In this experiment, soil application effects of certain synthetic zinc-amino chelates i.e., Zn-glutamine [Zn(Gln) 2 ], Zn-glycine [Zn(Gly) 2 ], Zn-arginine [Zn(Arg) 2 ], and Zn-histidine [Zn(His) 2 ], on yield and grain nutritional quality of wheat were compared with a commercial Zn-sulfate fertilizer. Two bread ( Triticumeastivum L. cvs. Back Cross and Kavir) and a durum wheat genotype ( Triticum durum L. cv. Durum) differing in Zn-deficiency tolerance were exposed to 0, 20, and 40 mg kg -1 Zn. All Zn sources were equally applied at planting, tillering, and heading stages at a total rate of 15 mg Zn kg -1 soil. The experiment was set up on factorial arranged in a completely randomized design, each treatment contained three replicates. Plants were sampled at the tillering sta ge for analysis of catalase (CAT) and ascorbateproxidase (APX) in the shoots and at the maturity stage for grain yield and quality attributes. Soil application of Zn fertilizer significantly increased grain yield of all three wheat genotypes, although the magnitude of this increase varied dependent on the applied Zn source and plant genotype. Application of 20 mg kg -1 Zn from all Zn fertilizer sources, except Zn(His) 2 significantly increased the grain yield of 'Durum'. The grain yield of wheat plants supplied with Zn(Gly) 2 and Zn(Gln) 2 was 46 and 14% higher than those supplied with Zn-sulfate, respectively. Soil application of Zn(Gly) 2 and Zn-sulfate had no significant effect on grain protein content. In contrast, Zn(Gln) 2 , Zn(Arg) 2 , and Zn(His) 2 treatments increased grain protein content of all three wheat genotypes in comparison with Zn-sulfate and control treatments. The wheat plants supplied with Zn(Arg) 2 and Zn(His) 2 also accumulated higher Zn and Fe in their grains than those supplied with the other Zn fertilizers. Soil application of Zn(Arg) 2 reduced molar ratio of phytic acid to Zn in wheat grain. The effect of Zn-amino chelates on activity of catalase (CAT) and ascorbate proxidase (APX) was dependent on the amino chelate type and wheat cultivar. Zinc-amino chelates resulted in increase of CAT activity in the leaves of Kavir and Back Cross cultivars while they were ineffective in Durum cultivar. In all three wheat cultivars, leaf activity of APX was also significantly increased by Zn(His) 2 and Zn(Arg) 2 over the Zn-sulfate treatment. The results obtained from the present study showed that soil applied Zn-amino acid chelates are more effective than Zn-sulfate in supplying Zn for wheat.
