Genetics and breeding of seed phosphorus and phytic acid

The isolation of cereal low phytic acid (lpa) mutants provides a novel appr oach 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 nutritio nal 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 ma ize (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 ma tched by corresponding increases in inorganic P. In "lpa2-like" mutants, se ed phytic acid P reductions ranging from 50 % to 75 % are matched by increa ses in both inorganic P and in myo-inositol (Ins) phosphates containing fiv e or fewer P esters (compared with phytic acid's six P esters). In all case s the sum of seed Ins phosphates (including phytic acid) and inorganic P re mains constant and similar to that in normal seeds. Some Ipa alleles are le thal 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 genetic s and breeding, and the animal and human nutrition studies conducted with t hese new crop types, will be reviewed.