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Plant and Cell Physiology, 1979, Vol. 20, No. 4 715-724
© 1979

Article

Effects of incubation of nuclei from a long-day duckweed, Lemna gibba G3, under different ionic conditions on the activity of RNA synthesis

Hideaki Nakashima

Biological Institute, Nagoya University Nagoya, Japan

The effects of medium compositions used for incubation of nuclei isolated from a duckweed, Lemna gibba G3, on maintenance of RNA synthetic activity were examined. The activity in the isolated nuclei decreased rapidly when they were incubated at 30°C. Part of this decrease was regulated by the ionic conditions of the incubation medium. The optimum concentration of MgCl2 for the maintenance of the activity was 30 mM. MgCl2 could be replaced by CaCl2. Potassium ion concentration above 100 mM caused a drastic decrease in activity. Magnesium ion had two different functions: stabilization of the binding of RNA polymerase I and of stimulating factors to nuclei. The patterns of Sephacryl S-200 column chromatography of the stimulating factors present in the nuclei during the day phase in a diurnal cycle were different from those of the night phase. This pattern also changed according to whether the nuclei were extracted with a low (3 min) Mg medium or an optimum (30 mM) Mg medium. We will discuss the role of magnesiumion in the occurrence of the diurnal rhythm of RNA synthesis in the duckweed.

(Received September 26, 1978; )
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