Isozymes of Superoxide Dismutase in Mitochondria and Peroxisomes Isolated from Petals of Carnation (<i>Dianthus caryophyllus</i>) during Senescence

Abstract

The balance between reactions involving free radicals and processes which ameliorate their effect plays an important role in the regulation of plant senescence. In this study a method was developed to isolate peroxisomes and mitochondria from carna- tion (Dianthus caryophyllus L. cv Ember) petals. Based on elec- tron microscopy and marker enzyme levels, the proportion of peroxisomes to mitochondria increases during senescence. The superoxide dismutase (SOD) content of these fractions was ex- amined. Mitochondria and peroxisomes were shown to contain two electrophoretically distinct SODs, a manganese-, and an iron- containing SOD. The Mn-and Fe-SOD were found to have relative molecular weights of 75,000 and 48,000 and isoelectric points of 4.85 and 5.00, respectively. The presence of a Fe-SOD in mito- chondria and peroxisomes is unique because this enzyme is usually located in chloroplasts. The activity of these two isoen- zymes decreased during senescence in mitochondria but re- mained high in peroxisomes from senescent tissue. It is suggested that peroxisomes play a particular role in the process of senescence.