Selection In vitro pour la tolerance aux stress salin et thermique chez le ble tendre (Triticum aestivum l.)

Abstract

Study results of response for seedlings of two bread wheat varieties ( Triticum aestivum L.) , Mahon-Demias (MD) and Hidhab (HD) to salt stress, indicate the highlight negative impact of salinity on the rate of germination and show the sensitivity of MD compared to HD. Salt stress significantly reduced the length of roots and epicotyls of both varieties. MD showed a greater reduction in length of two characters than HD. Under salt stress of 200mM NaCl, the leaf area is reduced by 50.2 % for MD against 24.8 % for HD. Changes in water potential values and relative water content indicates that MD is more sensitive to salinity than HD. Monitoring the ionic content indicates that the accumulation of Na + is higher in the sheath of HD and the blade of MD, with little difference between varieties for the content of the roots. HD uses an additional mechanism to counter salinity, sequestering preferentially over sodium in the sheath unlike in the blade of MD variety. HD has a greater ability to accumulate K + ion in the limb and in the roots compared to MD. The K +/Na + ratio of leaf blade is higher in HD compared to MD. This indicates that it is mainly their leaves HD restores the balance of the osmotic potential via K+ and thus minimizes the effect of osmotic stress caused by NaCl. HD capacity to pump K + in the nutrient solution, and then to transfer to the limb, therefore a strategy for adaptation to salt stress via osmotic regulation. Results of study for the embryogenic capacity and power regeneration in vitro thermal and salt stress in MD and HD using mature embryos as explants show that MD responds better than HD in vitro selection. MD has a higher rate of induction of callus with a better callus induced proliferation, but with fewer embryos induced by cal. The rate of regeneration of plantlets from proliferating callus was null for HD and very low for MD. The index sensitivity (IS)confirmed the tolerance of MD compared to HD for salt and thermal stress in vitro to a given parameter is the length of the roots. The results suggest the possibility of using the in vitro technique in selection for no biotic stress. Results of study for the expression analysis of five candidate genes for tolerance to salinity indicate that HKT1,5 and HKT2,2 are expressed in the roots, but not in sheaths and limbs, with better HKT1,5 gene expression in the roots of HD. This suggests a more active role HKT1, 5 genes in HD. The expression of anti-porter vacuolar Na +/H+, TNHX-1 roots, sheaths and limbs is higher in HD than in MD. Roots and sheath of the two genotypes accumulate more transcripts of the vacuolar pyrophosphatase TVP1 than blades. Type similarity of gene expression TNHX1 and TVP1, observed in MD and HD, suggesting that vacuolar compartmentalization is equal efficiency in both genotypes. More gene transcripts TaSOS-1, accumulate in the roots and sheath of MD compared to HD, suggesting that in addition to more effective retention of Na + in sheaths, HD avoids accumulation of Na + in the blade by activating its sodium efflux via high expression of SOS1 gene in this compartment. Results indicate that salinity tolerance in the bread wheat seems to be related to the ability to prevent the accumulation of toxic levels of Na +, associated with a high osmo-regulation and/or ability to maintain an acceptable level of K +, especially in the leaf blade. This information is useful for selection of plant material in cereal breeding programs.