching (NPQ) was enhanced. Under water deficit, the allocation of electrons to CO2 assimilation was diminished by 49 % at AC and by 26 % at EC while the allocation to O2 reduction was increased by 15 % at AC and by 12 % at EC.

Lettuce production and antioxidant capacity are differentially modified by salt stress and light intensity under ambient and elevated CO2.

As a consequence of the increasing importance of vegetables in the human diet, there is an interest in enhancing both the productivity and quality of vegetables. A number of factors, including plant genotype and environmental growing conditions, can impact the production and quality of vegetables. The objective of this study was to determine whether elevated CO2, salinity, or high light treatments assayed individually, or salinity or high light in combination with elevated CO2, increased biomass production and antioxidant capacity in two lettuce cultivars. Elevated CO2 and its combination with salinity or high light increased biomass production in both cultivars, while high light treatment alone increased production in green-leaf lettuce but not in red-leaf lettuce. On the other hand, elevated CO2 and its combination with salinity or high light increased the antioxidant capacity of both cultivars, while high light treatment alone increased the antioxidant capacity of red-leaf lettuce, but not of green-leaf lettuce.

Sequential effects of acidic precipitation and drought on photosynthesis and chlorophyll fluorescence parameters of Pinus radiata D. Don seedlings

Summary We studied the sequential effect of simulated acid rain (SAR) and water stress on net photosynthesis (A), internal CO 2 concentration ( Ci ), stomatal conductance (g), and instantaneous water use efficiency (A/E), and the photochemical damage caused by these stressors by analysing chlorophyll fluorescence parameters such as Fv/Fm, Fv/Fo and Fm/Fo. SAR caused inhibition of photosynthesis. The depletion of CO 2 assimilation seems not to be solely a stomatal effect as effects on chloroplasts contribute to this photosynthetic inhibition. No noticeable damage seems to occur to the photochemical apparatus since well-watered plants treated with acid rain did not show any change in the chlorophyll fluorescence. Water stress produced a large effect on both gas exchange and chlorophyll fluorescence parameters, indicating structural and functional damage. Interactions among SAR and drought had a larger impact on all parameters studied. However, after rewatering, significant recovery in both gas exchange and chlorophyll fluorescence parameters occurred within 6 days, although the values measured prior to the imposition of treatments were not recovered. We conclude that Pinus radiata exposed to acid rain were affected in a wide range of components in the photosynthetic apparatus, thereby modifying its response to sequential drought stress.

Sequential Effects of Acidic Precipitation and Drought on Water Relations of Pinus radiata Seedlings

Summary In this work we investigated the sequential effects of simulated acid rain and drought on water relations of radiata pine ( Pinus radiata D. Don) seedlings. Whole seedlings were firstly subjected during 1 month to acid rain, pH 3.0, applied 5 times a week at 3 mm precipitation equivalent per day. Afterwards, drought treatment was applied by withholding water for 20 days and subsequent rewatering for 6 days to analyze the sequential effect of acid precipitation and drought. Water status parameters were determined before the initiation of acid rain treatment and within 3 weeks after the end of treatment. Acid rain treatment in well-watered plants did not affect either water potential or relative water content, whereas a marked effect on electrolyte leakage from the needles and on instantaneous transpiration was recorded. Drought treatment had great effects on leaf water potential (-2.5 MPa), RWC (50 % diminution), membrane permeability (340 % increase) and transpiration rate (25 % inhibition). Interactions involving acid precipitation and drought led to much greater impacts on all of the parameters analyzed. We conclude that although acid rain had slight, if any, direct effects on the water relations of well-watered radiata pine, it altered the drought tolerance of this tree species. Under conditions of soil-water deficit, plants exposed previously to acid rain are more sensitive to drought and desiccation.

The type of competition modulates the ecophysiological response of grassland species to elevated CO2 and drought

The effects of elevated CO2 and drought on ecophysiological parameters in grassland species have been examined, but few studies have investigated the effect of competition on those parameters under climate change conditions. The objective of this study was to determine the effect of elevated CO2 and drought on the response of plant water relations, gas exchange, chlorophyll a fluorescence and aboveground biomass in four grassland species, as well as to assess whether the type of competition modulates that response. Elevated CO2 in well-watered conditions increased aboveground biomass by augmenting CO2 assimilation. Drought reduced biomass by reducing CO2 assimilation rate via stomatal limitation and, when drought was more severe, also non-stomatal limitation. When plants were grown under the combined conditions of elevated CO2 and drought, drought limitation observed under ambient CO2 was reduced, permitting higher CO2 assimilation and consequently reducing the observed decrease in aboveground biomass. The response to climate change was species-specific and dependent on the type of competition. Thus, the response to elevated CO2 in well-watered grasses was higher in monoculture than in mixture, while it was higher in mixture compared to monoculture for forbs. On the other hand, forbs were more affected than grasses by drought in monoculture, while in mixture the negative effect of drought was higher in grasses than in forbs, due to a lower capacity to acquire water and mineral nutrients. These differences in species-level growth responses to CO2 and drought may lead to changes in the composition and biodiversity of the grassland plant community in future climate conditions.

Glutamine synthetase from mesophyll and bundle sheath maize cells: isoenzyme complements and different sensitivities to phosphinothricin.

Abstract Anion-exchange FPLC has been used to resolve the isoforms of glutamine synthetase (GS, EC 6.3.1.2) from Zea mays mesophyll (MC) and bundle sheath cells (BSC). Two different isoforms were detected in both types of photosynthetic cells. The predominantly active isoform was GS1 (61%) in MC and GS2 (67%) in BSC. The relative contribution of GS1 and GS2 to the overall GS activity in BSC in maize here reported resembles the proportion described for most C3 plants. Differences among these isoforms in terms of their susceptibility to phosphinothricin (PPT), an analogue of glutamate and known inhibitor of GS, were found. The GS1 isoenzyme from MC was the most sensitive form, being inhibited by 50% at approximately 2.0 μM DL-PPT, whereas the GS2 from BSC presented the highest tolerance to the inhibitor (I50=30 μM). The transferase-to-semibiosynthetic activity ratio for the MC isoforms, which was higher than the ratio for the BSC isoforms, and the differences shown by the isoforms in susceptibility to PPT predict important differences in the biochemical properties and regulation of GS isoenzymes. In this regard, the cytoplasmic isoenzymes, and especially the one in MC, due to its relatively high contribution to mesophyll cell GS activity, could play a vital role in nitrogen metabolism in maize.

Does Elevated CO2 Mitigate the Salt Effect on Photosynthesis in Barley Cultivars

The Lower Decreases Of Pigment Content And Assimilation Rates And The Higher Rates Of Instantaneous Water Use Efficiency Observed In Plants Grown Under Salinity And Elevated Co2 Would Indicate A Better Photosynthetic CapaCity Than Their Counterparts At Ambient Co2.