الفهرس 
The target plant: Hordeum vulgare LOnly 14 pages are availabe for public view
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Abstract
This study was applied on two varieties of barely (Hordeum vulgare
L.), Giza 132 and Giza 134 with different tolerance to salinity and osmotic
stresses in attempt to find out physiological, biochemical and molecular
responses. Preliminary experiment was carried out to determine the sublethal
dose of NaCl, and plants were treated periodically with three different
concentrations of NaCl (100, 150 and 200 mM) till the post-vegetative stage.
Results showed inhibitory effects on the growth and yield parameters at 200
mM. Thus, barely seedlings were treated with NaCl (150 mM) as well as isoosmotic
polyethylene glycol 6000 (19.5% PEG) and collected after two
Salinity and osmotic stresses are main reasons of reduced plant growth
and productivity and cause complex set of responses at physiological,
cellular, and molecular levels. Since both osmotic and ionic effects are
interrelated and co-exist under saline conditions, separating the two
components is an important step in understanding the basis of salt tolerance.
In the current study, barely seedlings (cultivars: Giza 132 and 134) were
treated with NaCl (150 mM) as well as iso-osmotic polyethylene glycol
(PEG 6000) (19.5%). Results showed decreasing of almost all growth
parameters in seedlings treated with PEG rather than NaCl. The higher levels
of different oxidative markers, non-enzymatic antioxidants, in addition to
enzymatic antioxidants were recorded mainly under osmotic stress.
Furthermore, osmoregulators including proline (Pro) and glycine betaine
(GB) increased in the root tissue, in conjunction with enhancement in the
antioxidant status of shoots by applying PEG. Results also suggested that
different regulatory mechanisms may exist in the regulation of salt tolerance
under different situations including types of both cultivar and stress
component. Based on molecular analysis using RT-PCR, HvNHX gene
(coding for Na+/H+ antiporter) was highly expressed after 48 h from
treatment in the roots of salt-stressed seedlings, but its expression level was
more pronounced in osmotic-stressed shoots than salt-treated ones, and the
opposite was true for HvGORK gene (regulates voltage-gated K+-permeable
channels). On the other hand, HvDREB gene (coding for dehydration
responsive element binding protein) recorded higher expression in the roots
under PEG compared to control. The current study suggested that salttolerant
cultivar (Giza 134) performed consistently better under salt stress
and poor under osmotic one with regard to salt-sensitive cultivar (Giza 132).
Keywords: Barely, PEG, salinity, osmotic stress, oxidative markers,
antioxidants, gene expression.