Induced pore formation in membranes of cortex cells in excised Sorghum roots: its effect on membrane potential and nucleotide leakage

Abstract

Measurements of membrane potentials were used for screening various molecules capable of inducing pore formation in cellular membranes for their ability to penetrate into excised roots of Sorghum bicolor (L.) Moench.Poly‐l‐lysine (30 000 MW) and amphotericin B did not affect cortical cells even though they affected epidermal cells; the lysine polymer and the amphotericin B micelle were apparently too large to diffuse into the roots. Polymyxins and filipin depolarized the epidermal cells as well as the cells of the cortex. Depolarization of cortical cells by filipin was slower than that by polymixins.Leakage of adenylate nucleotides was measured to obtain information concerning the size of the pores induced by polymyxins. Incubation with 200 μg/ml polymyxin B caused leakage of ATP from root segments. Leaked nucleotides were found in the medium; however, with time they were dephosphorylated, presumably by cell wall phosphatases. In situ ATP formation was observed when root segments were incubated with polymyxin, ADP, Pi, succinate and glucose, confirming that the induced pores were larger than the size of a nucleotide.