Lanthanum improves salt tolerance of maize seedlings

In this study, the effects of lanthanum were investigated on contents of pigments, chlorophyll (Chl) fluorescence, antioxidative enzymes, and biomass of maize seedlings under salt stress. The results showed that salt stress significantly decreased the contents of Chl and carotenoids, maximum photochemical efficiency of PSII (F_v/F_m), photochemical quenching (q_P), and quantum efficiency of PSII photochemistry (Φ_PSII), net photosynthetic rate (P_N), and biomass. Salt stress increased nonphotochemical quenching (q_N), the activities of ascorbate peroxidase, catalase, superoxide dismutase, glutathione peroxidase, and the contents of malondialdehyde and hydrogen peroxide compared with control. Pretreatment with lanthanum prior to salt stress significantly enhanced the contents of Chl and carotenoids, F_v/F_m, q_P, q_N, Φ_PSII, P_N, biomass, and activities of the above antioxidant enzymes compared with the salt-stressed plants. Pretreatment with lanthanum also significantly reduced the contents of malondialdehyde and hydrogen peroxide induced by salt stress. Our results suggested that lanthanum can improve salt tolerance of maize seedlings by enhancing the function of photosynthetic apparatus and antioxidant capacity.     

Plant shading increases lipid peroxidation and intensifies senescence-induced changes in photosynthesis and activities of ascorbate peroxidase and glutathione reductase in wheat

Plants of spring wheat (Triticum aestivum L. cv. Saxana) were grown during the autumn. Over the growth phase of three leaves (37 d after sowing), some of the plants were shaded and the plants were grown at 100 (control without shading), 70, and 40 % photosynthetically active radiation. Over 12 d, chlorophyll (Chl) and total protein (TP) contents, rate of CO₂ assimilation (P _N), maximal efficiency of photosystem 2 photochemistry (F_V/F_P), level of lipid peroxidation, and activities of antioxidative enzymes ascorbate peroxidase (APX) and glutathione reductase (GR) were followed in the 1_st, 2_nd, and 3_rd leaves (counted according to their emergence). In un-shaded plants, the Chl and TP contents, P _N, and F_V/F_P decreased during plant ageing. Further, lipid peroxidation increased, while the APX and GR activities related to the fresh mass (FM) decreased. The APX activity related to the TP content increased in the 3_rd leaves. The plant shading accelerated senescence including the increase in lipid peroxidation especially in the 1^st leaves and intensified the changes in APX and GR activities. We suggest that in the 2_nd and 3_rd leaves a degradation of APX was slowed down, which could reflect a tendency to maintain the antioxidant protection in chloroplasts of these leaves.     

Boron excess affects photosynthesis and antioxidant apparatus of greenhouse Cucurbita pepo and Cucumis sativus

This study aimed to evaluate the behavior of zucchini (Cucurbita pepo L.) and cucumber (Cucumis sativus L.) under boron (B) excess. Plants were grown under greenhouse conditions in a sandy soil–peat mixture using a nutrient solution containing 0.2 (control), 10 and 20 mg L^?1 B. Visible symptoms were quantified and leaf B accumulation, gas exchanges, chlorophyll (Chl) a fluorescence, malondialdehyde by-products and antioxidants were investigated 20 days after the beginning of the treatments. Boron toxicity induced oxidative load and leaf necrotic burns coupled with the reduction of leaf growth and biomass accumulation in both species. Boron excess resulted in a decrease of Chl a/b ratio, potential (F_v/F_m) and actual (Φ_PSII) PSII quantum efficiency, photosynthetic rate (Pn), stomatal conductance (g_s), and transpiration (E) as well. A general stimulation of the antioxidant enzymes ascorbate peroxidase, catalase and superoxide dismutase was observed, and a significant increase in the oxidized form of ascorbate and glutathione was evidenced for treated plants of both species. A difference between the two species was observed: C. pepo appeared to be more sensitive to B stress being damaged at all B concentration. C. sativus grown at 10 mg L^?1 B in nutrient solution showed some down-regulated mechanisms, i.e. increase in Chl b content and a good photochemical PSII efficiency as well as a higher amount of constitutive antioxidant molecules, that, however, are not sufficient to contrast the negative effects of B.     

Effects of solar UV radiation and temperature on morphology and photosynthetic performance of Chaetoceros curvisetus

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_PSII) 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_PSII 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.     

Increase in unsaturated fatty acids in membrane lipids of Suaeda salsa L. enhances protection of photosystem II under high salinity

In order to examine the possible role of unsaturated fatty acids in photosynthesis of halophytes under high salinity, the effect of salinity on plant growth, chlorophyll (Chl) content, photochemical efficiency of PSII, membrane lipid content and fatty acids composition of a C₃ euhalophyte Suaeda salsa L. was investigated. Salt stress induced a slight increase of the maximal photochemical efficiency of PSII (F_v/F_m), actual PSII efficiency (Φ_PSII), Chl a content and Chl a/b ratio. The unsaturated fatty acid content also increased under salt stress. The proportion of MGDG, DGDG, SQDG, and PC decreased, while the proportion of PG increased from 10.9% to 26.9% under salt stress. These results suggest that S. salsa displays high resistance to photoinhibition under salt stress and that increased concentration of unsaturated fatty acids in membrane lipids of S. salsa enhances the tolerance of photosystem II to salt stress.     

Chill-induced inhibition of photosynthesis was alleviated by 24-epibrassinolide pretreatment in cucumber during chilling and subsequent recovery

To investigate whether brassinosteroids (BRs) could be used to alleviate chill-induced inhibition of photosynthesis in cucumber (Cucumis sativus L) during chilling and subsequent recovery, the effects of exogenously applied 24-epibrassinolide (EBR) on gas exchange, chlorophyll fluorescence parameters, and antioxidant enzyme activity were studied. Cucumber plants were exposed to chilling under low light (12/8°C and 100 μmol m⁻² s⁻¹ PPFD) for 3 days and then recovered under normal temperature and high irradiance (28/18°C and 600 μmol m⁻² s⁻¹ PPFD) for 6 days. Chilling significantly decreased the net photosynthetic rate (P _N) and stomatal conductance (g _s), and increased rate of O₂ ^·− formation and H₂O₂ and malondialdehyde (MDA) content in cucumber leaves, but did not influence the optimal quantum yield of PSII (F_v/F_m). Chilling also decreased the effective quantum yield of PSII photochemistry (Φ_PSII) and photochemical quenching (q_P), but induced an increase in nonphotochemical quenching (NPQ), and the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX). High irradiance (600 μmol m⁻² s⁻¹) further aggravated the decrease in P _N, g _s, Φ_PSII and q_P, and enhanced the increase in reactive oxygen species (ROS) generation and accumulation in the first day of recovery after chilling. However, high irradiance induced a sharp decrease in F_v/F_m and NPQ, as well as the activities of SOD and APX on the first day of recovery. EBR pretreatment significantly alleviated chill-induced inhibition of photosynthesis during chilling stress and subsequent recovery period, which was mainly due to significant increases in g _s, Φ_PSII, q_P and NPQ. EBR pretreatment also reduced ROS generation and accumulation, and increased the activities of SOD and APX during chilling and subsequent recovery. Those results suggest that EBR pretreatment alleviates the chill reduction in photosynthesis and accelerated the recovery rate mainly by increasing of the stomatal conductance, the efficiency of utilization and dissipation of leaf absorbed light, and the activity of the ROS scavenging system during chilling and subsequent recovery period.     

Analysis of ascorbate peroxidase genes expressed in resistant and susceptible wheat lines infected by the cereal cyst nematode, Heterodera avenae

Changes in ascorbate peroxidase (APX) enzyme activity in response to nematode (Heterodera avenae) attack were studied in roots of three hexaploid wheat lines carrying Cre2, Cre5, or Cre7 nematode resistance genes and the susceptible Triticum aestivum cv. Anza. A spectrophotometric analysis was carried out with root extracts of infected plants 4, 7, 11, and 14 days after nematode inoculation using uninfected plant as control. APX induction in infected resistant genotypes was similar and higher than in the susceptible control. The introgression wheat/Aegilops ventricosa H-93-8 line, carrying the Cre2 gene, and its parental line H-10-15 as susceptible control were used to analyze whether this increase of activity was correlated with the induction of APX gene expression. Genes encoding cytosolic forms of APX were induced in roots of both lines in response to nematode infection. This induction took place both earlier and with greater intensity in the resistant line than in the susceptible one, and it was also higher in the root area at the site of nematode attachment.     

Responses of photosynthetic characteristics and antioxidative metabolism in winter wheat to post-anthesis shading

In a field experiment, two winter wheat (Triticum aestivum L.) cultivars, Tainong 18 (a large-spike cultivar) and Jinan 17 (a multiple-spike cultivar), were treated with 78% (S1), 50% (S2), and 10% (S3) of full sunshine (S0, control) from anthesis to maturity to determine the responses of photosynthetic characteristics and antioxidative enzyme activities in a flag leaf. Compared with S0 treatment, the chlorophyll (Chl) content and maximal efficiency of photosystem II (PSII) photochemistry (F_v/F_m) of flag leaves were enhanced in treatments S1 and S2. From 0 to 7 d post flowering, the Chl content and F_v/F_m in S3 were also higher than those in S0, but significantly lower than those in controls, respectively. With the increase of shading intensity, the effective quantum yield of PSII (Φ_PSII) was promoted; whereas, the ratio of Chl a/b declined. Compared with S0, treatments S2 and S3 significantly suppressed the activities of superoxide dismutase (SOD) and peroxidase (POD), net photosynthetic rate (P _N), and contents of total soluble sugar, nevertheless, S1 treatment showed positive effects on the above parameters. Under the same shading condition, Jinan 17 had larger Chl content and higher activities of PSII and antioxidative enzymes, but lower malondialdehyde (MDA) content than Tainong 18. The results indicated that multiple-spike cultivar was more advantageous for the Huang-Huai-Hai Plain, where shading problem occurs later during the growth period, than the large-spike cultivar, because of the lesser damage in a flag leaf and better photosynthetic function of the former one. Wheat plants under S1 shading condition had relatively high activities of antioxidative enzymes and a low degree of membrane lipid peroxidation, which was in favor of stress resistance, maintaining high P _N duration, and accumulation of photosynthates in wheat plants.     

Acclimation of winter wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis>, cv. Yangmai 13) to low levels of solar irradiance

Winter wheat is a grass species widely planted in northern and central China, where the increase of aerosols, air pollutants and population density are causing significant reduction in solar irradiance. In order to investigate the adaptation of winter wheat (Triticum aestivum L., cv. Yangmai 13) to low irradiance conditions occurring in the downstream plain of the Yangtze River (China), plants were subjected to four solar irradiance treatments (100%, 60%, 40%, and 20% of environmental incident solar irradiance). Significant increases in chlorophyll (Chl) and xanthophyll (Xan) pigments, and decreases in Chl a/b and Xan/Chl ratios were observed in plants under low light. Light-response curves showed higher net photosynthetic rates (P _N) in fully irradiated plants, that also showed a higher light-compensation point. Shaded plants maintained high values of minimal fluorescence of dark-adapted state (F_o) and maximum quantum efficiency of PSII photochemistry (F_v/F_m) that assess a lower degree of photoinhibition under low light. Reduced irradiance caused decreases in effective quantum yield of PSII photochemistry (Φ_PSII), electron transport rate (ETR), and nonphotochemical quenching coefficient (q_N), and the promotion of excitation pressure of PSII (1 − q_P). The activities of the antioxidant enzymes superoxide dismutase and peroxidase were high under reduced light whereas no light-dependent changes in catalase activity were observed. Thiobarbituric acid reactive species content and electrolyte leakage decreased under shaded plants that showed a lower photooxidative damage. The results suggest that winter wheat cv. Yangmai 13 is able to maintain a high photosynthetic efficiency under reduced solar irradiance and acclimates well to shading tolerance. The photosynthetic and antioxidant responses of winter wheat to low light levels could be important for winter wheat cultivation and productivity.     

Subsurface chlorophyll maximum (SCM) location and extension in the water column as governed by a density interface in the strongly stratified Kattegat estuary

The aims of the study were to analyse the relations between the physics of a water column and the location of the subsurface chlorophyll maximum (SCM) peaks in a strongly stratified estuary. Could extension and depth location of the SCM be explained by the physical conditions in terms of water column stratification and density interface? Questions were addressed by obtaining data on water column density (CTD), chlorophyll a (Chl a), nutrients, (F _v/F _m), σ_PSII and K _d(PAR) at 15 positions along a 575 km transect in the Kattegat estuary. Results showed that the estuary was strongly stratified with mixed surface and bottom layers intercepted by a layer where density increased with depth. The SCM occurred only in this density interface, and widths of SCM and density interface were highly correlated. The surface waters were nearly depleted of inorganic nitrogen, phosphate and silicate though with significant higher concentrations in the waters below the interface. The Chl a concentration was comparatively higher in the SCM peak as well as maximum quantum efficiency (F _v/F _m) and functional cross sectional area (σ_PSII). The SCM was maintained at very low light levels and by a diapycnal nitrogen flux, with a stratified water column and nutrient depleted surface waters as predecessors. It was concluded that the depth location and vertical extension of the SCM in the estuary were closely linked to the physical structure of the water column in terms of density interface and stratification.     

Ecophysiological adaptation of <Emphasis Type="Italic">Calligonum roborovskii</Emphasis> to decreasing soil water content along an altitudinal gradient in the Kunlun Mountains,central Asia

To understand the ecophysiological adaptation mechanisms of Calligonum roborovskii to altitude variation, this study analyzed chlorophyll a (Chl a), chlorophyll b (Chl b), Chl (a + b), carotenoid (Car), malondialdehyde (MDA), ascorbate (AsA), proline (Pro), membrane permeability (MP), reactive oxygen species (ROS), specific leaf area (SLA), leaf mass per area (LMA), leaf nitrogen content based on mass (N_mass), and the activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX) in leaves of plants inhabiting different altitudes (A1: 2100 m, A2: 2350 m, A3: 2600 m) on the northern slope of the Kunlun Mountains. The results showed that Chl a, Chl b, Chl (a + b), SLA, N_mass, and the activity of CAT increased with increasing altitude. LMA, MP, MDA, Car, Pro, AsA, O₂⁻, H₂O₂ and the activities of SOD, POD, and APX decreased with increasing altitude. The test results also showed that, changes in venvironmental factors along an altitudinal gradient are not obvious. Soil water content is the main ecological factor. With increasing altitude, soil water content increased significantly. More non-enzymatic and enzymatic antioxidants played an important role in eliminating intracellular ROS. They kept the cell membrane in a stable state and ensured the normal growth of C. roborovskii.     

Variation of photosynthetic performance, nutrient uptake, and elemental composition of different generations and different thallus parts of Saccharina japonica

In order to illustrate the physiological variation of different generations and different thallus parts of Saccharina japonica, physiological parameters such as maximum and effective PSII photochemical efficiency, nutrient uptake, and elemental composition were determined in the laboratory. Photosynthetic analysis in different generations indicated that, although gametophytes had higher pigment contents than the sporophyte, they had lower values of F _v/F _m and ΔF/F′_m. The highest Chl a/Chl c ratio was found in sporophyte generation (3.98?±?0.01) and in the basal part of fresh thallus (2.66?±?0.02). The sporophyte had significantly higher values of nitrate uptake but lower values of phosphorus uptake than the gametophytes. The contents of nitrogen and carbon as well as C/N in gametophytes were significantly higher than those in sporophytes. In addition, the basal part of the S. japonica thallus had the highest C content (22.31?±?1.50 %) but the lowest N content (2.02?±?0.16 %), as well as the highest value of C/N (11.02?±?0.34).     

Chromium effect on ROS generation and detoxification in pea (Pisum sativum) leaf chloroplasts

Pea plants were exposed to 0, 20, 50, and 100 µM chromium [Cr(VI)] to investigate oxidative stress in isolated chloroplasts. Leaf area and biomass accumulation were significantly reduced at higher Cr supply. Generation of superoxide, hydrogen peroxide, and ·OH radical generation was enhanced in the chloroplasts isolated from Cr-exposed pea plants. Cr(VI) significantly reduced F _v/F _m ratio of chlorophyll (Chl) fluorescence, Chl content, and whole chain electron transport rate. Superoxide dismutase (SOD) activity increased at lower Cr supply while it decreased at higher Cr supply. Ascorbate peroxidase (APX) was found to be most sensitive to Cr stress. Monodehydroascorbate reductase activity remained higher at 20 and 50 µM Cr but decreased at 100 µM Cr. Increased activities of dehydroascorbate reductase (DHAR) and glutathione reductase (GR) in the isolated chloroplasts were observed during the initial 3 days of Cr exposure of pea plants. Activities of DHAR and GR were increased up to day 3 only. Ascorbate and glutathione (GSH) pools showed similar decrease that was more evident in the GSH pool as the duration of Cr treatment increased. Observed changes in reactive oxygen species concentration, photosynthetic characteristics, and antioxidant system indicate that chloroplasts in Cr-exposed pea plants are an important target of oxidative stress.     

The responses of photosynthetic gas exchange and chlorophyll a fluorescence to changes of irradiance and temperature in two species of Miscanthus

Photosynthetic CO₂ uptake and chlorophyll (Chl) a fluorescence of C₄ perennial grasses, Miscanthus floridulus (Labill) Warb and M. transmorrisonensis Hayata, from altitudes in central Taiwan of 390 and 2700 m, respectively, were studied at 10 and 25 °C to find if the species differ in their photosynthetic responses to a low temperature, and whether their photosystems 2 become more susceptible to the photoinhibition at low temperatures. For both species, the maximum photosynthetic rate (P_max) was reduced when the leaves were exposed to 10 °C. At irradiances higher than 400 µmol m^-2 s^-1, the values of F_v/F_m were reduced in both species at 10 °C but not at 25 °C, which indicated the photoinhibition at 10 °C. Reductions in P_max and the values of F_v/F_m at 10 °C were lesser in M. transmorrisonensis than in M. floridulus.     

The responses of photosynthetic gas exchange and chlorophyll a fluorescence to changes of irradiance and temperature in two species of Miscanthus

Photosynthetic CO₂ uptake and chlorophyll (Chl) a fluorescence of C₄ perennial grasses, Miscanthus floridulus (Labill) Warb and M. transmorrisonensis Hayata, from altitudes in central Taiwan of 390 and 2700 m, respectively, were studied at 10 and 25 °C to find if the species differ in their photosynthetic responses to a low temperature, and whether their photosystems 2 become more susceptible to the photoinhibition at low temperatures. For both species, the maximum photosynthetic rate (P_max) was reduced when the leaves were exposed to 10 °C. At irradiances higher than 400 μmol m^-2 s^-1, the values of F_v/F_m were reduced in both species at 10 °C but not at 25 °C, which indicated the photoinhibition at 10 °C. Reductions in P_max and the values of F_v/F_m at 10 °C were lesser in M. transmorrisonensis than in M. floridulus. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of low temperature stress on the antioxidant system and photosynthetic apparatus of Kappaphycus alvarezii (Rhodophyta,Solieriaceae)

To understand the effects of low temperature stress on Kappaphycus alvarezii and the responses of antioxidant systems and photosystem II (PSII), behaviour in K. alvarezii thalli exposed to low temperatures (20°C, 17°C and 14°C) for 2 hours was evaluated. Compared with the control at 26°C, activities of some antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and the level of antioxidant substance (reduced glutathione) increased in K. alvarezii thalli when exposed to lowered temperatures (20°C, 17°C). Hydroxyl free radical (·OH) scavenging activity of K. alvarezii thalli also increased at 20°C and 17°C compared with the control. This indicated that the resistance to low temperature stress in the antioxidant system of K. alvarezii increased at lowered temperatures of 20°C and 17°C. However, at the lowest temperature (14°C), no significant increases of this algal antioxidant were observed. Under low temperature stress, the maximum quantum yield of PSII photochemistry (F_V/F_M) and PSII actual photochemical efficiency (Φ_PSII) decreased in K. alvarezii thalli, suggesting that the photosynthetic capacity declined. Components of the photosynthetic apparatus (such as the oxygen-evolving complex, light absorption antennas, reaction centres, electron acceptor sides and electron donor sides of PSII) were damaged by low temperature stress to varying degrees. In addition, it was found that low temperature stress led to decreases of both D1 protein and Rubisco LSU (Rubisco large subunit) protein levels. This work is a significant contribution towards understanding the basic mechanism involved in the resistance and the adaptation of K. alvarezii to low temperature stress conditions.     

NaCl-Inhibited Chlorophyll Synthesis and Associated Changes in Ethylene Evolution and Antioxidative Enzyme Activities in Wheat

Effect of NaCl was studied on chlorophyll (Chl) synthesis and its intermediates (protoporphyrin IX, Mg-protoporphyrin IX, and protochlorophyllide), dry mass, ethylene evolution, and activities of superoxide dismutase (SOD) and peroxidase (APX) in wheat (Triticum aestivum L.) seedlings at 24, 48, and 72 h after germination. A conspicuous decrease in Chl synthesis, associated with increase in ethylene evolution and SOD and APX activities, was noted as NaCl concentration was increased from 0 to 100 mM. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fluorescence F 0 of photosystems II and I in developing C3 and C4 leaves,and implications on regulation of excitation balance

This work addresses the question of occurrence and function of photosystem II (PSII) in bundle sheath (BS) cells of leaves possessing NADP-malic enzyme-type C₄ photosynthesis (Zea mays). Although no requirement for PSII activity in the BS has been established, several component proteins of PSII have been detected in BS cells of developing maize leaves exhibiting O₂-insensitive photosynthesis. We used the basal fluorescence emissions of PSI (F _0I) and PSII (F _0II) as quantitative indicators of the respective relative photosystem densities. Chl fluorescence induction was measured simultaneously at 680 and 750 nm. In mature leaves, the F _m(680)/F ₀(680) ratio was 10.5 but less in immature leaves. We propose that the lower ratio was caused by the presence of a distinct non-variable component, F _c, emitting at 680 and 750 nm. After F _c was subtracted, the fluorescence of PSI (F _0I) was detected as a non-variable component at 750 nm and was undetectably low at 680 nm. Contents of Chls a and b were measured in addition to Chl fluorescence. The Chl b/(a + b) was relatively stable in developing sunflower leaves (0.25–0.26), but in maize it increased from 0.09 to 0.21 with leaf tissue age. In sunflower, the F _0I/(F _0I + F _0II) was 0.39 ± 0.01 independent of leaf age, but in maize, this parameter was 0.65 in young tissue of very low Chl content (20–50 mg m^?2) falling to a stable level of 0.53 ± 0.01 at Chl contents >100 mg m^?2. The values of F _0I/(F _0I + F _0II) showed that in sunflower, excitation was partitioned between PSII and PSI in a ratio of 2:1, but the same ratio was 1:1 in the C₄ plant. The latter is consistent with a PSII:PSI ratio of 2:1 in maize mesophyll cells and PSI only in BS cells (2:1:1 distribution). We suggest, moreover, that redox mediation of Chl synthesis, rather than protein accumulation, regulates photosystem assembly to ensure optimum excitation balance between functional PSII and PSI. Indeed, the apparent necessity for two Chls (a and b) may reside in their targeted functions in influencing accumulation of PSI and PSII, respectively, as opposed to their spectral differences.     

Effect of Glomus mosseae on chlorophyll content, chlorophyll fluorescence parameters, and chloroplast ultrastructure of beach plum (Prunus maritima) under NaCl stress

The present study was undertaken to investigate the effect of Glomus mosseae on chlorophyll (Chl) content, Chl fluorescence parameters and chloroplast ultrastructure of beach plum seedlings under 2% NaCl stress. The results showed that compared to control, both Chl a and Chl b contents of NaCl + G. mosseae treatment were significantly lower during the salt stress, while Chl a/b ratio increased significantly. The increase of minimal fluorescence of darkadapted state (F₀), and the decrease of maximal fluorescence of dark-adapted state (F_m) and variable fluorescence (F_v) values were inhibited. The maximum quantum yield of PSII photochemistry (F_v/F_m), the maximum energy transformation potential of PSII photochemistry (F_v/F₀) and the effective quantum yield of PSII photochemistry (??_PSII) increased significantly, especially the latter two variables. The values of the photochemical quenching coefficient (q_P) and the nonphotochemical quenching (NPQ) were similar between G. mosseae inoculation and noninoculation. It could be concluded that G. mosseae inoculation could protect the photosystem II (PSII) of beach plum, enhance the efficiency of primary light energy conversion and improve the primitive response of photosynthesis under salinity stress. Meanwhile, G. mosseae inoculation was beneficial to maintain the integrity of thylakoid membrane and to protect the structure and function of chloroplast, which suggested that G. mosseae can alleviate the damage of NaCl stress to chloroplast.