Wallace W, Secor J, Schrader L E
Department of Agronomy, University of Wisconsin, Madison, Wisconsin 53706.
Plant Physiol. 1984 May;75(1):170-5. doi: 10.1104/pp.75.1.170.
Soybean (Glycine max [L.] Merr) leaves contain a low level (0.05 micromole per gram fresh weight) of gamma-aminobutyric acid (Gaba) but the concentration of this non-protein amino acid increased to 1 to 2 micromoles per gram fresh weight within 5 minutes after transfer of plants or detached leaves from 33 degrees C to 22 degrees C or lower temperatures. A parallel decrease occurred in the concentration of glutamate. Accumulation of Gaba was also triggered by mechanical damage to the soybean leaves, but in plants subjected to a gradual reduction in temperature (2 degrees C per minute) only a small increase in Gaba occurred. A rapid increase in the concentration of alanine and decrease in glycine occurred upon transfer of the soybean plants to darkness and was not influenced by temperature. When plants were returned to normal growing conditions, all changes in amino acid concentrations were fully reversed in 1 hour.In soybean leaf discs incubated with [(14)C]glutamate, a rapid accumulation of [(14)C]Gaba was detected, and glutamate decarboxylase activity of the soybean leaf considerably exceeded (>30-fold) that of Gaba pyruvate transaminase. Part of the transaminase was localized in the mitochondria, but glutamate decarboxylase was not associated with any organelle or membrane component of the leaf cell. We consider that Gaba accumulation results from some change in intracellular compartmentation of the cell triggered by low temperature shock or mechanical damage. The accumulation of alanine due to a light-dark transition could be accounted for by transamination. [(14)C]Alanine formation was demonstrated when soybean leaf extracts were incubated with glutamate, aspartate, or serine and [(14)C]pyruvate.The changes in amino acid concentrations described for soybean leaves were demonstrated for all the vegetative tissues of the soybean plant and at variable rates in the leaves of a range of plant species. The response in detached tomato (Lycopersicon esculentum Mill.) leaves was of a similar magnitude to soybean. Thus, precautions are necessary to minimize changes in amino acid composition induced by manipulation and extraction of plant material.
大豆（Glycine max [L.] Merr）叶片中γ-氨基丁酸（Gaba）含量较低（每克鲜重0.05微摩尔），但当将植株或离体叶片从33℃转移至22℃或更低温度后5分钟内，这种非蛋白质氨基酸的浓度会增至每克鲜重1至2微摩尔。谷氨酸浓度则会相应降低。对大豆叶片的机械损伤也会引发Gaba的积累，但在温度逐渐降低（每分钟2℃）的植株中，Gaba仅有少量增加。将大豆植株转移至黑暗环境时，丙氨酸浓度迅速增加，甘氨酸浓度降低，且不受温度影响。当植株恢复到正常生长条件时，氨基酸浓度的所有变化在1小时内完全逆转。在用[¹⁴C]谷氨酸孵育的大豆叶圆片中，检测到[¹⁴C]Gaba迅速积累，且大豆叶片的谷氨酸脱羧酶活性大大超过（>30倍）Gaba丙酮酸转氨酶活性。部分转氨酶定位于线粒体中，但谷氨酸脱羧酶与叶细胞的任何细胞器或膜成分均无关联。我们认为，Gaba的积累是由低温冲击或机械损伤引发的细胞内区室化的某些变化导致的。光暗转变导致的丙氨酸积累可通过转氨作用来解释。当大豆叶片提取物与谷氨酸、天冬氨酸或丝氨酸以及[¹⁴C]丙酮酸一起孵育时，可证明[¹⁴C]丙氨酸的形成。大豆叶片中描述的氨基酸浓度变化在大豆植株的所有营养组织中均有体现，并且在一系列植物物种的叶片中变化速率不同。离体番茄（Lycopersicon esculentum Mill.）叶片的反应程度与大豆相似。因此，必须采取预防措施，以尽量减少因处理和提取植物材料而引起的氨基酸组成变化。
