Abstract

The steady state mRNA levels of Lhc genes in Pharbitis nil were investigated using the wheat Lhcbl *1 (cabi) gene as a heterologous probe. A circadian rhythm in P. nil Lhc gene expression was detected in constant light. This rhythm was initiated or reset to a constant phase by the initial light-on signal received by the plants, and was detectable for at least five days in constant light. The rhythm continued to be detectable for 2 cycles in constant darkness, although the amplitude of the rhythm was reduced. Transfer to constant darkness after a prolonged light period caused a phase shift in the rhythm, the size and direction of which was determined by the time at which the light-off signal was given. It was concluded from these results that the rhythm in Lhc gene expression is governed by a different underlying oscillator from those which govern the photoperiodic response rhythm or leaf movement rhythm in P. nil. These results indicate that the Lhc rhythm may, however, share a common
underlying oscillator with the transpiration rhythm in P. nil.