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Plant and Cell Physiology, 1985, Vol. 26, No. 5 923-929
© 1985

Article

Measurement of the Critical Nyctoperiod by Lemna paucicostata 6746 Grown in Continuous Light

Yukito Oota

National Institute for Basic Biology Myodaiji, Okazaki 444, Japan

The short-day duckweed Lemna paucicostata 6746 could be induced to flower in two days at 26°C when continuous illumination for entrainment was followed by continuous darkness. This 48-h dark period or the minimum darkness requirement for floral induction was called the induction period. The length of the induction period (IP) was routinely computed as the number of 24-h cycles using the equation of regression of flower number in logarithm on culture time. A light pulse given about 7 h after the start of the induction period increased the apparent IP value from two to three, suggesting that the interrupted first day had functioned as a noninductive day. A pulse given at any other part of the induction period did not modify the IP value. The light-sensitive part is probably the inducible phase, and the first 7-h period of darkness terminated by it seems to be the critical nyctoperiod. These and relevant facts suggest that the light-off oscillator measures the critical night length, 7 h.

Either red or far-red irradiation at the inducible phase extended the IP value by one. No red/far-red photoreversibility was detected. As expected, however, red or far-red irradiation of any other part of the critical nyctoperiod could not modify the IP value.

(Received February 8, 1985; Accepted May 14, 1985)
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