Bolwell G P, Butt V S, Davies D R, Zimmerlin A
Department of Biochemistry, Royal Holloway and Bedford New College, University of London, Egham, Surrey, UK.
Free Radic Res. 1995 Dec;23(6):517-32. doi: 10.3109/10715769509065273.
A large number of publications recently have drawn strong analogies between the production of active oxygen species in plant cells and the "oxidative burst" of the phagocyte, even to the point of constructing elaborate models involving receptor mediated G-protein activation of a plasmalemma NADPH oxidase in plant cells. However there are potentially other active oxygen species generating systems at the plant cell surface. The present work examines these alternatives with particular emphasis on the rapid production of active oxygen species, in common with a number of other systems, by suspension-cultured cells of French bean on exposure to an elicitor preparation from the fungal pathogen Colletotrichum lindemuthianum. The cells show a rapid increase in oxygen uptake which is followed shortly afterwards by the appearance of a burst of these active oxygen species, as measured by a luminescence assay, which is probably all accounted for by hydrogen peroxide. An essential factor in this production of H2O2 appears to be transient alkalinization of the apoplast where the pH rises to 7.0-7.2. Dissipation of this pH change with a number of treatments, including ionophores and strong buffers, substantially inhibits the oxidative burst. Little evidence was found for enhanced activation of a membrane-bound NADPH oxidase. However the production of H2O2 under alkaline conditions can be modelled in vitro with a number of peroxidases, one of which, an M(r) 46,000 wall-bound cationic peroxidase, is able to sustain H2O2 production at neutral pH unlike the other peroxidases which only show low levels of this reaction under such conditions and have pH optima at values greater than 8.0. On the basis of such comparative pH profiles between the cells and the purified peroxidase and further inhibition studies a direct production of H2O2 from the wall peroxidase in French bean cells is proposed. These experiments may mimic some of the responses to plant pathogens, particularly the hypersensitive response, which is an important feature of resistance. A cell wall peroxidase-origin for the oxidative burst is clearly different from a model consisting of receptor activation of a plasmalemma-localised NADPH oxidase generating superoxide. An alternative simple and rapid mechanism thus exists for the generation of H2O2 which does not require such multiple proteinaceous components.
最近大量的出版物对植物细胞中活性氧的产生与吞噬细胞的“氧化爆发”进行了强烈类比，甚至构建了复杂的模型，涉及受体介导的植物细胞质膜NADPH氧化酶的G蛋白激活。然而，在植物细胞表面可能还存在其他活性氧生成系统。本研究对这些替代系统进行了考察，特别强调了与许多其他系统一样，菜豆悬浮培养细胞在接触来自真菌病原体菜豆炭疽菌的激发子制剂后活性氧的快速产生。细胞显示出氧气摄取迅速增加，随后不久通过发光测定法检测到这些活性氧的爆发，这可能全部由过氧化氢引起。这种过氧化氢产生的一个关键因素似乎是质外体的瞬时碱化，其pH值升至7.0 - 7.2。用包括离子载体和强缓冲剂在内的多种处理方法消除这种pH变化，会显著抑制氧化爆发。几乎没有证据表明膜结合的NADPH氧化酶的激活增强。然而，在碱性条件下过氧化氢的产生可以在体外由多种过氧化物酶模拟，其中一种分子量为46,000的壁结合阳离子过氧化物酶，与其他过氧化物酶不同，它能够在中性pH下维持过氧化氢的产生，其他过氧化物酶在这种条件下仅显示低水平的该反应，并且在pH值大于8.0时有最佳活性。基于细胞与纯化过氧化物酶之间的这种比较pH谱以及进一步的抑制研究，提出菜豆细胞中壁过氧化物酶直接产生过氧化氢。这些实验可能模拟了对植物病原体的一些反应，特别是过敏反应，这是抗性的一个重要特征。氧化爆发的细胞壁过氧化物酶起源显然不同于由质膜定位的NADPH氧化酶受体激活产生超氧化物的模型。因此，存在一种不需要如此多蛋白质成分的简单快速的过氧化氢生成替代机制。
