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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+).

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+).

The circadian movement of the lamina of primary leaves of Phaseolus coccineus L. is mediated by antagonistic changes in the length of the extensor and flexor cells of the laminar pulvinus. The cortex of the pulvinus is a concentric structure composed of hexagonal disc-like cells, arranged in longitudinal rows around the central stele. Observations with polarization optics indicate that the cellulose microfibrils are oriented in a hoop-like fashion in the longitudinal walls of the motor cells. This micellation is the structural basis of the anisotropic properties of the cells: tangential sections of the extensor and flexor placed in hypotonic mannitol solutions showed changes only in length. As a consequence a linear correlation between length and volume was found in these sections. Based on the relationship between the water potential (which is changed by different concentrations of mannitol) and the relative volume of the sections and on the osmotic pressure at 50% incipient plasmolysis, osmotic diagrams were constructed for extensor and flexor tissues (cut during night position of the pulvinus). The bulk moduli of extensibility, [Formula: see text], were estimated from these diagrams. Under physiological conditions the [Formula: see text] values were rather low (in extensor tissue below 10 bar, in flexor tissue between 10 to 15 bar), indicating a high extensibility of the longitudinal walls of the motor cells. They are strongly dependent on the turgor pressure at the limits of the physiological pressure range.In well-watered plants, the water potentials of the extensor and flexor tissues were surprisingly low,-12 bar and-8 bar, respectively. This means that the cells in situ are by no means fully turgid. On the contrary, the cell volume in situ is similar to the volume at the point of incipient plasmolysis: the cell volumes of extensor and flexor cells in situ were only 1.01 times and 1.1 times larger, respectively, than at the point of incipient plasmolysis, whereas at full turgidity (cells in water) the corresponding factors were 1.8 and 1.5. It is suggested that the high elasticity of the longitudinal walls, the anisotropy of the cell walls, and the low water potential of the sections which is correlated with slightly stretched cell walls in situ, are favourable and effective for converting osmotic work in changes in length of the pulvinus cells, and thus for the up and down movement of the leaf.

The light-induced phase-response curves of circadian leaf movements of Solanum nigrum and Lycopersicon esculentum differ from each other. The light-induced phase-response curve of the monectochimera Solanum koelreuterianum (Lycopersicon esculentum with the epidermis from Solanum nigrum) is different from that of either of the constituent species, but shows more similarities with the light-induced phase-response curve of Lycopersicon esculentum. The differences between Solanum koelreuterianum and Lycopersicon esculentum are in the quality and especially in the range of the phase-shifting.The temperature-induced phase-response curves of Solanum nigrum and Lycopersicon esculentum are similar to the light-induced ones. However, the light-and temperature-induced phase-response curves of the chimera Solanum koelreuterianum differ markedly from each other.The temperature-induced phase-response curve of the chimera Solanum koelreuterianum differs from that of Solanum nigrum, but is identical with the temperature-induced phaseresponse curve of Lycopersicon esculentum.These results offer reasons to attribute a decisive role to the epidermis in the perception of the phase-shifting light but none in the temperature influence.

1 Two species of plants (Taraxacum arcticum and Arnica angustifolia), collected in Spitsbergen (geogr. latitude 76-80 degrees) exhibit endogenous circadian leaf movements but also movements with shorter periods. Astragalus frigidus, A. alpinus and Hedysarum hedysaroides, collected in arctic regions of continental Europe, also show endogenous diurnal leaf movements. 2. In most of the species tested, there was no difference in the length of the free running periods of plants from arctic and Central-European regions. This is also the case when individuals of the same species collected in different regions are compared. However, in Taraxacum arcticum the period is shorter than in T. officinale In general, under constant conditions the circadian oscillations of arctic plants persist for a shorter period than those of other plants. 3. The free running periods of several of the investigated species from tropical regions are much longer than 24 hours, i.e., much longer than those of species from Central-European and arctic regions. 4. The free running periods of several tropical species are temperature-independent (Erythrina senegalensis, Albizzia lophanta, Rhynchosia memmonia, Vigna catjang, Phaseolus multiflorus). In other tropical species, however, the periods decrease rather strongly with increasing temperature (Phaseolus mungo, Canavalia obtusifolia, Clitoria ternatea, Dolichos lablab, Vigna sesquipedalis, Dolichos zebra). The temperature does not influence the amplitudes in Phaseolus mungo and Vigna sesquipedalis, but it strongly influences the amplitudes in Erythrina senegalensis, in LD-cycles as well as in continuous light. 5. The arctic plant Astragalus frigidus still shows free running oscillations at 12°C, whereas several tropical species oscillate only at temperatures above 17°C. 6. The differences in the periods of tropical and non-tropical species (see under [3]) disappear if the plants are compared not at the same temperature but at temperatures which are optimal for them. If tropical plants are tested 27°C and Central-European and arctic species at 17°C, the periods always approach the value of 24 hours.

The length of the free-running periods of circadian leaf movements in the primary and secondary pulvini of Phaseolus coccineus was measured in constant darkness (DD) and continuous light (LL) of different intensities. The periods for the two pulvini do not differ from each other in DD and LL 30000 lx. However, they differ in LL 60 lx, 600 lx and 6000 lx, indicating a state of internal desynchronization. These results show a difference in the light intensity dependence of the 2 oscillations and a lack of mutual synchronization between them.