Grapevine varieties with differential tolerance to Zinc analysed by morpho-histological and cytogenetic approaches

Zinc (Zn) is an essential micronutrient to plants, but in most of the vineyard soils, its amount surpasses the threshold value recommended by the European Union. With this work, we intended to evaluate the growth, morpho-histological traits and nucleolar activity in leaves and roots of three grapevines (Vitis vinifera L.) varieties (‘Donzelinho Branco’, ‘Verdelho’ and ‘Bastardo’). Forced cuttings of those varieties were placed in hydroponic solutions supplemented with 1.5, 3 and 5 mM Zn for two weeks to extrapolate their tolerance to Zn. Hoagland's nutritive solution (0 mM Zn) was used as control. The Zn treatments stimulated the leaf growth in all varieties, confirmed by the increase of the leaf mitotic index (MI). Leaf growth was higher in ‘Donzelinho Branco’ treated with 5 mM Zn, but it was accompanied by a significant reduction of the leaf thickness. The increase of Zn concentration contributed to the roots thickening and the decrease of the root MI, mean nucleolar number and area. The inhibition of root elongation and the leaf and root nucleolar activity changes seen in the Zn-treated plants are compatible with osmotic stress responses. The integration of the multidisciplinary data of this work allowed us to suggest that ‘Verdelho’ and ‘Donzelinho Branco’ were more tolerant than ‘Bastardo’ to higher Zn concentrations.