Cell osmolarity adjustment inLycopersiconin response to stress pretreatments1

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Abstract
Plant cell adjustments in water and osmotic status in response to heat, cold, and osmotic stress were investigated using microcultured plants from four assessions of Lycopersicon. Changes in plant water potentials were determined with an osmometer solution method, and osmolarity by a cell sap extraction method. Heat stress decreased water potential (raised osmolarity) and cold stress increased water potential (depressed osmolarity) for all species, but the magnitude of the adjustment was significantly greater for L. peruvianum (a drought resistant genotype). Microcultures produced on growth medium with elevated levels of osmotic agents (sorbitol, dextran, or glucose) developed correspondingly higher cell sap osmolarity. Plant water potential shifted in the same direction, but not to the same degree, as osmotic potential in response to stress. Since osmotic adjustment is a reported mechanism of stress (salt, temperature, and water deficit) tolerance, these tests suggest a method for prescreening of germplasm at the microculture plant level.