Distribution of label from 3H-glucose and 3H-leucine in lettuce cotyledons during the early stages of infection with Bremia lactucae

Abstract

Light and electron microscope autoradiography were used to study the distribution of label from 3H-glucose and 3H-leucine in lettuce cotyledons that had been supplied either labelled compound through their petioles before inoculation with Bremia lactucae Regel. The distribution and intensity of label in the fungus and host have been analyzed statistically. The pathogen accumulated label from 3H-glucose before penetration and thereafter. During the early stages of infection there was virtually no label from 3H-leucine in fungal structures. However, at 14 and 16 h after inoculation, intercellular hyphae and haustoria were heavily labelled. More glucose than leucine was exuded onto epidermal surfaces and inoculum droplets on cotyledons supplied with 3H-glucose were about 10-fold more radioactive than those on cotyledons supplied with 3H-leucine. When either labelled compound was added in the inoculum drop to non-radioactive cotyledons, the fungus but not the host accumulated tritium. Both labelled substances were metabolized by the spores when germinated in isolation.