Phenylalanine ammonia‐lyase activity in callus cultures of Pinus elliotii

Phenylalanine ammonia‐lyase (PAL) activity increased 8‐ to 12‐fold in pine (Pinus elliotii Engelm.) callus tissue within 2 days after subculturing on fresh medium. Factors such as increasing the sucrose content of the media, imposing additional tissue in jury or subculturing more frequently did not cause additional stimulation of PAL activity. The rapid increase in PAL activity appeared to be due to enzyme activation, since cycloheximide did not appreciably reduce the stimulation of PAL activity. The subsequent loss of increased PAL activity with age was reduced by cycloheximide and a cool growth environment.