Agriculture Reference
In-Depth Information
implicated as antioxidants, because it is similar to ASH and flavonols in terms of
protection for plants. A recent study also showed that ethylene induced guard cell-
specific flavonoid synthesis, suppressed ROS accumulation and decreased the rate
of ABA-dependent stomatal closure (Watkins et al.
2014
).
10.3 Biological Roles of ROS Related to ABA
ROS play a dual role in plants: at low concentrations, they act as signal molecules
involved in acclamatory signalling that triggers tolerance to stresses, and at high
concentrations, they lead to damage to biological molecules and cells (Quan et al.
2008
). Research has shown that H
2
O
2
acts as a key regulator that mediates many
physiological processes, such as stomatal movement (Bright et al.
2006
), pho-
torespiration and photosynthesis (Noctor and Foyer
1998
), senescence (Peng et al.
2005
), the cell cycle (Mittler et al.
2004
) and growth and development (Foreman
et al.
2003
). ROS influence the expression of a number of genes and signal trans-
duction pathways that modulate the plant stress-response processes.
Besides reacting with and damaging cellular components, ROS can also partici-
pate in signal transduction. Owing to its relatively long life and high permeability
across membranes, H
2
O
2
has been accepted as a secondary messenger. ROS sig-
nalling is a core regulator of plant cell physiology and cellular responses to the
environment. For example, ROS act as intermediates in many hormone-regulated
plant biology events: auxin, ethylene, MJ and ABA signals all appear to recruit
ROS (Acharya and Assmann
2009
).
10.3.1 Oxidative Damage
Abiotic stress leads to excessive generation of ROS in plants, which causes
reduced crop productivity worldwide (Mittler
2002
; Apel and Hirt
2004
). Being
highly reactive, most ROS can damage cell structures, nucleic acids, lipids and
proteins. When the equilibrium between the production of ROS and the antioxi-
dant defence system is perturbed by various biotic and abiotic stresses, increased
ROS at the intracellular level can cause significant damage to cell structures.
Damage to DNA molecules induced by ROS includes base deletion, pyrimidine
dimers, cross-links, strand breaks and base modification (Tuteja et al.
2001
). Being
the most reactive, OH
can damage both the purine and pyrimidine bases and also
the deoxyribose backbone of the DNA molecule (Halliwell
2012
). DNA damage
influences many aspects of plant physiology, which include the disturbance of
transcription, reduction of protein synthesis, destruction of the cell membrane and
genomic instability (Britt
1999
); these events affect the growth and development
of the whole plant.
ROS or by-products of oxidative stress can also cause protein oxidation
by covalent modification. Some of these forms of oxidation are essentially
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