title: Antioxidant responses of cucumber (Cucumis sativus) to photoinhibition and oxidative stress induced by norflurazon under high and low PPFDs.
abstract: Photooxidative damage is exacerbated by norflurazon (NF), which blocks carotenoid biosynthesis. This study examined the influence of photosynthetic photon flux density (PPFD) on the overall responses of both non-enzymatic and enzymatic antioxidants to NF-caused oxidative damage in leaves of cucumber (Cucumis sativus). Seven-day-old cucumber plants were exposed to NF under either low PPFD (30 µmol m(-2) s(-1)) or high PPFD (300 µmol m(-2) s(-1)) for 3 days. The NF plants exposed at high PPFD had lower levels of F(v)/F(m) ratio, quantum yield of electron transport, and 33-kDa protein of photosystem II as compared with the NF plants at low PPFD. In the NF plants, there was a reduction in total chlorophylls and carotenoids except newly formed zeaxanthin in either PPFD. The NF plants at high PPFD resulted in less level of photochemical quenching, q(P), and Stern-Volmer quenching, NPQ, than those of the plants at low PPFD, whereas both plants had similar level of non-photochemical quenching coefficient, q(N). However, the level of PPFD did not significantly affect the NF-caused induction of antioxidant enzymes including peroxidase, superoxide dismutase, glutathione reductase, and ascorbate peroxidase.
authors.affiliation: Screening Research Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yusung, Taejon, South Korea
authors.initials: S
authors.lastname: Jung
authors.initials: JS
authors.lastname: Kim
authors.initials: KY
authors.lastname: Cho
authors.initials: GS
authors.lastname: Tae
authors.initials: BG
authors.lastname: Kang