K+ starvation causes a differential effect on shoot and root K+ (Rb+) uptake in sunflower plants

Sunflower plants (Helianthus annuus L. cv Sun-Gro) with different K+ nutritional status were used to study the effect of K+ starvation on shoot and root Rb+ uptake as well as its distribution in the plant. The plants were grown in hydroponic medium during 21 d. At the end of this period, Rb+ treatments were applied either to shoot or root. In one set of plants, an aqueous solution of RbCl was sprayed uniformly on shoot, while in another set, K+ from the growth nutrient solution was replaced by Rb+. The results obtained in this study indicate that K+ starvation affects differently to Rb+ uptake by shoot and roots. The root's Rb+ uptake, as it was expected, was higher in those plants with low internal content than in plants with adequate levels of K+. Conversely, K+ starvation inhibited the uptake of Rb+ by the shoot. In addition, the results showed that K+ starvation favored the accumulation of Rb+ from foliar treatment in both root and growing parts of the shoot whereas inhibited its accumulation on totally expanded leaves. These results suggest that K+ foliar treatments become less efficient in improving K+ concentration in leaves when plants are under serve K+ deprivation conditions.

► K+ (Rb+) foliar uptake becomes less effective when plants are starved in K+.
► The root's Rb+ uptake is higher in plants with low internal content of K+.
► K+ starvation favors the accumulation of Rb+ from foliar treatment in roots.