Chloroplast structure in normal and pigment-deficient soybeans grown in continuous red or far-red light

Clark L1, a normal green soybean [ Glycine max (L.) Merrill] and Clark y₉y₉, a backross-developed isoline exhibiting pigment deficiency, were grown under continuous red (11 W m⁻² and far-red (9 W m⁻²) light. Chloroplast thylakoids from the unifoliolate leaf (9–10 days old) were isolated and analyzed for pigments, pigment-protein, membrane polypeptides, electron transport and ultrastructural differences. Chloroplasts of soybean plants grown under far-red light have decreased chlorophyll a to chlorophyll b ratio, increased light-harvesting complexes, and grana structure with few stroma-type thylakoids. Photosystem II/photosystem I ratios (PSII/PSI) are higher in far-red due to decreased synthesis of PSI reaction center and/or less antenna associated with PSI.     

Electrophysiological response of honey bee labial palp contact chemoreceptors to sugars and electrolytes

ABSTRACT. The sensilla chaetica on segments II, III and IV of honey-bee labial palps were investigated electrophysiologically. The responses (spikes/s) correlated with the log of the concentrations of sucrose, glucose, fructose, NaCl, KCl and LiCl, but not with CaCl₂ or MgCl₂, which gave inconsistent responses. The firing rates were higher and thresholds lower to the sugars than to the electrolytes. The sensitivity of the segments fell in the order: III > II > IV for most of the stimulants, which elicited responses in the order: sucrose > glucose = fructose' KCl > LiCl > NaCl. The sensilla adapted logarithmically with time. No synergism of response was noted when mixed-sugar solutions were applied, but inhibition of response was seen when glucose–sucrose, fructose–sucrose, and glucose–fructose–sucrose mixtures were applied. None of the sensilla tested responded to water.     

At low monovalent cation concentrations K+ can have a specific effect on the amoebo-flagellate transformation in Naegleria gruberi

Abstract The amoebo-flagellate transformation that occurs when Naegleria gruberi is transferred from growth medium to distilled water can be suppressed by the addition of ions. At concentrations of 3.2 mM and above the percentage of amoeba enflagellating decreases as the concentration of KCl, NaCl, LiCl, CaCl₂ and MgCl₂ is increased. KCl, alone, shows a marked trough, with a minimum at 1.2 mM, in enflagellation over the concentration range 0–3.2 mM.     

Incorporation of [35S]methionine in higher plants reveals that stimulation of the D1 reaction centre II protein turnover accompanies tolerance to heavy metal stress

The effects of cadmium stress (CdCl₂) on photochemical activity and protein behaviour of photosystem II (PSII) were studied in vivo and in vitro . Treatments of pea ( Pisum sativum ) and broad bean ( Vicia faba ) plants with 0·05–5 m M cadmium (CdCl₂) modified PSII activity with a resulting increase in electron transfer followed by an inhibition and damage to the oxygen-evolving complex. Pulse-chase experiments with [³⁵S]methionine in vivo followed by the separation of the radiolabelled thylakoids into grana and stroma exposed regions indicated that the synthesis, degradation and assembly of the D1 protein were greatly affected by cadmium. Initially D1 synthesis increased, later slowing down when the stress became advanced; at the same time the D1 degradation was increased. Binding studies with radiolabelled [¹⁴C]herbicide revealed that the Q_B pocket activity was also altered. However, the primary consequence of cadmium stress was the disassembly of the stacked regions. The measurements indicated differential tolerance to cadmium stress between the two plant species, which was not caused by either differential metal uptake or binding to the PSII complex. This suggests that the resulting changes in D1 turnover are a consequence of an unknown primary effect of cadmium on the PSII apparatus. However, we show that the higher tolerance to heavy metal stress found in broad bean plants relative to pea is accompanied by stimulation of D1 turnover. These experiments supported by previous data suggest that modulation of D1 turnover under stress is a commonly occurring process.     

The effects of cadmium on photosynthesis of Phaseolus vulgaris – a fluorescence analysis

Bean plants ( Phaseolus vulgaris L. cv. Scarlett), germinated in darkness for I week, were transferred to light (200 μmol m⁻² s⁻¹) and cultivated for I week in a complete nutrient solution. After this period, cadmium ions in the form of CdSO₄ were added at the concentrations of 0.10.20 and 50 μ M . The effects of this metal on the properties of photosystem II photochemistry were studied by means of modulated fluorescence analysis. Steady state photochemical quenching. non-photochemical quenching and terminal fluorescence were determined in control and cadmiumtreated plants. We postulate that, during short term exposure of plants to cadmium in the early stages of growth, the Calvin cycle reactions are more likely than photosystem II to be the primary target of the toxic influence of cadmium. The reduced demand for ATP and NADPH upon Calvin cycle inhibition causes a down-regulation of photosystem II photochemistry and of the yield of linear electron transport.     

Influence of air pollutants and nutrient deficiency on D-1 protein content and photosynthesis in young spruce trees

Long-term fumigation with different mixtures of air pollutants, such as O₃, NO₂ and SO₂, in combination with potassium deficiency in 4-year-old spruce trees shows clearly that the photosynthetic apparatus reacts very sensitively to environmental stress. Even when no change in photosynthetic oxygen evolution of the leaves was measurable, the content of D-1 protein in the reaction center of photosystem II already increased significantly at low stress conditions. With increasing concentrations of pollutants, the content of D-1 protein decreased considerably. This pattern was observed with all combinations of gases, although they differed in effectiveness. The most potent effect on the content of D-1 protein was found with a combined fumigation of SO₂ plus NO₂. Obviously, the ratio between synthesis and degradation of the D-1 protein is influenced by stress factors. However, the content of D-1 protein was not strongly correlated with photosynthetic oxygen evolution in whole needles nor with electron transport rate in isolated thylakoids. Under controlled potassium deficiency, effects similar to those observed upon ozone fumigation developed. The results suggest unspecific stress answers for the D-1 content and the photosynthetic reactions rather than specific responses.     

On the participation of chloride in bicarbonate-induced reversal of anion inhibition of photosystem II electron transport in spinach thylakoids

Inhibition of electron transport through photosystem II (PS II) by formate (HCO⁻₂) or nitrite (NO⁻₂) in the presence or absence of chloride ions was studied. The inhibition induced by HCO⁻₂ or NO⁻₂ is overcome by HCO⁻₃ more in the presence, than in the absence of Cl⁻. The data on electron transport are supported by chlorophyll a fluorescence measurements. In experiments. In experiments in which water oxidation was blocked. Cl⁻ was found to facilitate electron transport between bound quinone A (Q⁻_A) and the plastoquinone (PQ) pool. It can thus be concluded that in addition to the well known site of action of Cl⁻ on water oxidation, another site of Cl⁻ action is between Q⁻_A and the PQ pool.     

Properties of Thylakoid Membranes of the Mangroves, Avicennia germinans and Avicennia marina, and the Sugar Beet, Beta vulgaris, Grown under Different Salinity Conditions

Properties of thylakoids isolated from leaves of three salt tolerant species, Avicennia germinans L., Avicennia marina var resinifera, and Beta vulgaris L., were not affected by the salinity in which the plants were grown. With increase in the growth salinity from 50 to 500 millimolar NaCl, there were no major effects on the per chlorophyll concentrations of lipids or proteins, or on the rates of uncoupled electron transport per chlorophyll mediated by either the whole chain or the partial reactions of photosystems I and II. Responses of the partial and whole chain reactions to variation in the sorbitol and NaCl concentrations in the assay media were independent of the salinity experienced during leaf growth and not substantially different from those of a salt-sensitive species, Cucurbita sativus L. Uncoupled rates of electron flow from water to p-benzoquinone mediated by photosystem II were insensitive to the NaCl concentration unless thylakoids were rendered Cl⁻ deficient by treatment with uncoupler under alkaline conditions. Loss of 65% to 85% of the photosystem II activity in these Cl⁻-deficient thylakoids was restored by addition of 10 to 20 millimolar Cl⁻.     

Responses of photosynthesis to NaCl in gametophytes of Acrostichum aureum

Gametophytes of Acrostichum aureum were cultured in 0.0 to 1.0% NaCl solutions or in NaCl‐free solution and then transferred to 1.0% NaCl solution. Photosynthetic light‐response curves, efficiency of the primary photochemical reaction, relative electron transport rate, and photochemical and non‐photochemical quenching at steady state were determined by photosynthetic O₂ evolution and in vivo chlorophyll fluorescence. Results obtained showed that the chlorophyll fluorescence parameters, F_v/F_m and F'_v/F'_m and αO₂ (the initial linear slope of the photosynthetic light‐response curve) increased in gametophytes grown in NaCl. Linear electron transport rate was stimulated by NaCl. Based on the chlorophyll content, light‐saturated photosynthesis in gametophytes grown in 0.2 to 0.7% NaCl increased slightly; it decreased in gametophytes grown in 1.0% NaCl. Photochemical quenching decreased in NaCl‐grown gametophytes at all photosynthetic photon flux density (PPFD) levels measured, but there was no increase in non‐photochemical quenching. The chlorophyll a/b ratio increased with increasing NaCl concentration in culture solutions. These results indicated that NaCl enhanced photochemical efficiency of photosystem II (PSII) and photosynthetic linear electron transport, thus resulting in the development of an excitation pressure in PSII. Such excitation pressure might act as a signal for photosynthetic acclimation to salt stress, thus allowing the gametophytes to grow in their natural habitats.     

Induction of Encystment in Acanthamoeba palestinensis. Factors Influencing Cyst Formation

SYNOPSIS. The effect of osmotic pressure, different electrolytes and organic compounds on cyst formation in Acanthamoeba palestinensis has been tested. The optimal osmolarity for encystment was similar to that of the growth medium. Iso-osmotic solutions of NaCl, KCl, MgCl₂, CaCl₂, glycine and sucrose led to maximum cyst formation. The involvement of various agents in the induction of encystment is discussed.     

Salt stimulation of growth and photosynthesis in an extreme halophyte, Arthrocnemum macrostachyum

Halophytes that are capable of tolerating a wide range of salinity may grow best at intermediate salinities, but the physiological mechanisms underlying positive growth responses to salinity are not clear. This work investigated the growth of Arthrocnemum macrostachyum (Moric) C. Koch (a halophytic C3 shrub) over a wide range of salinities, and the extent to which its responses can be explained by photosynthetic physiology. Growth, gas exchange and chlorophyll fluorescence characteristics of plants were examined in a glasshouse experiment; tissue concentrations of photosynthetic pigments, ash, sodium, potassium, calcium and nitrogen were also determined. Plants showed marked stimulation of growth by salt, with a broad optimum of 171–510 m m NaCl for relative growth rate (RGR). Stimulation of RGR appeared to depend mainly on an increase in specific shoot area, whereas reduced RGR at high salinity (1030 m m ) could be attributed to a combination of lower unit shoot (leaf) rate and lower shoot mass fraction. The non-saline treatment plants had the greatest fraction of non-photosynthetic, atrophied surface area. However, net photosynthesis (A) was also stimulated by NaCl, with an optimum of c. 510 m m NaCl. The responses of A to salinity could be accounted for largely by limitation by stomatal conductance (Gs) and intercellular CO₂ concentration (Ci). Even the most hypersaline treatment apparently had no effect on photosystem II (PSII) function, and this resistance could be an important strategy for this halophyte in saline soils. In contrast, Fv/Fm indicated that absence of salt represents an environmental stress for A. macrostachyum and this could be a contributory factor to salt stimulation of A. Notwithstanding the importance of the ability to develop and maintain assimilatory surface area under saline conditions, stimulatory effects on A also appear to be part of a suite of halophytic adaptations in this plant.     

Modulation of Neuropeptide FF Receptors by Guanine Nucleotides and Cations in Membranes of Rat Brain and Spinal Cord

Abstract: Using a radioligand binding assay, we examined ionic modulation and G protein coupling of neuropeptide FF(NPFF) receptors in membranes of rat brain and spinal cord. We found that NaCl (but not KCl or LiCl) and MgCl₂ increased specific ¹²⁵I-YLFQPQRFamide (¹²⁵I-Y⁸Fa) binding to NPFF receptors in both tissues in a dose-dependent manner, with optimal conditions being 60 m M NaCl and 1 m M MgCl₂. Guanine nucleotides dose-dependently inhibited specific ¹²⁵I-Y⁸Fa binding to rat brain and spinal cord membranes with maximal effects of 64 ± 6 and 71 ± 2%, respectively. The order of potency was nonhydrolyzable GTP analogues > GTP GDP > GMP, ATP. The guanine nucleotide inhibition was observed in the absence and presence of NaCl and MgCl₂. The mechanism of inhibition in spinal cord membranes appeared to be a reduction in the number of NPFF receptors; in one experiment, control K_D and B_max values were 0.068 n M and 7.2 fmol/mg of protein, respectively, and with 0.1 μ M guanylylimidodiphosphate the respective values were 0.081 n M and 4.9 fmol/mg, a 32% reduction in receptor number. Similar results were obtained with guanosine 5'-0-(3-thiotriphosphate). Our data suggest that ¹²⁵I-Y8Fa binding sites in rat CNS are G protein-coupled NPFF receptors regulated by GTP and cations.     

Light-dependent inhibition of photosynthetic electron transport by zinc

The effects of zinc concentrations up to 400 μ M were examined on three photosynthetic electron transport reactions of thylakoids isolated from Pisum sativum L. cv. Meteor. Zinc (400 μ M ) had no effect on photosystem I mediated electron transport from reduced N,N,N',N'-tetramethyl- p -phenylenediamine to methyl viologen, but inhibited uncoupled electron flow from water to methyl viologen by ca 50% and to 2,6-dichlorophenol-indophenol (DCPIP) by ca 30% at saturating light levels. Zinc inhibition of DCPIP photoreduction was independent of the light intensity to which thylakoids were exposed. Decreasing the photon flux density below 400 μmol m⁻² s⁻¹ produced a logarithmic reduction in the zinc-induced inhibition of methyl viologen photoceduction; a stimulation of this reaction was observed below 80 μmol photons m⁻² s⁻¹. Increasing light intensity decreased the amount of zinc tightly bound to the thylakoid membranes, but increased the weakly associated zinc which could be removed by washing the membranes with buffer containing Mg². The results suggest that zinc acts on the photosynthetic electron transport system at two sites. Site 1 is on the oxidizing side of photosystem 2 and the inhibition by zinc is independent of the light intensity. Site 2 is between photosystems 1 and 2 and the electron flow can be positively or negatively affected by zinc depending on the light intensity.     

Probing the events of photoinhibition by altering electron-transport activity and light-harvesting capacity in chloroplast thylakoids

Abstract. The effect of photoinhibition on the activity of photosystem II (PSII) in spinach chloroplasts was investigated. Direct light-induced absorbance change measurements at 320 nm (Δ A ₃₂₀) provided a measure of the PSII charge separation reaction and revealed that photoinhibition prevented the stable photoreduction of the primary quinone acceptor Q_A. Sensitivity to photoinhibition was substantially enhanced by treatment of thylakoids with NH₂OH which extracts manganese from the H₂O-splitting enzyme and prevents electron donation to the reaction centre. Incubation with 3-(3,4,-dichlorophenyl)-1,1-dimethylurea (DCMU) during light exposure did not affect the extent of photoinhibitory damage. The chlorophyll (Chl) b -less chlorina (2 mutant of barley displayed a significantly smaller light-harvesting antenna size of PSII (about 20% of that in wild type chloroplasts) and, simultaneously, a lower sensitivity to photoinhibition. These observations suggest that photoinhibition depends on the amount of light absorbed by PSII and that the process of photoinhibition is accelerated when electron donation to the reaction centre is prevented. It is postulated that the probability of photoinhibition is greater when excitation energy is trapped by P680⁺, the oxidized form of the PSII reaction centre. The results are discussed in terms of the D1/D2 heterodimer which contains the functional PSII components P680, pheophytin, Q_A and Q_B.     

盐度和CO2倍增环境下碱蓬幼苗呼吸酶活性的变化

研究了生长在正常大气CO₂和CO₂倍增环境中的盐生植物碱蓬(Suaedasalsa)幼苗呼吸酶活性对KCl和NaCl的反应。结果表明,在CO₂倍增(700μl·L^-1)和正常大气CO₂(350μl·L^-1)下,300mmol·L^-1KCl和NaCl均能抑制琥珀酸脱氢酶(SDH)和苹果酸脱氢酶(MDH)活性,而异柠檬酸脱氢酶(IDH)活性为NaCl抑制、KCl促进; NaCl和KCl明显抑制细胞色素氧化酶(CO)和光呼吸中乙醇酸氧化酶(GO)、羟基丙酮酸还原酶(HPR)活性; 并指出在KCl胁迫下,CO₂使三羧酸循环(TCAC)的运行变慢,NaCl胁迫下使其加快,TCAC运行限速步骤与MDH无关,CO为盐对呼吸代谢影响的重要位点。另外,K⁺、Na⁺对蛋白表达的影响有差异,CO₂可使盐胁迫下的碱蓬幼苗蛋白表达降低。     

High light fluence impairs light-harvesting Chl a/b complex apoprotein syntheses and/or membrane uptake in the CD3 mutant of wheat

The CD3 mutant of wheat is a chlorophyll(Chlo-deficient mutant the phenotype of which depends upon the accumulation of the light-harvesting Chl a/b protein complex in leaves in response to the intensity of illumination. In the present studies, the rates of synthesis and/or uptake, and degradation of the light-harvesting Chl apoprotein in chloroplasts of wild-type wheat ( Triticum aestivum L. selection ND 496) and CD3 wheat leaf segments were examined in response to two different intensities of illumination. We were interested particularly in the 21. 23 kDa proteins of the light-harvesting Chl a/b complex of photosystem I (LHCI) and the 25. 27. 29 kDa proteins of the light-harvesting Chl a/b complex of photosystem II (LHCII). The accumulation of [³⁵S]-Met into the light-harvesting Chl protein of CD3 wheat chloroplasts was impaired by a high but not by a low light fluence. The levels of radiolabel in the supernatant fractions of leaf tissue homogenates from the wild-type and CD3 wheats were not significantly different over time, suggesting that the cellular uptake of [³⁵S]-Met was not limiting in the mutant. The high fluence did not enhance the degradation of light-harvesting Chl protein from CD3 wheat thylakoids. Our data indicate an impairment in the light-harvesting Chl protein synthesis/membrane uptake system in CD3 wheat leaves under high fluence. A recovery in levels of the inner LHCPII, but not of LHCPI, was observed in the Chl-deficient wheat mutant after a prolonged (4 days) exposure to high fluence. Under low fluence, LHCP was added to both photosystem II (PSH) and photosystem I (PSI) but only that added to PSI remained in thylakoids after seedlings were switched to high fluence.     

Relationship between photosystem II activity and CO2 fixation in leaves

There is now potential to estimate photosystem II (PSII) activity in vivo from chlorophyll fluorescence measurements and thus gauge PSII activity per CO₂ fixed. A measure of the quantum yield of photosystem II, Φ_II (electron/photon absorbed by PSII), can be obtained in leaves under steady-state conditions in the light using a modulated fluorescence system. The rate of electron transport from PSII equals Φ_II times incident light intensity times the fraction of incident light absorbed by PSII. In C₄ plants, there is a linear relationship between PSII activity and CO₂ fixation, since there are no other major sinks for electrons; thus measurements of quantum yield of PSII may be used to estimate rates of photosynthesis in C₄ species. In C₃ plants, both CO₂ fixation and photorespiration are major sinks for electrons from PSII (a minimum of 4 electrons are required per CO₂, or per O₂ reacting with RuBP). The rates of PSII activity associated with photosynthesis in C₃ plants, based on estimates of the rates of carboxylation (v_o) and oxygenation (v_o) at various levels of CO₂ and O₂, largely account for the PSII activity determined from fluorescence measurements. Thus, in C₃ plants, the partitioning of electron flow between photosynthesis and photorespiration can be evaluated from analysis of fluorescence and CO₂ fixation.     

Effects of abiotic stresses on the turnover of the D1 reaction centre II protein

In the 1990's, evidence has accumulated that various unfavourable environmental conditions substantially affect the turnover of the D₁ protein of reaction centre II, the psb A gene product. Biochemical, molecular and physiological studies in higher plants indicate that alterations of D₁ protein turnover occur under drought, nutrition deficiency, heat, chemical stress, ozone fumigation as well as UV-B and visible photo-stresses. The behaviour of photosystem II under these various stress conditions indicates that the response of D₁ protein turnover can be interpreted as a general adaptive response to environmental extremes.     

Role of a serine-type d-alanyl-d-alanine carboxypeptidase on the survival of Ochrobactrum sp. 11a under ionic and hyperosmotic stress

The plant growth-promoting rhizobacterium, Ochrobactrum sp. 11a displays a high intrinsic salinity tolerance and has been used in this work to study the molecular basis of bacterial responses to high concentrations of NaCl. A collection of Ochrobactrum sp. 11a mutants was generated by Tn 5 -B21 mutagenesis and screened for sensitivity to salinity. One clone, designated PBP and unable to grow on glutamate mannitol salt agar medium supplemented with 300 mM NaCl was selected and further characterized. The PBP mutant carries a single transposon insertion in a gene showing a high degree of identity to the serine-type d -alanyl- d -alanine carboxypeptidase gene of Ochrobactrum anthropi . Interestingly, the expression of this gene was shown to be upregulated by salt in the PBP mutant. Moreover, evidence is presented for the requirement of the gene product for adaptation to high-salt conditions as well as to overcome the toxicity of LiCl, KCl, sucrose, polyethylene glycol (PEG), AlCl₃, CuSO₄, and ZnSO₄. In addition to the altered tolerance to both ionic and osmotic stresses, the PBP mutant exhibited changes in colony and cell morphology, exopolysaccharide production, and an increased sensitivity to detergents.     

Gloeobacter violaceus— investigation of an unusual photosynthetic apparatus. Absence of the long wavelength emission of photosystem I in 77 K fluorescence spectra

The deeply purple cyanobacterium Gloeobacter violaceus is subject of this investigation. It does not contain thylakoids, and the photosynthetic apparatus is located in the only membrane of the cell, the plasma membrane. Upon excitation with blue light, the 77 K fluorescence emission spectra of neither intact cells (excited with 427 nm) nor of the isolated plasma membrane (excited with 430 nm), show the expected long wavelength photosystem I emission characteristic for low energy chlorophylls. Maximal fluorescence emission was observed at 688 nm. independent on the excitation wavelength, 427 (430) nm blue light, exciting mainly chlorophyll, or 550 nm green light, exciting mainly phycoerythin. The ratio of P700 to chlorophyll was 175. O₂-evolution was 160 μmol mg_-1 chlorophyll h_-1 in saturating white light; the compensation point was reached at 6 μmol m₂ s_-1 in cultures grown at 25 μmol m₂ s_-1. Dark O₂ uptake was 50 μmol mg_-1 chlorophyll h_-1. During adaptation to increasing white light intensities Gloeobacter reduces the amount of phycocyanin and chlorophyll per cell and strongly increases the concentration of carotenoids relative to chlorophyll. The carotenoid concentration per cell increases with increasing light intensity. Apparently, part of the carotenoids is not located in the plasma membrane.