Wound-induced increases in phenolic content of fresh-cut lettuce is reduced by a short immersion in aqueous hypertonic solutions

Wounding during the preparation of fresh-cut lettuce induces the synthesis of phenylalanine ammonia lyase (PAL, EC 4.3.1.5), and the synthesis and accumulation of specific phenolic compounds (e.g., chlorogenic acid) that contribute to subsequent tissue browning. Increased PAL activity and phenolic content were not induced in non-wounded lettuce that was kept in close proximity to wounded tissue through either a vapor or aqueous signal. The phenolic content of fresh-cut Iceberg and Romaine lettuce was reduced in tissue pieces immediately immersed for 2 h in hypertonic aqueous mannitol solutions (0.3 /0.9 M) after cutting. Re-wounding tissue segments 1 day after the initial excision did not produce a second rise in PAL activity in those pieces in which wound-induced increases in PAL activity had been suppressed by a previous soak in hypertonic aqueous mannitol solutions. It appears that the hypertonic solution did not cause the loss of a portion of the wound signal through efflux of water from the tissue, but rather induced a general stress-related resistance to further abiotic stresses. # 2003 Elsevier B.V. All rights reserved.