Regulation of bud dormancy by manipulation of ABA in isolated buds of Rosa hybrida cultured in vitro

In vitro cultures showed that the proximal buds isolated from a rose (Rosa hybrida L. cv. Ruidriko Vivaldi(R)) stem were endodormant. Growth and a high percentage of bud break could be observed when cultures were treated with fluridone, an inhibitor of carotenoid synthesis. Flow cytometry determination of nuclear DNA content revealed that cell cycle activity of endodormant buds was arrested in the G(1) phase. Upon culture, the large decrease in bud ABA content was responsible for the progress from G(1) to G(2) phase whatever the culture medium. However, in control culture, neither cell division nor leaf primordium initiation could be observed and cells appeared stably arrested in G(2). By contrast, with fluridone, an additional ABA decrease was observed resulting from an inhibition of its synthesis inside the bud. New leaf primordia were initiated and many figures of mitosis could be observed, indicating that intense activity of cell division occurred after DNA replication. Therefore, the results indicate that, as long as ABA was synthesized inside the buds, cell cycle was arrested in G(2) phase and buds remained dormant. Continued in situ ABA biosynthesis appears, therefore, to be required for the maintenance of bud dormancy.