PHYTIC ACID AND PHOSPHORUS CONCENTRATIONS IN SEEDS OF WHEAT CULTIVARS GROWN WITH AND WITHOUT ZINC FERTILIZATION^*

Abstract

Seeds of twenty wheat cultivars grown with (+Zn = 23 kg Zn ha⁻¹) and without zinc (Zn) fertilization in a Zn-deficient calcareous soil in Central Anatolia were analyzed for the levels of Zn, phosphorus (P), phytic acid, and phytase activity. Additionally, seeds of four wheat cultivars grown on 55 different locations in Turkey were also analyzed for Zn, P, and phytic acid. In the field experiment with 20 wheat cultivars, seed Zn concentrations showed a range between 7 to 11 mg kg⁻¹ under Zn-deficient and 14 to 23 mg kg⁻¹ under Zn-added conditions. Zinc fertilization reduced seed concentrations of P and phytic acid of all cultivars. On average, the reductions caused by Zn fertilization were from 3.9 to 3.5 mg g⁻¹ for P and from 10.7 to 9.1 mg g⁻¹ for phytic acid. Irrespective of Zn fertilization, seed phytic acid concentrations showed a large genotypic variation, i.e., from 7 to 12 mg g⁻¹ with Zn fertilization and 8 to 13 mg g⁻¹ at nil Zn treatment. As a result of decreases in phytic acid and increases in Zn concentrations by Zn fertilization, phytic acid to Zn molar ratios in seeds of cultivars markedly decreased. On average for all cultivars, phytic acid to Zn molar ratios decreased from 126 to 56 with Zn fertilization. Seed phytase activity of cultivars was not consistently influenced by varied Zn supply. However, on average for 20 cultivars, Zn fertilization tended to decrease phytase activity. In seeds of four wheat cultivars collected from 55 locations, the concentrations of Zn, P, and phytic acid ranged from 8 to 34 mg kg⁻¹, 2.1 to 4.9 mg g⁻¹, and 5.8 to 14.3 mg kg⁻¹, respectively. Results obtained in the present study indicate that seed Zn concentrations of wheat cultivars grown in different locations of Turkey, especially under Zn-deficient conditions, are very low. Considering very high phytic acid : Zn molar ratios it can be suggested that bioavailability of Zn would be very low for humans.

^*Dedicated to the memory of the late Professor Dr. Ferhan Hatipoglu.

ACKNOWLEDGMENTS

This study was supported by NATO Scientific Affairs Division in the framework of the Science for Stability Programme and by the DANIDA Project coordinated by the International Food Policy Research Institute, Washington, D.C., USA.

Notes

^*Dedicated to the memory of the late Professor Dr. Ferhan Hatipoglu.