Plant Toxicology and Molecular Biology of Microorganism, Faculty of Sciences of Bizerta, 7021, Zarzouna, Tunisia.
Department of Biochemistry, Institute of General and Molecular Biology, Nicolaus Copernicus University, ul. Gagarina 9, 87-100, Torún, Poland.
J Plant Physiol. 2018 Jul;226:64-76. doi: 10.1016/j.jplph.2018.02.009. Epub 2018 Apr 16.
This work aims to give more insight into mechanisms of action of cadmium (Cd) on germinating pea seeds (Pisum sativum L. var. douce province), specifically the different ways by which Cd cations may interfere with the principal factors involved during germination process, notably storage proteins mobilization, amino acids freeing and proteolytic activities. Obtained results revealed that the process of hydrolysis of main storage proteins showed a significant disruption, which resulted in the decrease of the release of free amino acids, thus imposing a lack in nitrogen supply of essential nutrients to growing embryo under Cd stress. This hypothesis was evidenced by Cd-induced changes occurring in main purified protein fractions; Albumins, Legumins and Vicilins, during their breakdown. Besides, at enzymatic level, the activities of main proteases responsible for this hydrolysis were altered. Indeed, assays using synthetic substrates and specific protease inhibitors followed by protease activity measurements demonstrated that Cd inhibited drastically the total azocaseinolytic activity (ACA) and activities of different proteolytic classes: cysteine-, aspartic-, serine- and metallo-endopeptidases (EP), leucine- and proline-aminopeptidases (LAP and PAP, respectively), and glycine-carboxypeptidases (Gly-CP). The data here presented may suggest that the vulnerability of the embryonic axes towards Cd toxicity could be explained as a result of eventual disruption of metabolic pathways that affect mobilization of reserves and availability of nutrients. In vitro studies suggest that Cd cations may act either directly on the catalytic sites of the proteolytic enzymes, which may cause their deactivation, or indirectly via the generation of oxidative stress and overproduction of free radicals that can interact with enzymes, by altering their activity and structure.
本研究旨在深入探讨镉（Cd）对萌发豌豆种子（Pisum sativum L. var. douce province）作用的机制，特别是 Cd 阳离子可能通过哪些不同方式干扰萌发过程中主要因素，尤其是贮藏蛋白的动员、氨基酸的释放和蛋白水解酶活性。研究结果表明，主要贮藏蛋白的水解过程受到显著干扰，导致游离氨基酸的释放减少，从而在 Cd 胁迫下，生长胚缺乏必需营养物质的氮供应。这一假说得到了 Cd 诱导的主要纯化蛋白组分（白蛋白、豆球蛋白和伴白蛋白）在其降解过程中发生变化的证据支持。此外，在酶水平上，负责水解的主要蛋白酶的活性也发生了改变。实际上，使用合成底物和特定蛋白酶抑制剂进行的酶活性测定实验表明，Cd 严重抑制了总偶氮酪蛋白水解活性（ACA）和不同蛋白水解类别的活性：半胱氨酸、天冬氨酸、丝氨酸和金属内肽酶（EP）、亮氨酸和脯氨酸氨肽酶（LAP 和 PAP）以及甘氨酸羧肽酶（Gly-CP）。本文提出的数据表明，胚胎轴对 Cd 毒性的敏感性可能是由于影响储备动员和营养物质可用性的代谢途径受到破坏而导致的。体外研究表明，Cd 阳离子可能直接作用于蛋白水解酶的催化部位，导致其失活，或者通过产生氧化应激和自由基的过度产生间接作用，自由基可以与酶相互作用，改变其活性和结构。
