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Plant Physiology 79:625-629 (1985) © 1985 American Society of Plant Biologists Stem Extension Rate in Light-Grown Plants 1Effects of Photo- and Thermoperiodic Treatments on the Endogenous Circadian Rhythm in Chenopodium rubrumInstitut de Physiologie Végétale, CNRS, 91190 Gif-sur-Yvette, France, Institut für Biologie II, Universität Freiburg, Schänzlestr. 1, 7800 Freiburg, Federal Republic of Germany
Low temperature pulses have two effects on the circadian rhythm exhibited by stem extension rate of green Chenopodium rubrum plants. First, low temperature pulses have the same effect on the phasing of the rhythm as a dark period interrupting continuous light. Second, low temperature pulses stimulate stem extension rate during the 10 hours immediately following the end of the pulse. A difference in temperature between soil and air increases this effect. In any case, it is the change in temperature which is essential and not a specific temperature. Effects of light and temperature on phasing and amplitude of the rhythm explain why the maximal stem growth is observed under normal photo-thermoperiodic conditions, i.e. a high temperature during the photoperiod and a low temperature during the dark period.
1 Supported by Deutsche Forschungsgemeinschaft (grant Wa 263/15-1). A grant from the Alexander-von-Humboldt Stiftung to A. L. is gratefully acknowledged.
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