Effect of sugars on salt reception in true slime moldPhysarum polycephalum

Summary

Interaction between salt and sugar receptions in plasmodium ofPhysarum polycephalum was studied by using double-chamber method. Effect of sugars on salt reception was evaluated by measuring membrane potential and the motive force of tactic movement of the slime mold, where salt concentration in one compartment was increased successively with a fixed sugar concentration. Results are summarized as follows: (1) The presence ofd-glucose,d-mannose,d-maltose, or sucrose in medium led to increase of the threshold concentration,C _th , for salts (chlorides and nitrates of Li, Na, K), whereasd-ribose decreased the threshold for salt reception.d-galactose showed no appreciable effect onC _th of every salt species examined. No change inC _th for salt reception was observed until concentration of sugars exceeded their respective thresholds. (2) Double logarithmic plots ofC _th for salts against sugar concentration followed different straight lines for different cations, whose slopes being closely correlated with the effects of lyotropic number of anions in the absence of sugars. (3) Plots of logC _th against the reciprocal of the absolute temperature, 1/T, gave linear relations, and the slopes of the straight line became small with increase of sugar concentration above their respective thresholds.

Experimental results obtained here suggest that the structure of water at the interface of cell membrane plays an indispensable role in the interaction between salt and sugar receptions.