The invention relates to a promoter that is provided with tissue-specific activity and is more active in xylem parenchyma cells of plant roots than it is in other cells of said plant. The inventive promoter allows transgenic plants to be produced with particular characteristics: (a) improved xylem charging and discharging processes in the root; (b) improved nitrogen supply; (c) reduced accumulation of harmful nitrogen in the root; (d) improved resistance to salt; (e) improved resistance to stress due to dry conditions; (f) improved tolerance to frost; (g) modified Na+/K+ concentration in the root; (h) greater resistance/tolerance to pathogens.