Structural and functional aspects of the Nuphar lutea (L.) Smith heterophylly: Ultrastructure and photosynthesis

The ultrastructure and functional characteristics of the photosynthetic apparatus of floating and submersed leaves of the heterophyllous plant Nuphar lutea (L.) Smith have been examined. Differences have been revealed in mesophyll cell chloroplasts, content of pigments, and chlorophyll fluorescence parameters between floating and submersed leaves and submersed leaves at different depths. A sharp decline in the PSII (photosystem II) efficiency of submersed leaves when exposed to an actinic light intensity of more than 60 ??mol m^?2 s^?1 has been noted. The described differences may be considered as an adaptation mechanism of submersed leaves to life in an aquatic environment with a reduced light intensity and changed light spectral composition.