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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters A 128 (1988), S. 283-285 
    ISSN: 0375-9601
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 383 (1996), S. 125-127 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] PHYSICS is, for the most part, either macroscopic and classical, or microscopic and quantum mechanical á€" scientists tend to shy away from the difficult middle ground. But in a remarkable synthesis of molecular chemistry and low-temperature physics, two experiments (first by ...
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  • 3
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: This investigation was undertaken to study the effects of colchicine, L-proline and a post-inoculation cold temperature of 14°C for 7 days, either as a single or as combined treatments, on the parameters of anther culture of the DH83Z118.32 wheat genotype. Results indicate that the addition of 100 mg/1 colchicine to the induction medium for a period of 3 days and at an incubation temperature of 28°C yielded the highest success index. This treatment, although it significantly reduced embryogenesis, improved embryoid quality so that not only the total regeneration, but also the percentage of green plantlets increased significantly, In addition, it raised the percentage of doubled haploids and, consequently, led to a significantly better final success index. Combining the colchicine treatment with a reduced post-inoculation temperature did not intensify its beneficial effect, although a treatment of reduced temperature alone was superior to normal temperature (28°C) for most parameters studied. The beneficial effects of adding L-proline (200 mg/1) to the induction medium, combined with a low temperature (10°C for 4 days) treatment, were diminished when this treatment was combined with a colchicine treatment.
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  • 4
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary There is a lack of information on the combined effects of preceding crop, reduced tillage (especially no-tillage) and the time of herbicide application on the development of weed populations and the efficiency of weed control in winter wheat in humid temperate climates. An experiment was conducted with a crop rotation (winter wheat – oilseed rape – winter wheat – maize) on a sandy loam and a loamy silt soil in the Swiss midlands to investigate the impact of different preceding crops and pre- and post-emergence control of weeds in conventional tillage (CT; mouldboard plough), minimum tillage (MT; chisel plough) and no-tillage (NT; no soil disturbance systems). When winter wheat was grown after maize and winter wheat was grown after oilseed rape, the ranking order of weed density in treatments without herbicide application was NT 〈 MT 〈 CT and CT 〈 MT 〈 NT respectively. Analysis of variance and canonical discriminant analysis showed that Epilobium spp., Sonchus arvensis, Myosotis arvensis and volunteer crops were more abundant in NT than in MT and CT. The efficiency of post-emergence weed control was generally better than that of pre-emergence weed control, regardless of tillage intensity.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 20 (1997), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Leaves of Zea mays L. seedlings which developed at optimal (25°C) or suboptimal (15°C) temperature were exposed to high irradiance (1000 μmol m−2 s−1) and a severe chilling temperature (5°C) for up to 24 h to investigate their ability to withstand photooxidative stress. During this stress, the degradation of the endogenous antioxidants ascorbate, glutathione and α-tocopherol was delayed and less pronounced in 15°C leaves. Similarly, the decline in chlorophyll a, chlorophyll b, β-carotene and lutein was slower throughout the stress period. Faster development and a higher level of non-photochemical quenching (NPQ) of chlorophyll fluorescence, related to a stronger de-poxidation of the larger xanthophyll cycle pool in 15°C leaves, could act as a defence mechanism to reduce the formation of reactive oxygen species during severe chilling. Furthermore, plants grown at suboptimal temperature exhibited a higher amount of the antioxidants glutathione and α-tocopherol. The higher α-tocopherol content in leaves (double based on leaf area; 4-fold higher based on chlorophyll content) which developed at suboptimal temperature may play an especially important role in the stabilization of the thylakoid membrane and thus prevent lipid peroxidation.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 19 (1996), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The performance of the photosynthetic apparatus was examined in the third leaves of Zea mays L. seedlings grown at near-optimal (25 °C) or at suboptimal (15 °C) temperature by measuring chlorophyll (ChI) a fluorescence parameters and oxygen evolution in different temperature and light conditions. In leaf tissue grown at 25 and 15 °C, the quantum yield of PSII electron transport (ψPSII) and the rate of O2 evolution decreased with decreasing temperature (from 25 to 4 °C) at a photon flux density of 125 μmol m−2 s−1. In leaves grown at 25 °C, the decrease of ψPSII correlated with a decrease of photochemical ChI fluorescence quenching (qp), whereas in leaves crown at 15 °C qp was largely insensitive to the temperature decrease. Compared with leaves grown at 25 °C, leaves grown at 15 °C were also able to maintain a higher fraction of oxidized to reduced QA (greater qp) at high photon flux densities (up to 2000 μmol m−2 s−1), particularly when the measurements were performed at high temperature (25 °C). With decreasing temperature and/or increasing light intensity, leaves grown at 15 °C exhibited a substantial quenching of the dark level of fluorescence F0 (q0) whereas this type of quenching was virtually absent in leaves grown at 25 °C. Furthermore, leaves grown at 15 °C were able to recover faster from photo inhibition of photosynthesis after a photoinhibitory treatment (1200 μmol m−2 s−1 at 25, 15 or 6 °C for 8 h) than leaves grown at 25 °C. The results suggest that, in spite of having a low photosynthetic capacity, Z. mays leaves grown at sub optimal temperature possess efficient mechanisms of energy dissipation which enable them to cope better with photoinhibition than leaves grown at near-optimal temperature. It is suggested that the resistance of Z. mays leaves grown at 15 °C to photoinhibition is related to the higher content of carotenoids of the xanthophyll cycle (violaxanthin + antheraxanthin + zeaxanthin) measured in these leaves than in leaves grown at 25 °C.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 63 (1985), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Three inbred lines of maize (Zea mays L.) from cool temperate regions and three from warm regions were grown at 14, 22, 30 and 38°C up to the same physiological age, the full expansion of the third leaf. The laminae of the second leaf were studied for anatomical traits of the chlorenchyma. The genotypic variation was considerable for all properties. Nevertheless, general temperature response curves existed for many properties with few deviations of single lines. The cross-sectional area of mesophyll cells and cross-sectional area and number of chloroplasts declined from 14 to 22°C, increased up to 30°C and declined again up to 38°C. The ratio of shortest to longest diameter of chloroplasts was low in mesophyll cells at intermediate temperatures, and maximum in bundle sheath cells at 30°C. Temperature response curves for other properties of the bundle sheath cells were predominantly genotype specific. Chloroplasts in bundle sheath cells were sometimes smaller than those of mesophyll cells, dependent on temperature and genotype. Values of lines from cool temperate and warm regions were mostly overlapping, but the cross-sectional area of mesophyll cells was larger in the latter than in the former lines at low temperature. The results are discussed in relation to the expression of photosynthetic properties.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 71 (1987), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Four genotypes of maize (Zea mays L.), one from North-West Europe, two from tropical highlands and one from tropical lowlands were grown at 24°C until full expansion of the second leaf. Seedlings were then subjected to 2 days at 5°C, with or without a previous conditioning phase at 10°C for 4 days. After stress plants were allowed to recover at 24°C for 5 days. Previous conditioning protected the tropical lowland variety to some extent against losses in chlorophyll content and ribulose I,5-bisphosphate carboxylase (EC 4.1.1.39) activity by severe chilling stress. Without conditioning heavy losses occurred during the recovery phase. In all other genotypes the values of these traits decreased more with than without conditioning. Phosphoenolpyruvate carboxylase (EC 4.1.1.31) activity was little affected during stress, but declined considerably during the recovery phase, with the exception of the North-West European genotype. Previous conditioning prevented or retarded losses of NADP+ malate dehydrogenase (EC 1.1.1.82) activity during the stress phase. However, at the end of the recovery phase losses were as high with as without conditioning, and activity was very low in one tropical highland genotype and in the tropical lowland genotype. In summary, the chilling stability of photosynthetic traits was better in the North-West European genotype than in the tropical ones.
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  • 9
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Six inbred lines of maize (Zea mays L.) from cool temperate regions (C) and from warm regions (W) were grown at 14, 22, 30 and 38°C up to the same physiological age, the full expansion of the third leaf. Generally, plants developed smaller shoot dry weights and leaf areas at extreme temperatures. The shoot:root ratio was lowest at 22°C and highest at 30°C. Most lines had a minimum for specific leaf dry weight at 30°C, but W lines had a second lower minimum at 14°C. Phosphofructokinase activity scarcely reacted to temperature between 22° and 38°C; at 14°C one C line and all W lines had rather low activities. Generally, the chlorophyll content increased steeply from 14 to 22°C and decreased somewhat from 30 to 38°C. In C lines the carotenoid level decreased from 14 to 38°C. No uniform temperature response was found for PEP carboxylase activity, but the highest activity was mostly attained at 38°C. RuBP carboxylase activity increased considerably from 14 to 22°C and remained comparatively constant at higher temperatures. The highest activity of NADP malate dehydrogenase was found at 22°C, with a decrease up to 38°C and with second lowest values at 14°C. C lines possessed larger leaf areas, shoot dry weights and higher shoot:root ratios than W lines at 14 and 22°C, and higher specific leaf dry weights over the whole temperature range. The genotypic pattern of shoot dry weight at 14°C corresponded reasonably well with that of phosphofructokinase activity. A better adaptation of C lines to suboptimal temperatures was mostly clearly indicated for photosynthetic traits which have a well proven relationship with the chloroplast membranes: chlorophyll, carotenoids and RuBP carboxylase. The least distinct effects of origin were observed at 38°C; a tendency prevailed for a better performance of C lines with regard to phosphofructokinase, carotenoids, RuBP carboxylase and NADP malate dehydrogenase.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 103 (1989), S. 0 
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A diallel cross from nine early-maturing lines of maize was grown in northern Germany during 1981 and 1982 in order to study the genotypic variation of shoot biomass at early and late stages of development. Inbred lines had been chosen from breeding programmes for early and medium early cultivars. Nevertheless, the date of maturity varied between them which can have some influence on the correlation between plant parameters. Plants were harvested at the fourth and sixth leaf stages, at anthesis and at maturity. S.c.a. effects were highly significant for traits during the vegetative stage. G.c.a. effects were highly significant for traits of the mature plant including grain yield components. The ratio of g.c.a. to s.c.a. effects for shoot biomass was dominated throughout the growing season by s.c.a. effects. Hybrids from the diallel cross had a superior growth rate until the fourth leaf stage; thereafter, relative growth rates of lines and hybrids were similar for the average of both groups until maturity. The correlation of g.c.a. effects and s.c.a. effects between shoot biomass throughout the season revealed that no significant relationship existed between early and late stages. G.c.a. and s.c.a. effects for grain yield components, with the exception of hundred kernel weight, were negatively correlated with shoot biomass at an early stage while correlation was positive at maturity. This would probably make it a difficult task to improve shoot growth and grain yield components simultaneously through the season.
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