[Period-lengthening and phase-shifting of the circadian rhythm of Phaseolus coccineus L. by theorphylline].

Under the continuous influence of theophylline the period of the circadian leaf movement rhythm of Phaseolus is lengthened under conditions of continuous darkness and under conditions of continuous light. Four-h pulses of theophylline shift the rhythm as a function of the phase.It is hypothesized that these theophylline effects are based not upon inhibition of the phosphodiesterase which hydrolyses 3',5'-cAMP but on the influence on membrane function, particularly the transport and binding of Ca(2+).