Two gamma-tubulin isoforms are differentially expressed during developmentin Helianthus annuus

The cytoskeleton is involved in major developmental events in plant cell gr owth and differentiation. Nucleation events play a key role in the dynamic and organization of the microtubule (Mt) cytoskeleton. Among many proteins involved in Mt nucleation, gamma -tubulin has been identified as an essenti al component of the Mt organizing centers (MTOC), In protoplasts, somatic e mbryogenesis induction has been correlated with remodeling of Mt cytoskelet on. We have investigated the specific developmental expression of gamma -tu bulin in Helianthus annuus. Two gamma -tubulin isoforms have been detected by immunoblotting, with bands at 52 and 58 kDa, The larger gamma -tubulin ( 58 kDa) is present in all the sunflower tissues tested and is associated wi th the nucleus. The smaller gamma -tubulin (52 kDa), differing from the for mer at the carboxy-terminal end, is only present in meristematic and dediff erentiated cells and is not bound to the nucleus. This first demonstration of the presence of two gamma -tubulins in plant cells is discussed in terms of distinct roles in the nucleation and organization of Mts.