Genetic analysis and physiology of a trait for enhanced K⁺/Na⁺ discrimination in wheat

Abstract

SUMMARYVariation for K" and Na^ accumulation at low salinities in hydroponic (water) culture were observed in shoots of different wheat species. Greater discrimination (in favour of K+ and against Na+ accumulation) was shown by hexaploid bread wheat {Triticum aestivum L.) than by tetraploid durum wheat (T. turgidum L.). Since Aegilops tauschii Cosson {A. squarrosa L.), the source of the D genome in bread wheat, also exhibited high discrimination between K"^ and Na^, it was concluded that the character resided in the D genome. Studies of aneuploid bread wheat lines and disomic substitution lines of D genome chromosomes for their A and B genome homoeologues in durum wheat cv. Langdon revealed that the trait was controlled by the long arm of chromosome 4D. Since the aneuploid and disomic substitution lines showed better relative salt tolerance than durum wheat, but had lower yield potentials, we recombined chromosome 4D with chromosome 4B in a tetraploid wheat background using a homoeologous pairing mutant. This produced families of 4D/4B recombinant lines, some of which exhibited the enhanced K'^/Na'^ discrimination trait. RFLP analysis confirmed that the trait was controlled by a single gene (Knal) which was completely linked to five markers on the distal third of the long arm of 4D. A second cycle of homoeologous recombination was employed to remove the distal 4D genetic material from the recombined Knal 4B/4D chromosome and to map Kfial in greater detail. By this strategy, Knal was mapped within a short 2 cM region. Genetic analysis of K"^: Na"^ ratios showed very high LOD scores in this region for plants grown in solution culture, but lower values for plants grown in the field.In general, recombinant lines which exhibited the enhanced K+/Na+ trait were slightly more tolerant of salinity in the field and in sand culture than recombinants lacking the trait. There was, however, considerable variation between individual lines. Ion discrimination and relative tolerance were also higher in a Knal recombinant (line no. R3) than in a knal recombinant (line no. R165) in sodic conditions. In these two lines the enhanced K+/Na+ discrimination trait did not alter responses to low potassium or calcium supply.

Osmogenetics: Aristotle to Arabidopsis

“…Eventually this adaptability was concluded to be a multigenetic trait that defied simple genetic introgression. Later, studies with rice confirmed the multigenic basis of tolerance responses but also indicated that substantial tolerance may be mediated by just a few genes (Gorham et al, 1997). Evidence that single genes could affect tolerance to osmotic stress continued to appear sporadically from the 1960s through the 1980s.…”

Morphological and physio-biochemical characterization ofBrassica junceaL. Czern. & Coss. genotypes under salt stress

“…The important control mechanism under salt stress is the high K ' / Na ' selectivity in plants. It has been suggested to be an important selection criterion for salt tolerance (Rains 1972;Flowers et al 1977;Greenway and Munns 1980;Gorham et al 1997;Ashraf 2002;Wenxue et al 2003). A similar trend has been reported in present study with respect to Na ' and K ' content in leaf ( Figure 5).…”

Responses of physiological parameters, grain yield, and grain quality to foliar application of potassium nitrate in two contrasting winter wheat cultivars under salinity stress

“…Potassium is the major inorganic constituent of plant cells (Abebe et al, 2003) and is involved in many physiological processes including regulation of turgor potential, cell elongation, and stomatal movement (Meneguzzo and Navari-Izzo, 2000;Rascio et al, 2001). A proper K + : Na + ratio is vital for the adjustment of cell osmoregulation, activation of enzymes, oxidant metabolism, and photosynthesis (Gorham et al, 1997;Shabala et al, 2003).…”