Agriculture Reference
In-Depth Information
seeds remain largely unknown. Firstly, ROS are ubiquitous and present in seeds
at all stages, from embryogenesis through to germination; they also exist in vari-
ous forms (e.g. O
2
, H
2
O
2
,
1
O
2
and OH
) in seeds (Bailly et al.
2008
). Secondly,
these compounds have a very short life span (Moller et al.
2007
). Thirdly, indi-
vidual ROS can be integrated into several different transduction pathways
(Mittler et al.
2011
), they show various levels of reactivity towards a wide
range of macromolecules that can propagate the oxidative signal (e.g. proteins,
Moller et al.
2007
) and they have an effect on the cellular redox status (Dietz
et al.
2010
).
It is well known that ROS are produced at a certain level during seed imbi-
bition. It has been proposed that the germination is completed only when the
ROS content is within an oxidative window that allows ROS signalling (Bailly
et al.
2008
). Levels of ROS above or below this 'oxidative window for germi-
nation' would not permit progression towards germination. According to this
model, seed dormancy—the inability of seeds to germinate in favourable envi-
ronmental conditions (Finch-Savage and Leubner-Metzger
2006
)—is regulated
by ROS signalling. Imbibition of pea seeds in the presence of ABA also reduced
the endogenous H
2
O
2
contents of pea seedlings in control and thioproline (TP)-
treated seeds. The incubation of pea seeds with TP and/or H
2
O
2
in the presence
or absence of ABA decreased the activity of H
2
O
2
-scavenging enzymes. The
increase of the endogenous H
2
O
2
contents observed in TP and/or H
2
O
2
treat-
ments in the absence of ABA could be correlated with the decrease in these activ-
ities (Barba-Espín et al.
2012
).
The crosstalk between ROS and ABA or gibberellin metabolism and signalling
might control barley seed dormancy (Bahin et al.
2011
). Through its effects on
ABA metabolism (Liu et al.
2009
), NO promotes the release of seed dormancy
in
Arabidopsis
(Bethke et al.
2006
,
2007
). Exogenous H
2
O
2
reduces ABA synthe-
sis and stimulates gibberellin synthesis, thus releasing dormancy (Liu et al.
2010
).
A membrane-bound enzyme, RBOHB (respiratory burst oxidase homologue B),
which produces O
2
−
−
, affects seed after-ripening and germination in
Arabidopsis
(Mller et al.
2009
). Expression of a set of genes related to dormancy upon
imbibition in
cat2
-
1
and
vet1
-
1
seeds revealed that their nondormant phenotype
was probably not related to ABA or gibberellin metabolism, but suggested that
ROS could trigger germination through the activation of gibberellin signalling
(Leymarie et al.
2012
).
10.4.3 Development of Root System
Plants are anchored in the soil by their roots and depend on their root systems
for water and nutrients. The vital functions of roots make it important to under-
stand the development of root systems. Root growth is regulated by hormones
and many environmental variables (Teale et al.
2008
; Fukaki and Tasaka
2009
).
Although cell cycle progression is negatively controlled by ROS, H
2
O
2
is essential
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