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This study investigated the effect of solar ultraviolet radiation (UVR) and temperature on a chain length and photosynthetic performance of diatom Chaetorceros curvisetus. The cells were cultured in large quartz tubes and exposed to PAR, PAR + UV-A (PA), or PAR + UV-A + UV-B (PAB) radiation at 20°C and 28°C for six days, respectively. After recovery for 1 h, the cells were exposed again to three different radiations for 1 h. Then, a change in the photochemical efficiency (F) was examined and UVR-induced photoinhibition was calculated. The percentage of long chains (more than five single cells per chain) in C. curvisetus significantly increased from 8.2% (PAR) to 38.9% (PAB) at 20°C; while it was not notably affected at 28°C. Mycosporine-like amino acids (MAAs) concentration obviously increased by irradiance increment from PAR to PAB at 20°C. Chlorophyll (Chl) a concentration significantly declined with increasing irradiance at 20°C. Both MAAs and Chl a concentrations were not obviously changed by irradiance at 28°C. Before and after reexposure, F was significantly reduced both at 20°C and 28°C. UVR-induced photoinhibition at 20°C (39%) was higher than that at 28°C (30.9%). Solar UV radiation, especially UV-B, could significantly influence the percentage of long chains of C. curvisetus, especially at low temperature. UVR-induced photoinhibition can be alleviated by higher temperatures. [ABSTRACT FROM AUTHOR]

Aims: The principal objective was to evaluate the interference by the invasive species, H. pilosella, on native grassland species at the physiological performance level. We hypothesised that the invasive species is able to alter the nitrogen uptake of native plant species, and can modify community functioning. Methods: This study was performed under field conditions in the Magellanic Steppe (Argentina). We compared stable isotope signatures, nutrient content and several functional physiological traits in four grassland species with and without H. pilosella interference. Results: We found significant interference effects from the invasive species on native species, mostly through changes in nitrogen uptake. The variation in the natural abundance of foliar δN suggests that the native plants switched nitrogen sources due to interference with the exotic species. A linear relationship between chlorophyll and proline content that disappears when species are under H. pilosella interference, suggests major changes in the N allocation of native species. Grassland species under interference with exotic species exhibit lower photochemical efficiency and higher water use efficiency. Canonical discriminant analysis evidenced the existence of a different set of functional traits between invasive and native plants, and also among native species with and without H. pilosella interference. Conclusions: Our results support the hypothesis that H. pilosella exerts intense interference with native species through shifting the N sources available for native species, a lower leaf N content, and increasing water stress. [ABSTRACT FROM AUTHOR]

Ecological theory suggests that in harsh environments major abiotic stress factors may act as environmental filters, thereby reducing the range of possible plant strategies through environmental trait selection. This would lead to functional similarity of species coexisting in hostile environments. To test this prediction, we evaluated six functional leaf traits at three different times of year in five species coexisting in a coastal dune ecosystem. The functional traits examined were associated with water status and light interception and use - two of the most limiting factors that lead to stress in dune systems. Species differed in traits associated with light absorption, namely chlorophyll content, the vigour index NDVI, and the proportion of the light absorbed that is used in photochemistry (as expressed by the effective and maximum quantum yield of PSII and the photochemical reflectance index). For most of the traits, the relative performance of species depended significantly on time. This research revealed a significant divergence in functional traits of coexisting species, which does not conform to findings in other harsh environments where species tend to functional convergence. The data provide experimental support for the hypothesis that there is no single combination of traits for a given environment, but that alternative functional designs of similar fitness may evolve in the same environment as a result of complex interactions and trade-offs among traits. This suggests that factors claimed to promote divergence, such as limiting similarity and disturbance processes, may play an important role in structuring the dune community under study. The high variability in functional traits suggests a significant degree of functional diversity and highlights the importance of preserving the species composition of threatened coastal dune habitats in order to preserve distinctive functional processes that may be unique to the systems. [ABSTRACT FROM AUTHOR]

Abstract: Flooding imposes severe selection pressure on plants, principally because excess water in their surroundings deprives the plants certain basic resources such as oxygen, carbon dioxide, and light for photosynthesis. In recent years, reports of damage caused by flooding to rice plants have increased concomitantly with the expansion of rainfed lowland rice cultivation throughout the world. Strong submergence-induced elongation, a common escape mechanism, helps submerged individuals regain and retain contact with the aerobic environment. This study analyzed physiological mechanisms of escape from complete submergence by evaluating photosynthesis, photochemical reaction, and plant behavior during and after submergence in Oryza glaberrima Steud. Partially submerged plants were unaffected by excess water because their photosynthetic rate was maintained during and after submergence. Escape mechanisms, when under complete submergence, restrain shoot elongation per shoot dry weight per day during submergence (shoot elongation index). Our results demonstrate that the leaf area and shoot biomass of the submerged plants during submergence affects their post-submergence photosynthetic rate and the PSII maximum efficiency to some degree. Under deeply prolonged submergence, O. glaberrima genotypes were characterized by faster shoot elongation, anaerobic tillering, larger leaf area extension, higher photosynthetic rate, and maintenance of PSII maximum efficiency compared with Oryza sativa genotypes without an escape mechanism. O. glaberrima employs a submergence escape strategy that effectively uses stored carbohydrates for shoot elongation and leaf extension in a severely photosynthesis-limited environment under complete submergence. [Copyright &y& Elsevier]

Measurements of Sorbus stomata size and density, maximal photochemical efficiency of photosystem II (F/F), variable-to-initial fluorescence ratio (F/F) and potential electron acceptor capacity ('area') were performed during leaf development in four parental diploid species, S. aria, S. aucuparia, S. chamaemespilus, S. torminalis, and two hybrid species, S. hazslinszkyana and S. intermedia. In fully expanded mature leaves, stomata lengths and densities were significantly larger in the shrub S. chamaemespilus than in the five tree species. The best performance of both the F/F and the F/F ratio was recorded in S. intermedia, whereas S. chamaemespilus had the highest value of 'area'. From a physiological point of view, the results of this study showed that the photosystem II reaction centers remained intact functionally through all phenological stages of leaf expansion for all examined species of Sorbus. [ABSTRACT FROM AUTHOR]

Positive interactions between species are known to play an important role in the structure and dynamics of alpine plant communities. The balance between negative and positive interactions is known to shift along spatial and temporal gradients, with positive effects prevailing over negative ones as the environmental stress increases. Thus, this balance is likely to be affected by climate change. We hypothesized that increases in temperature (a global warming scenario) should decrease the importance of positive interactions for the survival and growth of alpine plant species. To test this hypothesis, we selected individuals of the native grass species Hordeum comosum growing within the nurse cushion species Azorella madreporica at 3,600 m.a.s.l. in Los Andes (Chile), and performed nurse removal and seedling survival experiments under natural and warmer conditions. For warmer conditions, we used open-top chambers, which increased the temperature by 4 °C. After two growing seasons, we compared the effect of nurse removal on the survival, biomass, and photochemical efficiency of H. comosum individuals under warmer and natural conditions. Nurse removal significantly decreased the survival, biomass, and photochemical efficiency of H. comosum, demonstrating the facilitative effects of nurse cushions. Seedling survival was also enhanced by cushions, even under warmer conditions. However, warmer conditions only partially mitigated the negative effects of nurse removal, suggesting that facilitative effects of cushions do not wane under warmer conditions. Thus, facilitative interactions are vital to the performance and survival of alpine species, and these positive interactions will continue to be important in the warmer conditions of the future in high-alpine habitats. [ABSTRACT FROM AUTHOR]

Abstract: The thylakoid lumen proteins are highly associated with photosynthesis functionally. In this study, we characterized the OsTLP27 gene from rice (Oryza sativa), which encodes a 27-kDa of 257-amino acid with 53% homology to the AtTLP gene from Arabidopsis thaliana. OsTLP27 was predicted to encode a thylakoid lumen protein of unknown function in chloroplast, and chloroplast targeting of OsTLP27 was confirmed by transient expression of a fusion protein with green fluorescent protein (GFP). OsTLP27 transcripts accumulated specifically in green tissues such as the leaf blade and leaf sheath, and the levels of its transcripts followed a circadian rhythm. Constitutive expression of OsTLP27 under the control of CaMV 35S promoter resulted in increased pigment content and enhanced photochemical efficiency in terms of the values of maximal photochemical efficiency of photosystem II (PSII) (F v/F m), effective quantum yield of PSII (ΦPSII), electron transport rate (ETR) and photochemical quenching (qP). Overexpression of OsTLP27 also enhanced transcript levels of genes related to chloroplast function and caused changes in the grana size and number. Further study showed that the structure and polypeptide composition of the photosynthetic apparatus were altered in transgenic lines overexpressing OsTLP27. These data suggested that OsTLP27 encodes a protein with a novel function in photosynthesis and chloroplast development in rice. [Copyright &y& Elsevier]

Sex dimorphic plants often show sex-specific differences in growth and biomass allocation. These differences have been explained as a consequence of the different reproductive functions performed by the sexes. Such differences may determine the performance of each sex in different habitats and therefore might explain the spatial segregation of the sexes described in many dimorphic plants. We examined the growth, reproductive and physiological responses of the sexes of the subdioecious plant Honckenya peploides to two levels each of salt spray and nutrients, which are assumed to be important selective forces in coastal environments. We found sex-related differences in H. peploides. In particular, females allocated proportionally more dry mass to reproduction and grew less and more slowly than males regardless of salt spray and nutrient conditions, which is interpreted as a trade-off between reproductive and vegetative growth. Regarding physiological response, nutrients significantly increased values of photochemical reflectance index (PRI) in females but not in males, suggesting that photochemical efficiency is more limited by nutrients in females than in males. PRI values also suggest intersexual differences in protection requirements against photoinhibition. The study did not find sex-differential responses to salt spray, which caused a decrease in reproductive effort in both sexes. The sex-related differences in relative growth rates, reproductive allocation and photosynthetic features found here may contribute to explaining habitat-related between-sex differences in performance and, therefore, the spatial segregation of the sexes observed in H. peploides. [ABSTRACT FROM AUTHOR]

Seedling performance may determine plant distribution, especially in water-limited environments. Plants of Caragana korshinskii commonly grow in arid and semiarid areas in northwestern China, and endure water shortage in various ways, but little is known about their performance when water shortage occurs at early growth stages. The water relations, photosynthetic activity, chlorophyll (Chl) content and proline accumulation were determined in 1-year-old seedlings growing in a 1:1 mixture of Loess soil and Perlite and subjected to ( 1) a water deficit for 20 days and ( 2) kept adequately watered throughout. The water deficit induced low (−6.1 MPa) predawn leaf water potentials (LWP), but did not induce any leaf abscission. Stomatal conductance ( g), leaf transpiration rate ( E), and net photosynthetic rate ( P) decreased immediately following the imposition of the water deficit, while the maximal photochemical efficiency of photosystem II (PSII) (F/F) and the effective quantum yield of PSII (Φ) decreased 15 days later. An early and rapid decrease in g, reduced E, increased Chl ( a+b) loss, increased the apparent rate of photochemical transport of electrons through PSII (ETR)/ P, as well as a gradual increase in non-photochemical quenching of fluorescence (NPQ) and proline may have contributed to preventing Φ from photodamage. C. korshinskii seedlings used a stress-tolerance strategy, with leaf maintenance providing a clear selective advantage, considering the occasional rainfall events during the growing season. [ABSTRACT FROM AUTHOR]

Abstract: The uptake of Se (VI) by two aquatic plants, Myriophyllum spicatum L. and Ceratophyllum demersum L., and its effects on their physiological characteristics have been studied. Plants were cultivated outdoors under semi-controlled conditions and in two concentrations of Na selenate solution (20μgSeL−1 and 10mgSeL−1). The higher dose of Se reduced the photochemical efficiency of PSII in both species, while the lower dose had no effect on PSII. Addition of Se had no effect on the amounts of chlorophyll a and b. The concentration of Se in plants grown in 10mgSeL−1, averaged 212±12μgSeg−1 DM in M. spicatum (grown from 8–13d), and 492±85μgSeg−1 DM in C. demersum (grown for 31d). Both species could take up a large amount of Se. The amount of soluble Se compounds in enzyme extracts ranged from 16% to 26% in control, and in high Se solution from 48% to 36% in M. spicatum and C. demersum, respectively. Se-species were determined using HPLC-ICP–MS. The main soluble species in both plants was selenate (∼37%), while SeMet and SeMeSeCys were detected at trace levels. [Copyright &y& Elsevier]

Abstract: In plants, the decline of poly(ADP-ribosyl)ation activity is involved in energy homeostasis and stress tolerance. By reducing stress-induced poly(ADP-ribosyl)ation activity, NAD+ breakdown is inhibited preventing high energy consumption. Under these conditions, plants preserve their energy homeostasis without an overactivation of mitochondrial respiration, thus avoiding the production of reactive oxygen species. Therefore, plants with lowered poly(ADP-ribosyl)ation activity appear tolerant to multiple stresses. In this study, the evergreen species Cistus incanus L. was used as a model because of its capacity to overcome successfully the environmental constraints of the Mediterranean climate. The aim of the present work was to characterize and assess the role of poly(ADP-ribosyl)ation in C. incanus plants kept under different temperature in greenhouse (GH), outdoor during winter (WO) and outdoor during spring (SO). Data showed that in C. incanus polyADPribose metabolism occurs. The enzyme responsible for poly(ADP-ribose) chains synthesis is a poly(ADP-ribose)polymerase of about 80 kDa, lacking “zinc finger” N-terminal domain and able to automodify. The lowest PARP activity, as well as the lowest quantum yield of PSII linear electron transport (ΦPSII) and photochemical quenching (qP), was found in WO plants. Instead, in SO plants the recovery of photochemical activity associated to a poly(ADP-ribose)polymerase activity increase of about 50%, as compared to GH plants, was observed. Taking into account both biochemical and eco-physiological responses, a possible explanation for the poly(ADP-ribosyl)ation deficiency in WO plants has been hypothesized. [Copyright &y& Elsevier]

Background and Aims Reproductive costs imply trade-offs in resource distribution at the physiological level, expressed as changes in future growth and/or reproduction. In dioecious species, females generally endure higher reproductive effort, although this is not necessarily expressed through higher somatic costs, as compensatory mechanisms may foster resource uptake during reproduction. Methods To assess effects of reproductive allocation on vegetative growth and physiological response in terms of costs and compensation mechanisms, a manipulative experiment of inflorescence bud removal was carried out in the sexually dimorphic species Corema album. Over two consecutive growing seasons, vegetative growth patterns, water status and photochemical efficiency were measured to evaluate gender-related differences. Key Results Suppression of reproductive allocation resulted in a direct reduction in somatic costs of reproduction, expressed through changes in growth variables and plant physiological status. Inflorescence bud removal was related to an increase in shoot elongation and water potential in male and female plants. The response to inflorescence bud removal showed gender-related differences that were related to the moment of maximum reproductive effort in each sexual form: flowering in males and fruiting in females. Delayed costs of reproduction were found in both water status and growth variables, showing gender-related differences in resource storage and use. Conclusions Results are consistent with the existence of a trade-off between reproductive and vegetative biomass, indicating that reproduction and growth depend on the same resource pool. Gender-related morphological and physiological differences arise as a response to different reproductive resource requirements. Delayed somatic costs provide evidence of gender-related differences in resource allocation and storage. Adaptive differences between genders in C. album may arise through the development of mechanisms which compensate for the cost of reproduction. [ABSTRACT FROM AUTHOR]

Abstract: The effects of solar UV radiation (280–400nm) on growth, quantum yield and pigmentation in Gracilaria lemaneiformis were investigated when the thalli were cultured under solar radiation with or without UV for a period of 15days. Presence of UV-A (315–400nm) enhanced the relative growth rate, while UV-B (218–315nm) inhibited it. The positive effect of UV-A and negative effect of UV-B counteracted to result in an insignificant impact of UVR on growth. During the noon period, both UV-A and UV-B resulted in the decrease of maximum quantum yield (Fv/Fm), but UV-B aided in the recovery of the yield in the late afternoon, reflecting that UV-B might be used as a signal in photorepair processes. UV induced the accumulation of UV-absorbing compounds (UVAC) to defend against the harmful UVR. However, the accumulation of UVAC took a much longer time compared to that previously reported, which was probably due to the lower levels of solar radiation and water temperature in the early spring period. Unknown UV-absorbing compounds (UVAC), which peaked at 265nm, probably the precursor of MAAs (UVAC325), accumulated under moderate levels of solar radiation and were transformed to MAAs under higher solar radiation. [ABSTRACT FROM AUTHOR]

To assess the short- and long-term impacts of UV radiation (UVR, 280–400 nm) on the microalga Scrippsiella trochoidea, we exposed cells to three different radiation treatments (PAB: 280–700 nm, PA: 320–700 nm, and P: 400–700 nm). A significant decrease in the photochemical efficiency (ΦPSII) at high irradiance (100% of incident solar radiation, 216.0 W m−2) was observed. Photoinhibition was reduced from 62.7 to 10.9% when the cells were placed in 12% solar radiation (26.1 W m−2). In long-term experiments (11 days) using batch cultures, cell densities during the first 5 days were decreased under treaments P, PA, and PAB, reflecting a change in the irradiance experienced in the laboratory to that of incident solar irradiance. Thereafter, specific growth rates increased and UV-induced photoinhibition decreased, indicating acclimation to solar UV. Cells were found to exhibit both higher ratios of repair to UV-related damage, shorter period for recovery and increased concentrations of UV-absorbing compounds (UVabc), whose maximum absorption was found to be at 336 nm. Our data indicate that S. trochoidea is sensitive to ultraviolet radiation, but was able to acclimate relatively rapidly ( ca. 6 days) by synthesizing UVabc and by increasing the rates of repair processes of D1 protein in PSII. [ABSTRACT FROM AUTHOR]

Abstract: Coccolithophores are exposed to solar UV radiation (UVR, 280–400nm) in their natural habitats. However, little has been documented on their physiological responses to UVR. We investigated the UV impacts on the photosynthesis, calcification, photochemical efficiency and growth of Emiliania huxleyi while culturing the cells under solar radiation. Presence of UVR significantly decreased the rates of photosynthesis and calcification. Shorter wavelengths of UV-B led to more damages to photosynthetic apparatus than to calcifying machinery, while longer wavelengths of UV-A resulted more harms to the calcification. As the cells were grown during long-term exposures to solar radiation, the ratios of repair to UV-related damage increased, indicating their acclimation to UV. The specific growth rate of the acclimated cells was inhibited by natural levels of UVR by about 25%, and the cells became bigger with more coccoliths, reflecting a slower cell division and enhanced calcification per cell, a trade off to counteract the UV-induced harms. The absorptivity of UV-absorbing compounds (peaked at 280nm) increased tremendously in response to the exposure of UVR. UV-induced stress led to a protective strategy of E. huxleyi, sacrificing the growth by allocating energy for accumulation of these compounds and calcification. [Copyright &y& Elsevier]

Abstract: During the six month dry period in the intermittent lake Cerknica in 2003, fluorescence parameters in 14 amphibious plants were measured to estimate the possible disturbance to photosystem II. Environmental changes due to intermittence caused no evident irreversible damage, since the potential photochemical efficiency of the majority of species and forms remained close to the optimal value at 0.83. Actual photochemical efficiency varied, showing different levels of temporary stress. Sudden submergence of aerial forms caused little disturbance to PS II. The results revealed the acclimation of plants thriving in intermittent habitats that enabled continuous harvesting of solar energy. [Copyright &y& Elsevier]

Quercus ilex and Phillyrea latifolia growing in a holm oak forest in Prades mountains (NE Spain) were subjected to experimental drought conditions. Soil water availability was reduced about 15% by plastic strips and funnels that partially excluded rain throughfall and by ditch exclusion of water runoff. Diurnal courses of maximum photochemical efficiency of PSII (Fv/Fm), apparent photosynthetic electron transport rate (ETR), net photosynthetic rate (A), transpiration rate (E) and water use efficiency (WUE) were measured in sunlit and shade leaves of both species during 2 years. Moreover, the responses of photosynthetic rates to PPFD and CO2 concentrations were also measured. Q. ilex experienced lower E rates and higher A rates and WUE than P. latifolia throughout the experimental period, but during summer drought these differences disappeared. Q. ilex exhibited a less cold sensitive behavior whereas P. latifolia showed a more heat–drought resistant behavior. Under severe summer drought conditions none of the two species was able to reach a positive carbon gain. Drought treatment produced a slight decrease in Fv/Fm values of Q. ilex plants and a strong decrease in Fv/Fm values of P. latifolia only in winter 2000, when drought stress coincided with cold stress. Drought treatment produced also a slight decrease in ETR values of both species. During midday, A and E rates decreased in drought plots in both species associated to lower photochemical efficiencies. In those drought plots, only P. latifolia was able to increase WUE by reducing transpiration losses during midday. Both species tended to present higher A rates for a given soil humidity in drought than in control plots. However, whereas Q. ilex A rates increased with soil humidity, P. latifolia A rates did not increase above 17% soil humidity, showing no water availability response above such threshold. It is very likely that mesic species such as Q. ilex lose competitive advantage in the drier environment forecasted for next decades than the more xeric P. latifolia. [Copyright &y& Elsevier]

Five-day exposure of clary sage (Salvia sclarea L.) to 100 μM cadmium (Cd) in hydroponics was sufficient to increase Cd concentrations significantly in roots and aboveground parts and affect negatively whole plant levels of calcium (Ca) and magnesium (Mg), since Cd competes for Ca channels, while reduced Mg concentrations are associated with increased Cd tolerance. Total zinc (Zn), copper (Cu), and iron (Fe) uptake increased but their translocation to the aboveground parts decreased. Despite the substantial levels of Cd in leaves, without any observed defects on chloroplast ultrastructure, an enhanced photosystem II (PSII) efficiency was observed, with a higher fraction of absorbed light energy to be directed to photochemistry (ΦPSΙΙ). The concomitant increase in the photoprotective mechanism of non-photochemical quenching of photosynthesis (NPQ) resulted in an important decrease in the dissipated non-regulated energy (ΦNO), modifying the homeostasis of reactive oxygen species (ROS), through a decreased singlet oxygen (1O2) formation. A basal ROS level was detected in control plant leaves for optimal growth, while a low increased level of ROS under 5 days Cd exposure seemed to be beneficial for triggering defense responses, and a high level of ROS out of the boundaries (8 days Cd exposure), was harmful to plants. Thus, when clary sage was exposed to Cd for a short period, tolerance mechanisms were triggered. However, exposure to a combination of Cd and high light or to Cd alone (8 days) resulted in an inhibition of PSII functionality, indicating Cd toxicity. Thus, the rapid activation of PSII functionality at short time exposure and the inhibition at longer duration suggests a hormetic response and describes these effects in terms of "adaptive response" and "toxicity", respectively. [ABSTRACT FROM AUTHOR]

Theoretical energy yields from CAM plants in dry climates are greater than theoretical energy yields from C4 and C3 plants cultivated in wet climates.There has been little attention paid to Crassulacean Acid Metabolism (CAM) as a mechanism for bioenergy crop tolerance to water limitation, in part, because potential yields of CAM plants have been assumed to be lower than those of most commonly studied bioenergy crops. The photochemical efficiency, water-use efficiency (WUE), biomass production, and fuel yield potentials of CAM, C3, and C4 plants that are considered or already in use for bioenergy are reviewed here. The theoretical photosynthetic efficiency of CAM plants can be similar to or greater than other photosynthetic pathways. In arid conditions, the greater WUE of CAM species results in theoretical biomass yield potentials that are 147% greater than C4 species. The realized yields of CAM plants are similar to the theoretical yields that account for water-limiting conditions. CAM plants can potentially be viable commercial bioenergy crops, but additional direct yield measurements from field trials of CAM species are still needed. [ABSTRACT FROM PUBLISHER]