The Effects on RNA Synthesis in a Long-Day Duckweed, Lemna gibba C 3, of Irradiation with Different Ratios of Red and Far Red Light During the Prolonged Dark Period

Abstract

Summary Changes in the proportion of Pfr in the long-day duckweed Lemna gibba G3 during the dark period were examined using the null response method. The dark period was interrupted for 5 minute periods at various times by lights containing different ratios of both red and far red light at an intensity of 120 µW/cm 2 . RNA synthesis was then determined at selected times following irradiation. The dark period can be divided into 3 different periods each of which has a different sensitivity to the mixed lights. The duckweed irradiated with 100 % red light showed the same or slightly stimulated RNA synthetic activity as the dark control up to the 22nd hour from the beginning of the dark period: the value of null % red was 100 % or near. The value of null % red then decreased rapidly during next 12 h period to a constant level of 40 % red and finally remained at this level until the 37th hour. We concluded that phytochrome can modulate the amplitude of RNA synthesis rhythm, but that since the Pfr level remained high until the 22nd hour from the beginning of the dark period, the diurnal change of RNA synthetic activity during the dark period is not a direct result of fluctuations in the Pfr level.