Enzymatische Aspekte zur Biosynthese des Blatt-Cutins bei Gasteria verricuosa-Blättern nach Verletzung

Abstract

1. Three fatty acid oxidizing enzymes, stearic and oleic acid oxidase as well as lipoxidase have been shown to be present in leaves of Gasteria verricuosa. 2. By following the activity of these enzymes after injury we considered that they are involved in cutin synthesis which takes place at the wounded top of the leaf. 3. Comparing the activity near the wounded part and the untreated inner sphere of the leaf lead to the conclusion that two of the oxidases (stearic and oleic oxidase) serve as substrate donors for lipoxydase by converting stearic into oleic and the latter into linoleic acid. 4. Since the level of polyenic acids in leaves is high in comparison to saturated fatty acids, the activity of stearic and oleic oxidase only increases in the late phase of cutin synthesis, while lipoxydase is highly activated at the top directly after wounding and in the inner part of the leaf 3 - 4 weeks after cutin synthesis has started. At the same time pectinase shows its highest activity, suggesting that the formation of the pectic layer is secondary to the formation of cutin. 5. Simultaneously to the enzymatic assays, cutin formation was followed by macro- and microscopic studies. 6. The mode of action of lipoxydase and the interrelationship of the oxidizing enzymes in the formation of cutin are discussed and a formula for the structure of Gasteria cutin is given. 7. According to the data presented here and the results obtained from literature, a possible scheme for cutin synthesis is given.