ศูนย์นวัตกรรมเทคโนโลยีหลังการเก็บเกี่ยว

Identification of a phenylalanine ammonia-lyase inactivating factor in harvested head lettuce (Lactuca sativa).

Ritenour, M. A.; Saltveit, M. E.;

Physiologia Plantarum Year: 1996 Vol: 97 Issue: 2 Pages: 327-331 Ref: 20 ref.

1996

บทคัดย่อ

Exposure of harvested crisphead and Iceberg lettuce leaf tissue to hormonal levels of ethylene (10 micro l/litre) at 5 deg C promoted the de novo synthesis of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) and an increase in its activity. It also promoted the appearance of the postharvest physiological disorder called russet spotting (RS). Discontinuing ethylene exposure after 4 days resulted in a rapid decline in PAL activity, which was delayed by treating excised mid-rib leaf tissue with actinomycin D [dactinomycin] or cycloheximide at 5 deg C. Only cycloheximide delayed the loss of PAL activity in tissue that was transferred from 5 to 15 deg C. Activity of PAL from Rhodotorula glutinis was slowly lost during incubation in buffer alone, but there was a logarithmic decline in its activity over time when it was incubated with aliquots of the resuspended 10 000 g pellet from homogenized lettuce tissue affected by RS. The in vitro loss in PAL activity was 9 times higher in extracts from lettuce sho

wing RS symptoms than from control lettuce, boiled samples or the buffer control. The PAL-inactivating factor isolated from lettuce affected with RS had a pH optimum around 8.0. It was concluded that the rapid loss in PAL activity after the discontinuation of exposure to ethylene is dependent on the de novo synthesis of a PAL-inactivating factor.