Environmental Engineering Reference
In-Depth Information
Mn-SOD (Wang et al. 2004; Wang et al. 2007). The detail was shown in Table 2. More
importantly, most of the transgenic plants with some over expressed antioxidant enzymes
acquire an elevated tolerance to almost all abiotic stresses instead of a specific stress. In our
opinion, the possible reason is that the oxidative stress is the result of almost all the abiotic
stresses, so the enhancement of the antioxidative capacity is able to boost resistance in
general. Although the transgenic plants with over expressed antioxidant enzymes acquire
enhanced tolerance, inevitable contradictions exist. The
Arabidopsis
mutants with a loss of
either or both cytosolic and chloroplastic APX show enhanced tolerance on the contrary
(Miller et al. 2007). Likewise, there is a decline in CAT activity in
A. doliolum
under NaCl
stress (Srivastava et al. 2005). In
Glycyrrhiza uralensis
seedlings, the CAT activity is also
decreased by salt and drought stress (Pan et al. 2006). In conclusion, the ROS pathway is
plastic and redundant, and more strategies and principles remain to be seen.
ROS play a dual role in plants. Superfluous ROS are detrimental to plant cells, yet
moderate ROS components are necessary playing important roles in signaling transduction
and cell homeostasis (Smékalová et al. 2013). In fact, the up-regulation of the enzyme genes
expression levels or the enhancement of the enzyme activities are the results of the cell
signaling. Ahead of their detoxification, they have initiated a series signaling in cells. MAK3
and MAK6 can be activated by the elevated content of ROS (Lumbreras et al. 2010), and the
activated MAK3 and MAK6 were relocated in the nucleus to strengthen or lessen gene
expression triggering plant responses to ROS. Nevertheless, the MAPK phosphatase 2
(MKP2) which is induced by oxidative stress is able to dephosphorylate MPK3 and MPK6 to
promote oxidative stress tolerance (Smékalová et al. 2013). Therefore, the signal regulatory
pathways are intricate.
P
HYTOHORMONE IN
S
ALT
S
TRESS
Plant hormones take part in almost all the processes in plants including different
positions, different tissues and different developmental stages. ABA is the foremost one and
is induced by various stresses obviously. It is able to regulate the adaption of the plants to
stresses such as cold, drought, salinity, pathogen attacks, wounding and oxidative stress
(Smékalová et al. 2013). It has been proved to be responsible for the change of salt-stress-
induced genes long ago (De Bruxelles et al. 1996). Its powerful functions in salt stress are
reflected in its involvement in the photosynthesis and growth, osmotic tolerance, ion
homeostasis and antioxidant defense responses which we mention above. Two decades ago,
Popova et al. has put forward that the inhibitory effect of salt stress on growth and
photosynthesis can be alleviated by ABA (Popova et al. 1995). Moreover, ABA participates
in regulating stress-related-genes expression. In ABA-deficient mutant, the P5CS which is the
rate-limiting enzyme of the synthesis of Pro is reduced or completely blocked (Xiong and Zhu
2001). For ion homeostasis, ABA has the ability to reduce anion channels to cut down Cl
-
transfer in saline condition (Gilliham and Tester 2005). The type 2C protein phosphatase
ABI2 which act as a vital component in ABA signaling is able to bind to SOS2 directly and
dephosphorylate it (Ohta et al. 2003). The involvement of ABA in antioxidant defense
responses is that ABA induces antioxidant defense. During the ABA-induced antioxidant
defense, H
2
O
2
, NO and MAPK are the major components (Hu et al. 2005; Zhang et al. 2006;
