Helleborus niger is an evergreen species, while Helleborus odorus is a herbaceus understorey species that develops flowers before the canopy layer closes. They have sepals that remain after flower senescence and have multiple functions. To further elucidate sepal function during flower development, we examined their optical and biochemical properties, and photochemical efficiency of PS II in the developing, flowering, and fruiting flowers. Sepals of both species differed significantly in the contents of photosynthetic pigments and anthocyanins, but less in the UV-absorbing substances contents. Significant differences in photosynthetic pigment contents were also obtained within different developmental phases. Sepal potential photochemical efficiency of PS II was high in all developmental phases in H. odorus, whereas it was initially low in H. niger. The shapes of the reflectance and transmittance spectra were similar. In the green H. odorus sepals, we obtained typical green leaf spectra with peaks in the green and NIR regions, and a low response in the UV region. On the other hand, in the white H. niger sepals in the developing and flowering phase, the response was relatively constant along the visible and NIR regions. Biochemical properties, especially chlorophylls, revealed to be important in explaining sepal optical properties, as together they explained 44 % and 34 % of the reflectance and transmittance spectra variability, respectively.
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