الفهرس 
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Abstract
This study was conducted in the Ornamental Plants Nursery and Greenhouses of El-Kanater El-Khairia Horticultural Station, Qalubia Governorate, Egypt during the two successive seasons of 2020-2021 and 2021-2022. The aim of this investigation was to study the response of two different species of Amaranthus species (Red and Green) to a salt-stress cycle (at 150 Mm NaCl) in addition to the role of brassinolide on mitigation of salinity stress under four salinity levels (Control, 2000 ,4000 and 7000 ppm NaCl). The results of both experiments showed that the growth, physio-biochemical, and molecular attributes of the both two tested Amaranthus species were strongly altered under salinity stress which negatively affected most of the studied characteristics. In the first experiment, plants initially exposed to a salinity-stress cycle at 150 mM NaCl later on decreased leaf total chlorophyll, and some mineral content. On the other hand, the activity of antioxidant enzymes (SOD and CAT), hormonal content (GA3, ABA, BA and IAA) and other antioxidants (MDA, H2O2 and proline) in addition to TSS and total carbohydrates were all increased. In the second experiment, foliar application with BR at 10 ppm enhanced number of leaves (in red Amaranthus species), plant height (in green Amaranthus species) and chlorophyll content, as SPAD reading (in both green and red Amaranthus species) when subjected to the highest salinity-stress treatment of 7000 ppm NaCl. The molecular characterization indicated from the transcriptome analysis led to identification of four genes expression (SOS1, DGR2, NHX1, and HKT1) profiling their response to salt tolerance of the two Amaranthus species.