Search

Neste estudo, foram avaliados os efeitos da supressão e do ressuprimento de fosfato (Pi) sobre a fotossíntese e eficiência fotoquímica de plantas de Medicago sativa cv. Flórida 77, em diferentes estádios do desenvolvimento vegetativo (V3, V4) e reprodutivo (R6, R8). O ensaio foi conduzido em casa de vegetação e as plantas cultivadas na solução nutritiva de HOAGLAND & ARNON (1950), contendo 0,14mmol L-1 de Pi. A supressão de Pi por dez dias reduziu os teores de fósforo nas folhas amostradas, em todos os estádios do desenvolvimento. Entretanto, com o ressuprimento, somente nos estádios vegetativos, os valores foram semelhantes ao tratamento controle. A fotossíntese por área foliar, em todos os estádios do desenvolvimento diminuiu com a supressão de Pi. De modo geral, o ressuprimento de Pi à solução nutritiva resultou em recuperação na fotossíntese, excetuando-se as plantas no estádio V3, uma indicação de que o período de supressão não causou danos permanentes no aparato fotossintético. Os teores dos pigmentos fotossintéticos e a eficiência fotoquímica do fotossistema II (FS II), avaliada pela relação Fv/Fm, não foram alterados quando as plantas foram submetidas à supressão de Pi. Esse resultado demonstra que o transporte de elétrons através do FS II não limitou a fotossíntese nas folhas amostradas, sob supressão de Pi, sugerindo que a supressão causou efeito mais pronunciado na etapa bioquímica da fotossíntese.This work evaluated the phosphate (Pi) suppression and ressupply on photosynthesis and photochemical efficiency from Medicago sativa plants cv. Florida 77, in different growth stages (V3 and V4) and reproductive (R6 and R8). The experiment was performed in a greenhouse, the plants being cultivated in HOAGLAND & ARMOND (1950) nutritive solution containing 0,14mmol L-1 of Pi. Pi suppression for ten days reduced Pi levels in sampled leaves, in all growth stages. However, with the re-supply only in the vegetative stages the values were similar to the control treatments. Photosynthesis per foliar area in all growth stages decreased with Pi suppression. In general, Pi ressupply into the nutritive solution resulted in recovery of photosynthesis, except for V3 plants, indicating that the suppression period did not cause permanent damage to the photosynthetic apparatus. Levels of photosynthetic pigments and the photosystem II (PS-II) photochemical efficiency evaluated as the Fv/Fm ratio were not altered when plants were submitted to Pi suppression. These results show that electons transport through PS-II did not limit photosynthesis in the sampled leaves under Pi supression, suggesting that Pi suppression caused a more pronunciated effect in the biochemical step of photosynthesis.

The present work aims to evaluate performance of a novel zigzag-flow column photobioreactor (ZZ-flow PBR) designed to achieve a high biomass during A. platensis cultivation. The ZZ-flow PBR was installed with four optimized zigzag baffle structures mounted over its outer (riser) section. The optimum parameters (w = 18 and h= 5 cm) for each zigzag baffle structure generated zigzag flow patterns throughout microalgae solution, which decreased mixing time (MT) by 51.1% but increased mass transfer coefficient (MTC) by 58.2% as compared with traditional PBR. The solution followed zigzag path along the baffles to facilitate frequent movement of microalgae cells across the PBR, where overall photochemical efficiency φPSII and Fv/Fm increased by 21.4% and 12.4%, respectively. The intracellular photosynthesis promoted electron transfer rate (ETR) by16.6% and chlorophyll a content by 8.3%, resulting in an increased biomass yield and CO 2 fixation by 28.8% and 36.3%, respectively, relative to conventional column PBR. [Display omitted] • A zigzag-flow PBR decreased mixing time and increased mass transfer by 51.1% and 58.2%. • Four layers of zigzag baffle improved nutrient homogeneity throughout solution. • Efficient mixing benefited A. platensis movement and enhanced photochemical efficiency. • Zigzag baffles significantly promoted CO 2 dissolution and fixation. • The biomass dry weight of A. platensis has increased by 28.8% and reached to 3.15 g/L. [ABSTRACT FROM AUTHOR]

Copyright of Revista Brasileira de Engenharia Agricola e Ambiental - Agriambi is the property of Revista Brasileira de Engenharia Agricola e Ambiental and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Estimation of the carbon balance of coconut ( Cocos nucifera L.) requires characterization of its photosynthetic irradiance response. Accordingly, the objectives of this work were to determine an appropriate photosynthetic irradiance response function, estimate its parameters for different canopy strata and compute canopy photosynthetic rates of two contrasting coconut genotypes in Sri Lanka. Photosynthetic irradiance response was measured in the upper (1 st to 10 th fronds counted from top down), middle (11 th to 20 th fronds), and lower (21 st to 30 th fronds) on clear, sunny days under near optimal conditions in field-grown adult palms (30 ± 2 years of age) of Sri Lankan Tall × Sri Lankan Tall (SLT, CRIC60) and Dwarf Green × Sri Lankan Tall (DGT, CRIC65) cultivars. Out of four models tested, the asymptotic exponential was selected as the best-fitting to quantify the photosynthetic irradiance of coconut. The two cultivars showed different patterns of variation across different canopy strata in irradiance-saturated photosynthetic rate ( P max ), photochemical efficiency ( ϕ ), irradiance compensation- ( φ ) and saturation points ( I sat ). In SLT, P max decreased from upper stratum to middle and lower strata while ϕ did not differ among strata. In contrast, P max of DGT decreased from upper and middle strata to the lower stratum while ϕ increased. SLT had higher φ and I sat than DGT but did not show significant variation between strata. In DGT, φ was higher and I sat lower in the lower stratum. The total canopy photosynthesis ( P c ) of SLT was 23% greater than DGT, primarily because it had higher partial LAI in all strata. Leaf N% and chlorophyll content did not show significant variation among strata. The different variation patterns of P max and ϕ among canopy strata in the two cultivars reflected their adaptations to different patterns of radiation penetration in to their respective canopies. Accordingly, it is concluded that SLT is better adapted to coconut-growing environments in the humid tropics such as in Sri Lanka where irradiance can often be limiting due to cloudiness during rainy seasons. On the other hand, DGT showed evidence of within-canopy adaptations to decreasing irradiance in the lower strata by optimizing resource allocation between efficient capture of light energy and its maximum utilization. The absence of a positive correlation between P c and yield of the two cultivars showed that allocation of assimilates to harvested nuts has a greater influence than assimilate production in the yield determination of coconut. [ABSTRACT FROM AUTHOR]

The study aimed to unravel the interaction between ocean acidification and solar ultraviolet radiation (UVR) in Chaetoceros curvisetus. Chaetoceros curvisetus cells were acclimated to high CO2 (HC, 1000 ppmv) and low CO2 concentration (control, LC, 380 ppmv) for 14 days. Cell density, specific growth rate and chlorophyll were measured. The acclimated cells were then exposed to PAB (photosynthetically active radiation (PAR) + UV-A + UV-B), PA (PAR + UV-A) or P (PAR) for 60 min. Photochemical efficiency (ΦPSII), relative electron transport rate (rETR) and the recovery of ΦPSII were determined. HC induced higher cell density and specific growth rate compared with LC. However, no difference was found in chlorophyll between HC and LC. Moreover, ΦPSII and rETRs were higher under HC than LC in response to solar UVR. P exposure led to faster recovery of ΦPSII, both under HC and LC, than PA and PAB exposure. It appeared that harmful effects of UVR on C. curvisetus could be counteracted by ocean acidification simulated by high CO2 when the effect of climate change is not beyond the tolerance of cells. [ABSTRACT FROM PUBLISHER]

The uptake of Se(IV) and its effects on the physiological and biochemical characteristics of duckweed ( Lemna minor L.) have been studied. Duckweed plants were cultivated in controlled conditions for 7 weeks in different concentrations of Na selenite: 0.5, 1, 2, 5 (exposed 42 days) and 10 mg Se L (survived 7-21 days). The addition of 1 mg Se L did not negatively affect photochemical efficiency whilst respiratory potential increased in weeks 2-4 compared to control. The addition of 1 mg Se(IV) L increased the amount of chlorophyll a in weeks 3 and 4 and the amount of carotenoids in weeks 1, 3 and 5. Concentrations of 2 and 5 mg Se L negatively affected photochemical efficiency in weeks 3 and 4, and increased respiratory potential in comparison to the control in weeks 1-4, whilst beyond week 4, the respiratory potential decreased. Plants exposed to the highest concentration of Se(IV) had to be replaced twice during the experiment because they were dying. That was reflected in photochemical efficiency as well as in respiratory potential, which decreased in time. The content of Se in duckweed increased with the increasing concentration of Se: plants growing in 0.5 mg Se L contained 0.9 mg Se g DM and plants exposed to 5 mg Se L contained 5.8 mg Se g DM. The group of plants exposed to 10 mg Se L for 21 days contained 19.5 mg Se g DM. Our study revealed that duckweed absorbed high amount of Se(IV) from the water. [ABSTRACT FROM AUTHOR]

In harsh environments facilitation alleviates biotic and abiotic constraints on tree recruitment. Under ongoing drier climate change, we expect facilitation to increase as a driver of coexistence. However, this might not hold under extreme abiotic stress and when the outcome depends on the interaction with other drivers such as altered herbivore pressure due to land use change. We performed a field water-manipulation experiment to quantify the importance of facilitation in two coexisting Mediterranean trees (dominant Juniperus thurifera and coexisting Quercus ilex subsp. ballota) under a climate change scenario. Shifts in canopy dominance favouring Q. ilex could be based on the extension of heterospecific facilitation to the detriment of conspecific alleviation. We found that saplings of both species transplanted under the canopy of nurse trees had greater survival probability, growth and photochemical efficiency. Intra- and interspecific facilitation mechanisms differed: alleviation of abiotic stress benefited both species during summer and J. thurifera during winter, whereas browsing protection was relevant only for Q. ilex. Facilitation was greater under the dry treatment only for Q. ilex, which partially agreed with the predictions of the stress gradient hypothesis. We conclude that present rainfall availability limits neither J. thurifera nor Q. ilex establishment. Nevertheless, under current global change scenarios, imposing increasing abiotic stress together with altered herbivore browsing, nurse trees could differentially facilitate the establishment of Q. ilex due to species-specific traits, i.e. palatability; drought, heat and cold tolerance, underlying species differences in the facilitation mechanisms and eventually triggering a change from pure juniper woodlands to mixed formations. [ABSTRACT FROM AUTHOR]

• Higher sensitivity of microcystin producer to hydrogen peroxide and light stress. • Efficiency to repair photodamage is genotype-dependant. • Variations of microcystin quotas appear as a consequence of photosynthetic activity. The increasing incidence of cyanobacterial blooms with their associated production of cyanotoxins lead managers of aquatics systems to control their biomass to limit the health risk. Among the variety of existing treatment approaches, hydrogen peroxide (H 2 O 2) shows increasing use but the effects of environmental parameters on its effectiveness are still not completely known. With the aim to assess the efficiency of H 2 O 2 treatments in the control of cyanobacterial blooms and decrease toxic risk, we tested three Microcystis strains according to their ability to produce cyanotoxins (a microcystin-producing, non-microcystin-producing and mcyB- knockout mutant). Photochemical efficiency, percentage of living cells and microcystin cell content were compared under various hydrogen peroxide concentrations coupled with stress conditions encountered during the life cycle of cyanobacteria as darkness and high light. The microcystin-producing strain appeared the more sensitive to hydrogen peroxide treatment and to light condition, probably due to a lower rate of repair of Photo System II (PSII). We also highlighted various responses of PSII activity according to Microcystis strains which could partly explain the shift of dominant genotypes often occurring during a bloom event. Our results confirm the link between light and microcystin content and variations of microcystin contents appear as a consequence of photosynthetic activity. These findings could be of particular interest regarding water quality management, especially the use of H 2 O 2 as a potential algaecide which seems to be more effective to use during periods of high light. [ABSTRACT FROM AUTHOR]

Cool-season creeping bentgrass (Agrostis stolonifera) has the ability to form fine sports turf, but high temperatures result in summer bentgrass decline (SBD), especially in transitional and subtropical zones. Physiological responses in combination with the alteration in turf quality (TQ) will contribute to a better understanding of SBD in a subtropical zone. Field experiments were conducted from 2017 to 2019 to test the adaptability to summer stress among four cultivars (13M, Penncross, Seaside II, and PA-1). A constant ambient high temperature above 30 °C significantly decreased the TQ of the four cultivars during the summer months in 2017, 2018, and 2019. Significant declines in the chlorophyll content, photochemical efficiency of photosystem II (Fv/Fm and PIABS), leaf relative water content (RWC), and osmotic potential (OP) were induced by summer stress, whereas gradual increases in water-soluble carbohydrates, proline, hydrogen peroxide (H2O2), malondialdehyde (MDA), and electrolyte leakage (EL) were observed in the four cultivars during the summer months. The 13M and Penncross cultivars exhibited better performance than Seaside II and PA-1 in response to summer stress from 2017 to 2019, which is associated with better maintenance of photosynthesis, water status, WSC and proline accumulation, and cell membrane stability. The 13M and Penncross cultivars could be used as potential candidates for turf establishment in a subtropical zone. Physiological responses together with alterations in TQ also provided critical information for the breeding and development of germplasm with heat tolerance in creeping bentgrass species. [ABSTRACT FROM AUTHOR]

Following the theory on costs of reproduction, sexually dimorphic plants may exhibit several trade-offs in energy and resources that can determine gender dimorphism in morphological or physiological traits, especially during the reproductive period. In this study we assess whether the sexes of the dioecious species Empetrum rubrum differ in morphological and ecophysiological traits related to water economy and photochemical efficiency and whether these differences change in nearby populations with contrasting plant communities. We conducted physiological, morphological, sex ratio, and cover measurements in E. rubrum plants in the Magellanic steppe, North-Eastern part of Tierra del Fuego (Argentina), from two types of heathlands with differing community composition. We found differences between sites in soil pH and wind speed at the canopy level. E. rubrum plants exhibited lower photosynthetic height and higher LAI (leaf area index), lower RWC (relative water content) and higher water-use efficiency (lower Δ 13 C) in the heathland with harsher environmental conditions. Gender dimorphism in the physiological response was patent for photochemical efficiency and water use (RWC and Δ 13 C discrimination), with males showing a more conservative strategy in relation to females. Accordingly, male-biased sex ratio in the stress-prone community suggested a better performance of male plants under stressful environmental conditions. The integrated analysis of all variables (photochemical efficiency, RWC, leaf dry matter content (LDMC), pigments, and Δ 13 C) indicated an interaction between gender and heathland community effects in the physiological response. We suggest that female plants may exhibit compensatory mechanisms to face their higher reproductive costs. [ABSTRACT FROM AUTHOR]

The effects of irrigation and planting pattern on wheat in field conducted at Taian, northern China during 2011-12. The experiments consisted of two planting patterns (single and double rows) and two irrigation levels (0 and 180 mm) resulting in the same plant density (200 × 104 plant/ha). Each experiment plot was 3 m × 3 m in size and replicated thrice in split-plot design. During course of study net photosynthetic rate, H2O conductance, transpiration rate, and maximum photochemical efficiency of flag leaves and grain yield of winter wheat were recorded. At the maturity stage, the net photosynthetic rate of the plants grown in a double-row planting pattern was higher than that of the plants grown in a single-row planting pattern without irrigation. H2O conductance and transpiration rate of plants in the double-row planting pattern were higher than those grown in the single-row planting pattern without and with irrigation. The double-row planting pattern exhibited higher capacity utilization to high light and higher resistivity to photo inhibition than the single-row planting pattern. The spike number per square meter of the double-row planting pattern was higher than that of the single-row planting pattern under the same water treatment. The 1000-kernel weight of the non-irrigated plants grown in the double-row planting pattern was higher than that in the single-row planting pattern. Hence, the double-row planting pattern improved the photosynthetic capacity of winter wheat under water stress (non-irrigated plants). [ABSTRACT FROM AUTHOR]

The role of exogenously applied Methyl jasmonate (MeJA) in morphological responses, photochemical efficiency, changes of malondialdehyde content, and the activities of some antioxidant enzymes were investigated in four Iranian grapevine cultivars. MeJA improved morphological traits containing dry and fresh weight, node number, and shoot length. MeJA induced an oxidative stress, as shown by an increase in lipid peroxidation. Activities of catalase, peroxidase, and ascorbate peroxidase were higher in MeJA-treated grapevines than in controls while the relative water content and leaf water loss of grapevine cultivars demonstrated a non-significant difference between the control and varying levels of MeJA. MeJA was positively affected in recovery of the leaf chlorophyll fluorescence (photochemical efficiency) of grapevine cultivars, although the mean proline content of MeJA-treated grapevines indicated a significant decrease when compared with those of the controls. These results suggest that MeJA could act as an intervener in grapevine responses by the enhancing the activity of antioxidants and recovery of photochemical efficiency, leading to enhanced grapevine performance. [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]

Photoinhibition in leaves in response to high and/or excess light, consisting of a decrease in photosynthesis and/or photosynthetic efficiency, is frequently equated to photodamage and often invoked as being responsible for decreased plant growth and productivity. However, a review of the literature reveals that photoinhibited leaves characterized for foliar carbohydrate levels were invariably found to possess high levels of sugars and starch. We propose that photoinhibition should be placed in the context of whole-plant source-sink regulation of photosynthesis. Photoinhibition may represent downregulation of the photosynthetic apparatus in response to excess light when (1) more sugar is produced in leaves than can be utilized by the rest of the plant and/or (2) more light energy is harvested than can be utilized by the chloroplast for the fixation of carbon dioxide into sugars. [ABSTRACT FROM AUTHOR]

Two submersed macrophytes (Ceratophyllum demersum and Myriophyl- lum spicatum) were exposed to water containing 10 mg Se(IV) L–1, later transferred to water without Se and exposed again to 10 mg Se(IV) L–1 with the aim to observe the recovery of plants. After each transplantation trial, potential photochemical efficiency of photosystem II, respiratory potential and the amount of photosynthethic pigments and anthocyanins were measured. Photochemical efficiency was similar in all three trials. Electron transport system (ETS) activity increased dramatically in C. demersum plants that were transferred from the water with Se to the water without Se, while ETS activity strongly increased in M. spicatum specimens, when the second time transferred to water containing Se. Alternation in the concentration of Se in the growth media demanded metabolic changes in studied plants. The amount of chlorophylls was higher in plants of M. spicatum growing in water without Se than in exposed plants, while the amount of carotenoids and anthocyanins decreased in the same species grew in water without Se. The amount of Se was higher in plants exposed to Se, while plants that grew in water without Se had lower amount of Se in the tissues.

• Reduction of CHL concentration in leaves did not affect the number of papaya fruits per plant. • Dark-green papaya leaves had reduced number of fruits under water stress. • The ψ soil of around −38 kPa can be considered as a threshold for papaya irrigation at studied soil type. • -Pale-green papaya genotypes had an increased agronomic water use efficiency. • -Pale-green papaya genotypes can have potential use as an alternative to mitigate the effects of water stress. In the context of increasing drought frequencies, water sensitive plant species need to have defined irrigation thresholds. One such species is papaya (Carica papaya L.), with a current demand for the selection of drought tolerance genotypes. The aim of this study was to evaluate the growth, leaf gas exchanges, sap flow and chlorophyll (Chl) fluorescence in two papaya genotypes (pale-green leaf 'Golden' - G and dark-green leaf 'Aliança' – AL) under soil water deficit (Ψ soil) conditions. The experiments were carried out in the field, in an unconsolidated alluvial sediment soil type. The two papaya genotypes, contrasting in their leaf Chl contents, were grown under irrigated (I, Ψ soil of -12 kPa), and non-irrigated (NI, Ψ soil gradually diminished from - 23 to -311 kPa) conditions for 41 days. Leaf gas exchanges, xylem sap-flow, green intensity (SPAD index), plant height, trunk diameter and leaf area were measured five times, following Ψ soil decreases. At the lowest Ψ soil (-311 kPa), the Chl photochemistry and fruit number measurements were performed. Intrinsic water use efficiency was higher in the G NI than in the AL NI genotype. Leaf temperature and photochemical efficiency was not affected by soil water restrictions in G NI and AL NI. The water deficit effect on growth traits was linked to whole canopy assimilation, due to the higher leaf area in AL I than G I , or in AL NI than in G NI , once the leaf assimilation rate was similar between those treatments. The ψ soil of ca. -30 kPa can be considered as a threshold for papaya irrigation for the soil type studied here. Soil water stress did not affect the number of fruits in G NI , whilst this was reduced by 83% in AL NI compared to irrigated plants, indicating that pale-green leaf papaya genotypes are an alternative to cope with water stress. [ABSTRACT FROM AUTHOR]

Greenhouse production of baby leaf vegetables grown in hydroponic floating trays has become extremely popular in recent years. Rocket (Eruca sativa Mill.) can grow in temperatures varying between 10 and 20 °C; nevertheless, a root-zone temperature (RZT) range of 18–23 °C is considered optimal for high productivity, photosynthesis, and production of metabolites. Maintaining such temperatures in winter raises production costs and prevents sustainability. In this study, we tested the impact of lower RZT on plants' status and recorded their responses while providing energy for heating using photovoltaic solar panels. We used three hydroponic tanks for cultivation; a non-heated (control) tank (12 °C) and two heated tanks; a solar panel-powered one (16 °C) and a public grid-powered one (22 °C). Methylation-sensitive amplified polymorphisms (MSAP) analysis of global methylation profiles and chlorophyll fluorescence analysis were employed to assess methylation and physiology levels of rocket leaves. We found that there is demethylation at 16 °C RZT in comparison to 22 °C RZT. Reduction of temperature at 12 °C did not reduce methylation levels further but rather increased them. Furthermore, at 16 °C, the effective quantum yield of photosystem II (PSII) photochemistry (ΦPSII) was significantly higher, with a higher PSII electron transport rate (ETR) and a significantly decreased non-regulated energy loss (ΦΝO), suggesting a better light energy use by rocket plants with higher photosynthetic performance. ΦPSII was significantly negatively correlated with DNA methylation levels. Our results show that at 16 °C RZT, where plants grow efficiently without being affected by the cold, DNA methylation and photosynthesis apparatus systems are altered. These findings corroborate previous results where hydroponic production of rocket at RZT of 16 °C is accompanied by sufficient yield showing that rocket can effectively grow in suboptimal yet sustainable root-zone temperatures. [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]

The effect of variable temperatures (10-50 °C) on photosynthesis and chlorophyll fluorescence in Conocarpus lancifolius was evaluated. Additionally, the ability of the species to synthesize heat-shock proteins (HSPs) to protect against high temperatures, and malondialdehyde (MDA) as a by-product of lipid peroxidation was investigated. Plants at 10 °C showed virtually no measurable growth, leaf discoloration and a few brown lesions, while high temperatures (40 and 50 °C) promoted growth and lateral branch development. Chlorophyll content index, photochemical efficiency ( F/ F) of PS II, electron transport rate and photosynthetic rate declined with decreasing temperature but increased significantly at higher temperatures. Heat-shock protein (HSP 70 kDa) was produced at temperatures 30-50 °C and an additional 90 kDa protein was also produced at 50 °C. Increase in the efficiency of excitation energy captured by the open PS II reaction centers ( F/ F) increased linearly ( P ≤ 0.05) with the accumulation of HSP 70 at higher temperatures. However, at low temperatures the concentration of MDA increased significantly, indicating lipid peroxidation due to oxidative stress. The production and accumulation of HSP 70 and 90 kDa coupled with increased electron transport rate and photochemical efficiency can be used to assess survival, growth capacity and to some extent the tolerance of C. lancifolius to elevated temperatures. [ABSTRACT FROM AUTHOR]

Abstract: The uptake of Se(IV) by Myriophyllum spicatum, Ceratophyllum demersum and Potamogeton perfoliatus, and the effects of Se(IV) on their physiological and biochemical characteristics were studied. Plants were cultivated outdoors under semi-controlled conditions in water solution containing Na selenite (20μgSeL−1 and 10mgSeL−1). The higher concentration of Se lowered the photochemical efficiency of PSII in all species studied, while the lower concentration had no effect on any species. The higher concentration of Se lowered respiratory potential in M. spicatum. The response of M. spicatum and C. demersum to Se(IV) regarding chlorophylls was variable, however in the majority of cases, there was a trend of increasing the amount of chlorophylls, while in P. perfoliatus the amount of chlorophyll a decreased. The concentration of Se in plants cultured in 10mgSe(IV)L−1 ranged from 436 to 839μgSeg−1 DM in M. spicatum, 319 to 988μgSeg−1 DM in C. demersum and 310 to 661μgSeg−1 DM in P. perfoliatus. The amount of soluble Se compounds in enzyme extracts of high Se treatment was 27% in M. spicatum, 41% in C. demersum and 35% in P. perfoliatus. Se compounds were determined using HPLC–ICP-MS. It was observed that the applied Se(IV) was mainly transformed to insoluble Se. [Copyright &y& Elsevier]

Abstract: Patterns of intraspecific variation in functional traits have been widely studied across plant species to find out what general suites of traits provide functional advantage under specific environmental conditions. Much less is known about this variation within tree species and, in particular, about its relationship with performance variables such as photosynthetic rates under water deficit. Nevertheless, this knowledge is fundamental to understand the adaptive potential of drought sensitive tree species to increased aridity as predicted in the context of climate change. Intraspecific variation in photosynthetic performance and other leaf functional traits in response to water availability were examined in a glasshouse experiment using seedlings of six European beech populations. The physiological response of seedlings to a “water stress” treatment was compared to a “control” treatment along an experimental cycle of progressive soil water deficit and recovery. We found evidence of intraspecific variation in beech''s photosynthetic performance and other leaf functional traits in response to water availability. We also detected intraspecific variation in leaf-level tolerance of water deficit and phenotypic plasticity to water availability suggesting a pattern shaped by both regional and local scale effects. The Swedish population was particularly sensitive to water deficit, being the only population showing impaired photochemical efficiency under the experimental water deficit. Leaf-level tolerance of water deficit was related to PNUE, but not to other functional traits, such as WUE, SLA or leaf nitrogen content, that have been described to vary across species in adaptation to drought tolerance. Our results support the idea that general trends for variation in functional traits across species do not necessarily reflect a similar pattern when observed at the intraspecific level. The observed functional variation between beech populations reaffirms the importance of local adaptation to water deficit in the context of climate change. [Copyright &y& Elsevier]

Porphyra katadai Miura var. hemiphylla Tseng & T.J. Chang, a native species of China, is monoecious with female and male parts in distinct halves separated by a longitudinal line in the blades, and photosynthetic characteristics and pigment contents were compared among different tissues. Female parts contained significantly more phycobiliprotein and carotenoids than male parts did, accompanied by higher photochemical efficiency of photosystem II than the latter. Vegetative tissues had more pigments and higher Δ F/ F′ and F/ F than their respective reproductive tissues, and male reproductive tissues even exhibited lower P based on oxygen evolution than their vegetative tissues at 5-10 °C. Female vegetative tissues showed the highest Δ F/ F′ among all tissues, while male reproductive tissues had the lowest P at low temperatures and the lowest pigment contents. Photosynthesis rates reached the highest values at 10 °C and the lowest values at 20 °C in most tissues, but male reproductive tissues exhibited the best performances at 20 °C, which rarely happened in its natural habitats and growth season. Thus growth capacity and response to seasonal temperature change varied not only between vegetative and reproductive tissues but also between female and male tissues in P. katadai var. hemiphylla, accompanied by their different color and size on wild plants. [ABSTRACT FROM AUTHOR]

Abstract: The effects of exogenous spermine (Spm) on plant growth, chlorophyll fluorescence, ultrastructure and anti-oxidative metabolism of chloroplasts were investigated in Cucumis sativus L. under NaCl stress. Salt stress significantly reduced plant growth, chlorophylls content and F v/F m. These changes could be alleviated by foliar spraying with Spm. Salt stress caused an increase in malondialdehyde (MDA) content and superoxide anion generation rate in chloroplasts. Application of Spm significantly increased activities of superoxidase dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), and ascorbate peroxidase (APX, EC 1.11.1.11) which decreased the levels of and MDA in the salt-stressed chloroplasts. Salt stress decreased the activities of dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2) in the chloroplasts and reduced the contents of dehydroascorbate (DAsA) and glutathione (GSH), but increased monodehydroascorbate reductase (MDAR, EC 1.6.5.4) activity. On the other hand, Spm significantly increased the activities of antioxidant enzymes and levels of antioxidants in the salt-stressed chloroplasts. Further analysis of the ultrastructure of chloroplasts indicated that salinity induced destruction of the chloroplast envelope and increased the number of plastoglobuli with aberrations in thylakoid membranes. However, Spm application to salt-stressed plant leaves counteracted the adverse effects of salinity on the structure of the photosynthetic apparatus. These results suggest that Spm alleviates salt-induced oxidative stress through regulating antioxidant systems in chloroplasts of cucumber seedlings, which is associated with an improvement of the photochemical efficiency of PSII. [Copyright &y& Elsevier]

Abstract: To investigate the impact of Se on Tartary buckwheat (Fagopyrum tataricum Gaertn.) plants, the plant foliage was sprayed with 10 mg Se(VI) L−1 at the beginning of flowering. The Se was effectively assimilated by the plants and taken into the seeds, where its concentration was more than double that in untreated plants. The seeds were collected and sown to obtain the progeny of these Se-treated plants. To assess the physiological characteristics of control plants and these Se-treated progeny plants, the estimated respiratory potential via electron transport system (ETS) activity and the photochemical efficiency of photosystem II were measured. Three weeks after germination, the Se-treated progeny plants showed higher ETS activity compared to the controls. Through weeks 4 and 5, this high ETS activity approximately halved, and the difference in ETS activity seen at 3 weeks was lost. On the other hand, at week 4, the potential photochemical efficiency was higher in the Se-treated progeny plants than the controls. In adult plants, the leaves dry mass was significantly greater in the Se-treated progeny plants than the controls. This study demonstrates an impact of Se in Tartary buckwheat on the progeny plants of Se sprayed plants, as shown previously in pea plants. [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]

Abstract: Phytoplankton and bacterioplankton dynamics were studied around South Shetland Islands (Antarctica) with special emphasis on the Drake Passage region, during austral summer, in order to expand our knowledge on the coupling between the autotrophic and heterotrophic microbial plankton compartments in polar ecosystems. In addition, we directly estimated bacterial growth efficiency in the Drake Passage with the aim of better constraining total bacterial carbon utilization in this important polar ecosystem. Integrated chlorophyll-a concentration (21–86mgm−2), primary production rates (0.7–19.3mgCm−3 d−1) and mean water-column photochemical efficiency (0.24–0.60) were significantly correlated with Si⁎ tracer (r 2=0.55, 0.46 and 0.64, respectively), which indirectly points to iron as the major limiting factor for phytoplankton growth in the area. Bacterial production was considerably low (0.002–0.3mgCm−3 d−1) and was best explained by chlorophyll-a concentration, protein-like fluorescence of dissolved organic matter and temperature (r 2=0.53, p<0.001). Water temperature appeared to influence bacterial activity when organic substrate availability is high. Bacterial production accounted on average for only 3.9% of co-occurring primary production, which has been frequently interpreted as an indicator of the marked uncoupling between bacteria and phytoplankton in cold waters. However, using the experimentally derived mean bacterial growth efficiency for the photic zone (6.1±1.3%) the bacterial carbon demand represented on average 63±18% of concomitant primary production, similar to what is found in warmer productive waters. Thus, our study suggests that bacterioplankton and phytoplankton appear to be connected in this polar area. [Copyright &y& Elsevier]