Growth and photosynthesis of Lemna minor L. exposed to different light conditions and sucrose supplies

Duckweed (Lemna minor L.) is a model plant suitable for investigation into plant physiology, biochemistry and ecotoxicology. Depending on the type of the experiment, duckweed is cultivated on different nutrient media under various chamber conditions. In our work, duckweed was cultivated on Pirson-Seidel's nutrient solution supplemented with 5, 7.5 or 10 g L-1 sucrose under cool white (CW) or Gro-Lux (GL) light sources. When different light sources and sucrose supplies are compared, a significant stimulative effect of GL light on duckweed grown on 7.5 and 10 g L-1 sucrose was seen to start on day 9. Considering photosynthetic performance the results showed that there were no significant differences in maximum quantum yield of PSII (F-v/F-m) after 7 and 16 days of exposure, regardless of light source and sucrose supply. Effective quantum yield of PSII (FPSII) decreased only after 16 days of exposure to 5 g L-1 sucrose under CW light. The higher growth rate and photosynthetic performance in plants exposed to GL light is a consequence of its spectral distribution resembling the action spectrum of photosynthesis. Furthermore, enhanced growth noticed in plants cultivated on higher sucrose contents (7.5 and 10 g L-1) indicated the promotive effect of sucrose in plants grown under low light conditions.