Plastid and cytosolic isozymes of pyruvate kinase, hexose-phosphate isomerase, and 6-phosphogluconate dehydrogenase have been isolated and separated from seeds of the castor oil plant (Ricinus communis L.) at different stages of development. These enzymes can be detected 24 days after pollination, when the plastids contain 14% of the total cellular activities of both the pyruvate kinase and hexose-phosphate isomerase and 40% of the 6-phosphogluconate dehydrogenase activities. At this stage the seed consists mainly of nucellus, that is subsequently replaced by endosperm. The activities of the plastid isozymes increase faster than the cytosolic isozymes, until after 40 days, when endosperm fills the seed, the plastids contain 25% of the hexose-phosphate isomerase, 70% of the 6-phosphogluconate dehydrogenase, and 40% of the pyruvate kinase activities. The development of the plastid isozymes correlates with the increase in oil synthesis. This supports a central role for plastids in oil synthesis.
Efficient mesophyll protoplast isolation and development of a transient expression system for castor-oil plant (Ricinus communis L.)
