Responses to Water Stress in Adapted and Unadapted Carrot Cell Suspension Cultures

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Abstract
The responses of suspension-cultured cells of carrot to polyethylene glycol (PEG)-induced water stress were studied after transfer to culture medium containing PEG at concentrations between 0% and 25%. Growth characteristics, cellular osmotic potential and organic solute concentration changes were followed in unadapted cells and in cell lines adapted to growth in various PEG concentrations. A decline in fresh and dry weight increase occurred in unadapted cells with decreasing water potential, while dry weight gain was unaffected in adapted lines. Substantial osmotic adjustment was observed in adapted lines, due mainly to increased glucose, fructose and sucrose. Proline concentration increased up to 40-fold in adapted and 12-fold in unadapted cells and other amino acids including alanine, histidine and arginine showed similar, though smaller, responses. Polyamines and glycinebetaine did not increase significantly in either adapted or unadapted cells. Changes leading to long-term adaptation to water stress are discussed in relation to short-term stress—shock responses.