Chemistry Reference
In-Depth Information
reduced growth rate (Schroeder, J.I. et al., 2001). ABA also plays a vital role in adapting to
cold temperatures. Cold stress induces the synthesis of ABA and the exogenous application
of ABA enhances the cold tolerance of plants. A large number of genes associated with ABA
biosynthesis and ABA receptors-encoding genes and downstream signal relays have been
characterized in Arabidopsis thaliana (reviewed by Cutler SR et al., 2010). ABA activates the
expression of many stress-responsive genes independently or synergistically with stresses,
which makes it become the most studied stress-responsive hormone.
Other hormones, in particular CK, SA, ET, and JA, also have substantial direct or indirect
performances in abiotic stress responses. CK is an antagonist to ABA, and under water
shortage situation, CK levels usually decrease. But transgenic tomato rootstocks expressing
IPT (isopentenyl transferase, a gene encoding a key step in CK biosynthesis) had improved
root CK synthesis shown raised salinity stress tolerance (Ghanem ME et al., 2011).
Meanwhile, by checking public microarray expression data for A. Thaliana, numerous genes
encoding proteins associated with CK signaling pathways have been found affected by
various abiotic stresses (Argueso CT et al., 2009). Although auxins, GAs, and CKs have been
implicated primarily in developmental processes in plants, they regulate responses to stress
or coordinate growth under stress conditions (Günther F. E. Scherer et al., 2012; F. Eyidogan
et al., 2012). Auxins taking part in drought tolerance was postulated by researchers (ZhangS-
W et al., 2009). What's more, BR was reported (mainly researches on exogenous application
of BR) to induce stress-related genes' expression, which results in the maintenance of
photosynthesis activity, the activation of antioxidant enzymes, the accumulation of
osmoprotectants, and the induction of other hormone responses (Divi UK et al., 2009). In
conclusion, there do exist a complex network for phytohormones to contribute to stress-
induced reactions for plants. And due to the overlap between hormone-regulated gene
suites in the adaptive responses, we have to discuss cross-talk between the different
hormone signaling pathways as a extensive part of that complex network.
Earlier, it was reported that ABA can inhibit the biosynthesis of ethylene and may also
potentially reduce the sensitivity of plants to ethylene (Sharp, R.E., 2002). Recently the
expression of many other genes associated with auxin synthesis, perception, and action has
been shown to be regulated by ethylene (Stepanova AN, Alonso JM, 2009). And it is not
surprising that auxin has been found involved in ethylene biosynthesis very early.
Meanwhile, CK was shown to be a positive regulator of auxin biosynthesis (Jones B et al.,
2010).
Furthermore, GA and BR regulate many common physiological processes like the growth
and development in rice seedlings (Wang L et al., 2009). Except BR, GA has another partner
- SA. Transgenic A. thaliana plants constitutively overexpressing a GA-responsive gene
became more tolerant under abiotic stress and this stronger tolerance was correlated with
increased endogenous levels of SA (Alonso-Ramirez A et al., 2009).
Discussed above, ABA can regulate stomatal actions under stress conditions; however, it is
not alone in that process. CK, ET, BR, JA, SA, and NO also affect stomatal function
(reviewed by Acharya B, Assmann S, 2009). In detail, ABA, BR, SA, JA, and NO induce
