Fusicoccin receptors. Evidence for endogenous ligand.

The binding of fusicoccin to the microsomal preparations of maize roots in vitro is increased several-fold when segments of the tissue are washed for 2 h in distilled water before homogenization. Addition of freeze-dried wash solution to microsomal preparations of spinach leaves or fresh roots, washed roots, or coleoptiles of maize inhibited the binding of fusicoccin to particulate fractions. The freeze-dried material also blocked fusicoccin-promoted H(+) extrusion from maize root segments. Roots may contain one or more water-soluble compounds competing with fusicoccin at the receptor level; such ligands might play a physiological role as modulators of the H(+)/K(+) exchange system in higher plants.