Souza Sarah C R, Mazzafera Paulo, Sodek Ladaslav
Department of Plant Biology, Institute of Biology, University of Campinas-UNICAMP, PO Box 6109, Campinas, SP, 13083-970, Brazil.
Amino Acids. 2016 May;48(5):1285-95. doi: 10.1007/s00726-016-2179-2. Epub 2016 Jan 29.
Nitrogen fixation of the nodule of soybean is highly sensitive to oxygen deficiency such as provoked by waterlogging of the root system. This study aimed to evaluate the effects of flooding on N metabolism in nodules of soybean. Flooding resulted in a marked decrease of asparagine (the most abundant amino acid) and a concomitant accumulation of γ-aminobutyric acid (GABA). Flooding also resulted in a strong reduction of the incorporation of (15)N2 in amino acids. Nodule amino acids labelled before flooding rapidly lost (15)N during flooding, except for GABA, which initially increased and declined slowly thereafter. Both nitrogenase activity and the expression of nifH and nifD genes were strongly decreased on flooding. Expression of the asparagine synthetase genes SAS1 and SAS2 was reduced, especially the former. Expression of genes encoding the enzyme glutamic acid decarboxylase (GAD1, GAD4, GAD5) was also strongly suppressed except for GAD2 which increased. Almost all changes observed during flooding were reversible after draining. Possible changes in asparagine and GABA metabolism that may explain the marked fluctuations of these amino acids during flooding are discussed. It is suggested that the accumulation of GABA has a storage role during flooding stress.
大豆根瘤的固氮作用对缺氧高度敏感，例如根系受涝引发的缺氧。本研究旨在评估水淹对大豆根瘤氮代谢的影响。水淹导致天冬酰胺（最丰富的氨基酸）显著减少，同时γ-氨基丁酸（GABA）积累。水淹还导致氨基酸中（15）N2掺入量大幅降低。水淹前标记的根瘤氨基酸在水淹期间迅速失去（15）N，但GABA除外，其最初增加，之后缓慢下降。水淹时固氮酶活性以及nifH和nifD基因的表达均大幅降低。天冬酰胺合成酶基因SAS1和SAS2的表达降低，尤其是前者。除GAD2增加外，编码谷氨酸脱羧酶（GAD1、GAD4、GAD5）的基因表达也受到强烈抑制。排水后，水淹期间观察到的几乎所有变化都是可逆的。讨论了天冬酰胺和GABA代谢中可能解释水淹期间这些氨基酸显著波动的变化。研究表明，GABA的积累在水淹胁迫期间具有储存作用。
