Effect of bicarbonate and Fe supply on Fe nutrition of grapevine

Grapevine grafts (Yi:lis vinifera L. cv. Riesling on rootstocks of Vitis sp. L. cv. 5BB) were grown hydroponically in complete nutrient solution (control), Fe-free nutrient solution and complete nutrient solution with added 10 mM HCO3-. The concentration of total chlorophyll was significantly reduced in Fe deficient plants, particularly in NCO3- supplied nutrient solution. The concentration of extracellular (extraplasmatic) root Fe decreased in the case of -Fe treatment and increased in that of HCO3- treatment, while the concentration of symplastic Fe decreased in both treatments. However, the concentration of total root Fe decreased in roots of plants grown in -Fe solution and increased in those grown in HCO3- supplied solution. Fe-deficient plants showed lowering of total Fe and "active Fe" (extractable in 1 M HCl or o-phenanthroline) concentration in leaves. These results indicate that bicarbonate in the nutrient solution may be a major inducing factor of Fe-deficiency chlorosis in grapevine presumably due to inhibited Fe acquisition by roots, but do not confirm Fe inactivation in leaves