title: Polyamine biosynthesis and degradation are modulated by exogenous gamma-aminobutyric acid in root-zone hypoxia-stressed melon roots.
abstract: We detected physiological change and gene expression related to PA metabolism in melon roots under controlled and hypoxic conditions with or without 5 mM GABA. Roots with hypoxia treatment showed a significant increase in glutamate decarboxylase (GAD) activity and endogenous GABA concentration. Concurrently, PA biosynthesis and degradation accelerated with higher gene expression and enzymes activity. However, endogenous GABA concentrations showed a large and rapid increase in Hypoxia + GABA treated roots. This led to a marked increase in Glu concentration by feedback inhibition of GAD activity. Hypoxia + GABA treatment enhanced arginine (Arg), ornithine (Orn) and methionine (Met) levels, promoting enzyme gene expression levels and arginine decarboxylase (ADC), ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) activities in roots. Hypoxia + GABA treatment significantly increased concentrations of free putrescine (Put), spermidine (Spd) and spermine (Spm) from day two to eight, promoting the PA conversion to soluble conjugated and insoluble bound forms. However, PA degradation was significantly inhibited in hypoxia + GABA treated roots by significantly decreasing gene expression and activity of diamine oxidase (DAO) and polyamine oxidase (PAO). However, exogenous GABA showed a reduced effect in control compared with hypoxic conditions. Our data suggest that alleviating effect of exogenous GABA to hypoxia is closely associated with physiological regulation of PA metabolism. We propose a potential negative feedback mechanism of higher endogenous GABA levels from combined effects of hypoxia and exogenous GABA, which alleviate the hypoxia damage by accelerating PA biosynthesis and conversion as well as preventing PA degradation in melon plants.
authors.affiliation: College of Horticulture, Agricultural University of Hebei, Lekai South Street 2596, Baoding 071001, Hebei, China.
authors.forename: Chunyan
authors.initials: C
authors.lastname: Wang
authors.affiliation: College of Horticulture, Agricultural University of Hebei, Lekai South Street 2596, Baoding 071001, Hebei, China.
authors.forename: Longquan
authors.initials: L
authors.lastname: Fan
authors.affiliation: College of Horticulture, Agricultural University of Hebei, Lekai South Street 2596, Baoding 071001, Hebei, China. Electronic address: hongbogao@hebau.edu.cn.
authors.forename: Hongbo
authors.initials: H
authors.lastname: Gao
authors.affiliation: College of Horticulture, Agricultural University of Hebei, Lekai South Street 2596, Baoding 071001, Hebei, China.
authors.forename: Xiaolei
authors.initials: X
authors.lastname: Wu
authors.affiliation: College of Horticulture, Agricultural University of Hebei, Lekai South Street 2596, Baoding 071001, Hebei, China.
authors.forename: Jingrui
authors.initials: J
authors.lastname: Li
authors.affiliation: College of Horticulture, Agricultural University of Hebei, Lekai South Street 2596, Baoding 071001, Hebei, China.
authors.forename: Guiyun
authors.initials: G
authors.lastname: Lv
authors.affiliation: College of Horticulture, Agricultural University of Hebei, Lekai South Street 2596, Baoding 071001, Hebei, China.
authors.forename: Binbin
authors.initials: B
authors.lastname: Gong
mesh_terms: D015687:Cell Hypoxia / Q000502:physiology*; D019662:Cucurbitaceae / Q000187:drug effects* / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects* / Q000378:metabolism*; D011073:Polyamines / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D011073:Polyamines; D005680:gamma-Aminobutyric Acid
keywords: Hypoxia stress; Melon seedlings; PA biosynthesis; PA degradation; γ-Aminobutyric acid