Chemistry Reference
In-Depth Information
players in intercellular regulation are plant hormones." (Wolfgang Busch, Philip N. Benfey,
2010). Owing to the broad and diverse functions, many of phytohormones were discovered
before the dawn of molecular genetics (Sachs and Thimann, 1967; Thimann and Skoog,
1933). In generation, they are a large bunch of trace amount growth regulators, the best-
known group comprises auxin (IAA), cytokinin (CK), gibberellic acid (GA), abscisic acid
(ABA), jasmonic acid (JA), ethylene (ET), salicylic acid (SA), but the name list is growing by
time. Here we add brassinosteroids (BR), nitric oxide (NO), polyamines, and strigolactone
(SL). Indubitably phytohormones have various functions in growth and development.
Indeed, they play central roles in nutrient allocation, and source/sink transitions. However
based on former description relating to sensors and second messengers, we have to focus on
here is that these low-molecular-weight compounds are indispensable for coordinating
various signal transduction pathways during responses to various abiotic stresses.
Firstly, they function as systemic signals that can transmit information over large distances.
Like ABA, it can be transported and play physiological roles at sites far away from where it
is synthesized (Sauter, A. et al., 2001). And different types of cells have their own
understanding even for the same hormones signal. And information from diverse hormones
always triggers coherent responses of cells. This is signal perception at cellular level. Lucky
for us, modern transcriptome profiling technologies have provided a global view of
hormones' effects at the molecular level and identified hundreds to thousands of genes, the
expression levels of which are modified by individual hormones (Goda et al., 2008). A large
number of data have proved that treating plants with exogenous hormones will rapidly and
transiently alter genome-wide transcript profiles (Chapman and Estelle 2009).
Secondly, complex networks of gene regulation by phytohormones under abiotic stresses
involve various
cis
- or
trans
-acting elements. Some of the transcription factors regulated by
phytohormones include ARF, AREB/ABF, DREB, MYC/MYB, NAC, WRKY and other key
components functioning in signaling pathways of phytohormones under abiotic stresses will
be briefly mentioned later. And they often rapidly alter gene expression by inducing or
preventing the degradation of transcriptional regulators via the ubiquitin-proteasome
system (Santner A, Estelle M, 2010).
Thirdly, the ability of plants to a wide range of environmental stresses is also finely
balanced through the interaction of hormonal plant growth regulators and the redox
signaling hub. Plant hormones produce reactive oxygen species (ROS) as second messengers
in signaling cascades that convey information concerning changes in hormone
concentrations and/or sensitivity to mediate a whole range of adaptive responses (Carlos G.
Bartoli et al., 2012). For example, Brassinosteroids (BRs) can induce plant tolerance to
diverse abiotic stresses by triggering H
2
O
2
generation in cucumber leaves (Cui et al., 2011).
In the following part we will simply introduce how phytohormones work in signal
transduction, and how they talk with each other when they exchange information.
Let's start from ABA, whose synthesis is one of the fastest responses to abiotic stress for
plants. Under water stress, ABA synthesis triggers ABA-inducible gene expression leading
to stomatal closure, thereby reducing water loss through transpiration, and consequently, a
