Decrease in glycolate pathway enzyme activities in plastids and peroxisomes of the albostrians mutant of barley ( Hordeum vulgare L.)

Abstract

The in-vitro activities of various enzymes involved in the glycolate pathway were analyzed in crude leaf extracts of the albostrians mutant of barley. This mutant line is characterized by the lack of plastid ribosomes in white leaf tissue, thus causing a complex modification of nuclear gene expression. In white leaf cells the activities of the plastidic enzymes phosphoglycolate phosphatase and glycerate kinase, as well as the activities of the peroxisomal enzymes glycolate oxidase, catalase, and hydroxypyruvate reductase, are drastically reduced by as much as 80–99% compared to green wild-type leaf tissue. The activity of plastidic NADPH-glyoxylate reductase, the total activity of serine hydroxymethyltransferase and the activity of mitochondrial fumarase was reduced by only 30–52%. The activities of the glyoxysomal enzymes isocitrate lyase and malate synthase were neither detectable in green nor white mutant leaf tissue. Electron microscopy showed fewer and smaller peroxisomes in white leaf tissue, accounting for at least part of the reduction of peroxisomal enzyme activities. Northern blot analysis for the catalase and glycolate oxidase transcripts revealed strongly reduced levels of steady-state mRNA accumulation. It is suggested that a putative plastidic signal(s) influences the expression of nuclear-encoded plastidic and peroxisomal enzymes of the glycolate pathway.