title: Gibberellins negatively regulate light-induced nitrate reductase activity in Arabidopsis seedlings.
abstract: In the present study, the role of phytohormone gibberellins (GAs) on regulating the nitrate reductase (NR) activity was tested in Arabidopsis seedlings. The NR activity in light-grown Col-0 seedlings was reduced by exogenous GA₃ (an active form of GAs), but enhanced by exogenous paclobutrazol (PAC, a gibberellin biosynthesis inhibitor), suggesting that GAs negatively regulate the NR activity in light-grown seedlings. Light is known to influence the NR activity through both photosynthesis and phytochromes. When etiolated seedlings were transferred to white or red light, both exogenously applied GA₃ and PAC were found to function on the NR activity only in the presence of sucrose, implying that GAs are not involved in light signaling-induced but negatively regulate photoproducts-induced NR activity. NR is regulated by light mainly at two levels: transcript level and post-translational level. Our reverse transcription (RT)-PCR assays showed that GAs did not affect the transcript levels of NIA1 and NIA2, two genes that encode NR proteins. But the divalent cations (especially Mg²⁺) were required for GAs negative regulation of NR activity, in view of the importance of divalent cations during the process of post-translational regulation of NR activity, which indicates that GAs very likely regulate the NR activity at the post-translational level. In the following dark-light shift analyses, GAs were found to accelerate dark-induced decrease, but retard light-induced increase of the NR activity. Furthermore, it was observed that application of G₃ or PAC could impair diurnal variation of the NR activity. These results collectively indicate that GAs play a negative role during light regulation of NR activity in nature.
authors.affiliation: School of Life Sciences, Lanzhou University, Lanzhou, Gansu 730000, People's Republic of China.
authors.forename: Yongqiang
authors.initials: Y
authors.lastname: Zhang
authors.forename: Zhongjuan
authors.initials: Z
authors.lastname: Liu
authors.forename: Rongzhi
authors.initials: R
authors.lastname: Liu
authors.forename: Liguang
authors.initials: L
authors.lastname: Wang
authors.forename: Yurong
authors.initials: Y
authors.lastname: Bi
mesh_terms: D017360:Arabidopsis / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000235:genetics; D005875:Gibberellins / Q000494:pharmacology*; D008027:Light; D050901:Nitrate Reductase / Q000378:metabolism*; D009565:Nitrate Reductases / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D036226:Seedlings / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D014230:Triazoles / Q000494:pharmacology
chemical_list: D005875:Gibberellins; D014230:Triazoles; C053370:paclobutrazol; D009565:Nitrate Reductases; D050901:Nitrate Reductase