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I – Modern approaches of ripening physiology |
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Veraison is a step between
vegetative growth and maturation making the fruit attractive and edible
by animals, and favouring seed dispersion. The main events are: Softening of cell wall, by pectine depolymerization or demethylation. Flavonoids pathways are induced (anthocyanins) or inhibited (stilbenes). Sucrose is mostly stored instead to feed the biosynthetic or energetic pathways. Storage of nitrogen as amino acids (mainly arginin) Organic acid (malic, tartaric, citric...) net synthesis ceases. Vacuolar membrane became leaky and malic acid is metabolized Extracellular and Stress proteins are synthetized General signals related to veraison In the field veraison occurs after a defined thermal time counted after anthesis. The realisation of the development steps till veraison rely on trophic signals provides by the vine to the berries. Sugar starvation delay veraison of the berries. Other trophic signals, water or nitrogen status has only indirect effect by affecting source-sink relationships and sugar availability to the berries. Local signals related to veraison. Among many tested hormones only abscissic acid and ethylene variations suggest their direct role on the veraison process. But the precise mechanism is not known. Recent studies involve other signals as transcription factors, protein kinases or new classes of hormones (steroides) during veraison. Conclusion: Veraison is at the beginning of a huge change in the berry metabolism, from vegetative growth to scheduled senescence. Molecular studies confirm the very big change in the gene expression profiles. They are till not sufficiently targeted to identify the chronological steps which lead berries to the inception of maturation |
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