Die Permeabilität des Plasmalemmas für Säuren.

Row 3 of Table 1 gives the times required to kill the leaf protoplasts of Eiodea densa in solutions containing 0.05 M of different acids and 0.05 M of their primary sodium salts per litre. A priori there are, of course, two conceivable alternatives regarding the killing effects of the acids: (a) the plasmalemma is directly damaged by the H⁺-ions of the external solution, (b) the acid penetrates the undamaged plasmalemma and then exerts its toxic effects in the interior of the protoplasm. In our experiments, the first alternative was largely eliminated by avoiding too low pH values of the test solutions. On the other hand, the intracellular toxic actions may depend either (b₁) on the H⁺-ions or (b_2.3) on the acid molecules, or acid anions or both. In the experiments on which the present paper is based, however, the intracellular action of the H⁺-ions appears to dominate in most cases. Taking into account that all the solutions tested contained the same concentration of undissociated acid molecules, it may be inferred that the death rates observed are probably, on the whole, fairly reliable measures of the permeability of the plasma-lemma towards the acid molecules in question. The death rates observed are correlated with the relative ether solubilities and molecular sizes of the acids in much the same way as the permeation power of non-electrolytes towards Nitella protoplasts is correlated with their ether solubility and molecular size. It thus seems that the diffusion resistance offered by the plasmalemma towards acids is fairly similar to that offered by the protoplast as a whole. When nutrient solutions containing increasing concentrations of different acids were inoculated with conidia of Aspergillus niger, it was found that there exists a fairly close correlation between the killing velocities of different acids towards Elodea cells, on the one hand, and their power to prevent the germination of the conidia of Aspergillus, on the other. This suggests a certain resemblance between these two organisms regarding the permeability of their plasmalemmas. [ABSTRACT FROM AUTHOR]