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  • 1
    Electronic Resource
    Electronic Resource
    Chlorophyll fluorescence in the resurrection plant Selaginella lepidophylla (Hook. & Grev.) Spring during high-light and desiccation stress, and evidence for zeaxanthin-associated photoprotection (1993)
    Springer
    Planta 189 (1993), S. 30-38 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Desiccation tolerance ; Fluorescence quenching (non-photochemical, photochemical) ; Photoprotection ; Selaginella ; Zeaxanthin (xanthophyll cycle)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The function of photosystem (PS)II during desiccation and exposure to high photon flux density (PFD) was investigated via analysis of chlorophyll fluorescence in the desert resurrection plant Selaginella lepidophylla (Hook. and Grev.) Spring. Exposure of hydrated, physiologically competent stems to 2000 μmol · m−2 · s−1 PFD caused significant reductions in both intrinsic fluorescence yield (FO) and photochemical efficiency of PSII (FV/FM) but recovery to pre-exposure values was rapid under low PFD. Desiccation under low PFD also affected fluorescence characteristics. Both FV/FM and photochemical fluorescence quenching remained high until about 40% relative water content and both then decreased rapidly as plants approached 0% relative water content. In contrast, the maximum fluorescence yield (FM) decreased and non-photochemical fluorescence quenching increased early during desiccation. In plants dried at high PFD, the decrease in FV/FM was accentuated and FO was reduced, however, fluorescence characteristics returned to near pre-exposure values after 24-h of rehydration and recovery at low PFD. Pretreatment of stems with dithiothreitol, an inhibitor of zeaxanthin synthesis, accelerated the decline in FV/FM and significantly increased FO relative to controls at 925 μmol · m−2 · s−1 PFD, and the differences persisted over a 3-h low-PFD recovery period. Pretreatment with dithiothreitol also significantly decreased non-photochemical fluorescence quenching, increased the reduction state of QA, the primary electron acceptor of PSII, and prevented the synthesis of zeaxanthin relative to controls when stems were exposed to PFDs in excess of 250 μmol · m−2 · s−1. These results indicate that a zeaxanthin-associated mechanism of photoprotection exists in this desert pteridophyte that may help to prevent photoinhibitory damage in the fully hydrated state and which may play an additional role in protecting PSII as thylakoid membranes undergo water loss.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201340
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  • 2
    Electronic Resource
    Electronic Resource
    Fluorescence quenching during photosynthesis and photoinhibition of Ulva rotundata blid. (1993)
    Springer
    Planta 190 (1993), S. 97-106 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Photoinhibition ; Photoprotection ; Ulva (photosynthesis)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationships between photoinhibition and photoprotection in high and low-light-grown Ulva were examined by a combination of chlorophyll-fluorescence-monitoring techniques. Tissues were exposed to a computer-controlled sequence of 5-min exposures to red light, followed by 5-min darkness, with stepwise increases in photon flux. Coefficients of chlorophyll fluorescence quenching (1−qP and NPQ) were calculated following a saturating pulse of white light near the end of each 5-min light treatment. Dark-adapted chlorophyll fluorescence parameters (F0 and FV/FM) were calculated from a saturating pulse at the end of each 5-min dark period. Low-light-grown Ulva showed consistently higher 1−qP, i.e. higher reduction status of Q (high primary acceptor of photosystem II), and lower capacity for nonphotochemical quenching (NPQ) at saturating light than did high-light-grown plants. Consequently, low-light plants rapidly displayed photoinhibitory damage (increased F0) at light saturation in seawater. Removal of dissolved inorganic carbon from seawater also led to photoinhibitory damage of high-light-grown Ulva at light saturation, and addition of saturating amounts of dissolved inorganic carbon protected low-light-grown plants against photoinhibitory damage. A large part of NPQ was abolished by treatment with 3 mM dithiothreitol and the processes so inhibited were evidently photoprotective, because dithiothreitol treatment accelerated photoinhibitory damage in both low- and high-light-grown Ulva. The extent of photoinhibitory damage in Ulva was exacerbated by treatment with chloramphenicol (1 mM) without much effect on chlorophyll-quenching parameters, evidently because this inhibitor of chloroplast protein synthesis reduced the rate of repair processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195680
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  • 3
    Electronic Resource
    Electronic Resource
    Changes of fluorescence and xanthophyll pigments during dehydration in the resurrection plantSelaginella lepidophylla in low and medium light intensities (1993)
    Springer
    Oecologia 94 (1993), S. 528-533 
    Details
    ISSN: 1432-1939
    Keywords: Fluorescence ; Photoinhibition ; Photoprotection ; Selaginella lepidophylla ; Xanthophyll cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The changes in photosynthetic efficiency and photosynthetic pigments during dehydration of the resurrection plantSelaginella lepidophylla (from the Chiuhahuan desert, S.W. Texas, USA) were examined under different light conditions. Changes in the photosynthetic efficiency were deduced from chlorophyll a fluorescence measurements (Fo, Fm, and Fv) and pigment changes were measured by HPLC analysis. A small decrease in Fv/Fm was seen in hydrated stems in high light (650 μmol photons·m−2·s−1) but not in low light (50 μmol photons·m−2·s−1). However, a pronounced decline in Fv/Fm was observed during dehydration in both light treatments, after one to two hours of dehydration. A rise in Fo was observed only after six to ten hours of dehydration. Concomitant with the decrease in photosynthetic efficiency during dehydration a rise in the xanthophyll zeaxanthin was observed, even in low-light treatments. The increase in zeaxanthin can be related to previously observed photoprotective non-photochemical quenching of fluorescence in dehydrating stems ofS. lepidophylla. We hypothesize that under dehydrating conditions even low light levels become excessive and zeaxanthin-related photoprotection is engaged. We speculate that these processes, as well as stem curling and self shading (Eickmeier et al. 1992), serve to minimize photoinhibitory damage toS. lepidophylla during the process of dehydration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566968
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  • 4
    Electronic Resource
    Electronic Resource
    Type 2 (non-insulin-dependent) diabetes mellitus, hypertension and hyperlipidaemia (syndrome X): relation to reduced fetal growth (1993)
    Springer
    Diabetologia 36 (1993), S. 62-67 
    Details
    ISSN: 1432-0428
    Keywords: Type 2 (non-insulin-dependent) diabetes mellitus ; hypertension ; hyperlipidaemia ; syndrome X ; reduced fetal growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Two follow-up studies were carried out to determine whether lower birthweight is related to the occurrence of syndrome X — Type 2 (non-insulin-dependent) diabetes mellitus, hypertension and hyperlipidaemia. The first study included 407 men born in Hertfordshire, England between 1920 and 1930 whose weights at birth and at 1 year of age had been recorded by health visitors. The second study included 266 men and women born in Preston, UK, between 1935 and 1943 whose size at birth had been measured in detail. The prevalence of syndrome X fell progressively in both men and women, from those who had the lowest to those who had the highest birthweights. Of 64-year-old men whose birthweights were 2.95 kg (6.5 pounds) or less, 22% had syndrome X. Their risk of developing syndrome X was more than 10 times greater than that of men whose birthweights were more than 4.31 kg (9.5 pounds). The association between syndrome X and low birthweight was independent of duration of gestation and of possible confounding variables including cigarette smoking, alcohol consumption and social class currently or at birth. In addition to low birthweight, subjects with syndrome X had small head circumference and low ponderal index at birth, and low weight and below-average dental eruption at 1 year of age. It is concluded that Type 2 diabetes and hypertension have a common origin in sub-optimal development in utero, and that syndrome X should perhaps be re-named “the small-baby syndrome”.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00399095
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  • 5
    Electronic Resource
    Electronic Resource
    Fetal growth and impaired glucose tolerance in men and women (1993)
    Springer
    Diabetologia 36 (1993), S. 225-228 
    Details
    ISSN: 1432-0428
    Keywords: Impaired glucose tolerance ; non-insulin-dependent diabetes mellitus ; fetal growth ; ponderal index at birth ; placental weight to birthweight ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A follow-up study was carried out to determine whether reduced fetal growth is associated with the development of impaired glucose tolerance in men and women aged 50 years. Standard oral glucose tolerance tests were carried out on 140 men and 126 women born in Preston (Lancashire, UK) between 1935 and 1943, whose size at birth had been measured in detail. Those subjects found to have impaired glucose tolerance or non-insulin-dependent diabetes mellitus had lower birthweight, a smaller head circumference and were thinner at birth. They also had a higher ratio of placental weight to birthweight. The prevalence of impaired glucose tolerance or diabetes fell from 27% in subjects who weighed 2.50 kg (5.5 pounds) or less at birth to 6% in those who weighed more than 3.41 kg (7.5 pounds) (p 〈 0.002 after adjusting for body mass index). Plasma glucose concentrations taken at 2-h in the glucose tolerance test fell progressively as birthweight increased (p 〈 0.004), as did 2-h plasma insulin concentrations (p 〈 0.001). The trends with birthweight were independent of duration of gestation and must therefore be related to reduced rates of fetal growth. These findings confirm the association between impaired glucose tolerance in adult life and low birthweight previously reported in Hertfordshire (UK), and demonstrate it in women as well as men. It is suggested that the association reflects the long-term effects of reduced growth of the endocrine pancreas and other tissues in utero. This may be a consequence of maternal undernutrition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00399954
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  • 6
    Electronic Resource
    Electronic Resource
    Interpretations of gradients in δ13C value in thick photosynthetic tissues of plants with Crassulacean acid metabolism (1993)
    Springer
    Planta 190 (1993), S. 271-276 
    Details
    ISSN: 1432-2048
    Keywords: Carbon isotope ratio (gradients) ; Crassulacean acid metabolism ; Epidermis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In Ceropegia dichotoma, Crassula argentea, Esheveria colorata, Kalanchoë beharensis, Opuntia ficus-indica, Sansveria stuckyi and Opuntia inermis the carbon-isotope ratio (δ 13C) of tissues close to the epidermis is 2–4.3‰ more negative than those in the centre of the leaf or cladode. The greatest change in δ 13C value occurs between the epidermal layer and the layer of mesophyll tissue immediately underneath. Analysis of major metabolic and structural components in successive layers of Crassula argentea grown under controlled environmental conditions conducive to Crassulacean acid metabolism confirmed that much of the variation in δ 13C values of bulk carbon is caused by differences in chemical composition. Thus the steep gradient in δ 13C value at the epidermis reflects, in part, the contribution of more-negative δ 13C values of lipids in these tissues. Moreover, during nocturnal CO2 fixation the amount of malic acid synthesised decreases with depth and the δ 13C value of the methanol-soluble fraction is less negative with distance away from the upper epidermis. These results are consistent with diffusion limitation to CO2 uptake in these thick leaf tissues, which also contributes to the observed gradients in δ 13C value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196621
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    Paper (German National Licenses)
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