Biology Reference
In-Depth Information
chronic exposure. In the different studies described below, ozone varied
between ambient levels (30-50 ppb) to high levels (600 ppb) and exposure
times ranged from 3 h to several years. In addition, plant age varied between
3 weeks and 4 years. Ozone increased PAL enzyme activity in Pinus sylvestris
(
Rosemann et al., 1991
), parsley (Petroselinum crispum;
Eckey-Kaltenbach
et al., 1994
), soybean (Glycine max;
Booker and Miller, 1998
), grape (Vitis
vinifera;
Sgarbi et al., 2003
), poplar (Populus spp.;
Caban´ et al., 2004; Di
Baccio et al., 2008
) and Centaurea jacea (
Francini et al., 2008
). 4CL activity
was also increased in soybean (
Booker and Miller, 1998
) and CAD activity
increased in response to ozone in Picea abies (
Galliano et al., 1993a; Heller
et al., 1990
), parsley (
Eckey-Kaltenbach et al., 1994
), soybean (
Booker and
Miller, 1998
), P. sylvestris (
Zinser et al., 1998
) and poplar (
Caban
´
et al.,
2004; Di Baccio et al., 2008
). Transcript abundance of genes encoding
phenylpropanoid pathway enzymes responded in the same way suggesting
that ozone-induced lignification involved transcriptional regulation. For
example, PAL transcript levels were more abundant following ozone treat-
ment in parsley (
Eckey-Kaltenbach et al., 1994
), A. thaliana (
Sharma and
Davis, 1994
), birch (Betula pendula;
P¨¨kk¨nen et al., 1998; Tuomainen
et al., 1996
), poplar (
Koch et al., 1998; Wustman et al., 2001
) and C. jacea
(
Francini et al., 2008
). Increased transcript levels were also observed for 4CL
in parsley (
Eckey-Kaltenbach et al., 1994
) and for COMT in poplar (
Koch
et al., 1998
) and beech (Fagus sylvatica;
Jehnes et al., 2007; Olbrich et al.,
2005
). CAD transcripts increased in P. abies (
Galliano et al., 1993b
),
P. sylvestris (
Zinser et al., 1998
) and poplar (
Caban´ et al., 2004
). Transcrip-
tomic studies indicated that PAL, 4CL, C3H, CCoAOMT and CCR
responded to ozone treatment in rice (Oryza sativa;
Frei et al., 2011
),
COMT in beech and Arabidopsis (
Olbrich et al., 2005, 2009; Tosti et al.,
2006
) and CCR in birch (
Kontunen-Soppela et al., 2010
). The responses of
the phenylpropanoid metabolism can be both fast (
Koch et al., 1998; Sharma
and Davis, 1994
) and substantial (
Caban´ et al., 2004
). Within an experi-
ment, induction levels were correlated with ozone concentrations (
Caban
´
et al., 2004; Galliano et al., 1993a; Rosemann et al., 1991
). Stimulation of the
phenylpropanoid pathway was often maintained during the whole period of
ozone exposure (
Caban
´
et al., 2004; Galliano et al., 1993b
) and could even
continue after the end of the treatment (
Tuomainen et al., 1996
). Interesting-
ly, the shikimate pathway, which supplies substrates to the phenylpropanoid
pathway, was also found to be upregulated by ozone treatment (
Betz et al.,
2009a,b; Caban´ et al., 2004; Guidi et al., 2005; Janzik et al., 2005
). This
observation suggests a strong coordination between primary and secondary
metabolism to provide substrates to the phenylpropanoid pathway. Most of
the above results were obtained from plants cultivated in controlled or open