Environmental and Economical Opportunities for the Valorisation of the Genus Atriplex: New Insights - Crop Improvement: New Approaches and Modern Techniques - page 446

was observed during growth. Similar result was also achieved in transgenic trifoli-
ate orange (Fu et al. 2011 ). The enhanced salt tolerance was correlated, at least in
part, with reduced lipid peroxidation, greater abundance in photosynthetic proteins,
stimulation of K + uptake, and low Na + /K + ratios. The BADH gene that originated
from A. hortensis was also transformed into the most important forage crop alfalfa
with Agrobacterium -mediated transformation method. The transgenic plants grew
vigorous in salt stress condition, whereas the wild type plants was retarded and
did not survive. The expression of BADH gene in alfalfa genome enhanced its salt
tolerance through improved membrane protection as measured by relative electrical
conductivity and malondialdehyde (MDA) content, scavenge of free radicals by
increase of peroxidase (POD) and SOD activities, and the osmotic adjustment
(Liu et al. 2011 ).
Transcription factor genes play important roles in stress survival by serving as
master regulators of sets of downstream stress-responsive genes via binding to spe-
cific elements ( cis -elements) in target genes. Functional analysis of the promoter
regions of some of stress-inducible genes has led to identification of the cis -element
DRE (Dehydration-responsive element), which is responsible for dehydration-
inducible transcription (Yamaguchi-Shinozaki and Shinozaki 1994 ). Full-length
DRE-binding transcription factor ( AhDREB1 ) gene has been isolated from A.
hortensis (Shen et al. 2003 ). In transgenic tobacco, AhDREB1 led to the accu-
mulation of its putative downstream genes and these transgenic lines showed an
increased stress tolerance, suggesting that the AhDREB1 protein functions as a
DRE-binding transcription factor and play roles in the stress tolerant response of A.
hortensis . DREB in A. halimus ( AsDBRE ) is regulated by the osmotic component
but not by the ionic one of salt stress (Khedr et al. 2011 ). It seemed that DREB
was not involved in the regulation of sodium manipulating genes like NHX1 , SOS1
or H + - PPase . Moreover, DREB could be involved directly of indirectly in CMO
regulation because of timing of induction. Also, DREB was the most up-regulated
gene under salt (fivefold) and drought (twofold) conditions, which reinforced the
importance of this gene in A. halimus tolerance to stress. Moreover, its constitutive
expression under normal conditions also indicated its involvement in other growth
and developmental programs (Khedr et al. 2011 ).
Microsatellites are widely used in population genetic studies and may prove to
be useful in studies of closely related species to infer relationships when sequence
variation is very low or there are few or no genome resources available. Ortíz-Dorda
et al. 2005 has evaluated the genetic structure of 51 populations of A. halimus from
the Mediterranean Basin using RAPD (random amplified polymorphic DNA)-PCR
technique. The authors found that there are a clear intrapopulational diversity of
A. halimus . Such heterogeneity could be exploited to select clones or develop syn-
thetic populations with a combination of good traits such as high palatability, high
edible biomass production, and good adaptability to environmental limiting factors
in semi-arid Mediterranean environments. 12 polymorphic loci were isolated in A.
nummularia (Byrne et al. 2008 ) which will be useful to describe levels of genetic
variability across the range of the species and in a breeding programme.