1.D.7 The Beticolin (Beticolin) Family
Beticolins are non-host-specific toxins produced by the phytopathogenic fungus, Cercospora beticola which causes leap spot disease in sugar beets. Fifteen non-peptide compounds are known which share the same polycyclic skeleton and have a chlorine atom and partially hydrogenated anthraquinone and xanthone moieties. They are named beticolin 0 to 14. They are not only phytotoxic but also bactericidal and anti tumorigenic. They chelate Mg2+ to form an electrically neutral dimeric complex consisting of two beticolins and two Mg2+. Mg2+ increases partitioning into the bilayer where in plants they induce loss of solutes, depolarize the membrane potential, and inhibit H+ extrusion and K+ uptake. They form poorly selective ion channels permeable to K+, Na+, Ca2+ and Cl-. They are the only sequenced pore-forming elicitors of plant defense reactions.