Biology Reference
In-Depth Information
In another study, acclimation to chilling induced nine peroxidase isozymes
in maize mesocotyls. Two of them were localized in the cell wall and lignin
content was enhanced in acclimated mesocotyls (
Anderson et al., 1995
).
Lignin could be involved in the chilling tolerance process by increasing the
rigidity of the mesocotyl. Cold acclimation of winter wheat (Triticum aestivum)
was associated with accumulation of phenolic compounds in leaves, and
increased lignin content in tillering nodes and roots (
Olenichenko and
Zagoskina, 2005; Zagoskina et al., 2005
). Increased lignin deposition was
also observed in poplar plants (Populus tremula
tremuloides) obtained from
cuttings and exposed for 14 days to a chilling temperature (10
C). Lignin
content started to increase within 2 days of treatment and continued until the
end of chilling exposure (
Hausman et al., 2000
). Taken together, these different
observations suggest that chilling/freezing induces lignin synthesis and depo-
sition, which could lead to a reinforcement of the cell wall, potentially to
combat mechanical stress and/or cell dehydration. Results supporting a role
for cold-induced lignification in cell wall stability were recently provided by
a study of the EARLI1 (early Arabidopsis aluminium-induced gene1) gene in
Arabidopsis. This gene is induced by low temperature and the corresponding
protein was localized in the cell wall where it is believed to maintain the
stability between the plasma membrane and the cell wall through binding
with other proteins. EARLI1 RNAi plants showed a lower lignin content
than wild type and downregulation of the CCR1 gene (
Shi et al., 2011
). These
findings suggest that induction of EARLI1 under cold stress could modulate
lignin deposition, although more analyses are necessary.
8
F. OZONE
Tropospheric ozone is one of the main pollutants known to have a detrimen-
tal effect on plants (
Booker et al., 2009; Karnosky et al., 2007
). Since the
beginning of the industrial era, tropospheric ozone concentration has been
increasing and is predicted to keep increasing in the future (
IPCC, 2007
).
Plants exposed to ozone displayed reduced photosynthesis resulting in
decreased growth and yield (
Booker et al., 2009; Wittig et al., 2007, 2009
).
In addition, ozone has been shown to cause visible damages to leaves. This
gas enters the leaf through the stomata and reacts with the apoplast consti-
tuents generating ROS. It has also been suggested that ozone may function as
an abiotic elicitor of plant defence reactions such as programmed cell death
(
Sandermann et al., 1998
).
In addition to inducing a diverse range of defence responses, ozone has
been shown to stimulate phenylpropanoid metabolism in leaves of many
species and under different fumigation protocols involving both acute and
