Biochemical and histological changes associated with in vitro responses in sunflower cotyledonary explants

Abstract

In vitro shoot regeneration from sunflower cotyledonary explants can be obtained in the presence of kinetin and indole-3-acetic acid. In contrast, callus prolif- eration is obtained in the presence of 2,4-dichlorophenoxy- acetic acid on culture medium. The purpose of this study was to investigate changes in protein profiles during callus and shoot development from cotyledonary explants and to correlate them with ontogenic stages during in vitro culture. Cotyledons cultured in the presence of 2,4-dichlorophe- noxyacetic acid produced friable callus as a result of early division of parenchymatic cells associated with the vascular bundles of the explant. The callogenic ability was indepen- dent of the cotyledonary region used as starting explant. Direct shoot organogenesis was observed from the same type of cells growing in culture media supplemented with kinetin and indole-3-acetic acid. In this case, the regener- ation potential varied among regions from which the explants were obtained. Protein profiles revealed differ- ences associated with shoots or callus developmental programs. A 27-kDa polypeptide was uniquely detected in the explants undergoing shoot organogenesis. The amount of this polypeptide during the first 4 d of culture increased and was followed by the appearance of meristematic centers in histologically analyzed samples. This polypeptide could be used as a specific marker for in vitro shoot development in this species.