The effects of infection by stem-rust fungus on polyribosomal RNA fractions and protein synthesisin vitroandin vivoin near-isogenic resistant (Sr6) and susceptible (sr6) lines of wheat were determined. In infected resistant leaves the proportion of ribosomes present as polyribosomes was greater than that in healthy (uninfected) leaves at 1, 3, and 6 days and that in susceptible leaves at 1 and 3 days after inoculation. In the latter there were large increases in the pelletable RNA content (ribosomes, ribosomal subunits, and polyribosomes) and proportion of ribosomes present as polyribosomes from day 6.In vitrotranslation failed to detect any marked differences in polyribosomal translation products in resistant and susceptible leaves in response to infection. Labelling of polypeptidesin vivoand separation by one- and two-dimensional electrophoresis showed that at 1 day after inoculation, two groups of high molecular mass polypeptides (80ndash;96 and 100ndash;110ensp;kDa) were more heavily labelled and two novel polypeptides were present in resistant and susceptible leaves in response to infection. Synthesis of the high molecular weight and two novel polypeptides was maintained in infected resistant leaves up to 6 days after inoculation. In susceptible leaves the amount of radiolabel incorporated into these polypeptides and several proteins prominently labelled in uninfected controls declined rapidly from 3 days after inoculation.
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