Influence of ruthenium red on calcium (⁴⁵Ca²⁺) absorption by sorghum seedling roots

Abstract

Root tips (1 cm) from sorghum [Sorghum bicolor (L.) Moench cv SC574, SC283, GP‐10, and Funk G522DR] cultivars were exposed concomitantly to ⁴⁵Ca²⁺ and ruthenium red (0,0.001,0.01, 0.1, or 1 mM) at pH 5.5 in 0.01M sodium acetate buffer. Ruthenium red induced a decreased ⁴⁵Ca²⁺ uptake that was 50% inhibited between 0.01 ‐ 0.1 mM ruthenium red. Ruthenium red is known to inhibit Ca²⁺‐ATPase but not H⁺‐ATPase. When the roots were exposed to 0.1 mM ruthenium red at pH 6.0, 5.5, 5.0, 4.5, or 4.0, deceased ⁴⁵Ca uptake occurred as H⁺ concentration increased. Although there were differences between ⁴⁵Ca in total uptake when plotted as percentages of the uptake at 0 ruthenium red (pH 5.5) or at pH 6.0 (0.1 mM ruthenium red), inhibition of ⁴⁵Ca uptake by increased H⁺ or ruthemum red concentrations was equivalent among the cultivars.