Quantum Yield Of PSII Photochemistry Research Articles

Effect of rain shelters and drought on leaf water status and photosynthetic parameters in tomato

The present study explored the effect of rain shelter and drought on photosynthetic activity and changes in leaf water status. Tomatoes were grown in the trial plot located at Hohai University, China, in 2011 and 2012, and allotted to five treatments [80% field capacity under open field (T1, control) and rain shelter (T2), 70%, 60%, and 50% of T2 (T3, T4, and T5)]. The lowest sap flow rate and relative water content and the highest values for specific leaf area were obtained from plants in T5. T2 decreased the average net photosynthetic rate (PN) by 5.35% compared to the control, although there was no reduction in intercellular CO2 concentration and stomatal conductance. The average reduction of transpiration rate registered under rain shelters was only around 10.2% in both the years. The PN, maximum quantum yield of PSII photochemistry (Fv/Fm) and activity of the water-splitting complex on the donor side of the PSII (Fv/Fo) decreased with irrigation volume. Quenching analyses showed the development of a lower photochemical quenching (qP) in plants under rain shelters, accompanied by the development of a higher nonphotochemical quenching (qN). Drought-stressed tomato exhibited a decrease in qP parallel to an increase in qN.

The importance of blue light for leaf area expansion, development of photosynthetic apparatus, and chloroplast ultrastructure of Cucumis sativus grown under weak light

The objective of this study was to evaluate the significance of blue light (B) in the growth and photosynthetic capacity of cucumber. Gas exchange, chlorophyll (Chl) fluorescence kinetics, chloroplast ultrastructure, and leaf growth were investigated to explore the influence of three different light qualities of light emitting diodes (LEDs) on plant morphogenesis and the development of photosynthetic apparatus in cucumber (Cucumis sativus) leaves from emergence to full expansion under weak light [50 μmol(photon) m-2 s-1]. We found that B could significantly increase the leaf area (LA), shoot elongation, Chl a/b, net photosynthetic rate, and stomatal conductance (g s). In addition, the comparisons of maximal quantum yield of PSII photochemistry and the photosynthetic performance index between B-, W (white light)-, and R (red light)-grown leaves suggested that B was essential for the development of photosynthetic apparatus under weak light. B-grown leaves had the lowest Chl content under weak light, however, they had well-developed chloroplasts with the highest degree of stacked lamellae and the lowest starch accumulation. This could explain to a considerable extent the highest net photosynthetic rate per Chl unit. The results demonstrated that B optimized photosynthetic performance by improving the photosynthetic rate, increasing LA, and prolonging active photosynthesis duration under low irradiance. Therefore B is necessary to ensure healthy development of chloroplasts and highly efficient photosynthetic functions in cucumbers under a weak light environment. More importantly, our study also provided theoretical and technical support for the development of light environmental control technology.

Effect of exogenous 24-epibrassinolide on chlorophyll fluorescence, leaf surface morphology and cellular ultrastructure of grape seedlings (Vitis vinifera L.) under water stress

The effects of 24-epibrassinolide (EBR) on chlorophyll fluorescence, leaf surface morphology and cellular ultrastructure of grape seedlings (Vitis vinifera L.) under water stress were investigated. The grape seedlings were subjected to 10 % (w/v) polyethylene glycol (PEG-6000) and treated with 0.05, 0.10 or 0.20 mg L−1 EBR, respectively. EBR application increased chlorophyll contents, the effective photochemical quantum yield of PSII, maximum photochemical efficiency of PSII, maximal fluorescence and non-photochemical quenching coefficient under water stress in each concentration. Compared with water stress control, higher stomatal density and stomatal length were observed in young leaves under EBR treatments, but not in mature leaves. In-depth analysis of the ultrastructure of leaves indicated that water stress induced disappearance of nucleus, chloroplast swelling, fractured mitochondrial cristae and disorder of thylakoid arrangement both in young leaves and mature leaves. However, EBR application counteracted the detrimental effects of water stress on the structure of the photosynthetic apparatus better in young leaves than in mature leaves. Compared to the other treatments, treatment of 0.10 mg L−1 EBR had best ameliorative effect against water stress. These results suggested that exogenous EBR could alleviate water stress-induced inhibition of photosynthesis on grape possibly through increasing chlorophyll content, lessening the stomatal and non-stomatal limitation of photosynthesis performance.

Monitoring cashew seedlings during interactions with the fungus Lasiodiplodia theobromae using chlorophyll fluorescence imaging

The chlorophyll (Chl) fluorescence imaging technique was applied to cashew seedlings inoculated with the fungus Lasiodiplodia theobromae to assess any disturbances in the photosynthetic apparatus of the plants before the onset of visual symptoms. Two-month-old cashew plants were inoculated with mycelium of L. theobromae isolate Lt19 or Lt32. Dark-adapted and light-acclimated whole plants or previously labelled, single, mature leaf from each plant were evaluated weekly for Chl fluorescence parameters. From 21 to 28 days, inoculation with both isolates resulted in the significantly lower maximal photochemical quantum yield of PSII (Fv/Fm) than those for control samples, decreasing from values of 0.78 to 0.62. In contrast, the time response of the measured fluorescence transient curve from dark-acclimated plants increased in both whole plants and single mature leaves in inoculated plants compared with controls. The Fv/Fm images clearly exhibited photosynthetic perturbations 14 days after inoculation before any visual symptoms appeared. Additionally, decays in the effective quantum yield of PSII photochemistry and photochemical quenching coefficient were also observed over time. However, nonphotochemical quenching increased during the evaluation period. We conclude that Fv/Fm images are the effective way of detecting early metabolic perturbations in the photosynthetic apparatus of cashew seedlings caused by gummosis in both whole plants and single leaves and could be potentially employed in larger-scale screening systems.

Photosynthetic acclimation in shade-developed leaves of Euterpe edulis Mart (Arecaceae) after long-term exposure to high light

To analyze acclimation of Euterpe edulis seedlings to changes in light availability, we transferred three-year-old seedlings cultivated for six months under natural shade understory [≈ 1.3 mol(photon) m−2 d−1] to a forest gap [≈ 25.0 mol(photon) m−2 d−1]. After the transfer, changes in chlorophyll fluorescence and leaf gas-exchange parameters, as well as in the light-response curves of photosynthesis and photosynthetic induction parameters, were analyzed during the following 110 days. Simultaneously measured photosynthetic characteristics in the shaded seedlings grown in understory served as the control. Despite the fact that the understory seedlings were under suboptimal conditions to achieve their light-saturated net photosynthetic rate (PNmax), light-response curves and photosynthetic induction parameters indicated that the species had the low respiration rate and a fast opening of stomata in response to the intermittent occurrence of sunflecks, which exerted a feed-forward stimulation on PNmax. Sudden exposure to high light induced photoinhibition during the first week after the transfer of seedlings to gap, as it was shown by the abrupt decline of the maximal quantum yield of PSII photochemistry (Fv/Fm). The photoinhibition showed the time-dependent dynamics, as the Fv/Fm of the seedlings transferred to the forest gap recovered completely after 110 days. Furthermore, the net photosynthetic rate increased 3.5-fold in relation to priorexposure values. In summary, these data indicated that more than 21 days was required for the shade-acclimated seedlings to recover from photoinhibition and to relax induction photosynthetic limitations following the sudden exposure to high light. Moreover, the species responded very quickly to light availability; it highlights the importance of sunflecks to understory seedlings.

Effect of Ammonium:Nitrate Ratios in the Response of Strawberry to Alkalinity in Hydroponics

Strawberry (Fragaria ananasa) plants were grown in hydroponics in a greenhouse, where the supply of different ammonium (NH4+): nitrate (NO3−) ratios, was investigated to reduce the negative effect of alkalinity in nutrient solutions. The experiment was arranged in factorial combination with two factors, NH4+:NO3− ratios (0%:100%, 25%:75%, 50%:50%, 75%:25%, and 100%:0%) and bicarbonate (0, 25, 50, and 75 mM; NaHCO3). Plants treated with increasing bicarbonate concentrations exhibited significantly inhibited growth. In plants treated with NH4+ and NO3− simultaneously, there was a counteraction of the bicarbonate-induced growth suppression. Sole NO3− application in the presence of high bicarbonate resulted in poor growth and plant death due to high alkalinity. The adverse effect of alkalinity on SPAD values and maximal quantum yield of PSII photochemistry (Fv/Fm) alleviated with increasing proportion of NH4+ in nutrient solutions. The results showed that fruit numbers and yield of strawberry increased with elevation of NH4+ in nutrient solutions.

Variation in leaf photosynthetic response of rice genotypes to post-anthesis water deficit

Variation in the response of six diverse rice genotypes to imposed water stress was investigated in terms of leaf photosynthetic traits and leaf water potential measurements (Ψleaf) during and following a period of water stress. The Ψleaf reduced from 0 days up to 6th day of irrigation deprivation and the reduction in Ψleaf was more pronounced in Swarna and minimum in PA-6201. A gradual recovery in Ψleaf was observed in all the tested varieties after re-irrigation. Similarly, water stress significantly reduced rate of photosynthesis (P N), stomatal conductance (g s), transpiration (E) and internal CO2 concentration (C i). Significant differences were noticed amongst the varieties in their response to water stress. The P N partially recovered in all tested varieties after re-irrigation. Vandana recorded greater recovery (65 %), where as the recovery was only 32 % in Sugandha Samba. Water stress (6 days of irrigation deprivation) significantly decreased the mean Chl a, Chlb, total chlorophyll and total carotenoid content. However, a marginal increase in total chlorophyll was observed under water stress in Vandana and N-22. Water stress had no significant effect on maximum photochemical efficiency (F v/F m) for all the tested varieties. However, in Sugandha Samba and Swarna a significant reduction was noticed. Water stress reduced the efficiency of excitation capture (Φe), in vivo quantum yield of PSII photochemistry (ΦPSI), coefficient of photochemical quenching (qP) and increased the coefficient of non-photochemical quenching (qN). The data on photosynthetic traits and chlorophyll fluorescence parameters indicate that Vandana, N-22, DRR-Dhan-38 and PA-6201 which maintained relatively higher, Ψleaf, P N and g s under water stress and could also maintain high values of photochemical efficiency (Fv/Fm, Φe, ΦPSI and ETR) than Sugandha Samba and Swarna and the genotypic differences in the response of PSII activity could be exploited as traits for the selection of drought tolerant rice genotypes.

Effects of NaCl stress on the growth and photosynthetic characteristics of Ulmus pumila L. seedlings in sand culture

The effects of NaCl stress on the growth and photosynthetic characters of Ulmus pumila L. seedlings were investigated under sand culture condition. With increasing NaCl concentration, main stem height, branch number, leaf number, and leaf area declined, while Na+ content and the Na+/K+ ratio in both expanded and expanding leaves increased. Na+ content was significantly higher in expanded leaves than in those just expanding. Chlorophyll (Chl) a and Chl b contents declined as NaCl concentration increased. The net photosynthetic rate, intercellular CO2 concentration, stomatal conductance, and transpiration rate also declined, but stomatal limitation value increased as NaCl concentration increased. Both the maximal quantum yield of PSII photochemistry and the effective quantum yield of PSII photochemistry declined as NaCl concentration rose. These results suggest that the accumulation of Na+ in already expanded leaves might reduce damage to the expanding leaves and help U. pumila endure high salinity. The reduced photosynthesis in response to salt stress was mainly caused by stomatal limitation.

Effect of soil water availability on photosynthesis in Ziziphus jujuba var. spinosus in a sand habitat formed from seashells: Comparison of four models

The photosynthetic and chlorophyll fluorescence parameters were studied in Ziziphus jujuba var. spinosus under different soil water gradients obtained by irrigation and natural water consumption. We used the rectangular hyperbola model, the nonrectangular hyperbola model, the exponential model, and the modified rectangular hyperbola model to fit our data and evaluate them quantitatively. Based on the relationship among the parameters, the effects of the availability of soil water on photosynthesis were elucidated. The results showed that: (1) The relationship between water content and photosynthetic parameters were fitted best by the modified rectangular hyperbola model, followed by the nonrectangular hyperbola model, the exponential model, and the rectangular hyperbola model. The modified rectangular hyperbola model fitted best the maximum net photosynthetic rate (P Nmax) and the light-saturation point (LSP), while the nonrectangular hyperbola model fitted best the dark respiration rate (R D), the apparent quantum yield (AQY), and the light-compensation point (LCP). (2) The main reason for the net photosynthetic rate (P N) decline was that it reached a stomatal limit when the soil relative water content (RWC) was greater than 25% and it reached a nonstomatal limit when the RWC was lesser than 25%. Under these conditions, the photosynthetic apparatus of Z. jujuba was irreversibly damaged. (3) P max, R D, AQY, and LSP increased first and then decreased, while LCP increased contrary to the RWC. The P N light-response parameters reached optimum when the RWC was 56-73%. (4) The quantum yield of PSII photochemistry reached a maximum when RWC was 80%. Nonphotochemical quenching decreased rapidly, and the minimum fluorescence in the dark-adapted state increased rapidly when RWC was lesser than 25%. Under these conditions, PSII was irreversibly damaged. (5) The RWC range of 11-25% resulted in low productivity and low water use efficiency (WUE). The RWC range of 25-56% resulted in moderate productivity and moderate WUE, and the RWC range of 56-80% resulted in high productivity and high WUE. The RWC range of 80-95% resulted in moderate productivity and low WUE. In summary, photosynthesis of Z. jujuba was physiologically adaptable in response to water stress in sand formed from seashells. The photosynthetic and physiological activity was maintained relatively high when the RWC was between 56 and 80%; Z. jujuba seedlings grew well under these conditions.

Characterization of Barley Leaf Tolerance to Drought Stress by Chlorophyll Fluorescence and Electron Paramagnetic Resonance Studies

AbstractTwo kinds of barley genotypes with various water‐stress tolerances, tolerant Cam/B1 and sensitive Maresi, were subjected to 10‐day soil‐drought stress in seedling and flag leaf developmental phases. After this time, both genotypes regardless of the growth stage showed a decrease in quantum yield of PSII photochemistry (ΦPSII) upon stress treatment; however, this effect was stronger in the sensitive plants than in the tolerant ones. The drought stress in the flag leaf stage was associated with an increase in superoxide dismutase (SOD) level in both genotypes, whereas in seedlings, this effect was observed only for Maresi. The activity of other enzymes (catalase and peroxidase) was changed only in small degree. An increase in proline levels and activities of Δ1‐pyrroline‐5‐carboxylate synthetase (P5CS) and ornithine delta‐aminotransferase (OAT) were observed independently of genotype and the phase of plant development, whereas the activity pyruvate dehydrogenase (PDH) decreased in tolerant genotype. Moreover, changes in the concentration of monocarbohydrates (glucose and fructose) and dicarbohydrates (saccharose, raffinose and maltose) were found: in seedlings, the amount of all soluble sugars increased, while in flag leaves decreased. The drought treatment resulted in a drop in starch level in the tolerant genotype, but in the sensitive one, the content of this substance increased in both developmental stages. EPR studies allowed the determination of the amount and character of organic radicals present in leaves. In control conditions, the content of these radical species was higher in the sensitive genotype than in tolerant one and decreased upon water stress, with the exception of flag leaves of the sensitive plant. Simulation procedure revealed four types of signals in the EPR spectra. One of them was attributed to a chlorophyll a cation and decreased upon drought. The second, ascribed to semiquinone radicals, reflected the redox balance disturbed by water deficit. The two remaining signals were connected with carbon‐centred radicals situated in the carbohydrate matrix. Their number was correlated with starch concentration.

Effects of light intensity and temperature on the photosynthetic irradiance response curves and chlorophyll fluorescence in three picocyanobacterial strains of Synechococcus

Chrococcoid cyanobacteria of the genus Synechococcus are the important component of marine and freshwater ecosystems. Picocyanobacteria comprise even 80% of total cyanobacterial biomass and contribute to 50% of total primary cyanobacterial bloom production. Chlorophyll (Chl) fluorescence and photosynthetic light response (P-I) curves are commonly used to characterize photoacclimation of Synechococcus strains. Three brackish, picocyanobacterial strains of Synechococcus (BA-132, BA-124, BA-120) were studied. They were grown under 4 irradiances [10, 55, 100, and 145 μmol(photon) m-2 s-1] and at 3 temperatures (15, 22.5, and 30°C). Photosynthetic rate was measured by Clark oxygen electrode, whereas the Chl fluorescence was measured using Pulse Amplitude Modulation fluorometer. Based on P-I, two mechanisms of photoacclimation were recognized in Synechococcus. The maximum value of maximum rate of photosynthesis (P max) expressed per biomass unit at 10 μmol(photon) m-2 s-1 indicated a change in the number of photosynthetic units (PSU). The constant values of initial slope of photosynthetic light response curve (α) and the maximum value of P max expressed per Chl unit at 145 μmol(photon) m-2 s-1 indicated another mechanism, i.e. a change in PSU size. These two mechanisms caused changes in photosynthetic rate and its parameters (compensation point, α, saturation irradiance, dark respiration, P max) upon the influence of different irradiance and temperature. High irradiance had a negative effect on fluorescence parameters, such as the maximum quantum yield and effective quantum yield of PSII photochemistry (φPSII), but it was higher in case of φPSII.

Roles of the Cyclic Electron Flow Around PSI (CEF-PSI) and O2-Dependent Alternative Pathways in Regulation of the Photosynthetic Electron Flow in Short-Term Fluctuating Light in Arabidopsis thaliana

To assess the roles of the cyclic electron flow around PSI (CEF-PSI) and O₂-dependent alternative pathways including the water-water cycle in fluctuating light, we grew the wild type and pgr5 mutant of Arabidopsis thaliana in constant light, and measured Chl fluorescence and P700 parameters in their leaves in the fluctuating light alternating between 240 (HL) and 30 µmol photons m⁻² s⁻² (LL) every 2 min. At 20% O₂, the photochemical quantum yield of PSII decreased, in particular in the pgr5 plants, soon after the start of the fluctuating light treatment. PSI of the pgr5 plants was markedly photoinhibited by this treatment for 42 min. Slight PSI photoinhibition was also observed in the wild type. We measured energy sharing between PSII and PSI and estimated the PSI and PSII electron transport rates (ETRs). pgr5 showed larger energy allocation to PSI. In contrast to the wild type, the ratio of the PSI to the PSII ETR in pgr5 was higher in LL but lower in HL at 20% O₂ due to PSI acceptor-side limitation. At 2.7% or 0% O₂, the CEF-PSI of the pgr5 plants was enhanced, the acceptor-side limitation of PSI electron flow was released and PSI photoinhibition was not observed. The results suggest that the light fluctuation is a potent stress to PSI and that the CEF-PSI is essential to protect PSI from this stress.

Rice photosynthetic productivity and PSII photochemistry under nonflooded irrigation.

Nonflooded irrigation is an important water-saving rice cultivation technology, but little is known on its photosynthetic mechanism. The aims of this work were to investigate photosynthetic characteristics of rice during grain filling stage under three nonflooded irrigation treatments: furrow irrigation with plastic mulching (FIM), furrow irrigation with nonmulching (FIN), and drip irrigation with plastic mulching (DI). Compared with the conventional flooding (CF) treatment, those grown in the nonflooded irrigation treatments showed lower net photosynthetic rate (P N), lower maximum quantum yield (F v/F m), and lower effective quantum yield of PSII photochemistry (ΦPSII). And the poor photosynthetic characteristics in the nonflooded irrigation treatments were mainly attributed to the low total nitrogen content (TNC). Under non-flooded irrigation, the P N, F v/F m, and ΦPSII significantly decreased with a reduction in the soil water potential, but these parameters were rapidly recovered in the DI and FIM treatments when supplementary irrigation was applied. Moreover, The DI treatment always had higher photosynthetic productivity than the FIM and FIN treatments. Grain yield, matter translocation, and dry matter post-anthesis (DMPA) were the highest in the CF treatment, followed by the DI, FIM, and FIN treatments in turn. In conclusion, increasing nitrogen content in leaf of rice plants could be a key factor to improve photosynthetic capacity in nonflooded irrigation.

Chlorophyll fluorescence emission can screen cold tolerance of cold acclimated Arabidopsis thaliana accessions.

BackgroundAn easy and non-invasive method for measuring plant cold tolerance is highly valuable to instigate research targeting breeding of cold tolerant crops. Traditional methods are labor intensive, time-consuming and thereby of limited value for large scale screening. Here, we have tested the capacity of chlorophyll a fluorescence (ChlF) imaging based methods for the first time on intact whole plants and employed advanced statistical classifiers and feature selection rules for finding combinations of images able to discriminate cold tolerant and cold sensitive plants.ResultsChlF emission from intact whole plant rosettes of nine Arabidopsis thaliana accessions was measured for (1) non-acclimated (NAC, six week old plants grown at room temperature), (2) cold acclimated (AC, NAC plants acclimated at 4°C for two weeks), and (3) sub-zero temperature (ST) treated (STT, AC plants treated at -4°C for 8 h in dark) states. Cold acclimation broadened the slow phase of ChlF transients in cold sensitive (Co, C24, Can and Cvi) A. thaliana accessions. Similar broadening in the slow phase of ChlF transients was observed in cold tolerant (Col, Rsch, and Te) plants following ST treatments. ChlF parameters: maximum quantum yield of PSII photochemistry (FV/FM) and fluorescence decrease ratio (RFD) well categorized the cold sensitive and tolerant plants when measured in STT state. We trained a range of statistical classifiers with the sequence of captured ChlF images and selected a high performing quadratic discriminant classifier (QDC) in combination with sequential forward floating selection (SFFS) feature selection methods and found that linear combination of three images showed a reasonable contrast between cold sensitive and tolerant A. thaliana accessions for AC as well as for STT states.ConclusionsChlF transients measured for an intact whole plant is important for understanding the impact of cold acclimation on photosynthetic processes. Combinatorial imaging combined with statistical classifiers and feature selection methods worked well for the screening of cold tolerance without exposing plants to sub-zero temperatures. This opens up new possibilities for high-throughput monitoring of whole plants cold tolerance via easy and fully non-invasive means.

Changes in chlorophyll content and fluorescence and fruit yield contributing traits in different genotypes of strawberry (Fragaria x ananassa DUCH.)

Analysis of changes in chlorophyll fluorescence parameters in strawberry leaves was based on a field experiment performed in the years 2009–2010. Ten genotypes including 5 cultivars: ‘Kent’, ‘Teresa’, ‘Senga Sengana’, ‘Chandler’ and the breeding clone 1387 as well as their inbred progeny, were the object of the study. During the experiment the following indicators were evaluated: chlorophyll a and b content in fresh leaf mass as well as fluorescence parameters: minimum (F0) and maximum fluorescence yield (Fm), photochemical efficiency of PS II (Fv/Fm), actual quantum yield of PSII photochemistry (Y), minimum (F0’) and maximum efficiency of fluorescence (Fm’) in the light, coefficient of photochemical (qP) and non-photo- chemical (qN) fluorescence quenching. In this work, we also examined the effect of repeated inbreeding on strawberry fruit yield and yield components. The analysis of changes of these parameters showed that inbreeding caused a reaction in all tested cultivars. In all inbred progeny, chlorophyll a and b content decreased compared to the cultivars. Generally, the photoche- mical efficiency of photosystem II (Fv/Fm) and the parameter ΔF/ Fm’ were not affected by strong inbreeding. In analyzing the values of the coefficients qP and qN, it has been observed that changes in their values depend on the sensitivity of the examined genotypes to self-pollination. The functioning of PS II is the most sensitive indicator of the effect of various factors on plants and is useful, among others, in breeding to select plants with a required genotype. The yield – determining features such as: fruit yield per plant, weight of single fruit, number of fruit per plant and weight of leaves per plant in S3 generation, were lower as compared with parental forms.

Photosynthesis of two moss crusts from the Tengger Desert with contrasting sensitivity to supplementary UV-B radiation

Predicting the effects of increased ultraviolet-B (UV-B) radiation due to stratospheric ozone depletion on temperate desert ecosystems requires better knowledge of the ecophysiological response of common moss species. The aim of the current work was to determine whether elevated UV-B radiation affected photosynthetic performance and chloroplast ultrastructure of two moss crusts and whether response differences were observed between the crusts. In laboratory experiments, Bryum argenteum and Didymodon vinealis, which show microdistributions and are dominant in soil crusts at the Tengger Desert, Northern China, were subjected to four levels of UV-B radiation of 2.75 (control), 3.08, 3.25, and 3.41 W m−2 for 10 days, simulating 0, 6, 9, and 12% of stratospheric ozone at the latitude of Shapotou, respectively. The results showed that chlorophyll a fluorescence parameters (i.e., the maximal quantum yield of PSII photochemistry, the effective quantum yield of PSII photochemistry, and photochemical quenching coefficient), pigment contents, soluble protein contents, and the ultrastructure were negatively influenced by elevated UV-B radiation and the degree of detrimental effects significantly increased with the intensity of UV-B radiation. Moreover, results indicated that B. argenteum was probably more sensitive to supplementary UV-B radiation than D. vinealis. Therefore, we propose the use of B. argenteum crusts as a bioindicator of responses to elevated UV-B radiation.

Combining Gas Exchange and Chlorophyll Fluorescence to Assess the Adaptability of Medicinal Plant <i>Aesculus chinensis</i> Compared to Two Imported <i>Aesculus</i> Species

Analysis of gas exchange and determination of chlorophyll fluorescence parameters in leaves of three tree species including Aesculus chinensis, A. octandra and A. hybrida were conducted under field conditions and then comparison was carried out. The results showed that the light compensation point (LCP) was significantly different among the three tree species, of which the LCP of A. chinensis with 12.53 μmol·m-2·s-1 that of the lowest was notable lower than that of the other two species (36.11 and 46.41 μmol·m-2·s-1respectively). On the other hand, the light saturation point (LSP) of the three tree species also showed remarked different and the LSP of A. chinensis was 1475 μmol·m-2·s-1 which was dramatic higher than that of the other two species respective to 1366.67 and 1025 μmol·m-2·s-1. Beside, the maximum net photosynthetic rate (MNPR) was different too, MNPR of A. chinensis was 9.47μmol CO 2·m-2·s-1which was higher than the other two species (5.91 and 2.30 μmol CO 2·m-2·s-1 respectively), indicating A. chinensis had a higher photosynthetic capacity and stronger utilization ability for light energy. Moreover, the electron transport rate (ETR) of A. chinensis was higher than A. octandra and A. hybrida, the ETR of the former was 55.800 that were 1.33 and 1.44 times of the later two respectively. Quantum yield of PSII photochemistry (ФPSII) in A. chinensis was higher than A. octandra and A. hybrida, the ФPSII of the former was 0.470 that were 1.21 and 1.15 times of the later two respectively. Furthermore, the photochemical quenching (qP) of A. chinensis was 0.975 much higher than A. octandra and A. hybrida respective to 1.10 and 1.10 times of the later two respectively. These three photochemical parameters with dramatic different among the three different tree species suggested A. chinensis had a high activity of electron transport and conversion efficiency for light energy.

Elevated ozone negatively affects photosynthesis of current-year leaves but not previous-year leaves in evergreen Cyclobalanopsis glauca seedlings

To assess the effects of leaf age/layer on the response of photosynthesis to chronic ozone (O3), Cyclobalanopsis glauca seedlings, a dominant evergreen broadleaf tree species in sub-tropical regions, were exposed to either ambient air (AA) or elevated O3 (AA + 60 ppb O3, E-O3) for two growing seasons in open-top chambers. Chlorophyll content, gas exchange and chlorophyll a fluorescence were investigated three times throughout the 2nd year of O3 exposure. Results indicated that E-O3 decreased photosynthetic parameters, particularly light-saturated photosynthesis rate, stomatal conductance and effective quantum yield of PSII photochemistry of current-year leaves but not previous-year leaves. Stomatal conductance of plants grown under ambient conditions partially contributed to the different response to E-O3 between leaf layers. Light radiation or other physiological and biochemical processes closely related to photosynthesis might play important roles. All suggested that leaf ages or layers should be considered when assessing O3 risk on evergreen woody species.

Foliar application of 24-epibrassinolide alleviates high-temperature-induced inhibition of photosynthesis in seedlings of two melon cultivars

Brassinosteroids (BRs), an important class of plant steroidal hormones, play a significant role in the amelioration of various biotic and abiotic stresses. 24-epibrassinolide (EBR), an active brassinosteroid, was applied exogenously in different concentrations to characterize a role of BRs in tolerance of melon (Cucumis melo L.) to high temperature (HT) stress and to investigate photosynthetic performance of HT-stressed, Honglvzaocui (HT-tolerant) and Baiyuxiang (HTsensitive), melon variety. Under HT, Honglvzaocui showed higher biomass accumulation and a lower index of heat injury compared with the Baiyuxiang. The exogenous application of 1.0 mg L−1 EBR, the most effective concentration, alleviated dramatically the growth suppression caused by HT in both ecotypes. Similarly, EBR pretreatment of HTstressed plants attenuated the decrease in relative chlorophyll content, net photosynthetic rate, stomatal conductance, stomatal limitation, and water-use efficiency (WUE), as well as the maximal quantum yield of PSII photochemistry (Fv/Fm), the efficiency of excitation capture of open PSII center, the effective quantum yield of PSII photochemistry (ΦPSII), photochemical quenching coefficient, and the photon activity distribution coefficients of PSI (α). EBR pretreatment further inhibited the increase in intracellular CO2 concentration, leaf transpiration rate, minimal fluorescence of dark-adapted state, nonphotochemical quenching, thermal dissipation, and photon activity distribution coefficients of PSII. Results obtained here demonstrated that EBR could alleviate the detrimental effects of HT on the plant growth by improving photosynthesis in leaves, mainly reflected as up-regulation of photosynthetic pigment contents and photochemical activity associated with PSI.

Interactive effects of temperature and light intensity on photosynthesis and antioxidant enzyme activity in Zizania latifolia Turcz. plants

We compared the interactive effects of temperature and light intensity on growth, photosynthetic performance, and antioxidant enzyme activity in Zizania latifolia Turcz. plants in this study. Plants were grown under field (average air temperature 9.6–25°C and average light intensity 177–375 W m−2) or greenhouse (20–32°C and 106–225 W m−2) conditions from the spring to the early summer. The results indicated that greenhouse-grown plants (GGP) had significantly higher plant height, leaf length, and leaf width, but lower leaf thickness and total shoot mass per cluster compared with field-grown plants (FGP). Tiller emergence was almost completely suppressed in GGP. Significantly higher chlorophyll (Chl) content and lower Chl a/b ratio were observed in GGP than in FGP. From 4 to 8 weeks after treatment (WAT), net photosynthetic rate (PN) was significantly lower in FGP than in GGP. However, from 9 to 12 WAT, PN was lower in GGP, accompanied by a decrease in stomatal conductance (gs) and electron transport rate (ETR) compared with FGP. Suppressed PN in GGP under high temperature combined with low light was also indicated by photosynthetic photon flux density (PPFD) response curve and its diurnal fluctuation 10 WAT. Meanwhile, ETR in GGP was also lower than in FGP according to the ETR — photosynthetically active radiation (PAR) curve. The results also revealed that GGP had a lower light saturation point (LSP) and a higher light compensation point (LCP). From 4 to 8 WAT, effective quantum yield of PSII photochemistry (ΦPSII), photochemical quenching (qP), and ETR were slightly lower in FGP than in GGP. The activities of ascorbate peroxidase (APX), guaiacol peroxidase (POD), glutathione reductase (GR), superoxide dismutase (SOD), and malondialdehyde (MDA) content were significantly higher from 4 to 8 WAT, but lower from 10 to 12 WAT in FGP. However, catalase (CAT) activity was significantly lower in FGP from 4 to 8 WAT. Our results indicated that the growth and photosynthetic performance of Z. latifolia plants were substantially influenced by temperature, as well as light intensity. This is helpful to understand the physiological basis for a protected cultivation of this crop.