Decrease in Chloroplast Content of Barley Leaves infected with Powdery Mildew

Abstract

POWDERY mildew fungi (the Erysiphales) cause many important plant diseases. These fungi are obligate parasites, as they attack only living host tissue and cannot yet be cultured axenically. They exhibit extreme host specific parasitism and the biochemical mechanisms which determine host resistance or susceptibility are still obscure. Because of their basic metabolic importance, people have sought to determine whether alterations occur in nucleic acids after infection. Millerd and Scott¹ reported that infection of susceptible barley leaves with powdery mildew resulted in increased amounts of RNA in host tissue and four days after inoculation there was approximately 20% more RNA/μg DNA than in non-infected leaves. In contrast, no change was observed in the amount of RNA after inoculation of resistant barley varieties. Malca et al.² determined the base composition of RNA in susceptible mildew-infected barley leaves at various stages of disease development. They found a relative increase in guanylic acid and larger amounts of all nucleotides, reflecting the higher RNA content of mildewed leaves. Plumb et al.³ also reported a slight increase in RNA in susceptible wheat leaves infected with powdery mildew.