A physiological characterization of Mn-tolerant tobacco plants selected byin vitro culture

In previous research, an in vitro stepwise procedure permitted us to obtain Nicotiana tabacum regenerated plant lines able to grow in the presence of Mn at 2 and 5 mM (Mn-tolerant plants). These plants showed several morpho-p hysiological and cytological differences in comparison to the Mn-sensitive regenerated plants In particular, the number of xylem cells and the degree of lignification appeared to be influenced differently by these Mn concentr ations. In the present work these Mn-tolerant and Mn-sensitive N. tabacum p lants, maintained in the presence of Mn 2 and 5 mM, have been characterized with regards to the uptake of Mn and Fe, the activity of extracellular per oxidases in the stems, and the activity of superoxide dismutase, ascorbate peroxidase, and glutathione reductase in the leaves. The leaf response to a n increasing Mn concentration in the medium, corresponded a parallel decrea se of Fe content. Plants tolerant of 5 mM Mn showed almost a doubling Mn co ntent over that of the 5 mM Mn-sensitive plants. In the stem, 2 and 5 mM Mn inhibited the extracellular free peroxidases (guaiacol peroxidases) either in the Mn-tolerant plants or in the Mn-sensitive plants. In the Mn-sensiti ve plants treated with 2 mM Mn the activity of the peroxidases of the ionic ally and covalently bound wall peroxidases was also depressed. In 5 mM Mn-t olerant plants, an enhanced activity of the covalently bound wall peroxidas es was observed. The effect of Mn on the covalently bound wall. syringaldaz ine peroxidases was identical to that observed in the guaiacol peroxidases; the activity was significantly higher in the Mn-tolerant plants grown in t he presence of 5 mM Mn. In the leaf, the increase of Mn content inhibited t he activity of guaiacol peroxidase, ascorbate peroxidase and superoxide dis mutase in the Mn-tolerant as well as in the Mn-sensitive plants. However, t he effect was greater in the Mn-sensitive plants. Only glutathione reductas e did not show significant variation except for the 2 mM Mn-sensitive plant s, where an increased activity was detected. (C) 2000 Elsevier Science Irel and Ltd. All rights reserved.