Agriculture Reference
In-Depth Information
ASH is the most abundant and water-soluble antioxidant. Owing to its ability to
donate electrons in a number of enzymatic and non-enzymatic reactions, ASH has
been considered as the most powerful ROS scavenger for the prevention of oxida-
tive damage in plants (Athar et al.
2008
). It can protect membranes by directly
scavenging O
2
and OH
and by regenerating
ʱ
-tocopherols from tocopheroxyl
radicals. ASH mostly remains available in reduced form in leaves and chloroplasts
under normal physiological conditions (Smirnoff
2000
).
GSH, which is necessary to maintain the normal reduced state of cells, has
been considered to be the most important source of intracellular defence against
ROS-induced oxidative stress (Meyer
2008
). All plant cell compartments contain
GSH, and most GSH is in reduced form (Mittler and Zilinskas
1992
; Jimenez et al.
1998
). GSH and other antioxidants together contribute to the regulation of cel-
lular redox status; these regulatory systems respond rapidly to a complex range
of different changes in the environment. The nuclear pool of glutathione changes
dynamically in plants (Diaz et al.
2010
). GSH plays a pivotal role in the regula-
tion of sulphate transport, signal transduction, conjugation of metabolites, detox-
ification of xenobiotics and the expression of stress-responsive genes (Xiang
et al.
2001
). GSH also plays important roles in plant cell differentiation, cell
death and senescence, pathogen resistance and enzyme regulation (Rausch and
Wachter
2005
).
Thiol/disulphide exchange reactions link two glutathione molecules by a disul-
phide bond to form glutathione disulphide (GSSG), the oxidised form of GSH.
The balance between the relative levels of GSH and GSSG is a central compo-
nent in maintaining the cellular redox state (Foyer and Noctor
2005
). Depletion of
GSH in
Arabidopsis
cell suspensions renders them susceptible to oxidative dam-
age (May and Leaver
1993
). ROS, particularly H
2
O
2
, can influence the recycling
of GSSG and GSH, so they have an impact on the redox status of the cell (by
changing the thiol/disulphide ratio), which can ultimately instigate cellular redox
signalling. Reversibly oxidised cysteine sulphhydryl groups serve as redox sen-
sors or targets of redox sensing that are important in different physiological pro-
cesses. Treatment of
Brassica napus
guard cells with ABA identified 65 potential
redox-responsive proteins. Of these, a SNRK2 kinase and an isoform of isopro-
pylmalate dehydrogenase were confirmed to be redox-regulated and involved in
stomatal movement regulated by ABA (Zhu et al.
2014
). However, considerably
little is known about the roles of GSH and GSSG in the signal transduction system
of plants.
The asserted links between antioxidant metabolism and ABA are derived from
the observation that the ASH-deficient mutant
vtc1
(Conklin et al.
2000
) has ABA
levels 1.6-fold higher than those of the wild type (Pastori et al.
2003
). It has been
suggested that cellular responses to an alteration in ASH levels might be mediated
by ABA (Pastori et al.
2003
). Correlation of ABA with regulation of the size of the
ASH pool and comparison of the regulation of transcript abundance in the starch-
biosynthetic mutant
adg1
, the ascorbate biosynthesis mutant
vtc1
and the ABA
biosynthetic mutant
aba2
showed a link between sugar induction of APX and ASH
biosynthesis (Heiber et al.
2014
). Flavonols are plant metabolites that have been
−
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