Physiology and Molecular Biology of Stress ... - KHAM PHA MOI

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B. Rathinasabapathi and R. Kaur
In Arabidopsis, overexpression of bacterial chyB gene encoding β-carotene
hydroxylase exhibited enhancement in photooxidative stress tolerance due to specific
increase in xanthophyll (Davison et. al., 2002). Similarly, transgenic tobacco plants
overexpressing a bacterial carotene hydroxylase gene responsible for zeaxanthin synthesis
(Götz et. al., 2002), and plants with Norway spruce defence related phenol-oxidizing
peroxidases (spi 2) showed marked tolerance to UV-B (Jansen et. al. 2001; Jansen et.
al. 2004). Transgenic rice plants with increased levels of heat shock protein (sHSP17.7)
exhibited significantly greater resistance to UV-B stress than untransformed control
plants (Murakami et al 2004).
4. VACUOLE TRANSPORT ENGINEERING
The presence of large, acidic-inside, membrane bound vacuoles in many halophytic
plants allows the efficient compartmentalization of sodium into the vacuole through the
operation of vacuolar Na+/H+ antiports (Blumwald and Poole, 1985; Rausch et al., 1996;
Apse et al 1999). Understanding of this stress adaptation – transport of sodium into the
vacuole and ion homeostasis of plant cells - has tremendously increased in recent times
(Martinoia et. al., 2000).
Interestingly transgenic tomato overexpressing this vacuolar antiporter gene
accumulated sodium in its leaves but not in the fruits (Zhang and Blumwald, 2001).
Transgenic Arabidopsis (Apse et. al., 1999), tomato (Drozdowicz et. al., 1999; Zhang
and Blumwald, 2001; Zhang et. al., 2001), and Brassica (Zhang et. al., 2001)
overexpressing a vacuolar Na+/H+ antiport gene from Arabidopsis (AtNHX1), were
able to grow and produce in the presence of 200 mM sodium chloride without any
reduction in yield or quality. The A. thaliana SOS 1 gene encodes a plasma membrane
Na + /H + antiporter that is essential for salt tolerance (Shi et. al., 2000, 2002, 2003; Qiu et.
al., 2002). Similarly, many genes encoding proton pumps in cell membranes have successfully
been modified since proton pumps generate the proton electrochemical gradients
in the membranes. Gaxiola et. al. (2001) showed that transgenic plants
overexpressing AVP1 H + pump were resistant to drought and salinity. Increased salt
tolerance in the transgenic plants is correlated with reduced Na + accumulation under
salt stress (Shi et. al., 2003). This work illustrates that it is possible to achieve dramatic
improvements in plant stress tolerance by the manipulation of single target transporter
gene, signal transduction pathways and gene regulation networks (Hasegawa et. al.,
2000; Zhu, 2001).
5. REGULON ENGINEERING
Transcription factors have been identified as an additional target group to direct gene
regulation for improved salt/drought stress tolerance (Shinozaki and Yamaguchi-
Shinozaki, 1997; Winicov and Bastola, 1997; Broun, 2004). Understanding of stress
signaling pathways has paved the way to this regulon engineering strategy. The