Department of Crop Science and ‡Department of Bio-Environmental Chemistry, Chungnam National University , 99 Daehak-ro, Yuseong-gu, Daejeon 305-764, Republic of Korea.
J Agric Food Chem. 2013 Sep 11;61(36):8624-31. doi: 10.1021/jf401956v. Epub 2013 Aug 27.
Glutamate decarboxylase (GAD; EC 4.1.1.15) is an important enzyme in γ-aminobutyric acid (GABA) biosynthesis. Here we report the influence of light on amino acid accumulation and investigate the molecular mechanism by which light influences GABA biosynthesis at the seedling stage of two mustard (Brassica juncea) cultivars (green-leaf and purple-leaf). Gene expression profiles of four GAD-encoding genes (GAD1, GAD2, GAD4a, and GAD4b) and their impact on GABA biosynthesis were analyzed. Light exerted an obvious influence on amino acid accumulation in mustard seedlings. GAD gene expression was also significantly regulated by light/dark or dark treatment, which differentially regulated GABA biosynthesis in B. juncea seedlings. High-performance liquid chromatography (HPLC) revealed that the seeds of purple cultivars contain a higher amount of free amino acids and GABA than do the seeds of green cultivars. After seed germination, however, the accumulation of free amino acids peaked in dark-treated seedlings on day 9 in both cultivars, whereas GABA synthesis peaked at 9 days under light conditions. This study may provide a foundation for understanding the effect of light on amino acids, particularly GABA biosynthesis in Brassica plants.
谷氨酸脱羧酶（GAD；EC 4.1.1.15）是γ-氨基丁酸（GABA）生物合成中的一种重要酶。在这里，我们报告了光对氨基酸积累的影响，并研究了光在两个芥菜（芥菜）品种（绿叶和紫叶）幼苗阶段影响 GABA 生物合成的分子机制。分析了四个 GAD 编码基因（GAD1、GAD2、GAD4a 和 GAD4b）的基因表达谱及其对 GABA 生物合成的影响。光对芥菜幼苗中氨基酸积累有明显的影响。GAD 基因表达也明显受到光/暗或暗处理的调控，这对芥菜幼苗中 GABA 的生物合成有不同的调控作用。高效液相色谱法（HPLC）显示，与绿叶品种相比，紫叶品种的种子中含有更高含量的游离氨基酸和 GABA。然而，在种子发芽后，在两种品种中，黑暗处理的幼苗在第 9 天达到游离氨基酸积累的峰值，而在光照条件下，GABA 的合成在第 9 天达到峰值。本研究可能为理解光对氨基酸，特别是 Brassica 植物中 GABA 生物合成的影响提供基础。
