Passage IV

Some plants produce mannitol (a sugarlike molecule) when exposed to a high-salt solution. Mannitol production results in an increase in the solute concentration within the plant cells and thus a decrease in the net movement of water between the high-salt solution and the cytoplasm of the cells exposed to the high-salt solution.

To investigate this effect, researchers created 5 genetically identical tobacco plant lines that could not produce mannitol. They then used genetic engineering techniques to insert genes to transform 3 of the lines (M1, M2, and M3) into mannitol-producing lines (Ms). The fourth line (NMI) was also exposed to the genetic engineering procedures, but no genetic material was inserted into NMI. The fifth line (NM2) was not genetically engineered. Thus, NMI and NM2 were non-mannitol-producing lines (NMS). Two experiments were then conducted.

Experiment 1

Five 6-week-old plants from each line were grown for 10 days in a nutrient solution with a normal salt concentration. Each line had the same average height and mass at the start of the experiment. The average percent increase in height and mass during the experiment appears in Table 1.

Experiment 2

Five 6-week-old plants from each line were grown fo 30 days in a nutrient solution with a high salt concentration. Each line had the same average height and mass at the start of the experiment. The average percent changes in height and mass after 14 days and after 30 days appear in Table 2.

Tables adapted from MichellIC. Tarczynskl, Richard G, Jansen, and Hans J. Bohnert, "Stress Protection of Transgenic Tobacco by Production of the Osmolyte Mannitol." @1993 by the American Association for Advancement of Acience.