Ultrastructure of the mesophyll cells of leaves of a catalase-deficient mutant of barley (Hordeum vulgare L.).

The ultrastructure of mesophyll cells from leaves of a catalase-deficient homozygous mutant of barley (RPr 79/4), which grows poorly in air but normally in carbon-dioxide-enriched air, has been examined and compared with that of the cultivar Maris Mink with normal catalase levels, and with that of the F1 progeny of the cross RPr 79/4xGolden Promise with 50% normal catalase levels. In Maris Mink, the F1 progeny, and the mutant in which photorespiration had been suppressed by growing in air enriched to 0.2% CO2, the ultrastructure of the mesophyll cells was typical of young festucoid leaves with the peroxisomes containing thread-like inclusions. In air-grown leaves of the mutant RPr 79/4 which had developed lesions and become shrivelled, all the chloroplasts were irregular in outline, and in some the granal membranes were disrupted into abnormal honeycomb configurations and the plastid envelope was absent. In necrotic tissue, membrane fragments and osmiophilic droplets marked the sites of severely damaged chloroplasts. The peroxisomes contained diffuse tufts of electron-opaque material as well as fibrous strands. Catalase activity, visualised cytochemically by DAB, was located exclusively in the peroxisomes of Maris Mink and the F1 progeny, but none was found in the mutant grown either in CO2-rich air, or in normal air. The role of catalase in preventing ultrastructural damage by hydrogen peroxide during photorespiration is discussed.