Modulation by Gibberellic Acid of Aquaporin Genes Expression during Berry Development of Grapevine (Vitis vinifera L.)

In grapevine, berry growth after veraison is paralleled by a notable intake of water and sugar. Our results show that in 'Sultanina', a seedless variety, this intake is significantly improved by gibberellic acid (GA(3)), which is normally sprayed to get a commercial berry size. As at this stage the pedicel xylem functionality is lost, it is presumed that water transport occurs via the phloem. This implies a possible role of water channels in cell membranes (aquaporins). Two complementary approaches were used to evaluate the effect of GA(3) on the expression of aquaporin genes. In the first one, PIP and TIP probes derived from 'Sultanina' cloned amplicons and ESTs were used for Northern blotting. Results from these experiments showed that there was not a uniform type of response, with some genes exhibiting a more intense expression at early developmental stages than at veraison, and others showing a lower expression difference. In second place, we confirmed a possible role for GA controlling PIP/TIP gene expression, but again, the results were quite diverse in terms of timing and level of response to the hormonal treatment. In spite of this diversity, a tendency to maintain a higher expression level during post-veraison in GA(3)-treated plants was observed. Microarray hybridizations showed a heterogeneous response to GA-treatment for different genes of the aquaporin family. However, these last experiments must be considered preliminary, both because of technical issues, mainly the requirement of a better reproducibility level, and because of pre-veraison being the developmental stage when one of the lowest levels of aquaporin genes expression was observed.