Characteristics of Cultured Tomato Cells after Prolonged Exposure to Medium Containing Polyethylene Glycol

Cell lines of tomato (Lycopersicon esculentum Mill., cv. VFNT-Cherry) have been isolated, which are capable of growing in media containing polyethylene glycol (PEG) 6000 with water potentials as low as -15 or -22 bar. After prolonged exposure to media containing PEG, these cell populations have reduced abilities to grow in the absence of PEG. Upon resuspension in PEG-free medium, the cells swell and begin to release metabolites, including protein. Measurement by plasmometry of the osmotic potential of cells selected in medium with -22 bar water potential indicates that they maintain, at the end of the growth cycle, an osmotic potential of approximately -26 bar. This is compared to an osmotic potential of -9 bar for nonselected cells in medium without PEG, having an initial water potential of -4 bar. Thus, considerable osmotic adjustment occurs as a result of exposure to external low water potential. The results also indicate that PEG does not contribute significantly to osmotic adjustment of the cells.