Effects of cAMP, theophylline, imidazole, and 4-(3,4-dimethoxybenzyl)-2-imidazolidone on the leaf movement rhythm of Trifolium repens-a test of the cAMP-hypothesis of circadian rhythms.

The period length of the leaf movement rhythm of Trifolium repens L. is lengthened by continuously offered cAMP (0.5-1.0 mol m(-3)) and theophylline (0.5-4 mol m(-3)). At the higher concentrations this effect is more pronounced and the rhythm damps out faster. Imidazole (0.5 and 1 mol m(-3)) has no effect on the period length; however, after 5 mol m(-3) the rhythm is abolished. Offered as 4 h pulses the resulting phase response curves for cAMP and imidazole are similar and show delays of up to 4 h during the day position of the leaves. Theophylline pulses lead to delays of up to 5 h during closure and advances of up to 3 h during opening. No phase shift is brought about by 4-(3,4-dimethoxybenzyl)-2-imidazolidone. The results do not support the cAMP-model of the circadian clock which has been proposed by Cummings (J. theor. Biol. 55, 455-470; 1975). The effect of the substances tested could, however, be based upon influences on the transport of Ca(2+).