Distribution In Rice Research Articles

Responses of Dry Matter Production and Distribution in Rice (<I>Oryza sativa</I> L.) to Ozone and High Nitrogen Supply

An ozone free-air control enrichment(O3-FACE) experiment was conducted in 2011 to study the effects of O3 and high nitrogen(N) supply on dry matter production and distribution of rice.Two cultivars,Shanyou 63(SY63,three-line hybrid indica cultivar) and Yangdao 6(YD6,inbred indica cultivar),were investigated.The results showed:(1) Elevated O3 concentration significantly reduced the biomass of stems and foliages in the mid-filling stage by 30.20%,21.95% for SY63 and 21.71%,11.12% for YD6,respectively,due to the significant decrease of the net photosynthetic rate.O3 exposure also significantly reduced the yield,the biomass of roots and panicles in the harvesting stage by 45.75%,48.62%,37.15% for SY63,and 28.91%,35.22%,28.01% for YD6,respectively.Increasing N supply could mitigate O3-induced reduction of the net photosynthetic rate,the dry matter and yield,where the yield and biomass of stems,foliages,roots and panicles were changed by elevated O3only by-26.88%,-13.52%,-5.84%,-26.33%,-16.19% for SY63,and-12.68%,-16.26%,+5.19%,-14.55%,-20.22% for YD6,respectively;(2) In SY63 and YD6 exposed to O3,the root-shoot ratio and root dry matter distribution in whole plant decreased significantly,and the ratio of foliage dry matter distribution increased significantly,but there was no significant effect on the ratio of stem or panicle dry matter distribution.High N supply could increase the ratio of root or foliage dry matter and the root-shoot ratio at O3-FACE treatments;(3) O3 exposure could reduce N accumulation of SY63 and YD6,which would show upward trends after high N treatments.These results implied that increasing N supply could mitigate O3-induced changes in dry matter production and distribution of SY63 and YD6.

Photosynthesis, photosystem II efficiency, amino acid metabolism and ion distribution in rice (Oryza sativa L.) in response to alkaline stress

Alkalies are important agricultural contaminants complexly affecting plant metabolism. In this study, rice seedlings were subjected to alkaline stress (NaHCO3:Na2CO3 = 9:1; pH 8.9) for 30 days. The results showed that stress mightily reduced net photosynthetic rate (PN), but slightly decreased transpiration rate and stomatal conductance. This indicated that decline of PN might be a result of nonstomatal factors. Alkaline stress caused a large accumulation of Na+ in leaves up to toxic concentration, which possibly affected chloroplast ultrastructure and photosynthesis. We found that alkaline stress reduced chlorophyll fluorescence parameters, such as ratios of Fv′/Fm′, Fv/Fm, photosystem (PS) II efficiency, and electron transport rates in rice plants, i.e. it influenced the efficiencies of photon capture and electron transport by PSII. This might be a main reason for the decrease of PN under such conditions. Deficiency of minerals could be another reason for the decline of PN. Alkaline stress lowered contents of N, K, Cu, Zn, P, and Fe in rice plants. In addition, the stress strongly affected metabolism of amino acids. This might be caused by imbalance in carbon metabolism as a result of photosynthesis reduction.

Accumulation of arsenic in rice plant: a study of an arsenic-contaminated site in Taiwan

A study conducted in 2006 showed that over 100 ha of rice paddies in Beitou, Taiwan, irrigated over the years using water mixed with hot spring, was heavily polluted by arsenic. Thus, the objective of the present study is to measure arsenic content in different parts of rice and paddy soils, and eventually explain the arsenic distribution in ratoon rice, including its relationship to the soil. Arsenic levels of rice in grains, straws, roots, and soils were obtained from 15 rice paddies, selected based on different arsenic soil concentrations ranging from 67 to 438 mg kg−1 (n = 15). The mean arsenic content in grains was measured at 0.20 mg kg−1 (n = 60) and the highest grain arsenic of the survey was at 1.183 mg kg−1. Meanwhile, the mean total arsenic levels were 244 mg kg−1 (n = 28) in root and 4.4 mg kg−1 (n = 28) in straw. In comparison, regression of topsoil arsenic levels with rice grains (r2 = 0.00) and straws (r2 = 0.56) were less significant compared to that with rice roots (r2 = 0.93), and the mean arsenic level in rice from root to grain was also shown to have a decreasing trend. Though concentrations of arsenic in compositive rice grain each field did not exceed food hygiene concentration limit, arsenic level in root strongly depended on arsenic concentrations of soil suggesting that the high arsenic concentration may have the potential for translocation from root to grain which ultimately effects on the human health.

Impacts of acute ozone stress on superoxide dismutase (SOD) expression and reactive oxygen species (ROS) formation in rice leaves

Tropospheric ozone is an air pollutant harmful to plants and animals. Its rapid increase at the ground surface has raised serious concern over damage to the quality and yield of agricultural crops. Reactive oxygen species (ROS) are formed in plant cells when that are exposed to a high concentration of ozone, and the ROS are thought to alter gene expression and result in cellular death. Clarification of the ROS formation will provide us with a better understanding of the physiological responses to and signaling pathways of ozone stress in plants. In this study, we investigated the mechanisms of the ROS formation in rice (Oryza sativa L.), the premier crop in Asia. To determine ROS distribution in rice leaves under acute ozone stress, we analyzed superoxide dismutase (SOD) expression, lipid peroxidation, NADPH oxidase activity, and invivo H2O2 formation. Interestingly, chloroplastic, peroxisomal and mitochondrial SODs down-regulated their expression levels under ozone stress, whereas cytosolic SODs maintained their expression level. Higher lipid peroxidation occurred after the end of ozone exposure, which suggests lipid peroxidation may not be due to ozone directly, but rather to metabolic changes caused by the ozone exposure. Activity of NADPH oxidase did not show significant change. The in vivo analysis indicated accelerated formation of H2O2 about 24h after the onset of exposure, which suggests that cellular death occurred around this time.

Identification of quantitative trait loci for cadmium accumulation and distribution in rice (Oryza sativa)

Cadmium (Cd) poses a serious risk to human health due to its biological concentration through the food chain. To date, information on genetic and molecular mechanisms of Cd accumulation and distribution in rice remains to be elucidated. We developed an independent F7 RIL population derived from a cross between two japonica cultivars with contrasting Cd levels, 'Suwon490' and 'SNU-SG1', for QTLs identification of Cd accumulation and distribution. 'Suwon490' accumulated five times higher Cd in grain than 'SNU-SG1'. Large genotypic variations in Cd accumulation (17-fold) and concentration (12-fold) in grain were found among RILs. Significant positive correlations between Cd accumulation in grain with shoot Cd accumulation and shoot to grain distribution ratio of Cd signify that both shoot Cd accumulation and shoot to grain Cd distribution regulate Cd accumulation in japonica rice grain. A total of five main effect QTLs (scc10 for shoot Cd accumulation; gcc3, gcc9, gcc11 for grain Cd accumulation; and sgr5 for shoot to grain distribution ratio) were detected in chromosomes 10, 3, 9, 11, and 5, respectively. Of these, the novel potential QTL sgr5 has the strongest effect on shoot to grain Cd distribution. In addition, two digenic epistatic interaction QTLs were identified, suggesting the substantial contribution of nonallelic genes in genetic control of these Cd-related traits.

YSL16 Is a Phloem-Localized Transporter of the Copper-Nicotianamine Complex That Is Responsible for Copper Distribution in Rice

Cu is an essential element for plant growth, but the molecular mechanisms of its distribution and redistribution within the plants are unknown. Here, we report that Yellow stripe-like16 (YSL16) is involved in Cu distribution and redistribution in rice (Oryza sativa). Rice YSL16 was expressed in the roots, leaves, and unelongated nodes at the vegetative growth stage and highly expressed in the upper nodes at the reproductive stage. YSL16 was expressed at the phloem of nodes and vascular tissues of leaves. Knockout of this gene resulted in a higher Cu concentration in the older leaves but a lower concentration in the younger leaves at the vegetative stage. At the reproductive stage, a higher Cu concentration was found in the flag leaf and husk, but less Cu was present in the brown rice, resulting in a significant reduction in fertility in the knockout line. Isotope labeling experiments with (65)Cu showed that the mutant lost the ability to transport Cu-nicotianamine from older to younger leaves and from the flag leaf to the panicle. Rice YSL16 transported the Cu-nicotianamine complex in yeast. Taken together, our results indicate that Os-YSL16 is a Cu-nicotianamine transporter that is required for delivering Cu to the developing young tissues and seeds through phloem transport.

Cadmium transport and tolerance in rice: perspectives for reducing grain cadmium accumulation.

Cadmium (Cd) is a toxic heavy metal which harms human health. In Japan, a major source of human Cd-intake is rice grains and contamination of paddy soils by Cd and accumulation of Cd in rice grains are the serious agricultural issues. There also exist Cd contamination of rice and its toxicity in several populations in countries including China and Thailand. Understanding the Cd transport mechanisms in rice can be a basis for regulating rice Cd transport and accumulation by molecular engineering and marker-assisted breeding. Recently, a number of studies have revealed the behavior of Cd in rice, genetic diversity of Cd accumulation, quantitative trait loci controlling Cd accumulation and transporter molecules regulating Cd accumulation and distribution in rice. In this article, we summarize recent advances in the field and discuss perspectives to reduce grain Cd contents.

Effects of Water Management and Nitrogen Application Strategies on Nutrient Absorption, Transfer, and Distribution in Rice

Hybrid rice Gangyou 527 was used to investigate the effects of three irrigation regimes(submerged irrigation,W1;dry cultivation,W3;and the treatment W2 that was damp irrigation before booting stage,shallow irrigation at booting stage,wet-ting-drying alternation irrigation from heading stage to mature stage) and different nitrogen(N) application ratios on absorption,transport action and distribution of N,phosphorus(P),potassium(K),and yield in rice under the high yield condition of 180 kg N ha?1.The results showed that there was an obvious interaction between water management and N application strategies on grain yield and N,P and K absorption and transfer at the mainly growth stages.Under water-nitrogen interaction condition,there ex-isted significantly positive correlations between the amounts of N,P and K absorption at various growth stages,and there existed highly significantly positive correlations between the accumulations of N,P,and K at heading stage and their transfer amounts during filling stage,but excess the ratio of postponed N application to the total N rate or W3 treatment resulted in the transport amounts of N,P,and K significantly decreased during grain filling e.g.2.73-18.00%,8.03-19.70%,6.52-17.02%,respectively.Furthermore,there were positive correlations between yield and the accumulations of N,P,and K with the max correlation coeffi-cients at heading stage,mature stage,and heading stage.The accumulations of N,K before heading stage could promote nutrient transfer and yield.According to yield performance and its relationship with N,P,and K absorption characteristics,the optimum ratio of postponed N application to the total N rate was 40-60% under W1.The N application of base(30%),tillering(30%),and panicle(40%) fertilizers equally applied at stages of 4th and 2nd leaves emerged from the top under W2,was the best model in this paper referred to as the water-nitrogen application coupling management model.However,W3 treatment was suitable for using 20-40% of the ratio of postponed N application to the total N application rate.

Root growth and distribution in rice cultivars as affected by nitrogen and water supply

Aims Quantitative study of root growth pattern in rice(Oryza sativa) is of great significance for guiding man-agement regulation and genetic improvement.Our objective was to elucidate the characteristics of root growth and distribution in rice under different conditions of cultivation.Methods We conducted pot experiments involving different nitrogen rates,water regimes and rice cultivars with the root shelf method.Root indices were measured at the jointing and heading stages,including total dry weight(TRW),adventitious root number(ARN),and morphological indices(length,surface area and volume) of three types of roots(adventitious,fine and coarse lateral roots).Important findings The observed root indices increased from the jointing stage to the heading stage in all treat-ments.There were significant differences in root indices among the three nitrogen rates,and each index increased with increasing nitrogen rates at both stages.In the water regime experiment,there was no significant difference in ARN between irrigation(W2) and constant water(W1),but the other indices of W2 were highest at both stages.There were no significant differences in TRW and morphological indices of coarse lateral roots between W1 and dry cultivation(W3) at the jointing stage.The other indices at the jointing stage and all indices at the heading stage were lowest with W3.All indices were significantly highest in the 'Yangdao 6'(V3) cultivar,but similar in 'Nipponbare'(V1) and 'Wuxiangjing 14'(V2) cultivars.In addition,the roots extended more deeply into soil from the jointing to the heading stage,but were mainly distributed in the top 5 cm.Lower nitrogen and water supply would promote spreading of roots in the subsoil(5 cm) and enhance the proportions of fine and coarse lateral roots.As compared with V3,the roots of V1 and V2 extended more deeply into soil.We concluded that proper nitrogen fertilization and water control could optimize the growth and distribution characteristics of different types of rice roots and this could be influenced by the specific cultivar.

Genome-scale computational analysis of DNA curvature and repeats in Arabidopsis and rice uncovers plant-specific genomic properties

BackgroundDue to its overarching role in genome function, sequence-dependent DNA curvature continues to attract great attention. The DNA double helix is not a rigid cylinder, but presents both curvature and flexibility in different regions, depending on the sequence. More in depth knowledge of the various orders of complexity of genomic DNA structure has allowed the design of sophisticated bioinformatics tools for its analysis and manipulation, which, in turn, have yielded a better understanding of the genome itself. Curved DNA is involved in many biologically important processes, such as transcription initiation and termination, recombination, DNA replication, and nucleosome positioning. CpG islands and tandem repeats also play significant roles in the dynamics and evolution of genomes.ResultsIn this study, we analyzed the relationship between these three structural features within rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana) genomes. A genome-scale prediction of curvature distribution in rice and Arabidopsis indicated that most of the chromosomes of both genomes have maximal chromosomal DNA curvature adjacent to the centromeric region. By analyzing tandem repeats across the genome, we found that frequencies of repeats are higher in regions adjacent to those with high curvature value. Further analysis of CpG islands shows a clear interdependence between curvature value, repeat frequencies and CpG islands. Each CpG island appears in a local minimal curvature region, and CpG islands usually do not appear in the centromere or regions with high repeat frequency. A statistical evaluation demonstrates the significance and non-randomness of these features.ConclusionsThis study represents the first systematic genome-scale analysis of DNA curvature, CpG islands and tandem repeats at the DNA sequence level in plant genomes, and finds that not all of the chromosomes in plants follow the same rules common to other eukaryote organisms, suggesting that some of these genomic properties might be considered as specific to plants.

Analysis of assimilate distribution by 3H-tracing during recovery period after rice seedling transplanting

In order to characterize assimilate distribution in rice (Oryza sativa L.) seedlings during recovery period after transplanting, the experiments were conducted by using 3H-isotope tracer technique with three rice hybrid combinations. The label introduced into the leaf sheath was distributed and redistributed to young roots, tillers, and young leaves, thus promoting these organs to grow at the initial stage after transplanting. During period from 10 to 30 days after labeling, 3H-assimilate redistribution occurred mainly from the sheath of the main stem; some radioactivity moved to tillers and roots emerged after transplanting. The activity and percentage of 3H-compounds transporting to rooting nodes and roots emerged after transplanting were higher in root-pruned plants than in control, indicating that growth of root-pruned seedlings more depended on the export of the compounds from the sheath of the main stem than growth of control seedlings.

Changes in Pattern of Microtubule Organization During Meiosis in Pollen Mother Cell of Autotetraploid Rice

Changes in microtubule distribution and chromosome behavior in autotetraploid rice during meiosis of pollen mother cell (PMC) were observed in detail using indirect-immunofluorescence laser scanning confocal microscopy. The result showed that microtubule distribution pattern in PMC of the autotetraploid rice was similar to that of the diploid rice during meiosis, but the microtubule behaviors were different, e.g., longer circumferential microtubules and more spindle microtubules in autotetraploid rice. At prophase I, microtubules were decreased in number and distributed unevenly at leptotene. At zygotene, microtubules with unobvious polar distribution formed a diffuse network. At pachytene, nucleolus disintegrated and distorted microtubules structures were found. At diplotene, no circumferential microtubule was found and microtubules depolymerization was observed in advance. At diakinesis, microtubules were decreased in number. Perinuclear microtubules were knitted abnormally. At metaphase I, many abnormalities appeared in spindle. At telophase I, phragmoplast was abnormal, and speckled microtubules were found in the cell. At telophase II-tetra stage, 2 daughter cells did not separate, and microtubules randomly arranged in trifission. These results showed that microtubule abnormal reorganization pattern had a close relationship with abnormal chromosome behavior, which may act synergistically on pollen fertility and seed setting rate of autotetraploid rice.

Distribution and in Vitro Availability of Selenium in Selenium-Containing Storage Protein from Selenium-Enriched Rice Utilizing Optimized Extraction

Selenium (Se) distribution in Se-enriched rice and optimization of extraction for Se-containing protein were studied. Se availability in Se-containing protein product was simulated using an in vitro gastrointestinal digestion. The results showed that Se was predominately found as organic Se, whereas inorganic Se comprised only 2.85% of the total Se. The glutelin fraction contained the largest amount of Se, approximately 31.3% of the total Se in the rice gain. Utilizing orthogonal analysis, the optimum extraction conditions were selected at a volume to weight of 20:1, 0.08 M NaOH, an extraction time of 3 h, and at a temperature of 35 degrees C. A Se-containing rice protein product with 83.5% protein and 9.09 microg g(-1) Se was sequestered using the optimal extraction method. This rice protein product with high molecular weight Se-containing protein can readily be digested to low molecular weight peptides and selenomethionine (52.3% of total Se in protein extract).

Trace metals distribution and uptake in soil and rice grown on a 3-year vermicompost amended soil

This study was designed to investigate the influence of vermicompost (VC) on trace metals distribution and uptake in soil and rice plant in research field as split plot arrangement based on randomized complete block design with three replications in 2008. Main-plot was VC and chemical fertilizer (CF) that were added to soil in 6 levels (20 and 40 ton/ha VC, 20 and 40 ton/ha VC + 1/2 CF, CF and control). Application years considered as sub-plot comprised 1, 2 and 3 years. The results indicated that fertilizers and application periods treatments influenced micronutrients in soil and rice. Available copper (Cu) had no significant difference under different treatments. The highest available iron (Fe) was found in the 40 ton treatment group. During the 3 years, application of 20 ton and enriched 40 ton gave the most available zinc (Zn) and manganese (Mn). In VC and enriched VC, treatments happened to give the highest Zn uptake by rice. Under the 3 years, application of 40 ton/ha VC, the highest Fe (91.19 ppm) and Cu (13.66 ppm) concentration was seen in flag leaf, while Fe (31.35 ppm) and Mn (27.56 ppm) was seen in grain. With the application of enriched 20 ton VC, the maximum uptake of Mn by flag leaf and Cu by grain was obtained.

Genotypic variation of cadmium accumulation and distribution in rice

An effective way to reduce the risk of cadmium (Cd) entering the food chain is to use low Cd-accumulation rice cultivars, particularly in Asia. The fundamental requirement for breeding low grain Cd-accumulation cultivars is to know the genotypic variation in Cd accumulation and the physiological processes and genetic basis governing the Cd accumulation in rice grain. In this experiment, genotypic variation in Cd accumulation and distribution among rice organs was studied using thirty-five rice varieties. They were grown with irrigation water containing 2 ppm Cd throughout rice growing season under field condition in 2007. At harvest, plants were sampled and analyzed for Cd concentration and accumulation in each rice organ. Significant variation of Cd concentration and accumulation in rice organs were found among thirty-five rice cultivars, revealing more than 8-fold varietal differences in grain Cd concentration and shoot Cd accumulation. Cd concentration and accumulation in grain were significantly different among cultivar groups, showing the highest in indica and the lowest in temperate japonica. Tongil-type and tropical japonica rice showed a Cd concentration intermediate to that of temperate japonica and indica rice. The higher Cd accumulation in grain of indica rice was attributable to the greater ability of Cd uptake. The greater ability of root-shoot translocation in tropical japonica and shoot-grain redistribution in tongil-type resulted in the significantly higher grain Cd concentration in these cultivar groups than in temperate japonica. For over 35 cultivars tested, grain Cd concentration revealed a significant positive correlation with root Cd concentration and shoot Cd concentration and accumulation while no significant correlation with root-shoot translocation factor and shoot-grain redistribution ratio. However, correlation analyses within each cultivar group showed that grain Cd concentration was significantly correlated with root-shoot translocation factor in indica, with root Cd concentration in tongil-type, with shoot Cd concentration and accumulation in tropical japonica, and with shoot Cd accumulation and shoot-grain redistribution ratio in temperate japonica. These results indicate that genotypic variation in grain Cd accumulation, in general, is controlled by all the three physiological processes but the major physiological process governing its genotypic variation within cultivar group is different depending on cultivar groups.

Survey of total arsenic and arsenic speciation in US-produced rice as a reference point for evaluating change and future trends

Rice generally contains higher levels of arsenic than most terrestrial-based foods. Studies related to dietary intake of arsenic from rice must take into account arsenic speciation due to toxicity differences in arsenic species. In this study, microwave-assisted extraction with trifluoroacetic acid was used to prepare rice samples for arsenic speciation analysis by high-performance liquid chromatography-inductively coupled plasma mass spectrometry. Fifty-three samples collected directly from the fields in four major rice-producing states in 1980 and 1981 were analysed for total and speciated arsenic and the results were compared with each other and with results for several more recently collected samples from local markets. The average content of total arsenic was 210 ± 190 ng As g−1. This study demonstrates that US rice samples with higher levels of total arsenic have higher levels of dimethylarsinic acid; however, inorganic arsenic levels, regardless of the total arsenic content, rarely exceed 150 ng As g−1 dry weight. These data are consistent with more recent findings, thus establishing trends that arsenic content in US-grown rice has been relatively constant throughout the last 30 years. To the authors’ knowledge, the presented data are unique in that they provide a historical reference point for arsenic distribution in US-produced rice. These data would be invaluable for several applications including long-term arsenic exposure studies, environmental clean-up assessments, and to establish models for future trends in arsenic contribution in total diet studies.

Risk assessment of potentially toxic element pollution in soils and rice ( Oryza sativa) in a typical area of the Yangtze River Delta

Soil pollution with potentially toxic elements (PTEs) resulting from rapid industrial development has caused major concerns. Selected PTEs and their accumulation and distribution in soils and rice ( Oryza sativa) collected from Changshu, east China, were analyzed to evaluate the potential health risk to the local population. The soils were primarily contaminated with Hg, followed by Cu, Cd, Pb, and Zn. The concentrations of Pb, Hg, and Cd of 46, 32, and 1 rice samples exceeded their national maximum allowable levels in foods, respectively. Spatial distributions of total Cr, Cu, Pb, Zn, and Cd in soils shared similar geographical trends. The risk assessment of PTEs through rice consumption suggests that the concentrations of Cu, Pb, and Cd in some rice samples exceed their reference oral dose for adults and children. In general, there was no target hazard quotient value of any individual element that was greater than 1, but hazard index values for adults and children were 1.726 and 1.523, respectively.

Genome-wide analysis of rice (Oryza sativa L. subsp. japonica) TATA box and Y Patch promoter elements

The TATA box is one of the best characterized transcription factor binding sites. However, it is not a ubiquitous element of core promoters, and other sequence motifs such as Y Patches seem to play a major role in plants. Here, we present a first genome-wide computational analysis of the TATA box and Y Patch distribution in rice (Oryza sativa L. subsp. japonica) promoter sequences. Utilizing a probabilistic sequence model, we ascertain that only approximately 19% of rice genes possess the TATA box, but approximately 50% contain one or more Y Patches in their core promoters. By computational processing of identified elements, we generated extended TATA box and Y Patch nucleotide frequency matrices capable of predicting these motifs in plants with a high degree of confidence.

Characteristics of Nitrogen Distribution and Translocation in Conventional Indica Rice Varieties with Different Nitrogen Use Efficiency for Grain Output

To investigate the characteristics of nitrogen distribution and translocation in conventional indica rice ( Oryza sativa L.) varieties with high nitrogen use efficiency for grain output (NUEg), a total of 88 and 122 conventional indica rice varieties were solution-cultured in 2001 and 2002, respectively. These varieties were classified into 6 types on the basis of NUEg. Dry matter weight and nitrogen content of roots, culm and sheath, leaf, and panicle were measured at heading and maturity stages, and the grain yield and the grain number per panicle, filled grain percentage, and one thousand-grain weight of each variety were tested after harvest. The NUEg of the tested varieties varied from 20.51 to 50.92 g g −1 in 2001 and from 24.33 to 50.00 g g −1 in 2002, respectively. For varieties with high NUEg, the nitrogen content percentages in culm and sheath and leaf were lower than varieties with low NUEg at heading and maturity stages. On the contrary, nitrogen content percentage in panicle was larger in high-NUEg varieties, especially at maturity stage. The amount and rate of nitrogen translocation in culm and sheath and leaf in the varieties with high NUEg were high during grain-filling period. Thus, enhancement of the amount and rate of nitrogen translocation in culm, sheath, and leaf during grain filling could improve dry matter translocation and harvest index in rice.

Use of 13C labeling to assess carbon partitioning in transgenic and nontransgenic (parental) rice and their rhizosphere soil microbial communities

Photosynthetic assimilation of CO2 is a primary source of carbon in soil and root exudates and can influence the community dynamics of rhizosphere organisms. Thus, if carbon partitioning is affected in transgenic crops, rhizosphere microbial communities may also be affected. In this study, the temporal effects of gene transformation on carbon partitioning in rice and rhizosphere microbial communities were investigated under greenhouse conditions using the 13C pulse-chase labeling method and phospholipid fatty acid (PLFA) analysis. The 13C contents in leaves of transgenic (Bt) and nontransgenic (Ck) rice were significantly different at the seedling, booting and heading stages. There were no detectable differences in 13C distribution in rice roots and rhizosphere microorganisms at any point during rice development. Although a significantly lower amount of Gram-positive bacterial PLFAs and a higher amount of Gram-negative bacterial PLFAs were observed in Bt rice rhizosphere as compared with Ck at all plant development stages, there were no significant differences in the amount of individual 13C-PLFA between Bt and Ck rhizospheres at any growing stage. These findings indicate that the insertion of cry1Ab and marker genes into rice had no persistent or adverse effect on the photosynthate distribution in rice or the microbial community composition in its rhizosphere.