Untersuchungen zur Funktionsänderung der Microbodies in den Keimblättern von Helianthus annuus L.

Summary

The enzyme patterns in sunflower cotyledons indicate that the glyoxysomal function of microbodies is replaced by the peroxisomal function of these organelles during the transition from fat degradation to photosynthesis. The separation of the microbody population into glyoxysomes and peroxisomes during this transition period is reported. The mean difference in density between the activity peaks of glyoxysomal and peroxisomal marker enzymes on a sucrose gradient was calculated to be 0.007±0.004 g/cm³ and turned out to be significant (t=7.8>4.04=t _5;0.01). The activity peak of catalase coincides with that of isocitrate lyase in early stages of development, but shifts to the activity peak of peroxisomal marker enzymes during the transition period. No isozymes of the catalase could be detected by gel electrophoresis in the microbodies with the two different functions.

During the rise of the peroxisomal marker enzymes no synthesis of the common microbody marker, catalase, could be demonstrated using the inhibitor allylisopropylacetamide. Using D₂) for density labeling of newly-formed catalase, no difference is observed between the density of catalase from cotyledons grown on 99.8% D₂O during the transition period and the density of enzyme from cotyledons grown on H₂O. The activity of particulate glycolate oxidase is reduced 30–50% by allylisopropylacetamide, but is not affected by D₂O. The chlorophyll formation in the cotyledons is strongly inhibited by both substances.