Osmotic regulation via carbohydrate metabolism drives petal expansion and floret opening in gentian 'Showtime Spotlight'

- Accumulation and hydrolysis of gentianose and gentiobiose were stage-specific.
- Changes in carbohydrates were paralleled by changes in glycoside hydrolase activity.
- Changes in carbohydrates imply an important role in controlling floret development.
- Carbohydrate metabolism influences development via osmotically driven cell expansion.

During the development and senescence of florets in gentian 'Showtime Spotlight', there was a dramatic change in petal non-structural carbohydrates (NSCs), including accumulation, and hydrolysis. Gentianose concentration increased more than ten-fold with the development of florets, to a maximum of 26.1 mg g−1 fresh weight (FW) just before floret opening. Subsequently, as florets began opening, the gentianose concentration sharply decreased to almost nothing as flowers progressed from fully open to naturally senesced. Gentiobiose concentration increased gradually during early development of florets, with the pattern of increase with each stage of development being slightly behind that for gentianose, reaching a maximum of 21.2 mg g−1 FW as florets began opening. These stage-specific changes in concentrations in each NSC were paralleled by significant changes in activity of both gentianose and gentiobiose glycoside hydrolase. In a plant system devoid of starch, and where changes in sucrose and glucose concentration were comparatively small, the stage-specific and intensive fluctuation of the unique carbohydrates gentianose and gentiobiose imply an important role in controlling gentian floret development and opening. The significant positive correlation between the osmolality of soluble NSCs and pressure potential supports the hypothesis that this carbohydrate metabolism role is via osmotically driven cell expansion.