Grain Quality And Developmental Characteristics And Related Molecular Genetical Analysis Of Low Phytate Mutant Rice (Oryza Sativa L.)

Phytic acid (myo-inositol 1,2,3,4,5,6-hexakisphosphate) typically represents at least 65% of seed total P for cereal grains. As a strong anti-nutritional chelator, phytic acid can form salt compounds with mineral nutrients, i.e., Fe and Zn. These phytates, however, are largely indigestible by humans and other non-ruminant animals, therefore, the bioavailability of mineral nutrients is greatly decreased, which appears to be the most important reason responsible for micro-mineral deficiency of human beings depending on cereals and legumes as staple foods. In addition, phytic acid can also affect the absorption by humans of protein, starch and fat utilisation. Furthermore, more and more attention has been drawn to the increase of feed cost and water pollution resulting from the decreased bioavailability of phosphorus deposited in phytic acid. Recently, breeding of low phytic acid crops has opened a new approach to settle nutritional and environmental issues related with phytic acid.In the present study, hull, bran, milled rice, brown rice, and whole rice grain of three non-allelic mutant lines and their wild-types, i.e., the indica mutant HIPi1 vs Xieqingzao (XQZ), and japonica mutant lines HIPj1 and HIPj2 vs Xiushui 110 (XS110), were analyzed for the concentration of six different types of phosphorus (P) and mineral elements. The environmental impacts on the concentration of these items were also investigated. The characteristics of protein and starch in milled rice, and kernel filling profiles including changes in inorganic P (IP) and phytic acid P (PAP) during grain development were studied, the direct and indirect effects of low phytic acid mutation were thus evluated in detail. At the same time, the expression of the MIPS and RM48-PA(t) (linkage to HIPil mutated locus) genes was also studied. The main results were as follows:1. In every component and on the basis of brown rice and whole rice grain, all mutants had the same concentration of total P (TP) as their corresponding wild-types, but significantly decreased Ins polyphosphates (InsP) and phytic acid P (PAP) and increased inorganic P (IP) concentration; In miled rice and rice hull, and on the basis of brown rice and whole rice grain, HIPi1 and HIPj1 had lower concentration of lower Ins polyphosphates (LInsP: Ins bis-, tris, tetrakis-, and pentakisphosphates) than their corresponding parents, and onthe opposite in the bran, while HIPj2 kept similar to XS110 in all parts.; the concentration of cellular P (CP) in every component together with brown rice and rice grain of HIPi1 and HIPj1 was decreased, while the concentration in these fractions of HIPj2 was increased. As compared with their corresponding wild-type, the distribution of TP within the kernels of all mutants was almost the same; all mutants fractioned more InsP, PAP, IP, and CP into bran, and equivalently partitioned less into milled rice; the distributional variation of LInsP among kernels of mutants was irregular in contrast to their corresponding wild-types. The concentration of every type of P in hull and bran, IP and CP in brown rice and rice grain of both mutants and their wild-types were all be greatly effected by environmental factors.2. Whether on the basis of rice grain or brown rice, the concentrations of mineral macronutrients (K, Ca and Mg) in HIPil were significantly increased compared to those in XQZ, while all kept similar in HIPj1 and HIPj2 to that in XS110. On the basis of whole rice grain, the concentration of Fe and Cu in all mutants was less than that in their wild-types, but that of Zn was higher in mutant lines; however, on the baseis of brown rice, the concentration of Fe and Zn in mutants was higher than that in wild-types. All mutant lines had increased percentage of all mineral elements analyzed except Zn in milled rice over whole grain compared with their correponding wild-types. Phytate/Zn molar ratio in milled rice and brown rice of mutants was fallen between 5 and 15 (more than 15 for wild-types), in addition, phytate/Fe molar ratio was also markedly reduced, these pheno...