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Over-expression of ascorbate oxidase in the apoplast of transgenic tobacco results in altered ascorbate and glutathione redox states and increased sensitivity to ozone

Lookup NU author(s): Dr Pavlina Drogoudi, Dr Thomas Lyons, Emeritus Professor Jerry Barnes


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Transgenic tobacco (Nicotiana tabacum L. cv. Xanthi) plants expressing cucumber ascorbate oxidase (EC. were used to examine the role of extracellular ascorbic acid in mediating tolerance to the ubiquitous air pollutant, ozone (O3). Three homozygous transgenic lines, chosen on the basis of a preliminary screen of AO activity in the leaves of 29 lines, revealed up to a 380-fold increase in AO activity, with expression predominantly associated with leaf cell walls. Overexpression of AO resulted in no change in the total ascorbate content recovered in apoplast washing fluid, but the redox state of ascorbate was reduced from 30% in wild-type leaves to below the threshold for detection in transgenic plants. Levels of ascorbic acid and glutathione in the symplast were not affected by AO overexpression, but the redox state of ascorbate was reduced, while that of glutathione was increased. AO overexpressing plants exposed to 100 nmol mol-1 ozone for 7 h day-1 exhibited a substantial increase in foliar injury, and a greater pollutant-induced reduction in both the light-saturated rate of CO2 assimilation and the maximum in vivo rate of ribulose-1,5-bisphosphate carboxylase/oxygenase carboxylation, compared with wild-type plants. Transgenic plants also exhibited a greater decline in CO2 assimilation rate when exposed to a brief ozone episode (300 nmol mol-1 for 8 h). Stomatal conductance, hence O3 uptake, was unaffected by AO over-expression. Our findings illustrate the important role played by ascorbate redox state and sub-cellular compartmentation in mediating the tolerance of plants to ozone-induced oxidative stress.

Publication metadata

Author(s): Sanmartin M, Drogoudi PD, Lyons T, Pateraki I, Barnes J, Kanellis AK

Publication type: Article

Publication status: Published

Journal: Planta

Year: 2003

Volume: 216

Issue: 6

Pages: 918-928

ISSN (print): 0032-0935

ISSN (electronic): 1432-2048

Publisher: Springer


DOI: 10.1007/s00425-002-0944-9

PubMed id: 12687359


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