Search

Grape berry Vitis vinifera L. is a non climacteric fruit that exhibits a double sigmoidal pattern of growth. The first phase corresponds to cellular multiplication and growth. Ripening occurs concomitantly with the second growth phase and involves significant changes. Sugar accumulation and colour change are well known. Many changes in cell wall polymer properties occur during softening and the implicated mechanisms are still unclear. Abscisic acid (ABA) and indole acetic acid (IAA) levels during grape berry development have been evaluated. The free ABA content of whole berries and separated pericarp increases during the change of colour. ABA accumulation is concomitant with a peak in IAA level. ABA seems to have a specific repartition between the different tissues of the berry during the development. Our results indicate that the pulp looses its ABA during ripening. On the contrary, ABA increases in the skin tissue. Calcium ion concentration develops in the same way while the skin tissue water content decreases. ABA may be involved in protein synthesis such as cell wall-modifying enzymes. Polygalacturonase (PG) activity is detected during colour change period and seems to be well correlated with ABA levels in the berry. We also note two types of development in the PG activity profile: In several cultivars, the berries show an increase of PG activity during change colour period whereas this activity appears earlier, at the beginning of change colour process for other Bordeaux cultivars. These results are also well correlated with free galacturonic acid levels in berry must.

Grape berry is classified as a non climacteric fruit which accumulates abscisic acid (ABA) at the beginning of ripening. It seems that this phytohormone is an activating signal of ripening and we intend to investigate this in depth. As a part of this investigation, we have performed treatments at the beginning of ripening process (1% of berries changed their colour). We have treated grape berries with ABA and the fungal toxin fusicoccin, with is known to have an antagonistic effect towards ABA in plant tissue. Both treatments delay the increase of berry weight. The exogenous application of ABA results in an advancement of the change of colour, by faster decreasing chlorophyll levels. The hormonal profile is modified during colour change period: ABA levels are enhanced and indole acetic acid (IAA) levels are decreased in the berry. This treatment seems to advance the ripening process. Application of fusicoccin to berries delays the chlorophyll degradation. This is accompanied by a decrease of ABA levels compared to the control. These results show that exogenous treatments with ABA modify the hormonal profile and the ripening process. The roles of ABA and IAA are discussed in relation to expression of some genes involved in the ripening process.