Comparison of the redox activities in plasma membranes from roots and shoots of etiolated bean seedlings

Plasma membrane (PM) vesicles were purified in parallel from the roots and shoots of 6-day-old etiolated bean (Phaseolus vulgaris L,) seedlings, grown in water culture at 25 degrees C, by aqueous polymer tu two-phase partitioning. The purity of PM fractions was determine by measuring the activity of known marker enzymes (vanadate-sensitive Mg-ATPase, 1,3-beta-glycan synthase, latent ID-Pase, cytochrome c oxidase, and antimycin-A-insensitive cytochrome c reductase). NADH-(acceptor) oxidoreductase activities were determined with the following electron accepters: ferricyanide, cytochrorne c, duroquinone, monodehydroascorbate, Fe3+-EDTA, and oxygen. Cytochrome b content was also determined. In general, results show that redox activities are higher in the root PM than in the shoot PM which follows the glycan synthase II (PM marker) pattern. The relative activities of the distinct redox enzymes measured (activity profile) are remarkably similar in the root and shoot PM preparations. The cytochrome b content and level of ascorbate reduction were also imilar in both plant organs. However, the ratio of NADH-(acceptor) oxidoreductase activity to cptochrome content was significantly higher in roots when compared to the shoots.