A RAPID AND SENSITIVE METHOD TO EVALUATE GENOTYPE SPECIFIC TOLERANCE TO PHOSPHINOTHRICIN-BASED SELECTIVE AGENTS IN CEREAL TRANSFORMATION

Isolated scutella from immature embryos of barley and wheat, commonly used as targets for genetic transformation, revealed a considerable va riation in susceptibility towards bialaphos and glufosinate (phosphino thricin) among a range of cultivars investigated. Using the pH indicat or chlorophenol-red, a rapid assay was established to determine within two days genotype specific basal level of tolerance based on spectrop hotometric determination of colour change in the medium. A strong corr elation was observed using the response of scutella incubated for 3 we eks on callus induction medium containing different amounts of bialaph os with their ability to change colour of chlorophenol-red in the medi um within two days. Thus it can be concluded that the amount of bialap hos which is needed by a given genotype to achieve an absorbance of 0. 5 at 575 nm, represents a tight selection condition for the appropiate genotype. The colour change of the medium caused by phosphinothricin based agents after exposure of explants results from the interaction b etween acidification due to metabolic processes and rise of pH caused by ammonia accumulation due to inhibition of glutamine synthetase.