The absolute configuration of phaseic and dihydrophaseic acids

A sample of phaseic acid methyl ester (5 mg, isolated from tomato plants fed (±)-abscisic acid, was reduced to a mixture of the epimeric dihydrophaseates which were separated by TLC. The more polar epimer was identical with the dihydrophaseate isolated from beans by Walton et al. [14]. Comparison of the NMR and IR spectra (H-bonding) of the two epimers shows the secondary hydroxyl of the less polar epimer is cis to the oxymethylene group, which is cis to the tertiary hydroxyl group. The absolute configuration of this centre is known so the absolute configuration of phaseic acid can be deduced. Phaseic acid is (−)-3-methyl-5{8[1(R), 5(R)-dimethyl-8(S)-hydroxy-3-oxo-6-oxabicyclo-(3,2,1)-octane]} 2-cis-4-trans-pentadienoic acid and both it and the reduction products exist in chair conformations. The more polar epimer isolated by Walton et al. is (−)-3-methyl-5{8[3(S,8(S)-dihydroxy-1(R,5(R)-dimethyl-6-oxabicyclo-(3,2,1)-octane]}2-cis-4-trans-pentadienoic acid. It is suggested that the less polar epimer should be referred to as epi-dihydrophaseic acid.     

Deuterium-labeled phaseic acid and dihydrophaseic acids for internal standards

The concentration of abscisic acid in plants is regulated not only by biosynthesis, but also by metabolism. Abscisic acid is metabolized to phaseic acid via 8'-hydroxyabscisic acid, and phaseic acid is then converted to dihydrophaseic acid and its epimer. A quantitative analysis of these metabolites is important as well as that of abscisic acid to understand changes in the concentration of abscisic acid in plants. However, no internal standards of the metabolites suitable for quantitative analysis have been reported. We prepared 7'-deuterium-labeled phaseic acid with a deuterium content of 86%, using the equilibrium reaction between phaseic acid and 8'-hydroxyabscisic acid. 7'-Deuterium-labeled dihydrophaseic acids were obtained by reducing 7'-deuterium-labeled phaseic acid. The levels of the metabolites in plant organs were determined by using the deuterated metabolites as internal standards.     

Simultaneous and independent effects of abscisic acid on stomata and the photosynthetic apparatus in whole leaves

(±)-Abscisic acid (ABA) at 10^-5 M was added to the transpiration stream of leaves of 16 species (C₃ and C₄, monocotyledons and dicotyledons). Stomatal responses followed one of three patterns: i) stomata that were wide and insensitive to CO₂ initially, closed partially and became sensitive to CO₂; ii) for stomata that were sensitive to CO₂ before the application of ABA, the range of highest sensitivity to CO₂ shifted from high to low intercellular partial pressures of CO₂, for instance in leaves of Zea mays from 170–350 to 70–140 bar; iii) when stomata responded strongly to ABA, their conductance was reduced to a small fraction of the initial conductance, and sensitivity to CO₂ was lost. The photosynthetic apparatus was affected by applications of ABA to various degrees, from no response at all (in agreement with several previous reports on the absence of effects of ABA on photosynthesis) through a temporary decrease of its activity to a lasting reduction. Saturation curves of photosynthesis with respect to the partial pressure of CO₂ in the intercellular spaces indicated that application of ABA could produce three phenomena: i) a reduction of the initial slope of the saturation curve (which indicates a diminished carboxylation efficiency); ii) a reduction of the level of the CO₂-saturated rate of assimilation (which indicates a reduction of the ribulose-1,5-bisphosphate regeneration capacity); and iii) an increase of the CO₂ compensation point. Photosynthesis of isolated mesophyll cells was not affected by ABA treatments. Responses of the stomatal and photosynthetic apparatus were usually synchronous and often proportional to each other, with the result that the partial pressure of CO₂ in the intercellular spaces frequently remained constant in spite of large changes in conductance and assimilation rate. Guard cells and the photosynthetic apparatus were able to recover from effects of ABA applications while the ABA supply continued. Recovery was usually partial, in the case of the photosynthetic apparatus occasionally complete. Abscisic acid did not cause stomatal closure or decreases in the rate of photosynthesis when it was applied during a phase of stomatal opening and induction of photosynthesis that followed a transition from darkness to light.Abbreviations and symbols A rate of CO₂ assimilation - ABA (±)-abscisic acid - c _a partial pressure of CO₂ in the ambient air or in the gas supplied to the leaf chambers - c _i partial pressure of CO₂ in the intercellular spaces of a leaf - e _a partial pressure of H₂O in the air - g conductance for water vapor - J quantum flux - T ₁ leaf temperature     

Effects of abscisic Acid treatment on the thermostability of the photosynthetic apparatus in barley chloroplasts

Thermostability of the photosynthetic apparatus of abscisic acid (ABA)-treated seedlings of barley (Hordeum vulgare) was studied by light-scattering and by fluorescence measurements of isolated chloroplasts. ABA treatment markedly decreased heat damage of the chloroplast ultrastructure; an exogenous ABA concentration of 10⁻⁵ molar was most effective. Heat-induced increase of the 77 kilodalton fluorescence ratio F₇₄₀/F₆₈₅ was also smaller at this ABA concentration. The heat-induced increase of the initial chlorophyll fluorescence level (F_o) was virtually eliminated in ABA-treated (10⁻⁵ molar) chloroplasts up to 45°C and slightly increased at 50°C, relative to control chloroplasts where F_o increased even at 35°C and reached its maximal value at 45°C. In control chloroplasts, F_o increased with a 5-minute pretreatment temperature, an effect observed as low as 35°C. F_o was maximal at 45°C. In contrast, chloroplasts treated with 10⁻⁵ molar ABA did not exhibit a heat-induced increase in F_o until 50°C.     

Identification of a dihydrophaseic Acid aldopyranoside from soybean tissue

A previously unidentified abscisic acid metabolite has been isolated and characterized. (±)-[2-¹⁴C]Abscisic acid was incubated in intact soybean leaves and pods; the radiolabeled metabolite was purified by high performance liquid chromatography with on-line scintillation spectrometry detection. Gas chromatography-mass spectrometry was used to obtain spectra of the acetylated and methyl esterified derivatives. The data were consistent with a proposed dihydrophaseic acid-aldopyranoside identity. Conjugation through the 4′-hydroxyl of dihydrophaseic acid is suggested.     

Incorporation of oxygen into abscisic Acid and phaseic Acid from molecular oxygen

Abscisic acid accumulates in detached, wilted leaves of Xanthium strumarium. When these leaves are subsequently rehydrated, phaseic acid, a catabolite of abscisic acid, accumulates. Analysis by gas chromatography-mass spectrometry of phaseic acid isolated from stressed and subsequently rehydrated leaves placed in an atmosphere containing 20% ¹⁸O₂ and 80% N₂ indicates that one atom of ¹⁸O is incorporated in the 6′-hydroxymethyl group of phaseic acid. This suggests that the enzyme that converts abscisic acid to phaseic acid is an oxygenase.

Analysis by gas chromatography-mass spectrometry of abscisic acid isolated from stressed leaves kept in an atmosphere containing ¹⁸O₂ indicates that one atom of ¹⁸O is present in the carboxyl group of abscisic acid. Thus, when abscisic acid accumulates in water-stressed leaves, only one of the four oxygens present in the abscisic acid molecule is derived from molecular oxygen. This suggests that either (a) the oxygen present in the 1′-, 4′-, and one of the two oxygens at the 1-position of abscisic acid arise from water, or (b) there exists a stored precursor with oxygen atoms already present in the 1′- and 4′-positions of abscisic acid which is converted to abscisic acid under conditions of water stress.

     

Effects of selenate and red Se-nanoparticles on the photosynthetic apparatus of Nicotiana tabacum

Photosynthesis Research - Selenium (Se) is a natural trace element, which shifts its action in a relatively narrow concentration range from nutritional role to toxicity. Although it has been well...     

Identification by combined gas chromatography-mass spectrometry of phaseic acid and dihydrophaseic acid and characterization of further abscisic acid metabolites in pea seedlings

Seven day old seedlings of Pisum sativum L., cv. Kleine Rheinländerin, were wilted for 3 days. After partially removing the roots, they were rewatered and at the same time radioactive abscisic acid([1-¹⁴C]ABA, spec. activity 1.7·10⁸d s^-1mmol^-1) was applied for 1 h via the xylem of the roots. After 24 h, 4 days, and 12 days the seedlings were extracted and the metabolites of ABA were analyzed by means of thin-layer and gas chromatography in combination with mass spectrometry, autoradiography, and scintillation counting. Phaseic acid (PA) and dihydrophaseic acid (DPA) were identified as metabolites of ABA. The presence of another ABA-metabolite was also demonstrated. From its mass spectrum it has been postulated that this metabolite is 4-desoxy-ABA. In addition to these substances, several other metabolites, which are more polar than ABA and its known degradation products, were present in the seedlings. The quantity and number of these unknown metabolites increased with time.Abbreviations ABA abscisic acid - PA phaseic acid - DPA dihydrophaseic acid - TLC thin-layer chromatography - GC gas chromatography - PPO 2,5-diphenyloxazole - POPOP 2,2-p-phenylen bis(5-phenyloxazole)     

Thermoluminescence from the photosynthetic apparatus

One of the fundamental discoveries of W. Arnold was the detection of thermally stimulated light emission from preilluminated photosynthetic material (Arnold and Sherwood (1957) Proc Natl Acad Sci USA 43: 105–114). This phenomenon, called thermoluminescence (TL), is characteristic of a wide range of materials (semiconductors, minerals, inorganic and organic crystals, and complex biological systems such as the photosynthetic apparatus) which share the common ability of storing radiant energy in thermally stabilized trap states.The original discovery of TL in dried chloroplasts later proved to be a phenomenon common to all photosynthetic organisms: photosynthetic bacteria, cyanobacteria, algae and higher plants. Following the pioneering work of Arnold, considerable effort has been devoted to identification and characterization of photosynthetic TL components. This work has firmly established the participation of various redox states of the water-oxidizing complex and the quinone electron acceptors of Photosystem II in the generation of photosynthetic glow curves. Since TL characteristics are very sensitive to subtle changes in redox properties of the involved electron transport components, the TL method has become a powerful tool in probing a wide range of PS II redox reactions. In this paper, we will review the impact of Arnold's work in initiating and promoting TL studies in photosynthesis and will cover the most important developments of this field of research until the present day.Abbreviations Chl chlorophyll - DL delayed luminescence - PS photosystem - TL thermoluminescence     

Polyamines in the photosynthetic apparatus

The three main polyamines putrescine (Put), spermidine (Spd) and spermine (Spm) were characterized by HPLC in intact spinach leaf cells, intact chloroplasts, thylakoid membranes, Photosystem II membranes, the light-harvesting complex and the PS II complex. All contain the three polyamines in various ratios; the HPLC polyamine profiles of highly resolved PS II species (a Photosystem II core and the rection center) suggest an enrichment in the polyamine Spm.Abbreviations Chl chlorophyll - HPLC high performance liquid chromatography - LHC light-harvesting complex - PS II Photosystem II - PS II-RC Photosystem II reaction center - Put putrescine - Spd spermidine - Spm spermine - 10%S-core D₁-D₂-Cyt b559-47 kD-43 kD complex     

Development of the bacterial photosynthetic apparatus

Anoxygenic photosynthetic bacteria have provided us with crucial insights into the process of solar energy capture, pathways of metabolic and societal importance, specialized differentiation of membrane domains, function or assembly of bioenergetic enzymes, and into the genetic control of these and other activities. Recent insights into the organization of this bioenergetic membrane system, the genetic control of this specialized domain of the inner membrane and the process by which potentially photosynthetic and non-photosynthetic cells protect themselves from an important class of reactive oxygen species will provide an unparalleled understanding of solar energy capture and facilitate the design of solar-powered microbial biorefineries.     

Effects of ozone on the photosynthetic apparatus and leaf proteins during leaf development in wheat

Leaves of Triticum aestivum cv. Avalon were grown in an atmosphere that contained 150 nmole mol^-1 ozone for 7h each day. After leaves had reached maximum size, the leaf blade was divided into three sections to provide tissue of different age, the youngest at the base of the blade and the oldest at the leaf tip. The ozone treatment was found to decrease significantly the light-saturated rate and quantum yield of CO₂ assimilation and the maximum quantum yield of photosystem II photochemistry in the oldest leaf section. No effects were found on the basal and middle sections of the leaf. These ozone-induced decreases in the photosynthetic parameters were associated with decreases in the efficiency of utilization of light for CO₂ assimilation at the photon flux density under which the leaves were grown. The depression in photosynthetic performance of tissue near the leaf tip was accompanied by large decreases in the contents of total, soluble and thylakoid proteins and chlorophyll. There was also found to be a preferential loss of ribulose-1,5-carboxylase-oxygenase. These ozone-induced changes in chlorophyll and protein contents and the photosynthetic activities of the leaf tissue were similar to changes normally associated with leaf senescence. Two-dimensional polyacrylamide gel analyses of leaf proteins demonstrated the loss of some minor, and unidentified, proteins, whilst another group of minor proteins appeared. It is concluded that daily exposure of the leaf to 150 nmol mol^-1 ozone for 7h had no effect on the development of the photosynthetic apparatus and its activities during leaf expansion, but it did promote the onset of premature senescence in fully expanded tissue that resulted in a loss of pigments, proteins and photosynthetic capacity and efficiency.     

Leaf shape,stomata density and photosynthetic rate of the common oak leaves

Leaf shape and size, stomata dimensions and density, chlorophyll content and photosynthetic rate of the common oak leaves were investigated in shoots of various growth phases (polycyclic growth). Mean and maximal daily net photosynthetic rates, shoot length, leaf area, stomatal density and chlorophyll contents were significantly higher in shoots of the second growth phase. Intraspecific differences in leaf shape were found within each shoot growth phase.     

High-temperature damage and acclimation of the photosynthetic apparatus

The influence of mono- (K⁺) and divalent (Mg²⁺) cations and protons (pH) on the temperature sensitivity of thylakoid membranes was investigated in three groups of young bean plants (control, heat-acclimated and non-acclimated). Thylakoid-membrane function was monitored by second and millisecond delayed fluorescence and 9-aminoacridine fluorescence quenching. It was established that metal ions at investigated concentrations decreased the thermostability of the photosynthetic parameters — an increase of MgSO₄ concentration from 0.1 to 20 mM decreased the temperature of their half-inactivation (T50) by 13°C. At the same time the pH dependence of the thermal stability of these parameters showed a maximum at pH 5.5–6.5. The half-inactivation temperatures of those photosynthetic parameters connected with the ability of the thylakoid membrane to form light-induced proton gradients increased by 6–7°C in the heat-acclimated plants compared with the control. It was assumed that the temperature inactivation of photosynthetic electron transfer and the energization of the thylakoid membrane was determined both by the thermoinduced dissociation of the light-harvesting chlorophyll a/b protein complex from PSII, leading to destruction of the excitation energy transfer to the reaction centres, and by the thermal denaturation of the membrane-protein components. The rate of these processes was probably controlled by the size of the negative surface charge and the viscosity of the thylakoid membrane.Abbreviations 9-AA 9-aminoacridine - DF delayed fluorescence - LHCP light-harvesting chlorophyll a/b protein complex - PSI (II) photosystem I (II) - T50 temperature of 50% inhibition of photosynthetic parameter - Tricine N-[2-hydroxy-1, 1-bis(hydroxymethyl)ethyl] glycine     

Effect of lead on the photosynthetic apparatus of annual grasses

The effect of lead (in the form of Pb(CH₃COO)₂ 3H₂O at concentrations of 200, 400, and 800 mg/kg substrate) on the photosynthetic apparatus of barley (cv. Dina) and oat (cv. Falensky) was studied. Exposure to low concentrations of lead (200 mg/kg) slightly increased the content of chlorophyll in leaves and the rate of photosynthesis. Medium concentrations of lead (400 mg/kg) had no marked effect on the parameters analyzed, whereas high concentrations (800 mg/kg) decreased the area of leaves, the content of green pigments in them, and the rate of photosynthesis.Translated from Izvestiya Akademii Nauk, Seriya Biologicheskaya, No. 2, 2005, pp. 184–188.Original Russian Text Copyright © 2005 by Kaznina, Laidinen, Titov, Talanov.