Regulation of bud dormancy by manipulation of ABA in isolated buds of Rosahybrida 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 hig h percentage of bud break could be observed when cultures were treated with fluridone, an inhibitor of carotenoid synthesis. Flow cytometry determinat ion 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 b ud ABA content was responsible for the progress from G(1) to G(2) phase wha tever the culture medium. However, in control culture, neither cell divisio n nor leaf primordium initiation could be observed and cells appeared stabl y 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 obs erved, indicating that intense activity of cell division occurred after DNA replication. Therefore, the results indicate that, as long as ABA was synt hesized inside the buds, cell cycle was arrested in G(2) phase and buds rem ained dormant. Continued in situ ABA biosynthesis appears, therefore, to be required for the maintenance of bud dormancy.