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  • 1
    Electronic Resource
    Electronic Resource
    Probing corticular photosynthesis through in vivo chlorophyll fluorescence measurements: evidence that high internal CO2 levels suppress electron flow and increase the risk of photoinhibition (2004)
    Oxford, UK; Malden, US : Munksgaard International Publishers
    Physiologia plantarum 120 (2004), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Twigs of many woody plants possess chlorenchyma under a well-developed periderm which lacks stomata and impedes both gas diffusion and light penetration. The so-called corticular photosynthesis, occurring in the shade and under extremely high CO2 concentrations, was probed in this study through in vivo chlorophyll fluorescence measurements. Field comparisons between twigs and corresponding leaves in five species indicated that both the dark- and light-adapted PSII photochemical efficiencies are considerably lower in twigs at all incident photon fluence rates, in spite of the significant attenuation of solar radiation by the periderm. Light saturation curves for linear electron transport rates (corrected according to the actual light intensities reaching twig chlorenchyma) were compatible with a shade-acclimated photosynthetic machinery, showing very low maximum electron transport rates (at approximately 5% of the corresponding leaf values) and threshold irradiances for light saturation. However, removing periderms from twig segments (i.e. relieving the twig interior form the high CO2 partial pressures) considerably improved the light-adapted (but not the dark-adapted) PSII photochemical efficiency, allowing the assumption that the high internal CO2 levels may interfere with the smooth functioning of photosynthesis. Indeed, laboratory experiments with twig segments equilibrated under various CO2 levels (0.036–20%), resulted in a progressive decrease of light-adapted PSII photochemical yield, with the values obtained at 20% CO2 being similar to those obtained with intact twigs in the field. Further experiments indicated that high CO2 combined with high light suppressed the development of a photoprotective non-photochemical quenching through a reduction of its fast relaxing component, accompanied by a higher risk of photoinhibition. It is suggested that high internal CO2 concentrations in twigs impede photosynthesis possibly through acidification of protoplasm and impairment of the pH-dependent high energy state quenching followed by reduction in the efficiency of heat dissipation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0031-9317.2004.00256.x
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  • 2
    Electronic Resource
    Electronic Resource
    Ultraviolet-B radiation absorbing capacity of leaf hairs (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 86 (1992), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Pubescence layers with their native structure and orientation were isolated from the leaves of Olea europaea L. and Olea chrysophylla L. They were almost transparent in the visible, but considerable absorptance was evident in the ultraviolet-B region (UV-B), with maximum at 310 nm. Methanolic extracts of hairs from Olea and a variety of other pubescent species consistently showed the existence of UV-screening pigments. Absorptance of trichomes varied, but a trend towards more effective UV-B radiation attenuation in the sub-alpine Verbascum species may be claimed. In all cases, pigments were located within hair cells and in Olea they were characterized as phenolics with considerable flavonoid contribution. It is suggested that leaf hairs, besides other functions, may constitute a shield against UV-B radiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1992.tb01337.x
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  • 3
    Electronic Resource
    Electronic Resource
    Diurnal changes in phosphoenolpyruvate carboxylase and pyruvate, orthophosphate dikinase properties in the natural environment: interplay of light and temperature in a C4 thermophile (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 80 (1990), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Activities of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) were measured in leaf extracts of field grown Amaranthus paniculatus L. (C4) during a natural diurnal irradiance and temperature pattern. Enzyme assays were run at both fixed (30°C) and the corresponding leaf temperature at the time of harvest. Light activation of PEP carboxylase (PEPCase) at fixed assay temperatures was expressed as a decrease in S0–5 (PEP) after a threshold (〉 330 μmol m–2 s–1) photon fluence rate was surpassed at noon. Earlier in the morning, increase in apparent enzyme affinity for PEP was observed when the assay was run at leaf temperature, indicating a physiologically meaningfull effect of temperature on S0.5 (PEP). The 3.3-fold increase in PEPCase activity at low PEP and fixed assay temperature between the minimal and maximal irradiance and temperature hours of the day, became 12.8-, 11.5- and 7.4-fold when assays were run at the corresponding leaf temperature during three diurnal cycles with respective temperature differences (max minus min) of 9.0, 8.3 and 7.4°C. The extent of malate inhibition was the same for both day and night forms of PEPCase assayed at 35°C, but increased considerably with night enzyme at 25°C. The results indicate that light increases the apparent affinity of PEPCase for PEP and that at lower temperatures malate becomes more inhibitory. Pyruvate orthophosphate dikinase activity started to increase immediately after sunrise and the 10-fold increase at fixed temperature became 14.8-, 14.2- and 13.1-fold when assays were run at the above leaf temperatures. This indicates that the light effect predominates with pyruvate, orthophosphate dikinase, while with phosphoenolpyravate carboxylase, light and temperature co-operate to increase the day enzyme activities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1990.tb05683.x
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  • 4
    Electronic Resource
    Electronic Resource
    Enhanced UV-B radiation alleviates the adverse effects of summer drought in two Mediterranean pines under field conditions (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 94 (1995), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effects of enhanced UV-B (290-320 nm) radiation on two native Mediterranean pines (Pinus pinea L., Pinus halepensis Mill.) were recorded during a one-year field study. Plants received ambient or ambient plus supplemental UV-B radiation (simulating a 15% stratospheric ozone depletion over Patras. Greece, 38.3°N. 29.1°E) and only natural precipitation, i.e. they were simultaneously exposed to other natural stresses. particularly water stress during summer. Supplemental UV-B irradiation started in early February, 1993 and up to late June, no effects were observed on growth and photochemical efficiency of photosystem II, as measured by chlorophy II fluorescence induction. Water stress during the summer was manifested in the control plants as a decline in the ratio of variable to maximum fluorescence (Fv/Fm), the apparent photon yield for oxygen evolution (φl) and the photosynthetic capacity at 5% CO2 (Pm). In addition, a partial needle loss was evident. Under supplemental UV-B radiation, however, the decreases in Fv/Fm, φi, and Pm. as well as needle losses were significantly less. Soon after the first heavy autumn rains. photosynthetic parameters in both control and UV-B treated plants recovered to similar values. but the transient summer superiority of UV-B irradiated plants resulted in a significant increase in their dry weight measured at plant harvest. during late January. 1994. Plant height. UV-B absorbing compounds, photosynthetic pigments and relative water content measured at late spring. late summer and at plant harvest, were not significantly affected by supplemental UV-B radiation. The results indicate that enhanced UV-B radiation may be beneficial for Mediterranean pines through a partial alleviation of the adverse effects of summer drought.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb00781.x
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  • 5
    Electronic Resource
    Electronic Resource
    The transiently pubescent young leaves of plane (Platanus orientalis) are deficient in photodissipative capacity (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 101 (1997), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We have analyzed reflectance changes and carotenoid composition of young and mature leaves of Platanus orientalis L. in order to test the hypothesis that the transient occurrence of highly absorptive and reflective leaf hairs of young leaves (M. Ntefidou and Y. Manetas 1996, Aust. J. Plant Physiol. 23: 535–538) may be correlated to a weakly developed photodissipative capacity in the chloroplast. Compared to mature leaves, young leaves showed negligible reflectance changes at 530 nm upon sudden illumination, possibly indicating a limited production of zeaxanthin. In addition, actual pigment analysis confirmed lower pools of xanthophyll cycle components and reduced capacity for violaxanthin photoconversion in young leaves. Accordingly, the epoxidation state at saturating photon fluence rates was particularly high. A notable feature of xanthophyll cycle interconversions in young leaves was the inability to drive the system to complete de-epoxidation, as antheraxanthin in the light was always higher than zeaxanthin. Among the rest of the carotenoids, the levels of β-carotene were particularly low. Moreover, most of the photosynthetic pigments were considerably bleached when young leaves were exposed to high light. The above results strongly suggest that young leaves possess a limited photodissipative capacity and therefore, the presence of leaf hairs affords protection against excess light. When the leaf has matured and presumably the concentrations of photoprotective compounds are adequate, the loss of hairs is not of consequence. In fact, their presence on mature leaves may reduce the photosynthetically active radiation to non-saturating levels for photosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1997.tb01011.x
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  • 6
    Electronic Resource
    Electronic Resource
    Are-examination of NaCI effects on phosphoenolpyruvate carboxylase at high (physiological) enzyme concentrations (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 78 (1990), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Inhibition of phosphoenolpyruvate carboxylase (EC 4.1.1 31) from the C4-halophyte Salsola soda L. by NaCI is compeutive to phosphoenolpyruvate (PEP). Physiological (betaine, glycerol) and synthetic (polyethylene glycol) osmotica and the allosteric activator glucose-6-phosphate (G6P) increase the apparent affinity of the enzyme for PEP and also alleviate the inhibition by NaCl. Physiological osmotica that either increase the Km(PEP) (proline) or are neutral (sorbitol), do not protect the enzyme against NaCI attack. In the absence of cosolutes and, G6P, the enzyme is self-protected when its concentration in the assay medium is increased to more physiological values. In addition, the amount of betaine needed for complete protection is inversely related to native protein concentration in the assay. Exogenous protein (bovine serum albumin or bovine skin gelatin) have no effect on either Km(PEP), or extent of NaCl inhibition. These results can be better explained with the exclusion volume theory and the inferred assumption that both cosolutes and high protein concentration strengthen intrinsic aggregation properties of enzymes. It is suggested that the extremely high phosphoenolpyruvate carboxylase concentration in the cytoplasm and the accumulation of compatible solutes in response to water stress fully protect the enzyme in vivo against the chaotropic effects of NaCI.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1990.tb02085.x
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  • 7
    Electronic Resource
    Electronic Resource
    Changes in properties of phosphoenolpyruvate carboxylase from the CAM plant Sedum praealtum D.C. upon dark/light transition and their stabilization by glycerol (1982)
    Springer
    Photosynthesis research 3 (1982), S. 321-333 
    Details
    ISSN: 1573-5079
    Keywords: Crassulancean acid metabolism ; dark/light transition ; PEPCase ; Sedum praealtum D.C. ; stabilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A prenounced decrease in phosphoenolpyruvate earboxylase (PEPC) activity is observed upon dark/light transition in Sedum praealtum D.C., only when glycerol is included in the extraction medium. If glycerol is omitted, the activity extracted in light is initially low, but soon reaches night levels. The stabilization of the light-induced form of the enzyme by glycerol, in crude or desalted extracts, made it possible to study its kinetic properties in comparison to those of the dark form. The behaviour towards substrate (PEP) changes from hyperbolic (dark) to sigmoid (light), S0.5 is increased and the enzymic activity becomes more sensitive to malate inhibition. Quite different activity/pH profiles are also obtained for the two forms of PEPC. It is inferred that the in vivo regulation of PEPC in CAM is effected by a concerted action of light, malate and pH shifting.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00034113
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  • 8
    Electronic Resource
    Electronic Resource
    Beneficial effects of enhanced UV-B radiation under field conditions: improvement of needle water relations and survival capacity of Pinus pinea L. seedlings during the dry Mediterranean summer (1997)
    Springer
    Plant ecology 128 (1997), S. 101-108 
    Details
    ISSN: 1573-5052
    Keywords: Cuticle ; Pinus pinea ; UV-B radiation ; Water relations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The possible mechanism(s) by which supplemental UV-B radiation alleviates the adverse effects of summer drought in Mediterranean pines (Petropoulou et al. 1995) were investigated with seedlings of Pinus pinea. Plants received ambient or ambient plus supplemental UV-B radiation (biologically equivalent to a 15% ozone depletion over Patras, 38.3° N, 29.1° E) and natural precipitation or additional irrigation. Treatments started on 1 February, 1994 and lasted up to the end of the dry period (29 September). In well-watered plants, UV-B radiation had no influence on photosystem II photochemical efficiency and biomass accumulation. Water stressed plants suffered from needle loss and reduced photosystem II photochemical efficiency during the summer. These symptoms, however, were less pronounced in plants receiving supplemental UV-B radiation, resulting in higher total biomass at plant harvest. Laboratory tests showed that enhanced UV-B radiation did not improve the tolerance of photosystem II against drought, high light, high temperature and oxidative stress. Enhanced UV-B radiation, however, improved the water economy of water stressed plants, as judged by measurements of needle relative water content. In addition, it caused an almost two-fold increase of cuticle thickness. No such UV-B radiation effects were observed in well-watered pines. The results indicate that the combination of water stress and UV-B radiation may trigger specific responses, enabling the plants to avoid excessive water loss and, thereby, maintain a more efficient photosynthetic apparatus during the summer. The extent of this apparently positive UV-B radiation effect would depend on the amount of summer precipitation. Abbreviations: DW – dry weight, Fv/Fm – ratio of variable to maximum fluorescence, A 300 – absorbance at 300 nm, PAR – photosynthetically active radiation, PS II – photosystem II, RWC – relative water content, TCA – trichloroacetic acid, UV-BBE – biologically effective ultraviolet-B radiation
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009706806427
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  • 9
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    Compatible solutes and in vitro stability of Salsola soda enzymes: Proline incompatibility (1991)
    Elsevier
    Details
    Publication Date: 1991-01-01
    Print ISSN: 0031-9422
    Electronic ISSN: 1873-3700
    Topics: Biology , Chemistry and Pharmacology
    Published by Elsevier
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  • 10
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    Effects of enhanced UV-B radiation on Mentha spicata essential oils (1998)
    Elsevier
    Details
    Publication Date: 1998-12-01
    Print ISSN: 0031-9422
    Electronic ISSN: 1873-3700
    Topics: Biology , Chemistry and Pharmacology
    Published by Elsevier
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