The influence of exogenous potassium hexacyanoferrate (III) (HCF III) on elongation of maize (Zea mays L.) coleoptile segments was investigated. Addition of HCF III led to a strong stimulation of growth both in the presence and absence of indole-3-acetic acid (IAA). The magnitude of growth stimulation was dependent on the presence of IAA, HCF III concentration, incubation time, and phase growth. The reduced form, potassium hexacyanoferrate (II), was without effect on growth. In the presence of HCF III, elongation was suppressed when coleoptile segments were treated with N,N'-dicyclohexylcarbodiimide, cycloheximide or atebrine (quinacrine). The addition of HCF III stimulated the IAA-induced proton extrusion, and the e(-)/H+ ratio decreased with incubation time. HCF III also strongly stimulated elongation of Avena sativa L. coleoptile segments and Glycine max L. hypocotyl segments. These results suggested that a plasma membrane redox system (NADH oxidase type I) may be involved in the regulation of growth through the activity of the plasma membrane-bound ATPase.
