Growth and physiological responses of sunflower plants exposed to ultraviolet-B radiation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Análise de crescimento e trocas gasosas de erva-cidreira (Lippia alba (Mill.) N.E.Br. ex Britt & Wilson) cultivada em solução nutritiva

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Propagação e desenvolvimento inicial defícus adhatodifolia Schott ex Spreng. (Moraceae) em diferentes temperaturas, intensidades luminosas e substratos

Pós-graduação em Agronomia (Horticultura) - FCA

Mentha piperita cultivada com variação de cálcio. Trocas gasosas e óleo essencial

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Nitric oxide reduces oxidative damage induced by water stress in sunflower plants

Drought is one of the main environmental constraints that can reduce plant yield. Nitric oxide (NO) is a signal molecule involved in plant responses to several environmental stresses. The objective of this study was to investigate the cytoprotective effect of a single foliar application of 0, 1, 10 or 100 µM of the NO donor sodium nitroprusside (SNP) in sunflower plants under water stress. Water stressed plants treated with 1μM SNP showed an increase in the relative water content compared with 0 μM SNP. Drought reduced the shoot dry weight but SNP applications did not result in alleviation of drought effects. Neither drought nor water stress plus SNP applications altered the content of photosynthetic pigments. Stomatal conductance was reduced by drought and this reduction was accompanied by a significant reduction in intercellular CO2 concentration and photosynthesis. Treatment with SNP did not reverse the effect of drought on the gas exchange characteristics. Drought increased the level of malondialdehyde (MDA) and proline and reduced pirogalol peroxidase (PG-POD) activity, but did not affect the activity of superoxide dismutase (SOD). When the water stressed plants were treated with 10 μM SNP, the activity of PG-POD and the content of proline were increased and the level of MDA was decreased. The results show that the adverse effects of water stress on sunflower plants are dependent on the external NO concentration. The action of NO may be explained by its ability to increase the levels of antioxidant compounds and the activity of ROS-scavenging enzymes.

Cotton leaf gas exchange responses to irradiance and leaf aging

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Sensitivity of yellow passion fruit plants to ultraviolet-B radiation

The objective of this work was to evaluate the effects of UV-B radiation on the vegetative growth and on the gas exchange characteristics of passion fruit plants (Passiflora edulis) grown in greenhouse. The average unweighted UV-B radiation near the apex of the plants was 8 W m-2 for the UV-B treatment (high UV-B), and 0.8 W m-2 for the control plants (low UV-B). Plants were irradiated with UV-B for 7 hours per day, centered on solar noon, during 16 days. High UV-B radiation resulted in lower shoot dry matter accumulation per plant. The content of UV-B absorbing compounds and anthocyanins was increased in the plants exposed to high UV-B radiation, when compared with the control. UV-B radiation did not affect stomatal conductance or transpiration rate, but reduced photosynthesis and instantaneous water‑use efficiency, and increased intercellular CO2 concentration. The accumulation of UV-B-absorbing compounds and anthocyanins did not effectively shield plants from supplementary UV-B radiation, since the growth and photosynthetic processes were significantly reduced.

Growth at moderately elevated temperature alters the physiological response of the photosynthetic apparatus to heat stress in pea (Pisum sativum L.) leaves

The impact of heat stress on the functioning of the photosynthetic apparatus was examined in pea (Pisum sativum L.) plants grown at control (25 °C; 25 °C-plants) or moderately elevated temperature (35 °C; 35 °C-plants). In both types of plants net photosynthesis (Pn) decreased with increasing leaf temperature (LT) and was more than 80% reduced at 45 °C as compared to 25 °C. In the 25 °C-plants, LTs higher than 40 °C could result in a complete suppression of Pn. Short-term acclimation to heat stress did not alter the temperature response of Pn. Chlorophyll a fluorescence measurements revealed that photosynthetic electron transport (PET) started to decrease when LT increased above 35 °C and that growth at 35 °C improved the thermal stability of the thylakoid membranes. In the 25 °C-plants, but not in the 35 °C-plants, the maximum quantum yield of the photosystem II primary photochemistry, as judged by measuring the Fv/Fm ratio, decreased significantly at LTs higher than 38 °C. A post-illumination heat-induced reduction of the plastoquinone pool was observed in the 25 °C-plants, but not in the 35 °C-plants. Inhibition of Pn by heat stress correlated with a reduction of the activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Western-blot analysis of Rubisco activase showed that heat stress resulted in a redistribution of activase polypeptides from the soluble to the insoluble fraction of extracts. Heat-dependent inhibition of Pn and PET could be reduced by increasing the intercellular CO2 concentration, but much more effectively so in the 35 °C-plants than in the 25 °C-plants. The 35 °C-plants recovered more efficiently from heat-dependent inhibition of Pn than the 25 °C-plants. The results show that growth at moderately high temperature hardly diminished inhibition of Pn by heat stress that originated from a reversible heat-dependent reduction of the Rubisco activation state. However, by improving the thermal stability of the thylakoid membranes it allowed the photosynthetic apparatus to preserve its functional potential at high LTs, thus minimizing the after-effects of heat stress.

Inhibition of photosynthesis by high temperature in oak (Quercus pubescens L.) leaves grown under natural conditions closely correlates with a reversible heat-dependent reduction of the activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase

Inhibition of the net photosynthetic CO2 assimilation rate (Pn) by high temperature was examined in oak (Quercus pubescens L.) leaves grown under natural conditions. Combined measurements of gas exchange and chlorophyll (Chl) a fluorescence were employed to differentiate between inhibition originating from heat effects on components of the thylakoid membranes and that resulting from effects on photosynthetic carbon metabolism. Regardless of whether temperature was increased rapidly or gradually, Pn decreased with increasing leaf temperature and was more than 90% reduced at 45 °C as compared to 25 °C. Inhibition of Pn by heat stress did not result from reduced stomatal conductance (gs), as heat-induced reduction of gs was accompanied by an increase of the intercellular CO2 concentration (Ci). Chl a fluorescence measurements revealed that between 25 and 45 °C heat-dependent alterations of thylakoid-associated processes contributed only marginally, if at all, to the inhibition of Pn by heat stress, with photosystem II being remarkably well protected against thermal inactivation. The activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) decreased from about 90% at 25 °C to less than 30% at 45 °C. Heat stress did not affect Rubisco per se, since full activity could be restored by incubation with CO2 and Mg2+. Western-blot analysis of leaf extracts disclosed the presence of two Rubisco activase polypeptides, but heat stress did not alter the profile of the activase bands. Inhibition of Pn at high leaf temperature could be markedly reduced by artificially increasing Ci. A high Ci also stimulated photosynthetic electron transport and resulted in reduced non-photochemical fluorescence quenching. Recovery experiments showed that heat-dependent inhibition of Pn was largely, if not fully, reversible. The present results demonstrate that in Q. pubescens leaves the thylakoid membranes in general and photosynthetic electron transport in particular were well protected against heat-induced perturbations and that inhibition of Pn by high temperature closely correlated with a reversible heat-dependent reduction of the Rubisco activation state.

Leaf Gas Exchange and Nutrient Use Efficiency Help Explain the Distribution of Two Neotropical Mangroves under Contrasting Flooding and Salinity

Rhizophora mangle and Laguncularia racemosa cooccur along many intertidal floodplains in the Neotropics. Their patterns of dominance shift along various gradients, coincident with salinity, soil fertility, and tidal flooding. We used leaf gas exchange metrics to investigate the strategies of these two species in mixed culture to simulate competition under different salinity concentrations and hydroperiods. Semidiurnal tidal and permanent flooding hydroperiods at two constant salinity regimes (10 g L−1 and 40 g L−1) were simulated over 10 months. Assimilation ( ), stomatal conductance ( ), intercellular CO2 concentration ( ), instantaneous photosynthetic water use efficiency (PWUE), and photosynthetic nitrogen use efficiency (PNUE) were determined at the leaf level for both species over two time periods. Rhizophora mangle had significantly higher PWUE than did L. racemosa seedlings at low salinities; however, L. racemosa had higher PNUE and and, accordingly, had greater intercellular CO2 (calculated) during measurements. Both species maintained similar capacities for A at 10 and 40 g L−1 salinity and during both permanent and tidal hydroperiod treatments. Hydroperiod alone had no detectable effect on leaf gas exchange. However, PWUE increased and PNUE decreased for both species at 40 g L−1 salinity compared to 10 g L−1. At 40 g L−1 salinity, PNUE was higher for L. racemosa than R. mangle with tidal flooding. These treatments indicated that salinity influences gas exchange efficiency, might affect how gases are apportioned intercellularly, and accentuates different strategies for distributing leaf nitrogen to photosynthesis for these two species while growing competitively.

Alterações fisiológicas causadas por fungicidas em soja infectada naturalmente por oídio

Soybean crop is substantially important for both Brazilian and international markets. A relevant disease that affects soybeans is powdery mildew, caused by fungus Erysiphe diffusa. The objective of this master’s thesis was to analyze physiological changes produced by fungicides in two greenhouse-grown soybean genotypes (i.e., Anta 8500 RR and BRS Santa Cruz RR) naturally infected with powdery mildew. A complete randomized block design was used with six replications in a 2x5 factorial arrangement. Treatments consisted of applications of Azoxystrobin, Biofac (fermented solution of Penicillium sp.), Carbendazim or Picoxystrobin fungicides, and a Control (no fungicide application). Three applications were performed in the experimental period, and each eventually represented a period of data collection. Gas exchanges, chlorophyll content, fluorescence of chlorophyll a and disease severity were measured twice a week. Dry grain mass production was measured at the end of the experiment. Areas under progression curve of variables were submitted to both ANOVA and Tukey’s test at 5% significance. Treatments Azoxystrobin, Biofac and Picoxystrobin had higher photosynthetic rates than Control in the second period, with genotype Anta having higher rate than Santa Cruz. Biofac had higher transpiration rate than Control in the second period, while Biofac and Picoxystrobin had higher figures in Santa Cruz in the third period. Carbendazim had greater stomatal conductance in Anta, whilst Azoxystrobin, Biofac and Picoxystrobin had greater values than Carbendazim in Santa Cruz. Biofac and Picoxystrobin had greater intercellular CO2 concentration in Santa Cruz. Azoxystrobin and Picoxystrobin had greater instantaneous water use efficiency than Control, with Anta being more efficient than Santa Cruz. Biofac and Picoxystrobin had greater intrinsic water use efficiency in Anta, while Carbendazim increased efficiency in Santa Cruz. Azoxystrobin, Biofac and Picoxystrobin had greater carboxylation efficiency than Control in the second period, with Anta being more efficient than Santa Cruz. Azoxystrobin and Biofac had greater contents of chlorophylls a, b and a+b than Control in the second period. Azoxystrobin had greater effective quantum yield than Control and Picoxystrobin. All treatments faced increasing disease severity over time, with Anta being less resistant than Santa Cruz. As for production, data showed that: (1) Santa Cruz was more productive than Anta, having the greatest dry grain mass with Carbendazim, and (2) Anta’s lower disease severity did not translate into higher productions. In conclusion, strobilurins (Azoxystrobin and Picoxystrobin) and Biofac performed similarly as to their physiological effects on soybeans; however, these effects did not lead to increased dry grain mass by the end of the experiment.

Acclimation of photosynthesis to elevated CO2 in onion (Allium cepa) grown at a range of temperatures

Onion (Allium cepa) was grown in the field within temperature gradient tunnels (providing about -2.5degreesC to +2.5degreesC from outside temperatures) maintained at either 374 or 532 mumol mol(-1) CO2. Plant leaf area was determined non-destructively at 7 day intervals until the time of bulbing in 12 combinations of temperature and CO2 concentration. Gas exchange was measured in each plot at the time of bulbing, and the carbohydrate content of the leaf (source) and bulb (sink) was determined. Maximum rate of leaf area expansion increased with mean temperature. Leaf area duration and maximum rate of leaf area expansion were not significantly affected by CO2. The light-saturated rates of leaf photosynthesis (A(sat)) were greater in plants grown at normal than at elevated CO2 concentrations at the same measurement CO2 concentration. Acclimation of photosynthesis decreased with an increase in growth temperature, and with an increase in leaf nitrogen content at elevated CO2. The ratio of intercellular to atmospheric CO2 (C-i/C-a ratio) was 7.4% less for plants grown at elevated compared with normal CO2. A(sat) in plants grown at elevated CO2 was less than in plants grown at normal CO2 when compared at the same C-i Hence, acclimation of photosynthesis was due both to stomatal acclimation and to limitations to biochemical CO2 fixation. Carbohydrate content of the onion bulbs was greater at elevated than at normal CO2. In contrast, carbohydrate content was less at elevated compared with normal CO2 in the leaf sections in which CO2 exchange was measured at the same developmental stage. Therefore, acclimation of photosynthesis in fully expanded onion leaves was detected despite the absence of localised carbohydrate accumulation in these field-grown crops.

Acclimation of photosynthesis to elevated CO2 in onion (allium cepa) grown at a range of temperatures

Onion (Allium cepa) was grown in the field within temperature gradient tunnels (providing about -2.5 degrees C to +2.5 degrees C from outside temperatures) maintained at either 374 or 532 mumol mol (-1) CO2. Plant leaf area was determined non-destructively at 7 day intervals until the time of bulbing in 12 combinations of temperature and CO2 concentration. Gas exchange was measured in each plot at the time of bulbing, and the carbohydrate content of the leaf (source) and bulb (sink) was determined. Maximum rate of leaf area expansion increased with mean temperature. Leaf area duration and maximum rate of leaf area expansion were not significantly affected by CO2. The light-saturated rates of leaf photosynthesis (A(sat)) were greater in plants grown at normal than at elevated CO2 concentrations at the same measurement CO2 concentration. Acclimation of photosynthesis decreased with an increase in growth temperature, and with an increase in leaf nitrogen content at elevated CO2. The ratio of intercellular to atmospheric CO2 (C-i/C-a ratio) was 7.4% less for plants grown at elevated compared with normal CO2. A(sat) in plants grown at elevated CO2 was less than in plants grown at normal CO2 when compared at the same C-i Hence, acclimation of photosynthesis was due both to stomatal acclimation and to limitations to biochemical CO2 fixation. Carbohydrate content of the onion bulbs was greater at elevated than at normal CO2. In contrast, carbohydrate content was less at elevated compared with normal CO2 in the leaf sections in which CO2 exchange was measured at the same developmental stage. Therefore, acclimation of photosynthesis in fully expanded onion leaves was detected despite the absence of localised carbohydrate accumulation in these field-grown crops.

Overexpression of Iron Superoxide Dismutase in Transformed Poplar Modifies the Regulation of Photosynthesis at Low CO2 Partial Pressures or Following Exposure to the Prooxidant Herbicide Methyl Viologen1

Chloroplast-targeted overexpression of an Fe superoxide dismutase (SOD) from Arabidopsis thaliana resulted in substantially increased foliar SOD activities. Ascorbate peroxidase, glutathione reductase, and monodehydroascorbate reductase activities were similar in the leaves from all of the lines, but dehydroascorbate reductase activity was increased in the leaves of the FeSOD transformants relative to untransformed controls. Foliar H2O2, ascorbate, and glutathione contents were comparable in all lines of plants. Irradiance-dependent changes in net CO2 assimilation and chlorophyll a fluorescence quenching parameters were similar in all lines both in air (21% O2) and at low (1%) O2. CO2-response curves for photosynthesis showed similar net CO2-exchange characteristics in all lines. In contrast, values of photochemical quenching declined in leaves from untransformed controls at intercellular CO2 (Ci) values below 200 μL L−1 but remained constant with decreasing Ci in leaves of FeSOD transformants. When the O2 concentration was decreased from 21 to 1%, the effect of FeSOD overexpression on photochemical quenching at limiting Ci was abolished. At high light (1000 μmol m−2 s−1) a progressive decrease in the ratio of variable (Fv) to maximal (Fm) fluorescence was observed with decreasing temperature. At 6oC the high-light-induced decrease in the Fv/Fm ratio was partially prevented by low O2 but values were comparable in all lines. Methyl viologen caused decreased Fv/Fm ratios, but this was less marked in the FeSOD transformants than in the untransformed controls. These observations suggest that the rate of superoxide dismutation limits flux through the Mehler-peroxidase cycle in certain conditions.

Low coral cover in a high-CO2 world

Coral reefs generally exist within a relatively narrow band of temperatures, light, and seawater aragonite saturation states. The growth of coral reefs is minimal or nonexistent outside this envelope. Climate change, through its effect on ocean temperature, has already had an impact on the world's coral reefs, with almost 30% of corals having disappeared since the beginning of the 1980s. Abnormally warm temperatures cause corals to bleach ( lose their brown dinoflagellate symbionts) and, if elevated for long enough, to die. Increasing atmospheric CO2 is also potentially affecting coral reefs by lowering the aragonite saturation state of seawater, making carbonate ions less available for calcification. The synergistic interaction of elevated temperature and CO2 is likely to produce major changes to coral reefs over the next few decades and centuries. Known tolerances of corals to projected changes to sea temperatures indicate that corals are unlikely to remain abundant on reefs and could be rare by the middle of this century if the atmospheric CO2 concentration doubles or triples. The combination of changes to sea temperature and carbonate ion availability could trigger large- scale changes in the biodiversity and function of coral reefs. The ramifications of these changes for the hundred of millions of coral reef - dependent people and industries living in a high- CO2 world have yet to be properly defined. The weight of evidence suggests, however, that projected changes will cause major shifts in the prospects for industries and societies that depend on having healthy coral reefs along their coastlines.