A solution culture study of manganese-tolerant and -sensitive tobacco genotypes

Genotypic differences in tolerating toxic levels of heavy metals have been observed in various plant species, This research was conducted to study the effect of manganese (Mn), iron (Fe), calcium (Ca), and magnesium (Mg) accumulation on two tobacco genotypes, Tobacco Introduction (T.I.) 1112 and KY 14, that have exhibited different sensitivity to toxic levels of Mn. The investigation was carried out employing a solution culture technique in which combinations of three levels of Mn exposure at varying strengths and pH of an Hoagland solution were made. Increasing the strength of the Hoagland solution suppressed Mn uptake and the occurrence of Mn toxicity symptoms in both genotypes, suggesting the potential role of other ions on reducing Mn toxicity. A change in solution pH from 4.5 to 6.5 had no significant effect on the accumulation of Mn, Fe, Ca, and Mg in tobacco leaves as well as the occurrence of Mn toxicity symptoms in the tobacco plant. Accumulations of Mn, Fe, Ca and Mg were significantly higher in leaves of the Mn-tolerant genotype (T.I. 1112) than in those of the Mn-sensitive genotype (KY 14), but ratios of Mn/cation (cation denotes Fe or Ca or Mg) were almost the same in both genotypes. These data suggest that the difference between the Mn-sensitive and Mn-tolerant tobacco genotypes were not due to the simple imbalance of Mn in relation to Ca, Mg and Fe in the plant. Plant physiological studies are currently under way to elucidate this difference in Mn tolerance between the two genotypes.