Effects of beauvericin on root cell transmembrane electric potential, electrolyte leakage and respiration of maize roots with different susceptibility to Fusarium

Effect of beauvericin on root cell transmembrane electric potential (EM), electrolyte leakage and respiration of roots were studied in two maize cultivars (Zea mays L.) with different susceptibility to this toxigenic metabolite produced by Fusarium. Beauvericin treatment induced rapid and significant depolarisation of membrane potentials of the outer cortical cells of maize roots of tolerant cv. Lucia. The range of depolarisation was dose dependent with maximum depolarisation of 55 mV (55 ± 7 mV, n = 7) at 200µM beauvericin. In contrast, membrane potentials of beauvericin susceptible cv. Pavla was only slightly depolarised by identical concentrations of beauvericin and the value of depolarisation represented only half of the value of tolerant cv. Lucia (27 ± 6 mV, n = 8). The values of membrane potentials of root cells of tolerant cv. Lucia were higher (137 ± 9 mV, n = 26) and more electrogenic (60 ± 2 mV, n = 3) than in susceptible cv. Pavla (125 ± 7 mV, n = 28), (47 ± 2 mV, n = 3), respectively. Our results confirmed that 2 h treatment with 50µM beauvericin does not cause irreversible changes in plasma membrane H+-ATPase, because fusicoccin, an H+-ATPase activator diminished the depolarizing effect of beauvericin on the EM. Further experiments revealed beauvericin-induced increase of membrane conductivity in root cells of Pavla but not in root cells of Lucia. Time-coarse experiments showed that 25µM beauvericin induced slight, but significant inhibition of root respiration in both cultivars during the first two hours of treatment, and the inhibition was higher in cv. Lucia than in cv. Pavla. The depolarisation of EM in the outer cortical cells of maize roots may be the result of a cumulative effect of beauvericin on ATP supply, activity of H+-ATPase and mainly on the permeability of plasmalemma. Increased beauvericin tolerance in maize might be associated with the increased ability of tolerant plant to maintain normal ion fluxes and membrane potentials across the plasmalemma of root cells in the presence of beauvericin.