EFFECTS OF MANGANESE ON NICOTIANA SPECIES CULTIVATED IN-VITRO AND CHARACTERIZATION OF REGENERATED MN-TOLERANT TOBACCO PLANTS

Increasing manganese (Mn) concentrations to 5, 10, 15 and 20 mM caused a significant decrease in callus formation and shoot regeneration in comparison to 0.1 (control medium) and 2 mM in Nicotiana tabacum var. EEL W3 grown on Murashige and Skoog's medium (MS) with 1 mg l(-1) alph a-naphtaleneacetic acid and 1 mg l(-1) kinetin. Concentrations of Mn h igher than 5 mM also reduced callus growth in Nicotiana bigelovii bige lovii grown on MS solid medium. Callus cultures of N. tabacum with enh anced tolerance to Mn were selected by progressively elevating the lev el of MnSO4 . 4H(2)O in the culture medium. Selection of Mn-tolerant p lants occurred only at 2 and 5 mM, because higher concentrations inhib ited callus and shoot growth. Differences in mitotic phase indices in plants grown at 2 and 5 mM Mn were found in comparison to the control. In these plants, several mitotic alterations as well as damaged chlor oplasts and a reduction in chloroplast number were also observed, espe cially for those treated with 5 mM Mn. Mn was also shown to affect the number of xylem elements and the degree of lignification, which diffe red between plants grown at 2 or 5 mM compared to the control. (C) 199 8 Elsevier Science Ireland Ltd. All rights reserved.