Geoscience Reference
In-Depth Information
SAL1
(3′(2′), 5′-biphosphate nucleocidase,
MSI1
(multi-copy sup-
pressor of Ira1),
TOC1
(timing of CAB expression 1) and many
other genes are transcriptionally regulated by ABA-mediated
pathway and are crucial in controlling the stomatal aperture
and drought resistance. ABA signal transduction has charac-
terised the cell biological and genetic mechanisms upstream
and downstream of ROS production. ABA regulated the ROS
level in
itn1
(increased tolerance to NaCl),
abi1-1
(ABA insen-
sitive1) and
ost1
(
open stomata 1) mutants.
ABA induces the
gene expression of ROS-producing enzyme nicotinamide ade-
nine dinucleotide phosphate (NADPH) oxidase (RBOHC and
RBOHD)
itn1
mutant. In response to cold, ABA increases the
cold-responsive gene expression SCOF-1 DNA-binding activity
to the bZIP SGBF-1 in ABRE sequence, suggesting a coopera-
tive role of the two proteins to induce cold tolerance of plants
(Kim et al., 2001). Besides these, many genes are regulated by
transcription factors responding to drought, salt and cold
via
ABA-dependent or ABA-independent pathways.
Brassinosteroids
BRs are plant steroidal hormones that regulate various aspects
of plant growth and development, including cell elongation,
photomorphogenesis, xylem differentiation, seed germination
and fruit ripening (Clouse and Sasse, 1998). BRs induce gene
expression and the ability to enhance resistance in plants in the
changing environmental condition or stresses, such as heavy
metal stress, water stress, salt stress, high- and low-temperature
stress and pathogen attack (Bajguz and Hayat, 2009). BRs treat-
ment induces the expression of three regulatory genes, such as
RBOH
,
MAPK1
and
MAPK3
, and genes involved in defence and
antioxidant responses (Xia et al., 2009). BR induces the expres-
sion of genes-encoding transcription factors, such as WRKY6,
WRKY30, MYB and MYC. The 24-epibrassinolide (bioac-
tive BRs) induces the expressions of genes-encoding proteins
involved in the heat-shock response (HSP and DnaJ), defence
(PR-1, PAL and HPL), detoxification (GST, GPX and POD)
and antioxidant (CAT, cAPX and MDAR) (Xia et al., 2009).
These gene expression results suggest that the involvement of
BR induces plant stress tolerance to a variety of environmen-
tal stresses. Analysis of T-DNA insertion mutants of four BR
response genes indicated that WRKY17, WRKY33, ACP5 and
BRRLK have stress-related functions (Divi et al., 2010). For
osmotic permeability, BR-deficient
cpd
and BR-insensitive
bri1
mutants showed that BR treatment produced an increase
in the osmotic permeability of protoplasts prepared from
cpd
plants (Morillon et al., 2001). The 24-epibrassinolide treatment
