THE PHYSIOLOGY OF HOST–PARASITE RELATIONS: VI. OXIDATION–REDUCTION CHANGES IN WHEAT LEAF SAP CAUSED BY RUST INFECTION

Abstract

Extracts of healthy and rusted leaves of Little Club and Khapli wheats were made under anaerobic conditions. Oxidation–reduction potentials in the extracts were measured at two different levels both in the presence and in the absence of both methylene blue and riboflavin as redox mediators. At the lower level (i.e. in the absence of mediators) a reversible rise in potential was noted during the course of rust infection on Little Club; with Khapli the rise was similar but was not reversed. The response to rust infection of resistant and susceptible plants was also reflected in characteristic changes in the average potentials at higher levels (i.e. in the presence of mediators). After infection the oxidation–reduction balance of susceptible tissue was reorganized by the introduction of new systems which were found in the reduced state only. After infection the oxidation–reduction potential of resistant tissue was only poorly poised as indicated by a rise in the average potentials and as demonstrated by oxidation– reduction titrations.The results are discussed and the possibility is considered that a rust-induced catalyst may “short circuit” the chain of hydrogen transport, thus initiating all the observed redox changes.