Einfluß verschiedener flavonole auf das lamellarsystem der chloroplasten in vitro

Abstract

The influence of various flavonoles on light triggered reactions of isolated chloroplasts was examined in order to receive some more detailed information about the problem just in discussion, wether those substances of the secondary metabolism are involved in reactions of primary metabolism of plants. Among the substances examined kaempferol was the most active one. 1. ATP synthesis is inhibited by kaempferol at a concentration of about 8 · 10 −5 M. Inhibition is due to an influence on the chloroplast membrane itself. 2. Calcium dependent, trypsin activated ATPase is stimulated at the mentioned concentration range, whereas magnesium dependent light triggered ATPase is inhibited as cyclic photophosphorylation too. 3. Electron transfer, measured with various Hill-reagents, is neither inhibited severely nor stimulated. 4. Kaempferol inhibits the methylamine uncoupled electron transfer up to 40 0/o. These results suggest that kaempferol does not act as an energy transfer inhibitor according to Good. Though kaempferol does not stimulate electron transport, it is assumed that kaempferol acts more like an uncoupling substance influencing a reaction site near electron transport chain, preventing the energy transfer from electron transport chain to ATPase. 5. Bovine serum albumine prevents the kaempferol inhibition up to 50%, if it is adjected to the medium before kaempferol. Polyvinylpyrrolidon, which is an usefull reactivator of tannin inhibited reactions, does not reactivate kaempferol inhibited membrane bound enzyme reactions. 6. Flavonole glucosides inhibit pseudocyclic photophosphorylation at the same concentration range up to 40 %. From these results it is concluded, that a part of the measurable kaempferol inhibition is due to a more specific reaction, whereas a second part seems to be due to an unspecific reaction between a protein and kaempferol. Nevertheless it is clear that flavonoles do have an influence on the primary metabolism of chloroplasts. But it seems to be impossible to postulate a corresponding effect of flavonoles in vivo, since kaempferol was not found in spinach chloroplasts.