Genetics and breeding of seed phosphorus and phytic acid

The isolation of cereal low phytic acid ( lpa) mutants provides a novel approach to studying the biology of seed phytic acid ( myo-inositol-1,2,3,4,5,6-hexa kisphosphate or Ins P 6), and to dealing with environmental and nutritional problems associated with it. Seed produced by lpa lines contain normal levels of total phosphorus (P), but greatly reduced levels of phytic acid P. Two phenotypically distinct types of lpa mutants have been isolated in maize ( Zea mays L.), barley ( Hordeum vulgare L.), and rice ( Oryza sativa L.). In « lpa1-like» mutants, seed phytic acid P reductions ranging from 50 percnt; to 95 percnt; (in comparison with levels typical of non-mutant seed) are largely matched by corresponding increases in inorganic P. In « lpa2-like» mutants, seed phytic acid P reductions ranging from 50 percnt; to 75 percnt; are matched by increases in both inorganic P and in myo-inositol (Ins) phosphates containing five or fewer P esters (compared with phytic acid's six P esters). In all cases the sum of seed Ins phosphates (including phytic acid) and inorganic P remains constant and similar to that in normal seeds. Some lpa alleles are lethal as homozygotes, others have a negative effect on plant or seed growth and function but are viable, still others have little effect and are being used to breed «low phytate» maize and barley types. Progress in lpa genetics and breeding, and the animal and human nutrition studies conducted with these new crop types, will be reviewed.