Phytosiderophore release in Aegilops tauschii and Triticum species under zinc and iron deficiencies

Using three diploid (Triticum monococcum, AA), three tetraploid (Triticum t urgidum, BBAA), two hexaploid (Triticum aestivum and Triticum compactum, BB AADD) wheats and two Aegilops tauschii (DD) genotypes, experiments were car ried out under controlled environmental conditions in nutrient solution (i) to study the relationships between the rates of phytosiderophore (PS) rele ase from the roots and the tolerance of diploid, tetraploid, and hexaploid wheats and Ae. tauschii to zinc (Zn) and iron (Fe) deficiencies, and (ii) t o assess the role of different genomes in PS release from roots under diffe rent regimes of Zn and Fe supply. Phytosiderophores released from roots wer e determined both by measurement of Cu mobilized from a Cu-loaded resin and identification by using HPLC analysis. Compared to tetraploid wheats, dipl oid and hexaploid wheats were less affected by Zn deficiency as judged from the severity of leaf symptoms. Aegilops tauschii showed very slight Zn def iciency symptoms possibly due to its slower growth rate. Under Fe-deficient conditions, all wheat genotypes used were similarly chlorotic; however, de velopment of chlorosis was first observed in tetraploid wheats. Correlation between PS release rate determined by Cu-mobilization test and HPLC analys is was highly significant. According to HPLC analysis, all genotypes of Tri ticum and Ae. tauschii species released only one PS, 2 ' -deoxymugineic aci d, both under Fe and Zn deficiency. Under Zn deficiency, rates of PS releas e in tetraploid wheats averaged 1 mu mol (30 plants)(-1) (3 h)(-1), while i n hexaploid wheats rate of PS release was around 14 mu mol (30 plants)(-1) (3 h)(-1). Diploid wheats and Ae. tauschii accessions behaved similarly in their capacity to release PS and intermediate between tetraploid and hexapl oid wheats regarding the PS release capacity. All Triticum and Aegilops spe cies released more PS under Fe than Zn deficiency, particularly when the ra te of PS release was expressed per unit dry weight of roots. On average, th e rates of PS release under Fe deficiency were 3.0, 5.7, 8.4, and 16 mu mol (30 plants)(-1) (3 h)(-1) for Ae. tauschii, diploid, tetraploid and hexapl oid wheats, respectively, The results of the present study show that the PS release mechanism in wheat is expressed effectively when three genomes, A, B and D, come together, indicating complementary action of the correspondi ng genes from A, B and D genomes to activate biosynthesis and release of PS .