Serraj Rachid, Shelp Barry J, Sinclair Thomas R
R. Serraj, Laboratoire de Physiologie Végétale, Dépt de Biologie, Faculté des Sciences-Semlalia, BP S 15 Marrakech, Morocco; B. J. Shelp, Dept of Horticultural Science, Univ. of Guelph, Guelph, ON, N1G 2W1, Canada; T. R. Sinclair (corresponding author, e-mail
Physiol Plant. 1998 Jan;102(1):79-86. doi: 10.1034/j.1399-3054.1998.1020111.x.
Nitrogen fixation and nodule permeability to O diffusion are decreased by drought stress. Since γ-aminobutyric acid (GABA) synthesis is rapidly stimulated by a variety of stress conditions including hypoxia, it was hypothesized that decreased O availability in nodules stimulates glutamate decarboxylase (GAD) activity (EC 4.1.1.15), thereby resulting in GABA accumulation. First, the amino acid composition of xylem sap was determined in plants subjected to soil water deficits. While the xylem sap concentration of several amino acids increased when the plant was subjected to a water deficit, the greatest increase was in GABA. GABA accumulation was examined in response to stress induced by hypoxia or the addition of polyethylene glycol (PEG) to the nutrient solution. The exposure of soybean nodules to hypoxia for 6 h enhanced the GABA concentration by 6-fold, but there was no change in GABA concentration in response to the PEG treatment. No major changes in the in vitro GAD activity were measured in nodule cytosol or bacteroids. The present data do not support the hypothesis that decreased nodule O permeability and a resulting O deprivation inside nodules may stimulate in vitro GAD activity and thus GABA accumulation. However, the data could indicate a possible effect of hypoxia and drought stress on the in vivo activity of GAD.
干旱胁迫会降低固氮作用以及根瘤对氧气扩散的通透性。由于包括缺氧在内的多种胁迫条件都会迅速刺激γ-氨基丁酸（GABA）的合成，因此有人推测，根瘤中氧气供应的减少会刺激谷氨酸脱羧酶（GAD，EC 4.1.1.15）的活性，从而导致GABA积累。首先，测定了遭受土壤水分亏缺的植物木质部汁液的氨基酸组成。当植物遭受水分亏缺时，几种氨基酸在木质部汁液中的浓度会增加，其中增加最多的是GABA。研究了对缺氧或在营养液中添加聚乙二醇（PEG）诱导的胁迫的响应中GABA的积累情况。大豆根瘤暴露于缺氧环境6小时后，GABA浓度提高了6倍，但PEG处理对GABA浓度没有影响。在根瘤细胞质或类菌体中未检测到体外GAD活性的重大变化。目前的数据不支持以下假设：根瘤氧气通透性降低以及由此导致的根瘤内部氧气剥夺可能会刺激体外GAD活性，进而导致GABA积累。然而，这些数据可能表明缺氧和干旱胁迫对GAD体内活性可能有影响。
