Moschou Panagiotis N, Delis Ioannis D, Paschalidis Konstantinos A, Roubelakis-Angelakis Kalliopi A
Department of Biology, University of Crete, PO Box 2280, 71409 Heraklion Crete, Greece.
Physiol Plant. 2008 Jun;133(2):140-56. doi: 10.1111/j.1399-3054.2008.01049.x. Epub 2008 Feb 12.
The molecular and biochemical mechanism(s) of polyamine (PA) action remain largely unknown. Transgenic tobacco plants overexpressing polyamine oxidase (PAO) from Zea mays exhibited dramatically increased expression levels of Mpao and high 1,3-diaminopropane (Dap) content. All fractions of spermidine and spermine decreased significantly in the transgenic lines. Although Dap was concomitantly generated with H(2)O(2) by PAO, the latter was below the detection limits. To show the mode(s) of H(2)O(2) scavenging, the antioxidant machinery of the transgenics was examined. Specific isoforms of peroxidase, superoxide dismutase and catalase were induced in the transgenics but not in the wild-type (WT), along with increase in activities of additional enzymes contributing to redox homeostasis. One would expect that because the antioxidant machinery was activated, the transgenics would be able to cope with increased H(2)O(2) generated by abiotic stimuli. However, despite the enhanced antioxidant machinery, further increase in the intracellular reactive oxygen species (ROS) by exogenous H(2)O(2), or addition of methylviologen or menadione to transgenic leaf discs, resulted in oxidative stress as evidenced by the lower quantum yield of PSII, the higher ion leakage, lipid peroxidation and induction of programmed cell death (PCD). These detrimental effects of oxidative burst were as a result of the inability of transgenic cells to further respond as did the WT in which induction of antioxidant enzymes was evident soon following the treatments. Thus, although the higher levels of H(2)O(2) generated by overexpression of Mpao in the transgenics, with altered PA homeostasis, were successfully controlled by the concomitant activation of the antioxidant machinery, further increase in ROS was detrimental to cellular functions and induced the PCD syndrome.
多胺（PA）作用的分子和生化机制在很大程度上仍然未知。过量表达来自玉米的多胺氧化酶（PAO）的转基因烟草植株表现出Mpao表达水平显著增加以及高含量的1,3 - 二氨基丙烷（Dap）。转基因株系中精胺和亚精胺的所有组分均显著降低。尽管PAO会伴随H₂O₂产生Dap，但H₂O₂低于检测限。为了揭示H₂O₂清除的方式，对转基因植株的抗氧化机制进行了研究。转基因植株中诱导了过氧化物酶、超氧化物歧化酶和过氧化氢酶的特定同工型，而野生型（WT）中未诱导，同时有助于氧化还原稳态的其他酶的活性也有所增加。人们可能会认为，由于抗氧化机制被激活，转基因植株将能够应对非生物刺激产生的增加的H₂O₂。然而，尽管抗氧化机制增强，但通过外源H₂O₂进一步增加细胞内活性氧（ROS），或向转基因叶盘添加甲基紫精或甲萘醌，会导致氧化应激，这表现为PSII的量子产率降低、离子渗漏增加、脂质过氧化以及程序性细胞死亡（PCD）的诱导。氧化爆发的这些有害影响是由于转基因细胞无法像野生型那样进一步做出反应，野生型在处理后很快就明显诱导了抗氧化酶。因此，尽管转基因植株中由于Mpao过表达产生的较高水平的H₂O₂以及PA稳态的改变通过抗氧化机制的同时激活得到了成功控制，但ROS的进一步增加对细胞功能有害并诱导了PCD综合征。
