Characterization of the storage of phosphorus, inositol phosphate and cations in grain tissues of four barley (Hordeum vulgare L.) low phytic acid genotypes

Phosphorus (P), phytic acid (myo-inositol hexakisphosphate or Ins P-6) and mineral storage were studied in grains homozygous for barley (Hordeum vulgare L.) low phytic acid (lpa) mutations named lpal-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. Most of the inositol phosphate (Ins P) was phytic acid. Proportional reductions in both embryo and aleurone layer Ins P contributed to whole-grain Ins P6 reductions in M 635 and M 955, with little 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 lpal-1 and lpa2-1 is solely or largely aleurone layer specific. In lnal-1 the distribution of total P shifted in part, from rest-of-grain to embryo, with a net reduction in total P. Electron microscopy showed a general reduction, as compared with WT, in electron-dense globoids in both aleurone and scutellum cells 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, generally, relative levels were similar in mutant and WT aleurone layer and scutellum tissues. Likely inorganic P found in lpa grains is stored as salts of K and Mg, as is Ins P6 in WT grain. (C) 2004 Elsevier Ireland Ltd. All rights reserved.