Transcriptional and translational regulation of defense enzymes induced by neem fruit extract in tomato

Abstract

Fruit extract of neem (Azadirachta indica A. Juss.) induces defense response through enhanced activities of phenylalanine ammonia-lyase (PAL), tyrosine ammonia-lyase (TAL), polyphenol oxidase (PPO), peroxidase (POX) along with isoenzymes of PPO and POX in tomato. The increase in PAL, POX activity and induction of specific isoenzymes of acidic PPO, POX and basic POX by neem fruit extract were completely inhibited due to pre-treatment with actinomycin D or cycloheximide. Their activation was found to be time course-dependent. Synergistic enhancement of TAL activity by neem extract was observed when plants were pre-treated with cycloheximide, whereas similar observations were made for PPO activity by neem extract when plants were pre-treated with either actinomycin D or cycloheximide. These results suggest that the enhanced activities of defense enzymes and altered isoenzyme patterns of PPO and POX by neem extract was regulated at both transcriptional and translational levels which may contribute to the induction of defense responses in tomato.