Verma Giti, Sharma Samir
Department of Biochemistry, University of Lucknow, Lucknow 226007 [U.P], India.
Indian J Biochem Biophys. 2010 Aug;47(4):249-53.
Plant cell wall expresses monoamine oxidases (MAOs) that catalyze oxidation of secreted amines and produce H2O2 in the process. The H2O2, so produced is used by cell wall peroxidases for lignification of cell wall or for plant defense. The natural substrates for these MAOs are elusive, but polyamines and certain catecholamines have been proposed as candidates. Reactive oxygen species are also known to act as signaling molecules controlling plant metabolism. Mungbean (Vigna radiata) has long served as the plant model of choice while studying molecular programs followed during germination and seed development. In this study, we tested the effect of externally added MAO substrates epinephrine and H2O2 on storage protein mobilization in germinating seeds of Vigna radiata. The seeds were imbibed in the presence of 50 microM epinephrine and 10 microM H2O2. These low concentrations of the two compounds were used to exclude direct effects on proteolysis and were arrived at after testing a range of the two and choosing the most effective concentration. These seeds showed 11% and 7% decrease in fresh weight respectively, indicating greater storage mobilization and a corresponding 19% and 46% increase in axis length as compared to untreated seeds. Soluble protein in seeds treated with epinephrine and H2O2 decreased significantly by 34% and 33% as compared to untreated seeds. Electrophoretic analysis of seed proteins revealed a startling and selective depletion of storage proteins in treated seeds. The results indicated a clear involvement of H2O2 in storage protein mobilization in the cotyledons. We propose that H2O2 generated within cell walls of seeds serves as a signaling molecule guiding germination events, including protein reserve mobilization.
植物细胞壁表达单胺氧化酶（MAOs），其催化分泌胺的氧化并在此过程中产生过氧化氢。如此产生的过氧化氢被细胞壁过氧化物酶用于细胞壁的木质化或植物防御。这些单胺氧化酶的天然底物难以捉摸，但多胺和某些儿茶酚胺已被提出作为候选底物。活性氧也被认为是控制植物代谢的信号分子。在研究发芽和种子发育过程中遵循的分子程序时，绿豆（Vigna radiata）长期以来一直是首选的植物模型。在本研究中，我们测试了外部添加的单胺氧化酶底物肾上腺素和过氧化氢对绿豆发芽种子中储存蛋白动员的影响。种子在50微摩尔肾上腺素和10微摩尔过氧化氢存在下吸水。使用这两种化合物的低浓度来排除对蛋白水解的直接影响，这是在测试了一系列浓度并选择最有效浓度后得出的。与未处理的种子相比，这些种子的鲜重分别下降了11%和7%，表明储存物质动员增加，相应地轴长增加了19%和46%。与未处理的种子相比，用肾上腺素和过氧化氢处理的种子中的可溶性蛋白分别显著下降了34%和33%。种子蛋白的电泳分析显示，处理过的种子中储存蛋白出现了惊人的选择性消耗。结果表明过氧化氢明显参与了子叶中储存蛋白的动员。我们提出，种子细胞壁内产生的过氧化氢作为一种信号分子，引导包括蛋白质储备动员在内的发芽事件。
