Transgenic tobacco plants overexpressing polyamine oxidase are not able to cope with oxidative burst generated by abiotic factors.
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.
Moschou
Panagiotis N
PN
Department of Biology, University of Crete, PO Box 2280, 71409 Heraklion Crete, Greece.
Delis
Ioannis D
ID
Paschalidis
Konstantinos A
KA
Roubelakis-Angelakis
Kalliopi A
KA
D000975:Antioxidants / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D005110:Extracellular Space / Q000201:enzymology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006868:Hydrolysis / Q000187:drug effects; D007525:Isoelectric Focusing; D007527:Isoenzymes / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000235:genetics* / Q000378:metabolism; D018515:Plant Leaves / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011073:Polyamines / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D016897:Respiratory Burst / Q000187:drug effects; D013481:Superoxides / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D014170:Transformation, Genetic; D019076:Transgenes; D024483:Vitamin K 3 / Q000494:pharmacology; D003313:Zea mays / Q000187:drug effects / Q000201:enzymology*; D000097667:Polyamine Oxidase
D000975:Antioxidants; D006861:Hydrogen Peroxide; D007527:Isoenzymes; D000587:Oxidoreductases Acting on CH-NH Group Donors; D010940:Plant Proteins; D011073:Polyamines; D017382:Reactive Oxygen Species; D013481:Superoxides; D024483:Vitamin K 3; D000097667:Polyamine Oxidase