Vicia faba germination: Synchronized cell growth and localization of nucleolin and α-tubulin

The first cell cycle of Vicia faba L. seeds, which begins upon imbibition of dry seeds and is completed at the first mitosis after radicle protrusion, was characterised by the flow cytometry and immunodetection of nucleolin and tubulins in root tip meristems. Flow cytometry revealed highly synchronised profiles from the quiescent G₁ phase to the late G₂ phase, indicating uniform cell cycle progression within a root tip until the first mitosis. Using immunoblotting, nucleolin was detected in two distinct bands with the apparent molecular masses of 89 and 99 kD; the former was detected only in seeds imbibed at 4°C for 1 day whereas the latter was found at all stages examined, suggesting that the 89 kD nucleolin may be seed-specific. Unusual localization of nucleolin in cold-imbibed seeds, undetectable in half of the cells and present in nucleoplasm, was revealed by immunofluorescence microscopy. While α- and β-tubulin were detected at all stages and no significant changes in accumulation of the proteins were observed, few microtubules were detected at the beginning of germination when cells were still in the G₁ phase, suggesting that microtubules may be depolymerized in the dry seeds.