PLANT PHYSIOLOGY , Vol 114, Issue 2 529-537, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Overproduction of Ascorbate Peroxidase in the Tobacco Chloroplast Does Not Provide Protection against Ozone
G. Torsethaugen, L. H. Pitcher, B. A. Zilinskas and E. J. Pell
Department of Biology, University of Oslo, P.O. Box 1045 Blindern, 0316 Oslo, Norway (G.T.)
Transgenic tobacco (Nicotiana tabacum cv Bel W3) plants were used to test
the hypothesis that protection from O3 injury could be conferred by
overproduction of ascorbate peroxidase (APX) in the chloroplast. The
10-fold increase in soluble APX activity in the chloroplast was expected to
alleviate an implied increase in oxidative potential and prevent damage
caused by O3. Three different O3 exposure experiments (one acute and two
chronic) with two replicates each were conducted. APX activity in
nontransgenic plants increased in response to chronic O3 exposure. However,
most responses to O3 were similar between transgenic and nontransgenic
plants. These included reductions in net photosynthesis and stomatal
conductance, increases in ethylene emission and visible injury, and a
decline in the level of the small subunit of ribulose-1,5-biphosphate
carboxylase/oxygenase mRNA transcripts observed in response to the air
pollutant in the acute and/or chronic experiments. No O3-induced effect on
ribulose-1,5-biphosphate carboxylase/oxygenase quantity was observed in the
chronic experiments. O3 did not induce acceleration of senescence, as
expected from studies with most other species; rather, the tobacco plants
rapidly developed necrotic lesions. Thus, overproduction of APX in the
chloroplast did not protect this cultivar of tobacco from O3.
