Arsenic accumulation by rice grown in soil treated with roxarsone

Poultry litter is widely used as a fertilizer for lowland rice in Taiwan and China. However, the organic‐arsenic compound roxarsone (additive of poultry feed) in poultry litter can be absorbed by the plants and the resulting arsenic (As) contamination may pose a serious threat to human health. This study used various amounts of poultry litter contaminated with roxarsone in pot experiments to evaluate the effect of roxarsone on rice agronomic parameters and the bioaccumulation of total and inorganic As in rice‐plant tissues. Rice‐grain yield decreased significantly with increasing As content of the soil, and the critical threshold that killed rice was 200 mg roxarsone (kg soil)^–1. The As concentrations in root, straw, leaf, husk, and grain increased with increasing soil As (p < 1%). At 100 mg roxarsone per kg of soil, the As concentration in the rice grain exceeded the statutory permissible limit of 1.0 mg As (kg dry weight)^–1 and at 25 mg roxarsone (kg soil)^–1, the inorganic As concentrations in grains exceeded the statutory limit of 0.15 mg of inorganic As kg^–1 in China. For all treatments, the As concentrations in various plant tissues at maturity follow the order: root > stem > leaf > husk > grain. Arsenite was the predominant species in root, straw, and grain, while arsenate was the predominant species in leaf and husk. No significant difference existed between the amounts of arsenite and arsenate when various amounts of poultry litter were applied. This result illustrates that large amounts of added roxarsone are not only toxic to rice but also accumulate in grains in the inorganic As forms, potentially posing a threat to human health via the food chain.     

Cadmium concentrations in the phloem sap of rice plants (Oryza sativa L.) treated with a nutrient solution containing cadmium

To obtain direct evidence for the translocation of cadmium (Cd) via the phloem, we measured the Cd concentrations in the phloem sap of 5-week-old rice plants (Oryza sativa L. cv. Kantou) treated with a nutrient solution containing Cd. The phloem sap was collected from the leaf sheaths through the cut ends of stylets of the brown planthopper (Nilaparvata lugens Stål.). Cd concentrations in the phloem sap from the plants treated with 10 and 100 µM Cd for 3 d were 4.6 ± 3.4 and 17.7 ± 9.8 µM, respectively. Detection of Cd in the phloem sap indicated that Cd was translocated via sieve tubes in rice plants. Cd concentrations in the xylem exudate collected from the cut basis of the leaf sheaths of the plants treated with 10 and 100 µM Cd for 3 d were 18.9 ± 6.4 and 64.2 ± 14.6 µM, respectively. Cd concentrations in the phloem sap were significantly lower than those in the xylem exudate, indicating that Cd is not concentrated during the transfer from xylem to phloem. To our knowledge, this is the first determination of Cd concentrations in the phloem sap of plants, and the first direct proof that Cd is translocated via sieve tubes in rice plants.     

Tolerance of rice cultivars to iron toxicity

Iron toxicity is an important growth‐limiting factor for flooded rice production in various parts of the world, including Brazil. Data related to the reaction of rice cultivars to iron concentrations are limited, especially for large numbers of cultivars. Forty rice cultivars were grown in a greenhouse in nutrient solutions containing 0.09, 0.89, and 1.78 mM Fe (5, 50 and 100 ppm Fe). The effects of excess iron were measured on plant height, root length, and root and shoot dry weight. Root and shoot dry weight were found to be more sensitive to excess iron concentration. Based on dry matter yield, reduction of shoots at higher Fe concentrations compared to the optimum or control treatment, rice cultivars were classified as tolerant, moderately tolerant, moderately susceptible or susceptible.

The effect of Fe concentrations on concentrations and contents of other nutrient was also investigated. Higher concentration of Fe in the nutrient solution exerted an inhibiting effect on the concentrations and contents of almost all macro and micronutrients.     

Cloning of the phloem-specific small heat-shock protein from leaves of rice plants

The N-terminal amino-acid sequence of a major rice phloem-sap protein, designated as RPP23, was determined. The complete amino-acid sequence of RPP23 was deduced from the corresponding rice EST- clone and contained an extra 46 amino acids at the N-terminus, that was apparently cleaved off to form mature RPP23 in sieve tubes. RPP23 shared a similarity to plant small heat-shock proteins (smHSPs), though the N-terminal region of RPP23 was distinct from that of known smHSPs. Immunocytological analyses using leaf sections showed that RPP23 was located only in the phloem regions of leaves, and was present in non-stressed plants. In mature leaves, stronger immunocytological signals were detected in sieve elements than in companion cells.     

Impact of plant genotype and nitrogen level on rice growth response to inoculation with Azospirillum sp. strain B510 under paddy field conditions

Abstract

Twenty rice cultivars, including three genetically-distinct groups (japonica, indica-1, and indica-2), were evaluated for their response to inoculation with Azospirillum sp. strain B510 in paddy fields with standard nitrogen (SN) and low nitrogen (LN) fertilization. In the SN field, the tiller numbers in most indica-2 cultivars, 37?days after transplanting (DAT), were significantly increased by the B510 inoculation, whereas those in 4 japonica cultivars were significantly decreased. A similar growth response was observed in the LN field, although the impacts of the B510 inoculation were more varied than in the SN field. At 58 DAT, the tiller numbers in most cultivars were lower or unaffected by the B510 inoculation under both SN and LN conditions, except that the tiller number of the Nipponbare cultivar, which is classified as japonica, was significantly higher in the LN field only. These results suggest that the effects of inoculation with Azospirillum sp. strain B510 on the growth of rice plants, especially on tiller numbers at the early growth stage, vary depending on the rice genotype, as well as nitrogen level. Therefore, the plant genotypes, growth stages, and fertilization managements must be considered when a plant-associated bacterium is evaluated for beneficial effects under field conditions.     

Quantification of zinc transport via the phloem to the grain in rice plants (Oryza sativa L.) at early grain-filling by a combination of mathematical modeling and 65Zn tracing

Zinc (Zn) is an essential nutrient for human beings, and most Zn intake occurs through vegetables or cereals such as rice (Oryza sativa L.) grains. Recently, we detected Zn as well as cadmium, which may be partitioned to rice grains, in the phloem saps from the uppermost internodes of rice and in the xylem saps from the cut stems at early grain-filling. To quantify Zn transport to the grains via the phloem and xylem, a mathematical model previously developed for cadmium transport to rice grains was applied. We examined the translocation of zinc into the grains of rice plants at early grain-filling by feeding zinc-65 (⁶⁵Zn) via a root-bathing medium, through culm cuts above and below the flag-leaf nodes, and through the flag leaves. The estimate made using the mathematical model and experimental data for three types of ⁶⁵Zn transport suggests that the grain Zn may be accumulated predominantly via the phloem through two means of transport, phloem transport of stored Zn from the leaves and, more importantly, xylem-to-phloem transfer at the nodes from Zn as it is being absorbed. The Zn transport via the phloem to the grains is more selective than that of cadmium, a non-nutrient element, as also evidenced by the greater transport of cadmium to the glumes via the xylem.     

水稻雄蕊导管发育研究

本文以水稻粤泰保持系为材料，采用ATPase定位方法研究了单核至三核花粉期雄蕊导管的发育。单核边位花粉期，分化的导管胞质变浓厚、细胞核染色质浓缩、核转变为新月形并出现凋亡小体；此外，导管内物质也可以大分子形式直接撤离。单核边位晚期，雄蕊导管发育成熟。在二核和三核花粉期，导管内重新出现具有ATPase活性的物质，同样的现象也存在于农垦58s可育花药成熟导管中。以上结果暗示水稻雄蕊导管分化存在程序性死亡及非程序性死亡多种途径，水稻成熟导管内具有ATPase活性物质可能是一种普遍现象。     

Irrigation and Zn fertilizer management improves Zn phyto‐availability in various rice production systems

Zinc (Zn) is an important micronutrient for rice (Oryza sativa L.) production and its deficiency has been observed in various production systems. High grain Zn concentration is equally important for high rice yield and human health. In this work, the effects of Zn fertilization on seedling growth, grain yield, grain Zn concentration, and their association with root traits were studied under alternate wetting and drying (AWD), aerobic rice (AR), system of rice intensification (SRI), and continuous flooding (CF). Zinc fertilization (15 kg ha^?1) improved nursery seedlings chlorophyll and Zn concentrations, root length, and number of roots with highest values observed in CF. At harvesting, maximum plant height, panicle length, total and panicle bearing tillers, and kernel yield were found with Zn addition in AWD and CF rice systems. Mid season drainage provided at maximum tillering and Zn fertilization increased its concentration in leaves, culms, panicles, and grains under CF and AR at physiological maturity. Most of Zn applied was allocated into culms and panicles, nevertheless, a significant increase in grain Zn concentration was also observed in all production systems. Association of leaf Zn with grain Zn concentration was stronger than with culm and panicle Zn. The results indicate that Zn application after rice nursery transplanting is more important for grain Zn enrichment in all rice systems than for increase in grain yield in all systems except AWD where grain yield was also increased. More grain yield in CF and AWD as compared to SRI and AR can also be attributed to decreased spikelet sterility and to better Zn phyto‐availability in these rice systems at physiological maturity.     

水稻OsNPR1基因RNA干涉载体的构建及其对水稻的转化

拟南芥NPR1基因是拟南芥中系统获得抗性的正调节基因.为鉴定水稻中的一个与拟南芥NPR1基因同源的基因OsNPR1的功能,用PCR扩增的该基因cDNA的667～1088核苷酸,构建了一个以OsNPR1为靶基因的RNA干涉水稻表达载体pONPR422-I,并用根癌农杆菌介导法转化水稻桂99,共获得了6株潮霉素抗性的再生苗.Southern杂交证实,这些再生苗均为转基因植株,能生长、结实,为进一步鉴定该基因功能奠定了基础.     

缺钾对水稻不同品种光合和能量耗散的影响

试验测定了钾敏感型(二九丰)和钾钝感型(原丰早)两个水稻品种在缺钾处理41.d后其剑叶的生长、光合光响应曲线、叶绿素荧光参数光响应曲线和暗弛豫动力学曲线。结果表明,缺钾降低了水稻剑叶的光合作用,显著抑制了生长。但是缺钾条件下导致两个水稻品种净光合速率(Pn)下降的主导因子并不相同。在缺钾条件下,原丰早(YFZ)剑叶的Pn随气孔导度(Gs)和胞间CO2浓度(Ci)的下降而下降,但叶绿素荧光参数和叶绿素含量几乎没有变化,说明其Pn下降主要归于气孔的限制。缺钾处理41.d后,二九丰(EJF)在低光强下[500mol/(m2.s)],Pn随Gs和Ci下降,但在更强的光强下,Pn和Gs继续下降,而Ci开始上升,并在1200mol/(m2.s)处超越了对照,说明此时主导因子不单受气孔限制,还受非气孔因子限制;它的光饱和点从1200mol/(m2.s)下降到大约500mol/(m2.s);同时,其荧光参数Fv/Fm、ФPSII、qP和ETR随光强上升而迅速下降,而L(PFD)、E和PP迅速增加,NPQ在1200mol/(m2.s)光强下上升,但是在高光强下却迅速降低,甚至低于对照,而且Fm、Fv/Fm下降,Fo上升,均说明缺钾处理可能使光合机构受到了伤害,发生了光抑制。对非光化学猝灭的分析得到其中间组分qNm可能起了更大的能量耗散作用,部分激发能从PSⅡ转移到PSⅠ,降低了PSⅡ耗散能量的压力。以上结果表明,两品种对钾敏感性不同极可能也与缺钾条件下光保护能力的差异有关。     

水稻栽后植株氮素积累特征及其与根系生长的关系

以冈优22、Ⅱ优162和K优047为材料,通过大田试验研究了不同种植方式下水稻秧苗栽后根系和地上部氮素积累的动态特征及其与根重的关系。结果表明,栽后40.d内,地上部及根系氮素积累量呈指数模型增加。茎鞘、发根节和叶片氮含量与根重呈极显著正相关;根系氮含量与根重呈显著负相关;各器官氮积累动态与根重均呈极显著的正相关关系。全生育期植株氮积累量拟合Logistic曲线较好,决定系数在0.988以上,氮素积累量与根重呈显著的正相关关系,生育期越靠前,相关系数值越大。3种种植方式中,自移栽至孕穗期氮积累量以常耕插秧最高,常耕抛秧其次,免耕高留茬抛秧较低;孕穗后免耕高留茬抛秧各器官氮含量最高,氮积累量也逐渐超过常耕抛秧。3个杂交稻组合中,前期以冈优22的氮积累量最高,后期Ⅱ优162增加速率较快,K优047在整个生育期中均最低。     

根癌农杆菌介导水稻基因转化研究进展

简要综述了根癌农杆菌介导水稻基因转化的优点及转化后代的遗传学行为 ,着重分析了影响农杆菌介导水稻基因转化的各种因素和存在问题     

Effects of soil water content on growth,tillering, and manganese uptake of lowland rice grown in the water‐saving ground‐cover rice‐production system (GCRPS)

A 2‐year field experiment and a pot experiment were carried out to compare Mn uptake, tillering, and plant growth of lowland rice grown under different soil water conditions in the ground‐cover rice‐production system (GCRPS) in Beijing, North China. The field experiment was conducted in 2001 and 2002, including two treatments: lowland‐rice variety (Oryza sativa L. spp. japonica) grown under thin (14 μm) plastic‐film soil cover (GCRPS_plastic) at 80%–90% water‐holding capacity (WHC) and traditional lowland rice (paddy control) grown with 3 cm standing‐water table. The pot experiment was conducted in a greenhouse with four treatments: (1) traditional lowland rice: paddy control; (2) GCRPS, water‐saturated soil: GCRPS_saturated; (3) GCRPS at 90% water‐holding capacity (WHC): GCRPS_90%WHC; and (4) GCRPS at 70% WHC: GCRPS_70%WHC. Results of the field experiment showed that dry‐matter production, number of tillers, as well as N and Mn concentrations in rice shoots of GCRPS were significantly lower than in paddy control, while there was no significant difference in shoot Fe, Cu, Zn, and P concentration and nematode populations. In the pot experiment, shoot Mn concentration significantly decreased with decreasing soil water content, while soil redox potential increased. Shoot–dry matter production and tiller number of GCRPS_saturated were significantly higher than in other treatments. Significant correlations were observed between the shoot Mn concentration and tiller number at maximum tillering stage in the field and pot experiment, respectively. We therefore conclude that the limitation of Mn acquisition might contribute to the growth and yield reduction of lowland rice grown in GCRPS. The experiment provides evidence that GCRPS_plastic combined with nearly water‐saturated soil conditions helps saving water and achieving optimum crop development without visual or latent Mn deficiency as observed under more aerobic conditions.     

水稻蜡质合成相关基因OsGL1-5的表达模式及逆境响应特征分析

通过生物信息学方法对水稻蜡质合成相关基因OsGLl-5启动子序列特点进行分析;并以水稻中花11不同组织和发育时期的穗子为材料,通过半定量RT-PCR及mRNA原位杂交技术分析OsGLl-5的时空表达特征;同时,分别以200mmol·L-1 NaCl、100μmol· L-1 ABA和1.0％ H2O2处理水稻幼苗,通过半定量RT-PCR分析逆境胁迫下OsGL1-5的表达模式.生物信息学分析表明,OsGL1-5启动子中包括大量与干旱、冷、盐等多种逆境胁迫相关的调控序列.时空表达特征分析表明,OsGL1-5主要在不同发育时期的穗子中表达,且表达部位集中在稃片的毛状体和花药绒毡层中,叶中表达量相对较低,而茎和根中没有检测到表达.NaCl、ABA以及H2O2等逆境胁迫下,OsGL1-5表达量在不同处理时间有所增加.     

Growth of rice plants under red light with or without supplemental blue light

Abstract

The effects of blue light supplementation to red light on growth, morphology and N utilization in rice plants (Oryza sativa L. cv. Sasanishiki and Nipponbare) were investigated. Plants were grown under two light quality treatments, red light alone (R) or red light supplemented with blue light (RB; red/blue-light photosynthetic photon flux density [PPFD] ratio was 4/1), at 380 mol m^?2 s^?1 PPFD. The biomass production of both cultivars grown under RB conditions was higher than that of plants grown under R conditions. This enhancement of biomass production was caused by an increase in the net assimilation rate (NAR). The higher NAR was associated with a higher leaf N content per leaf area at the whole-plant level, which was accompanied by higher contents of the key components of photosynthesis, including Rubisco and chlorophyll. In Sasanishiki, preferential biomass investment in leaf blades and expansion of wider and thinner leaves also contributed to the enhancement of biomass production. These morphological changes in the leaves were not observed in Nipponbare. Both the changes in physiological characteristics, including leaf photosynthesis, and the changes in morphological characteristics, including leaf development, contributed to the enhancement of biomass production under RB conditions, although the extent of these changes differed between the two cultivars.     

In vivo staining of reduced iron by 2,2′ bipyridine in rice exposed to iron toxicity

A protocol for a novel method to visualize Fe(II) in rice tissues is proposed. The method is based on the selective formation of a purple‐red color complex of 2,2′ bipyridine and Fe(II). Rice genotypes were exposed to 18 mM Fe(II) in nutrient solution for 2 d. Root systems of intact plants were subsequently placed in 2,2′ bipyridine solutions. The formation of the [Fe(bipy)<$>_3^{2+}<$>] color complex was visualized using bifocal microscopy. The method may improve the selection of genotypes during breeding for Fe‐toxicity resistance of rice.     

Subcellular distribution and chemical forms of chromium in rice plants suffering from different levels of chromium toxicity

The subcellular distribution and chemical forms of different heavy metals in rice are correlated with their bio‐toxicity. An experiment was conducted to investigate the subcellular distribution and chemical forms of chromium (Cr) in two rice genotypes (Oryza sativa L. cv. Xiushui 113 and cv. Dan K5) differing in Cr accumulation, to understand the mechanisms of Cr toxicity and resistance in rice plants. The results show that Cr in the roots of rice plants exposed to Cr stress was mainly localized in cell walls, whereas Cr in leaves and stems was mainly present in both cell walls and vacuoles, suggesting that both compartments act as important protective barriers against Cr toxicity in rice plants. Although Cr ions in all plant tissues exist predominantly in the forms extracted by 80% ethanol and distilled water, the amount of Cr in the chemical forms extracted by 2% HAc, 0.6 M HCl, and in residues was significantly increased under the highest Cr level (100 μM Cr) compared to the plants grown under lower Cr levels. These results indicate that excess Cr accumulated in rice plants under Cr stress is bound to undissolved or low‐bioavailable compounds, such as undissolved phosphate and oxalate, being beneficial for rice plants to alleviate Cr toxicity. In addition, under the highest Cr level (100 μM), Dan K5 had a higher percentage of Cr in the chemical forms extracted by 2% HAc, 0.6 M HCl, and in residues compared to Xiushui 113 in both stems and leaves, indicating that more Cr ions in shoots of Dan K5 were bound to undissolved or low‐bioavailable compounds, in comparison with those of Xiushui 113. It is evident that the low bioavailability of Cr in the shoots of Dan K5 is related to a high Cr accumulation.