Impact of simulated acidic rain on growth, photosynthetic pigments, cell metabolites, and leaf characteristics of green gram

Seedlings of green gram (Vigna radiata cv. ADT-1 and CO-5) were exposed to daily showers of simulated acidic rain (H2SO4 : HNO3 : HCl, 4 : 2 : 1, v/v) for 10 d. The effects were analysed after 5 and 10 showers, respectively. Rain of pH 2.5 inhibited seedling growth and biomass accumulation, though in other acidic levels the effects were mostly inconsistent. Both cultivars had high degree of surface wettability indicated by high leaf surface contact angles and water-holding capacity. Treated leaves were thinner with smaller mesophyll cells. Stomatal index and trichome density were lower in contrast to epidermal cell density and stomatal frequency which increased with increasing acidity. Decreases in chlorophyll (Chl), carotenoid (Car), and starch contents in cv. ADT-1 at pH 2.5 were observed after 5 showers, while in cv. CO-5 decreases were noted only after 10 showers. In contrast to total sugar levels, the protein content of cv. CO-5 was augmented significantly after simulated acidic rain (SAR) treatment.     

Effect of simulated acid rain on nodulation and nitrogen metabolism in Vigna radiata cultivars

Nodulation was inhibited in plants of green gram (Vigna radiata, cvs. ADT-1 and CO-5) exposed to different levels of simulated acid rain using a mixture of H2SO4, HNO3 and HCl (6:3:1) of pH 2.5, 4.0 and 5.5 in comparison with control (pH 7.0). Protein content of leaves increased in cv. CO-5 but decreased in cv. ADT-1 whereas the nitrate content of leaves increased in cv. ADT-1 but lowered in cv. CO-5. Nitrate reductase activity was increased in the nodular roots of cv. ADT-1 but was decreased in leaves. In cv. CO-5 it was increased in leaves but was insignificantly reduced in the nodules at pH 2.5. The nodule nitrogenase activity increased at pH 4.0 and 2.5 in cv. ADT-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of nitrogen supply restriction on gas exchange and photosystem 2 function in flag leaves of a traditional low-yield cultivar and a recently improved high-yield cultivar of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

The effects of nitrogen (N) supply restriction on the CO₂ assimilation and photosystem 2 (PS2) function of flag leaves were compared between two contrastive Japanese rice cultivars, a low-yield cultivar released one century ago, cv. Shirobeniya (SRB), and a recently improved high-yield cultivar, cv. Akenohoshi (AKN). Both cultivars were solution-cultured at four N supply levels from N4 (control) to N1 (the lowest). With a reduction in N-supply, contents of N (LNC), ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO), and chlorophyll (Chl) in flag leaves decreased in both cultivars. In parallel with this, the net photosynthetic rate (P _N), mesophyll conductance (g _m), and stomatal conductance (g _s) decreased. P _N was more dominantly restricted by g _m than g _s. The values of P _N, g _m, and RuBPCO content were larger in AKN than SRB at the four N supply levels. The content of Chl greatly decreased with N deficiency, but the reduction in the maximum quantum yield of PS2 was relatively small. Quantum yield of PS2 (Φ_PS2) decreased with N deficiency, and its significant cultivar difference was observed between the two cultivars at N1: a high value was found in AKN. The content ratio of Chl/RuBPCO was also significantly low in AKN. The low Chl/RuBPCO is one of the reasons why AKN maintained a comparatively high P _N and Φ_PS2 at N deficiency. The adequate ratio of N distribution between Chl and RuBPCO is the important prerequisite for the efficient and sustainable photosynthesis in a flag leaf of rice plant under low N-input.     

Activity of Photosystem 2, Lipid Peroxidation,and the Enzymatic Antioxidant Protective System in Heat Shocked Barley Seedlings

The impact of heat shock on minimising the activity of photosystem 2 (PS2) initiating high lipid peroxidation (POL) level and consequently changes in the enzymatic-antioxidant protective system was studied in seedlings of two Egyptian cultivars of barley (Giza 124 and 125). Heat doses (35 and 45 °C for 2, 4, 6, and 8 h) decreased chlorophyll (Chl) contents coupled with an increase in Chl a/b ratio, diminished Hill reaction activity, and quenched Chl a fluorescence emission spectra. These parameters reflect the disturbance of the structure, composition, and function of the photosynthetic apparatus as well as the activity of PS2. POL level, as dependent on the balance between pro- and anti-oxidant systems, was directly correlated with temperature, exposure time, and their interaction. Heat shock caused an increase in the electric conductivity of cell membrane, and malonyldialdehyde content (a peroxidation product) coupled with the disappearance of the polyunsaturated linolenic acid (C_18:3), reflecting the peroxidation of membrane lipids which led to the loss of membrane selective permeability. Moreover, it induced distinct and significant changes in activities of antioxidant enzymes. Superoxide dismutase and peroxidase activities have been progressively enhanced by moderate and elevated heat doses, but the most elevated one (45 °C for 8 h) showed a decrease in activities of both enzymes. In contrast, catalase activity was reduced with all heat shocks.     

Photosystem II chlorophyll a fluorescence lifetimes and intensity are independent of the antenna size differences between barley wild-type and chlorina mutants: Photochemical quenching and xanthophyll cycle-dependent nonphotochemical quenching of fluorescence

Photosystem II (PS II) chlorophyll (Chl) a fluorescence lifetimes were measured in thylakoids and leaves of barley wild-type and chlorina f104 and f2 mutants to determine the effects of the PS II Chl a+b antenna size on the deexcitation of absorbed light energy. These barley chlorina mutants have drastically reduced levels of PS II light-harvesting Chls and pigment-proteins when compared to wild-type plants. However, the mutant and wild-type PS II Chl a fluorescence lifetimes and intensity parameters were remarkably similar and thus independent of the PS II light-harvesting antenna size for both maximal (at minimum Chl fluorescence level, F_o) and minimal rates of PS II photochemistry (at maximum Chl fluorescence level, F_m). Further, the fluorescence lifetimes and intensity parameters, as affected by the trans-thylakoid membrane pH gradient (pH) and the carotenoid pigments of the xanthophyll cycle, were also similar and independent of the antenna size differences. In the presence of a pH, the xanthophyll cycle-dependent processes increased the fractional intensity of a Chl a fluorescence lifetime distribution centered around 0.4–0.5 ns, at the expense of a 1.6 ns lifetime distribution (see Gilmore et al. (1995) Proc Natl Acad Sci USA 92: 2273–2277). When the zeaxanthin and antheraxanthin concentrations were measured relative to the number of PS II reaction center units, the ratios of fluorescence quenching to [xanthophyll] were similar between the wild-type and chlorina f104. However, the chlorina f104, compared to the wild-type, required around 2.5 times higher concentrations of these xanthophylls relative to Chl a+b to obtain the same levels of xanthophyll cycle-dependent fluorescence quenching. We thus suggest that, at a constant pH, the fraction of the short lifetime distribution is determined by the concentration and thus binding frequency of the xanthophylls in the PS II inner antenna. The pH also affected both the widths and centers of the lifetime distributions independent of the xanthophyll cycle. We suggest that the combined effects of the xanthophyll cycle and pH cause major conformational changes in the pigment-protein complexes of the PS II inner or core antennae that switch a normal PS II unit to an increased rate constant of heat dissipation. We discuss a model of the PS II photochemical apparatus where PS II photochemistry and xanthophyll cycle-dependent energy dissipation are independent of the Peripheral antenna size.Abbreviations Ax antheraxanthin - BSA bovine serum albumin - c_x lifetime center of fluorescence decay component x - CP chlorophyll binding protein of PS II inner antenna - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DTT dithiothreitol - f_x fractional intensity of fluorescence lifetime component x - F_m, F_m maximal PS II Chl a fluorescence intensity with all Q_A reduced in the absence, presence of thylakoid membrane energization - F_o minimal PS II Chl a fluorescence intensity with all Q_A oxidized - F_v=F_m–F_o variable level of PS II Chl a fluorescence - HPLC high performance liquid chromatography - k_A rate constant of all combined energy dissipation pathways in PS II except photochemistry and fluorescence - k_F rate constant of PS II Chl a fluorescence - LHCIIb main light harvesting pigment-protein complex (of PS II) - N_pig mols Chl a+b per PS II - NPQ=(F_m/F_m–1) nonphotochemical quenching of PS II Chl a fluorescence - PAM pulse-amplitude modulation fluorometer - PFD photon-flux density, mols photons m^–2 s^–1 - PS II Photosystem II - P680 special-pair Chls of PS II reaction center - Q_A primary quinone electron acceptor of PS II - V_x violaxanthin - w_x width at half maximum of Lorentzian fluorescence lifetime distribution x - Zx zeaxanthin - pH trans-thylakoid proton gradient - % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqef0uAJj3BZ9Mz0bYu% H52CGmvzYLMzaerbd9wDYLwzYbItLDharqqr1ngBPrgifHhDYfgasa% acOqpw0xe9v8qqaqFD0xXdHaVhbbf9v8qqaqFr0xc9pk0xbba9q8Wq% Ffea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8frFve9Fve9Ff0dme% GabaqaaiGacaGaamqadaabaeaafiaakeaacqGH8aapcqaHepaDcqGH% +aGpdaWgaaWcbaGaamOraiaad2gaaeqaaaaa!4989!\[< \tau > _{Fm}\],% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqef0uAJj3BZ9Mz0bYu% H52CGmvzYLMzaerbd9wDYLwzYbItLDharqqr1ngBPrgifHhDYfgasa% acOqpw0xe9v8qqaqFD0xXdHaVhbbf9v8qqaqFr0xc9pk0xbba9q8Wq% Ffea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8frFve9Fve9Ff0dme% GabaqaaiGacaGaamqadaabaeaafiaakeaacqGH8aapcqaHepaDcqGH% +aGpdaWgaaWcbaGaamOraiaad+gaaeqaaOGaeyypa0Zaaabqaeaaca% WGMbWaaSbaaSqaaiaadIhaaeqaaOGaam4yamaaBaaaleaacaWG4baa% beaaaeqabeqdcqGHris5aaaa!50D3!\[< \tau > _{Fo} = \sum {f_x c_x }\] average lifetime of Chl a fluorescence calculated from a multi-exponential model under F_m, F_o conditions     

Low-night temperature (LNT) induced changes of photosynthesis in grapevine (Vitis vinifera L.) plants.

Changes of leaf pigments, ribulose-1,5-bisphosphate carboxylase (RuBPC) and photosynthetic efficiency were examined in grapevine (Vitis vinifera L.) plants grown under ambient irradiation (maximum daily PAR = 1500 micromol m(-2) s(-1)) for 7 days to low night temperature (LNT) of 5 degrees C (daily from 18:00 to 06:00). The contents of chlorophyll (Chl) and carotenoids (Car) per fresh mass were lower in LNT leaves than in control leaves. The contents of alpha + beta carotene and lutein-5,6-epoxide remained unaffected, but the de-epoxidation state involving the components of xanthophyll cycle increased. RuBPC activity and soluble proteins were also significantly reduced in LNT leaves. In isolated thylakoids, a marked inhibition of whole chain (PS I + PS II) and PS II activity were observed in LNT leaves. Smaller inhibition of PS I activity was observed in LNT leaves. The artificial exogenous electron donors, MnCl2, DPC and NH2OH did not restored the loss of PS II activity in LNT leaves. The same results were obtained when F(v)/F(m) was evaluated by Chl fluorescence measurements. The marked loss of PS II activity in LNT leaves was due to the marked loss of D1 protein which was determined by immunological studies.     

Action spectra and functional antenna sizes of Photosystems I and II in relation to the thylakoid membrane organization and pigment composition

The functional organization of competent photosynthetic units in developing thylakoids from intermittent-light grown pea as well as in the unstacked, stacked and phosphorylated stacked thylakoids from its mature chloroplasts was characterized by polarographic measurements of action spectra, reaction centre contents and optical cross-sections for PS I-mediated O2 uptake and PS II-mediated O2 evolution. The minimum antenna sizes of 60 and 37 chlorophyll a molecules for PS I and PS II, respectively, were determined in developing thylakoids with a ratio of Chl a/Chl b>50. In mature chloroplasts, the embedded light-harvesting chlorophyll a/b-binding (LHC) protein complexes increased the PS I and PS II effective antenna sizes by 3–6 times depending on the thylakoid membrane organization. In unstacked thylakoids, a randomization of PS I, PS II and LHC II led to the most uniform spectral distribution of light harvesting between the two photosystems but caused the maximal difference of their antenna sizes to be 370 and 100 Chls for the competent PS I and PS II units, respectively. Following the Mg2+-induced stacking of thylakoids, opposite complementary changes of the action spectra, antenna sizes and Chl a/Chl b ratios indicated a redistribution of a LHC II pool of 100 Chl ( a + b) molecules from PS I to PS II. Unlike to the stroma-exposed PS II in unstacked thylakoids, the granal PS II units of 200 Chls demonstrated an additional 2-fold increase of the effective antenna size due to energy transfer within PS II dimers under strong background illumination, which closed >90% of reaction centres. Protein phosphorylation of the stacked thylakoids induced a significant inactivation of the O2-evolving PS II centres but did not cause complementary changes of the action spectra and antenna sizes of the competent PS I and PS II. In this case, light harvesting parameters of the O2-evolving PS II units were nearly unaffected, whereas the obvious relative increase of the PS I activity at 650 nm and its decrease at >700 nm both in the action spectrum and optical cross-section measurements might suggest a substitution of PS I units in the O2-reducing fraction by another distinct fraction of -type which in turn is not the same to PS I units in unstacked thylakoids.     

Protective Effect of Triacontanol Against Acidic Mists in Samanea saman (Jacq.) Merrill Seedlings: Differential Responses in Growth, 14CO2 Fixation,Ribulose-1,5-Bisphosphate Carboxylase,and Electron Transport Activities

Seedlings of tropical leguminous tree Samanea saman (Jacq.) Merrill were exposed for 7 d to acidic mist (AM, induced by H₂SO₄) of pH 5.6, 4.0, and 2.0. AM significantly reduced seedling growth (root and shoot length, leaf density, leaf area, fresh and dry mass accumulation) and photosynthetic activities. In thylakoids isolated from leaves treated at pH 4.0 and 2.0 a decrease in the activities of photosystem (PS) 2 and whole chain electron transport was observed, but PS1 activity did not change. When the seedlings were subsequently sprayed with triacontanol (TRIA), the AM effect was partially or completely reversed indicating that TRIA can protect from AM effects. The artificial electron donors, di-phenylcarbazide (DPC) and hydroxylamine (NH₂OH), markedly restored the loss of PS2 activity in AM (pH 2.0) treated leaves. This is the first report of alleviating the AM by TRIA in tropical tree seedlings.     

Enantioselective HPLC of potentially CNS-active acidic amino acids with a Cinchona carbamate based chiral stationary phase

A tert-butylcarbamoylquinine-based chiral stationary phase (Chiralpak QN-AX) has been employed for the enantiomer separation of underivatized chiral acidic amino acids, viz. 4-carboxyphenylalanine (4-CPHE), 1-aminoindan-1,5-dicarboxylic acid (AIDA), 2-(5-carboxy-3-methyl-2-thienyl)glycine (3-MATIDA), 2-(4-carboxy-5-methyl-2-thienyl)glycine (5-MATIDA), and 2-(2'-carboxy-3'-phenylcyclopropyl)glycine (PCCG). Some of the acidic amino acids have potential activity on the central nervous system and are thus of great interest. A stereoselective HPLC method that allows the baseline resolution of all the five test solutes has been developed. For that purpose the mobile phase composition (pH, organic modifier, and type) and flow rate were optimized. The final method makes use of mild elution conditions, namely methanol - 0.8 M ammonium acetate buffer (97.5:2.5; v/v) pH 5.5 which are also compatible with mass spectrometric detection.     

The coleoptile chloroplast: Distinct distribution of xanthophyll cycle pigments,and enrichment in Photosystem II

Recent studies have shown that coleoptile chloroplasts operate the xanthophyll cycle, and that their zeaxanthin concentration co-varies with their sensitivity to blue light. The present study characterized the distribution of photosynthetic pigments in thylakoid pigment–protein complexes from dark-adapted and light-treated coleoptile and mesophyll chloroplasts, the low temperature fluorescence emission spectra, and the rates of PS I and PS II electron transport in both types of chloroplasts from 5-day-old corn seedlings. Pigments were extracted from isolated PS I holocomplex, LHC IIb trimeric and LHC II monomeric complexes and analyzed by HPLC. Chlorophyll distribution in coleoptile thylakoids showed 31% of the total collected Chl in PS I and 65% in the light harvesting complexes of PS II. In mesophyll thylakoids, the values were 44% and 54%, respectively. Mesophyll and coleoptile PS I holocomplexes differed in their Chl t a/Chl t b ratios (8.1 and 6.1, respectively) and -carotene content. In contrast, mesophyll and coleoptile LHC IIb trimers and LHC II monomers had similar Chl t a/Chl t b ratios and -carotene content. The three analyzed pigment–protein complexes from dark-adapted coleoptile chloroplasts contained zeaxanthin, whereas there was no detectable zeaxanthin in the complexes from dark-adapted mesophyll chloroplasts. In both chloroplast types, zeaxanthin and antheraxanthin increased markedly in the three pigment–protein complexes upon illumination, while violaxanthin decreased. In mesophyll thylakoids, zeaxanthin distribution as a percentage of the xanthophyll cycle pool was: LHC II monomers > LHC IIb trimers > PS I holocomplex, and in coleoptile thylakoids, it was: LHC IIb trimers > LHC II monomers = PS I holocomplex. Low temperature (77 K) fluorescence emission spectra showed that the 686 nm emission of coleoptile chloroplasts was approximately 50% larger than that of mesophyll chloroplasts when normalized at 734 nm. The pigment and fluorescence analysis data suggest that there is relatively more PS II per PS I and more LHC I per CC I in coleoptile chloroplasts than in mesophyll chloroplasts. Measurements of t in vitro uncoupled photosynthetic electron transport showed approximately 60% higher rates of electron flow through PS II in coleoptile chloroplasts than in mesophyll chloroplasts. Electron transport rates through PS I were similar in both chloroplast types. Thus, when compared to mesophyll chloroplasts, coleoptile chloroplasts have a distinct PS I pigment composition, a distinct chlorophyll distribution between PS I and PS II, a distinct zeaxanthin percentage distribution among thylakoid pigment–protein complexes, a higher PS II-related fluorescence emission, and higher PS II electron transport capacity. These characteristics may be associated with a sensory transducing role of coleoptile chloroplasts.     

Effect of pH,irradiance and population size on the toxicity of Furadan to two species of Anabaena

In two selected nitrogen-fixing cyanobacterial speciesAnabaena fertilissima andAnabaena variabilis pH, irradiance and different inocula sizes considerably modified the toxic effect of 50 % effective concentration (EC 50) dose of the pesticideFuradan (carbofuran 75 DB). Maximum growth and chlorophyll (Chl)a content ofA. fertilissima was observed in the pH range of 8 - 9 and that ofA. variabilis at pH 7-8, while at acidic pH (5 - 6) and at pH above 9 these parameters were considerably retarded. Toxicity of the EC 50 dose ofFuradan was increased further at pH 5-6, whereas reduction in the toxicity to the test cyanobacteria was observed at pH 7.8 - 9.0. The experimental organisms grew comparatively better and synthesized higher amount of Chl a at an irradiance of 12.5 than at 7.5 or 2.5 W m^-2. The toxicity of EC 50 dose of the pesticide gradually decreased with the increasing irradiance. The toxic effect ofFuradan was larger when the initial cyanobacterial population concentration was low andvice versa.     

Chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence transient during freezing and recovery in winter wheat

Chlorophyll (Chl) a fluorescence measurements as evaluators of plant freezing tolerance are frequently insufficiently sensitive to detect the early metabolic changes that are initiated following exposure to freezing temperatures. Using cold-acclimated winter wheat, I analysed the polyphasic transience (from 50 μs to 1 s) of Chl a fluorescence. This enabled detailed studies of the progressive energy flows and efficiencies within the photosystem 2 (PS2) complex that ensue following initial exposure to freezing temperatures right through to the plant recovery stage. The initial consequences of mild frosts that may cause primary damage involve a disturbance to the energy transfer subsequent to Q_A (the primary quinone electron acceptor of PS2). Lower freezing temperatures, on the other hand, may deter energy flow between the PS2 reaction centre (RC), Chl, and Q_A. All primary damage could only be repaired partially. Further freezing-triggered dysfunction of the electron transfer between the PS2 RCs and Q_A was connected with secondary damage that could lead to PS2 deactivation. Both primary and secondary freezing damages were reflected in decreased PI_ABS, the Performance Index based on equal absorption that characterizes all energy bifurcations in PS2. PI_ABS also differentiated cultivars with contrasting freezing-tolerance either subsequent to the onset of freezing or during the recovery stage. In contrast, the potential quantum yield of PS2 (F_v/F_m), which characterizes efficiency of energy trapping in the PS2 RCs, was only different in cultivars with contrasting freezing-tolerance during the recovery stage.     

Xanthophyll cycle-dependent nonphotochemical quenching in Photosystem II: Mechanistic insights gained from Arabidopsis thaliana L. mutants that lack violaxanthin deepoxidase activity and/or lutein

This study compares Photosystem II (PS II) chlorophyll (Chl) a fluorescence yield changes of Arabidopsis thaliana L. nuclear gene mutants, thoughtfully provided by the authors of Pogson et al. (1998 Proc Natl Acad Sci USA 95: 13324–13329). One single mutant (npq1) inhibits the violaxanthin deepoxidase that converts violaxanthin to antheraxanthin and zeaxanthin. A second single mutant (lut2) inhibits the -cyclization enzyme step between lycopene and ,-carotene causing accumulation of ,-carotene derivatives, primarily the violaxanthin cycle pigments, at the expense of lutein. The double mutant (lut2-npq1) incorporates both lesions. PS II Chl a fluorescence was characterized in leaves and thylakoids using both steady state and time-resolved methods, the intrathylakoid pH was estimated by 9-aminoacridine fluorescence quenching and chloroplast pigments were determined by HPLC. Under maximal PS II Chl a fluorescence intensity conditions without intrathylakoid acidification, the main 2 nanosecond (ns) fluorescence lifetime distribution mode parameters were similar for the WT and mutants both before and after illumination. The light and ATPase mediated intrathylakoid pH levels were also similar and caused similar changes in the fluorescence lifetime distribution widths and centers for the WT and each mutant. The npq1 exhibited low antheraxanthin and zeaxanthin and high violaxanthin levels and the uncoupler-sensitive amplitudes of short (< 1 ns) PS II Chl a fluorescence distribution modes were strongly inhibited compared to the WT. Lutein deficiency coincided with pleiotropic effects on PS II energy dissipation and probably altered conformations of PS II carotenoid-chlorophyll binding proteins. The lut2 exhibited separate active and inactive pools of antheraxanthin and zeaxanthin with respect to all deepoxidation, epoxidation and fluorescence quenching activities. The active xanthophyll cycle pool in lut2 exhibited a lower (35% of WT) concentration efficiency, for a given intrathylakoid pH, to increase the sub-nanosecond distribution amplitudes, which predicts and explains inhibited induction kinetics and fluorescence quenching. The lut2-npq1 mutant exhibited a constant pool of antheraxanthin and zeaxanthin, no deepoxidation and little or no pH-reversible fluorescence decrease. It is concluded that in addition to intrathylakoid acidification, a certain level of zeaxanthin and antheraxanthin (or lutein) is absolutely required for the major reversible component of PS II Chl a fluorescence quenching.This revised version was published online in October 2005 with corrections to the Cover Date.     

Submergence effects on rice genotypes during seedling stage: Probing of submergence driven changes of photosystem 2 by chlorophyll a fluorescence induction O-J-I-P transients

The effects of submergence on chlorophyll (Chl) a fluorescence were compared in seven Oryza sativa (L.) cultivars, namely FR 13A, Khoda, Khadara, Kalaputia (tolerant), Sabita, and Hatipanjari (avoiding type), and IR 42 (susceptible). Seedlings were submerged for 4 d under complete darkness. Oxygen concentration of flood water decreased with the period of submergence with concomitant increase in concentration of carbon dioxide. Submergence caused diminution in the amount of total Chl. Genotypic differences were observed for Chl content and survival percentage. Quantification of the Chl a fluorescence transients (JIP-test) revealed large cultivar differences in the response of photosystem 2 (PS2) to submergence. The kinetics of Chl a fluorescence rise showed complex changes in the magnitudes and rise of O-J, J-I, and I-P phases caused by submergence. The selective suppression of the J-I phase of fluorescence especially after 2 d of submergence provided evidence for weakened electron donation from the oxygen evolving complex whereas under severe submergence stress (4 d) both O-J and J-I steps were suppressed greatly with highly suppressed P-step, which resulted in lowering of variable fluorescence. Grouping probability or energetic connectivity between PS2 obtained through JIP-test from the data after 2 d of submergence showed a direct relation with survival percentage, i.e. fluorescence measurements contained the information of the survival chance of a plant under submerged conditions. The information could be used in identifying the submergence tolerant cultivars when the damage is not very severe.     

Survival and Plant Growth Promotion of Detergent-Adapted Pseudomonas fluorescens ANP15 and Pseudomonas aeruginosa 7NSK2

Four detergents were tested as selective C sources for the plant growth-promoting rhizobacteria Pseudomonas aeruginosa 7NSK2 and Pseudomonas fluorescens ANP15. CO-720 (Igepal CO-720) or DOS (dioctyl sulfosuccinate), applied at 0.2% to the soil, increased the number of detergent-adapted, inoculated strains by almost 1.5 log units after 25 days, accounting for virtually the entire increase in total bacteria. The same dose of Tween 80 or N-laurylsarcosine, on the other hand, increased the indigenous populations by almost 2.5 log units, with only minor increases in the number of detergent-adapted inoculated strains. When CO-720 or DOS was initially supplied, the number of detergent-adapted 7NSK2 organisms was about 2 log units higher after 3 months of incubation than for the detergent-unadapted strain. This better survival resulted in a significantly higher root colonization of maize in a pot experiment with soil inoculation, with a significantly (P <= 0.05) higher shoot dry weight (18 to 33%). In a first field experiment with rhizosphere inoculation of 1-month-old maize plants, no effects on the height of two maize cultivars could be observed 1 month after inoculation. In a second field experiment, leaf and stem dry weights of yellow mustard and grass dry weight were increased in the treatments with seed and soil inoculation of the detergent-adapted 7NSK2 in combination with CO-720 application by, respectively, 7 to 8%, 19 to 23%, and 20 to 31%, although only the increases in grass dry weight were statistically significant at P <= 0.1. To some extent, 7NSK2 and DOS application also positively affected the mineral content of yellow mustard.     

Photosynthetic utilization of radiant energy by CAM Dendrobium flowers

14CO2 fixation was observed in orchid Dendrobium flowers; its rate decreased with the flower development. Chlorophyll (Chl) fluorescence in different developmental stages of flowers was compared to other green plant parts (leaf, inflorescence stalk, and fruit capsule). The photochemical efficiency of photosystem 2 (PS2) (Fv/Fm) of a leaf was 14-21 % higher than that of a mature flower perianth (sepal, petal, and labellum) which had a much lower total Chl content and Chl a/b ratio. A higher quantum yield of PS2 (PS2) than in the mature flowers was observed in all green parts. Flower sepals had higher Chl content, Chl a/b ratio, and Fv/Fm values than the petal and labellum. During flower development the Chl content, Chl a/b ratio, Fv/Fm, and qN decreased while PS2 and qP remained constant. An exposure of developing flowers to irradiances above 50 µmol m-2 s-1 resulted in a very drastic drop of PS2 and qP, and a coherent increase of qN as compared to other green plant organs. A low saturation irradiance (PFD of 100 µmol m-2 s-1) and the increase in qN in the flower indicate that irradiation stress may occur since there is no further protection when the flower is exposed to irradiances above 100 µmol m-2 s-1. A low Chl/carotenoid ratio in mature flower perianth as a consequence of Chl content reduction in the course of flower development suggests a relief of irradiation stress via this mean.     

Annexin A4 binding to anionic phospholipid vesicles modulated by pH and calcium

Annexin A4 belongs to a class of Ca(2+)-binding proteins for which different functions in the cell have proposed, e.g. involvement in exocytosis and in the coagulation process. All these functions are related to the ability of the annexins to bind to acidic phospholipids. In this study the interaction of annexin A4 with large unilamellar vesicles (LUV) prepared from phosphatidylserine (PS) or from phosphatidic acid (PA) is investigated at neutral and acidic pH. Annexin A4 strongly binds to either lipid at acidic pH, whereas at neutral pH only weak binding to PA and no binding to PS occurs. Addition of 40 microM Ca(2+) leads to a strong binding to the lipids also at neutral pH. This is caused by the different electric charge of the protein below and above its isoelectric point. Binding of annexin A4 induces dehydration of the vesicle surface. The strength of the effects is much greater at pH 4 than at pH 7.4. At pH 7.4 annexin A4 reduces the Ca(2+)-threshold concentration necessary to induce fusion of PA LUV. The Ca(2+) induced fusion of PS LUV is not affected by annexin A4 at pH 7.4. At pH 4 annexin A4 induces fusion of either vesicles without Ca(2+). Despite the low binding extents at neutral pH annexin A4 induces a Ca(2+) independent leakage of PS- or PA-LUV. The leakage extent is increased at acidic pH. From the data two suggestions are made: (1) At pH 4 annexin A4 (at least partially) penetrates into the bilayer in contrast to the preferred location at the vesicle surface at neutral pH. The conformation of annexin A4 seems to be different at the two conditions. (2) At neutral pH, Annexin A4 seems to be able to bind two PA vesicles simultaneously; however, only one PS vesicle at the same time. This behavior might be related to a recently described double Ca(2+) binding site, which appears to be uniquely suited for PS.     

Decline of Photosynthetic Pigments,Ribulose-1,5-Bisphosphate Carboxylase and Soluble Protein Contents,Nitrate Reductase and Photosynthetic Activities,and Changes in Thylakoid Membrane Protein Pattern in Canopy Shade Grapevine (Vitis Vinifera L. cv. Moscato Giallo) Leaves

In canopy shade leaves of grapevine (Vitis vinifera L. cv. Moscato giallo) grown in the field the contents of chlorophyll (Chl), carotenoids (Car), and soluble protein per fresh mass were lower than in sun leaves. RuBPC activity, in vivo nitrate reductase activity (indicator of nitrate utilisation), apparent electron transport rate, and photochemical fluorescence quenching were also significantly reduced in canopy shade leaves. When various photosynthetic activities were followed in isolated thylakoids, canopy shade leaves exerted a marked inhibition of whole chain and photosystem (PS) 2 activity. Smaller inhibition of PS1 activity was observed even in high-level canopy shade (HS) leaves. The artificial exogenous electron donors, DPC and NH₂OH, significantly restored the loss of PS2 activity in HS leaves. Similar results were obtained when F_v/F_m was evaluated by Chl fluorescence measurements. The marked loss of PS2 activity in canopy shade leaves was due to the loss of 47, 43, 33, 28–25, 23, 17, and 10 kDa polypeptides.