Threshold phenomena in chemoreception and taxis in slime mold Physarum polycephalum.

Abstract

The plasmodium of Physarum polycephalum reacts to various kinds of chemical substances and moves towards or away from them. Threshold concentration of recognition of chemicals was examined in terms of membrane potential and of the averaged motive force of tactic movement by using a double-chamber method, i.e., a single plasmodium was placed between two compartments through a narrow ditch, and differences in membrane potential and in pressure between two compartments were measured. Results are summarized as follows: (a) By increasing the concentration of various substances in one compartment, the membrane potential started to change at a certain threshold concentration, Cth, for each chemical. Chemotactic movement of the plasmodium took place at the same threshold concentration. These results held both for attractants (glucose, galactose, phosphates, pyrophosphates, ATP, c-AMP, etc.) and for repellents (various inorganic salts, sucrose, fructose, etc.). (b)The threshold concentration, Cth, for inorganic salts decreased remarkably with increase of the valences of cations, z, and was proportional to z -'6, i.e., the Shultze-Hardy rule known in the field of colloid chemistry was found to be applicable. (c) The plasmodium distinguished the species of monovalent cations in the following order: H(Li(K(Na(Rb(Cs(NH4. Plots of log Cth against the lyotropic number of anion fell on different straight lines for each monovalent cation species. (d) Plots of log Ct~ against the reciprocal of the absolute temperature followed different straight lines for different substances. The slopes of the lines were almost the same and gave a value of 12 kcal/mol for the enthalpy change. These results suggest that the recognition of chemical substances appears as the result of a structural change of the membrane at the threshold point, and that the change in membrane structure is transmitted simultaneously to the motile system of the plasmodium.

Discontinuous Change in Membrane Activities of Plasmodium of <I>Physarum polycephalum</I> Caused by Temperature Variation: Effects on Chemoreception and Ameboid Motility

“…The fact that changes in the membrane potential agree with those in the zeta potential confirms the previous assertion that chemoreception in the plasmodium of Phy- sarum polycephalum takes place at the membrane surface (10,22). The temperature variations of the potentials (Fig.…”

“…exists in the plasmodium of Physarum polycephalum and that the receptive membrane has manifold characters when it reacts to chemical stimuli, e.g., the plasmodium discriminates Ca2+ and Sr2+ at the membrane potential level below Tc, and a similar depolarization of the membrane potential is induced by Ca2+ and Sr2+ salts when T>Tc (10,22). The fact that changes in the membrane potential agree with those in the zeta potential confirms the previous assertion that chemoreception in the plasmodium of Phy- sarum polycephalum takes place at the membrane surface (10,22).…”

Allometry in Physarum plasmodium during free locomotion: size versus shape, speed and rhythm

“…The plasmodium of Physarum polycephalum (strain HU195×HU200) (Akitaya et al, 1985) was fed with oat flakes (Quaker Oats Co.) on agar gel at 24°C in the dark (Ueda et al, 1975). Agar gels used for all experiments were nutrient free (Wako Pure Chemicals Inc.) and their concentrations were fixed at 1.0% weight by volume.…”

Habituation in non-neural organisms: evidence from slime moulds

“…Here we designed a protocol to investigate habituation phenomena in slime moulds using chemotaxis as the behavioural response under scrutiny. Chemotaxis is the directed motion of an organism towards favourable chemicals (attractants) and away from unfavourable ones (repellents) [19,20]. To test whether slime moulds are capable of habituation, individuals were repeatedly exposed to quinine or caffeine, known repellents for P. Polycephalum [21,22] and their behavioural responses were recorded.…”