Altered apoplastic ascorbate redox state in tobacco plants via ascorbate oxidase overexpression results in delayed dark-induced senescence in detached leaves
Date Issued
May 2009
Author(s)
Abstract
Ascorbate oxidase (AO) is an apoplastic enzyme that uses oxygen to catalyze the oxidation of ascorbate
(AA) to dehydroascorbate (DHA) via the unstable radical monodehydroascorbate (MDHA). Here, we report
that transgenic tobacco plants (Nicotiana tabacum L. cv. Xanthi) with an in vivo lowered apoplast AA redox
state through increased AO expression demonstrate signs of delayed dark-induced senescence compared
with wild-type plants, as shown by chlorophyll loss and lipid peroxidation assays. In situ localization of
H2O2 suggests that although transgenic plants have higher constitutive levels of H2O2 under normal growth
conditions, imposed dark-induced senescence results in smaller induction levels of H2O2, an observation which
correlates with increased antioxidant enzyme activities and an induction in the expression of AA recycling
genes compared with that in wild-type plants. Our current findings, combined with previous studies which
showed the contribution of AO in the regulation of AA redox state, suggest that the reduction in AA redox state
in the leaf apoplast of these transgenic plants results in an increase in the endogenous levels of H2O2, which
provides a form of ‘acquired tolerance’ to oxidative stress imposed by dark-induced senescence.
(AA) to dehydroascorbate (DHA) via the unstable radical monodehydroascorbate (MDHA). Here, we report
that transgenic tobacco plants (Nicotiana tabacum L. cv. Xanthi) with an in vivo lowered apoplast AA redox
state through increased AO expression demonstrate signs of delayed dark-induced senescence compared
with wild-type plants, as shown by chlorophyll loss and lipid peroxidation assays. In situ localization of
H2O2 suggests that although transgenic plants have higher constitutive levels of H2O2 under normal growth
conditions, imposed dark-induced senescence results in smaller induction levels of H2O2, an observation which
correlates with increased antioxidant enzyme activities and an induction in the expression of AA recycling
genes compared with that in wild-type plants. Our current findings, combined with previous studies which
showed the contribution of AO in the regulation of AA redox state, suggest that the reduction in AA redox state
in the leaf apoplast of these transgenic plants results in an increase in the endogenous levels of H2O2, which
provides a form of ‘acquired tolerance’ to oxidative stress imposed by dark-induced senescence.
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