Manganese Toxicity in Yeast and Plants

Abstract

Manganese (Mn) is normally present in soils as the insoluble, harmless MnO2. Toxic Mn of manganese is formed in acid soils but there is little consensus on the physiological basis of Mn toxicity in plants. Yeast, algae and vascular plants share similar membrane transport mechanisms and so yeast (Saccharomyces cerevisiae) and Chlorella vulgaris provides a convenient model system for studies of Mn-toxicity. Early effects upon Mn toxicity in S. cerevisiae in the exponential growth phase over of 24 hours was examined in culture tubes and for 6 days in the freshwater aquatic angiosperm Lemna minor in petri dishes at various Mn concentrations (10, 30, 100, 300, 1000, 3000 mmol m3). While C. vulgaris was examined with oxygenic photosynthesis after incubated 2 hours in 1, 2, 3, 5, 7 and 10 mol m3 Mn concentration. S. cerevisiae grew exponentially and growth was followed by measuring optic density (OD). C. vulgaris was followed oxygenic photosynthesis using junior PAM machine. Growth of L. minor was followed using leaf count, Chlorophyll a content and absorptance of the plants. Mn has toxic effects on the S. cerevisiae cells (K; = 1.884 ± 0.673 mol m3) and L. minor (K; = 1.154 ± 0.282 mol m3). Mn2+ toxicity was reversible in S. cerevisiae by a chelation agent (EDTA), but not in the case of L. minor. Therefore, our results showed that Mn is toxic to S. cerevisiae and L. minor (greater than or equal to 1.000 and 0.100 mol m3, respectively) and inhibited growth at higher concentration (more than 3.000 and 1.000 mol m3, respectively). Chelation of Mn did not consistently reduce the toxicity of Mn in L. minor and so Mn toxicity in L. minor is different to that found in S. cerevisiae. However, effect of Mn did not reduce oxygenic photosynthesis C. vulgaris (less than 10 mol m3).