Oxygen Diffusion from the Roots of Rice Grown under Non-waterlogged Conditions

Three rice varieties, cv. Norin 36, cv. Norin 37 and cv. Yubae, were grown in a loam with a 20 cm water-table which gave aerobic conditions to a depth of not less than 15 to 17 cm. Under these conditions Norin 36 grew more vigorously and tillered more frequently than the other two varieties. The rates of oxygen diffusion at 23°C from roots up to 11 cm in length were however appreciably lower for Norin 36 (4.3 × 10^?8g · cm^?2 of root surface · min^?1) than for Norin 37 or Yubae (c. 7.8 × 10^?8g). A considerable increase (up to 200 %) in the oxygen diffusion rate (ODR) from the roots occurred if they were cooled to 3°C, and at this temperature differences in ODR between the varieties were not significant. For a purely physical system, because of the decrease in the diffusion coefficient of oxygen in water, and, the increase in oxygen solubility, a drop of c. 20 % in ODR should accompany the above 20°C drop in temperature. A 16 % drop was recorded for artificial ‘roots’ under these conditions. It was concluded that respiratory activity at the higher temperature must have been responsible for the low readings and intervarietal differences observed at 23°C. By increasing the 3°C values by 25 % a mean value of 14.2 × 10^?8g · cm^?2 of root surface · min^?1 was recorded for the three varieties, being the probable ODR at 23°C in the absence of a respiratory factor. Calculations show that respiratory activity removed enough oxygen to reduce the ODR for Norin 36 by more than 9 × 10^?8g, and for Norin 37 and Yubae by c. 6.7 × 10^?8g · cm^?2 of root surface · min^?1. Anatomical investigations showed that cortical breakdown was always extensive at 4 to 4.5 cm from the apex of the roots. In some cases however breakdown had not occurred in the basal segment of the root. No opinion could be formed as to whether differences in the amount of cortical breakdown between the varieties might have occasioned the respiratory differences observed. An interesting feature of the root anatomy was the failure of breakdown in those regions of the roots through which lateral roots emerged.     

The Oxidising Activity of Roots in Waterlogged Soils

Root oxidising activity has been studied quantitatively in two species, Menyanthes trifoliata and Molinia coerulea, using a non-specific dye technique, and an oxygen-specific “polarographic” technique in conjunction with artificial roots constructed from silicone rubber tubing. Oxidising activity in these two species has been found to be up to nine times greater than can be accounted for by oxygen diffusing from the roots. Enzymatic oxidation is thought to be the cause of such high oxidising activity. The characteristic patterns of iron oxidation found on and around roots are discussed, and oxidation of iron at the rhizophere ‘boundary’ is illustrated. Earlier work on root oxidising activity is briefly reviewed.     

The Use of Polarography in the Assay of Oxygen Diffusing from Roots in Anaerobic Media

A “polarographic” technique by which the rate of outward diffusion of oxygen from plant roots may be measured, is described in detail. Oxygen has been found to diffuse from the roots of all of the ten species of bog-plants so far tested, and the oxygen diffusion rates (ODR) of eight of these species show the existence of interspecific differences. Model roots made from silicone rubber tubing give “polarographs” identical with those obtained around the living roots. Suberization accompanying root maturation is thought to account for a. the association of oxygen diffusion with the apical regions of roots, and b. the lowered diffusion rates associated with winter dormancy. This localisation of root oxygen diffusion may be of survival value in reduced soils. Experiments suggest that aerenchyma can function as an oxygen reservoir in the plant if the stomata were closed for long periods. Calculations of expected ODR based on the internal gas concentrations of a model system give readings very similar to the ODR obtained experimentally using the silicone rubber tubing models. Further calculations, based on reported internal gas concentrations for Menyanthes, rice, Spartina, and Schoenus, also show a close similarity between real and expected values. It is concluded that in these species at least, there is negligible resistance in certain regions of the root to the passage of oxygen from the root intercellular spaces to the surrounding medium. Results have shown that root bases are relatively impermeable to oxygen, and it is suggested that oxygen intake into roots in the basal regions reported by other workers, probably occurs through basally-borne laterals. One important function of diffusing oxygen from the root is probably the supply of an external source of oxygen to the root meristem.     

Rice: sulfide-induced barriers to root radial oxygen loss, Fe2+ and water uptake, and lateral root emergence

BACKGROUND AND AIMS: Akagare and Akiochi are diseases of rice associated with sulfide toxicity. This study investigates the possibility that rice reacts to sulfide by producing impermeable barriers in roots. METHODS: Root systems of rice, Oryza sativa cv. Norin 36, were subjected to short-term exposure to 0.174 mm sulfide (5.6 ppm) in stagnant solution. Root growth was monitored; root permeability was investigated in terms of polarographic determinations of oxygen efflux from fine laterals and the apices of adventitious roots, water uptake, anatomy and permeability to Fe2+ using potassium ferricyanide. KEY RESULTS: Both types of root responded rapidly to the sulfide with immediate cessation of growth, decreased radial oxygen loss (ROL) to the rhizospheres and reduced water uptake. Profiles of ROL measured from apex to basal regions of adventitious roots indicated that more intense barriers to ROL than normal were formed around the apices. Absorption of Fe2+ appeared to be impeded in sulfide-treated roots. In adventitious roots, deposition of lipid material (suberisation) and thickenings of walls within the superficial cell layers were obvious within a week after lifting the treatment and could prevent the emergence of laterals and commonly result in their upward longitudinal growth within the cortex. Death of laterals sometimes occurred prior to emergence; emergent laterals eventually died. In adventitious roots, blockages formed within the vascular and aeration systems in response to the sulfide. CONCLUSIONS: In both adventitious and lateral roots, sulfide-induced cell wall suberization and thickening of the superficial layers were correlated with reduced permeability to O2, water and Fe2+. This study sheds light on some of the symptoms of diseases such as Akiochi. The results correlate with the authors' previous findings on the effects on roots of sulfide and lower organic acids in Phragmites and of acetic acid in rice.     

两个特用稻的营养供应水平与32P、14C分布和谷产量的关系

香稻(竹香粘)的分蘖数多,其分蘖期根系吸收³²P和³²P分布到分蘖,以高、中肥和高N,高K肥处理的为高;¹⁴C-葡萄糖同化物分布在分蘖比黑米稻(黑优粘)和常规稻“双桂36”的高,但灌浆期和黄熟期¹⁴C分布在稻穗较少.低肥处理的稻谷产量较高.而在高、中肥条件下结实率降低,实粒数减少,成穗率稍低,谷产量也比“黑优粘”和“双桂36”低. “黑优粘”在高肥、高N条件下的分蘖多,成穗率高、结实粒数也较多,稻谷产量比“竹香粘”高,在高、中肥、高 N高 P条件下,³²P分布于分蘖多,分蘖的¹⁴C分布则以高 N,高 K肥条件下的多;开花和灌浆用稻穗的¹⁴C分布皆以高 K肥水平的为高。“黑优粘”是耐肥和需钾肥品种,高肥、高K可提高其稻谷产量,但仍比“双桂36”低.     

褐飞虱侵害对不同抗性水平水稻根部吸收氮、磷、钾的影响

为了解褐飞虱Nilaparvata lugens侵害后水稻抗性水平与根系吸收氮（N）、磷（P）、钾（K）的关系,对不同抗性水平的水稻受褐飞虱侵害后的平均受害水平、植株功能损失指数及水稻吸收水培液营养元素N,P,K情况进行了研究。结果表明：不同水稻品种（TN1、协优63、协优963和超级培矮64S/E32）接种褐飞虱后,TN1受害最严重,协优63和超级培矮64S/E32 次之;受害最轻的是协优963,30头/株侵害后植株功能损失指数仅为0.661。40,60和80头/株侵害水稻后根系对K吸收下降程度最显著,其次为P,最后为N;且随褐飞虱侵害时间的延长（6 d, 9 d）影响愈显著。60头/株侵害TN1、协优63、协优963和超级培矮64S/E32后9 d,根系对K吸收下降率分别为164.11%,74.61%,55.16%和46.60%。由此可见,随水稻品种抗性水平的下降,接种褐飞虱后,水稻根部对水培液营养元素吸收下降程度愈显著。本研究结果可对深入阐明不同抗性水平水稻抗（耐）虫机制与根系吸收能力关系提供参考。     

褐飞虱为害对不同抗性水稻品种苗期根系几种营养物质和总酚含量的影响

本文以对褐飞虱Nilaparvata lugens(St?l)具不同抗性水平的水稻品种为研究对象,通过在苗期接入不同密度褐飞虱后测定水稻根系可溶性糖、游离氨基酸、可溶性蛋白质和总酚变化情况,以明确水稻抗虫性与根系生理生化物质含量的关系.研究结果表明,根系中的可溶性糖除了苗龄8d不接虫的处理,其余处理均以感虫品种TN1含...     

Rhizosphere Oxidation in Rice and other Species: A Mathematical Model Based on the Oxygen Flux Component

A mathematical model is presented from which one can predict the likely dimensions of oxidised rhizospheres due to oxygen diffusing from roots into anaerobic media such as wet soil. The analysis applies Fick's law of diffusion to the diffusion of oxygen from a cylindrical object (the root) into a sink (the soil) which is absorbing oxygen at a constant rate M. Solution of the final equation gives the dimensions of the oxygenated rhizosphere, i.e. the distance from the root at which the oxygen concentration becomes zero. The results obtained supoprt the view that oxygen diffusing from roots will produce a rhizosphere ‘sheath’ charged with oxygen. Furthermore, some of the predicted limits for this oxygen sheath correspond with those of ferric iron sheaths around roots in waterlogged soils. Calculations also show that oxygenated rhizospheres around the roots of plants very tolerant of reducing conditions. e.g. Menyanthes trifoliata, Oryza sativa and Eriophorum angustifolium, should be from two to three times as broad as for Molinia coerulea which is a species intolerant of strong reducing conditions. Consequently if oxidation reactions are not instantaneous but occur only gradually as quantities of reduced products enter the oxygenated zone, then the plants with the larger rhizospheres will be significantly better protected from absorbing large amounts of reduced products than will those plants with smaller oxygenated zones. This may in part explain the reason for intervarietal defferences in physiological disease resistance in rice. Finally the observation is made that small lateral roots can be expected to oxygenate a zone nearly as large as, or probably larger, than the primary root from which they have arisen.     

Study of the relationship between the content of the rare earth element Eu in rice plants and in Nilaparvata lugens (Hemiptera: Delphacidae)

Abstract The current study investigated changes in the content of the rare earth element Europium (Eu) in roots, shoots and leaves of rice plants and in Nilaparvata lugens Stål (Hemiptera: Delphacidae) using an Eu marker and hydroponic culture. The results showed that N. lugens infestation significantly reduced Eu content in roots, shoots and leaves of two rice varieties, Shenyou 1 and Xieyou 963. The Eu content in roots, shoots and leaves of the susceptible variety, Shenyou 1, was significantly higher than that in the resistant variety, Xieyou 963. The Eu content of N. lugens fed on Shenyou 1 was significantly higher than of those fed on Xieyou 963. In addition, the Eu level was elevated at a higher density of N. lugens infestation. Eu content in the bodies of N. lugens was related to their weight and honeydew excretion, with a significant positive correlation. Thus, Eu content in the bodies of N. lugens can be considered an index of the amount of phloem sap taken in by N. lugens because the amount of honeydew excretion is proportional to the amount of phloem sap consumed. The ratios of Eu content in N. lugens to that in roots, shoots and leaves of rice plants were elevated at a higher N. lugens infestation density. That ratio was maximal in leaves, was intermediate in shoots and was minimal in roots. There was no significant difference in ratios between the two plant varieties. An Eu marker may be useful in the screening of resistant varieties and in the study of the mechanisms of resistance.     

Influence of Different Cultivars on Populations of Ammonia-Oxidizing Bacteria in the Root Environment of Rice

Comparisons of the activities and diversities of ammonia-oxidizing bacteria (AOB) in the root environment of different cultivars of rice (Oryza sativa L.) indicated marked differences despite identical environmental conditions during growth. Gross nitrification rates obtained by the ¹⁵N dilution technique were significantly higher in a modern variety, IR63087-1-17, than in two traditional varieties. Phylogenetic analysis based on the ammonium monooxygenase gene (amoA) identified strains related to Nitrosospira multiformis and Nitrosomonas europaea as the predominant AOB in our experimental rice system. A method was developed to determine the abundance of AOB on root biofilm samples using fluorescently tagged oligonucleotide probes targeting 16S rRNA. The levels of abundance detected suggested an enrichment of AOB on rice roots. We identified 40 to 69% of AOB on roots of IR63087-1-17 as Nitrosomonas spp., while this subpopulation constituted 7 to 23% of AOB on roots of the other cultivars. These results were generally supported by denaturing gradient gel electrophoresis of the amoA gene and analysis of libraries of cloned amoA. In hydroponic culture, oxygen concentration profiles around secondary roots differed significantly among the tested rice varieties, of which IR63087-1-17 showed maximum leakage of oxygen. The results suggest that varietal differences in the composition and activity of root-associated AOB populations may result from microscale differences in O₂ availability.     

Responses by the brown planthopper,Nilaparvata lugens,to conspecific density on resistant and susceptible rice varieties

This study examines the nature of intraspecific interactions among Nilaparvata lugens (Stål) (Hemiptera: Delphacidae) planthoppers feeding on resistant and susceptible rice varieties. Planthopper nymphs produced less honeydew and gained less weight when feeding on rice variety IR62 (resistant) compared to susceptible rice varieties. A series of bioassays was conducted that varied N. lugens nymph densities on IR62 and IR22 (susceptible). Increasing nymph density facilitated feeding by conspecifics; however, intraspecific competition increased mortality of nymphs on IR62 (but rarely on IR22). Furthermore, nymph weights declined with increasing conspecific density on IR22, and the effects were weak on IR62. More female nymphs than males survived on IR62 but this was not affected by density. Nitrogenous fertilizer increased competition among N. lugens on young plants of IR22, but not on IR62. Results indicate that nymphs have a low efficiency in accessing resources when feeding on IR62, even where the plants have received fertilizer. Female‐biased survival and biomass compensation for mortality may promote population recovery after development on the resistant plant and accelerate adaptation to the resistant variety.     

The dependence of methane transport in rice plants on the root zone temperature

Large diurnal and seasonal variations in methane flux from rice paddies have been found in many studies. Although these variations are considered to result from changes in methane formation rates in the soil and the transport capacity (e.g. biomass, physiological activities, and so on) of rice plants, the real reasons for such variations are as yet unclear. This study was conducted to clarify the effects of temperature on the rate of methane transport from the root zone to the atmosphere using hydroponically grown rice plants. Methane emission rates from the top of the rice plants whose roots were soaked in a solution with a high methane concentration were measured using a flow-through chamber method with the top or root of the rice plants being kept at various temperatures. The methane emission rates and methane concentrations in solution were analyzed using a diffusion model which assumes that the methane emission from a rice paddy is driven by molecular diffusion through rice plants by a concentration gradient. In the experiment where the temperature around the root was changed, the conductance for methane diffusion was typically 2.0-2.2 times larger when the solution temperature was changed from 15 to 30 °C. When the air temperature surrounding the top of the rice plant was changed, the change in conductance was much less. In addition, from measurements of methane flux and methane concentration in soil water in a lysimeter rice paddy during the 2 growing seasons of rice, it was found that the conductance for methane transport was correlated with the soil temperature at 5 cm depth. These results suggest that the temperature around the root greatly affects the methane transport process in rice plants, and that the process of passing through the root is important in determining the rate of methane transport through rice plants.     

辽宁水稻品种抗灰飞虱鉴定及其抗性机制研究

为探明辽宁地区水稻品种对本地灰飞虱Laodelphax striatellus(Fallén)的抗性水平及其抗虫机制,本研究利用改进的苗期集团鉴定法,以IR36为抗虫对照品种、武育粳3号为感虫对照品种,对42份辽宁地区主栽水稻品种和研究待推广品种进行了水稻苗期对灰飞虱抗性鉴定,并从中选取20份不同抗性水平的品种进行了排趋性和抗生性的测定。结果表明:从42份水稻材料中仅筛选出1份抗虫材料辽优5218,中抗品种11份,其余均为感虫或高感品种。在不同水稻类型中,杂交稻的抗虫性普遍较常规稻强,而从水稻株型上看,抗性品种大多为披散型。抗虫机制研究发现,抗虫品种辽优5218和中抗品种港育129兼具排趋性和抗生性,是非常理想的抗性种质资源,中抗品种港源8号和粳优558具有很强的排趋性,也是较为理想的抗性资源,为抗性机制的深入研究提供了材料。但大部分省内主栽主推品种不具备对灰飞虱的抗性,应引起重视。     

水稻品种对褐飞虱的田间抗性及其生态学机制

评价了7个水稻品种(浙粳22、宜香845、中组14、秀水123、二优倍九、感虫对照品种TN1和抗虫对照品种IR36)在田间成株期对褐飞虱Nilaparvata lugens(Stl)的抗性表现,并初步分析了它们的抗性机制。结果表明,在田间网室人工诱发条件下,浙粳22、宜香845、秀水123和中组14等4个品种的抗性水平与抗虫品种IR36相同,均小于3级,表现为抗虫,而二优培九则与感虫品种TN1相同,表现为感虫。在自然发生条件下的水稻分蘖期至乳熟期,宜香845和中组14上褐飞虱数量仅为TN1上的7.84%～24.44%,秀水123和浙粳22则为TN1上的30.19%～60.27%。在4个抗性品种上褐飞虱的产卵量和卵孵化率明显减少,而若虫存活率仅为TN1上的20%～30%。与IR36相同,4个抗性品种上褐飞虱的若虫存活率和种群增长倍数均显著低于TN1上,说明他们对褐飞虱的抗性主要表现为抗生性。     

STUDIES ON CULTIVAR-INDUCED CHANGES IN INSECTICIDE SUSCEPTIBILITY AND ITS RELATED ENZYME ACTIVITIES OF THE WHITE BACKED PLANTHOPPER, SOGATELLA FURCZFERA (HORVÁTH) (HOMOPTERA:DELPHACIDAE)

Abstract  The susceptibility of Sogatella furcifera female adults on N22 to malathion increased as feeding time prolonged, while the day change of susceptibility to isoprocarb showed a inverse tendency. The activities of esterase and carboxylesterase were induced significantly after on N22 for one day, and then declined. The non-susceptible level of adults to insecticides and enzyme activities seemed to be heightened after feeding on ASD7, a variety resistant to Nilaparvata lugens . The total phenol content in rice leaf sheath was the highest in N22, and could be regaded as one of the factors, which caused chages in susceptibility of S. furicfera to insecticide after feeding different rice varieties. It was recommended that suitable insecticides and planthopper resistant varieties should be coordinately used in practice 90 that they contribute more effects respectively.     

Influence of different cultivars on populations of ammonia-oxidizing bacteria in the root environment of rice

Comparisons of the activities and diversities of ammonia-oxidizing bacteria (AOB) in the root environment of different cultivars of rice (Oryza sativa L.) indicated marked differences despite identical environmental conditions during growth. Gross nitrification rates obtained by the 15N dilution technique were significantly higher in a modern variety, IR63087-1-17, than in two traditional varieties. Phylogenetic analysis based on the ammonium monooxygenase gene (amoA) identified strains related to Nitrosospira multiformis and Nitrosomonas europaea as the predominant AOB in our experimental rice system. A method was developed to determine the abundance of AOB on root biofilm samples using fluorescently tagged oligonucleotide probes targeting 16S rRNA. The levels of abundance detected suggested an enrichment of AOB on rice roots. We identified 40 to 69% of AOB on roots of IR63087-1-17 as Nitrosomonas spp., while this subpopulation constituted 7 to 23% of AOB on roots of the other cultivars. These results were generally supported by denaturing gradient gel electrophoresis of the amoA gene and analysis of libraries of cloned amoA. In hydroponic culture, oxygen concentration profiles around secondary roots differed significantly among the tested rice varieties, of which IR63087-1-17 showed maximum leakage of oxygen. The results suggest that varietal differences in the composition and activity of root-associated AOB populations may result from microscale differences in O2 availability.     

水稻品种对白背飞虱的耐虫性反应及稻株营养成分的变化

测定了不同水稻品种对白背飞虱的耐虫性反应及稻株营养成分的变化。结果表明,中抗品种N22、绿源占1号、Mudgo、K89—B5和94D—22具有较高的耐虫性,抗虫品种Ptb33和中组74以抗生性为主,感虫品种秀水11、汕优63和感虫对照品种TN1不具有耐虫性,在白背飞虱为害后,耐虫品种稻株中全N量和可溶性总糖量增加,N／糖比变化率明显下降;而感虫品种的全N量和可溶性总糖量下降,N／糖比变化率明显增加,不同品种受害后体内大多数氨基酸含量均有不同程度的增加,但品种间氨基酸含量减少的种类不同,TN1品种只有丙氨酸含量减少,N22品种除丙氨酸外蛋氨酸和苏氨酸含量也明显减少,Ptb33品种仅精氨酸略有减少。     

Survival rate and stylet penetration behavior of current Korean populations of the brown planthopper,Nilaparvata lugens,on resistant rice varieties

To understand the development of host plant resistance-breaking ability of the current BPH populations in Korea, we conducted nymphal survivorship tests and electrical penetration graph (EPG) studies on susceptible and resistant rice varieties with four different BPH populations, which were collected in the early 1980s (S-BPH) and in 2005, 2006, and 2007. The S-BPH had low survival rates on resistant rice varieties carrying either Bph1 or bph2. However, the current BPH populations have high resistance-breaking ability on the varieties with their elevated survival rates, whereas their survival rates were still low on the other resistant varieties, Gayabyeo (Bph1  the other unknown gene) and Rathu Heenati (Bph3). The EPG analysis also revealed that the ratio of BPH that could reach the phloem sap ingestion waveform (N4-b) within 15 h on the resistant rice varieties containing Bph1 or bph2 was higher in the current BPH populations (16.7–50%) than in the S-BPH population (0-4.2%). However, the pre-reaching time from the penetration start to the first N4-b waveform in the current BPH populations was significantly longer on resistant varieties (Bph1 or bph2) than on susceptible varieties. Furthermore, the total duration of N4-b waveform was significantly shorter on the resistant varieties.From these results, we suggest that, although the current BPHs collected in Korea have a high resistance-breaking ability through the increase of survival rate on resistant rice varieties carrying either Bph1 or bph2, they still have some difficulties feeding on the phloem sap of the resistant rice varieties.     

水稻品种诱导白背飞虱药剂敏感性及其相关酶活性变化的研究

白背飞虱雌成虫取食N22后,对马拉硫磷敏感性随取食天数增加呈增高趋势;而对叶蝉散的敏感性变化则正相反,在取食N22 1天后酯酶／羧酸酯酶即表现高水平的诱导活性,尔后随取食时间延长而降低,取食抗褐飞虱品种ASD7后,其体内酶活及对药剂抗性呈升高趋势。不同水稻品种中总酚含量以N22显著为高,相关分析表明,水稻叶鞘中的酚类物质可能是品种影响飞虱药剂敏感性的主要因素之一,因此,在生产实践中,适宜的杀虫剂与飞虱抗性品种应协同使用,以充分发挥各自的有效作用。     

Nitrogen-Fixing (Acetylene Redution) Activity and Population of Aerobic Heterotrophic Nitrogen-Fixing Bacteria Associated with Wetland Rice

Nitrogen-fixing activity associated with different wetland rice varieties was measured at various growth stages by an in situ acetylene reduction method after the activities of blue-green algae (cyanobacteria) in the flood water and on the lower portion of the rice stem were eliminated. Nitrogen-fixing activities associated with rice varieties differed with plant growth stages. The activities increased with plant age, and the maximum was about at heading stage. The nitrogen fixed during the whole cropping period was estimated at 5.9 kg of N per ha for variety IR26 (7 days) and 4.8 kg of N per ha for variety IR36 (95 days). The population of aerobic heterotrophic N₂-fixing bacteria associated with rice roots and stems was determined by the most-probable-number method, using semisolid glucose-yeast extract and semisolid malate-yeast extract media. The addition of yeast extract to the glucose medium increased the number and activity of aerobic heterotrophic N₂-fixing bacteria. The glucose-yeast extract medium gave higher counts of aerobic N₂-fixing bacteria associated with rice roots than did the malate-yeast extract medium, on which Spirillum-like bacteria were usually observed. The lower portion of the rice stem was also inhabited by N₂-fixing bacteria and was an active site of N₂ fixation.