QUICK SCREENING OF PHOSPHINOTHRICIN-RESISTANT TRANSGENIC TOBACCO PLANTS USING CHLOROPHYLL FLUORESCENCE

The effects of a herbicide, phosphinothricin (PPT), on the photosynthe tic apparatus of tobacco (Nicotiana tabacum L. cv. Xanthi) leaves were investigated using a chlorophyll fluorescence assay. Among parameters analyzed in this assay, decreases in Fm/Fo and qQ and increases in Fv and qR were observed in wild-type leaves incubated in the presence of 100 mg/L PPT in the light (30 mu mol . m(-2). s(-1)). Fm/Fo was chose n as a sensitive parameter for screening, and the value was reduced in half within 12 h after the treatment of PPT. Because the rapid decrea se in Fm/Fo was presumed to be due to glyoxylate accumulation rather t han the accumulation of ammonia, the PPT toxicity was monitored under conditions favorable for photorespiration. Ln the high light (70 mu mo l . m(-2). s(-1)), a significant decrease in Fm/Fo was observed within 3 h after the PPT treatment. By elevating the temperature from 26 deg rees C to 36 degrees C, an increase in PPT toxicity was also observed. In tobacco plants transformed with the bar gene coding for the PPT-ac etyl transferase (PAT), no significant changes in Fm/Fo were observed, and all the screened transgenic plants showed PAT activities. These r esults suggest that bar gene-containing plants can be screened very qu ickly by employing the chlorophyll fluorescence assay under photorespi ratory conditions.