VA菌根在植物生态学研究中的意义

植物生态学是研究植物和环境之间相互作用关系规律的科学。土壤、地形、气候、各种生物都是重要的环境因素 ,它们影响着植物群落的区系组成、结构、空间分布、物种多样性以及生态系统的稳定性、生产力等 ,因而在生态学研究中受到了充分的重视[2 0 ] 。然而植物与土壤微生物之间的关系 ,尤其是植物与ＶＡ菌根菌形成的共生体 ,即ＶＡ菌根在植物生态学研究中则很少有人注意。近 30年来的发现和研究证实 ,ＶＡ菌根菌与植物形成的ＶＡ菌根共生关系也是植物生态学研究中不可忽视的一种重要关系 ,这是因为 :①在自然生态系统中 ,80 %的维管束植物具…     

蕨类植物的VA菌根与蕨类植物系统演化关系的研究

通过对云南热带、亚热带生长的２５６种蕨类植物ＶＡ菌根的调查,发现蕨类植物ＶＡ菌根营养者所占的比例低于被子植物;在真蕨类植物中,植物具有由ＶＡ菌根营养经兼性ＶＡ菌根营养向自养方向进化的趋势。     

水稻米粒延伸性的遗传剖析

以籼稻ZYQ8与粳稻JX17为亲本的DH群体作为研究材料,考察DH群体及双亲的米粒延伸率相关性状,并使用该群体的分子连锁图谱进行QTL分析.共检测到14个与稻米延伸性有关的QTL,包括2个粒长QTL、7个饭粒长QTL和5个米粒延伸率QTL,分别位于第1、2、3、5、6、7、10、11和12染色体.所有QTL的LOD值介于2.26～9.25,分别解释性状变异的5.31%～17.21%.在第3染色体上的G249～G164、第6染色体上的G30～RZ516和第10染色体上的G1082～GA223区间同时检测到控制饭粒长和米粒延伸率的QTL.米粒延伸性受多基因控制,Wx基因与位于第6染色体上的qCRE-6的G30～RZ516区间相近,对米饭的延伸性具重要影响.     

水稻体细胞无性系变异

水稻体细胞无性系变异研究取得了很大进展 ,获得了大量抗病、抗逆、优质、矮杆等突变体。对这些突变体遗传分析表明 ,大多数突变性状由 1对或 2对基因控制。水稻体细胞无性系变异的发生与基因型、性状、继代时间、培养方式等有关 ,并具有内在的机制 ,点突变和反转录转座子插入可能是引起水稻无性系变异的两个重要原因。     

水稻纹枯病抗性QTL分析

对灿稻窄叶青8号（ZYQ8）和粳稻京系17（JX17）以及由它们构建的加倍单倍体（DH）群体,分别在杭州和海南岛,采用注射器接种法进行纹枯病抗性鉴定,并使用该群体的分子链锁图谱进行数量性状座位（QTL）分析。共检测到4个抗纹枯病的QTL（qSBR-2、qSBR-3、qSBR-7和qSBR-11）,分别位于第2、第3、第7和第11染色体。其中qSBR-2、qSBR-3、qSBR-7的抗性基因由抗病亲本ZYQ8贡献,而qSBR-11的抗性基因来自感病亲本JX17。qSBR-2、qSBR-3、qSBR-7在杭州和海南岛都能检测到,而qSBR-11只在杭州检测到。在杭州的实验中,纹枯病病级与秆长和抽穗期呈显著负相关;在控制秆长和抽穗期的QTL中,控制秆长的qCL-3与qSBR-3位于同一染色体区域,其余QTL与抗纹枯病的QTL之间无连锁关系。     

NaCl-induced Senescence in Leaves of Rice (Oryza sativa L.) Cultivars Differing in Salinity Resistance

The influence of NaCl on senescence-related parameters (proteinand chlorophyll concentrations, membrane permeability and chlorophyllfluorescence) was investigated in young and old leaves of fiverice cultivars differing in salt resistance. NaCl hastened thenaturally-occurring senescence of rice leaves which normallyappears during leaf ontogeny: it decreased chlorophyll and proteinconcentrations and increased membrane permeability and malondialdehydesynthesis. Such an acceleration of deteriorative processes affectedall leaves in salt-sensitive cultivars while it was more markedin oldest than in youngest leaves of salt-resistant genotypes.NaCl-induced senescence also involved specific modifications,such as an increase in basal non-variable chlorophyll fluorescence(F ₀) recorded in all cultivars or a transient increase in solubleprotein concentration recorded in salt-resistant genotypes only.Alteration of membrane permeability appeared as one of the firstsymptoms of senescence in rice leaves and allowed discriminationamong cultivars after only 7 d of stress. In contrast, F _v/F _mratio (variable fluorescence/maximal fluorescence) was thesame for all cultivars during the first 18 d of stress and thuscould not be used for identifying salt-resistant rice exposedto normal light conditions. Relationships between parametersinvolved in leaf senescence are discussed in relation to salinityresistance of rice cultivars. Chlorophyll concentration; chlorophyll fluorescence; electrolyte leakage; magnesium; malondialdehyde; membrane permeability; NaCl; Oryza sativa L.; protein; rice; salinity resistance; senescence; UV absorbing substances     

水稻柱头外露率的QTL分析

利用高柱头外露率的籼稻窄叶青8号(ZYQ8)和极低外露率的粳稻京系17(JX17)以及由它们构建的加倍单倍体(DH)群体,在海南对各DH株系的柱头外露率进行调查,并使用该群体的分子连锁图谱进行数量性状座位(QTL)分析。共检测到2个控制水稻柱头外露率的QTL(qPES-2,qPES-3),分别位于第2、第3染色体;并发现控制柱头单边外露率的QTL与柱头外露率完全一致,而控制柱头双边外露率的QTL在第2染色体上检测到;其增效基因均来源于ZYQ8。同时定位的控制穗粒数的QTL位于第6染色体和第8染色体上,与柱头外露率之间没有连锁关系。     

Characterization of Root Exudates at Different Growth Stages of Ten Rice (Oryza sativa L.) Cultivars

Abstract: Plant root exudates play important roles in the rhizosphere. We tested three media (nutrient solution, deionized water and CaSO₄ solution) for three periods of time (2, 4 and 6 h) for collecting root exudates of soil‐grown rice plants. Nutrient culture solution created complications in the analyses of exudates for total organic C (TOC) by the wet digestion method and of organic acids by HPLC due to the interference by its components. Deionized water excluded such interference in analytical analyses but affected the turgor of root cells; roots of four widely different rice cultivars excreted 20 to 60 % more TOC in deionized water than in 0.01 M CaSO₄. Furthermore, the proportion of carbohydrates in TOC was also enhanced. Calcium sulfate solution maintained the osmotic environment for root cells and did not interfere in analytical procedures. Collection for 2 h avoided under‐estimation of TOC and its components exuded by rice roots, which occurred during prolonged exposure. By placing plants in 0.01 M CaSO₄ for 2 h, root exudates of soil‐grown traditional, tall rice cultivars (Dular, B40 and Intan), high‐yielding dwarf cultivars (IR72, IR52, IR64 and PSBRc 20), new plant type cultivars (IR65598 and IR65600) and a hybrid (Magat) were collected at seedling, panicle initiation, flowering and maturity and characterized for TOC and organic acids. The exudation rates were, in general, lowest at seedling stage, increased until flowering but decreased at maturity. Among organic acids, malic acid showed the highest concentration followed by tartaric, succinic, citric and lactic acids. With advancing plant growth, exudation of organic acids substituted exudation of sugars. Root and shoot biomass were positively correlated with carbon exudation suggesting that it is driven by plant biomass. As root exudates provide substrates for methanogenesis in rice fields, large variations in root exudation by cultivars and at different growth stages could greatly influence CH₄ emissions. Therefore, the use of high‐yielding cultivars with lowest root excretions, for example IR65598 and IR65600, would mediate low exudate‐induced CH₄ production. The screening of exciting rice cultivars and breeding of new cultivars with low exudation rates could offer an important option for mitigation of CH₄ emission from rice agriculture to the atmosphere.     

Differences in the Sensitivity to UVB Radiation of Two Cultivars of Rice (Oryza sativa L.)

The effects of UVB radiation on the growth of two cultivarsof Japanese lowland rice (Oryza sativa L.), Sasanishiki andNorin 1, were examined in a phytotron. Supplementation of visibleradiation with UVB radiation reduced plant length, tiller number,the fresh and dry weights of the aboveground parts of plants,and the amounts of total leaf nitrogen, chlorophyll, solubleprotein and ribulose-1,5-bisphosphate carboxylase/oxygenase(Rubisco) in the eighth leaf, the youngest fully expanded leaf.By contrast, UVB radiation significantly increased the accumulationof UV-absorbing compounds. There was a difference between thetwo cultivars in the resistance to the effects of UVB radiation.The reduction in the amounts of Rubisco was smaller in Sasanishiki,while the increase in the accumulation of UV-absorbing compoundswas greater in Sasanishiki. Parameters of plant growth, withthe exception of the amount of Rubisco, decreased in directproportion to decreases in total leaf nitrogen in plants grownunder lower or higher doses of UVB radiation. However, the decreasein the Rubisco content of Norin 1 grown under a high dose ofUVB radiation was exceptionally marked, and was not observedsimilarly in Sasanishiki. These results suggest that the remarkablereduction in Rubisco content in Norin 1 might have been dueto the specific effects of UVB radiation. It is also suggestedthat the difference between cultivars in the resistance to UVBradiation might be due to the differences in the levels of Rubiscoand in UV-absorbing compounds that are induced by UVB radiation. (Received January 29, 1996; Accepted May 31, 1996)     

Isolation and Characterization of Matrix Associated Region DNA Fragments in Rice (Oryza sativa L.)

To investigate the interactions between chromosomal DNA andnuclear matrices in higher plants, matrix associated regions(MARs) of rice (Oryza sativa L.) DNAs were cloned. First, weprepared nuclear matrices from isolated nuclei by digestingthem with EcoRl and then extracting with 2 M NaCl. About 6%of the total DNA remained in the nuclear matrices after thisdigestion and extraction. The residual DNA fragments in thenuclear matrices were cloned. Some of the cloned DNA fragmentsshowed binding to certain nuclear proteins. One of the MAR fragmentscontained sequences related to known consensus motifs and ahairpin loop structure. A method is presented for isolationof matrix associated region (MAR) DNAs from plant cells. (Received January 13, 1997; Accepted July 10, 1997)     

五种丛枝菌根真菌对枳实生苗耐锌污染的影响

通过盆栽实验研究丛枝菌根(AM)真菌Glomus versiforme(G.v)、G.mosseae(G.m)、G.intraradices(G.i)、G.aggregatum(G.a)和G.etunicatum(G.e)在锌污染条件下枳实生苗的菌根侵染、生长、叶片和根系锌、磷含量及部分生理指标的影响.结果表明:锌污染...     

Mechanism of Anther Dehiscence in Rice (Oryza sativa L.)

This paper presents a new explanation of the mechanism of antherdehiscence in rice during the period from floret opening topollen dispersal. The theca dehisced on the stomium in the apicalpart and the anther wall in the basal part of the large locule.Comparison of the anther dehiscence process under various airhumidity conditions showed that the process, until the splittingat the apical and basal parts, was a moisture-requiring processwhereas the widening of the splits in both parts was a desiccatoryprocess. Observation of the anther transverse section, revealedthe marked development of the U-shaped thick cell wall in theendothecium adjacent to these two splits. From these observations,the anther dehiscence mechanism may be explained as follows.At the time of anthesis, pollen grains swell rapidly in responseto the floret opening and cause the theca to bulge, rupturingthe septum. The pollen pressure combined with the inward bendingof the locule walls adjacent to the stomium causes splittingof the stomium in the apical part of the theca. At the sametime, the septum rupture extends to the bottom of the largelocule supported by the pollen pressure. After these processes,the locule walls adjacent to both splits straighten probablydue to their water loss. This straightening widens the splitsand the swollen pollen grains overflow from the widened splits.Copyright1999 Annals of Botany Company Anther dehiscence, Oryza sativa L., pollen grain swelling, rice, septum, stomium, theca.     

Nitrogen Use Efficiency of Rice Cultivars (Oryza sativa L.) Under Salt Stress and Low Nitrogen Conditions

Improving nitrogen use efficiency (NUE) under salt stress has become crucial for rice as it is increasingly facing two major environmental constraints: excessive nitrogen fertilization and soil salinization. However, the interaction between salinity and N levels is very complex and has not yet been considered from the perspective of reduced nitrogen input. We conducted a hydroponic experiment at the early tillering stage on the Yoshida solution to evaluate the impact of rising NaCl and decreasing N application on NUE of four rice cultivars cultivated under three NaCl (0, 56, and 113 mM) and four N (2.86, 1.43, 0.72, and 0.36 mM) concentrations. After 4 weeks, physiological NUE (pNUE), absorption NUE (aNUE), agronomical NUE (agNUE), N transport efficiency (NTE), and physiological traits were evaluated. Significant interactions between N and NaCl-applied concentrations were found in all measured parameters. In all cultivars, increasing the NaCl-applied concentration markedly decreased aNUE and agNUE. For each NaCl treatment, lowering the N applied sharply increased aNUE and agNUE, and this effect was stronger when the NaCl applied was higher. The effect of N lowering on pNUE depended on the NaCl treatment: it enhanced pNUE in the absence of NaCl but had no influence under the highest NaCl-applied concentration. Cultivars largely differed in response to NaCl. The aNUE—but not pNUE—differed between salt-tolerant and salt-sensitive cultivars: aNUE markedly decreased with NaCl concentration in the most salt-sensitive cultivar, whereas it was the highest at the intermediate NaCl concentration in the most salt-tolerant cultivar, especially under low N levels. This finding suggests that under salt conditions, the use of salt-tolerant rice genotypes combined with reducing N level application is necessary to improve NUE. The study of NUE in rice should be focused on the improvement of aNUE with a strong emphasis on the salt tolerance of cultivars.

     

Uptake Kinetics of Arsenic in Upland Rice Cultivar Zhonghan 221 Inoculated with Arbuscular Mycorrhizal Fungi

Arbuscular mycorrhizal fungi (AMF) appear to be highly associated with arsenic (As) uptake in host plants because arsenate (As(V)) and phosphorus (P) share the same transporter, whereby AMF can enhance P uptake. A short-term experiment was conducted for low- (0 to 0.05 mM As) and high-affinity (0 to 2.5 mM As) uptake systems, to investigate the AMF role on As uptake mechanism in plants, which may explain As uptake kinetics in upland rice cultivar: Zhonghan 221. When concentration of As ranged from 0 to 0.05 mM, Funneliformis geosporum (Fg) significantly decreased arsenite (As(III)) and monomethylarsonicacid (MMA) uptake when (p < 0.05) compared to non-mycorrhizal (NM) treatment, since the major route for (As(III)) in rice roots—rice silicon transporter Lsi1 would be influenced by Fg inoculation at high As concentrations. Fg can also reduce As(V) uptake significantly (p < 0.05) under both uptake systems relative to NM treatment, whereas, Funneliformis mosseae (Fm) increased As(V) and MMA uptake in rice roots, with MMA uptake rate generally lower than As(III) and As(V). Using suitable AMF species inoculation with rice, As uptake and accumulation in rice grains can be reduced and the risk to human health, once consumed, can be minimized.     

Mycorrhiza of Brazil Pine (Araucaria angustifolia [Bert. O. Ktze.])

Abstract: Tropical and subtropical forests once covered large areas of Central and South America. An important member of forests of the southern hemisphere is the genus Araucaria. Because of clear cutting only small remnants of Araucaria angustifolia forests still exist in Southern Brazil. Attempts at reforestation have had only limited success because of lack of knowledge about the environmental requirements of this species. This is especially true with respect to the root/fungus symbiosis (mycorrhiza) which is necessary for enhanced water and nutrient uptake and present in more than 90 % of land plants. Analysis of the root systems of Araucaria trees from forest and grassland (campo) sites revealed mycorrhizal structures (appressoria, penetration and coiled hyphae, vesicles, arbuscules, spores) which are characteristic for the arbuscular mycorrhiza (AM) type. The spores of AM fungi at both sites - forest and campo - were identified. The biodiversity at the forest site was much higher, with 13 species, whereas only 6 different species could be identified at the campo site. Glomus and Acaulospora were the only genera present at the campo. The forest, however, also contained spores of Entrophospora and Scutellospora. In addition to the greater biodiversity, the spore number in soil as well as the percent mycorrhizal colonization in roots were significantly higher at the forest site than at the campo site. Because of the low frequency of hyphal coils and the dominating intercellular growth of hyphae, these mycorrhizas can be classified as an Arum -type, which is the first report of this kind in gymnosperms.     

Chronopathological Aspects of Disease Incidence in Rice (Oryza sativa L.)

Rice seedlings maintained under uncontrolled glasshouse conditions were inoculated with conidial suspensions of a fungal pathogen, Helminthosporium oryzae, at various times during the 24 h. Significant increase in the percent germination and germ tube length of conidia were observed in the rice samples inoculated at 02:00 and 06:00h. The 24 h temporal variation in leaf temperature was positively correlated with variation in stomatal movements. The results indicate a 24 h rhythm in the behavior of the fungal pathogen on the host in relation to the conditions of the growing environment. In all the inoculated seedlings, the appearance of a large number of brown leaf spots was confined to the light span. Among the plants inoculated, earlier initiation of brown leaf spot appearance, maximum number of leaf spots, and highest disease severity were observed when plants were inoculated at 02:00h. There was a positive correlation between disease severity of the host and in vivo values of percent germination of conidia and germ tube length of the pathogen in plants inoculated between 02:00 and 06:00h. The findings of this study implicate that light intensity and temperature could play a predominant role in controlling disease susceptibility rhythms in plants.     

QTL Analysis of Aluminum Resistance in Rice (Oryza sativa L.)

Aluminum (Al) toxicity is considered as one of the primary causes of low-rice productivity in acid soils. In the present study, quantitative trait loci (QTLs) controlling Al resistance based on relative root elongation (RRE) were dissected using a complete linkage map and a recombinant inbred lines (RILs) derived from a cross of Al-tolerant japonica cultivar Asominori (Oryza sativa L.) and Al-sensitive indica cultivar IR24 (O. sativa L.). A total of three QTLs (qRRE-1, qRRE-9, and qRRE-11) were detected on chromosomes 1, 9, and 11 with LOD score ranging from 2.64 to 3.60 and the phenotypic variance explained from 13.5 to 17.7%. The Asominori alleles were all associated with Al resistance at all the three QTLs. The existence of these QTLs was confirmed using Asominori chromosome segment substitution lines (CSSLs) in IR24 genetic background (IAS). By QTL comparative analysis, the two QTLs (qRRE-1and qRRE-9) on chromosomes 1 and 9 appeared to be consistent among different rice populations while qRRE-11 was newly detected and syntenic with a major Al resistance gene on chromosome 10 of maize. This region may provide an important case for isolating genes responsible for different mechanisms of Al resistance among different cereals. These results also provide the possibilities of enhancing Al resistance in rice breeding program by marker-assisted selection (MAS) and pyramiding QTLs.     

Epidermal Structure in the Ligule of Rice (Oryza sativa L.)

The structure of the abaxial epidermis of the ligule of rice(Oryza sativa L.) as seen in the light and scanning electronmicroscope is described. Long cells, silica cells, cork cells,prickle hairs, microhairs and stomata-like structures were found.Reasons for considering these latter structures to be true stomataare given. Results of an X-ray analysis for silicon are presentedand the distribution of silica discussed in relation to itsfunctional role in the ligule. Oryza sativa L, rice, Gramineae, ligule, epidermis, scanning electron microscopy, X-ray analysis, silica, stomata