Nucleoside/nucleotide pools in wheat leaves naturally infected with powdery mildew. II. Effects of leaf age and intensity of infection

Abstract

The effects of Erysiphe graminis infection on nucleoside/nucleotide pools in the different leaves of field grown wheat plants were determined. Plants protected by fungicides were used as controls. In non-protected plants infection intensity markedly increased with leaf age; some of the nucleotide pools were unaffected by any level of infection while others varied according to the degree of infection. Thus pools of total adenine nucleotides (as well as energy charge), adenosine and UDP-glucose were very similar in both infected and control plants only declining with leaf senescence. In contrast levels of UDP-N-acetylglucosamine, the precursor for fungal chitin synthesis, and uridine content, both low in uninfected control plants, increased as the level of infection increased. This latter result suggests that the fungus exploits host carbohydrate metabolism for precursor for hyphal wall synthesis. The observation of high uridine pools correlating with the degree of infection is indicative of recycling of the UDP moiety of UDP-N-acetylglucosamine during chitin synthesis.