Wang Chunyan, Fan Longquan, Gao Hongbo, Wu Xiaolei, Li Jingrui, Lv Guiyun, Gong Binbin
College of Horticulture, Agricultural University of Hebei, Lekai South Street 2596, Baoding 071001, Hebei, China.
College of Horticulture, Agricultural University of Hebei, Lekai South Street 2596, Baoding 071001, Hebei, China.
Plant Physiol Biochem. 2014 Sep;82:17-26. doi: 10.1016/j.plaphy.2014.04.018. Epub 2014 May 5.
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.
我们检测了在有或没有5 mM γ-氨基丁酸（GABA）的对照和缺氧条件下甜瓜根中与多胺（PA）代谢相关的生理变化和基因表达。经过缺氧处理的根中谷氨酸脱羧酶（GAD）活性和内源性GABA浓度显著增加。同时，PA的生物合成和降解加速，基因表达和酶活性更高。然而，在缺氧+GABA处理的根中，内源性GABA浓度大幅快速增加。这通过对GAD活性的反馈抑制导致谷氨酸（Glu）浓度显著增加。缺氧+GABA处理提高了精氨酸（Arg）、鸟氨酸（Orn）和蛋氨酸（Met）水平，促进了根中酶基因表达水平以及精氨酸脱羧酶（ADC）、鸟氨酸脱羧酶（ODC）和S-腺苷甲硫氨酸脱羧酶（SAMDC）的活性。从第二天到第八天，缺氧+GABA处理显著增加了游离腐胺（Put）、亚精胺（Spd）和精胺（Spm）的浓度，促进了PA向可溶性共轭和不溶性结合形式的转化。然而，通过显著降低二胺氧化酶（DAO）和多胺氧化酶（PAO）的基因表达和活性，缺氧+GABA处理的根中PA降解受到显著抑制。然而，与缺氧条件相比，外源GABA在对照中的作用有所降低。我们的数据表明，外源GABA对缺氧的缓解作用与PA代谢的生理调节密切相关。我们提出了一种潜在的负反馈机制，即缺氧和外源GABA的联合作用导致内源性GABA水平升高，通过加速PA生物合成和转化以及防止甜瓜植株中PA降解来减轻缺氧损伤。
