The Effects of Water Deficits on Slices of Beetroot and Potato Tissue:3

The effects of osmotically induced water deficits on the metabolism of aged beetroot and potato discs were investigated. In this paper the tissue-water relationships in two osmotica, mannitol, and Carbowax 1540, are described. Tissues in equilibrium with Carbowax solutions had lower fresh weights than those in isotonic mannitol solutions, particularly at water potentials below -0.7 J g-1 with potato and -2.0J g- with beetroot. Potato discs killed by freezing and thawing lost water to Carbowax but not to mannitol solutions. The extra effectiveness of Carbowax solutions in lowering fresh weight was attributed to an osmotic effect across the cell wall. Carbowax was found to penetrate plasmolysed potato tissue, however, at a rate of about 3.0 mg (g fresh weight)-1 h-. The extent to which water uptake occured on retransfer to water was unaffected by the nature of the soulte used, but depend on the degree of dehydration. The following phases were clearly defined: (1) recovery to the fresh weight at full turgor, when the water potential of potato tissue was not reduced below -0.5 J g- and of beetroot below -1.2 J g-1; (2) a declining degree of recovery with decreasing water potential over the ranges -0.5 to -1.0 J g-1 and -1.2 to -3.0 J g-1 for potato and beetroot, respectively, and (3)in potato, the absence of recovery of fresh weight following reduction of the water potential below -1.0 J g-1.