Morpho-physiological and gene expression responses of wheat by Aegilops cylindrica amphidiploids to salt stress
Aegilops cylindrica Host is one of the most salt-tolerant species in the Triticeae tribe. Amphidiploid plants derived from hybridization of Roshan x Aegilops cylindrica and Chinese Spring x Ae. cylindrica genotypes contrasting in salt tolerance were assessed for their morpho-physiological responses and the expression patterns of three genes related to ion homeostasis under 250 mM NaCl. Results showed that salt stress caused significant declines in both their morphological and phenological traits. Moreover, salt stress reduced not only their chlorophyll content but also their root and shoot K contents and K/Na ratios, while it led to significant enhancements in the remaining traits. Similar to Ae. cylindrica, the amphidiploids subjected to salt stress exhibited significantly higher H2O2 levels, root and shoot K contents, and root and shoot K/Na ratios accompanied by lower root and shoot Na contents and MDA concentrations when compared with the same traits in the wheat parents. Quantitative Real-Time PCR showed significant differential expression patterns of the HKT1;5, NHX1, and SOS1 genes between the amphidiploids and their parents. The transcript level of HKT1;5 was found to be higher in the roots than in the shoots of both the amphidiploids and Ae. cylindrica while NHX1 exhibited a higher expression in the shoot tissues. The consistency of these data provides compelling support for the hypothesis that active exclusion of Na from the roots and elevated vacuolar sequestration of Na in the leaves might explain the declining Na levels in the shoots and roots of both the amphidiploids and Ae. cylindrica relative to those measured in wheat parents. It is concluded that the hybridized amphiploids are potentially valuable resources for salt improvement in bread wheat through the backcrossing approach.