Grapevine carbohydrate and nitrogen allocation during berry maturation: Implications of source-sink relations and water supply

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Abstract

The post-véraison period is characterised by rapid berry sugar accumulation, and therefore, a substantial carbon (C) sink demand. In contrast to sugar accumulation, berry nitrogen (N) incorporation is often variable at distinct stages of the season, and does not necessarily predominate after véraison. Nevertheless, important alterations in fruit N content and composition likely occur during the post-véraison period. The fruit sugar requirement is sourced from leaf photoassimilation, however, total non-structural carbohydrate (TNC) remobilisation from perennial tissues may provide an alternative C source when photoassimilation is insufficient. N is translocated from the roots, leaves and shoots to the berries after véraison, when soil N uptake is expected to be restricted. The grapevine leaf-to-fruit ratio and water availability are major factors influencing canopy photoassimilation, and subsequently, the allocation of TNC among perennial organs and the fruit. Likewise, the leaf area and water supply also affect N distribution between the perennial and reproductive organs. Restricting the post-véraison leaf area and/or vine water availability may induce reserve TNC and N utilisation, and could subsequently be detrimental toward TNC and N storage. Therefore, the overall aim of this study was to evaluate the post-véraison distribution and partitioning of TNC and N among the different grapevine organs, as influenced by source-sink relationships and water supply.

Three distinct pot experiments, using three-year-old own rooted Vitis vinifera grapevines, were conducted during the post-véraison period. For the first experiment (2013-14), within each leaf-to-fruit ratio treatment (full and 50% leaves), grapevines were grown under full or 50% reduced irrigation. Changes in dry biomass, and starch and total sugar concentrations were monitored in the roots, trunks, shoots and leaves. Berry sugar and anthocyanin accumulation were also assessed. During the second experiment (2014-15), grapevines were grown with or without fruit from véraison, with water constraints sustained throughout the experiment. The root, trunk, shoot and leaf structural biomass, starch, total soluble sugar, total N, and amino N concentrations were determined, while the fruit sugar and N accumulation were also assessed. The root glucose, fructose and sucrose contents were additionally measured through high performance liquid chromatography. The final experiment (2015-16) consisted of a full leaf area control (100 primary shoot leaves and all laterals) and two defoliation treatments (25 primary leaves only and no leaves), and the vines were well watered throughout. Changes in fruit sugar, anthocyanin and N content, and juice yeast assimilable N (YAN) concentration were monitored. The root and leaf starch and N concentrations were also determined, and primary metabolite abundance in the fruit, roots and leaves was measured via untargeted gas chromatography/mass spectrometry analysis.

A sustained post-véraison water constraint caused root starch depletion, concurrent with the phase of rapid fruit sugar accumulation. As soon as fruit sugar accumulation slowed, roots accumulated starch reserves. When water constraints were sustained, root sucrose accumulation coincided with starch hydrolysis during peak fruit sugar accumulation. Leaf N depletion corresponded with fruit N accumulation, while the roots of defruited vines stored N reserves. Fruit sugar and anthocyanin accumulation continued during the post-véraison period in completely defoliated vines, albeit at reduced rates. However, defoliation had little impact on the fruit total N content, although the juice YAN increased after complete and partial defoliation. Most sugars and organic acids depleted in the roots after defoliation, while many amino acids accumulated in roots and
remaining leaves. Defoliation suppressed the root and leaf myo-inositol concentration, and similarly affected its sugar and organic acids derivatives. Shikimate pathwayderived amino acids accumulated in roots after full defoliation, while organic acids
derived from this pathway depleted in remaining leaves after partial defoliation. Although restricted, glucose, fructose and sucrose, and most minor sugars and sugar alcohols still accumulated in the fruit under leaf source restriction or absence. Fruit arginine accumulated after partial or full defoliation, while the content of various shikimate pathway products (such as anthocyanins and phenolic acids) increased or decreased to different extents in response to leaf area availability.

Among the different grapevine organs, TNC reserves were most abundant in the roots. Root TNC reserves subsequently supported the post-véraison fruit sugar content when canopy photoassimilation restriction was induced by water constraints and/or a reduced leaf area. The root starch reserves were replenished as soon as fruit sugar accumulation slowed, even occurring from a few weeks before harvest. During sustained postvéraison water constraints, root starch hydrolysis during peak fruit sugar accumulation yielded sucrose, which is subsequently transportable to the berries to support the fruit sugar content. The concentration of myo-inositol and its derivatives (e.g. galactinol and raffinose), in addition to that of amino acids derived from the shikimate pathway (e.g. phenylalanine), were significantly affected in roots during a post-véraison leaf C source limitation or absence. Myo-inositol metabolism seemingly played a distinct role during root starch remobilisation while berry sugar accumulation occurred. In contrast to the roots being an important TNC source when photoassimilation was restricted by limited water supply, leaf N seemed to be a significant contributor to fruit N content during the sustained water constraints. The presence of ripening fruit in conjunction with water constraints, subsequently prevented root N storage between véraison and fruit maturity. While root total N concentration was little affected by defoliation, root amino N composition was altered, for example prompting arginine accumulation. Arginine also subsequently accumulated in the fruit, effectively increasing the juice YAN of defoliated vines. This study provided a novel illustration of post-véraison TNC and N partitioning and distribution under differing water availability and/or source-sink relationships. The results contribute to the understanding of grapevine reserve TNC utilisation during a period of substantial fruit C demand. Furthermore, although the extent of fruit N sink requirement after véraison is not as clear as the corresponding fruit C demand, the study contributes to understanding grapevine N reserve utilisation during fruit maturation.
Original languageEnglish
QualificationDoctor of Philosophy
Supervisors/Advisors
  • Holzapfel, Bruno, Principal Supervisor
  • Smith, Jason, Co-Supervisor
  • Barril, Celia, Co-Supervisor
  • Deloire, Alain, Co-Supervisor
Award date31 Mar 2017
Publisher
Publication statusPublished - 2017

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