title: Phytochrome- and gibberellin-mediated regulation of abscisic acid metabolism during germination of photoblastic lettuce seeds.
abstract: Germination of lettuce (Lactuca sativa) 'Grand Rapids' seeds is regulated by phytochrome. The action of phytochrome includes alterations in the levels of gibberellin (GA) and abscisic acid (ABA). To determine the molecular mechanism of phytochrome regulation of ABA metabolism, we isolated four lettuce cDNAs encoding 9-cis-epoxycarotenoid dioxygenase (biosynthesis; LsNCED1-LsNCED4) and four cDNAs for ABA 8'-hydroxylase (catabolism; LsABA8ox1-LsABA8ox4). Measurements of ABA and its catabolites showed that a decrease in ABA level coincided with a slight increase in the level of the ABA catabolite phaseic acid after red light treatment. Quantitative reverse transcription-polymerase chain reaction analysis indicated that ABA levels are controlled by phytochrome through down-regulation of LsNCED2 and LsNCED4 expression and up-regulation of LsABA8ox4 expression in lettuce seeds. Furthermore, the expression levels of LsNCED4 decreased after GA(1) treatment, whereas the levels of expression of the other two genes were unaffected. The LsNCED4 expression was also down-regulated by red light in lettuce seeds in which GA biosynthesis was suppressed by AMO-1618, a specific GA biosynthesis inhibitor. These results indicate that phytochrome regulation of ABA metabolism is mediated by both GA-dependent and -independent mechanisms. Spatial analysis showed that after red light treatment, the ABA decrease on the hypocotyl side was greater than that on the cotyledon side of lettuce seeds. Moreover, phytochrome-regulated expression of ABA and GA biosynthesis genes was observed on the hypocotyl side, rather than the cotyledon side, suggesting that this regulation occurs near the photoperceptive site.
authors.affiliation: Course of the Science of Bioresource, United Graduate School of Agricultural Science, Iwate University, Morioka, Iwate, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Sawada
authors.forename: Miki
authors.initials: M
authors.lastname: Aoki
authors.forename: Kentaro
authors.initials: K
authors.lastname: Nakaminami
authors.forename: Wataru
authors.initials: W
authors.lastname: Mitsuhashi
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Tatematsu
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Kushiro
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Koshiba
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kamiya
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Inoue
authors.forename: Eiji
authors.initials: E
authors.lastname: Nambara
authors.forename: Tomonobu
authors.initials: T
authors.lastname: Toyomasu
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D003001:Cloning, Molecular; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D018076:DNA, Complementary; D049308:Dioxygenases; D015870:Gene Expression; D018525:Germination / Q000502:physiology*; D005875:Gibberellins / Q000378:metabolism; D018545:Lactuca / Q000254:growth & development / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000378:metabolism; D008969:Molecular Sequence Data; D010105:Oxygenases / Q000378:metabolism; D010834:Phytochrome / Q000378:metabolism*; D010940:Plant Proteins; D012639:Seeds / Q000254:growth & development / Q000378:metabolism*
chemical_list: D018076:DNA, Complementary; D005875:Gibberellins; D010940:Plant Proteins; D010834:Phytochrome; D000040:Abscisic Acid; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D010105:Oxygenases; D049308:Dioxygenases; C109043:9-cis-epoxy-carotenoid dioxygenase; C107203:abscisic acid 8'-hydroxylase