Effects of Different Nitrogen Fertilizer Levels and Native Soil Properties on Rice Grain Fe, Zn and Protein Contents

Deposition of protein and metal ions (Fe, Zn) in rice grains is a complex polygenic trait showing considerable environmental effect. To analyze the effect of nitrogen application levels and native soil properties on rice grain protein, iron (Fe) and zinc (Zn) contents, 32 rice genotypes were grown at three different locations each under 80 and 120 kg/hm2 nitrogen fertilizer applications. In treatments with nitrogen fertilizer application, the brown rice grain protein content (GPC) increased significantly (1.1% to 7.0%) under higher nitrogen fertilizer application (120 kg/hm2) whereas grain Fe/Zn contents showed non-significant effect of nitrogen application level, thus suggesting that the rate of uptake and translocation of macro-elements does not influence the uptake and translocation of micro-elements. The pH, organic matter content and inherent Fe/Zn levels of native soil showed significant effects on grain Fe and Zn contents of all the rice genotypes. Grain Zn content of almost all the tested rice genotypes was found to increase at Location III having loamy soil texture, neutral pH value (pH 6.83) and higher organic matter content than the other two locations (Locations I and II), indicating significant influence of native soil properties on brown rice grain Zn content while grain Fe content showed significant genotype × environment interaction effect. Genotypic difference was found to be the most significant factor to affect grain Fe/Zn contents in all the tested rice genotypes, indicating that although native soil properties influence phyto-availability of micronutrients and consequently influencing absorption, translocation and grain deposition of Fe/Zn ions, yet genetic makeup of a plant determines its response to varied soil conditions and other external factors. Two indica rice genotypes R-RF-31 (27.62 μg/g grain Zn content and 7.80% GPC) and R1033-968-2-1 (30.05 μg/g grain Zn content and 8.47% GPC) were identified as high grain Zn and moderate GPC rice genotypes. These results indicate that soil property and organic matter content increase the availability of Fe and Zn in rhizosphere, which in turn enhances the uptake, translocation and redistribution of Fe/Zn into rice grains.     

氮、磷、锌营养对水稻籽粒植酸含量的影响及与几种矿质元素间的相关性

以协青早、秀水110及其辐射诱变获得的低植酸突变系（HIPi1和HIPj1）为材料,通过水培试验对不同氮、磷、锌浓度处理下水稻籽粒植酸含量差异及与几种矿质元素间的相关性进行了比较分析。高水平氮、磷、锌浓度处理的籽粒植酸含量较同一品种的低氮、磷、锌处理均有所降低,但在水稻生育期间,籽粒植酸含量对磷、锌处理浓度变化的敏感性,则因品种的植酸类型特征而异;氮、磷浓度增加能分别提高铁或降低铜在籽粒中的积累,但在高锌处理下,籽粒铁含量明显降低、而钾和镁的含量等却有所升高; 籽粒植酸含量一般与K、Mg、Fe、Cu 4种矿质元素含量呈正相关、与籽粒Zn含量呈负相关,但统计显著水平因品种而异。低植酸突变体籽粒中的K、Mg、Fe、Zn等含量虽略有下降,但可以通过适当的介质营养条件来调节有关矿质营养在水稻籽粒中的积累。     

Response of Iron Content in Milled Rice to Nitrogen Levels and Its Genotypic Differences

To investigate the effect of nitrogen (N) level on iron (Fe) content in milled rice, a field experiment was carried out under three N application levels including 0, 150 and 300 kg/hm² by using 120 rice genotypes. In addition to the genotypic differences of iron content in milled rice, grain yield, 1000-grain weight and N content in grains under the same N level, there were also variations in the response of Fe content in milled rice to N levels. Based on the range and variation coefficient of Fe content in milled rice under the three N levels, the response of Fe content in milled rice to N levels could be classified into four types including highly insensitive, insensitive, sensitive and highly sensitive types. A significant quadratic correlation was found between the Fe content in milled rice and 1000-grain weight or the N content in grains. However, no significant correlation between the Fe content in milled rice and grain yield was detected. In conclusion, there are genotypic differences in the effects of N levels on Fe content in milled rice, which is favorable to breeding of Fe-rich rice under different N environments. Furthermore, high yield and Fe-rich rice could be grown through the regulation of nitrogen on Fe content in milled rice, 1000-grain weight and N content in milled rice.     

Localization of iron in rice grain using synchrotron X-ray fluorescence microscopy and high resolution secondary ion mass spectrometry

Cereal crops accumulate low levels of iron (Fe) of which only a small fraction (5–10%) is bioavailable in human diets. Extensive co-localization of Fe in outer grain tissues with phytic acid, a strong chelator of metal ions, results in the formation of insoluble complexes that cannot be digested by humans. Here we describe the use of synchrotron X-ray fluorescence microscopy (XFM) and high resolution secondary ion mass spectrometry (NanoSIMS) to map the distribution of Fe, zinc (Zn), phosphorus (P) and other elements in the aleurone and subaleurone layers of mature grain from wild-type and an Fe-enriched line of rice (Oryza sativa L.). The results obtained from both XFM and NanoSIMS indicated that most Fe was co-localized with P (indicative of phytic acid) in the aleurone layer but that a small amount of Fe, often present as “hotspots”, extended further into the subaleurone and outer endosperm in a pattern that was not co-localized with P. We hypothesize that Fe in subaleurone and outer endosperm layers of rice grain could be bound to low molecular weight chelators such as nicotianamine and/or deoxymugineic acid.     

Effects of Soil Salinity and Alkalinity on Grain Quality of Tolerant,Semi-Tolerant and Sensitive Rice Genotypes

Soil salinity and alkalinity adversely affects the productivity and grain quality of rice.The grain quality of 19 rice genotypes characterized as salt tolerant (T),semi-tolerant (ST) and sensitive (S) was assessed in lysimeters containing saline and highly alkaline soils.Head rice recovery was reduced by salinity stress whereas it was not affected by alkalinity stress.The ratio of length to width (grain dimensions) was significantly reduced in the T genotype even at low electrical conductivity (EC,4 mS/cm) and alkalinity (pH 9.5),whereas in the ST genotype,it was significantly reduced at high salinity (EC 8 mS/cm).There was no significant effect of any levels of salinity or alkalinity on grain dimensions in the S genotype.Amylose content was significantly reduced in T and ST groups even at low EC (4 mS/cm) and alkalinity (pH 9.5) and the effect in the S genotype was only at high salinity.Starch content showed significant reduction at high salinity and alkalinity (EC 8 mS/cm and pH 9.8) in the T and ST genotypes and no significant effect was observed in the S genotype.The effect of both levels of salinity (EC 4 and 8 mS/cm) and high alkalinity (pH 9.8) on gel consistency was observed only in the S genotype.The tolerant genotypes IR36 under high salinity,and CSR10 and CSR11 under alkali stress showed less reduction in amylose content.The T genotype BR4-10,and ST genotypes CSR30,CSR29 and CSR13 showed better gel consistency under saline and alkali stress.Amylose content was affected even at low salinity stress and thus important to be considered in breeding rice for salt tolerance.Overall,the grain quality of T and ST genotypes was less affected by saline and alkali stress compared to S ones.     

Influence of high temperature during filling period on grain phytic acid and its relation to spikelet sterility and grain weight in non-lethal low phytic acid mutations in rice

Low phytic acid (lpa) crop is considered as an effective strategy to improve crop nutrition. However, the inferior agronomic performance of lpa crops and their environmental growth adaptation have not yet been fully understood. Three rice lpa lines and their corresponding wild-types were used to compare their differences in grain phytic acid (PA) in response to high temperature (HT) and its relation to spikelet sterility and grain weight at a controlled temperature at the filling stage. Results showed that HT caused an increase in grain PA and inorganic phosphate contents, with more substantial increase of PA content for lpa lines compared with corresponding wild-types. This increase in PA content in high temperature-ripened grains was not simply attributed to the reduction in grain weight and relatively enhanced proportion of aleurone-layer fraction to whole grains. Significant increase in PA contents was also detected in milled rice. Moreover, spikelet sterility and grain plumpness of lpa lines were more susceptible to HT stress than those of wild-types. Exogenous PA spraying with an appropriate concentration could increase grain PA content, but it had only a slight contribution to the enhancement of heat-tolerance and injury alleviation for rice exposed to stressful HT.     

Grain quality changes and responses to nitrogen fertilizer of japonica rice cultivars released in the Yangtze River Basin from the 1950s to 2000s

While the yield potential of rice has increased but little is known about the impact of breeding on grain quality, especially under different levels of N availability. In order to investigate the integrated effects of breeding and N levels on rice quality 12 japonica rice cultivars bred in the past60 years in the Yangtze River Basin were used with three levels of N: 0 kg N ha-1, 240 kg N ha-1,and 360 kg N ha-1. During the period, milling quality(brown rice percentage, milled rice percentage, and head rice percentage), appearance quality(chalky kernels percentage, chalky size, and chalkiness), and eating and cooking quality(amylose content, gel consistency, peak viscosity, breakdown, and setback) were significantly improved, but the nutritive value of the grain has declined due to a reduction in protein content. Micronutrients, such as Cu, Mg, and S contents, were decreased, and Fe, Mn, Zn, Na, Ca, K, P, B contents were increased. These changes in grain quality imply that simultaneous improvements in grain yield and grain quality are possible through selection. Overall, application of N fertilizer decreased grain quality, especially in terms of eating and cooking quality. Under higher N levels, higher protein content was the main reason for deterioration of grain quality, although lower amylose content might contribute to improving starch pasting properties. These results suggest that further improvement in grain quality will depend on both breeding and cultivation practices, especially in regard to nitrogen and water management.     

Peptide Transporter OsNPF8.1 Contributes to Sustainable Growth under Salt and Drought Stresses,and Grain Yield under Nitrogen Deficiency in Rice

Peptide transport is important for plant tissues where rapid proteolysis occurs, especially during germination and senescence, to enhance redistribution of organic nitrogen (N). However, the biological role of peptide transporters is poorly investigated in rice. We characterized the function of the peptide transporter OsNPF8.1 of rice nitrate transporter 1/peptide transporter family (NPF). Ectopic expression of OsNPF8.1 in yeast revealed that OsNPF8.1 encoded a high-affinity di-/tri-peptide transporter, and the osnpf8.1 mutants had a lower uptake rate of the fluorescent-labelled dipeptide c in leaves of rice seedlings. Histochemical assays showed that OsNPF8.1 was highly expressed in mesophyll cells and vascular parenchyma cells, but not detected in root hairs and epidermises. Expression of OsNPF8.1 was induced by N deficiency, drought, NaCl and abscisic acid, and kept at a high level in senescing leaves. Under N deficiency conditions, compared with the wild type Zhonghua 11, the osnpf8.1 mutants grew slower at the seedling stage, and had lower grain yield and lower N content in the grains. In contrast, OsNPF8.1-over-expressing rice (OsNPF8.1-OE) grew faster at the seedling stage and had a higher grain yield. The osnpf8.1 seedlings were less tolerant to salt and drought stresses. These results suggested that stress-induced organic N transportation mediated by OsNPF8.1 might contribute to balance plant growth and tolerate to salt/drought stress and N-deficiency.     

Influences of Cadmium on Grain Mineral Nutrient Contents of Two Rice Genotypes Differing in Grain Cadmium Accumulation

A pot experiment was conducted to study the effects of Cd on grain Cd, K, P, Mg, Zn, Cu, Pb, Fe and Mn accumulation in two rice genotypes (Xiushui 63 and Xiushui 217) differing in grain Cd accumulation under four Cd levels, i.e. 0, 0.5, 2.5 and 12.5 mg/kg. Rice genotype greatly affected the grain K content, but not significantly for P, Mg, Zn, Cu, Pb, Fe and Mn contents. There were remarkable effects of additional Cd on the contents of P, Mg and Zn in grains, while not significant for K, Cu, Pb, Fe and Mn contents. No significant differences were found in the interaction of genotype by additional Cd on these nine element contents. The low grain Cd accumulation genotype Xiushui 217 had significantly higher grain K, Mg, Cu and Mn contents than the high grain Cd accumulation genotype Xiushui 63, but the case was opposite for Zn, Pb and Fe contents. It also showed that Cd addition levels significantly influenced the K, P, Mg, Zn, Cu, Pb, Fe and Mn contents in rice grains. Grain K, P, Mg, Zn, Fe and Mn contents reduced with the increasing rate of Cd addition.     

Molecular genetic approaches to increasing mineral availability and vitamin content of cereals

The present paper summarizes the current state of knowledge on molecular genetic approaches to increasing iron and zinc availability and vitamin content in cereals. We have also attempted to integrate the scientific issues into the wider context of human nutrition. In the cereal grain, iron and zinc are preferentially stored together with phytate in membrane-enclosed globoids in the protein storage vacuole (PSV) found in the aleurone and the embryo scutellum. The PSV is accordingly central for understanding mineral deposition during grain filling and mobilization of minerals during germination. Recent studies in Arabidopsis have led to the first identification of iron and zinc transporters of the PSV and further illustrate some of the dynamics associated with mineral and phytate transport and deposition into the vacuole. This provides new opportunities for modulating iron and zinc deposition in the cereal grain. Current strategies towards increasing the iron content of the endosperm are largely based on the expression of legume ferritin genes in an endosperm-specific manner. However, it is apparent that this approach, at least in rice, only allows a two- to three-fold increase in the iron content of the grain due to exhaustion of the iron stores in leaves. Further increases thus have to rely on additional uptake and transport of iron from the root. Phytate is generally considered to be the single most important anti-nutritional factor for iron and zinc availability. In the current paper we summarize attempts to increase phytase activity in the grain by transformation and evaluate the potential of this approach as well as the reduction of phytate biosynthesis for improving the bioavailability of iron and zinc. Vitamins constitute the second important group of micronutrients in grain and we discuss current efforts to increase the amounts of provitamin A, vitamin C and vitamin E.     

Seed physicochemical characteristics of field-grown US weedy red rice (Oryza sativa) biotypes: Contrasts with commercial cultivars

Red rice in the US is an aggressive weed that reduces the yield of rice and contaminates its grain. It is the same species as rice, which provides an opportunity for intercrossing. This genetic similarity complicates the management of red rice in fields and rice mills, but also indicates a potential for its use in rice breeding or niche markets. Physicochemical and cooking quality characteristics, which are important components of consumer desirability for rice, are virtually unknown for red rice. Thus, a survey of red rice accessions and rice × red rice crosses was conducted to characterize these traits. Grain amylose levels of most indigenous red rice accessions were similar to those of high amylose indica cultivars from Asia. Amylose levels in crosses were highly variable, ranging as low as those in medium-grain commercial rice to as high as those in long-grains. Alkali spreading value was generally greater in awned than in awnless red rice accessions and the aroma chemical, 2-acetyl-1-pyrroline, was detected in two red rice crosses. The generally high seed amylose levels in red rice indicate that its cooking quality would not be suitable for most common uses of US rice, but may be acceptable for niche uses.     

灌浆期夜间高温胁迫下耐热和热敏感水稻籽粒的比较蛋白质组分析

【目的】为了阐明水稻灌浆期耐夜间高温的分子机制,提高水稻耐热性,鉴定了水稻近等基因系耐热纯系XN0437T与热敏感纯系XN0437S在灌浆期夜间高温胁迫下的差异表达蛋白质。【方法】采用桶栽方法培育水稻,于开花期标记同一天扬花的颖花以保障所取颖花样品的生育进程一致;于水稻灌浆初期(花后第8天)进行夜间高温处理。高温处理结束后剪取带标记的颖花提取水稻籽粒总蛋白质,采用8-plex i TRAQ试剂盒进行蛋白质样品的差异显色标记,标记样品采用高效液相系统进行质谱鉴定及定量分析。【结果】鉴定并定量了3130个蛋白质,耐热与热敏感水稻纯系间存在36个差异表达蛋白质。蛋白质功能注释结果显示,鉴定的36个差异表达蛋白质中仅14个蛋白质(占38.9%)注释了功能,12个蛋白质(占33.3%)为推测性功能注释,10个(占27.8%)为功能未知的蛋白质。已注释功能的14个蛋白质中,5个蛋白质参与能量代谢,3个蛋白质参与物质转运与代谢,2个蛋白质参与光合作用,3个蛋白质为响应逆境的锌指蛋白质,1个蛋白质为响应逆境的热激蛋白质。【结论】灌浆期夜间高温影响水稻籽粒细胞内参与能量代谢、物质转运与代谢、光合作用等相关蛋白质的表达模式。水稻籽粒细胞中锌指蛋白质Q67TK9、Q10N88上调表达,锌指蛋白质Q5YLY5下调表达,有利于提高水稻灌浆期对夜间高温的耐热性。     

Growth and yield potential of Oryza sativa and O. glaberrima upland rice cultivars and their interspecific progenies

A recent breakthrough in generating fertile progeny from Oryza sativa×O. glaberrima crosses gives rice breeders access to a broader range of germplasm. Interspecific crosses might provide new solutions to the low productivity of upland rice systems prone to weed competition. Two field and one pot experiments conducted during 1995 and 1996 served to characterize growth and yield potential of CG14 (O. glaberrima), WAB56-104 (O. sativa) and their progeny. During the 1995 wet season and the 1996 dry and wet seasons, the lines were seeded in a well-drained upland field in Ivory Coast with supplemental sprinkler irrigation. A randomized complete-block design with three replications was used, with cultivar and nitrogen levels as sub-plots. Specific leaf area (SLA), leaf area index (LAI), leaf chlorophyll content (SPAD method) and tiller number were measured at 2-week intervals until flowering. Grain yield and yield components were measured at maturity. In all environments, CG14 produced two to three times the LAI and tiller numbers as WAB56-104. This was associated with a high SLA and low leaf chlorophyll content. Grain yields of CG14 did not respond to N inputs, although the sink potential did. The difference was mainly caused by grain shattering. The progenies had intermediate LAI, SLA and leaf chlorophyll content, but their grain yields, tiller numbers and resistance to lodging and grain shattering were similar to WAB56-104. Across lines, LAI and SLA were significantly correlated. A paddy field experiment confirmed the relationship between LAI and SLA for a wider range of rice cultivars and interspecific progenies. A pot experiment demonstrated that leaf net CO₂ assimilation rates (A_max) followed a common linear function of areal leaf chlorophyll content across cultivars. The main common cause of differential LAI and A_max appeared to have been genotypic patterns of SLA, which might be an important determinant of growth vigor and competitiveness with weeds. The possibility is discussed of combining, in a single line, high SLA during vegetative growth (for weed competitiveness) with low SLA during the reproductive growth phase (for high yield potential), to produce an efficient plant type for low-management conditions.     

Drought Tolerance in Rice: Focus on Recent Mechanisms and Approaches

Drought stress is a serious limiting factor to rice production,which results in huge economic losses.It is becoming a more serious issue with respect to the global climate change.Keeping in view of the current and forecasted global food demand,it has become essential to enhance the crop productivity on the drought-prone rainfed lands with priority.In order to achieve the production target from rainfed areas,there is a requirement of rice varieties with drought tolerance,and genetic improvement for drought tolerant should be a high priority theme of research in the future.Breeding for drought tolerant rice varieties is a thought-provoking task because of the complex nature and multigenic control of drought tolerant traits would be a major bottleneck for the current research.A great progress has been made during last two decades in our understanding of the mechanisms involved in adaptation and tolerance to drought stress in rice.In this review,we highlighted the recent progresses in physiological,biochemical and molecular adaptation of rice to drought tolerance.A brief discussion on the molecular genetics and breeding approaches for drought tolerance in rice will be focused for the future crop improvement program for development of drought tolerant rice varieties.     

施氮处理对水稻精米中铁含量的影响及基因型差异

以120份国内外水稻基因型为材料,设置0、150、300kg/hm23个氮素水平,研究施氮处理对水稻精米中Fe含量的影响及其基因型差异。除相同氮素条件下水稻精米中的Fe含量、产量、千粒重及籽粒含氮量存在基因型差异外,精米中的Fe含量对氮素反应的敏感性也存在显著差异。以各基因型水稻在不同氮素条件下精米中Fe含量的极差和变异系数为指标,通过系统聚类的方法,可将上述120份水稻基因型对氮素反应的敏感性分为极钝感型、钝感型、敏感型和极敏感型共4种类型。同时,相关性分析表明,水稻精米中的Fe含量与产量的相关性不显著,而与粒重、籽粒含氮量呈显著或极显著的二次曲线关系。由此说明,施氮处理对水稻精米中Fe含量的影响具有基因型差异,充分利用这种差异一方面有利于对氮环境适应性强的富铁水稻的选育;另一方面,由于精米中的Fe含量与产量无必然联系,可通过氮肥对水稻(尤其是敏感和极敏感类型水稻)精米中的Fe含量和粒重、籽粒含氮量的调节,实现富铁、高产水稻的种植。     

耐低钾基因型水稻成熟期籽粒淀粉与蛋白质含量变化

以2个耐低钾基因型水稻N18,N19和1个低钾敏感型水稻N27为材料,在缺钾条件下,分析耐低钾基因型水稻籽粒在成熟期淀粉含量、蛋白质含量的变化。结果表明：在不施钾肥即缺钾条件下,耐低钾基因型水稻籽粒中总淀粉含量较低钾敏感型的略有增加,且直链淀粉含量占总淀粉含量的比例低于钾敏感型;耐低钾基因型水稻籽粒中可溶性蛋白质含量也较低钾敏感型的高,但是钾元素的含量差异并不明显。     

Using stress tolerance indicator (STI) to select high grain yield iron-deficiency tolerant wheat genotypes in calcareous soils

Despite large variation among crop genotypes in response to Fe fertilization, there is no reliable indicator for identifying Fe-deficiency tolerant wheat genotypes with high grain yield. The aim of this investigation was to compare the grain yield response of 20 spring and 30 winter bread wheat genotypes to Fe fertilization under field conditions and to select high grain yield Fe-deficiency tolerant genotypes using a stress tolerance indicator (STI). Two individual trials, each one consisting two field plot experiments, were conducted during 2006–2007 and 2007–2008 growing seasons. Spring wheat genotypes (Trial l) and winter wheat genotypes (Trial 2) were planted at two different locations. Two Fe rates (0 and 20 kg Fe ha⁻¹ as Fe-EDTA) were applied. Spring and winter wheat genotypes differed significantly (P < 0.01) in the grain yield both with and without added Fe treatments. Application of Fe fertilizer increased grain yield of spring wheat genotypes by an average of 211 and 551 kg ha⁻¹ in Karaj and Isfahan locations, respectively. By Fe application, the mean grain yield of winter wheat genotypes increased 532 and 798 kg ha⁻¹ in Karaj and Isfahan sites, respectively. Iron efficiency (Fe-EF) significantly differed among wheat genotypes and ranged from 65% to 113% for spring wheat and from 69% to 125% for winter wheat genotypes. No significant correlation was found between Fe-EF and grain yield of spring wheat genotypes under Fe deficient conditions. For winter wheat genotypes grown in Mashhad, Fe-efficiency was not significantly correlated with the grain yield produced without added Fe treatment. The STI was significantly (P < 0.01) varied among spring and winter wheat genotypes. The interaction between location and genotype had no significant effect on the STI. According to these results, the STI should be considered as an effective criterion for screening programs, if a high potential grain yield together with more stable response to Fe fertilization in different environments is desired.     

氮、磷和钾肥对菜用大豆籽粒产量和主要矿质元素积累的影响

以大豆专用型品种南农9610为材料,研究了温室大棚条件下,氮、磷和钾肥不同肥料水平对菜用大豆籽粒产量和主要矿质元素含量的影响.结果表明:适量增施氮、磷和钾肥均可明显提高大豆籽粒产量,但施肥过多则降低产量.氮肥和磷肥对菜用大豆籽粒中氮有明显促进作用,磷和钾肥对籽粒磷有促进作用,氮、磷、钾肥对籽粒钾含量均具有明显的促进作用,而钾肥对籽粒中氮含量、氮对籽粒中磷含量具有负作用.施氮使籽粒中Mg、Mn和Fe的含量和积累量先上升再下降;而籽粒中Ca则在低氮时大幅度下降,此后逐渐回升;施磷和钾使Mg、Mn、Fe和Ca含量先上升再下降.