THE PHYSIOLOGICAL-STATE OF SUSPENSION-CULTURED CELLS AFFECTS THE EXPRESSION OF THE BETA-GLUCURONIDASE GENE FOLLOWING TRANSFORMATION OF TALL FESCUE (FESTUCA-ARUNDINACEA) PROTOPLASTS

Both the stage of the growth cycle and the age of the cell culture used to isolate protoplasts had a pronounced effect on both transient and stable expression of the GUS gene. A level of GUS gene transient expression of 9000 pmol 4MU/mu g protein/h and a frequency of GUS gene stable expression of 5.72% were obtained with protoplasts isolated from suspension cultures 10-20 weeks after initiation and 3-4 days after subculturing when an optimized transformation protocol and a rice actin 1 promoter-uidA gene construct were used. The effect of the cell growth cycle on GUS gene transient expression was closely correlated with the growth rate and the rate of protein synthesis in cell cultures whereas prolonged subculturing of the cells resulted in a gradual decline in both transient and stable expression. The length of time cells were digested in cell wall digestion enzyme and the osmolarity of the transformation medium were found to critically affect both the level of transient and stable GUS gene expression. The composition and osmolarity of the protoplast culture medium was less critical for transient GUS gene expression although the osmolarity of the medium was shown to have a significant effect on stable expression of the GUS gene.