The effect of polymyxin on plant roots

Abstract

Root growth of young seedlings of barley and other species was substantially inhibited when placed in 5-10 p.p.m. solutions of the antibiotic, polymyxin B. The inhibiting effect was suppressed by simultaneous presentation of an excess of calcium ions. Polymyxin solutions of the same concentration had no adverse effect on germination. Brief exposure of normal roots of seedlings to 50-100 p.p.m. polymyxin resulted in cessation of further growth or cation uptake, and irreversible injury accompanied by loss of organic and inorganic constituents from the root cells. Simultaneous presentation of calcium nullified these effects. It appears likely that calcium and polymyxin are retained at the same absorption sites, and that to prevent polymyxin absorption a large excess of calcium cations is required. If absorbed, however, polymyxin causes disorganization of cell membranes to the extent that cell contents are released into the medium. These observations parallel closely the bactericidal action of this antibiotic on certain microorganisms, and suggest that there are general features common to the cell walls of roots and bacteria.