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Photochemical Efficiency (photochemical + efficiency)
Kinds of Photochemical Efficiency Selected AbstractsSex-specific physiological, allocation and growth responses to water availability in the subdioecious plant Honckenya peploidesPLANT BIOLOGY, Issue 2 2009J. Sánchez-Vilas Abstract The gender of dimorphic plant species is often affected by ecophysiological variables. Differences have been interpreted as a response of the sexes to meet specific resource demands associated with reproduction. This study investigated whether sex-specific variations in ecophysiological traits in response to water availability determine the performance of each sex in different habitats, and therefore promote extreme spatial segregation of the sexes in the subdioecious plant, Honckenya peploides. Twenty-seven plants of each sex were individually potted in dune sand and assigned randomly to one of three water treatments. Well-watered plants were watered daily to field capacity, whereas plants in the moderate and high-water stress treatments received 40% and 20%, respectively, of the water given to well-watered plants. Photochemical efficiency, leaf spectral properties and components of relative growth rate (leaf area ratio and net assimilation rate) were measured. Photochemical efficiencies integrated over time were higher in male than in female plants. Water deficit decreased maximum quantum yield in female plants more rapidly than in male plants, but female plants (unlike male plants) had recovered to initial values by the end of the experiment. Maximum quantum yield in male plants was more affected by water stress than in female plants, indicating that male plants were more susceptible to photoinhibition. The two sexes did not differ in growth rate, but male plants invested a higher proportion of their biomass in leaves, had a higher leaf area per unit biomass and lower net assimilation rate relative to female plants. Female plants had a higher water content and succulence than male plants. Differences in stomatal density between the sexes depended on water availability. The results suggest that the two sexes of H. peploides have different strategies for coping with water stress. The study also provides evidence of sex differences in allocation traits. We conclude that between-sex differences in ecophysiological and allocation traits may contribute to explain habitat-related between-sex differences in performance and, therefore, the spatial segregation of the sexes. [source] Physiological and biochemical analyses of microcystin-RR toxicity to the cyanobacterium Synechococcus elongatusENVIRONMENTAL TOXICOLOGY, Issue 6 2004Zhi-quan Hu Abstract Freshwater Microcystis may form dense blooms in eutrophic lakes. It is known to produce a family of related cyclic hepatopeptides (microcystins, MC) that constitute a threat to aquatic ecosystems. Most toxicological studies of microcystins have focused on aquatic animals and plants, with few examining the possible effects of microcystins on phytoplankton. In this study we chose the unicellular Synechococcus elongatus (one of the most studied and geographically most widely distributed cyanobacteria in the picoplankton) as the test material and investigated the biological parameters: growth, pigment (chlorophyll-a, phycocyanin), photosynthetic activity, nitrate reductase activity, and protein and carbohydrate content. The results revealed that microcystin-RR concentrations above 100 ,g · L,1 significantly inhibited the growth of Synechococcus elongatus. In addition, a change in color of the toxin-treated algae (chlorosis) was observed in the experiments. Furthermore, MC-RR markedly inhibited the synthesis of the pigments chlorophyll-a and phycocyanin. A drastic reduction in photochemical efficiency of PSII (Fv/Fm) was found after a 96-h incubation. Changes in protein and carbohydrate concentrations and in nitrate reductase activity also were observed during the exposure period. This study aimed to evaluate the mechanisms of microcystin toxicity on a cyanobacterium, according to the physiological and biochemical responses of Synechococcus elongatus to different doses of microcystin-RR. The ecological role of microcystins as an allelopathic substance also is discussed in the article. © 2004 Wiley Periodicals, Inc. Environ Toxicol 19: 571,577, 2004. [source] Species richness and susceptibility to heat and drought extremes in synthesized grassland ecosystems: compositional vs physiological effectsFUNCTIONAL ECOLOGY, Issue 6 2004L. VAN PEER Summary 1We investigated effects of declining plant species richness (S) on resistance to extremes in grassland communities. 2Synthesized model ecosystems of different S, grown outdoors in containers, were exposed to a stress peak combining heat and drought. The heat wave was induced experimentally by infrared irradiation in free air conditions. 3Before the heat wave, the more species-rich communities produced more biomass as a result of a large and positive complementarity effect that outweighed a small negative selection effect. 4Water use during the heat wave was likewise enhanced by S, which could not be attributed to dominance of ,water-wasting' species. Instead, water consumption at high S exceeded that expected from changes in community biomass and biomass composition. The observed enhancement of resource (water) acquisition under stress with increasing S therefore probably originated from complementarity. 5Despite enhanced water use in the more diverse communities, plant survival was significantly less, affecting all species alike. Physiological stress, recorded as photochemical efficiency of photosystem II electron transport, was significantly greater. Before the heat wave, the changes in biomass composition that coincided with increasing S did not favour species that would later prove intrinsically sensitive or insensitive. 6Complementarity in resource use for biomass production had a cost in terms of reduced survival under stress, despite the likelihood of complementarity in water acquisition during exposure. The greater loss of individuals from the more diverse grasslands suggests enhanced risk of local extinction. [source] Performance of High Arctic tundra plants improved during but deteriorated after exposure to a simulated extreme temperature eventGLOBAL CHANGE BIOLOGY, Issue 12 2005Fleur L. Marchand Abstract Arctic ecosystems are known to be extremely vulnerable to climate change. As the Intergovernmental Panel on Climate Change scenarios project extreme climate events to increase in frequency and severity, we exposed High Arctic tundra plots during 8 days in summer to a temperature rise of approximately 9°C, induced by infrared irradiation, followed by a recovery period. Increased plant growth rates during the heat wave, increased green cover at the end of the heat wave and higher chlorophyll concentrations of all four predominating species (Salix arctica Pall., Arctagrostis latifolia Griseb., Carex bigelowii Torr. ex Schwein and Polygonum viviparum L.) after the recovery period, indicated stimulation of vegetative growth. Improved plant performance during the heat wave was confirmed at plant level by higher leaf photochemical efficiency (Fv/Fm) and at ecosystem level by increased gross canopy photosynthesis. However, in the aftermath of the temperature extreme, the heated plants were more stressed than the unheated plants, probably because they acclimated to warmer conditions and experienced the return to (low) ambient as stressful. We also calculated the impact of the heat wave on the carbon balance of this tundra ecosystem. Below- and aboveground respiration were stimulated by the instantaneous warmer soil and canopy, respectively, outweighing the increased gross photosynthesis. As a result, during the heat wave, the heated plots were a smaller sink compared with their unheated counterparts, whereas afterwards the balance was not affected. If other High Arctic tundra ecosystems react similarly, more frequent extreme temperature events in a future climate may shift this biome towards a source. It is uncertain, however, whether these short-term effects will hold when C exchange rates acclimate to higher average temperatures. [source] Different Patterns of Physiological and Molecular Response to Drought in Seedlings of Malt- and Feed-type Barleys (Hordeum vulgare)JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2010M. Rapacz Abstract A number of physiological and molecular characteristics are proposed as selection criteria for drought tolerance. This study measured the associations between physiological and molecular characteristics of drought response in malting and fodder spring barleys. Plants of 13 malt- and 14 feed-type Polish genotypes were exposed to drought at the four-leaf stage for 7 days. Drought susceptibility indexes (DSI) were calculated for membrane integrity, water status, gas exchange and PSII photochemical activity. Accumulation of HVA1 and SRG6 transcripts in drought was measured with real-time PCR. A wide range of variation in the drought response was observed among studied genotypes. Malting barleys were less sensitive to drought than feed-barleys according to all the traits studied. In both groups, different patterns of relationships between traits were observed. In malting genotypes only, CO2 assimilation rates in drought, as well as PSII efficiency were related to both water content and the accumulation of HVA1 transcript in leaves. On the other hand the SRG6 expression was highly correlated in both groups of barley with the photochemical efficiency of PSII. The results suggest that different physiological, biochemical and molecular characteristics should be applied in the selection towards drought resistance in the case of malting and fodder barleys. [source] Xanthophyll Cycle and Inactivation of Photosystem II Reaction Centers Alleviating Reducing Pressure to Photosystem I in Morning Glory Leaves under Short-term High IrradianceJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 7 2007Xin-Guo Li Abstract Under 30-min high irradiance (1500 ,mol m,2 s,1), the roles of the xanthophyll cycle and D1 protein turnover were investigated through chlorophyll fluorescence parameters in morning glory (Ipomoea setosa) leaves, which were dipped into water, dithiothreitol (DTT) and lincomycin (LM), respectively. During the stress, both the xanthophyll cycle and D1 protein turnover could protect PSI from photoinhibition. In DTT leaves, non-photochemical quenching (NPQ) was inhibited greatly and the oxidation level of P700 (P700+) was the lowest one. However, the maximal photochemical efficiency of PSII (Fv/Fm) in DTT leaves was higher than that of LM leaves and was lower than that of control leaves. These results suggested that PSI was more sensitive to the loss of the xanthophyll cycle than PSII under high irradiance. In LM leaves, NPQ was partly inhibited, Fv/Fm was the lowest one among three treatments under high irradiance and P700+ was at a similar level as that of control leaves. These results implied that inactivation of PSII reaction centers could protect PSI from further photoinhibition. Additionally, the lowest of the number of active reaction centers to one inactive reaction center for a PSII cross-section (RC/CSo), maximal trapping rate in a PSII cross-section (TRo/CSo), electron transport in a PSII cross-section (ETo/CSo) and the highest of 1-qP in LM leaves further indicated that severe photoinhibition of PSII in LM leaves was mainly induced by inactivation of PSII reaction centers, which limited electrons transporting to PSI. However, relative to the LM leaves the higher level of RC/CSo, TRo/CSo, Fv/Fm and the lower level of 1-qP in DTT leaves indicated that PSI photoinhibition was mainly induced by the electron accumulation at the PSI acceptor side, which induced the decrease of P700+ under high irradiance. [source] Regulation of Light Energy Utilization and Distribution of Photosynthesis in Five Subtropical Woody PlantsJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 3 2007Nan Liu Abstract The adaptations and responses of photosynthesis to long- and short-term growth light gradient treatments were investigated in five subtropical forest plants, namely Pinus massoniana Lamb., Schima superba Gardn. et Champ., Castanopsis fissa (Champ. ex Benth.) Rehd. et Wils., Acmena acuminatissima (BI.) Merr et Perry, and Cryptocarya concinna Hance. With diurnal changes in sunlight and air temperature, the de-epoxidation state and lutein content in the five woody plants under three light intensities first increased and then decreased during the day. However, maximal photochemical efficiency (Fv/Fm; where Fm is the maximum fluorescence yield and Fv is variable fluorescence) and the photochemical quantum yields of photosystem (PS) II (,PSII) of the species examined changed in the opposite manner, with those in plants grown under 100% natural light changing the most. After long-term treatment (21 months), anti-oxidant capacity (1, 1-diphenyl-2-picrylhydrazyl radical (DPPH·)-scavenging capacity) and utilization of excitation energy showed differences in modulation by different light intensities. It was shown that A. acuminatissima and C. concinna, as dominant species in the late succession stage of a subtropical forest in Dinghu mountain, South China, were better able to adapt to different light environments. However, P. massoniana, the pioneer species of this forest, exhibited less adaptation to low light intensity and was definitely eliminated by the forest succession process. [source] Antisense-Mediated Depletion of Tomato Chloroplast Omega-3 Fatty Acid Desaturase Enhances Thermal ToleranceJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 9 2006Xun-Yan Liu Abstract A chloroplast-localized tomato (Lycopersicon esculentum Mill.) ,-3 fatty acid desaturase gene (LeFAD7) was isolated and characterized with regard to its sequence, response to various temperatures, and function in antisense transgenic tomato plants. The deduced amino acid sequence had four histidine-rich regions, of which three regions were highly conserved throughout the whole ,-3 fatty acid desaturase gene family. Southern blotting analysis showed that LeFAD7 was encoded by a single copy gene and had two homologous genes in the tomato genome. Northern blot showed that LeFAD7 was expressed in all organs and was especially abundant in leaf tissue. Meanwhile, expression of LeFAD7 was induced by chilling stress (4 °C), but was inhibited by high temperature (45 °C), in leaves. Transgenic tomato plants were produced by integration of the antisense LeFAD7 DNA under the control of a CaMV35S promoter into the genome. Antisense transgenic plants with lower 18:3 content could maintain a higher maximal photochemical efficiency (Fv/Fm) and O2 evolution rate than wild-type plants. These results suggested that silence of the LeFAD7 gene alleviated high-temperature stress. There was also a correlation between the low content of 18:3 resulting from silence of the LeFAD7 gene and tolerance to high-temperature stress. (Managing editor: Li-Hui Zhao) [source] SHORT-TERM AND LONG-TERM EFFECTS OF TEMPERATURE ON PHOTOSYNTHESIS IN THE DIATOM THALASSIOSIRA PSEUDONANA UNDER UVR EXPOSURES,JOURNAL OF PHYCOLOGY, Issue 3 2007Cristina Sobrino Temperature is expected to modify the effects of ultraviolet radiation (UVR) on photosynthesis by affecting the rate of repair. We studied the effect of short-term (1 h) and long-term (days) acclimation to temperature on UVR photoinhibition in the diatom Thalassiosira pseudonana Hasle et Heimdal. Photosynthesis was measured during 1 h exposures to varying irradiances of PAR and UVR + PAR at 15, 20, and 25°C, the latter corresponding to the upper temperature limit for optimal growth in T. pseudonana. The exposures allowed the estimation of photosynthesis,irradiance (P,E) curves and biological weighting functions (BWFs) for photoinhibition. For the growth conditions used, temperature did not affect photosynthesis under PAR. However, photoinhibition by UVR was highly affected by temperature. For cultures preacclimated to 20°C, the extent of UVR photoinhibition increased with decreasing temperature, from 63% inhibition of PAR-only photosynthesis at 25°C to 71% at 20°C and 85% at 15°C. These effects were slightly modified after several days of acclimation: UVR photoinhibition increased from 63% to 75% at 25°C and decreased from 85% to 80% at 15°C. Time courses of photochemical efficiency (,PSII) under UVR + PAR were also fitted to a model of UVR photoinhibition, allowing the estimation of the rates of damage (k) and repair (r). The r/k values obtained for each temperature treatment verified the responses observed with the BWF (R2 = 0.94). The results demonstrated the relevance of temperature in determining primary productivity under UVR exposures. However, the results suggested that temperature and UVR interact mainly over short (hours) rather than long (days) timescales. [source] TEMPERATURE INDUCED PHOTOINHIBITION IN OUTDOOR CULTURES OF MONODUS SUBTERRANEUSJOURNAL OF PHYCOLOGY, Issue 2000A. Vonshak Outdoor algal cultures are continuously exposed to changes in environmental conditions, particularly irradiance and temperature. While the changes in light intensity take place in a range of one to two hours, the increase in temperature is a slower process and takes about four to five hours. This de-synchronization between the two important environmental factors governing photosynthesis and growth of algae results in a unique stress condition where photoinhibition can be induced at relatively low light intensity. Outdoors the early morning culture temperature was found to be about 12 to 14° C, and reaches 25 to 28° C at mid-day. In an experiment, such a natural temperature regime was compared to another one in which the morning temperature of the culture was increased to 20° C by using a heating system. A fast decline in the maximal photochemical efficiency of PSII (Fv/Fm) was observed starting as soon as sunrise. The decline was faster in the non-heated culture and was to a lower value. The diurnal changes in the electron transfer rate (ETR) and in the non-photochemical quenching (NPQ) of the cultures, indicated that the early morning exposure of cells to sub-optimal temperature results in a fast inactivation of PSII activity which was reflected in an inhibition of the photosynthetic activity even when the two cultures finally reached the same temperature at mid-day. Thus, under the same light and temperature mid-day conditions the ETR was higher and the NPQ was significantly lower in the heated culture. Significant changes in productivity of the cultures also were observed. [source] Vertical distribution of Hymenophyllaceae species among host tree microhabitats in a temperate rain forest in Southern ChileJOURNAL OF VEGETATION SCIENCE, Issue 4 2009Maria J. Parra Abstract Question: Are differences in microhabitat preferences of co-occurring epiphytic Hymenophyllaceae species (filmy ferns) correlated with differences in ecophysiological responses to light availability and humidity in the host tree? Location: The Andean foothills in south-central Chile. Methods: We evaluated the distribution pattern of nine filmy fern species in microhabitats that differ in light availability and humidity in four host tree species. A DCA was developed to assess Hymenophyllaceae species microhabitat preference in terms of canopy openness (CO) and relative humidity. We assessed whether differences in chlorophyll content, maximum photochemical efficiency (Fv/Fm), photosynthetic capacity (Amax), evapotranspiration (E) and instantaneous water use efficiency (WUE) are consistent with any pattern. Results: CO and relative humidity differed significantly with height in the host trees. While CO increased with height in a host tree, relative humidity decreased. DCA analysis showed that filmy fern species distribution within and among trees was mainly explained by the relative humidity of the microhabitat. Chlorophyll content, chlorophyll a/b ratio, Amax and E differed significantly among filmy fern species. Amax and E were correlated with axis 1 scores from the DCA analysis. Conclusions: The vertical distribution and abundance of filmy fern species in Chilean temperate rain forest seems to be closely related to the different microhabitats offered by host trees. This pattern may reflect interspecific differences in ecophysiological traits related both to light availability and humidity. Our results suggest that humidity is the main environmental factor driving functional responses and habitat preferences of these filmy fern species. [source] Leaf photoacclimatory responses of the tropical seagrass Thalassia testudinum under mesocosm conditions: a mechanistic scaling-up studyNEW PHYTOLOGIST, Issue 1 2007Napo M. Cayabyab Summary ,,Here, the leaf photoacclimatory plasticity and efficiency of the tropical seagrass Thalassia testudinum were examined. ,,Mesocosms were used to compare the variability induced by three light conditions, two leaf sections and the variability observed at the collection site. ,,The study revealed an efficient photosynthetic light use at low irradiances, but limited photoacclimatory plasticity to increase maximum photosynthetic rates (Pmax) and saturation (Ek) and compensation (Ec) irradiances under high light irradiance. A strong, positive and linear association between the percentage of daylight hours above saturation and the relative maximum photochemical efficiency (FV/FM) reduction observed between basal and apical leaf sections was also found. ,,The results indicate that T. testudinum leaves have a shade-adapted physiology. However, the large amount of heterotrophic biomass that this seagrass maintains may considerably increase plant respiratory demands and their minimum quantum requirements for growth (MQR). Although the MQR still needs to be quantified, it is hypothesized that the ecological success of this climax species in the oligotrophic and highly illuminated waters of the Caribbean may rely on the ability of the canopy to regulate the optimal leaf light environment and the morphological plasticity of the whole plant to enhance total leaf area and to reduce carbon respiratory losses. [source] Comparison by PAM Fluorometry of Photosynthetic Activity of Nine Marine Phytoplankton Grown Under Identical Conditions,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2005P. Juneau ABSTRACT The photosynthetic activity of marine phytoplankton from five algal classes (Phaeodactylum tricornutum, Skeletonema costatum, Thalassiosira oceanica, Thalassiosira weissflogii, Dunaliella tertiolecta, Mantoniella squamata, Emiliania huxleyi, Pavlova lutheri and Heterosigma akashiwo) was investigated under identical growth conditions to determine interspecies differences. Primary photochemistry and electron transport capacity of individual species were examined by pulse amplitude-modulated (PAM) fluorescence. Although few differences were found in maximal photosystem II (PSII) photochemical efficiency between various species, large differences were noticed in their PSII-photosystem I (PSI) electron transport activity. We found that species such as T. oceanica and M. squamata have much lower photochemical activity than H. akashiwo. It appeared that processes involved in electron transport activity were more susceptible to change during algal evolution compared with the primary photochemical act close to PSII. Large variations in the nonphotochemical energy dissipation event among species were also observed. Light energy required to saturate photosynthesis was very different between species. We have shown that M. squamata and H. akashiwo required higher light energy (>1300 ,mol m,2 s,1) to saturate photosynthesis compared with S. costatum and E. huxleyi (ca 280 ,mol m,2 s,1). These differences were interpreted to be the result of variations in the size of lightharvesting complexes associated with PSII. These disparities in photosynthetic activity might modulate algal community structure in the natural environment where light energy is highly variable. Our results suggest that for an accurate evaluation of primary productivity from fluorescence measurements, it is essential to know the species composition of the algal community and the individual photosynthetic capacity related to the major phytoplankton species present in the natural phytoplankton assemblage. [source] Interaction of UV Radiation and Inorganic Carbon Supply in the Inhibition of Photosynthesis: Spectral and Temporal Responses of Two Marine Picoplankters,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2005Cristina Sobrino ABSTRACT The effect of ultraviolet radiation (UVR) on inhibition of photosynthesis was studied in two species of marine picoplankton with different carbon concentration mechanisms: Nannochloropsis gaditana Lubián possesses a bicarbonate uptake system and Nannochloris atomus Butcher a CO2 active transport system. Biological weighting functions (BWFs) for inhibition of photosynthesis by UVR and photosynthesis vs irradiance (PI) curves for photosynthetically active radiation (PAR) were estimated for both species grown with an enriched CO2 supply (high dissolved inorganic carbon [DIC]: 1% CO2 in air) and in atmospheric CO2 levels (low DIC: 0.03% CO2). The response to UVR and PAR exposures was different in each species depending on the DIC treatment. Under PAR exposure, rates of maximum photosynthesis were similar between treatments in N. gaditana. However, the cultures growing in high DIC had lower sensitivity to UVR than the low DIC cultures. In contrast, N. atomus had higher rates of photosynthesis under PAR exposure with high DIC, but the BWFs were not significantly different between treatments. The results suggest that one or more processes in N. gaditana associated with HCO3, transport are target(s) for UV photodamage because there was relatively less UV inhibition of the high DIC-grown cultures in which inorganic carbon fixation is supplied by passive CO2 diffusion. Time courses of photochemical efficiency in PAR, during UV exposure and during subsequent recovery in PAR, were determined using a pulse amplitude modulated fluorometer. The results were consistent with the BWFs. In all time courses, a steady state was obtained after an initial decrease, consistent with a dynamic balance between damage and repair as found for other phytoplankton. However, the relationship of response to exposure showed a steep decline in activity that is consistent with a constant rate of repair. A novel feature of a model developed from a constant repair rate is an explicit threshold for photosynthetic response to UV. [source] Some photosynthetic responses to salinity resistance are transferred into the somatic hybrid descendants from the wild soybean Glycine cyrtoloba ACC547PHYSIOLOGIA PLANTARUM, Issue 3 2007Yong Yang The somatic hybrid descendants between a cultivated soybean Glycine max Melrose and a wild species Glycine cyrtoloba ACC547 were found to possess some salinity-resistant traits of the wild soybean. Under salt stress, two of the descendants as well as their wild parent grew better than their cultivated parent. In addition, salinity-induced decline in the net photosynthetic rate and the maximum photochemical efficiency was much less in the wild species and the descendants than in Melrose when stressed for more than 5 days. Analysis of the postillumination transient increase in chlorophyll fluorescence and the dark rereduction of the oxidized primary electron donor in photosystem I (PSI) (P700+) indicated that salinity induced a significant upregulation of the cyclic electron flow around PSI (CEF1) in the wild species and the hybrid descendants. Similar to their wild parent, the descendants maintained higher non-photochemical dissipation of excess excitation energy than their cultivated parent under salt stress. As a consequence, there were lower levels of superoxide radical and membrane lipid peroxidation in the plants of the descendants and the wild species. Based on these results, we proposed that the high salinity resistance of the descendants might be because of, at least partially, the trait inherited from the wild species of the enhanced CEF1 which contributed to the sufficient dissipation of excess excitation energy to protect photosynthetic apparatus from the damage of reactive oxygen species. [source] Rubisco expression in rice leaves is related to genotypic variation of photosynthesis under elevated growth CO2 and temperaturePLANT CELL & ENVIRONMENT, Issue 12 2003R. W. GESCH ABSTRACT Genetic modifications of agronomic crops will likely be necessary to cope with global climate change. This study tested the hypotheses that genotypic differences in rice (Oryza sativa L.) leaf photosynthesis at elevated [CO2] and temperature are related to protein and gene expression of Rubisco, and that high growth temperatures under elevated [CO2] negatively affect photosystem II (PSII) photochemical efficiency. Two rice cultivars representing an indica (cv. IR72) and japonica type (cv. M103) were grown in 350 (ambient) and 700 (elevated) µmol CO2 mol,1 at 28/18, 34/24 and 40/30 °C sinusoidal maximum/minimum, day/night temperatures in outdoor, sunlit, environment-controlled chambers. Leaf photosynthesis of IR72 favoured higher growth temperatures more than M103. Rubisco total activity and protein content were negatively affected in both genotypes by high temperatures and elevated CO2. However, at moderate to high growth temperatures, IR72 leaves averaged 71 and 39% more rbcS transcripts than M103 under ambient and elevated CO2, respectively, and likewise had greater Rubisco activity and protein content. Expression of psbA (D1 protein of PSII) in IR72 leaves increased with temperature, whereas it remained constant for M103, except for a 20% decline at 40/30 °C under elevated CO2. Even at the highest growth temperatures, PSII photochemical efficiency was not impaired in either genotype grown under either ambient or elevated CO2. Genotypic differences exist in rice for carboxylation responses to elevated CO2 and high temperatures, which may be useful in developing genotypes suited to cope with global climate changes. [source] Photosynthetic limitations in olive cultivars with different sensitivity to salt stressPLANT CELL & ENVIRONMENT, Issue 4 2003F. LORETO ABSTRACT Olive (Olea europea L) is one of the most valuable and widespread fruit trees in the Mediterranean area. To breed olive for resistance to salinity, an environmental constraint typical of the Mediterranean, is an important goal. The photosynthetic limitations associated with salt stress caused by irrigation with saline (200 mm) water were assessed with simultaneous gas-exchange and fluorescence field measurements in six olive cultivars. Cultivars were found to possess inherently different photosynthesis when non-stressed. When exposed to salt stress, cultivars with inherently high photosynthesis showed the highest photosynthetic reductions. There was no relationship between salt accumulation and photosynthesis reduction in either young or old leaves. Thus photosynthetic sensitivity to salt did not depend on salt exclusion or compartmentalization in the old leaves of the olive cultivars investigated. Salt reduced the photochemical efficiency, but this reduction was also not associated with photosynthesis reduction. Salt caused a reduction of stomatal and mesophyll conductance, especially in cultivars with inherently high photosynthesis. Mesophyll conductance was generally strongly associated with photosynthesis, but not in salt-stressed leaves with a mesophyll conductance higher than 50 mmol m,2 s,1. The combined reduction of stomatal and mesophyll conductances in salt-stressed leaves increased the CO2 draw-down between ambient air and the chloroplasts. The CO2 draw-down was strongly associated with photosynthesis reduction of salt-stressed leaves but also with the variable photosynthesis of controls. The relationship between photosynthesis and CO2 draw-down remained unchanged in most of the cultivars, suggesting no or small changes in Rubisco activity of salt-stressed leaves. The present results indicate that the low chloroplast CO2 concentration set by both low stomatal and mesophyll conductances were the main limitations of photosynthesis in salt-stressed olive as well as in cultivars with inherently low photosynthesis. It is consequently suggested that, independently of the apparent sensitivity of photosynthesis to salt, this effect may be relieved if conductances to CO2 diffusion are restored. [source] Midday depression of photosynthesis and effects of mist spray in citrusANNALS OF APPLIED BIOLOGY, Issue 1 2009M.-J. Hu Abstract Diurnal variations of gas exchange, chlorophyll a fluorescence and some related biochemical characteristics in sun-acclimated mature citrus leaves of mist-sprayed (treatment) and unsprayed (control) trees were compared on sunny days during summer to identify the environmental and physiological factors limiting carbon gain in citrus tree canopies. At midday, net photosynthesis and maximal photochemical efficiency of photosystem II (Fv/Fm) in citrus leaves decreased significantly under control conditions, but the decrease was mitigated by mist spraying. Although the content of malondialdehyde, hydrogen peroxide and activities of antioxidant enzymes increased at midday in both mist-sprayed and control leaves, they were much higher in control leaves than in mist-sprayed leaves. The level of D1 protein decreased significantly in control leaves at midday and then was partly recovered later, while that in treated leaves changed to a much lesser extent because of alleviation of photoinhibition by mist spraying. Both the fast and the slow phases of millisecond-delayed light emissions in treated citrus leaves were higher than those in control leaves, indicating that mist spraying protects the normal operation of the photosynthetic apparatus in leaves. Mist spraying also reduced leaf temperatures and the ratio of air to leaf vapour pressure deficit (ALVPD), leading to increases in stomatal conductance (gs) and alleviation of photoinhibition at midday. It is concluded that the decline of leaf gs under high-ALVPD conditions in summer is an important factor contributing to midday depression of photosynthesis in citrus, and mist spraying is effective in alleviating midday depression of photosynthesis in citrus leaves. [source] | |||||||||||||