title: Growth and phenolic compounds of Lactuca sativa L. grown in a closed-type plant production system with UV-A, -B, or -C lamp.
abstract: BACKGROUND
  The production of high-quality crops based on phytochemicals is a strategy for accelerating the practical use of plant factories. Previous studies have demonstrated that ultraviolet (UV) light is effective in improving phytochemical production. This study aimed to determine the effect of various UV wavelengths on growth and phenolic compound accumulation in lettuce (Lactuca sativa L.) grown in a closed-type plant production system.
  
  
  RESULTS
  Seven days, 1 day and 0.25 day were determined as the upper limit of the irradiation periods for UV-A, -B, and -C, respectively, in the lettuce based on physiological disorders and the fluorescence parameter F(v)/F(m). Continuous UV-A treatment significantly induced the accumulation of phenolic compounds and antioxidants until 4 days of treatment without growth inhibition, consistent with an increase in phenylalanine ammonia lyase (PAL) gene expression and PAL activity. Repeated or gradual UV-B exposure yielded approximately 1.4-3.6 times more total phenolics and antioxidants, respectively, than the controls did 2 days after the treatments, although both treatments inhibited lettuce growth. Repeated UV-C exposure increased phenolics but severely inhibited the growth of lettuce plants.
  
  
  CONCLUSIONS
  Our data suggest that UV irradiation can improve the accumulation of phenolic compounds with antioxidant properties in lettuce cultivated in plant factories.
authors.affiliation: Department of Horticultural Science, Chungbuk National University, Cheongju, 361-763, South Korea.
authors.forename: Min-Jeong
authors.initials: MJ
authors.lastname: Lee
authors.forename: Jung Eek
authors.initials: JE
authors.lastname: Son
authors.forename: Myung-Min
authors.initials: MM
authors.lastname: Oh
mesh_terms: D000383:Agriculture / Q000379:methods*; D000975:Antioxidants / Q000378:metabolism*; D004032:Diet; D015870:Gene Expression; D006801:Humans; D018545:Lactuca / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects*; D010636:Phenols / Q000378:metabolism*; D010650:Phenylalanine Ammonia-Lyase / Q000235:genetics / Q000378:metabolism*; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D000975:Antioxidants; D010636:Phenols; D010650:Phenylalanine Ammonia-Lyase
keywords: antioxidants; growth; lettuce; phenolics; plant factory; ultraviolet