University of Milan
Isolation and preliminary characterization of a maize low phytic acid mutant --Pilu,R, Gavazzi, G, Nielsen E*
*Dipartimento di Genetica e Microbiologia, Università degli Studi di Pavia
Phytic acid (phytine), myo-inositol 1,2,3,4,5,6-hexakisphosphate (IP6), is the major storage compound of phosphorous in plants, accumulating predominantly in seeds (up to 4-5% of dry weight) and pollen. In cereals, up to 80% of P is present as phytate P, which has generally very little bio-availability for monogastric animals due to their lack of phytase activity. As a consequence, it is common to supplement the animals' diet with inorganic phosphate or, in the last decade, with microbial phytase (Pointillart et al., 1987). The latter practice has been shown to increase the utilization of feed P by animals, as well as to decrease the amount of the phytic P excreted with manure, thus significantly reducing eutrophication of surface water. Recently, transgenic seeds were obtained accumulating Aspergillus phytase, which can then be included in feeds for animals (Pen et al., 1993).

An alternative strategy to tackle the problem consists in the isolation of cereal mutants accumulating less phytic P and more free phosphate in the seed (Raboy et al. 1990, Rasmussen et al. 1998). We have chosen to apply this approach in maize.

Since normal mature maize seeds contain high phytate phosphate and low free phosphate levels, a screening for high level of free phosphate in seeds provides a quick and inherently sensitive assay for the detection of lpa (low phytic acid) mutants. A population of EMS (ethyl methanesulfonate)-induced mutants was thus generated using the pollen-treatment method and approximately 600 M2 families were screened. The first assay was carried out by titrating free phosphate using the molybdate staining method. Putative mutants were then challenged by a TLC (Thin Layer Chromatography) method allowing the simultaneous detection of free phosphate and phytate.

One monogenic recessive mutation (named lpa 241), causing approximately a ten fold increase in the amount of free phosphate titratable and a reduction of about 90 % of phytic acid, apparently did not affect normal germination or seedling growth. Genetic analysis of this mutation, as well as its biochemical characterization aimed at identifying the biosynthetic step involved are under way.

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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