Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2006
Publication Date: 11/21/2006
Citation: Bowen, D.E., Guttieri, M.J., Peterson, K.L., Raboy, V., Souza, E.J. 2006. Phosphorus Fractions in Developing Seeds of Four Low Phytate Barley (Hordeum vulgare L.) Genotypes. Crop Science 46: 2468-2473
Interpretive Summary: Developing seeds accumulate essentially all the nutrients necessary for seedling growth following germination, including phosphorus. Phosphorus is a major nutrient of importance to all life, from bacteria and other microorganisms to plants and animals. From 60% to 80% or more of the total phosphorus in seeds is found as one compound called phytic acid. An important component of the remaining phosphorus, the “non-phytic acid phosphorus” in seeds, is inorganic P. The phosphorus fractions during seed development were studied in normal barley and a series of four low phytic acid mutations in barley. These mutations block the ability of developing seeds to convert inorganic P into phytic acid P. As a result low phytic acid seeds have reduced phytic acid P accompanied mostly by increased inorganic P, so that seed total P is largely unchanged. The four mutations studied are called low phytic acid 1-1. low phytic acid 2-1, low phytic acid 3-1, and M 955. They result in reductions in mature seed phytic acid of about 50%, 50%, 70% and 90%, respectively. This study demonstrated that in each case the effect of the mutation was observed at all points tested during seed development, and the block in the ability of the developing seeds to synthesize phytic acid did result in parallel increases in inorganic P. Understanding the chemistry of phosphorus in seeds is important to basic plant biology and to agriculture.
Technical Abstract: Low phytic acid (lpa) crops have reductions in the amount of seed phytic acid (myo-inositol hexakisphosphate, InsP6) and increases in inorganic phosphorus (Pi) with little change to the amount of total seed P. In this study, four barley lpa genotypes (lpa1 2, lpa2-1, lpa3-1, and M955), backcross wild-type (wt) sib-selections, and original parental line ‘Harrington’ were grown in the field over two years. Developing seed was harvested once a week for three weeks and then again at physiological maturity, and the seeds assayed for levels of total P, Pi, and phytic acid P. Total phosphorus concentration showed no consistent differences between the lpa genotypes and Harrington. Inorganic P declined during development in the wt genotypes; however in lpa genotypes, inorganic P declined during the first few weeks of development, and then increased from 24 days to maturity. Phytic acid concentration increased steadily during development for the wt lines and barley lpa1-1 and lpa2-1, although the increase was much slower in the lpa lines. The lpa3-1 and M955 had very little InsP6 accumulation until later in development, with little to no increase in the amount of phytic acid in mature seed of M955 compared to the developing seeds of lpa3-1. This information is useful in understanding timing of phosphorus accumulation in seeds, as well as the nature of the low phytic acid mutation in seed development.