The concentrations and distributions of phytic acid phosphorus and other mineral nutrients in wild-type and low phytic acid Js-12-LPA wheat (Triticum aestivum) grain parts

Concentrations of P, phytic acid (myo-inositol hexakisphosphate, IP6), and other mineral storage elements were studied in wild-type and low phytic acid (lpa) genotype Js-12-LPA wheat (Triticum aestivum L.) embryos and rest-of-grain fractions. Environmental scanning electron microscopy images revealed a decreased average size and an increased number of aleurone layer globoids in lpa grains compared with the wild type. Energy-dispersive X-ray analyses of unfixed aleurone layer and scutellum cell cytoplasm revealed mainly C, O, P, K, and Mg in both grain types. The starchy endosperm contained virtually no P, K, or Mg, demonstrating no shift of mineral nutrients to that compartment. Scanning transmission electron microscopy – energy-dispersive X-ray analyses of scutellum and aleurone layer globoids in both genotypes revealed that P, K, and Mg were the main mineral nutrients in globoids with low amounts of Ca, Fe, and Zn. Traces of Mn were only in scutellum globoids. Total P was similar between genotypes for the rest-of-grain fractions, which are 97% of grain mass. The main inositol phosphate was IP6, but a small amount of IP5 was present. Both lpa grain fractions exhibited major reductions in IP6 compared with the wild type and a threefold increase in inorganic P. The concentration of K decreased in both fractions, while Ca increased 25% in the Js-12-LPA rest-of-grain compared with the wild type. The lack of large differences in mineral concentration and distribution between the wild type and Js-12-LPA indicates that there is no direct role of localization of IP6 synthesis in mineral distribution.

The concentrations and distribution of phytic acid-phosphorus and other mineral nutrients in wild-type and low phytic acid1-1 (lpa1-1) corn (Zea mays L.) grains and grain parts

A comparison of mineral nutrient and phytic acid-phosphorus (PA-P) distribution in the grains of wild-type (WT) and low phytic acid1-1 (lpa1-1) corn (Zea mays L.) was conducted to determine how the lpa1-1 mutation influences mineral element concentrations in different grain parts and impacts the structure of phosphorus-rich inclusions (globoids) in the grain cells. This is the first report regarding total phosphorus (P) and PA-P concentrations in scutellum and root-shoot axis portions of cereal embryos of WT in comparison to its matching lpa1-1 genotype. In WT, 95% of the grain PA-P was located in the embryo, mostly in the scutellum. The lpa1-1 mutation reduced whole-grain PA-P by 62% but influenced the scutella more than the root-shoot axes and rest-of-grain fractions. In spite of the lpa1-1 mutants containing greatly reduced PA-P, whole-grain amounts of Mg, Fe, and Mn were higher in lpa1-1 than in WT, K and Zn were similar, and Ca was lower. Iron was 1/3 higher in lpa1-1 grains than WT while Ca was 18% lower. Decreased phytic acid in lpa1-1 grains resulted in reduction in globoid size in both scutellum and aleurone layer cells. Most lpa1-1 aleurone globoids were non-spherical and scutellum globoids were clusters of small spheres while WT globoids were large discrete spheres. X-ray analyses of globoids in both grain types revealed major amounts of P, K, and Mg and traces of Ca, Fe, and Zn. Both grain types contained almost no mineral nutrient stores in the starchy endosperm.Key words: corn (Zea mays L.), phytic acid-phosphorus, low phytic acid1-1 (lpa1-1) grains, mineral nutrients, globoids, electron microscopy.

Elements present in mineral nutrient reserves in dry Arabidopsis thaliana seeds of wild type and pho1, pho2, and man1 mutants

Comparison of wild type and mutants of Arabidopsis thaliana offers an opportunity to study the genetic control of nutrient storage in seeds. We used energy dispersive X-ray analysis to determine the elements present and their relative amounts in globoids of dry wild-type seeds, as well as seeds of a reduced total P uptake mutant (pho1), a phosphate accumulator (pho2), and a metal accumulator (man1). Globoids are spherical inclusions, rich in phytate that function as a store for inositol, P, K, Mg, Ca, Fe, and Zn. Key findings of this study were the following: (i) globoids in protein bodies from nine different tissues and (or) organs in dry Arabidopsis thaliana seeds contained P, K, Mg, and Ca, and sometimes traces of Fe and Zn; (ii) globoids contained higher Ca and lower Mg amounts than occur in globoids in seeds of most other plant species; (iii) globoids in comparable tissue and (or) organ regions of seeds were very similar in elemental composition for wild type and all mutant plants.Key words: Arabidopsis, dry seeds, phytate, mineral nutrient mutants, phosphorus, globoids.