Photophysiology of turion formation and germination in Spirodela polyrhiza

Standardized laboratory techniques for the vegetative growth of the duckweed Spirodela polyrhiza (Lemnaceae), and for formation as well as germination of their turions were described. Increasing photon fluence rates of blue or red light increased the yield of turions. A specific stimulating effect of blue light was demonstrated under autotrophic but not under mixotrophic conditions. Therefore the spectral composition of light is not important in mixotrophic formation of turions whereas in autotrophic formation light sources with a higher portion of blue light are recommended. Dark-grown (etiolated) turions showed accelerated germination and higher germination percentage in comparison with light-grown turions after induction by a single red light pulse, This difference was overcome in continuous red light by speeding up the germination response of light-grown turions. Use of Petri dishes (8 cm(3) nutrient solution) instead of Erlenmeyer flasks (50 cm(3) nutrient solution) retarded germination response. Especially for long term experiments the use of Erlenmeyer flasks is recommended. Storage of turions for 72 h at 25 degrees C following at 5 degrees C in darkness after-ripening resulted in a decreased lag phase of the light-induced germination both after induction by a single light pulse and in continuous light.