Submitted to: Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/9/2004
Publication Date: 11/1/2004
Citation: Ockenden, I., Dorsch, J.A., Reid, M.M., Lin, L., Grant, L.K., Raboy, V., Lott, J.N. 2004. Characterization of the storage of phosphorus, inositol phosphate and cations in grain tissues of four barley (hHordeum vulgare lL.) low phytic acid genetoypes. Plant Science 167: 1131-1142. Interpretive Summary: Phytic acid is the storage form of phosphorus in seeds. It is not readily digestible by non-ruminant livestock such as poultry, swine and fish, nor by humans. This can cause significant problems in the management of phosphorus in livestock production, and in human nutrition and health. Understanding how seeds make phytic acid and how this is altered in 'low phytic acid' mutations, is important to plant biology and to crop improvement. This research studied the storage of phosphorus, phytic acid and minerals in normal barley seeds versus low phytic acid barley seeds. It found that that the phosphorus and minerals in low phytic acid seeds were stored as they are in normal seeds. This indicates that the storage of phosphorus and minerals is not solely dependent on the ability of seeds to make phytic acid. This work also showed that one barley gene, barley lpa1 is specific to the aleurone layer, and has no effect on the germ. This information should prove useful in crop breeding.
Technical Abstract: The synthesis of phytic acid (myo-inositol hexakisphosphate or Ins P6), and its deposition as a mixed salt of mineral cations, is thought to be central to phosphorus (P) and mineral storage, homeostasis and redistribution during grain development. Phosphorus and mineral storage were studied in grains homozygous for four barley (Hordeum vulgare L.) low phytic acid (lpa) mutations named lpa1-1, M 635, M 955, and lpa2-1. In wild-type (WT) grain both the embryo and rest-of-grain (aleurone layer) contained about 10% and 90% of whole grain total P and Ins P, respectively, with Ins P primarily consisting of phytic acid. In M 635 and M 955 proportional reductions in both embryo and aleurone layer Ins P contributed to the whole-grain Ins P6 reductions typical of these mutations, with little or no effect on embryo or aleurone layer total P. In terms of total P these mutations show no grain tissue-specificity. In contrast, whole-grain Ins P6 reduction in lpa1-1 and lpa2-1 is solely or largely aleurone layer specific. In lpa1-1 grain the distribution of total P also shifted in part, from rest-of-grain to embryo, with a net reduction in whole grain total P. Electron microscopy showed a general reduction, as compared with WT, in electron-dense globoids (phytate deposits) in both aleurone and scutellum protein storage vacuoles in all mutants except lpa2-1, whose globoid morphology appeared indistinguishable from WT. Energy-dispersive X-ray analyses of P, K Mg, Ca, Fe, and Zn indicated that, with few exceptions, the relative levels were similar in mutant and WT aleurone layer and scutellum tissues. These analyses suggest that inorganic P found in lpa grains is stored as salts of K and Mg, as is phytic acid in WT grain, and that the cellular machinery for P and mineral storage and homeostasis in grains is not wholly dependent on phytic acid synthesis.