Effect of drought on aquaporin expression in grafted and ungrafted grapevine cultivars

Drought stress severely affects growth, development and productivity in most agricultural crops. Since ancient times, rootstocks have been used to enable crop cultivation in unsuitable soil conditions. In the present study, three factors were evaluated: 1) cultivar: Vitis vinifera L. cv. 'Horozkarasi' (drought-tolerant) and cv. 'Kabarcik' (drought-sensitive) were used; 2) rootstock: each cultivar was self-rooted and grafted onto 'Rupestris du Lot' rootstock; 3) drought stress: half of each cultivar/rootstock combination underwent drought stress and the other half was irrigated at field capacity for seven days. In order to estimate the responses of the cultivars, relative water content, proline content and aquaporin isoform expression levels (VvPIP2;1, VvPIP2;2, VvTIP1;1, and VvTIP2;1) were quantified. The results revealed that drought stress caused more reduction in relative water content (RWC) in 'Kabarcik' cultivar (drought-sensitive) than in 'Horozkarasi' cultivar (drought-tolerant). Proline content increased in both cultivars in response to drought stress but to a relatively greater extent in the grafted 'Kabarcik' cultivar. Considering expression levels of genes, VvPIP2;1, VvPIP2;2, and VvTIP2;1 were downregulated whilst VvTIP1;1 was upregulated in the leaf. Both 'Horozkarasi' and 'Kabarcik' cultivars showed similar trends in terms of their responses to drought stress. Grafting significantly increased the proline content in both cultivars exposed to drought stress. The rootstock conferred better drought protection to 'Kabarcik' cultivar than to 'Horozkarasi' cultivar.