ULTRASTRUCTURE OF DISPERSED AND IN SITU SPECIMENS OF THE DEVONIAN SPORE RHABDOSPORITES LANGII: EVIDENCE FOR THE EVOLUTIONARY RELATIONSHIPS OF PROGYMNOSPERMS

Abstract: The spore Rhabdosporites (Triletes) langii (Eisenack) Richardson, 1960 is abundant and well preserved in Middle Devonian (Eifelian) ‘Middle Old Red Sandstone’ deposits from the Orcadian Basin, Scotland. Here it occurs as dispersed individual spores and in situ in isolated sporangia. This paper reports on a detailed light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis of both dispersed and in situ spores. The dispersed spores are pseudosaccate with a thick walled inner body enclosed within an outer layer that was originally attached only over the proximal face. The inner body has lamellate/laminate ultrastructure consisting of fine lamellae that are continuous around the spore and parallel stacked. Towards the outer part of the inner body these group to form thicker laminate structures that are also continuous and parallel stacked. The outer layer has spongy ultrastructure. In situ spores preserved in the isolated sporangia are identical to the dispersed forms in terms of morphology, gross structure and wall ultrastructure. The sporangium wall is two‐layered. A thick coalified outer layer is cellular and represents the main sporangium wall. This layer is readily lost if oxidation is applied during processing. A thin inner layer is interpreted as a peritapetal membrane. This layer survives oxidation as a tightly adherent membranous covering of the spore mass. Ultrastructurally it consists of three layers, with the innermost layer composed of material similar to that comprising the outer layer of the spores. Based on the new LM, SEM and TEM information, consideration is given to spore wall formation. The inner body of the spores is interpreted as developing by centripetal accumulation of lamellae at the plasma membrane. The outer layer is interpreted as forming by accretion of sporopollenin units derived from a tapetum. The inner layer of the sporangium wall is considered to represent a peritapetal membrane formed from the remnants of this tapetum. The spore R. langii derives from aneurophytalean progymnosperms. In light of the new evidence on spore/sporangium characters, and hypotheses of spore wall development based on interpretation of these, the evolutionary relationships of the progymnosperms are considered in terms of their origins and relationship to the seed plants. It is concluded that there is a smooth evolutionary transition between Apiculiretusispora‐type spores of certain basal euphyllophytes, Rhabdosporites‐type spores of aneurophytalean progymnosperms and Geminospora‐/Contagisporites‐type spores of heterosporous archaeopteridalean progymnosperms. Prepollen of basal seed plants (hydrasperman, medullosan and callistophytalean pteridosperms) are easily derived from the spores of either homosporous or heterosporous progymnosperms. The proposed evolutionary transition was sequential with increasing complexity of the spore/pollen wall probably reflecting increasing sophistication of reproductive strategy. The pollen wall of crown group seed plants appears to incorporate a completely new developmental mechanism: tectum and infratectum initiation within a glycocalyx‐like Microspore Surface Coat. It is unclear when this feature evolved, but it appears likely that it was not present in the most basal stem group seed plants.     

A contribution to the rust flora (Uredinales) of southern Africa,with an emphasis on Namibia

Five new rust species are described and hitherto unknown spore states for the following seven species are reported: Puccinia desertorum on Evolvulus alsinoides, Uromyces comptus on Merremia bipinnatipartita, Puccinia halsei on Acacia hereroensis, Ravenelia transvaalensis on Acacia mellifera, Puccinia abutili on Abutilon angulatum, on Abutilon cf. austroafricanum, and on Abutilon cf. rehmannii, Puccinia lycii on Lycium sp. and Puccinia turgida on Lycium europaeum and on Lycium cf. oxycarpum. We also examined Uredo combreticola on Combretum cf. engleri, on Combretum hereroense, and on Combretum zeyheri, Puccinia afra on Lycium sp., and Uredopeltis cf. chevalieri on Grewia flavescens. All mentioned rust fungi are described in detail and are shown by line drawings. Selected species are illustrated with SEM-photographs. Part 220 in the series “Studies in Heterobasidiomycetes” from the Botanical Institute, University of Tübingen     

Lesion mimic associates with adult plant resistance to leaf rust infection in wheat

Lesion mimics (LM) that resemble plant disease symptoms in the absence of plant pathogens may confer enhanced plant disease resistance to a wide range of pathogens. Wheat line Ning7840 has adult plant resistance (APR) to leaf rust (Puccinia triticina) and shows LM symptoms at heading. A recessive gene (lm) was found to be responsible for LM in Ning7840 and located near the proximal region of chromosome 1BL using a population of 179 recombinant inbred lines (RIL) derived from the cross Ning7840/Chokwang. Genomic in situ hybridization showed that Ning7840 carries the short arm of 1R chromosome from rye (Secale cereale L.), on which the race-specific gene Lr26 resides. The RILs were infected with the isolate PRTUS 55, an isolate virulent to Lr26, at anthesis in two greenhouse experiments. The result showed that the lines with LM phenotype had a significantly higher rust resistance than the non-LM lines. Composite interval mapping consistently detected a QTL, Qlr.pser.1BL, for APR on chromosome 1BL. Qlr.pser.1BL peaked at lm and explained up to 60.8% of phenotypic variation for leaf rust resistance in two greenhouse experiments, therefore, lm from Ning7840 may have pleiotropic effects on APR to leaf rust. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Wachstum und Sporenbildung einer schweizerischen Rasse von Puccinia graminis tritici in vitro

Growth and spore formation of a Swiss race of Puccinia graminis f. sp. tritici in vitro On a medium containing Evans Pepton and yeast Extract, the rust formed aecidiospores in great number. The aecidiospores were able to infect wheat plants. On media 4–9 (Table 1) uredospores and teliospores are formed. Highest numbers of teliospores were produced on substrates with ATP, nucleotide bases, and ribose.     

Spore morphology and ultrastructure of Cyathea (Cyatheaceae,Pteridophyta) species from southern South America

Spore sculpture and wall structure of eight Cyathea (Cyatheaceae) species from southern South America were studied using light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Two layers, i.e. an inner and an outer layer, were observed in the perispore. The inner layer has two strata: the inner stratum is attached to the exospore and composed of rodlets tangentially oriented to the spore surface and randomly intermixed; the outer stratum consists of a three-dimensional network of rodlets with either free or fused distal edges forming spinules. The outer layer is thin, darkly contrasted and covers the rodlets. In most cases, the exospore has two layers and a pitted surface. In Cyathea atrovirens, the exospore surface is smooth, while in C. delgadii and C. myriotricha it is verrucate. The homogeneity of perispore features within the genus Cyathea is evident, while exospore features are heterogeneous. The exospore has different kinds of surface-structures that are of potential interest for assessing evolutionary trends within the group.     

Spore morphology and wall ultrastructure of Hymenophyllaceae Link (Pteridophyta) from north-west Argentina

The family Hymenophyllaceae is represented in the study area by six species in two genera, Hymenophyllum J. E. Smith and Trichomanes L. The study was based on herbarium material and spores were studied under light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope (TEM). Both genera have trilete spores, 23 to 45 μm in equatorial diameter, with an ornamentation of echinulae and cones in Hymenophyllum and of verrucae, gemmae and granules in Trichomanes. Mature spores have a sporoderm composed of a perispore, an exospore and a fibrillar endospore; the exospore is 0.5 to 2.5 μm thick, compact and with an irregular margin. In some cases radial channels and other channels associated with the middle and inner parts of the laesurae were evident. A series of cavities filled with an opaque content line the inner margin of the exospore. The perispore is 20 to 400 nm thick and unevenly differentiated along the surface of a same spore. Under TEM, two main differentially contrasted portions could be distinguished: a dark massive portion with structural components could not be distinguished, and a light portion with several plates arranged in piles. The inner surface of the perispore exhibit short scales. Globules are immersed within the perispore at some depth from the perispore surface and others connected to it by structural threads. The spore characters observed including shape, ornamentation, laesurae length and wall structure are useful in distinguishing the two genera studied, but less useful in differentiation at the species level.     

Untersuchungen über den chemischen Aufbau von Sporen- und Keimschlauchwänden der Uredosporen des Weizenrostes (Puccinia graminis var. tritici)

Zusammenfassung Zellwände und Keimschläuche von Uredosporen des Weizenrostes (Puccinia graminis var. tritici) wurden isoliert, und ihre chemische Zusammensetzung wurde quantitativ untersucht. Als gemeinsame Bausteine enthalten Sporenwände und Keimschlauchwände Proteine, Lipide und die Neutralzucker Galaktose, Glucose und Mannose. Die einzelnen Komponenten liegen in unterschiedlicher Menge vor. Auch qualitativ unterscheiden sich die Sporenwände und die Keimschlauchwände: Melanin ist nur in den Sporenwänden vorhanden, in den Keimschlauchwänden dagegen nicht. Der polymer gebundene Aminozucker der Keimschlauchwände ist N-Acetylglucosamin, das mit großer Wahrscheinlichkeit als Chitin vorliegt. Die Sporenwände enthalten dagegen polymeres Glucosamin (vermutlich Chitosan).Sporenwände sind in 3% iger NaOH löslich. Aus diesem Extrakt läßt sich mit Fehlingscher Lösung ein Galaktoglucomannan fällen, das überwiegend aus Mannose besteht. Aus der entsprechenden Fraktion der Keimschlauchwände, in der ebenfalls Mannose überwiegt, kann mit Fehlingscher Lösung kein Mannan gewonnen werden. Der in NaOH unlösliche Satz der Keimschlauchwände ist zum größten Teil aus Glucose und N-Acetylglucosamin aufgebaut. Es gibt keine identischen Polysaccharidfraktionen von Sporen- und Keimschlauchwänden. Sie sind heteropolymer und setzen sich jeweils aus Galaktose, Glucose und Mannose zusammen.

---

Investigations on the chemical composition of spore walls and germ tube walls of wheat rust (Puccinia graminis var. tritici) uredospores

Summary Spore walls and germ tube walls from uredospores of wheat stem rust (Puccinia graminis var. tritici) were isolated and their chemical compositions determined quantitatively. The spore and germ tube walls are commonly composed of proteins, lipids, and the neutral sugars mannose, glucose and galactose. Carbon and nitrogen content, total lipids, composition of bound amino acids, total glucosamine and chitin content, and neutral sugars of spore and germ tube walls were compared. While the carbon content of the germ tube walls is only slightly higher than that of the spore walls, the germ tube walls contain twice as much nitrogen and lipids as the spore walls. The higher nitrogen content of the germ tube walls is due to higher amounts of bound amino acids and hexosamine. The polymeric germ tube wall hexosamine is insoluble in 3% NaOH, while the bulk of the polymeric spore wall hexosamine will go into solution when treated with 3% NaOH. The polymeric amino sugar of the germ tube wall is N-acetylglucosamine, which in all probability is present as chitin. In comparison, spore walls contain polymeric glucosamine (probably chitosan).The predominant neutral sugar of the spore walls is polymeric mannose (90%) while the germ tube walls contain polymeric glucose and mannose in nearly equal amounts. Galactose occurs in both wall types as a minor constituent.From spore walls completely dissolved in 3% NaOH we were able to precipitate a galactoglucomannan with fehling's solution. This galactoglucomannan was composed mainly of mannose. The corresponding fraction of the germ tube wall gave no precipitate with Fehling's solution. An alkali insoluble fraction of the germ tube wall consists mainly of glucose and N-acetylglucosamine. There are no identical polysaccharide fractions in spore walls and germ tube walls. They are always heteropolymers. Melanine is found in spore walls but not in germ tube walls.

     

A rapid method for measuring production of yellow rust spores on single seedlings to assess differential interactions of wheat cultivars with Puccinia striiformis

Uredospore production of Puccinia striiformis in single wheat seedlings was assessed by weighing spores on an electrical microbalance, by counting on a haemocytometer or by measuring turbidity of spore suspensions with a spectrophotometer and compared with production from groups of seedlings determined by weighing spores on an analytical balance. The data were used to assess differential interaction of wheat cultivars Hybrid 46 and Joss Cambier with two isolates of race 104 E137 of P. striiformis and cvs Maris Templar and Joss Cambier with two isolates of race 41 E136. A significant differential interaction was shown in both experiments by each method but most rapidly and with the minimum of materials by the single-plant microbalance technique. Measurements of spore production demonstrated differences between isolates within races more clearly than the conventional visual assessment of yellow rust symptoms.     

Induced resistance to rust diseases and its possible role in the resistance of multiline varieties

Inoculation of wheat seedlings with a non-virulent race of Puccinia striiformis delayed the onset of sporulation of a virulent race and also decreased the spore mass produced. Similarly, the sporulation of a virulent race of Uromyces appendiculatus on bean seedlings was reduced by application of a weakly virulent race. We suggest that these effects of induced resistance could retard the development of rust diseases in the field particularly in multiline varieties.     

中国产石韦属植物孢子形态特征及分类学意义

利用光镜和扫描电镜,对石韦属(Pyrrosia)19种植物的孢子纹饰进行了研究。结果表明:19种石韦属孢子都为黄色,形态均为肾形,两侧对称,单裂缝,说明该属植物是一个自然类群。表面纹饰类型有3种,即瘤状、瘤状—疣状和瘤状—网脊状。孢子表面纹饰特征性状稳定,在种间存在较大差异。该研究结果可以为形态近似种的分类提供参考依据,同时也为石韦属属下分类系统的建立提供了重要证据。     

Silver enhancement of lectin-gold and enzyme-gold cytochemical labelling of eggs of the nematode Onchocerca gibsoni

Summary Wheat germ agglutinin—gold and chitinase—gold complexes were used to demonstrate the presence of chitin on the surfaces of eggs of the animal parasitic nematodeOnchocerca gibsoni. The gold complexes were enhanced by silver intensification and examined by light microscopy (LM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Distinctive labelling of the egg surfaces was obtained with both probes in all three microscope modes. The results indicate that the small colloidal gold markers (3–10 nm) commonly used for high resolution TEM studies may be silver enhanced and also used for sensitive LM and SEM studies.     

Is the quantity of orbicules released by Dactylis glomerata and Cynosurus echinatus (Poaceae) big enough to play an allergenic role?

Orbicule characteristics of Dactylis glomerata and Cynosurus echinatus (Poaceae) were investigated using light (LM), scanning electron (SEM) and transmission electron microscopy (TEM). Based on SEM micrographs, the number of orbicules per 100?µm² of the locule wall surface was determined in both dehisced and undehisced anthers and was further compared statistically. A total of 100 pollen grains were examined using SEM in search for orbicules attached to the pollen exine. Orbicules were not found distributed freely in the anther locules. They were attached to the locule wall surface through sporopolleninous fibrils, the orbicule wall being firmly embedded in, and often in continuity with the thin layer of sporopollenin lining each locule. The orbicule density on the locule wall surface of both the dehisced and undehisced anthers did not differ significantly. Only a few orbicules were seen attached to the pollen exine in both species. It is concluded that orbicules are not easily removed from the surface of the locule wall and, consequently, that the number of orbicules emitted from the two grass species is too low to play a significant role in triggering allergic diseases.     

ULTRASTRUCTURE OF CHAETOCEROS MUELLERI (BACILLARIOPHYCEAE): AUXOSPORE,RESTING SPORE AND VEGETATIVE CELL MORPHOLOGY1

The structure of the frustule of auxospores, resting spores and vegetative cells of Chaetoceros muelleri Lemm. are described with LM and SEM. Vegetative frustules are relatively small and lightly silicified, are not united into filaments, and appear unornamented under LM and SEM. The setae are circular to subcircular in transverse section with spines and puncta arranged in a spiral pattern. The resting spore and auxospore frustules are more silicified than the vegetative frustules and appear unornamented under LM and SEM. The auxospores of C. muelleri were previously unknown.     

三裂叶豚草锈菌侵染寄主叶片的显微和超微观察

【背景】三裂叶豚草是我国重要的外来入侵植物之一,其传播速度快,已给我国造成巨大的经济损失。近年来发现的三裂叶豚草锈菌是一种对其具有生物防治潜力的病原菌。【方法】本文利用显微技术研究了三裂叶豚草锈菌的侵染过程及其对寄主结构的影响。【结果】三裂叶豚草锈菌菌丝可从多处侵入同一个叶肉细胞,胞间菌丝与叶肉细胞相接触可使部分细胞壁增厚。锈菌侵染使三裂叶豚草叶脉末梢导管分枝增多,造成三裂叶豚草水分代谢失调;叶片细胞内膜系统破碎化,细胞器结构受到不同程度的破坏,导致细胞内膜系统紊乱,细胞器结构稳定性降低。【结论与意义】豚草锈菌侵染破坏了三裂叶豚草叶片的细胞结构。本研究为深入研究豚草锈菌的致病机理奠定了基础。     

Combined cryo- and thin sectioning (TEM) in the elucidation of mimosoid tetrad/polyad ultrastructure

Cryosections (freeze-sections) of tetrads/polyads and their subsequent examination in the SEM complement traditional methods (LM, SEM, and TEM) by providing both a dynamic three-dimensional overview of polyad morphology and clarifying aperture morphology, internal wall characters and tetrad/polyad cohesion mechanisms. Cryosections of Dinizia tetrads reveal that cohesion is maintained through adhesion/fusion of the apices of clavate elements in localized regions of the subproximal and proximal walls — a feature not discernible using traditional SEM preparations. Cryosections of the globose 20-grained polyads of Parkia species reveal small central grains and triradiate-shaped proximal apertures — features unobservable or misinterpreted using traditional LM, SEM and TEM methods. In Anadenathera polyads, cryosections have clarified the nature and distribution of small gaps present in the lateral and proximal walls of individual grains.     

Genetic control of durable resistance to yellow rust (Puccinia striiformis) in the wheat cultivar Hybride de Bersée

The wheat cultivar Hybride de Bersee is described as possessing durable resistance to yellow rust. Some races of Puccinia striiformis can infect it at the seedling stage but not severely in the field. Using euploid and aneuploid stocks of Bersee it was shown that a large part of this resistance was controlled by chromosome 5BS-7BS, the effect being detectable in seedlings and at later growth stages. Measurements of spore production from infected seedlings showed that the line ditelosomic for the 5BS arm of the chromosome was more resistant than the line ditelosomic for the 7BS arm under environments favouring high spore production, but more susceptible under environments favouring low spore production. Thus both arms of the chromosome could contribute to resistance in appropriate environments. Chromosome 5BS-7BS did not carry the factors controlling the race-specific resistance to race 37 E132 of P. striiformis. The possibility of exploiting the resistance carried by chromosome 5BS-7BS in wheat breeding programmes is discussed.     

Ultrastructural Studies on the Microconidia of Botrytis cinerea Pers. and their Phialoconidial Development

The genesis and ultrastructure of microconidia of Botrytis cinerea Pers. were studied, using TEM and SEM. Microconidia are produced in flask-shaped, terminal or lateral phialides. The first microconidium develops holoblastically, subsequent microconidia are formed enteroblastically, in basipetal succession from a fixed conidiogenous locus. Mature microconidia are characterized by a two-layered spore wall covered by mucilage, a single, sickle-shaped nucleus, one or two large lipid bodies, a few mitochondria of the cristae-type, ribosomes, sparse endoplasmatic reticulum close to the plasmalemma and a small amount of cytoplasma. The basal septum which is surrounded by a collar-like rim is perforated by a simple central pore with a pore plug. Differences in genesis and ultrastructure of microconidia compared with macroconidia are discussed in relation to the function of these two spore types.     

Observations on the ultrastructure of the uredinial stage ofPuccinia polypogonis onPolypogon monspeliensis

The ultrastructure of the uredinial stage of the rust fungus,Puccinia polypogonis onPolypogon monspeliensis is described, using scanning and transmission electron microscopy. This study examined the urediniospores, intercellular hyphae, and haustoria of the fungus. The formation and structure of urediniospores is similar to those of otherPuccinia species. The ultrastructure of intercellular hyphae and haustoria is similar to those of other rust fungi, but with some differences. No modifications are observed in the wall of the haustorial mother cells during penetration. A collar is found only around old haustoria. In most cases, one nucleus is detected inside the haustorial body and no nucleoli are seen in the nuclei of intercellular hyphae and haustoria. The host-parasite interface, including extrahaustorial matrix and extrahaustorial membrane, is also discussed and compared with those of other rust fungi.     

Interaction between barley yellow dwarf virus and rust in wheat, barley and oats, and the effects on grain yield and quality

In three separate experiments, the upper leaf surface of the fifth formed leaf of wheat cv. Highbury, the fourth and fifth leaves of barley cv. Julia and the third and fourth leaves of oat cv. Mostyn were inoculated in a spore settling tower with wheat brown rust (Puccinia recondita f. sp. tritici), barley brown rust (P. hordei) or oat crown rust (P. coronata f. sp. avenae), respectively. Fewer pustules developed on distal portions of leaves of plants infected with barley yellow dwarf virus (BYDV) than on similar portions of leaves from virus-free plants. There were no significant differences in the number of pustules on proximal leaf portions. In barley and oats, the number of pustules on distal leaf portions was negatively correlated with the amount of yellowing of the leaf areas scored. In wheat, symptoms of BYDV were mild and leaves were little affected by yellowing. The latent period of rust on wheat and oats was not affected by BYDV. In barley, BYDV reduced the latent period of rust on leaf 5, but not on leaf 4, and reduced it on proximal, but not distal, leaf portions. In other experiments, BYDV reduced the yield of wheat and oats by 44% and 66%, respectively, while BYDV-infected barley was almost sterile. The appropriate rust reduced the yield of wheat, barley and oats by 33%, 13% and 86%, respectively. When infected with both BYDV and rust, yield of wheat and oats was reduced by 63% and 91%, respectively. Neither BYDV nor rust affected the percentage crude protein content of wheat grain, nor did rust affect that of barley. In oats, BYDV and rust each significantly increased crude protein of grain, but rust infection of BYDV-infected plants tended to reduce it.     

QTL mapping of multiple foliar disease and root-lesion nematode resistances in wheat

A genetic linkage map, based on a cross between the synthetic hexaploid CPI133872 and the bread wheat cultivar Janz, was established using 111 F₁-derived doubled haploid lines. The population was phenotyped in multiple years and/or locations for seven disease resistance traits, namely, Septoria tritici blotch (Mycosphaeralla graminicola), yellow leaf spot also known as tan spot (Pyrenophora tritici-repentis), stripe rust (Puccinia striiformis f. sp. tritici), leaf rust (Puccinia triticina), stem rust (Puccinia graminis f. sp. tritici) and two species of root-lesion nematode (Pratylenchyus thornei and P. neglectus). The DH population was also scored for coleoptile colour and the presence of the seedling leaf rust resistance gene Lr24. Implementation of a multiple-QTL model identified a tightly linked cluster of foliar disease resistance QTL in chromosome 3DL. Major QTL each for resistance to Septoria tritici blotch and yellow leaf spot were contributed by the synthetic hexaploid parent CPI133872 and linked in repulsion with the coincident Lr24/Sr24 locus carried by parent Janz. This is the first report of linked QTL for Septoria tritici blotch and yellow leaf spot contributed by the same parent. Additional QTL for yellow leaf spot were detected in 5AS and 5BL. Consistent QTL for stripe rust resistance were identified in chromosomes 1BL, 4BL and 7DS, with the QTL in 7DS corresponding to the Yr18/Lr34 region. Three major QTL for P. thornei resistance (2BS, 6DS, 6DL) and two for P. neglectus resistance (2BS, 6DS) were detected. The recombinants combining resistance to Septoria tritici blotch, yellow leaf spot, rust diseases and root-lesion nematodes from parents CPI133872 and Janz constitute valuable germplasm for the transfer of multiple disease resistance into new wheat cultivars.