Degradabflity and phenolic components of cell walls of wheat in relation to susceptibility to Puccinia striiforntis

Cell walls of tips and bases of laminae of flag leaves from 11 cultivars of winter wheat of varying susceptibility to Puccinia striiforntis yellow rust) were compared by examining their phenolic components released by treatment with a commercial cellulase. Isolated cell walls of both susceptible and resistant cultivars released water-soluble carbohydrate esters of phenolic acids, the major acid detected being trans-ferulic. There was no relationship between the amount of phenolic esters released by cellulase and susceptibility to yellow rust. The leaf lamina tips, which were much more susceptible to yellow rust than the corresponding bases, had lower cell wall contents than the bases and their walls were more degradable by cellulase. Examination of transverse sections of leaf laminae of cv. Little Joss showed that cells whose walls contained phenolic groups that gave a red colour reaction with p-nitrobenzene diazonium tetrafluoroborate, occupied a larger area of leaf lamina bases than of the tips. A greater percentage of the abaxial epidermal cells of the bases, compared with the tips, had walls that gave this red colour reaction. We suggest that the presence of phenolic groups in these walls may be related to the greater resistance of the bases to P. striiforntis.