Analysis of rice grain protein composition in the context of rice grain quality

Protein (composed of prolamin, glutelin, globulin and albumin) is the second most abundant component in the milled rice grain. It has very diverse properties that may contribute to rice grain quality. Rice grain protein extraction and high-performance liquid chromatography methods were developed and applied into different sets of short, medium and long grain advanced breeding lines. Rice prolamin and albumin were extracted with 60% n-propanol, while the glutelin and globulin were extracted with 5M acetic acid. Analyses of protein extracts revealed differences in rice grain storage protein composition which were associated with rice grain texture and head rice yield

Prospects for Genetic Improvement in Internal Nitrogen Use Efficiency in Rice

While improving the efficiency at which rice plants take up fertiliser nitrogen (N) will be critical for the sustainability of rice (Oryza sativa L.) farming systems in future, improving the grain yield of rice produced per unit of N accumulated in aboveground plant material (agronomic N use efficiency; NUEagron) through breeding may also be a viable means of improving the sustainability of rice cropping. Given that NUEagron (grain yield/total N uptake) is a function of harvest index (HI; grain yield/crop biomass) × crop biomass/total N uptake, and that improving HI is already the target of most breeding programs, and specific improvement in NUEagron can only really be achieved by increasing the crop biomass/N uptake. Since rice crops take up around 80% of total crop N prior to flowering, improving the biomass/N uptake (NUEveg) prior to, or at, flowering may be the best means to improve the NUEagron. Ultimately, however, enhanced NUEagron may come at the expense of grain protein unless the N harvest index increases concurrently. We investigated the relationships between NUEagron, total N uptake, grain yield, grain N concentration (i.e., protein) and N harvest index (NHI) in 16 rice genotypes under optimal N conditions over two seasons to determine if scope exists to improve the NHI and/or grain protein, while maintaining or enhancing NUEagron in rice. Using data from these experiments and from an additional experiment with cv. IR64 under optimum conditions at an experimental farm to establish a benchmark for NUE parameters in high-input, high yielding conditions, we simulated theoretical potential improvements in NUEveg that could be achieved in both low and high-input scenarios by manipulating target NHIs and grain protein levels. Simulations suggested that scope exists to increase grain protein levels in low yielding scenarios with only modest (5–10%) reductions in current NUEagron by increasing the current NHI from 0.6 to 0.8. Furthermore, substantial scope exists to improve NUEveg (and therefore NUEagron) in high-yielding scenarios if maintaining current grain protein levels of 7.3% is not essential

Rice grain protein composition influences instrumental measures of rice cooking and eating quality

Rice cultivar starch composition differences do not completely explain variation in rice cooking and eating quality. Rice grain storage proteins possess divergent solubility properties suggesting they may contribute to cultivar differences in rice grain quality. Application of high-performance liquid chromatography (HPLC) analysis to protein extracts derived from medium and long grain advanced rice breeding lines revealed rice grain protein composition differences which were associated with instrumental measures of grain quality. Globulin content displayed little variation in both grain types. The mean glutelin content was higher in long grain rice lines than medium grains. Although the mean content of prolamins in medium and long grain rice were similar, the prolamin content of medium grains was more variable. Individual medium grain prolamin HPLC peaks, total prolamin content and the prolamin:glutelin + prolamin ratio were positively correlated with several rapid visco analyser (RVA) parameters. The long grain HPLC data displayed a similar pattern of correlations with RVA parameters but of reduced magnitude. Protein composition was associated with instrumental measures of grain quality in this set of germplasm and although the textural properties of rice are complex, these data suggest consideration of rice grain protein composition could contribute to breeding high quality rice

Rice grain protein composition influences head rice yield

Background and objectives: The objective of this study was to determine the extent to which differences in rice grain protein composition are associated with head rice yield (HRY). HRY, the mass of milled unbroken rice grain derived from a defined mass of paddy rice expressed as a percentage, is a commercially important trait targeted by rice breeders. Variation in rice grain protein composi- tion influences rice grain texture, and high grain protein content is associated with high HRY; however, the relations hip between rice grain protein composition and HRY is not well understood. Findings: HPLC analysis of protein extracts derived from broken and unbroken milled medium- and long-grain rice suggests that rice grain protein composition differences are associated with HRY. Glutelin, a major class of rice grain storage proteins, displayed the greatest difference between broken and unbroken rice grains but weakest association with HRY . Prolamin and globulin content dis- played relatively smaller differences between broken and unbroken medium and long grains, yet both protein fractions were associ ated with HRY. Conclusions: Rice grain protein composition, in addition to other known factors, influences rice HRY. Significance and novelty: Protein composition differences between broken and unbroken rice grains have significant implications for human nutrition and in part explain differences in HRY. Rice breeders face the challenge of balancing the two competing traits of HRY and soft grain texture

The End of the Constitutional Beginning

More than two billion people are micronutrient deficient. Polished grains of popular rice varieties have concentration of approximately 2 μg g−1 iron (Fe) and 16 μg g−1 zinc (Zn). The HarvestPlus breeding programs for biofortified rice target 13 μg g−1 Fe and 28 μg g−1 Zn to reach approximately 30% of the estimated average requirement (EAR). Reports on engineering Fe content in rice have shown an increase up to 18 μg g−1 in glasshouse settings; in contrast, under field conditions, 4 μg g−1 was the highest reported concentration. Here, we report on selected transgenic events, field evaluated in two countries, showing 15 μg g−1 Fe and 45.7 μg g−1 Zn in polished grain. Rigorous selection was applied to 1,689 IR64 transgenic events for insert cleanliness and, trait and agronomic performances. Event NASFer-274 containing rice nicotianamine synthase (OsNAS2) and soybean ferritin (SferH-1) genes showed a single locus insertion without a yield penalty or altered grain quality. Endosperm Fe and Zn enrichment was visualized by X-ray fluorescence imaging. The Caco-2 cell assay indicated that Fe is bioavailable. No harmful heavy metals were detected in the grain. The trait remained stable in different genotype backgrounds