PURIFICATION AND DISTRIBUTION OF PATHOTOXIN-ENHANCED PROTEINS IN SORGHUM

The synthesis of a group of four 16 kDa proteins in sorghum [Sorghum bicolor (L.) Moench] roots is enhanced by treatment with peritoxin, the host-selective toxin produced by the root rot fungus Periconia circinata (Mangin) Sacc. The proteins were purified by two-dimensional gel electrophoresis and partially characterized, and their distribution within the sorghum plant and in other plant species was determined. The four proteins were found to be charge isomers indistinguishable by electrophoretic analysis of the products of protease digestion and CNBr cleavage. In Western blots with polyclonal antibodies, the proteins were detected in all organs of mature sorghum plants in quantities that decreased from the roots upward toward the inflorescence. Multiple cross-reacting proteins from 15-21 kDa were also detected in all grass species tested and in some other monocotyledons. None of the dicotyledons analysed contained cross-reacting proteins. The results suggest that the 16 kDa proteins are conserved proteins whose constitutive synthesis is regulated and whose function is important in several plant species, especially grasses. The presence of these proteins in other plant species suggests that they are not the direct cause of disease symptoms and plant cell death in peritoxin-treated sorghum plants.