HEAT-TREATMENT RESULTS IN A LOSS OF TRANSGENE-ENCODED ACTIVITIES IN SEVERAL TOBACCO LINES

Heat treatment (37 degrees C) of transgenic tobacco (Nicotiana tabacum ) plants led to a reversible reduction or complete loss of transgene-e ncoded activities in about 40% of 10 independent transformants carryin g the luciferase-coding region fused to the 35S cauliflower mosaic vir us or the soybean small subunit promoter and the nopaline synthase pro moter driving the neomycin phosphotransferase gene, whereas the other lines had temperature-tolerant activities. Temperature sensitivity or tolerance of transgene-encoded activities was heritable. In some of th e lines, temperature sensitivity of the transgene-encoded activities d epended on the stage of development, occurring in either seedlings (40 % luciferase and 50% neomycin phosphotransferase) or adult plants (bot h 40%). The phenomenon did not correlate with copy numbers or the home -or hemizygous state of the transgenes. In lines harboring a temperatu re-sensitive luciferase activity, reduction of bioluminescence was obs erved after 2 to 3 h at 37 degrees C. Activity was regained after 2 h of subsequent cultivation at 25 degrees C. Irrespective of the reactio n to the heat treatment, the level of luciferase RNA was slightly incr eased at 37 degrees C. Only in lines showing temperature sensitivity o f transgene-encoded activities was the amount of luciferase and neomyc in phosphotransferase strongly reduced. In sterile culture, heat treat ment for 15 d did not cause visible damage or changes in plant morphol ogy. In all plants tested a slight induction of the heat-shock respons e was observed at 37 degrees C.