Generation of reducing power in chemosynthesis. VI. Energy-linked reactions in the chemoautotroph,Thiobacillus neapolitanus

Electron donors such as thiosulfate, sulfite, and ascorbate have been shown to enter the respiratory chain ofT. neapolitanus at the level of cytochromec. The enzymatic oxidation of these substrates catalyzed by the cytochrome oxidase (E. C. 1.9.3.1.) ofT. neapolitanus cell-free extracts was coupled to the generation of energy which could be utilized to drive the reverse electron flow from cytochromec to pyridine nucleotides.The reduction of endogenous or added flavin by thiosulfate or ascorbate has been shown to be ATP-dependent; likewise the reduction of cytochromeb by these electron donors also required energy. The rate of ATP-driven reversal of electron transfer from cytochromec to the pyridine nucleotides was much faster compared with the rate of electron reversal catalyzed by the substrate-linked generated energy. The pathway of energy-linked reversal of electron transfer from cytochrome c to pyridine nucleotides involved cytochromeb and flavoproteins.NADH oxidation byT. neapolitanus cell-free extracts is mediated by the flavoprotein and cytochrome systems and this process also appears to be coupled with energy generation. The NADH oxidase (NADH₂: cytochromec oxidoreductase) was partially inhibited by amytal or rotenone, antimycin A or HOQNO, and was relatively insensitive to cyanide or azide.This investigation was supported in part by a National Science Foundation Grant No. GB 6649 and in part by the Department of Interior, Office of Water Resources Research No. A-016-KY.     

In vivo photosynthetic electron transport does not limit photosynthetic capacity in phosphate-deficient sunflower and maize leaves

The effects of extreme phosphate (Pi) deficiency during growth on the contents of adenylates and pyridine nucleotides and the in vivo photochemical activity of photosystem II (PSII) were determined in leaves of Helianthus annuus and Zea mays grown under controlled environmental conditions. Phosphate deficiency decreased the amounts of ATP and ADP per unit leaf area and the adenylate energy charge of leaves. The amounts of oxidized pyridine nucleotides per unit leaf area decreased with Pi deficiency, but not those of reduced pyridine nucleotides. This resulted in an increase in the ratio of reduced to oxidized pyridine nucleotides in Pi-deficient leaves. Analysis of chlorophyll a fluorescence at room temperature showed that Pi deficiency decreased the efficiency of excitation capture by open PSII reaction centres (φ_e), the in vivo quantum yield of PSII photochemistry (φ_PSII) and the photochemical quenching co-efficient (q_P), and increased the non-photochemical quenching co-efficient (q_N) indicating possible photoinhibitory damage to PSII. Supplying Pi to Pi-deficient sunflower leaves reversed the long-term effects of Pi-deficiency on PSII photochemistry. Feeding Pi-sufficient sunflower leaves with mannose or FCCP rapidly produced effects on chlorophyll a fluorescence similar to long-term Pi-deficiency. Our results suggest a direct role of Pi and photophosphorylation on PSII photochemistry in both long-and short-term responses of photosynthetic machinery to Pi deficiency. The relationship between φ_PSII and the apparent quantum yield of CO₂ assimilation determined at varying light intensity and 21 kPa O₂ and 35 Pa CO₂ partial pressures in the ambient air was linear in Pi-sufficient and Pi-deficient leaves of sunflower and maize. Calculations show that there was relatively more PSII activity per mole of CO₂ assimilated by the Pi-deficient leaves. This indicates that in these leaves a greater proportion of photosynthetic electrons transported across PSII was used for processes other than CO₂ reduction. Therefore, we conclude that in vivo photosynthetic electron transport through PSII did not limit photosynthesis in Pi-deficient leaves of sunflower and maize and that the decreased CO₂ assimilation was a consequence of a smaller ATP content and lower energy charge which restricted production of ribulose, 1-5, bisphosphate, the acceptor for CO₂.     

Assunzione di Fosforo32 da Parte di Cuscuta Epithymum Parassita di Trifolium Repens

Abstract

Uptake of Phosporus-P³² by CUSCUTA EPITHYMUM parasitic of TRIFOLIUM REPENS. — Filaments of C. epithymum, parasitic on T. repens, partially immersed in a solution containing KH₂P³²O₄, uptake from the host solely, or mainly, radioactive ortophosphate. Radioactive hexose phosphates and radioactive nucleotides present in the extracts prepared from C. epithymum, appear to be the result of the metabolization by the dodder of the orthophosphate uptaken from the host.     

Fissazione Dell'Anidride Carbonica Da Parte Di « Cuscuta Epithymum »

Abstract

CO ₂ fixation by CUSCUTA EPITHYMUM. — Seedlings of Cuscuta epithymum or filaments detached from the host (Trifolium repens) fix carbon dioxide by mechanism(s) which are, though to a different extent, stimulated by light. Chromatographic analysis of plant extracts that have assimilated C¹⁴O₂ indicates that, in all cases, the radioactivity is detectable in the areas corresponding to the organic acids and the acidic amino acids. No labelling was associated in appreciable amounts with 3-pho-sphoglycerate and the mono- and diphosphate esters of hexoses and pentoses. Such results are substantiated by the finding that cell-free extracts of seedlings and filaments fix carbon dioxide by carboxylating phosphoenolpyruvic acid. It is concluded that, under the experimental conditions, malic enzyme, pyruvate carboxylase and ribulose-1,5-diphosphate carboxylase have little, if any, significance in the fixation of carbon dioxide by the tested species of Cuscuta.     

紫茎泽兰叶片水浸液对蚕豆的化感效应

外来入侵植物可以通过淋溶、自然挥发、根系分泌和植株凋落物分解等途径向周围环境释放化感物质,抑制伴生植物的生长、发育。该研究以不同浓度紫茎泽兰(Eupatorium adenophorum)叶片水浸液处理蚕豆(Vicia faba)种子,研究紫茎泽兰叶片水浸液对蚕豆根尖细胞微核、染色体畸变、细胞凋亡、蚕豆幼苗叶片叶绿素和N含量、光合生理特性、生物量的影响。结果表明:(1)紫茎泽兰叶片水浸液处理显著抑制蚕豆根尖的伸长和细胞的有丝分裂,并诱导蚕豆根尖细胞染色体畸变和细胞微核的产生,有丝分裂指数随着叶片水浸液浓度增加而减小,根尖细胞微核率随叶片水浸液浓度增加而增大,高浓度叶片水浸液处理对蚕豆根尖细胞的凋亡及坏死有明显影响。(2)紫茎泽兰叶片水浸液处理引起蚕豆幼苗叶片的叶绿素和N含量显著降低,并导致蚕豆幼苗最大净光合速率和生物量的显著下降。总之,紫茎泽兰叶片水浸液可能引起蚕豆根尖的氧化损伤和抑制根尖的伸长,且叶片水浸液的抑制作用呈现一定的剂量效应。紫茎泽兰叶片水浸液对蚕豆根尖的损伤和抑制作用可能影响了植株对氮素的吸收,进而对蚕豆幼苗光合生理表现以及生物量积累产生显著负面效应。     

A new species of Crossidium (Pottiaceae,Bryophyta) from South Africa

Abstract

A new species of Crossidium (Pottiaceae, Bryophyta), C. karoo, is described for South Africa. It uniquely differs from congeners in tight encapsulation of the photosynthetic filaments by the clasping upper lamina.     

干旱胁迫下AMF对云南蓝果树幼苗生长和光合特征的影响

采用盆栽试验与称重控水法,将土壤相对含水量分别控制在田间最大持水量的100%、91.68%、82.85%、60.00%、41.86%和21.28%,并在这6个不同的土壤相对含水量条件下,分别设添加苯菌灵(杀真菌剂)(低AMF)和不添加苯菌灵(高AMF)处理,研究干旱胁迫下AMF对极小种群野生植物云南蓝果树幼苗生长和光合特征的影响,揭示云南蓝果树濒危的微生物学机制,为云南蓝果树保护措施的制定与实施奠定基础。结果表明,添加苯菌灵处理显著降低了不同水分条件下的AMF侵染率,说明试验中AMF处理的实生苗在生长和光合特征上的差异是苯菌灵处理下侵染率下降导致的;随着干旱胁迫的加剧,云南蓝果树幼苗的根部AMF侵染率显著降低、叶面积等生长指标和净光合速率(Pn)等光合参数都发生显著变化;高AMF处理可以显著增加水分充足和轻度干旱胁迫条件下云南蓝果树幼苗的大部分生长指标和光合参数,而对重度胁迫下的云南蓝果树幼苗没有显著影响,说明重度干旱胁迫对其影响大于AMF的影响;另外,整合了可塑性指数分析和隶属函数分析两种方法对其抗旱性进行评价,云南蓝果树幼苗基本上无法通过调节形态和光合能力来适应水分环境的变化,但是高AMF处理可使云南蓝果树幼苗具有较强的可塑性和更强的抗旱性。实验结果为云南蓝果树的科学保育及种苗繁育提供了理论依据。     

Effects of water stress and nitrogen supply on leaf gas exchange and fluorescence parameters of <Emphasis Type="Italic">Sophora davidii</Emphasis> seedlings

Two-month-old seedlings of Sophora davidii were subjected to a randomized complete block design with three water (80, 40, and 20 % of water field capacity, i.e. FC₈₀, FC₄₀, and FC₂₀) and three N supply [N0: 0, Nl: 92 and Nh: 184 mg(N) kg⁻¹(soil)] regimes. Water stress produced decreased leaf area (LA) and photosynthetic pigment contents, inhibited photosynthetic efficiency, and induced photodamage in photosystem 2 (PS2), but increased specific leaf area (SLA). The decreased net photosynthetic rate (P _N) under medium water stress (FC₄₀) compared to control (FC₈₀) might result from stomatal limitations, but the decreased P _N under severe water deficit (FC₂₀) might be attributed to non-stomatal limitations. On the other hand, N supply could improve photosynthetic capacity by increasing LA and photosynthetic pigment contents, and enhancing photosynthetic efficiency under water deficit. Moreover, N supply did a little in alleviating photodamages to PS2 caused by water stress. Hence water stress was the primary limitation in photosynthetic processes of S. davidii seedlings, while the photosynthetic characters of seedlings exhibited positive responses to N supply. Appropriate N supply is recommended to improve photosynthetic efficiency and alleviate photodamage under water stress.     

Kinetics of Nicotinamide Adenine Dinucleotides during Dark-Light Transients in Chlorella

Nicotinamide adenine dinucleotides were extracted and assayed at frequent intervals for 30 seconds prior to and 60 seconds immediately following illumination of Chlorella cells. For these experiments a special illumination vessel was designed which dispensed 1 ml aliquots of algae with no dead volume. —White incandescent illumination of aerated Chlorella caused an immediate oxidation of its pyridine nucleotides. Under similar conditions blue light caused an initial reduction of these coenzymes. — White illumination of the alga perfused with CO₂-free air caused a transitory reduction of the pyridine nucleotide followed by an oxidation and a second reduction, Blue light, under similar conditions caused an immediate reduction but no oxidation as seen with white light. — When suspensions were perfused with N₂, illumination produced a prompt and rapid oxidation of NADH. The extent of this oxidation was greater in white than in blue light. Under these conditions NADP⁺ was initially reduced and subsequently, temporarily oxidised. — The evidence offers some support for Lundegårdh's theory that blue light is more effective than red light in the photo-reduction of NADP⁺. The results are discussed with referemce to the demonstrated in vitro reduction of nicotinamide adenine dinucleotides by chloroplasts and the conflicting reports from in vivo kinetic studies of living photosynthetic organisms. A scheme is proposed to explain the nicotinamide adenine dinucleotide kinetics as observed in these experiments.     

Effects of root residues on growth ofPinus radiata seedlings and a mycorrhizal fungus

The height of Pinus radiata Don seedlings grown on soils incorporating different proportions of root tissues (25 and 50%) was shown to be reduced by 20–80%. Seedlings watered with aqueous extracts from soil/root mixtures also showed a significant reduction in growth. This growth-retarding effect was partially overcome by the addition of nutrients or by soil sterilisation. It is postulated that growth retardation was caused not only by nutrient deficiency resulting from the addition of organic matter with a high C/N ratio, but also by phytotoxic substances present in the root tissue. The effect of water extracts of roots from old P. radiata trees on the growth of young P. radiata seedlings and on a mycorrhizal fungus (Rhizopogon sp.) under aseptic conditions was also studied. Extracts from the inner bark of roots caused complete growth inhibition of the mycorrhizal fungus as well as root necrosis and wilting of P. radiata seedlings. A water-soluble substance or substances, toxic both to the roots of P. radiata and to its mycorrhizal fungus, is postulated as the causal agent.     

Assunzione Di Metaboliti Da Parte Di « Cuscuta Epithymum » Parassita Di « Trifolium Repens »

Abstract

Uptake of metabolites by CUSCUTA. — The distribution of the radioactivity in the filaments of Cuscuta epithymum attached to the host (Trifolium repens) growing in an atmosphere of C¹⁴O₂ indicates that the dodder uptakes from the host solely, or mainly, sucrose. The other radioactive compounds present in the extracts of Cuscuta appear to be derived from the sucrose rather than uptaken from the host.     

Cell division and DNA topisomerase I activity in root meristems of pea seedlings during water stress

ABSTRACT

Low water potential, generated by PEG addition to the liquid medium of hydroponically grown pea seedlings, induces a fall in moisture content in the roots, followed by the arrest of elongation. This water stress reduces the mitotic index of root meristems during the treatment and induces the appearance of a peak of mitosis at 12 hours from the beginning of recovery. This peak suggests that during water stress the cell cycle is blocked in G2 or late S phase. In a first attempt to understand the biochemical events leading to cell cycle arrest, we tested the in vitro activity of DNA topoisomerase I extracted from stressed or control root meristems. The activity of this enzyme in extracts from stressed seedlings was lower than in controls, whereas it was higher in extracts from seedlings which had recovered from water stress for a few hours. The highest specific activity was observed with seedlings at 24 hours from the start of recovery. The fact that during stress treatments and recovery there was no variation in the synthesis of a 45 kDa protein, indicated as DNA topoisomerase I, suggested that the activity of this enzyme could be posttranslationally regulated. The hypothesis that variations in the concentration of unknown endogenous regulators of the activity of this enzyme may take place during water loss or uptake in the cytosol of meristematic cells is discussed.     

Control of the pyridine nucleotide-linked Ca release from mitochondria by respiratory substrates

Oxidation of mitochondrial pyridine nucleotides followed by their hydrolysis promotes Ca²⁺ release from intact liver mitochondria. In most of the previous studies oxidation was achieved with pro-oxidants which were added to mitochondria respiring on succinate in the presence of rotenone, a site I-specific inhibitor of the respiratory chain. Here we investigate pro-oxidant dependent and independent Ca²⁺ release from mitochondria when respiration is supported either by the NAD⁺-linked substrate β-hydroxybutyrate, or by succinate. In the presence, as well as in the absence, of the pro-oxidant t-butylhydroperoxide mitochondria retain Ca²⁺ much better with succinate than with β-hydroxybutyrate, as respiratory substrate. When Ca²⁺ release is induced by t-butylhydroperoxide succinate-supported Ca²⁺ retention is impeded by rotenone. Ca²⁺ release (pro-oxidant dependent or independent) is paralleled by oxidation and hydrolysis of intramitochondrial pyridine nucleotides, and Ca²⁺ retention is paralleled by reduction of pyridine nucleotides. It is concluded that the pyridine nucleotide-linked Ca²⁺ release from mitochondria can be controlled by respiratory substrates which regulate the intramitochondrial hydrolysis of oxidized pyridine nucleotides.     

Generation of reducing prower in chemosynthesis

Summary Cell-free preparations from T. neapolitanus catalyzed an ATP-dependent reduction of pyridine nucleotides by thiosulfate. The reduction of flavins by thiosulfate was also observed to be an energy-linked process. Optimal reaction occurred at pH 7.3–7.5 in the presence of 7 mM S₂O₃ ⁼, 1.5 mM ATP and 0.7 mM NAD⁺ or NADP⁺. The enzyme(s) catalyzing the energy-linked reactions appear to reside in the 144000 x g supernatant fraction since washed particles failed to catalyze the ATP driven NAD⁺ reduction by S₂O₃ ⁺; the cell-free preparations contained, however, S₂O₃ ⁼ oxidase and ferro-cytochrome c: O₂ oxidoreductase activities. The ATP-driven reduction of flavins or that of the pyridine nucleotides was inhibited bythe inhibitors that intersect the electron transport chain in the flavin or that of the cytochrome b and c regions. In the flavin-inhibited system, quinones could substitute as electron bypass carriers for the reduction of pyridine nucleotides. Uncouplers of oxidative phosphorylation and oligomycin inhibited the energy-transfer reactions. A utilization of 2 to 3 ATP equivalents was observed for the reduction of each equivalent of NAD⁺. Such observations indicate that the T. neapolitanus system operated with an efficiency of approximately 80% with respect to the utilization of energy for the generation of reducing power.Non-standard abbreviations HQNO 2-n-hyptyl-4-hydroxyquinoline N-oxide - TTFA Thenoyl triflouroacetone - CCCP m-chlorocarbonylcyanide-phenylhydrazone - DNP 2,4-dinitrophenol     

COMPARATIVE STUDIES ON THE CELL WALLS OF SEXUAL AND ASEXUAL BANGIA ATROPURPUREA (RHODOPHYTA). II ELECTROPHORETIC PATTERNS OF POLYSACCHARIDES1

Cellulose acetate electrophoresis of the hot water soluble polysaccharide extracts from whole filaments, as well as base, mid and tip segments, of marine asexual and sexual Bangia atropurpurea (Roth) C. Ag. Yielded distinctive patterns which demonstrated that changes occur in the outer cell walls during sexual reproduction. Heterogeneity of the sulfated polysaccharide components isolated from outer cell walls was shown to be specifically related to sexual reproduction. Two components (Band I and II) were detected in extracts from tips of sexual filaments, whole only one (Band I) was present in the vegetative segments of all filaments and in asexual reproductive regions. The faster running component (Band II) was detected during the later stages of sexual development, prior to maturation.     

Parziale purificazione della DPN-chinasi da foglie di pisello

Abstract

PARTIAL PURIFICATION OF DPN-KINASE FROM PEA LEAVES. — The presence of DPN-kinase has been demonstrated in pea leaves. The enzyme has been purified about 100 fold from this material. The possible significance of DPN-kinase and TPN-phosphatase (FORTI et Al., 1962) in the interconversion of pyridine nucleotides is discussed.     

Metabolic systems maintain stable non‐equilibrium via thermodynamic buffering

Here, we analyze how the set of nucleotides in the cell is equilibrated and how this generates simple rules that help the cell to organize itself via maintenance of a stable non‐equilibrium state. A major mechanism operating to achieve this state is thermodynamic buffering via high activities of equilibrating enzymes such as adenylate kinase. Under stable non‐equilibrium, the ratios of free and Mg‐bound adenylates, Mg²⁺ and membrane potentials are interdependent and can be computed. The adenylate status is balanced with the levels of reduced and oxidized pyridine nucleotides through regulated uncoupling of the pyridine nucleotide pool from ATP production in mitochondria, and through oxidation of substrates non‐coupled to NAD⁺ reduction in peroxisomes. The set of adenylates and pyridine nucleotides constitutes a generalized cell energy status and determines rates of major metabolic fluxes. As the result, fluxes of energy and information become organized spatially and temporally, providing conditions for self‐maintenance of metabolism.     

Photosynthesis and growth of Erythrina variegata as affected by water stress and triacontanol

Erythrina variegata Lam. seedlings were grown under water stress (Ψ = -3.2 MPa) and subsequently sprayed with triacontanol (Tria). Water stress significantly reduced shoot growth rate, while roots continued to grow. Content of chlorophyll (Chl) a decreased more than that of Chl b. Water stress also reduced photosynthetic activity of chloroplasts as measured by Chl fluorescence induction. Stress effect was identified at the oxidation site of photosystem (PS) 2 prior to the hydroxylamine donating site and perhaps close to or after the diphenylcarbazide donating site. The loss of O₂ evolving thylakoid polypeptides (33, 23, 17 kDa) and the large (55 kDa) and small (15 kDa) subunits of ribulose-1,5-bisphosphate carboxylase (RuBPC) were found in water stressed seedlings. The reduction in RuBPC activity was accompanied by reduction of CO₂ fixation and stomatal conductance. All photosynthetic parameters were improved by Tria. This revised version was published online in August 2006 with corrections to the Cover Date.     

A biochemical model of photosynthetic CO2 assimilation in leaves of C3 species

Various aspects of the biochemistry of photosynthetic carbon assimilation in C₃ plants are integrated into a form compatible with studies of gas exchange in leaves. These aspects include the kinetic properties of ribulose bisphosphate carboxylase-oxygenase; the requirements of the photosynthetic carbon reduction and photorespiratory carbon oxidation cycles for reduced pyridine nucleotides; the dependence of electron transport on photon flux and the presence of a temperature dependent upper limit to electron transport. The measurements of gas exchange with which the model outputs may be compared include those of the temperature and partial pressure of CO₂(p(CO₂)) dependencies of quantum yield, the variation of compensation point with temperature and partial pressure of O₂(p(O₂)), the dependence of net CO₂ assimilation rate on p(CO₂) and irradiance, and the influence of p(CO₂) and irradiance on the temperature dependence of assimilation rate.Abbreviations RuP₂ ribulose bisphosphate - PGA 3-phosphoglycerate - C=p(CO₂) partial pressure of CO₂ - O=p(O₂) partial pressure of O₂ - PCR photosynthetic carbon reduction - PCO photorespiratory carbon oxidation     

Enzymatic oxidation of p-nitrophenol.

A Moraxella sp. capable of growth with p-nitrophenol was isolated from activated sludge. Differential centrifugation of crude cell extracts gave a membrane preparation that oxidized p-nitrophenol to hydroquinone and nitrite. Enzymatic activity was dependent on the presence of oxygen and reduced pyridine nucleotides and was stimulated by the addition of flavin adenine dinucleotide. Experiments with ¹⁸O₂ showed that the incoming hydroxyl group was derived from molecular oxygen. The soluble fraction prepared from crude cell extracts oxidized hydroquinone to a product whose spectral properties were identical to those reported for γ-hydroxymuconic semialdehyde.