The Variation Of Phytic Acid Content And Its Related To Filling Physiological Property Of Rice Grain

Carbon, nitrogen and phosphorus metabolisms are most active during seed development in rice, which are closely related to the formation of yield and quality .In C metabolism, the assimilates transported from the leaves and stems are used for starch synthesis and deposited in the amyloplast of the starchy endosperm through carbon metabolism. The most nitrogen and phosphorus taken up from soil and stored in the shoots before flowering are assimilated and accumulated in the form of protein and phytic acid. In a matured rice grain, carbohydrates is predominant, occuping about 90% of total dry matter, followed by protein content, being about 8%, and phytic acid content is only around 0.8%, in addition to some minerals. Thus, minerals phytic acid and protein content in rice grain is actually final demonstration of C, N and P metabolism during grain development.In this papar, the variation of grain phytic acid among different environment condition and its relation to the characteristics of grain filling were investigated by field experiment with several cultivars. The results showed that several cultivars from different locations of China were evaluated on minerals phytic acid and protein content in rice grain, to determine the phytic acid variations in different cultivars and the effect of environment, and two pairs of mutated rice cultivars were used to investigate the time-course of phytic acid accumulation in rice grains and the characterics during grain filling. From the starch metabolism aspect, the effects on the enzyme related to starch metabolism of genes mutated of phytic acid is analyzed. The main results are shown as follows:1. phytic acid variations in different cultivars and the effect of environmentData from 2004 and 2005 were analyzed variations of phytic acid in different cultivars and agronomy characterics and correlation of total protein, phytic acid and minerals. The result showed that phytic acid content ranged from 0.553%-0.791% in 2004 and from 0.622%-0.774% in 2005, respectively. Two pairs of mutated rice cultivars were planted four plots in Zhejiang province. The results of the ANOVA show that effect of both locations and cultivars and locations×cultivars is significant, with the effect of locations×cultivars exhibting the largest. MS,implying that phytic acid is largely influnced by environments, There was significant difference in phytic acid of rice grains planted among different locations.2. Positional variation in grain mineral nutrients within a rice panicle and its relation to phytic acid concentrationSix japonica rice cultivars, differing in panicle type and grain density, were used to investigate the effect of grain position on the concentration of major mineral nutrients, including K, Mg, Na, Ca, Mn, Zn, Fe and Cu, and its relation to phytic acid (PA) and grain weight within a panicle. Grain position significantly affected the concentrations of all 8 metal minerals in both the vertical and horizontal axes of a rice panicle, with grains located on TPR (Top primary rachis) and MPR(Middle primary rachis) being substantially higher than those on BSR (Bottom secondary rachis) and MSR (Middle secondary rachis). The effects of grain positions on Na, Fe and Cu concentrations was more substantial than those on Ca and Zn, although no significant correlations were generally found for the concentrations of various mineral elements among 6 cultivars, in term of their averages of different positions. Heavy weight grains, located on PR (Primary rachis) and TR (Top rachis), generally had higher mineral concentrations and molar ratios of PA(Phytic acid)/Zn and PA/Zn, but lower PA concentration compared to the small weight grains located on PR (Secondary rachis) and BR (Bottom rachis), regardless of cultivars. However, On the basis of 6 rice cultivars, no significant correlations were found between PA and mineral elements, and between also grain weight and most of the desirable mineral concentrations, except for PA-Mg (0.903**)and weight grain-Ca (-0.878*). These results suggested that the concentrations of desirable minerals, especially Zn and Fe, and their bioavailability, could be enhanced simultaneously by the modification of their panicle patterns, and it might be feasible to select the rice cultivars with low PA and high mineral nutrients for further breeding strategy without sacrificing their high yields.3. Grain Phytic Acid Variation Among Different Nitrogen, Phosphorus and Zinc Concentrations at the Developing Stage and its Correlation With Several Minerals in Rice GrainsEffect of N, P and Zn treatments on grain phytic acid and its association with several mineral contents were examined under the solution cultivation condition using 4 rice cultivars, including indica cultivar-Xieqingzao (XQZ) and its low PA mutation (Os-1pa-XQZ1), and japonica cultivar-Xioushuil10 and its low PA mutation (Os-1pa-XS110-1). The results showed: there were generally higher grain phytic acid content for high N, P and Zn treatments in comparison of low N,P and Zn treatments at rice developing stage, although their response sensitivities to P and Zn treatments were cultivars-dependent; the concentrations of N, P and Zn in solution had a considerable influence on mineral accumulation in rice grains, with high N and P treatments enhancing Fe, but lowering Cu accumulation in rice grains, respectively. Compared with low Zn treatment, relatively lower grain Fe concentration, but more grain K, Mg accumulation could be found for high Zn treatment; Grain PA was positively correlated with K, Mg, Fe and Cu concentrations in rice grains, but negatively with grain Zn concentration among different solution treatments, despites of their statistically significance varying with cultivars. This result implied that their micro-nutritional quality could be synchronously improved for low PA mutations, if an appropriate cultivation method was applied to enhance K, Mg, Fe and Zn concentrations in rice grains.4. The effect of different cultivation patterns and nitrogen application on phytic acid accumulation and rice nutritional qualityThe experiment with conventional irrigation (c1), plastic film mulching cultivation(c2), drought cultivation(c3). On the basis of treatment ,three nitrogen levels was used. The result showed compared with conventional irrigation, drought cultivation increased total phosphorus of rice grain,reduced phytic acid and inorganic phosphorus. For the same nitrogen application, the grain nitrogen of drought cultivation, compared of those conventional irrigation and plastic film mulching cultivation was lower. These indicated that reasonable fertilizer and water management could change nitrogen nutrition of rice, promote protein content of rice grain, release phytic acid content and nitrogen can increase the total phosphorus.5. The effect on grain starch metabolism of phytic acid gene mutationTwo early indica rice genotypes, differing in PA, namely Xieqingzao and its low PA mutant (Os-1pa-XQZ1) , were conducted to investigate their difference in the pattern of grain PA and starch accumulation and its relation to sucrose content, starch and dry matter accumulation in leaf, stem and sheath,and also the time-course of some key enzymes involving in starch synthesis were discussed, The results showed that low ability of sucrose cleavage and starch synthesis in Os-1pa-XQZ1 grain were contributed to excessive accumulation of sucrose and poor synthesis of starch ,thus leading to poorer senescene and lower grain weight compared to Xieqingzao,in addition, the decline of ADPG-Ppase activity was responsible for low starch accumulation of Os-1pa-XQZ1.