Submitted to: Inositol Phosphates in the Plant and Soil System
Publication Type: Book / Chapter
Publication Acceptance Date: July 5, 2006
Publication Date: December 8, 2006
Repository URL: http://riley.nal.usda.gov/nal_web/digi/submission.html
Citation: Raboy, V. 2006. Seed Phosphorus and the development of low-phytate crops. Inositol Phosphates in the Plant and Soil System 111-132 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. Monogastric animals such as poultry, pigs and fish do not digest seed phytic acid efficiently. As a result, most of the phosphorus in seed-derived feeds used in non-ruminant production normally would end up in animal waste, and could contribute to water pollution. Since the major part of seed phosphorus is not digested by non-ruminants, feeds must be supplemented with either some form of available P, or a supplemental enzyme called phytase. Seed-derived phytic acid in human foods also may represent a nutritional problem, but for different reasons. Phytic acid in food may contribute to mineral deficiency, such as iron and zinc deficiency. This chapter reviews the genetics and biology of seed phytic acid. It then reviews plant breeding approaches to the problem of phytic acid in foods and feeds. Finally, it discusses future directions in studies of phytic acid in plant biology, plant breeding and nutrition.
Technical Abstract: Phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate or InsP6) represents 60% to 80% of mature seed total phosphorus (P), and is important to the nutritional quality of seeds when used in foods and feeds. Studies of the biochemistry of seed phytic acid synthesis indicates a complex, multibranched pathway. Genes encoding several steps in this pathway have been identified, but several steps, including those relating to regulatory and transport functions, remain unresolved at the biochemical or genetic levels. Alleles at several low phytic acid (lpa) loci have been identified in several major cereal crops and in soybean. Homozygosity for an lpa allele greatly reduces seed phytic acid P, but has little or no effect on seed total P. Instead non-phytate P is greatly increased, most often via increases in inorganic P. Poultry, swine and fish nutrition studies have shown that the increase in non-phytate P in lpa seed represents an increase in nutritionally available P. Reduced phytate P and/or increased inorganic P can also enhance calcium nutrition. Use of Low Phytate crops in non-ruminant feeds can also contribute to decreased waste P and may prove useful in reducing the environmental impact of animal production. Human nutrition studies have shown that iron, zinc and calcium are approximately 30% to 50% more available when consumed in meals prepared with lpa maize, as compared with normal maize. Low Phytate crops may therefore also prove useful in addressing nutrition issues important to human populations that rely on cereals and legumes as staple foods. The development of Low Phytate crops represents an alternative to other currently established approaches to dealing with issues related to seed phytic acid, such as the use of feed or food supplementation with P, minerals or the enzyme phytase. Future work is aimed at furthering our knowledge of the molecular biology of seed phytic acid and seed total P, and in developing Low Phytate or Low Total P crops that have optimal agronomic properties.