Selection and physiology of cell cultures of Douglas-fir grown under conditions of water stress.

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) cell cultures sampled 3, 6, or 9 days after subculture in nutrient medium were able to survive subsequent subculture in a medium containing 15% polyethylene glycol (PEG) (M(r) 6000-8000) (-1.21 MPa), whereas cell sampled 12 or 16 days after subculture in nutrient medium became senescent when transferred to a medium containing 15% PEG. Cells sampled after subculture for 3, 6, or 9 days in nutrient medium had lower fresh weight/dry weight ratios, lower osmotic potentials, smaller cell diameters, and higher turgor pressures than cells sampled after 12 or 16 days subculture in nutrient medium. Cells surviving subculture to a medium containing 15% PEG did not increase in dry weight for 5 weeks even though the medium was exchanged every 7 days. After 5 weeks, however, dry weight growth resumed and reached 75% of the level attained by control cells grown on PEG-free medium. Long-term growth on a medium containing 15% PEG (PEG-selected cells) could only be sustained if the medium was supplemented with 30 mM glutamine. The PEG-selected cells grew in small clusters, were isodiametric, and had chlorophyll contents 50% higher than unselected cells. The PEG-selected cells also showed lowered cellular osmotic potentials, presumably due to osmoregulation. Turgor pressures of PEG-selected cells were greater than or equal to those of unselected cells.