Photoinhibition Of Photosynthesis Research Articles

Impact of salinity on the kinetics of CO2 fixation by Spirulina platensis cultivated in semi-continuous photobioreactors

In this research, the physiological response of the microalgae Spirulina platensis to salinity stress (1 and 100 g L-1 ) was investigated. Spirulina platensis and Spirulina platensis (adapted to high salt concentration) were operated at laboratory scale in a semi-continuous photobioreactors. The responses examined were within 0.5 to 10% CO2 concentration, temperatures from 10 to 40 oC, light intensities from 60 to 200 μmol m-2 s -1 and presented better results in terms of all kinetic parameters. The highest rate of CO2 biofixation for Spirulina platensis was 25.1 gCO2 m-3 h -1 , and the maximum specific growth (μmax) achieved was 0.44 d-1 - 0.67 d-1 at 2.5% CO2, 150 µmol m-2 s -1 at 25 oC. Corresponding determined values of Spirulina platensis adapted were 18.2 gCO2 m-3 h -1 , 0.31 d-1 - 0.58 d-1 at 2.5% CO2, 60 µmol s-1 m-2 and 28 oC. However, both microalgae exhibited experimental limiting growth factors, CO2 10%, 40 oC and 200 µmol m-2 s -1 , conditions under which photosynthetic CO2 biofixation may be inhibited and photoinhibition of photosynthesis may be enhanced by salinity. The efficiency of 2.5% CO2 removal by Spirulina platensis achieved 99%, whereas Spirulina platensis adapted to 96%, respectively. The kinetic parameters estimated for Spirulina platensis can be used to improve photobioreactor design for reducing of atmospheric carbon dioxide.

Solar radiation regulates the leaf nitrogen and phosphorus stoichiometry across alpine meadows of the Tibetan Plateau

Leaf nitrogen (N) and phosphorus (P) stoichiometry covary with many aspects of climatic and edaphic factors, yet the effects of solar radiation (SR) on leaf stoichiometry are still unclear. In the Tibetan Plateau, the high level of SR can induce the plants to reach their light saturation point easily, which causes photoinhibition of photosynthesis. Here, the leaf N and P concentrations across the alpine meadow of the Tibetan Plateau were measured to explore the response of leaf N and P stoichiometry to SR. Our results showed that the concentrations of both leaf N and leaf P were negatively correlated with SR under the high SR level (SR > 15,000 KJ m−2 d-1). The structural equation model demonstrated that SR plays a vital role in leaf N and P stoichiometry, and SR has direct effects on leaf N and P stoichiometry through a physiological process (path coefficient =-0.293 and -0.343, respectively). In addition, the high SR level lowered the level of precipitation (path coefficient =-0.615) and temperature (path coefficient =-0.047), then changed the soil organic carbon, soil nitrogen and phosphorus content. Furthermore, precipitation, temperature, soil organic carbon, soil nitrogen and phosphorus also regulated leaf N and P stoichiometry, which caused the SR to have indirect effects on leaf N and P stoichiometry (path coefficient =-0.072 and -0.053, respectively). As a consequence, we highlighted that SR regulates leaf N and P stoichiometry across alpine meadows of the Tibetan Plateau, and the results provide guidance on grassland management.

黄土丘陵区沙棘、油松和刺槐光合生理特性及其环境适应性

PDF HTML阅读 XML下载 导出引用 引用提醒 黄土丘陵区沙棘、油松和刺槐光合生理特性及其环境适应性 DOI: 10.5846/stxb201808221783 作者: 作者单位: 中科院水土保持研究所,中科院水土保持研究所,西北农林大学水土保持研究所,西北农林科技大学水土保持研究所,西北农林科技大学林学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41501576，41371506）；公益性行业（国家气象局）科研专项（重大专项）（GYHY2015060013）；中央高校基本科研业务费专项（2452016105） Photosynthesis light response characteristics and environmental adaptability of Hippophae rhamnoides, Pinus tabuliformis, and Robinia pseudoacacia in the Loess hilly region of China Author: Affiliation: Institute of Soil and Water Conservation, Chinese Academy of Sciences and the Ministry of Water Resources,Institute of Soil and Water Conservation, Chinese Academy of Sciences and the Ministry of Water Resources,Institute of Soil and Water Conservation,Northwest Agriculture and Forestry University,Institute of Soil and Water Conservation, Northwest Agriculture and Forestry University,College of Forestry, Northwest Agriculture and Forestry University Fund Project: the National Natural Science Foundation of China ( 41501576，41371506), the China Special Fund for Meteorological Ｒesearch in the Public Interest ( Major Project) ( GYHY2015060013) and the Fundamental Ｒesearch Funds for the Central Universities ( 2452016105) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:植物光合生理特性在一定程度上能够体现其对生境的响应情况。通过测定黄土丘陵区安塞国家生态试验站人工纯林和混交林沙棘（Hippophae rhamnoides）、油松（Pinus tabuliformis）和刺槐（Robinia pseudoacacia）在不同水分条件下的光响应曲线，采用5种光响应模型进行拟合分析，以比较3个树种在不同水分条件下适宜的光响应模型及光合生理参数差异，探讨该地区主要造林树种的光合生理生态适应性。结果表明：（1）湿润时期（9月）纯林和混交林中3个树种叶片净光合速率（Pn）均显著高于干旱时期（7月）（P < 0.05），且7月，纯林沙棘、纯林刺槐和混交林刺槐出现光饱和、光抑制现象。（2）5种模型对各树种叶片光响应过程拟合效果的优劣顺序为：直角双曲线修正模型（MRH）、指数修正模型（MEM）、非直角双曲线模型（NRH）、指数模型（EM）、直角双曲线模型（RH）。（3）与9月相比，7月各树种叶片光合生理参数值（表观量子效率[φ]、光补偿点[LCP]、光饱和点[LSP]、暗呼吸速率[Rd]、最大净光合速率[Pnmax]）相对较低，表明在干旱时期，各树种光能利用减弱，光合能力也受到限制。（4）与纯林相比，混交林沙棘光合生理参数值整体呈上升趋势，表明混交造林有助于提高其光合潜力、对弱光的利用能力及光照生态幅宽度；油松整体呈下降趋势，表明混交种植可能会降低其光合作用能力；刺槐变化无明显规律，其叶片φ和Pnmax值下降，Rd增加，光照生态幅最宽，表明混交种植可能会增强其对强光的适应性，但会降低其对弱光的利用能力及光合潜力。 Abstract:The photosynthetic physiological characteristics of plants can reflect their response to environmental conditions. To understand the photosynthetic adaptability of the major tree species for afforestation in a hilly loess region, the light response curves of Hippophae rhamnoides, Pinus tabuliformis, and Robinia pseudoacacia in pure and mixed plantations under different water conditions were measured in Ansai National Ecological Experimental Station, and the data fitted to five models. The results indicated that (1) the Pn values of these three tree species during a wet period (September) were significantly higher than those during a dry period (July) (P < 0.05), and there was photo-inhibition of photosynthesis in the H. rhamnoides pure plantation, R. pseudoacacia pure plantation, and R. pseudoacacia mixed plantation in July; (2) The sequence of fitting effect of the five light response models was, in descending order, as follows:modified rectangular hyperbola, modified exponential, non-rectangular hyperbola, exponential, then rectangular hyperbola. (3) The light response parameters (apparent quantum yield[φ], light compensation point[LCP], light saturation point[LSP], dark respiration rate[Rd], and maximum net photosynthetic rate[Pnmax]) for the three tree species in pure and mixed plantations in July were lower than those in September, suggesting that the light-use capability was diminished, and photosynthetic capacity was inhibited under dry conditions. (4) Compared with the pure forest, the photosynthetic physiological parameters of H. rhamnoides in the mixed forest showed an increased (in general), indicating that mixed afforestation was helpful to improving its photosynthetic potential, light use capability, and the light ecological amplitude. The photosynthetic physiological parameters in P. tabuliformis were reduced (in general), suggesting that mixed afforestation might reduce its photosynthetic capacity. Meanwhile, there was no obvious trend in the photosynthetic physiological parameters in R. pseudoacacia:the values of φ and Pnmax of the leaves decreased, while Rd increased, and the light ecological amplitude was widest, indicating that mixed planting might enhance its adaptability to strong lighting conditions, but it would reduce its ability to utilize the lower levels of light and photosynthetic potential. 参考文献 相似文献 引证文献

Oxalic acid-mediated biochemical and physiological changes in the common bean-Sclerotinia sclerotiorum interaction

The success of Sclerotinia sclerotiorum infection relies mainly on the production of the non-host selective toxin named oxalic acid (OA). This toxin is known to play multiple roles in a host infected by the fungus, but its effect on photosynthesis and the antioxidant system of common bean plants remain elusive. Therefore, we performed detailed analysis of leaf gas exchange, chlorophyll a fluorescence, activities of antioxidant enzymes, concentrations of reactive oxygen species and photosynthetic pigments to investigate the OA's role during the S. sclerotiorum pathogenesis. To achieve this goal, common bean plants were sprayed with water or with oxalic acid (referred to as –OA and +OA plants, respectively) and either non-challenged or challenged with a wild-type (WT) or an OA-defective mutant (A4) of S. sclerotiorum. Irrespective of OA spray, the WT isolate was more aggressive than the A4 isolate and spraying OA increased OA concentration in the leaflets as well as the aggressiveness of both isolates. Biochemical limitations were behind S. sclerotiorum-induced photosynthetic impairments notably for the +OA plants inoculated with the WT isolate. Inoculated plants were not able to fully capture and exploit the collected energy due to the degradation of photosynthetic pigments. Photoinhibition of photosynthesis and photochemical dysfunctions were potentiated by OA. Higher activities of superoxide dismutase, peroxidase and ascorbate peroxidase besides reductions on catalase activity were noticed for plants inoculated with the WT isolate. OA was able to counteract most of the increases in the activities of antioxidant enzymes thereby increasing the generation of superoxide and hydrogen peroxide and the concurrent damage to the membranes of host cells as evidenced by the high malondialdehyde concentration. In conclusion, OA was found to enhance biochemical limitations to photosynthesis, photochemical dysfunctions and oxidative stress in the leaflets of common bean plants infected by S. sclerotiorum.

The hydroperoxide lyase branch of the oxylipin pathway protects against photoinhibition of photosynthesis.

This study describes a new role for hydroperoxide lyase branch of oxylipin biosynthesis pathway in protecting photosynthetic apparatus under high light conditions. Lipid-derived signaling molecules, oxylipins, produced by a multi-branch pathway are central in regulation of a wide range of functions. The two most known branches, allene oxide synthase (AOS) and 13-hydroperoxide lyase (HPL) pathways, are best recognized as producers of defense compounds against biotic challenges. In the present work, we examine the role of these two oxylipin branches in plant tolerance to the abiotic stress, namely excessive light. Towards this goal, we have analyzed variable chlorophyll fluorescence parameters of intact leaves of Arabidopsis thaliana genotypes with altered oxylipin profile, followed by examining the impact of exogenous application of selected oxylipins on functional activity of photosynthetic apparatus in intact leaves and isolated thylakoid membranes. Our findings unequivocally bridge the function of oxylipins to photosynthetic processes. Specifically, HPL overexpressing lines display enhanced adaptability in response to high light treatment as evidenced by lower rate constant of photosystem 2 (PS2) photoinhibition and higher rate constant of PS2 recovery after photoinhibition. In addition, exogenous application of linolenic acid, 13-hydroperoxy linolenic acid, 12-oxophytodienoic acid, and methyl jasmonate individually, suppresses photochemical activity of PS2 in intact plants and isolated thylakoid membranes, while application of HPL-branch metabolites-does not. Collectively these data implicate function of HPL branch of oxylipin biosynthesis pathway in guarding PS2 under high light conditions, potentially exerted through tight regulation of free linolenic acid and 13-hydroperoxy linolenic acid levels, as well as competition with production of metabolites by AOS-branch of the oxylipin pathway.

No evidence for photoinhibition of photosynthesis in alpine Caltha leptosepala DC

Alpine plants experience high levels of insolation, as well as cold nighttime temperatures throughout the summer growth period. These two stress factors in combination are now recognized as potentially important limitations to photosynthetic carbon gain. Although likely candidates, the possible occurrence of photoinhibition in alpine plants has been reported infrequently. We measured photoinhibitory stress under natural field conditions and after high-light treatments in an herbaceous species (Caltha leptosepala DC) with structural traits that appeared especially susceptible to photoinhibition, i.e., large, broad, laminar leaves with a near-horizontal leaf orientation. Although photosynthesis declined gradually during the afternoon under natural field conditions, no evidence was found for photoinhibition of photosynthesis, despite incident sunlight levels of >2500 µmol m−2 s−1. Also, values of \({{F_{\text{v}}^{{\prime }} } \mathord{\left/ {\vphantom {{F_{\text{v}}^{{\prime }} } {F_{\text{m}}^{{\prime }} }}} \right. \kern-0pt} {F_{\text{m}}^{{\prime }} }}\) (an indicator of dynamic photoinhibition) changed little (<10 %) from early morning to late afternoon values. Moreover, an experimental test of photoinhibition was conducted in the field using artificially applied low (250 µmol m−2 s−1) followed by unnaturally high (3500 µmol m−2 s−1) light levels, led to only small reductions in \({{F_{\text{v}}^{{\prime }} } \mathord{\left/ {\vphantom {{F_{\text{v}}^{{\prime }} } {F_{\text{m}}^{{\prime }} }}} \right. \kern-0pt} {F_{\text{m}}^{{\prime }} }}\) (20 % maximum). Also, afternoon declines in photosynthesis and other gas exchange parameters were associated with significant decreases in xylem water potentials. Thus, accumulating daily water stress appeared to be a possible, greater physiological limitation than photoinhibition, even in this common, hypothetically susceptible alpine species.

Photosynthetic Apparatus Responses to Short‐term low‐temperature Flooding May Contribute to Freezing Tolerance Changes in Forage Grasses

AbstractWinter conditions are subjected to rapid climate changes. Increased precipitation and snow melting during warmer winters may result in low‐temperature flooding. These factors probably affect plant overwintering strategies. This study investigated the relationships between the photosynthetic adjustment and freezing tolerance following a short‐term low‐temperature flooding in two forage grasses (Lolium perenne and Festuca pratensis). The effect of flooding on the photosynthetic apparatus acclimation to cold was determined using chlorophyll a fluorescence measurements. Freezing tolerance was estimated using an electrolyte leakage test. It has been shown that genotypes activating non‐photochemical mechanisms of photosynthetic acclimation to cold during low‐temperature flooding may show increased freezing tolerance. Freezing tolerance reduction observed in Festuca pratensis was probably connected with decreased photochemical activity and photoinhibition of photosynthesis. It can be concluded that photosynthetic apparatus response to low‐temperature flooding may contribute to changes in the freezing tolerance. The direction of the changes is associated with different photosynthetic apparatus performance.

Photoinhibition of photosynthesis in Antarctic lichen Usnea antarctica. II. Analysis of non-photochemical quenching mechanisms activated by low to medium light doses

The paper focus sensitivity of an Antarctic lichen Usnea antarctica to photoinhibition studied under controlled laboratory conditions. Main emphasis was given to the analysis of quenching mechanisms, i.e. deexcitation pathways of absorbed light energy exploited in non-photochemical processes. Thalli of U. antarctica were collected at the James Ross Island, Antarctica (57°52´57´´ W, 63°48´02´´ S) and transferred in dry state to the Czech Republic. After rewetting in a laboratory, they were exposed to medium light intensities (300, 600 and 1000 mmol m-2 s-1 of photosynthetically active radiation) for 6 h. Before and during photoinhibitory treatments, chlorophyll fluorescence parameters, photoinhibitory (qI), state 1-2 transition (qT), and energy-dependent quenching (qE) in particular were measured to evaluate dose- and time-dependent changes in these parameters. The results showed that among the components forming non-photochemical quenching (qN), qI contributes to the largest extent to qN, while qE and qT contribute less. This finding differs from our earlier studies made in a short term-, and high light-treated U. antarctica that found qE together with qI is the most important part of non-photochemical quenching. Possible explanation is that photoinhibition in PS II in U. ant-arctica, when induced by low to medium light, activates qE to only limited extend and for a relatively short time (tens of minutes). With prolonged high light treatment lasting several hours, qE tends to be reduced to the values close to zero and qI then forms a major part of qN.

Differential influence of water-flow on photoinhibition of photosynthesis in endosymbiotic algae among shallow-inhabiting scleractinian corals

Differential influence of water-flow on photoinhibition of photosynthesis in endosymbiotic algae among shallow-inhabiting scleractinian corals

Modelling photosynthesis in shallow algal production ponds

Shallow ponds with rapidly photosynthesising cyanobacteria or eukaryotic algae are used for growing biotechnology feedstock and have been proposed for biofuel production but a credible model to predict the productivity of a column of phytoplankton in such ponds is lacking. Oxygen electrodes and Pulse Amplitude Modulation (PAM) fluorometer technology were used to measure gross photosynthesis (P G) vs. irradiance (E) curves (P G vs. E curves) in Chlorella (chlorophyta), Dunaliella salina (chlorophyta) and Phaeodactylum (bacillariophyta). P G vs. E curves were fitted to the waiting-in-line function [P G = (P Gmax × E/Eopt) × exp(1 - E/Eopt)]. Attenuation of incident light with depth could then be used to model P G vs. E curves to describe P G vs. depth in pond cultures of uniformly distributed planktonic algae. Respiratory data (by O2-electrode) allowed net photosynthesis (P N) of algal ponds to be modelled with depth. Photoinhibition of photosynthesis at the pond surface reduced P N of the water column. Calculated optimum depths for the algal ponds were: Phaeodactylum, 63 mm; Dunaliella, 71 mm and Chlorella, 87 mm. Irradiance at this depth is &asymp; 5 to 10 &mu;mol m-2 s-1 photosynthetic photon flux density (PPFD). This knowledge can then be used to optimise the pond depth. The total net P N [&mu;mol(O2) m-2 s-1] were: Chlorella, &asymp; 12.6 &plusmn; 0.76; Dunaliella, &asymp; 6.5 &plusmn; 0.41; Phaeodactylum &asymp; 6.1 &plusmn; 0.35. Snell's and Fresnel's laws were used to correct irradiance for reflection and refraction and thus estimate the time course of P N over the course of a day taking into account respiration during the day and at night. The optimum P N of a pond adjusted to be of optimal depth (0.1-0.5 m) should be approximately constant because increasing the cell density will proportionally reduce the optimum depth of the pond and vice versa. Net photosynthesis for an optimised pond located at the tropic of Cancer would be [in t(C) ha-1 y-1]: Chlorella, &asymp; 14.1 &plusmn; 0.66; Dunaliella, &asymp; 5.48 &plusmn; 0.39; Phaeodactylum, &asymp; 6.58 &plusmn; 0.42 but such calculations do not take weather, such as cloud cover, and temperature, into account.

Effective population sizes of eastern oyster Crassostrea virginica (Gmelin) populations in Delaware Bay, USA

The Tikehau atoll (Tuamotu Archipelago, French Polynesia) is located at 14'5 148W. Phytoplankton and sand microalgae are the most important primary producers of the lagoon. They were studied for 4 years. The relationship between light energy and lagoonal primary production was measured by using the 14C method for phytoplankton and O, method for phytobenthos. Incubations, carried out in situ, were made at different depths and light exposition times. Irradiance was high and 17% of the light energy measured at the surface reached 25 m (lagoon average depth). Maxima of phytoplankton and phytobenthos productions occurred at low depths; there was therefore no photoinhibition of photosynthesis. Correlations between light energy and primary production were strong, especially for phytobenthos. Multiplicative linear regression models (production VS light) associated with an exponential linear regression model (light vs depth), allowed planktonic and benthic primary production to be predicted from the depth and the light energy received at the surface. The benthic primary production exceeded the phytoplanktonic production in the upper 18 m. The total primary production (benthos + plankton) was constant with depth and depended only on light energy at the surface. One Einstein received at the lagoon surface allowed the growth production of 14 mg of carbon (water column + sediments).

Photoinhibition of photosynthesis in Antarctic lichen Usnea antarctica. I. Light intensity- and light duration-dependent changes in functioning of photosystem II

The paper deals with the differences in sensitivity of Antarctic lichen to photoinhibition. Thalli of Usnea antarctica were collected at the James Ross Island, Antarctica (57°52´57´´W, 63°48´02´´S) and transferred in dry state to the Czech Republic. After rewetting in a laboratory, they were exposed to 2 high light treatments: short-term (30 min), and long-term (6 h). In short-term treatment, the sample were exposed to 1000 and 2000 µmol m-2 s-1 of photosynthetically active radiation (PAR). In long-term experiment, PAR of 300, 600, and 1000 µmol m-2 s-1 were used. Photosynthetic efficiency of U. antarctica thalli was monitored by chlorophyll fluorescence parameters, potential (FV/FM) and actual (FPSII) quantum yield of photochemical processes in photosystem II in particular. In short-term treatments, the F0, FV and FM signals, as well as the values of FV/FM, and FPSII showed light-induced decrease, however substantial recovery after consequent 30 min. in dark. Longer exposition (60 min) to high light led to more pronounced decrease in chlorophyll fluorescence than after 30 min treatment, however dark recovery was faster in the thalli treated before for longer time (60 min). Long-term treatment by high light caused gradual decrease in FV/FM and FPSII with the time of exposition. The extent of the decrease was found light dose-dependent. The time course was biphasic for FV/FM but not for FPSII. The study showed that wet thalli of Usnea antarctica had high capacity of photoprotective mechanisms to cope well either with short- or long-term high light stress. This might be of particular importance in the field at the James Ross Island, particularly at the begining of growing season when melting water is available and, simultaneously, high light stress may happen on fully sunny days.

The effects of cold, light and time of day during low-temperature shift on the expression of CBF6, FpCor14b and LOS2 in Festuca pratensis

Strictly controlled and coordinated induction of CBF regulon (a set of genes regulated by CBF proteins) promotes plant freezing tolerance. CBFs regulate the expression of COR genes that confer freezing tolerance. COR14b in barley is one of the effector genes which seems to be important in resistance to combined freezing and photoinhibition of photosynthesis. LOS2 represses the transcription of STS/ ZAT10 (a negative regulator of CBF-target genes) and thus acts as a positive regulator of COR genes. In Arabidopis, low temperature induction of CBFs was reported to be gated by the circadian clock. Moreover, light-quality signals have been shown to regulate some plants’ freezing tolerance genes. The aim of our study was to determine the effects of combined treatment with light and cold on the transcript levels of CBF6, FpCor14b and LOS2 genes in Festuca pratensis. We have demonstrated that the regulation of CBF6, FpCor14b and LOS2 induction kinetics in F. pratensis occurs through the interaction of temperature and light with time of day during low-temperature shift. The FpCOR14b transcript level was shown to be up-regulated by increasing light intensity. It was also proved that light quality strongly regulates CBF6, FpCor14b and LOS2 transcripts induction kinetics at low temperatures.

Leaf Wilting Movement Can Protect Water-Stressed Cotton (Gossypium hirsutum L.) Plants Against Photoinhibition of Photosynthesis and Maintain Carbon Assimilation in the Field

Under severe water stress, leaf wilting is quite general in higher plants. This passive movement can reduce the energy load on a leaf. This paper reports an experimental test of the hypothesis that leaf wilting movement has a protective function that mitigates against photoinhibition of photosynthesis in the field. The experiments exposed cotton (Gossypium hirsutum L.) to two water regimes: water-stressed and well-watered. Leaf wilting movement occurred in water-stressed plants as the water potential decreased to −4.1 MPa, reducing light interception but maintaining comparable quantum yields of photosystem II (PS II; Yield for short) and the proportion of total PS II centers that were open (qP). Predrawn F v/F m (potential quantum yield of PS II) as an indicator of overnight recovery of PS II from photoinhibition was higher than or similar to that in well-watered plants. Compared with water-stressed cotton leaves for which wilting movement was permitted, water-stressed cotton leaves restrained from such movement had significantly increased leaf temperature and instantaneous CO2 assimilation rates in the short term, but reduced Yield, qP, and F v/F m. In the long term, predrawn F v/F m and CO2 assimilation capacity were reduced in water-stressed leaves restrained from wilting movement. These results suggest that, under water stress, leaf wilting movement could reduce the incident light on leaves and their heat load, alleviate damage to the photosynthetic apparatus due to photoinhibition, and maintain considerable carbon assimilation capacity in the long term despite a partial loss of instantaneous carbon assimilation in the short term.

Comparative analysis of photosynthetic characteristics of different cotton cultivars

The photosynthetic and fluorescence characteristics of "Hai7124"(Gossypium barbadense),"Jinhuazhongmian"(G.arboreum),"Hongxinmian"(G.herbaceum) and "Su12"(G.hirsutum) were analyzed in this paper.The results show that total chlorophyll content,leaf mass per area,Pn,PSⅡ photochemical efficiency(Fv/Fm) and photochemical quenching(qP) of the cotton cultivars are the following order: "Hai7124" "Su12" "Jinhuazhongmian" "Hongxinmian";indicating that "Hai7124" has higher photosynthetic efficiency.Further investigation shows that diurnal variation curves of Pn for "Hai7124","Jinhuazhongmian" and "Su12" have two peaks that occur at 12:00 and 16:00,though Pn for "Hongxinmian" varies and has a uni-peak curve that occurs between 12:00 ~ 14:00.This is consistent with diurnal variations in stomatal conductance(Cs).Photoinhibition of photosynthesis at noon is related with decreasing Cs and PSⅡ photochemical efficiency.

Photo-oxidative stress in coconut seedlings: early events to leaf scorching and seedling death

Experiments were conducted on coconut seedlings to delineate events of photo-oxidative stress damage. Studies on chlorophyll fluorescence indicated a clear case of excess light energy under high light conditions causing stress to coconut seedlings raised under coconut palms. Quantum yield of photo-chemistry of leaflets exposed to high light was significantly less than those under shade. Seedlings exposed to high light and then shifted to shade have shown significant improvement in quantum yield. Excess light energy harvested by chlorophyll antenna caused high non-photochemical quenching resulting in production of biologically toxic super oxide, hydrogen peroxide and hydroxyl radicals. It is apparent that photoinhibition of photosynthesis takes place due to i) PSII down regulation and ii) damage to PS II system in initial stages of exposure to excess light and under prolonged exposures inhibition is caused due to iii) chlorophyll bleaching and iv) damage to chloroplast and cell membrane integrity, followed by reduction in photosynthetically active leaf area because of scorching thus reducing canopy photosynthesis. Protein concentration in leaf tissue was higher in seedlings in high light conditions. Three distinct low molecular weight proteins with pI of 4.9, 8.4 and 10.15 having Mr less than 20,000 were found in seedlings exposed to high light intensities. Results clearly demonstrate the events that take place at early stage to subsequent cascading effects leading to the scorching and death of leaf and even seedling death under severe conditions.

Research note: Irradiance of photosynthetically active radiation determines ultraviolet‐susceptibility of photosynthesis in Ulva lactuca L.(Chlorophyta)

SUMMARYThe respective ratio of photosynthetically active to ultraviolet radiation is of crucial importance to results obtained in ultraviolet (UV)‐research on photoautotrophic organisms. Specimens of the green macroalga Ulva lactuca L. were exposed to a constant irradiance of UV‐radiation at increasing irradiances of photosynthetically active radiation (PAR). The effects of experimental irradiance and spectral composition on photoinhibition of photosynthesis and its recovery were monitored by chlorophyll fluorescence measurements and the activity of the xanthophyll cycle was assessed by high performance liquid chromatography‐(HPLC) based pigment analysis. Results indicate a UV‐induced delay in recovery from PAR‐induced photoinhibition and a deceleration of violaxanthin conversion within the xanthophyll cycle due to the presence of UV‐radiation. Also the concentration of the protective pigment lutein increased considerably and could be indicative of the existence of an additional light‐protective mechanism, as, for example, the lutein‐epoxid cycle in Ulva. In total, results clearly show that the extent of UV‐induced inhibition of photosynthesis to be found in UV‐exposure experiments is highly dependent on the irradiance of background photosynthetically active radiation: with increasing irradiance of PAR the UV‐effects were diminished. Exemplified by the green algae Ulva lactuca this study demonstrates the crucial importance of the ratios of PAR:UV applied in UV‐research, particularly when conducting laboratory experiments in an ecological context.

Photoinhibition of photosynthesis in water deficit leaves of grapevine (Vitis vinifera L.) plants

Photoinhibition under irradiance of 2 000 µmol m−2 s−1 (HI) was studied in detached control (C) and water deficit (WD) leaves of grapevine (Vitis vinifera L.) plants. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence (Fv/Fm) and electron transport measurements. The potential efficiency of photosystem (PS) 2, Fv/Fm, marginally declined under HI in WD-leaves without significant increase of F0. In contrast, Fv/Fm ratio declined markedly with significant increase of F0 in C-leaves. In isolated thylakoids, the rate of whole chain and PS2 activity under HI were more decreased in C-than WD-leaves. The artificial exogenous electron donors diphenyl carbazide, NH2OH, and Mn2+ failed to restore the HI-induced loss of PS2 activity in both C-and WD-leaves. Thus HI operates at the acceptor side of PS2 in both leaf types. Quantification of the PS2 reaction centre protein D1 following HI exposure of leaves showed pronounced differences between C-and WD-leaves. The marked loss of PS2 activity under HI of C-leaves was due to the marked loss of D1 protein of the PS2 reaction centre.

Community photosynthesis of aquatic macrophytes

We compared 190 photosynthesis‐irradiance (P‐E) experiments with single‐ and multispecies communities of macroalgae and vascular plants from freshwater and marine habitats. We found a typical hyperbolic P‐E relation in all communities and no sign of photosaturation or photoinhibition of photosynthesis at the highest irradiances of about 2,000 µmol m‐2 s‐1. Macrophyte communities displayed much higher maximum gross production (GPmax), respiration, and light compensation point than separate phytoelements because of the multilayered structure and extensive self‐shading in the communities, whereas light use efficiency at low irradiance (a) was the same. Although GPmax and a varied extensively among the 190 communities, their upper limits increased linearly and predictably with community absorption reaching 26.3 µmol m‐2 s‐1 O2 and 0.090 mol mol‐1 photon at 100% absorption. The upper limit of a is close to a realistic limit of O2 of 0.10 mol mol‐1 photon. The upper limit of GPmax, however, is markedly below the theoretically attainable 180 mol m‐2 s‐1 O2, reflecting a suboptimal three‐dimensional structure and light distribution. Indirect measures supported this explanation as GPmax increased fourfold from communities with a very uneven to a more even light distribution. Photosynthetic characteristics of communities are strongly influenced by plant density, absorption, and distribution of light and cannot be interpreted from the photosynthetic behavior of phytoelements. Thus, many examples of carbon and nutrient limitation in experiments with separate phytoelements may not withstand at the relevant ecological scale of communities where light almost always constrains photosynthetic production.

Low concentrations of NaHSO&lt;sub&gt;3&lt;/sub&gt; increase photosynthesis, biomass, and attenuate photoinhibition in Satsuma mandarin (Citrus unshiu Marc.) plants

Spraying low concentrated (0.5–5.0 mM) solutions of NaHSO3 on Satsuma mandarin (Citrus unshiu Marc.) leaves resulted in enhancement (maximal about 15 % at 1 mM NaHSO3) of net photosynthetic rate (PN) for 6 d. The potential photochemical efficiency of photosystem 2 (PS2, Fv/Fm) and the quantum yield of PS2 electron transport (ΦPS2) were increased under strong photon flux density (PFD). The slow phase of millisecond delayed light emission (ms-DLE) was increased, showing that the transmembrane proton motive force related to photophosphorylation was enhanced. We also observed that low concentrations of NaHSO3 promoted the production of ATP in irradiated leaves. We suggest that the increase in PN in Satsuma mandarin leaves caused by low concentrations of NaHSO3 solution may have been due to the stimulation of photophosphorylation and, hence, the increase in photochemical efficiency through speeding-up of PS2 electron transport. Photoinhibition of photosynthesis in leaves was modified by NaHSO3 treatment under high PFD. Hence the increase in leaf dry mass seems to be associated with the mitigation of photoinhibition caused by strong PFD.