The Permeability of Plant Protoplasts to Small Molecules.

The very smallest molecules (e. g., those of formamide, ammonia, methylamine, water, and methanol) penetrate plant protoplasts with distinctly greater rapidity than would be expected if the permeation constants were proportional to k/M^1/2 where k denotes the oil/water partition coefficient and M the molecular weight. The plasma membranes thus exert a kind of sieve-effect which manifests itself in the accelerated permeation of the very-smallest molecules. [ABSTRACT FROM AUTHOR]