Comparative abundance of the large subunit of rubisco in aerial organs of the Japanese morning glory [Ipomoea (Pharbitis) nil] suggests a photosynthetic role for sepals

Levels of the large subunit (LSU) of rubisco (ribulose 1,5 bisphosphate carboxylase/oxygenase) were measured in vegetative and floral organs of 'Violet' Japanese morning glory (Ipomoea [Pharbitis] nit Roth). Identification of the LSU in polypeptides separated by two-dimensional gel electrophoresis allowed estimation of the relative abundance of this polypeptide in the organs examined. Further quantitation was achieved by immunoblotting protein extracts either alone or in combination with various amounts of extracts from other organs. The amount of LSU decreased in the order leaves > cotyledons > sepals > corollas > androecium, gynoecium. The relative abundance of LSU in sepals (74%) compared to photosynthetically competent organs [leaves (100%) and cotyledons (81%)] suggests that sepals may be photosynthetically competent in supporting development of the other floral organs.