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Cold-stressed leaves possess an elevated risk of photodamage due to an inefficient photosynthetic apparatus during winter conditions. Recovery of cold-stressed coffee seedlings treated with different concentrations of nitrogen applied as foliar urea sprays [control (0), 5, 10, 20, and 40 mM], was investigated under optimum growth chamber conditions (25/20°C) for three months. Concentrations of nitrogen and photosynthetic pigments in the leaves increased with increasing concentration of the foliar sprays up to 20 mM. This was accompanied with a recovery of the photosynthetic apparatus and increased net carbon assimilation rate. In addition, 10 and 20 mM-treated plants also had the highest maximal efficiency of PSII compared to their lower or higher nitrogen concentration treated counterparts. Conversely, these plants contained lower concentrations of 5-caffeoylquinic acid, mangiferin, trigonelline, and caffeine than control plants. We concluded therefore that foliar sprays of the appropriate nitrogen concentration were adequate for recuperating the photosynthetic apparatus and improved the photosynthetic performance of the cold-stressed coffee seedlings.

The aim of the work was to investigate thermal stress effect on photosynthetic activity of common buckwheat. Seedlings of common buckwheat were exposed to 20°C (control) and 30°C (thermal stress). The research involved the Polish cultivar 'Panda' and strain PA15 and determined kinetics of chlorophyll a fluorescence (Chlf), leaf gas exchange, soluble carbohydrate (SC) content in donor leaves, electrolyte leakage as a parameter of cell membrane permeability, and amount of abscisic acid and jasmonates. In 'Panda' and PA15 plants grown at 30°C, most of Chlf parameters improved. 'Panda' plants grown at 30°C demonstrated a higher increase in net photosynthetic rate, lower transpiration rate, and smaller SC reduction than those of PA15 strain. At this temperature, 'Panda' leaves accumulated greater amounts of jasmonates than that of the control. We concluded that studied genotypes demonstrated disparate responses to thermal stress, but for both, 30°C is more favourable temperature for vegetative growth than 20°C.

Cold-stressed leaves possess an elevated risk of photodamage due to an inefficient photosynthetic apparatus during winter conditions. Recovery of cold-stressed coffee seedlings treated with different concentrations of nitrogen applied as foliar urea sprays [control (0), 5, 10, 20, and 40 mM], was investigated under optimum growth chamber conditions (25/20°C) for three months. Concentrations of nitrogen and photosynthetic pigments in the leaves increased with increasing concentration of the foliar sprays up to 20 mM. This was accompanied with a recovery of the photosynthetic apparatus and increased net carbon assimilation rate. In addition, 10 and 20 mM-treated plants also had the highest maximal efficiency of PSII compared to their lower or higher nitrogen concentration treated counterparts. Conversely, these plants contained lower concentrations of 5-caffeoylquinic acid, mangiferin, trigonelline, and caffeine than control plants. We concluded therefore that foliar sprays of the appropriate nitrogen concentration were adequate for recuperating the photosynthetic apparatus and improved the photosynthetic performance of the cold-stressed coffee seedlings. [ABSTRACT FROM AUTHOR]

The aim of the work was to investigate thermal stress effect on photosynthetic activity of common buckwheat. Seedlings of common buckwheat were exposed to 20°C (control) and 30°C (thermal stress). The research involved the Polish cultivar 'Panda' and strain PA15 and determined kinetics of chlorophyll a fluorescence (Chlf), leaf gas exchange, soluble carbohydrate (SC) content in donor leaves, electrolyte leakage as a parameter of cell membrane permeability, and amount of abscisic acid and jasmonates. In 'Panda' and PA15 plants grown at 30°C, most of Chlf parameters improved. 'Panda' plants grown at 30°C demonstrated a higher increase in net photosynthetic rate, lower transpiration rate, and smaller SC reduction than those of PA15 strain. At this temperature, 'Panda' leaves accumulated greater amounts of jasmonates than that of the control. We concluded that studied genotypes demonstrated disparate responses to thermal stress, but for both, 30°C is more favourable temperature for vegetative growth than 20°C. [ABSTRACT FROM AUTHOR]

Seedlings of Chrysanthemum, cultivar 'Puma Sunny', were grown under a range of shading regimes (natural full sunlight, 55, 25, and 15% of full sunlight) for 18 days. Here, we characterized effects of varying light regimes on plant morphology, photosynthesis, chlorophyll fluorescence, anatomical traits, and chloroplast ultrastructure. We showed that leaf color was yellowish-green under full sunlight. Leaf area, internode length, and petiole length of plants were the largest under 15% irradiance. Net photosynthetic rate, water-use efficiency, PSII quantum efficiency, and starch grain were reduced with decreasing irradiance from 100 to 15%. Heavy shading resulted in the partial closure of PSII reaction centers and the CO assimilation was restricted. The results showed the leaves of plants were thinner under 25 and 15% irradiance with loose palisade tissue and irregularly arranged spongy mesophyll cells, while the plants grown under full sunlight showed the most compact leaf palisade parenchyma. Irradiance lesser than 25% of full sunlight reduced carbon assimilation and led to limited plant growth. Approximately 55% irradiance was suggested to be the optimal for Chrysanthemum morifolium. [ABSTRACT FROM AUTHOR]

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]

Globally, water deficit is one of the major constraints in chickpea ( Cicer arietinum L.) production due to substantial reduction in photosynthesis. Photorespiration often enhances under stress thereby protecting the photosynthetic apparatus from photoinhibition. Application of bioregulators is an alternative to counter adverse effects of water stress. Thus, in order to analyze the role of bioregulators in protecting the photosynthetic machinery under water stress, we performed an experiment with two contrasting chickpea varieties, i.e., Pusa 362 (Desi type) and Pusa 1108 (Kabuli type). Water deficit stress was imposed at the vegetative stage by withholding water. Just prior to exposure to water stress, plants were pretreated with thiourea (1,000 mg L), benzyladenine (40 mg L), and thidiazuron (10 mg L). Imposed water deficit decreased relative water content (RWC), photosynthetic rate ( P ), quantum efficiency of PSII (F/F), and enhanced lipid peroxidation (LPO). However, bioregulator application maintained higher RWC, P , F/F, and lowered LPO under water stress. Expression of Rubisco large subunit gene ( RbcL) was low under water stress both in the Kabuli and Desi type. However, bioregulators strongly induced its expression. Although poor expression of two important photorespiratory genes, i.e., glycolate oxidase and glycine decarboxylase H subunit, was observed in Desi chickpea under imposed stress, bioregulators in general and cytokinins in particular strongly induced their expression. This depicts that the application of bioregulators protected the photosynthetic machinery by inducing the expression of RbcL and photorespiratory genes during water deficit stress. [ABSTRACT FROM AUTHOR]

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]

The use of black leaf-clips for dark adaptation under high solar radiation conditions is reported to underestimate the maximum quantum yield of PSII photochemistry (F/F) measured by the continuous-excitation fluorometer Pocket PEA. The decrease in F/F was due to a rise in minimum fluorescence emission (F), probably resulting from increased leaf temperature (T). In field-grown tomato and pepper, fluorescence parameters and T in the region covered by the black leaf clip were measured in clipped leaves exposed to solar radiation during dark adaptation (clipped-only leaves) and in clipped leaves protected from solar radiation by aluminium foil (shrouded clipped leaves). Results confirmed significant F/F underestimates in clipped-only leaves primarily due to increased F. In one tomato experiment, T increased from 30 to 44.5°C in clipped-only leaves, with a negligible rise in shrouded clipped leaves. In two respective pepper experiments, T in clipped-only leaves increased from 27 to 36.2°C and 33 to 40.9°C. Based on the results of this study, a clip-effect parameter (P) on fluorescence emission is proposed as the difference for F/F (or −F/F) between shrouded clipped leaves and clipped-only leaves, which resulted to be 0.706 for tomato, and 0.241 and 0.358 for the two pepper experiments. [ABSTRACT FROM AUTHOR]

In the pursuit of knowledge on the biological behavior of Brazilian Atlantic Forest tree species, this study evaluated the susceptibility of the light-demanding species, Schinus terebinthifolia Raddi., Pseudobombax grandiflorum (Cav.) A. Robyns and Joannesia princeps Vell., and of the shade-tolerant species, Hymenaea courbaril L. var. stilbocarpa and Lecythis pisonis Camb, to photoinhibition and acclimation capacity. These species were first cultivated under two irradiance conditions, I (20% direct sunlight radiation) and I (all-sky or direct sunlight) and then transferred from I to I. The effects of the sudden increase in light radiation intensity on photosynthetic activity were then evaluated through chlorophyll (Chl) fluorescence imaging, HPLC xanthophylls analysis, and cell membrane lipid peroxidation measurements. Light-demanding species were found to present a higher photochemical efficiency and higher acclimation capacity under high light irradiance than shade-tolerant species. The higher photoinhibition tolerance observed in light-demanding species was associated to their higher capacity for photochemical dissipation and dissipation of excess excitation energy via the xanthophyll cycle, leading to a lower ROS generation. The obtained results suggested that a knowledge of acclimation capacity, by means of Chl fluorescence imaging yields, is a useful indicator of species successional grouping. [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]

Tomato and pepper leaves were clipped with black leaf clips for dark adaptation under solar radiation in the late spring or early summer 2010 in southern Italy. The leaves showed highly variable maximum PSII quantum yield (F/F = 0.026−0.802) using a continuous-excitation fluorometer Pocket PEA. These results were confirmed using the modulated fluorometer FMS1 on tomato leaves in mid summer, with F/F as low as 0.222 ± 0.277 due to nearly equal minimum (F) and maximum (F) fluorescence emission. A significant clip effect on F/F occurred after only 12 (tomato) or 25 (pepper) min. Increasing the leaf temperature from 25 to 50°C reportedly induced an F increase and Fm decrease so that F/F approached zero. The hypothesis that black leaf clips overheated under intense solar irradiance was verified by shrouding the clipped leaves with aluminum foil. In clipped leaves of pepper, F/F with the black clip/Pocket-PEA was 0.769 ± 0.025 (shrouded) and as low as 0.271 ± 0.163 (nonshrouded), the latter showing a double F and 32% lower F. An 8% clip effect on F/F was observed with the white clip/ FMS1. To avoid the clip effect in high irradiance environments, F/F measurements with black clip/ Pocket PEA system required leaf dark adaptation with radiation-reflecting shrouds. It would be useful if manufacturing companies could develop better radiation-reflecting leaf clips for the Pocket PEA fluorometer. [ABSTRACT FROM AUTHOR]

The present study was conducted to examine changes in photosynthetic pigment composition and functional state of the thylakoid membranes during the individual steps of preparation of samples that are intended for a separation of pigmentprotein complexes by nondenaturing polyacrylamide gel electrophoresis. The thylakoid membranes were isolated from barley leaves ( Hordeum vulgare L.) grown under low irradiance (50 μmol m s). Functional state of the thylakoid membrane preparations was evaluated by determination of the maximal photochemical efficiency of photosystem (PS) II (F/F) and by analysis of excitation and emission spectra of chlorophyll a (Chl a) fluorescence at 77 K. All measurements were done at three phases of preparation of the samples: ( 1) in the suspensions of osmotically-shocked broken chloroplasts, ( 2) thylakoid membranes in extraction buffer containing Tris, glycine, and glycerol and ( 3) thylakoid membranes solubilized with a detergent decyl-β-D-maltosid. F/F was reduced from 0.815 in the first step to 0.723 in the second step and to values close to zero in solubilized membranes. Pigment composition was not pronouncedly changed during preparation of the thylakoid membrane samples. Isolation of thylakoid membranes affected the efficiency of excitation energy transfer within PSII complexes only slightly. Emission and excitation fluorescence spectra of the solubilized membranes resemble spectra of trimers of PSII light-harvesting complexes (LHCII). Despite a disrupted excitation energy transfer from LHCII to PSII antenna core in solubilized membranes, energy transfer from Chl b and carotenoids to emission forms of Chl a within LHCII trimers remained effective. [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]

Two clones of Hevea brasiliensis (RRII 105 and PB 235) were grown for one year in two distinct agroclimatic locations (warmer and colder, W and C) in peninsular India. We simultaneously measured gas exchange and chlorophyll (Chl) fluorescence on fully mature intact leaves at different photosynthetic photon flux densities (PPFDs) and ambient CO2 concentrations ( Ca) and at constant ambient O2 concentration (21 %). Net photosynthetic rate ( PN), apparent quantum yield for CO2 assimilation (Φc), in vivo carboxylation efficiency (CE), and photosystem 2 quantum yield (ΦPS2) were low in plants grown in C climate and these reductions were more predominant in RRII 105 than in PB 235 which was also reflected in their growth. We estimated in these clones the partitioning of photosynthetic electrons between CO2 reduction (JA) and processes other than CO2 reduction (J*) at low and high PPFDs and Ca. At high Ca (700 µmol mol−1) most of the photosynthetic electrons were used for CO2 assimilation and negligible amount went for other processes when PPFD was low (200–300 µmol m−2 s−1) both in the C and W climates. But at high PPFD (900-1 100 µmol m−2 s−1), J* was appreciably high even at a high Ca. Hence at normal ambient Ca and high irradiance, electrons can be generated in the photosynthetic apparatus far in excess of what can be safely utilised for photosynthetic CO2 reduction. However, at high Ca there was increased diversion of electrons to photosynthetic CO2 reduction which resulted in improved photosynthetic parameters even in plants grown in C climate. [ABSTRACT FROM AUTHOR]

To explore the cause of difference in photosynthetic performance between different cultivars of crops, leaf net photosynt rate ( PN) and photosystem 2 (PS2) photochemical efficiency (Fv/Fm), apparent quantum yield of carbon assimilation (φc), electron transport rate, photophosphorylation activity, etc. were measured in two soybean cultivars, Heinong 42 and Heinong 37. At pod setting and filling, significant differences in PN between them were observed. The former with a higher PN (from 7 to 38 %) had a significantly higher leaf thickness, leaf dry mass/area (LMA), chlorophyll content, soluble protein content, apparent quantum yield of electron transport through PS2 (φe), carboxylation efficiency (CE), and ribulose-1,5-bisphosphate carboxylase (RuBPC) activity. The significantly higher PN of Heinong 42 is mainly due to its higher content and activity of RuBPC. [ABSTRACT FROM AUTHOR]

P. juliflora trees produce leaves during two growth periods. The first cohort of leaves is produced during spring in cool conditions, while the second cohort is produced during monsoon under warm conditions. I studied photosynthetic characteristics of young, mature, and old leaves of the previous season (monsoon) in the spring season. Maximum net photosynthetic rate of a young leaf was lower than that of the mature and old leaves. The total CO2 fixed per day by the young leaves was just 36 % of that in the mature leaves while the old leaves fixed 76 % of that of the mature leaf. The total transpiration rate and water use efficiency (WUE) were similar in the mature and old leaves, while they were much lower in the young leaves. Dark respiration rate was maximal in the young leaves as compared to the mature and old leaves. About 92 % of the total CO2 fixed per day were respired by the young leaves. The diurnal fluorescence characteristics (ΔF/Fm′, qp, and qN) of the young, mature, and old leaves showed that photochemical efficiency of photosystem 2 during midday decreased more in the young and old leaves than in the mature ones. However, the fluorescence characteristics showed that in all the three leaf types there was complete recovery of the photochemical efficiency at sunset from the midday depression. Fv/Fm in the young and mature leaves also confirmed this. Hence the young and old leaves were photosynthetically less efficient than mature leaves, but they were well adapted to withstand the harsh environmental conditions. [ABSTRACT FROM AUTHOR]

The effect of two elevated carbon dioxide concentrations, 700 µmol(CO2) mol−1 (C700) and 1 400 µmol(CO2) mol−1 (C1400), on photosynthetic performances of 1-year-old Prunus avium L. plant was studied. Plants grown at C700 were characterised by increased net photosynthetic rate ( PN) as compared to those grown at C1400. Plant photosynthetic adjustment to C1400 resulted in 27 % higher PN than in control at atmospheric CO2 concentration ( Ca) at the beginning of the experiment (3–4 weeks) with a consequent decline to the end of the experiment. Thus, 1 400 µmol(CO2) mol−1 had short-term stimulatory effect on plant PN. Both chlorophyll (Chl) a and b concentrations dramatically decreased during exposure to C1400. Compensation irradiance was increased by 57 % in C700 and by 87 % in C1400. Photochemical efficiency (φ) was affected by balloon environment, however, a clear stimulatory effect of C700 was detected. Opposite influence of both elevated CO2 concentrations on PNmax was established: slight increase by C700 (2.7 % at Ca), but considerable decrease by C1400 (63 % at Ca). Exposure to C700 enhanced compensation irradiance by 42 %, while C1400 by only 21 %. Either C700 or C1400 did not reduce stomatal conductance ( gs). Leaf area per plant (LAR) was more stimulated by C700 than by C1400. High unit area leaf mass, specific leaf area, and dry matter accumulation in roots without affecting tissue density characterised plants grown in C1400. However, when considering the root : shoot ratio, these plants allocated less carbon to the roots than plants from other treatments. [ABSTRACT FROM AUTHOR]

Significant differences in net photosynthetic rate ( PN) of leaves between two maize ( Zea mays L.) strains (Shuang 105 and 40×44) grown in the field were observed. At several growth stages, PN of 40×44 was higher than that of Shuang 105 (from 10.3 to 32.5 %). Moreover, the strain 40×44 had a higher plant height, larger leaf area, lower chlorophyll content, and higher photochemical efficiency of photosystem 2 (PS2) (Fv/Fm and ΔF/Fm′) than strain Shuang 105. Shuang 105, which showed lower PN, had lower stomatal conductances ( gs) but slightly higher intercellular CO2 concentrations ( Ci) than those of 40×44. Hence the differences in PN between the two strains did not result from the difference in gs, but probably from that in light reaction system. [ABSTRACT FROM AUTHOR]

Chlorophyll (Chl) a and Chl b absorbances were determined in extracts from leaves of Citrus aurantium L. using the solvents diethyl ether (100 %), buffered 80 % aqueous acetone, and N,N′-dimethyl formamide (DMF) (99.83 %). The respective standard deviations (σ) and coefficients of variability (CV) were used to establish the errors obtained when using impure solvents. Buffered 80 % aqueous acetone gave an error of 2.1 % for Chl a and 7.1 % for Chl b, while DMF gave errors of 3.5 and 6.7 %, respectively. For current Chl determination we propose a non-abrasive method, which extracts 15 leaf discs (diameter 6 mm) with 10 cm3 of buffered 80 % aqueous acetone or DMF in hermetically sealed flasks during 24 h in darkness at 4 °C. [ABSTRACT FROM AUTHOR]

Photosynthetic parameters were determined in disks from leaves of C. arabica cv. Red Catuaí and C. canephora cv. Kouillou grown in the field. Kouillou showed a relatively higher irradiance requirement for saturating photosynthesis, lower chlorophyll (Chl) content, and higher Chl a/b ratio than Catuaí. Photoinhibition of photosynthesis under bright irradiance was manifested by decreases in maximum photochemical efficiency (evaluated by the variable to maximum fluorescence ratio, Fv/Fm), as a consequence of an increased initial and a quenched maximum fluorescence. Restoration of Fv/Fm following photoinhibition in low irradiance was faster in Kouillou than in Catuaí. Chloramphenicol both accelerated photoinhibition (mainly in Kouillou) and blocked its recovery for at least 190 min in either cultivar. Photosynthetic oxygen evolution under photoinhibitory conditions was decreased by chloramphenicol; in control leaf disks this decrease was only observed in C. arabica, but with a rapid recovery within 90 min of low irradiance exposure. In both coffee cultivars, the depressed photochemical efficiency of photosystem 2 was not accompanied by a concomitant lowering in oxygen evolution during reversal from photoinhibition. [ABSTRACT FROM AUTHOR]