Seed phosphorus and inositol phosphate phenotype of barley low phytic acid genotypes.
myo-Inositol-1,2,3,4,5,6-hexakisphosphate (Ins P(6) or "phytic acid") typically represents approximately 75% of the total phosphorus and >80% of soluble myo-inositol (Ins) phosphates in seeds. The seed phosphorus and Ins phosphate phenotypes of four non-lethal barley (Hordeum vulgare L.) low phytic acid mutations are described. In seeds homozygous for M 635 and M 955 reductions in Ins P(6), approximately 75 and >90% respectively, are accompanied by reductions in other Ins phosphates and molar-equivalent increases in Pi. This phenotype suggests a block in supply of substrate Ins. In seeds homozygous for barley low phytic acid 1-1 (lpa1-1), a 45% decrease in Ins P(6) is mostly matched by an increase in Pi but also accompanied by small increases in Ins(1,2,3,4,6)P(5). In seeds homozygous for barley lpa2-1, reductions in seed Ins P(6) are accompanied by increases in both Pi and in several Ins phosphates, a phenotype that suggests a lesion in Ins phosphate metabolism, rather than Ins supply. The increased Ins phosphates in barley lpa2-1 seed are: Ins(1,2,3,4,6)P(5); Ins(1,2,4,6)P(4) and/or its enantiomer Ins(2,3,4,6)P(4); Ins(1,2,3,4)P(4) and/or its enantiomer Ins(1,2,3,6)P(4); Ins(1,2,6)P(3) and/or its enantiomer Ins(2,3,4)P(3); Ins(1,5,6)P(3) and/or its enantiomer Ins(3,4,5)P(3) (the methods used here cannot distinguish between enantiomers). This primarily "5-OH" series of Ins phosphates differs from the "1-/3-OH" series observed at elevated levels in seed of the maize lpa2 genotype, but previous chromosomal mapping data indicated that the maize and barley lpa2 loci might be orthologs of a single ancestral gene. Therefore one hypothesis that might explain the differing lpa2 phenotypes is that their common ancestral gene encodes a multi-functional, Ins phosphate kinase with both "1-/-3-" and "5-kinase" activities. A putative pyrophosphate-containing Ins phosphate, possibly an Ins P(7), was also observed in the mature seed of all barley genotypes except lpa2-1. Barley M 955 indicates that at least for this species, the ability to accumulate Ins P(6) can be nearly abolished while retaining at least short-term ( approximately 1.0 years) viability.
Dorsch
John A
JA
USDA-ARS, 1691 South 2700 West, Aberdeen, ID 83210, USA.
Cook
Allen
A
Young
Kevin A
KA
Anderson
Joseph M
JM
Bauman
Andrew T
AT
Volkmann
Carla J
CJ
Murthy
Pushpalatha P N
PP
Raboy
Victor
V
D002851:Chromatography, High Pressure Liquid; D005838:Genotype; D001467:Hordeum / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D007295:Inositol Phosphates / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D019906:Nuclear Magnetic Resonance, Biomolecular; D010641:Phenotype; D010758:Phosphorus / Q000032:analysis*; D010833:Phytic Acid / Q000096:biosynthesis*; D012639:Seeds / Q000737:chemistry / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D013237:Stereoisomerism; D003313:Zea mays / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D007295:Inositol Phosphates; D010758:Phosphorus; D010833:Phytic Acid