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Biomedical subjects

K Winter

Publications and source records attributed to K Winter.

At least 55 records · Page 3Linked to original sources
PubMed1990

Photosynthesis and Chlorophyll Fluorescence Characteristics in Relationship to Changes in Pigment and Element Composition of Leaves of Platanus occidentalis L. during Autumnal Leaf Senescence.

The loss of chlorophyll and total leaf nitrogen during autumnal senescence of leaves from the deciduous tree Platanus occidentalis L. was accompanied by a marked decline in the photosynthetic capacity of O(2) evolution on a leaf area basis. When expressed on a chlorophyll basis, however, the capacity for light-and CO(2)-saturated O(2) evolution did not decline, but rather increased as leaf chlorophyll content decreased. The photon yield of O(2) evolution in white light (400-700 nanometers) declined markedly with decreases in leaf chlorophyll content below 150 milligrams of chlorophyll per square meter on both an incident and an absorbed basis, due largely to the absorption of light by nonphotosynthetic pigments which were not degraded as rapidly as the chlorophylls. Photon yields measured in, and corrected for the absorptance of, red light (630-700 nanometers) exhibited little change with the loss of chlorophyll. Furthermore, PSII photochemical efficiency, as determined from chlorophyll fluorescence, remained high, and the chlorophyll a/b ratio exhibited no decline except in leaves with extremely low chlorophyll contents. These data indicate that the efficiency for photochemical energy conversion of the remaining functional components was maintained at a high level during the natural course of autumnal senescence, and are consistent with previous studies which have characterized leaf senescence as being a controlled process. The loss of chlorophyll during senescence was also accompanied by a decline in fluorescence emanating from PSI, whereas there was little change in PSII fluorescence (measured at 77 Kelvin), presumably due to decreased reabsorption of PSII fluorescence by chlorophyll. Nitrogen was the only element examined to exhibit a decline with senescence on a dry weight basis. However, on a leaf area basis, all elements (C, Ca, K, Mg, N, P, S) declined in senescent leaves, although the contents of sulfur and calcium, which are not easily retranslocated, decreased to the smallest extent.

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PubMed1989

Light Response of CO(2) Assimilation, Dissipation of Excess Excitation Energy, and Zeaxanthin Content of Sun and Shade Leaves.

Intact attached sun leaves of Helianthus annuus and shade leaves of Monstera deliciosa and Hedera helix were used to obtain light response curves of CO(2) uptake, the content of the carotenoid zeaxanthin (formed by violaxanthin de-epoxidation), as well as nonphotochemical quenching (q(NP)), and the rate constant of radiationless energy dissipation (k(D)). The latter two parameters were calculated from the decrease of chlorophyll a fluorescence at closed photosystem II traps in saturating pulses in the light. Among the three species, the light-saturated capacity of CO(2) uptake differed widely and light saturation of CO(2) uptake occurred at very different photon flux densities. Fluorescence quenching and zeaxanthin content exhibited features which were common to all three species: below light-saturation of CO(2) uptake nonphotochemical quenching occurred in the absence of zeaxanthin and was not accompanied by a decrease in the yield of instantaneous fluorescence. Nonphotochemical quenching, q(NP), increased up to values which ranged between 0.35 and 0.5 when based on a control value of the yield of variable fluorescence determined after 12 hours of darkness. As light saturation of CO(2) uptake was approached, q(NP) showed a secondary increase and the zeaxanthin content of the leaves began to rise. This was also the point from which the yield of instantaneous fluorescence began to decrease. The increase in zeaxanthin was paralleled by an increase in the rate constant for radiationless energy dissipation k(D), which opens the possibility that zeaxanthin is related to the rapidly relaxing "high-energy-state quenching" in leaves.

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PubMed1989

Zeaxanthin and the Induction and Relaxation Kinetics of the Dissipation of Excess Excitation Energy in Leaves in 2% O(2), 0% CO(2).

The relationship between the carotenoid zeaxanthin, formed by violaxanthin de-epoxidation, and nonphotochemical fluorescence quenching (q(NP)) in the light was investigated in leaves of Glycine max during a transient from dark to light in 2% O(2), 0% CO(2) at 100 to 200 micromoles of photons per square meter per second. (a) Up to a q(NP) (which can vary between 0 and 1) of about 0.7, the zeaxanthin content of leaves was linearly correlated with q(NP) as well as with the rate constant for radiationless energy dissipation in the antenna chlorophyll (k(D)). Beyond this point, at very high degrees of fluorescence quenching, only k(D) was directly proportional to the zeaxanthin content. (b) The relationship between zeaxanthin and k(D) was quantitatively similar for the rapidly relaxing quenching induced in 2% O(2), 0% CO(2) at 200 micromoles of photons per square meter per second and for the sustained quenching induced by long-term exposure of Nerium oleander to drought in high light (B Demmig, K Winter, A Krüger, F-C Czygan [1988] Plant Physiol 87: 17-24). These findings suggest that the same dissipation process may be induced by very different treatments and that this particular dissipation process can have widely different relaxation kinetics. (c) A rapid induction of strong nonphotochemical fluorescence quenching within about 1 minute was observed exclusively in leaves which already contained a background level of zeaxanthin.

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PubMed1989

Zeaxanthin Synthesis, Energy Dissipation, and Photoprotection of Photosystem II at Chilling Temperatures.

When leaves of a mangrove, Rhizophora mangle, were exposed to an excess of light at chilling temperatures, synthesis of zeaxanthin through violaxanthin de-epoxidation as well as nonphotochemical fluorescence quenching were markedly reduced. The results suggest a protective role of energy dissipation against the adverse effects of high light and chilling temperatures: leaves of R. mangle that had been preilluminated in 2% O(2), 0% CO(2) at low photon flux density and showed a high level of zeaxanthin, and leaves that had been kept in the dark and contained no zeaxanthin, were both exposed to high light and chilling temperatures (5 degrees C leaf temperature) in air and then held under control conditions in low light in air at 25 degrees C. Measurements of chlorophyll a fluorescence at room temperature showed that the photochemical efficiency of PSII and the yield of maximum fluorescence of the preilluminated leaf recovered completely within 1 to 3 hours under the control conditions. In contrast, the fluorescence responses of the predarkened leaf in high light at 5 degrees C did not recover at all. During a dark/light transient in 2% O(2), 0% CO(2) in low light at 5 degrees C, nonphotochemical fluorescence quenching increased linearly with an increase in the zeaxanthin content in leaves of R. mangle. In soybean (Glycine max) leaves, which contained a background level of zeaxanthin in the dark, a similar treatment with excess light induced a level of nonphotochemical fluorescence quenching that was not paralleled by an increase in the zeaxanthin content.

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PubMed1989

Crassulacean Acid Metabolism and Photochemical Efficiency of Photosystem II in the Adaxial and Abaxial Parts of the Succulent Leaves of Kalanchoë daigremontiana Grown at Four Photon Flux Densities.

Kalanchoë daigremontiana, a species possessing crassulacean acid metabolism, was grown at four photon flux densities (1300, 400, 60, and 25 micromole photons per square meter per second). In leaves which had developed at 1300 and 400 micromole photons per square meter per second, CO(2) was mainly incorporated through the lower, shaded leaf surfaces, and the chlorenchyma adjacent to the lower surfaces showed a higher degree of nocturnal acid synthesis than the chlorenchyma adjacent to the upper surfaces. In leaves acclimated to 60 and 25 micromole photons per square meter per second, the gradient in CAM activity was reversed, i.e. more CO(2) was taken up through the upper than through the lower surfaces and nocturnal acidification was higher in the tissue next to the upper surfaces. Total net carbon gain and total nocturnal acid synthesis were highest in leaves which had developed at 400 micromole photons per square meter per second. Chlorophyll content was markedly reduced in leaves which had developed at 1300 micromole photons per square meter per second, especially in the exposed adaxial parts. There was also a sustained reduction in photosystem II photochemical efficiency as indicated by measurements of the ratio of variable over maximum chlorophyll a fluorescence. These findings suggest that, at high growth photon flux densities, the reduced activity of the exposed portions of these succulent leaves is caused by (a) the adverse effects of excess light, (b) together with a genotypic component which favors CO(2) uptake and acid synthesis in the abaxial (lower) leaf parts even when light is not or only marginally excessive. This latter component is predominant at medium photon flux densities, e.g. at 400 micromole photons per square meter per second. It becomes overridden, however, under conditions of deep shade when strongly reduced light levels in the abaxial parts of the leaf chlorenchyma severely limit photosynthesis.

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PubMed1988

Zeaxanthin and the Heat Dissipation of Excess Light Energy in Nerium oleander Exposed to a Combination of High Light and Water Stress.

Upon termination of watering of plants of Nerium oleander exposed to high light, photochemical efficiency became reduced as leaf water content decreased. Evidence is presented that this type of photoinhibition reflects to a substantial degree radiationless dissipation of excitation energy, probably mediated by the carotenoid zeaxanthin. During the imposition of water stress, the zeaxanthin content of leaves increased at the expense of violaxanthin and beta-carotene as a water deficit developed over a period of several days. The increase in zeaxanthin content was linearly related to an increase in the rate of radiationless energy dissipation in the antenna chlorophyll as calculated from the characteristics of chlorophyll a fluorescence measured with a pulse amplitude modulated fluorometer at room temperature. The increase in the rate of radiationless dissipation was also linearly related to a decrease in PSII photochemical efficiency as indicated by the ratio of variable to maximum fluorescence. Leaves of well-watered shade plants of N. oleander exposed to strong light showed a similar increase in zeaxanthin content as sun leaves of the same species subjected to drought in strong light. Shade leaves possessed the same capacity as sun leaves to form zeaxanthin at the expense of both violaxanthin and beta-carotene. The resistance of this species to the destructive effects of excess light appears to be related to interconversions between beta-carotene and the three carotenoids of the xanthophyll cycle.

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PubMed1987

Magnetic resonance imaging in non-specific discitis.

In this 20-month-old girl with non-specific spondylodiscitis the typical clinical presentation was absent. A definite diagnosis was made by radiological examination. Several reports have appeared in the literature concerning the importance of MRI as a new imaging modality in the diseases of the spine, including spondylodiscitis. In the present report we discuss the potential role of MRI in early diagnosis of spondylodiscitis in childhood.

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PubMed1987

Induction of Crassulacean Acid Metabolism in Mesembryanthemum crystallinum by High Salinity: Mass Increase and de Novo Synthesis of PEP-Carboxylase.

Intact plants of the halophilic species Mesembryanthemum crystallinum were induced to exhibit Crassulacean acid metabolism by irrigation with nutrient solution containing 500 millimolar NaCl. During the induction period, the extractable activity of phosphoenolpyruvate carboxylase (PEPcase) increased approximately 40-fold. This increase was linearly correlated with a mass increase of PEPcase protein as measured by single radial immunodiffusion. De novo synthesis of PEPcase protein was shown by immunoprecipitation of the newly synthesized, radioactively labeled protein in leaf discs from salt-treated plants. Nontreated plants were characterized by a low level of the enzyme and low rates of PEPcase synthesis. Synthesis of this enzyme in leaf discs was correlated with the concentration of NaCl in the nutrient solution during growth.

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PubMed1987

Photoinhibition and zeaxanthin formation in intact leaves : a possible role of the xanthophyll cycle in the dissipation of excess light energy.

Comparative studies of chlorophyll a fluorescence, measured with a pulse amplitude modulated fluorometer, and of the pigment composition of leaves, suggest a specific role of zeaxanthin, a carotenoid formed in the xanthophyll cycle, in protecting the photosynthetic apparatus against the adverse effects of excessive light. This conclusion is based on the following findings: (a) exposure of leaves of Populus balsamifera, Hedera helix, and Monstera deliciosa to excess excitation energy (high light, air; weak light, 2% O(2), 0% CO(2)) led to massive formation of zeaxanthin and a decrease in violaxanthin. Over a wide range of conditions, there was a linear relationship between either variable, F(v), or maximum fluorescence, F(m), and the zeaxanthin content of leaves. (b) When exposed to photoinhibitory light levels in air, shade leaves of H. helix had a higher capacity for zeaxanthin formation, at the expense of beta-carotene, than shade leaves of M. deliciosa. Changes in fluorescence characteristics suggested that, in H. helix, the predominant response to high light was an increase in the rate of nonradiative energy dissipation, whereas, in M. deliciosa, photoinhibitory damage to photosystem II reaction centers was the prevailing effect. (c) Exposure of a sun leaf of P. balsamifera to increasing photon flux densities in 2% O(2) and 0% CO(2) resulted initially in increasing levels of zeaxanthin (matched by decreases in violaxanthin) and was accompanied by fluorescence changes indicative of increased nonradiative energy dissipation. Above the light level at which no further increase in zeaxanthin content was observed, fluorescence characteristics indicated photoinhibitory damage. (d) A linear relationship was obtained between the ratio of variable to maximum fluorescence, F(v)/F(m), determined with the modulated fluorescence technique at room temperature, and the photon yield of O(2) evolution, similar to previous findings (O Björkman, B Demmig 1987 Planta 170: 489-504) on chlorophyll fluorescence characteristics at 77 K and the photon yield of photosynthesis.

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PubMed1987

Reduction State of Q and Nonradiative Energy Dissipation during Photosynthesis in Leaves of a Crassulacean Acid Metabolism Plant, Kalanchoë daigremontiana Hamet et Perr.

Fluorescence was measured in leaves of the CAM plant Kalanchoë daigremontiana using a pulse modulation technique at room temperature. During a 12-h light period at 500 micromole photons per square meter per second (400-700 nanometers) in air containing 350 microbar CO(2), the component of fluorescence quenching related to the reduction state of Q, the primary electron transport acceptor of PSII, remained fairly constant and showed that only 20% of Q were in the reduced form. The reduction state was slightly increased at the onset and at the end of the light period. By contrast, the nonphotochemical component of fluorescence quenching which is a measure of the fraction of nonradiative deexcitation underwent marked diurnal changes. Nonradiative energy conversion was low during the phase of most active malic acid decarboxylation in the middle of the light period when uptake of atmospheric CO(2) was negligible, and when internal CO(2) partial pressures were higher than in air; this allowed for high rates of CO(2) reduction in the chloroplasts. Nonradiative energy conversion was high during the early and the late light period when atmospheric CO(2) was taken up and internal CO(2) partial pressures were below air level. Manipulation of the internal CO(2) partial pressure during the late light period by increasing or decreasing the external CO(2) partial pressure to 1710 and 105 microbar, respectively, led to changes in the magnitude of energy dependent fluorescence quenching which were consistent with the relationship between nonradiative energy dissipation and internal CO(2) partial pressure observed during the diurnal cycle. Again, the reduction state of Q was hardly affected by these treatments. Thus, changes in electron transport rate during the diurnal CAM cycle at a given photon flux density lead primarily to alterations in the rate of nonradiative energy dissipation, with the reduction state of Q being maintained at a relatively low and constant level. Conditions are described under which nonphotochemical dissipation of excitation energy reaches a maximum value and the reduction state of Q is increased.

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PubMed1986

Respiratory CO(2) as Carbon Source for Nocturnal Acid Synthesis at High Temperatures in Three Species Exhibiting Crassulacean Acid Metabolism.

TEMPERATURE EFFECTS ON NOCTURNAL CARBON GAIN AND NOCTURNAL ACID ACCUMULATION WERE STUDIED IN THREE SPECIES OF PLANTS EXHIBITING CRASSULACEAN ACID METABOLISM: Mamillaria woodsii, Opuntia vulgaris, and Kalanchoë daigremontiana. Under conditions of high soil moisture, nocturnal CO(2) gain and acid accumulation had temperature optima at 15 to 20 degrees C. Between 5 and 15 degrees C, uptake of atmospheric CO(2) largely accounted for acid accumulation. At higher tissue temperatures, acid accumulation exceeded net carbon gain indicating that acid synthesis was partly due to recycling of respiratory CO(2). When plants were kept in CO(2)-free air, acid accumulation based on respiratory CO(2) was highest at 25 to 35 degrees C. Net acid synthesis occurred up to 45 degrees C, although the nocturnal carbon balance became largely negative above 25 to 35 degrees C. Under conditions of water stress, net CO(2) exchange and nocturnal acid accumulation were reduced. Acid accumulation was proportionally more decreased at low than at high temperatures. Acid accumulation was either similar over the whole temperature range (5-45 degrees C) or showed an optimum at high temperatures, although net carbon balance became very negative with increasing tissue temperatures. Conservation of carbon by recycling respiratory CO(2) was temperature dependent. At 30 degrees C, about 80% of the dark respiratory CO(2) was conserved by dark CO(2) fixation, in both well irrigated and water stressed plants.

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PubMed1986

Analysis of Stomatal and Nonstomatal Components in the Environmental Control of CO(2) Exchange in Leaves of Welwitschia mirabilis.

In well-watered plants of Welwitschia mirabilis, grown in the glass-house under high irradiance conditions, net CO(2) assimilation was almost exclusively observed during the daytime. The plants exhibited a very low potential for Crassulacean acid metabolism, which usually resulted in reduced rates of net CO(2) loss for several hours during the night. In leaves exposed to the diurnal changes in temperature and humidity typical of the natural habitats, CO(2) assimilation rates in the light were markedly depressed under conditions resembling those occurring during midday, when leaf temperatures and the leaf-air vapor pressure differences were high (36 degrees C and 50 millibars bar(-1), respectively). Studies on the relationship between CO(2) assimilation rate and intercellular CO(2) partial pressure at various temperatures and humidities showed that this decrease in CO(2) assimilation was largely due to stomatal closure. The increase in the limitation of photosynthesis by CO(2) diffusion, which is associated with the strong decline in stomatal conductance in Welwitschia exposed to midday conditions, may significantly contribute to the higher (13)C content of Welwitschia compared to the majority of C(3) species.

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PubMed1985

Light Scattering as an Indicator of the Energy State in Leaves of the Crassulacean Acid Metabolism Plant Kalanchoë pinnata.

Both transmittance changes in a weak beam of green light (light scattering) and the slow decay of chlorophyll a fluorescence were used as indicators of the energy state of leaves of a Crassulacean acid metabolism plant, Kalanchoë pinnata, at frequent intervals during 12-hour light/12-hour dark cycles. To induce light scattering and fluorescence changes, leaves were exposed to red light for 6 minutes. When measurements were made during the light period, the leaves were kept in darkness for 6 minutes before illumination. In the middle of the light period, when malic acid decarboxylation was very active and stomatal conductance was low, light scattering changes were small and indicated that the energy state of leaves was low. This result was supported by determination of adenylate levels. Light scattering and ATP/ADP ratios increased during the late light period when the tissue was deacidified. Illumination produced maximum light scattering changes between the 2nd and 5th hour of the dark period, when rates of dark CO(2) fixation were highest. Light scattering and fluorescence measurements taken from leaves, which were illuminated with red or far-red light in the presence or absence of O(2) showed that, in addition to linear electron transport, K. pinnata has the potential for both cyclic and pseudocyclic electron transport. The results are relevant with regard to the high ATP demand during Crassulacean acid metabolism.

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