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Yiannis Manetas – One of the best experts on this subject based on the ideXlab platform.

  • Site-dependent differences in transmittance and UV-B-Absorbing Capacity of isolated leaf epidermes and mesophyll in Urginea maritima (L.) Baker
    Journal of Experimental Botany, 1999
    Co-Authors: George Grammatikopoulos, Y. Petropoulou, Yiannis Manetas

    Abstract:

    The spectral transmittance of isolated ‘intact’ upper and lower epidermes as well as the extractable UV-B-Absorbing Capacity of epidermes and mesophyll were studied in the leaves of exposed and deeply shaded, field-grown plants of Urginea maritima (L.) Baker. Epidermal transmittance in the visible part of the spectrum was high (>80%) in all cases. Transmittance in the UV-B (280-320 nm) was comparatively high (c. 14%) in both the upper and lower epidermes of shaded plants, but more than an order of magnitude lower in exposed plants, with the lowest values observed on the upper leaf epidermis. UV-B transmittance was negatively correlated with the methanol extractable UV-B-Absorbing Capacity of the epidermes, but was independent of epidermal thickness. The UV-B-Absorbing Capacity of the mesophyll, when expressed on an area basis, was not affected by exposure. However, it was significantly higher in shaded plants, when expressed on a dry mass basis. The results indicate that although the concentrations of the UV-B-Absorbing components of the whole leaf or its epidermis fluctuate according to the site-dependent radiation stress, the opposite is evident for the mesophyll. Therefore, high irradiance in U. maritima, apart from inducing an increase in UV-B-Absorbing compounds on a whole leaf basis, also caused a change in the distribution of these compounds between epidermis and mesophyll.

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  • The effects of seasons, exposure, enhanced UV-B radiation, and water stress on leaf epicuticular and internal UV-B Absorbing Capacity of Cistus creticus: a Mediterranean field study
    Journal of Experimental Botany, 1997
    Co-Authors: M. Stephanou, Yiannis Manetas

    Abstract:

    The seasonal variation in leaf epicuticular and internal (cellular) UV-B Absorbing compounds was followed in field-grown shrubs of Cistus creticus L. Fully exposed and permanently shaded (under a canopy of evergreen sclerophylls) individuals were used. Near monthly measurements were performed for three years. In addition, a 2-year field experiment was established, in which fully exposed plants received ambient or ambient plus supplemental UV-B radiation, simulating a 15% ozone depletion over Patras (38.3° N, 29.1° E). A second, six-month field experiment investigated the effects of additional summer irrigation on UV-B Absorbing compounds. It was found that: (a) exposed plants had considerably higher concentrations of UV-B Absorbing compounds (both epicuticular and internal), irrespective of season. (b) exposed and shaded plants exhibited dramatic and yearly consistent seasonal fluctuations in epicuticular material with a c. 18-fold difference between the summer maxima and winter minima. Internal UV-B Absorbing compounds showed the same seasonal trends, but with far less pronounced differences. (c) In the 2-year field experiment with enhanced UV-B radiation, an increase in both epicuticular and internal UV-B Absorbing Capacity was evident only during the summer dry period of the first year. Later on, however, and up to the termination of the experiment, the differences were abolished. (d) Well-watered and water-stressed plants showed the same levels of both epicuticular and internal UV-B Absorbing compounds. Although the results indicate that concentrations of epicuticular and, to a lesser extent, internal UV-B Absorbing compounds fluctuate according to the seasonally and site-dependent environmental stresses, no indications for an effect of water availability were obtained. Therefore it may be concluded that the main determinant of the levels of UV-B Absorbing compounds is the intensity of solar radiation. The relative influence of the various spectral regions of solar radiation cannot be assessed from the present results. It was predicted, however, that the effects of increased solar UV-B radiation, resulting from the expected ozone depletion over the next decades, will be negligible and probably masked by the much larger seasonal and site-dependent changes.

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  • Trichome density and its UV-B protective potential are affected by shading and leaf position on the canopy
    Environmental and Experimental Botany, 1997
    Co-Authors: Vally Liakoura, Yiannis Manetas, M. Stefanou, C. Cholevas, George Karabourniotis

    Abstract:

    Abstract In Olea europaea trichome density and UV-B Absorbing compounds of leaf hairs and the lamina proper of leaves located in south-facing, north-facing and the internal of the canopy were positively correlated to the UV-B midday instant irradiance measured in September at these three different positions of the canopy. The correlation between these three parameters and the receiving photosynthetically active radiation (PAR), however, was weaker. In Quercus ilex, trichome density and its UV-B Absorbing Capacity were considerably higher in the exposed, south-facing leaves, compared to the deeply shaded ones; the UV-B Absorbing Capacity of the de-haired lamina, however, was the same. In the broad-leaved, alpine rosette of Verbascum speciosum, one could distinguish two areas on the leaves, one exposed and one shaded by the superimposed lamina. Although trichome density and the UV-B Absorbing compounds of the de-haired leaf were the same in the two areas, the UV-B Absorbing Capacity of hairs was considerably increased in the exposed region. In V. speciosum, exposure induced also qualitative changes in the UV-B absorbance profile, apparently due to the formation of new flavonoid compounds Absorbing maximally at 345–350 nm. In all other cases, the differences were mainly quantitative. The results support the postulate of a function of leaf hairs as a UV-B radiation screen and suggest that trichome density and/or its UV-B Absorbing Capacity may depend on irradiance during leaf development.

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George Karabourniotis – One of the best experts on this subject based on the ideXlab platform.

  • Trichome layers versus dehaired lamina of Olea europaea leaves: differences in flavonoid distribution, UV-Absorbing Capacity, and wax yield
    Environmental and Experimental Botany, 2006
    Co-Authors: Georgios Liakopoulos, Sotiria Stavrianakou, George Karabourniotis

    Abstract:

    Leaf flavonoid compounds from six olive (Olea europaea L.) cultivars were analysed by HPLC. The composition of the soluble fractions of the dehaired lamina and the isolated trichome layers of the abaxial leaf surface were analysed in separate, as to study the distribution of flavonoids between the two leaf parts. Quercetin and quercetin 3-O-rhamnoside that have been reported to occur in the leaves seem to be located exclusively in the trichome layer. A greater variety of flavonoids was found in the lamina but the trichome layer was richer in terms of total flavonoids per unit mass. Trichome layer demonstrated an independent chemical character since its flavonoid concentration and composition was not coordinated with that of the lamina. The occurrence of flavonoid compounds in trichomes is related to the UV-filtering Capacity of these cells. The results of the present study showed that apart from the soluble fraction, the cuticular waxes and cell walls of the trichomes also showed significant UV-Absorbing Capacity, indicating the occurrence of UV-Absorbing compounds in these fractions as well. Moreover, the cuticular waxes of the trichome layer exhibited not only a higher investment of mass per unit of leaf area, but also a higher UV-Absorbing Capacity expressed per unit mass as compared to the cuticular waxes of the lamina surface. The importance for the separate chemical investigation of the phenolic composition of the leaf lamina and the trichome layers as well as the ecological significance of the findings is discussed.

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  • The ability of abaxial and adaxial epidermis of sun and shade leaves to attenuate UV‐A and UV‐B radiation in relation to the UV Absorbing Capacity of the whole leaf methanolic extracts
    Physiologia Plantarum, 2002
    Co-Authors: Vally Liakoura, Janet F. Bornman, George Karabourniotis

    Abstract:

    The UV-Absorbing Capacity (measured as A(310) cm(-2) and A(365) cm(-2) or AUVR cm(-2)) of the shade leaves of four representative evergreen sclerophylls of the Mediterranean region (Quercus coccifera, Q. ilex, Arbutus andrachne and A. unedo) was considerably lower than the corresponding one of sun leaves of the same species. However, fibre optic microprobe measurements showed that adaxial as well as abaxial epidermis of shade leaves of all examined plants, except abaxial epidermis of A. andrachne, were almost as effective as the corresponding ones of the sun leaves in screening out most of the incident UV-B radiation. There is probably a threshold, under which the concentration of the UV-B Absorbing compounds in the protective tissues is not furthermore reduced, in spite of the low levels of the stress factor (UV-B radiation) in the environment. On the other hand, the ability of both abaxial and adaxial epidermis to attenuate UV-A radiation, except of adaxial leaf epidermis of Quercus species, depended on the UV Absorbing Capacity of the whole-leaf extracts, with different correlation patterns between the two Quercus species and the two Arbutus species. This could be explained by the fact that shade leaves showed not only quantitative, but also qualitative differences (higher A(310)/A(365) ratio) in the absorbance of their methanolic extracts compared to these of sun leaves. The results of the present study showed that we should not always correlate the depth of penetration of UV radiation into sun and shade leaves according to the corresponding UV Absorbing Capacity of the whole leaf methanolic extracts, without taking into account all the anatomical, developmental and biochemical (such as different composition and distribution of the UV-Absorbing compounds among the different protective tissues) peculiarities of the leaves of each species. (Less)

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  • Trichome density and its UV-B protective potential are affected by shading and leaf position on the canopy
    Environmental and Experimental Botany, 1997
    Co-Authors: Vally Liakoura, Yiannis Manetas, M. Stefanou, C. Cholevas, George Karabourniotis

    Abstract:

    Abstract In Olea europaea trichome density and UV-B Absorbing compounds of leaf hairs and the lamina proper of leaves located in south-facing, north-facing and the internal of the canopy were positively correlated to the UV-B midday instant irradiance measured in September at these three different positions of the canopy. The correlation between these three parameters and the receiving photosynthetically active radiation (PAR), however, was weaker. In Quercus ilex, trichome density and its UV-B Absorbing Capacity were considerably higher in the exposed, south-facing leaves, compared to the deeply shaded ones; the UV-B Absorbing Capacity of the de-haired lamina, however, was the same. In the broad-leaved, alpine rosette of Verbascum speciosum, one could distinguish two areas on the leaves, one exposed and one shaded by the superimposed lamina. Although trichome density and the UV-B Absorbing compounds of the de-haired leaf were the same in the two areas, the UV-B Absorbing Capacity of hairs was considerably increased in the exposed region. In V. speciosum, exposure induced also qualitative changes in the UV-B absorbance profile, apparently due to the formation of new flavonoid compounds Absorbing maximally at 345–350 nm. In all other cases, the differences were mainly quantitative. The results support the postulate of a function of leaf hairs as a UV-B radiation screen and suggest that trichome density and/or its UV-B Absorbing Capacity may depend on irradiance during leaf development.

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Rong Xue – One of the best experts on this subject based on the ideXlab platform.

  • a polypyrrole cofe2o4 hollow glass microspheres three layer sandwich structure microwave Absorbing material with wide Absorbing bandwidth and strong Absorbing Capacity
    Journal of Materials Science: Materials in Electronics, 2017
    Co-Authors: Xingwei Wang, Hongxia Yan, Rong Xue

    Abstract:

    A new PPy/CoFe2O4/HGMs microwave Absorbing composite particle with three-layer sandwich structure, comprising cobalt ferrite (CoFe2O4) and polypyrrole (PPy) coating on the surface of hollow glass microspheres (HGMs), was synthesized by the method of co-precipitation and in situ polymerization. The surface morphology, phase structure and chemical component of the composite had been characterized by scanning electron microscope and X-ray diffractometer. The results indicated HGMs were coated by CoFe2O4 completely and the obtained CoFe2O4/HGMs composites were warped by PPy. The conductivity and the saturation magnetization Ms of the resulting PPy/CoFe2O4/HGMs composites are 0.09 S/cm and 46 emu/g, respectively. The vector network analyzer showed the composite performed better microwave absorption ability than that of PPy and PPy/HGMs. The reflection loss of the composite with 2.58 mm thickness is more than−10 dB which means over 90 % microwave is absorbed in X-band (8.38–12.4 GHz). The ternary composite that has light weight, wide Absorbing bandwidth, strong Absorbing Capacity and conductivity can be an attractive candidate in the field of microwave absorption.

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  • A Polypyrrole/CoFe2O4/Hollow Glass Microspheres three-layer sandwich structure microwave Absorbing material with wide Absorbing bandwidth and strong Absorbing Capacity
    Journal of Materials Science: Materials in Electronics, 2016
    Co-Authors: Xingwei Wang, Hongxia Yan, Rong Xue

    Abstract:

    A new PPy/CoFe2O4/HGMs microwave Absorbing composite particle with three-layer sandwich structure, comprising cobalt ferrite (CoFe2O4) and polypyrrole (PPy) coating on the surface of hollow glass microspheres (HGMs), was synthesized by the method of co-precipitation and in situ polymerization. The surface morphology, phase structure and chemical component of the composite had been characterized by scanning electron microscope and X-ray diffractometer. The results indicated HGMs were coated by CoFe2O4 completely and the obtained CoFe2O4/HGMs composites were warped by PPy. The conductivity and the saturation magnetization Ms of the resulting PPy/CoFe2O4/HGMs composites are 0.09 S/cm and 46 emu/g, respectively. The vector network analyzer showed the composite performed better microwave absorption ability than that of PPy and PPy/HGMs. The reflection loss of the composite with 2.58 mm thickness is more than−10 dB which means over 90 % microwave is absorbed in X-band (8.38–12.4 GHz). The ternary composite that has light weight, wide Absorbing bandwidth, strong Absorbing Capacity and conductivity can be an attractive candidate in the field of microwave absorption.

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