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-hexakisphosphate or Ins P-6) and to dealing with environmental and nutritional problems associated with ii. Seed produced by ipa lines contain normal levels of total phosphorus (P), but greatly reduced levels of phytic acid P. Two phenotypically distinct types of ipa 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 % to 95 % tin 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 % to 75 % 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 Ipa 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 Ipa genetics and breeding, and the animal and human nutrition studies conducted with these new crop types, will be reviewed.