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  • 1
    ISSN: 1432-2048
    Keywords: Cellulose ; Cx cellulase ; Fruit (ripening, softening) ; Persea (fruit ripening)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Avocado (Persea americana Mill.) fruit produce copious quantities of the enzyme Cx-cellulase (EC 3.2.1.4) during ripening. The possibility that Cx-cellulase is able to disrupt cellulose microfibril oranization was investigated using molecular weight (Mr), x-ray diffraction, and ultrastructural analyses of cell walls from unripe avocado fruit incubated with the purified enzyme. Results indicate that Cx-cellulase causes a downshift in the Mr of unbranched cell-wall polymers in the Mr range of 106–107 Da. There is an increase in the proportion of crystalline cellulose, and cellulose fibrils appear to lose cohesiveness in response to enzyme activity. We propose that Cx-cellulase attacks avocado cellulose at accessible sites in the peripheral and integral noncrystalline regions of the microfibril, resulting in a loss of cohesiveness within the fibril structure and an alteration in the binding of associated cell-wall matrix polysaccharides. The initial loss of avocado mesocarp firmness during fruit ripening may be linked to the onset of Cx-cellulase activity.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2242
    Keywords: Minimum ; Norm ; Restricted ; Likelihood ; Half-diallel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Computer simulation was used to compare minimum variance quadratic estimation (MIVQUE), minimum norm quadratic unbiased estimation (MINQUE), restricted maximum likelihood (REML), maximum likelihood (ML), and Henderson's Method 3 (HM3) on the basis of variance among estimates, mean square error (MSE), bias and probability of nearness for estimation of both individual variance components and three ratios of variance components. The investigation also compared three procedures for dealing with negative estimates and included the use of both individual observations and plot means as the experimental unit of the analysis. The structure of data simulated (field design, mating designs, genetic architecture and imbalance) represented typical analysis problems in quantitative forest genetics. Results of comparing the estimation techniques demonstrated that: estimates of probability of nearness did not discriminate among techniques; bias was discriminatory among procedures for dealing with negative estimates but not among estimation techniques (except ML); sampling variance among estimates was discriminatory among procedures for dealing with negative estimates, estimation techniques and unit of observation; and MSE provided no additional information to variance of the estimates. HM3 and REML were the closest competitors under these criteria; however, REML demonstrated greater robustness to imbalance. Of the three negative estimate procedures, two are of practical significance and guidelines for their application are presented. Estimates from individual observations were always preferable to those from plot means over the experimental levels of this study.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of statistical physics 65 (1991), S. 1155-1159 
    ISSN: 1572-9613
    Keywords: Frenkel excitons ; three-dimensional systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A numerical study is made of the effect of disorder on the trapping of Frenkel excitons in three-dimensional systems atT=0 K. A Gaussian distribution of optical transition frequencies is assumed. The disorder enhances the decay of ak = 0 exciton created by pulsed optical excitation, but reduces the overall exciton trapping rate. An interpretation of the results in terms of increased exciton scattering and reduced exciton mobility is outlined.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 1994-12-01
    Print ISSN: 0032-0935
    Electronic ISSN: 1432-2048
    Topics: Biology
    Published by Springer
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