Glyphosate tolerance of cultured Corydalis sempervirens cells is acquired by an increased rate of transcription of 5-enolpyruvylshikimate 3-phosphate synthase as well as by a reduced turnover of the enzyme.

Cell cultures of Corydalis sempervirens, tolerant to the herbicide glyphosate, have a 30-40-fold increased level of the herbicide's target enzyme 5-enolpyruvylshikimate 3-phosphate (EPSP) synthase, a ten-fold enhanced level of the corresponding mRNA but no amplification of the gene (Holländer-Czytko et al., Plant Mol Biol 11 (1988) 215-220). The increase at the transcriptional level is due to a higher rate of transcription of the gene, which was observed in run-off transcription assays with isolated nuclei. The further amplification at the protein level is the result of stabilization of the enzyme by the herbicide. In the presence of glyphosate the half-life of EPSP synthase was doubled leading to higher levels of both protein and enzyme activity. Overproduction of the enzyme in adapted cultures is stable at the transcriptional level, as cells from adapted cultures grown in the absence of glyphosate for three years still display an about ten-fold higher enzyme activity and transcript level than non-adapted cultures.