The drop in protein level as an index of senescence in tobacco leaf disks was examined in the dark in the presence of BA and/or inhibitors of protein synthesis. Cycloheximide at 10−6–10−5Mand 10−5g/ml actinomycin-D accelerated the senescence and interfered with the anti-senescence action of 10−6MBA. Chloramphenicol (10−8–10−4M) and puromycin (10−8–10−4M) did not modify the senescence or the action of BA. Cycloheximide was more effective at earlier stages of the dark culture of the disks. The rate of14C-leucine incorporation into the protein fraction was increased by BA and decreased with senescence, and this drop was removed by BA. The incorporation was also suppressed by cycloheximide equally in the presence and absence of BA. The drop in labeled protein of the disks during the chasing period was retarded by not only BA but cycloheximide also. The conclusion reached, based on these and relevant findings, was that BA affects the anti-senescence action by promoting synthesis and at the same time inhibiting d
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