Graduate Thesis Or Dissertation
 

Changes in developing strawberry fruit : I. Cell division and enlargement ; and II. Biosynthesis of anthocyanins and other phenolics and activity of associated enzymes

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  • Size and color are important visual quantity attributes of the fruit of strawberry (Fmgaria x ananassa Duch.). Strawberry cultivars produce fruit of a characteristic size and color, the later being the result of accumulation of particular anthocyanins. This research sought to determine the basis for genotypic differences in fruit size and to monitoring changes in the amount of anthocyanins and related phenols, and the activity of associated enzymes during strawberry fruit development. Fruit size (weight and volume), number cells per fruit, and mean cell size were determined throughout the development of secondary fruit of the day-neutral strawberry cultivars Tillikum, Tristar, and Selva. Fruit size among the cultivars showed a four fold range and resulted from differences in the number of cells per fruit. The number of cells per mature fruit was 0.72, 1.96, and 2.94 x 106 for `Tillikum', `Tristar', and `Selva', respectively. The relative difference in cell number among cultivars was established by anthesis. In all cultivars, mean size of fruit cells was similar (z 6 x 106 μm3 at maturity) and cell division continued for about 12 days after anthesis. Young green fruit of `Tillikum' contained high levels of soluble phenols, composed mostly of tannins (;u 44%) and flavonoids (=51%). The concentration of phenols rapidly decreased as fruit developed, but the amount per fruit slowly increased. The concentration of anthocyanins was low throughout most of fruit development, but at ripening showed an 18-fold increase in 3 days. The activity of phenylalanine ammonia-lyase (PAL), an initial and key regulatory enzyme in the biosynthesis of phenolics, peaked in green fruit and again during ripening. The second rise in activity paralleled the rapid accumulation of anthocyanins. The activity of PAL was low during the white berry stage, when fruit growth was rapid. A UDP-glucose:flavonoid glucosyltransferase was isolated and purified about 100 fold from ripening Tillikum' fruit. The soluble enzyme showed a pH optimum of 7.5 and a molecular weight of about 55,000 Da. The Km for UDP-glucose was 143 μM and for the flavonol, quercetin, 4.5 μM. The enzyme had a broad substrate specificity and the isoflavone, biochanin A, was the best substrate among the flavonoid aglycones examined.
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Déclaration de droits
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file details Cheng_Guiwen_1991.pdf 2017-08-14 Public Télécharger