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Gibberellins and the coordination of flower development in the Christmas rose (Helleborus niger L.)

Gibberellins (GAs) were identified and quantified during flower and fruit development in the Christmas rose (Helleborus niger L.), which differs from other popular model species in two ways (1) following anthesis the initially white or rose sepals turns green, which persists until fruit ripening, (2) the seed is shed before embryo maturation. Using an LC-MS/MS system, we identified GA1 and GA4 as major bioactive GAs in fruit and sepal tissues. In the fruits, the endogenous amounts of GA4 peaked during rapid pericarp and embryo growth whereas that of GA1 during the subsequent period of rapid nutrient deposition in the seeds and continued pericarp enlargement. In the sepals, the flux through the GA biosynthetic pathway was highest prior to the light green stage when the photosynthetic system was induced. The greening of unfertilized, depistillated, and deseeded flowers was less than the seed-bearing controls ; and the greening (chlorophyll accumulation) could be restored by treatment of the deseeded fruit with exogenous GA1 and GA4. The sepals of unfertilized and depistillated flowers indeed contained very low levels of GA4 and gradually decreasing levels of GA1. However, the concentrations of their precursors and metabolites were less affected. These data suggest that a signal(s) from the fruit stimulates GA biosynthesis and in turn greening in the sepals.

Christmas rose (Helleborus niger L.); Flower and fruit development; Gibberellins; LC-MS/MS analyses; plant hormones

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