Abstract
Effects of sugars or polyvalent cations in media on 1: 1 salts reception in slime mold Physarum poly-cephalum were investigated in terms of the threshold concentration, Cth, of salt reception. Membrane potential and motive force of tactic movement were measured by the aid of double chamber method, where salt concentration in one compartment was increased successively with a fixed concentration of a sugar or polyvalent cation species in media. Results were:
1) The presence of glucose, mannose, maltose or sucrose in media increased Cth for 1: 1 salts (Cl-and NO3-salts of Li, Na, and K), whereas ribose decreased Cth of salt reception. Galactose showed no appreciable effect on Cth for every salts examined.
2) Variation of Cth for salts in the presence of sugars were correlated with those caused by the difference in the lyotropic number of anions. Cth for Li-salts changed most both by sugars and by anions, while those for NH4-salts were not changed.
3) The presence of polyvalent cations (Ca2+, Sr2+, Mg2+, La3+, Th4+) in media led to an increase in Cth for Na-and Li-salts, whereas a decrease in Cth for K-, Rb-, and NH4-salts resulted. Cth for 1: 1 salts changed discontinuously when the concentration of polyvalent cation exceeded their respective thresholds.
4) Sequence of selectivity of univalent cations varied extensively by simultaneous receptions of 1: 1 salts with sugars or with polyvalent cations. The important roles of structural changes of membrane and the surrounding water in chemoreception were then discussed.
