The concentrations and distribution of mineral nutrients and phytic acid-phosphorus in wild-type and low phytic acid 1-1 (lpa 1-1) corn (Zea mays L.) grains and grain parts

Abstract

Mature grains of wild-type (WT) and low phytic acid 1-1 (lpa 1-1) mutant from corn (Zea mays L.) were studied for total phosphorus (total P), phytic acid-phosphorus (PA-P), and mineral cations. Whole grain PA-P in lpa 1-1 was reduced 61.6% compared to WT whereas whole grain total P remained constant. Scutellum and root-shoot axis PA-P was 91.6% and 3.6% of WT whole-grain amounts respectively, compared to 89.3% and 4.0% in lpa 1-1. Relative partitioning of PA-P between the scutellum and root-shoot axis was not altered in lpa 1-1 mutant embryos as compared to WT. In lpa 1-1 the total P was slightly decreased in the scutella and increased in both root-shoot axes and rest-of-grain fractions. Whole grain Mg, Fe, and Mn amounts were higher in lpa 1-1 grains than in WT grains; K and Zn were similar, and Ca was lower. The lpa 1-1 whole grains and embryos contained 1/3 higher Fe than WT. For both grain types all measured metallic elements, except Ca, were more concentrated in embryos than the rest-of-grain fractions. Studies showed that WT grains contained larger globoids than lpa 1-1 grains in both scutellum and aleurone layer cells. This globoid size reduction reflected the PA-P decrease. Most lpa 1-1 aleurone globoids were non-spherical and lpa 1-1 scutellum globoids were clusters of spheres while both scutellum and aleurone globoids of WT were discrete spheres. The lpa 1-1 mutation had an impact on the globoid formation. X-ray analyses of scutellum and aleurone layer globoids from both grain types revealed major amounts of P, K, and Mg and traces of Ca, Fe, and Zn. Analysis demonstrated lower P, K and Mg and higher Ca, Fe and Zn in aleurone globoids than scutellum globoids. Both grain types contained almost no mineral nutrient stores in the starchy endosperm, whereas the scutellum was the major site of PA-P and mineral nutrient deposition.