The respiration of protoplasts from leaves of barley infected by powdery mildew ( Erysiphe graminis F.SP. Hordei)

Abstract

Infection of barley leaves by powdery mildew ( Erysiphe graminis f.sp. hordei) causes increased dark respiration, par tof which is associated with active host responses to infection, and a consequence of which is reduced plant growth. The pathogen cannot be grown separately from the host. Therefore, in order to examine those changes in respiratory activity peculiar to the host, attempts were made to isolate protoplasts from infected tissues, and from healthy controls. Isolation of useful numbers ( > 10 6 cm −6 ) of viable mesophyll protoplasts from infected tissues was possible with one among several batches of commercial ‘Cellulysin’ tested; on analysis by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), this batch contained a low molecular weight protein at 20.1 kDa not found in other batches. In all isolated protoplasts, total respiration increased with the age of the source-leaf, but within 24 h of inoculation respiration was stimulated by infection. Protoplasts from infected leaves showed a small initial increase in the cyanide (CN)-sensitive component (cytochrome pathway) of total respiration, but an increase in the CN-insensitive component (alternative pathway) was the major cause of the stimulation of total respiration.