Chlorophyll biosynthetic enzymes and plastid membrane structures in mutants of barley (Hordeum vulgare L.)

Abstract

In barley a number of recessive lethal mutants deficient in chlorophyll biosynthesis have been identified previously. Selected mutants were analysed for activities of four different chlorophyll biosynthetic enzymes, in relation to the development of plastid membrane structures. According to the ultrastructure of membranes in developing plastids the mutants were divided into three groups. One group (xan-l35 and -g45) has normal development of prolamellar body (PLB) and prothylakoids (PTs) resembling the wild type. A second group (xan-i25, -k(42), -u21) has abnormal development of PLB membranes and PTs. The third group (xan-n74 and alb-e16) has normal development of PLB but PTs are deficient or, if present, they are highly deranged. In mutants with defective membrane structures, the activities of the membrane associated enzymes Mg-chelatase and methyltransferase were more affected than the activities of the soluble stroma enzymes ALA-dehydratase and PBG-deaminase. The two mutants xan-n74 and alb-e16, which are deficient in PT membranes, had no detectable methyltransferase activity, indicating that the enzyme methyltransferase is located in association with the PT membranes.