With respect to the previous details, the most importanteffects of salinity on plant growth appears to be byhyperosmotic and hyperionic processes. Plants act,under salinity stress, by different physiological, molecularand biological responses (Figure 2) including (1) theproduction of osmolytes, (2) activating hormonal signalingpathways, (3) regulation of cellular ionic concentration(ion homeostasis) and compartmentalization, and(4) production of antioxidant molecules and enzymes.Such responses by plants under salinity stress will resultin the expression of stress genes, which subsequentlyenhances plant tolerance under the stress. The expressionof genes under stress is regulated by epigeneticmechanisms, which are mainly the alteration of DNAand RNA activities as well as chromatin modification[51,52]. The most important cell signaling during saltstress is the SOS (salt overlay sensitive) pathway, whichresults in the exportation of sodium out of thecell [52,53].It has also been recently indicated that the mostrecent research topic about salt stress concerns theindication of the sodium sensors, which are sensed byplants under salt stress and they eventually trigger thesignaling pathways, enhancing plant salt tolerance [52].In addition, the new genes and the genetic pathways,which can enhance plant response under salt stress hasyet be elucidated in this context [54,55].With respect to the above-mentioned details, biotechnologyand breeding techniques can also be usedas the most important and useful methods for theincreased tolerance of wheat plants to salt stress. Forexample, Yang et al. [56] hypothesized that becausehexaploid bread wheat is more tolerant than tetraploidwheat, it may be more suitable for biotechnologicaland breeding investigations under salt stress, which israrely studied. Hence, the salt tolerance of a hexaploidwheat (neo-6x) from diploid and tetraploid parentshave been compared with a natural hexaploid breadwheat (nat-6x). The neo-6x had higher salt tolerancethan its parents because favorable traits includinghigher root capacity for Naþ withholding from the 2xparent and higher rate of germination from the 4x parentwere inherited by neo-6x. The allohexaploidizationalso resulted in a higher expression of HKT1;5 (as themain salt tolerance gene with a high affinity for Kþ),which allocate Naþ from the xylem vessels to the roots,similar to the nat-6x [56].
With respect to the previous details, the most important<br>effects of salinity on plant growth appears to be by<br>hyperosmotic and hyperionic processes. Plants act,<br>under salinity stress, by different physiological, molecular<br>and biological responses (Figure 2) including (1) the<br>production of osmolytes, (2) activating hormonal signaling<br>pathways, (3) regulation of cellular ionic concentration<br>(ion homeostasis) and compartmentalization, and<br>(4) production of antioxidant molecules and enzymes.<br>Such responses by plants under salinity stress will result<br>in the expression of stress genes, which subsequently<br>enhances plant tolerance under the stress. The expression<br>of genes under stress is regulated by epigenetic<br>mechanisms, which are mainly the alteration of DNA<br>and RNA activities as well as chromatin modification<br>[51,52]. The most important cell signaling during salt<br>stress is the SOS (salt overlay sensitive) pathway, which<br>results in the exportation of sodium out of the<br>cell [52,53].<br>It has also been recently indicated that the most<br>recent research topic about salt stress concerns the<br>indication of the sodium sensors, which are sensed by<br>plants under salt stress and they eventually trigger the<br>signaling pathways, enhancing plant salt tolerance [52].<br>In addition, the new genes and the genetic pathways,<br>which can enhance plant response under salt stress has<br>yet be elucidated in this context [54,55].With respect to the above-mentioned details, biotechnology<br>and breeding techniques can also be used<br>as the most important and useful methods for the<br>increased tolerance of wheat plants to salt stress. For<br>example, Yang et al. [56] hypothesized that because<br>hexaploid bread wheat is more tolerant than tetraploid<br>wheat, it may be more suitable for biotechnological<br>and breeding investigations under salt stress, which is<br>rarely studied. Hence, the salt tolerance of a hexaploid<br>wheat (neo-6x) from diploid and tetraploid parents<br>have been compared with a natural hexaploid bread<br>wheat (nat-6x). The neo-6x had higher salt tolerance<br>than its parents because favorable traits including<br>higher root capacity for Naþ withholding from the 2x<br>parent and higher rate of germination from the 4x parent<br>were inherited by neo-6x. The allohexaploidization<br>also resulted in a higher expression of HKT1;5 (as the<br>main salt tolerance gene with a high affinity for Kþ),<br>which allocate Naþ from the xylem vessels to the roots,<br>similar to the nat-6x [56].
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