Poster: Seed Biology

Abs # 550: Low Phytic Acid Rice: Grain Structure and Mineral Nutrients

Presenter:	Lott, John NA, lott@mcmaster.ca
Authors	Lott, John NA (D)   Liu, Jessica C (A)   Ockenden, Irene  (B)   Truax, Michael  (C)
Affiliations:	(A): McMaster University

The main mineral nutrient storage compound in seeds/grains is phytate, a cation salt of the effective chelator called phytic acid (PA). Phytic acid is not broken down in the digestive tract of monogastric animals including humans, poultry and swine and thus reduces the bioavailability of iron, zinc and calcium. Phytate also contributes to phosphate pollution of waterways through manure. This study describes differences and similarities between normal Kaybonnet rice grains and grains of a low phytic acid (lpa 1-1) mutant in which the PA concentration is reduced by about 45% while the total phosphorus concentration remains at about the normal level. Electron microscopy of aleurone cells revealed that protein bodies in the normal grain had much larger diameter phytate globoids than in the lpa grains, which had numerous smaller globoids. Reduction in globoid size/volume is consistent with the PA reduction in the lpa grains. Energy dispersive x-ray analysis showed that, in both types of dry grains, the globoids in aleurone cells contained mainly P, K and Mg with occasional traces of Ca, Mn, Fe, or Zn. The lpa mutant did not shift mineral nutrient stores into the starchy endosperm which has a low concentration of phytate in both strains. Atomic absorption analyses of K, Mg, Ca, Fe, Mn and Zn in grain fractions from both grain types showed small differences, but overall indicate that the lpa mutation did not radically alter the mineral nutrient element content compared to the normal Kaybonnet strain.