Sucrose transport from source to sink seeds in rice

In many higher plants, sucrose is loaded as a major carbon photoassimiliate into the phloem apoplastically by sucrose transporters (SUTs) and unloaded in sink tissues, where it serves as a storage material, carbohydrate backbone, and energy source. In sink tissues, a proportion of sucrose molecules are converted by cell wall invertases (CINs) into hexose that is imported into cells by monosaccharide transporters (MSTs). Thus, in developing seeds, co-ordinated regulation of SUTs, CINs, and MSTs is crucial in carbon distribution. Here, we summarize current efforts on the identification of SUTs, CINs, and MSTs in rice.     

Genotypic variation in partitioning of dry matter and manganese between source and sink organs of rice under manganese stress

Key message

Genetic variability in dry matter and manganese partitioning between source and sink organs was the key mechanism for Mn efficient rice genotypes to cope with Mn stress.

Abstract

Considerable differences exist among cereal genotypes to cope manganese (Mn) deficiency, but the underlying mechanisms are poorly understood. Minimal information regarding partitioning and/or remobilization of dry matter and Mn between source and sink organs exists in rice genotypes differing in Mn efficiency. The present study was aimed to assess the growth dynamics in terms of dry matter and Mn remobilization in the whole plant (leaves and tillers as source and panicles and grains as sink) during the grain development in diverse rice genotypes. The efficient genotypes accumulated higher dry matter than inefficient genotypes under low Mn level. The translocation index i.e., uptake in grain/total uptake was 0.11 in efficient genotype (PR 116) and 0.04 in inefficient genotypes (PR 111). The efficient genotype had higher grain Mn utilization efficiency of 0.71 in comparison to 0.48 of inefficient genotype indicating that in efficient genotype, Mn in grain produces more dry matter than inefficient genotypes. The efficient genotypes also had higher flag leaf area and nitrate reductase activity. The source of efficient genotypes contributed to a greater extent to developing sink but further mobilization to grain was hindered by panicle. The panicle of inefficient genotypes had higher per cent of Mn uptake than efficient genotypes indicating that Mn was least mobilized from panicle to grain in inefficient genotypes. The lower per cent uptake of Mn in efficient genotypes indicated that Mn was mobilized from panicle to developing grain and this led to higher Mn translocation index in grain of efficient genotypes. The uptake partitioning revealed that source of all genotypes mobilized the Mn towards the sink to almost same extent but it was the panicle where highest per cent uptake per plant was in inefficient genotypes and lowest in efficient genotypes. The lowest per cent uptake in panicle of efficient genotypes revealed that it supported developing grain to have highest translocation index.     

碳中和视角下秸秆处置方式对碳源汇的贡献

探明农作物秸秆在不同处置方式下的碳源汇时空变化特征,对优化我国秸秆资源利用政策、实现碳减排最大化、实现碳中和目标具有重要意义。本研究以国家统计年鉴数据为基础,对我国31个省农作物秸秆不同处置下的碳排放、碳减排、碳增汇及其价值量的变化趋势进行研究。结果表明: 2008—2019年间,我国秸秆焚烧年均碳排放量为874万t CO₂e,2014年以来碳排放年均减少率为17.3%;能源化利用年均碳减排量为3982万t CO₂e,其中,秸秆生产固体成型燃料碳减排贡献最大,约占能源化碳减排总量的98%;秸秆还田碳汇量总体呈逐年上升趋势,年均碳汇量为2.71亿t CO₂e;我国秸秆处置存在碳生态盈余,净碳减排量年均增长率为9.8%,净碳减排强度及其价值量均呈增长趋势,2019年分别高达2.62 t·hm^-2和76.19元·hm^-2。我国秸秆年均碳排放、能源碳减排、秸秆还田碳汇以及净碳减排大致呈“东高西低”的空间分布规律,且地区差异及空间聚集性是三者的最主要外部特征。     

不同氮素水平下水稻生育后期叶片和籽粒的蛋白质组学

以超级杂交水稻“两优培九”为试验材料,运用蛋白质双向电泳技术研究了水稻生育后期不同氮素水平下（正常供氮水平的1/2,20 mg·L^-1;正常供氮水平,40 mg·L^-1;正常供氮水平的2倍,80 mg·L^-1）叶片和籽粒蛋白质组水平的变化,并鉴定分析了其差异蛋白质点（共鉴定出16个叶片蛋白质、9个弱势粒蛋白质、4个强势粒蛋白质）的生物功能.结果表明：生育后期氮素是通过影响与光合有关的酶的活化、CO₂的活化及光系统单位和电子传递链构成来影响和调节植物的光合作用;氮素可促进弱势粒中与能量合成和生长相关酶的表达;高氮水平不利于强势粒淀粉的合成,但充足的氮素对水稻物质累积及代谢具有重要作用.因此,在生育后期合理运用氮肥对提高水稻剑叶光合性能、增强源的功能、延缓功能性早衰及强化籽粒灌浆具有积极作用.     

A proteomics approach towards understanding blast fungus infection of rice grown under different levels of nitrogen fertilization

Proteins extracted from leaf blades of rice plants infected with blast fungus, Magnaporthe grisea, were separated by two-dimensional polyacrylamide gel electrophoresis. The separated proteins were electroblotted onto a polyvinylidene difluoride membrane, and 63 proteins were analyzed by a gas-phase protein sequencer. The N-terminal amino acid sequences of 33 out of 63 proteins were determined in this manner. N-terminal regions of the remaining proteins could not be sequenced. The internal amino acid sequences of 12 proteins were determined by sequence analysis of peptides obtained by the Cleveland peptide mapping method. The amino acid sequences were compared with those of known plant and animal protein sequences to understand the nature of these proteins. As expected, leaf blades revealed predominantly the presence of photosynthetic proteins. Using this experimental approach named as proteome analysis, the functional proteins during blast fungus infection of rice with different levels of nitrogen nutrient were analyzed. Twelve proteins which appeared to change with different levels of nitrogen nutrient were identified. It was revealed that the level of ribulose-1,5-bisphosphate carboxylase/oxygenase was increased by top-dressing with nitrogen nutrient. Additionally, the pathogenesis related protein were observed following blast fungus infection using immunoblot analysis. It was conjectured that these proteins might be involved in incompatible interaction in rice plants following blast fungus infection. The information obtained on the amino acid sequences and antibodies interaction is expected to be helpful in predicting the function of these proteins.     

Cyanobacterial inoculation and nitrogen fertilization in rice

During three rice-growing seasons in Uruguay, field experiments were conducted to study the contribution of cyanobacterial inoculation and chemical N fertilization to rice production. Neither grain yield nor fertilizer recovery by the plant were affected by inoculation with native cyanobacterial isolates. A low fertilizer use efficiency (around 20%) was observed when labelled (NH₄)₂SO₄ was applied at sowing. Recovery of applied ¹⁵N by the soil–plant system was 50%. Inoculation did not modify ¹⁵N uptake by the plant when the fertilizer was three-split applied either. The total N-fertilizer recovery was higher when the fertilizer was split than when applied in a single dose. Plant N-fertilizer uptake was higher when the fertilizer was applied at tillering. Uptake of ¹⁵N from cyanobacteria by rice was studied in a greenhouse pots experiment without chemical nitrogen addition. Recovery of ¹⁵N from labelled cyanobacteria by rice in greenhouse growth conditions was similar to that of partial recovery of (NH₄)₂SO₄ applied at sowing in the field. Cyanobacterial N mineralization under controlled conditions was fast as cyanobacterial N was detected in plants after 25 days. Moreover 40 days after inoculation non-planted and inoculated soil had more inorganic N than the non-inoculated one.     

Cytokinin-mediated source/sink modifications improve drought tolerance and increase grain yield in rice under water-stress

Drought is the major environmental factor limiting crop productivity worldwide. We hypothesized that it is possible to enhance drought tolerance by delaying stress-induced senescence through the stress-induced synthesis of cytokinins in crop-plants. We generated transgenic rice (Oryza sativa) plants expressing an isopentenyltransferase (IPT) gene driven by P(SARK) , a stress- and maturation-induced promoter. Plants were tested for drought tolerance at two yield-sensitive developmental stages: pre- and post-anthesis. Under both treatments, the transgenic rice plants exhibited delayed response to stress with significantly higher grain yield (GY) when compared to wild-type plants. Gene expression analysis revealed a significant shift in expression of hormone-associated genes in the transgenic plants. During water-stress (WS), P(SARK)::IPT plants displayed increased expression of brassinosteroid-related genes and repression of jasmonate-related genes. Changes in hormone homeostasis were associated with resource(s) mobilization during stress. The transgenic plants displayed differential expression of genes encoding enzymes associated with hormone synthesis and hormone-regulated pathways. These changes and associated hormonal crosstalk resulted in the modification of source/sink relationships and a stronger sink capacity of the P(SARK)::IPT plants during WS. As a result, the transgenic plants had higher GY with improved quality (nutrients and starch content).     

Plant-mediated processess to acquire nutrients: nitrogen uptake by rice plants

The ways in which root–soil interactions can control nutrient acquisition by plants is illustrated by reference to the N nutrition of rice. Model calculations and experiments are used to assess how uptake is affected by root properties and N transport through the soil. Measurements of the kinetics of N absorption and assimilation and their regulation, and of interactions between NH₄ ⁺ and NO₃ ^– nutrition, are described. It is shown that uptake of N from the soil–-as opposed to N in ricefield floodwater which can be absorbed very rapidly but is otherwise lost by gaseous emission–-will often be limited by root uptake properties. Rice roots are particularly efficient in absorbing and assimilating NO₃ ^–, and NH₄ ⁺ absorption and assimilation are stimulated by NO₃ ^–. The uptake of NO₃ ^– formed in the rice rhizosphere by root-released O₂ may be more important than previously thought, with beneficial consequences for rice growth. Other root-induced changes in the rice rhizosphere and their consequences are discussed.     

不同供氮条件下水稻的化感抑草作用与资源竞争分析

为探讨化感水稻在不同氮素水平下的生物干扰现象,提出了一种新的测试方法———化感竞争分离法(allelopathyandcompetitionseparation basedbioassay,ACS),成功地区分了在稻/稗共生系统中水稻化感作用与资源竞争及其在不同N条件下的反应特性.结果表明,水稻PI312777具有较强的生物干扰能力.在不同N水平下,其资源竞争能力较强且表现稳定,但化感作用潜力则随供N水平的下降而明显增强.水稻Lemont不具化感作用潜力,在供N水平正常或充足条件下,其资源竞争能力减弱,但在N胁迫下却明显增强.这是在环境资源贫乏时,稻/稗共生系统中生态位竞争加剧的结果.     

Potential of indigenous cyanobacteria to contribute to rice performance under different schedules of nitrogen application

Rice, IR-28, was fertilized by urea at 48, 96, 144 or 192 kg N/ha under three application schedules: (1) complete basal application before submergence, (2) split application, basal and 30 days after transplanting, or (3) 15 and 45 days after transplanting. Plant growth, yield, N accumulation, and chemical fertilizer N-use efficiency were minimum under complete basal application. N fertilization at 15 and 45 days after transplanting was superior and formed the fastest and greatest colonization by cyanobacteria. The population profile comprised 64%Nostoc, 24%Anabaena and 8%Calothrix.Aulosira, Nodularia andTolypothrix were each less than 1% of the total heterocystous cyano-bacteria.     

Phloem-localizing sulfate transporter,Sultr1;3, mediates re-distribution of sulfur from source to sink organs in Arabidopsis

For the effective recycling of nutrients, vascular plants transport pooled inorganic ions and metabolites through the sieve tube. A novel sulfate transporter gene, Sultr1;3, was identified as an essential member contributing to this process for redistribution of sulfur source in Arabidopsis. Sultr1;3 belonged to the family of high-affinity sulfate transporters, and was able to complement the yeast sulfate transporter mutant. The fusion protein of Sultr1;3 and green fluorescent protein was expressed by the Sultr1;3 promoter in transgenic plants, which revealed phloem-specific expression of Sultr1;3 in Arabidopsis. Sultr1;3-green fluorescent protein was found in the sieve element-companion cell complexes of the phloem in cotyledons and roots. Limitation of external sulfate caused accumulation of Sultr1;3 mRNA both in leaves and roots. Movement of (35)S-labeled sulfate from cotyledons to the sink organs was restricted in the T-DNA insertion mutant of Sultr1;3. These results provide evidence that Sultr1;3 transporter plays an important role in loading of sulfate to the sieve tube, initiating the source-to-sink translocation of sulfur nutrient in Arabidopsis.     

不同施肥措施臭氧浓度升高对不同水稻品种光合特性的影响

近地层臭氧(O₃)已严重威胁到作物生产,而施肥可以调节土壤的养分平衡,进而促进作物生长。以两个水稻品种(徽两优898和南粳9108)为研究对象,利用开顶式气室,设置2个O₃浓度处理(NF:环境大气为对照;NF40:环境大气+40 nmol/mol O₃),每个O₃处理下嵌套设置3个肥料处理(Ino:施无机肥处理,270 kg N hm^-2 a^-1;Red:减施无机肥30%处理,189 kg N hm^-2 a^-1;Com:有机无机肥配施处理,Red+有机肥鸡粪5000 kg hm^-2 a^-1),通过测定不同生育期水稻光合参数,探究不同肥料处理下O₃对水稻不同生育阶段光合生理的影响。结果表明,NF40对水稻营养生长阶段的饱和光合速率(A_sat)没有显著影响,而显著地降低了水稻灌浆期的A_sat。基于两个水稻品种的A_sat和相对叶绿素含量(SPAD)相对减少量与O₃累积剂量关系的斜率,发现杂交稻徽两优898(A_sat和SPAD的斜率:-1.55和-0.98)比常规稻南粳9108(A_sat和SPAD的斜率:-0.92和0.06)对O₃更敏感。此外,基于不同O₃处理下水稻的气孔导度(g_s)和胞间二氧化碳浓度(C_i),可以看出O₃造成南粳9108光合速率降低的主要是非气孔因素,而徽两优898光合的降低是由气孔因素和非气孔因素共同限制。与Ino处理相比,Red处理主要通过降低叶片SPAD进而显著地抑制两种水稻品种的A_sat,但Ino处理和Com处理间A_sat没有显著差异,说明有机无机肥配施能部分缓解减施无机肥造成水稻光合的降低。O₃和肥料处理对两个水稻的所有光合参数都没有显著的交互影响,表明短期有机无机肥配施并不能有效缓解O₃对作物造成的负面影响。在O₃污染背景下,研究结果可以为通过合理的农田氮肥管理措施减缓O₃造成的作物减产提供理论依据。     

不同施氮处理玉米根茬在土壤中矿化分解特性

以黄土高原南部地区7a定位试验不同氮肥处理玉米根茬为研究对象,通过室内培养试验研究了施氮量分别为0、120和240 kg N/hm2处理玉米根茬(分别用R0、R120、R240表示)在15-20 cm和45-50 cm土层土壤中有机碳矿化及其对土壤微生物量碳、可溶性有机碳和矿质态氮含量的影响.结果表明,不同处理玉米根茬C/N为R0＞R240 ＞R120.培养条件下,R120和R240根茬的碳矿化速率高于R0根茬,R120与R240根茬之间差异不显著.不同处理根茬C/N与其培养过程中碳素累积表观矿化量呈极显著负相关关系.3种施氮量处理的玉米根茬在培养过程中有机碳矿化率、潜在碳矿化量、土壤微生物量碳、可溶性有机碳含量均为添加R120根茬的处理最高,R240次之,R0最低.添加R120和R240根茬显著提高了培养起始时土壤矿质态氮含量.R0、R120和R240根茬在15-20 cm土层土壤中的碳矿化率分别比其在45-50 cm土层土壤中高51.70％、26.41％和27.84％.在评价根茬还田对农田生态系统碳、氮等养分循环的作用时,应同时考虑施肥对根茬分解和转化的影响.     

追施氮肥对桉树各器官养分浓度及贮量的影响

采用田间定位试验的方法,研究了追施氮肥对2年生桉树各器官生物量积累及养分浓度与贮量的影响.结果表明:与对照相比,追施氮肥使桉树生物量增加24.2%,其中树枝增幅最高,为38.2%,树叶最少.追施氮肥显著促进了桉树对养分的吸收,其增幅顺序为PKNMgCaSi;叶片中N、P、Mg、Si含量最高,K在树干中的贮量最大,树枝部位的养分浓度与贮量增加最为显著.桉树N、P、K养分以内循环为主,叶片凋落前分别有73.8%、79.1%和72.9%的N、P、K养分被转移到植株体内,其外循环量仅为全树贮量的14.8%、7.7%和8.6%;Ca、Mg、Si养分则以外循环方式为主,其中Ca最明显,树叶中89.2%的Ca随叶片凋落,其外循环通量占全树Ca总贮量的25.9%.     

Nitrous oxide emissions from silage maize fields under different mineral nitrogen fertilizer and slurry applications

Intensive dairy farming systems are a large source of emission of the greenhouse gas nitrous oxide (N₂O), because of high nitrogen (N) application rates to grasslands and silage maize fields. The objective of this study was to compare measured N₂O emissions from two different soils to default N₂O emission factors, and to look at alternative emission factors based on (i) the N uptake in the crop and (ii) the N surplus of the system, i.e., N applied minus N uptake by the crop. Twelve N fertilization regimes were implemented on a sandy soil (typic endoaquoll) and a clay soil (typic endoaquept) in the Netherlands, and N₂O emissions were measured throughout the growing season. Highest cumulative fluxes of 1.92 and 6.81 kg N₂O-N ha^–1 for the sandy soil and clay soil were measured at the highest slurry application rate of 250 kg N ha^–1. Background emissions from unfertilized soils were 0.14 and 1.52 kg N₂O-N ha^–1 for the sandy soil and the clay soil, respectively. Emission factors for the sandy soil averaged 0.08, 0.51 and 0.26% of the N applied via fertilizer, slurry, and combinations of both. For the clay soil, these numbers were 1.18, 1.21 and 1.69%, respectively. Surplus N was linearly related to N₂O emission for both the sandy soil (R²=0.60) and the clay soil (R²=0.40), indicating a possible alternative emission factor. We concluded that, in our study, N₂O emission was not linearly related to N application rates, and varied with type and application rate of fertilizer. Finally, the relatively high emission from the clay soil indicates that background emissions might have to be taken into account in N₂O budgets.     

Contribution of different organs to increased glucose consumption after endotoxin administration

Glucose utilization of different organs (spleen, liver, ileum, kidney, skin, lung, and testis) was investigated in vivo in conscious rats 3, 24, or 48 h after treatment with 100 micrograms of endotoxin/100 g of body weight. Glucose uptake was determined by the 2-deoxyglucose technique, which was validated by demonstrating that endotoxin treatment did not alter either the intracellular retention of the phosphorylated metabolites (P-2-dGlc) of the tracer or the discrimination against 2-deoxyglucose in pathways of glucose metabolism. At 3 h after endotoxin the accumulation of P-2-dGlc was markedly increased in the liver (4.8-fold), spleen and skin (2.9-fold), lung (2.4-fold), and ileum and kidney (2.1-fold), as compared to time-matched controls. This effect was sustained in the liver at 24 and 48 h, was diminishing but still significant in spleen, ileum, and kidney, and absent in skin and lung. Accumulation of P-2-dGlc in the testis remained unchanged after endotoxin. Glucose uptake by individual organs and their contribution to whole body glucose utilization in control and endotoxin-treated rats were compared based on P-2-dGlc accumulation data. Organs rich in mononuclear phagocytes (liver and spleen) exhibited a marked and prolonged increase in glucose uptake after endotoxin. Yet the bulk of the increment in the whole body glucose disappearance rate (Rd) was due to three large tissues (skin, intestine, and muscle, accounting for more than 80% of the total P-2-dGlc accumulation in soft tissues), which showed a more moderate and transient increase in glucose utilization.     

Efficiency of algalization of rice in the Nile Delta with different amounts of nitrogen and potassium fertilization

Indica rice var. IR 28 was inoculated with cyanobacteria (blue-green algae) together with elther 0,72 and 144 kg N/ha or 0,60 and 120 kg K₂O/ha. Plant performance, yield, nitrogen contents and chemical fertilizer-N-use efficiency positively responded to inoculation with the cyanobacteria and increased further with increasing amounts of both N and K. Effects arising from the cyanobacteria, N or K differed under the other two factors.     

Contribution of N2 fixing cyanobacteria to rice production: availability of nitrogen from 15N-labelled cyanobacteria and ammonium sulphate to rice

This study investigate the potential contribution of nitrogen fixation by indigenous cyanobacteria to rice production in the rice fields of Valencia (Spain). N₂-fixing cyanobacteria abundance and N₂ fixation decreased with increasing amounts of fertilizers. Grain yield increased with increasing amounts of fertilizers up to 70 kg N ha^-1. No further increase was observed with 140 kg N ha^-1. Soil N was the main source of N for rice, only 8–14% of the total N incorporated by plants derived from ¹⁵N fertilizer. Recovery of applied ¹⁵N-ammonium sulphate by the soil–plant system was lower than 50%. Losses were attributed to ammonia volatilization, since only 0.3–1% of applied N was lost by denitrification. Recovery of ¹⁵N from labeled cyanobacteria by the soil–plant system was higher than that from chemical fertilizers. Cyanobacterial N was available to rice plant even at the tillering stage, 20 days after N application. This revised version was published online in June 2006 with corrections to the Cover Date.