Bunchstem Development in Vitis Vinifera: Links to Berry Ripening and Composition

    Research output: ThesisDoctoral Thesis

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    Abstract

    In grapevines, the bunchstem functions as a critical anchor point
    for developing flowers and berries. It also provides the only transport
    pathway between the vine and the berries for carbon, nutrient, water,
    signal molecules and other metabolites. The size and architecture of
    the bunchstem varies considerably between varieties and is
    influenced by abiotic factors such as temperature and light, as well
    as endogenous factors such as vine carbohydrate status.
    Inflorescence flower number and fruit set also respond to these
    factors, but it is uncertain how ovule and bunchstem development
    are linked. Bunchstem morphology, anatomy as well as xylem and
    phloem composition were investigated in Merlot and Cabernet
    Sauvignon grapevines to gain better understanding of the role of
    flower and berry number on its development. The link between
    bunchstem development with berry number, size and composition
    was also investigated.

    In both Merlot and Cabernet Sauvignon, inflorescences that were
    naturally small at flowering remained relatively smaller through until
    harvest. Large inflorescences typically bore more berries than small
    inflorescences, and at harvest these berries were higher in sugar
    content, anthocyanins and phenolics. In bunchstems of both
    varieties, phloem and xylem strands narrowed from the proximal to
    the distal end of the bunchstem, and were most narrow in the laterals
    and pedicels. The internal structures were linearly organised all
    through the bunchstem, and additional secondary tissues, including
    secondary phloem fibres and periderm were present in the hypoclade.

    In order to gain better understanding of the link between flower
    number and bunchstem development, 0 to 100% of flowers were
    removed manually from an inflorescence one week prior to capfall.
    Flower removal resulted in shorter bunchstems, with partial curving
    of the bunchstem when more than half of the flowers were removed.
    Complete flower removal resulted in the desiccation and dehiscence
    of the bunchstem. Internally, flower removal resulted in the
    development of disorganised vasculature with a decline in both xylem
    and phloem area as the number of remaining berries decreased.
    Flower removal was also accompanied by an inhibition and delay of
    secondary structure formation. From these results it was
    hypothesised that signals released from the flowers promoted normal
    vascular development of the bunchstem. Flower removal increased
    percentage fruit set of the remaining ovules and resulted in larger
    berries, likely due to the greater amount of photoassimilate
    availability per berry. Berry composition was, however, unchanged
    with flower removal. In a separate experiment, complete leaf removal
    one week prior to capfall did not alter the development of the
    bunchstem despite a decrease in fruit set. However, the removal of
    these carbon sources resulted in smaller berries, with significant
    changes in their final composition including phenolics and potassium
    concentrations as well as the amino acids profile.

    Cytokinins and gibberellins, hormones critical for normal plant
    development, were evaluated to determine their impact on
    inflorescence and berry development. Application of the synthetic
    cytokinin, BAP, one week before cap-fall, resulted in longer and
    slightly thicker bunchstems, without a significant effect on fruit set.
    The development of the vascular system was restricted by BAP in
    Cabernet Sauvignon, but not in Merlot. Conversely, GA3 application
    reduced fruit set, but increased the proportion of abnormal berries
    retained on the bunch. The development of the vascular system was
    not altered even though bunchstems were longer and thicker. Both
    hormonal treatments increased berry size, but basic berry
    composition parameters remained unchanged.

    Finally, diurnal and seasonal trends in bunchstem xylem and
    phloem composition were examined in Merlot and Cabernet
    Sauvignon. Bunchstem phloem amino acid concentration was
    greater than that of the xylem, and this was greater than that of
    petioles. The predominant amino acids of the xylem and phloem sap
    included glutamic acid, glutamine, aspartic acid, asparagine, proline
    and arginine. In the phloem, these amino acids were higher in the
    pre-veraison period than the post-veraison period; however,
    seasonal trends in the xylem were dependent on the individual amino
    acid. The predominant sugar in the phloem was sucrose, but glucose
    and fructose were also present. There was little change diurnally in
    the phloem sugar concentrations. Bunchstem phloem sugar
    concentration was also greater than that of petioles.

    In summary, bunchstem development is highly dependent on
    flower number and is responsive to the application of gibberellins and
    cytokinins. BAP limited vascular development in Cabernet
    Sauvignon, but GA3 application did not have an effect on the
    vasculature despite changes in overall morphology. Carbohydrate
    deprivation by leaf removal did not impinge on bunchstem
    development, but berry growth was hindered. Both the phloem and
    the xylem transport amino acids through the bunchstem and these
    change seasonally with berry development.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    • Charles Sturt University
    Supervisors/Advisors
    • Holzapfel, Bruno, Co-Supervisor
    • Rogiers, Suzy, Co-Supervisor
    • McCully, Margaret, Co-Supervisor
    • Canny, Martin J, Co-Supervisor, External person
    Award date12 Mar 2015
    Place of PublicationAustralia
    Publisher
    Publication statusPublished - 2015

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