Genetic variability in two hydrophilous species ofPotamogeton,P. pectinatus andP. filiformis (Potamogetonaceae)

Genetic variability inPotamogeton pectinatus andP. filiformis was studied by means of isozymes. The overall levels of variability were similar to some other well studied hydrophilous species, and were shown to be distributed more between than within populations. This partitioning of variability was attributed to three main factors. (1) Clonal growth (as measured by the frequency of multi-enzyme phenotypes) was shown to be a major factor in both species, although more important inP. pectinatus. (2) Low levels of sexual reproduction were shown to be a likely contributor to the partitioning of variability inP. pectinatus; such reproduction is probably limited by seedling recruitment rather than by infrequent flowering. (3) Geographical isolation was indicated as a factor regulating gene flow at distances of more than about 1000 km in both species, with the data suggesting that dispersal between populations is mainly by seed rather than by vegetative means.     

Genetic variation within and between populations of Potamogeton pusillus agg.

Patterns of isozyme variation were examined in 17 populations of P. pusillus and P. berchtoldii, together with one population of P. trichoides taken for comparison. Both P. pusillus and P. berchtoldii displayed low levels of variation within populations associated with high levels of interpopulation differentiation. This pattern of partitioning of genetic variation within and between populations is attributed to the founder effect, frequent vegetative propagation by turions, dominant self-fertilization and limited seedling recruitment. The mechanism of pollen transfer was investigated in cultivation. Effective pollination takes place in air above the water surface (autogamy, geitonogamy, anemogamy), on the water surface (epihydrogamy) or below water surface (hydroautogamy). The species are self-compatible. The low level of infra-population variation together with rare occurrence of heterozygotes suggest that selfing is the most frequent mode of pollination, although the protogynous flowers may occasionally permit some cross-pollination. Unique enzyme markers were found for P. pusillus and P. berchtoldii, and also for the single population of P. trichoides. All multienzyme phenotypes were species-specific. Isozyme data support the separate position of P. pusillus and P. berchtoldii. UPGMA dendogram based on enzyme data of 133 plant samples revealed three distinct main enzymatic entities perfectly corresponding to the three morphologically defined species.     

Clonal growth architecture and spatial dynamics of 10 species of the genus <Emphasis Type="Italic">Potamogeton</Emphasis> across different habitats in Kashmir Valley,India

The plasticity in clonal architecture may enable plants to effectively respond to environmental constraints and to enhance species ecological niche breadth but its role in plant tolerance to water flow is poorly documented. The present study was carried out to determine whether the clonal architecture varies with respect to water flow in 10 species of the genus Potamogeton colonizing habitats differing by flow conditions. For these 10 species, the traits describing clonal architecture were measured on individuals sampled in natural sites and plasticity in clonal architecture was examined in a common garden growth experiment. The clonal growth architecture did not vary significantly in the species which inhabit either standing (P. lucens, P. natans, and P. pusillus) or running water (P. amblyphyllus and P. berchtoldii). However, the species inhabiting both standing as well as running waters (P. crispus, P. nodosus, P. pectinatus, P. perfoliatus, and P. wrightii) showed considerable and significant variation in clonal growth architecture across these habitats. Transplantation experiment revealed that clonal architecture observed between the plants under different conditions is plastic and not due to genetic differentiation. The present study demonstrated that plasticity in the clonal architecture may enable these species to inhabit stressful conditions of flowing water.     

Dormancy in bulbils of several herbaceous plants: Effects of photoperiod,light, temperature,oxygen and gibberellic acid

Effects of some environmental conditions (photoperiod, white and colored lights, temperature, partial oxygen pressure) and growth regulators (gibberellic acid, 2-chloroethyltrimethylammonium chloride) on induction and release of dormancy of the bulbils ofDioscorea batalas, Laportea bulbifera, Elatostema involucratum andSedum bulbiferum were investigated. Bulbils were formed under short-day conditions inLaportea andElatostema, under long-day conditions inSedum, and irrespective of photoperiods inDioscorea. In all species exceptSedum, immature bulbils required light, particularly blue or far red, for sprouting (photo-sprouting stage), and mature bulbils required a cold treatment (thermo-sprouting stage). The duration of photo-sprouting and thermo-sprouting stages and the degree of dependency on light or low temperature of sprouting differed from species to species. Sprouting of chilled mature bulbils of these species was promoted by light, especially by red or green light. Both immature and mature bulbils ofSedum sprouted under short-day conditions. Continuous irradiation with blue, far-red and green light markedly inhibited their sprouting. Oxygen at high concentration inhibited the sprouting of immature bulbils inDioscorea; in the other species it promoted sprouting regardless of the maturation of the bulbils. Applications of gibberellic acid caused the sprouting of bulbils the absence of light, chilling or photoperiodic treatment in all species exceptDioscorea, in which gibberellic acid inhibited sprouting. Polyphenol oxidase activity was very high in the homogenates ofDioscorea bulbils, and increased further when the bulbils had been treated with gibberellic acid. In the other species, little or no such activity was observed.     

Zur Synonymie vonLitosiphon pusillus auf der Basis von Kulturversuchen

In June 1988,L. pusillus was collected for the first time in the Helgoland area. On the basis of observations in cultures, Pedersen's hypothesis that the microthalli ofL. pusillus are identical with those of threePilocladus species is discussed. The general morphology as well as the shape and dimensions of the unilocular sporangia are clearly different inPilocladus andLitosiphon microthalli. Therefore, Pedersen's opinion cannot be accepted.      

Identification of the polar constituents of Potamogeton species by HPLC-UV with post-column derivatization, HPLC-MSn and HPLC-NMR, and isolation of a new ent-labdane diglycoside

The polar extracts of Potamogeton pectinatus, P. lucens, P. perfoliatus and P. crispus (Potamogetonaceae) were analyzed by HPLC-UV-MS and their chromatographic profiles were very similar. The polar constituents of P. pectinatus were more exhaustively investigated by HPLC-UV with post-column derivatization, HPLC-MS(n) and HPLC-NMR, which allowed the on-line identification of various known flavones (dereplication). One of these compounds, luteolin 3'-O-glucoside, has never been characterized in the Potamogeton genus. The HPLC-UV-MS and HPLC-NMR analyses revealed also the presence of ent-labdane diterpene glycosides in the polar extracts of P. pectinatus and P. lucens and led to the isolation of a new ent-labdane diglycoside from P. pectinatus, beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl-15,16-epoxy-12-oxo-8(17),13(16),14-ent-labdatrien-19-oate.     

Microhabitats of stream invertebrates on two submersed macrophytes with contrasting leaf morphology

Larvae of Chironomidae, Simuliidae and Trichoptera exhibited various patterns of micro-distribution on the submersed macrophytes Potamogeton × zizii , with broad leaves, and P. pectinatus , with thread-like leaves. Seven common species of chironomid, six belonging to the subfamily Orthocladiinae and one to the Chironominae, showed four distinguishable patterns of distribution. The density of Simulium larvae was much greater towards the apices of the stems on both plants. Among three species of Trichoptera studied, the predatory Rhyacophila dorsalis had a pattern of distribution which was strongly related to prey density, particularly that of Simulium , on P . × zizii , but not on P. pectinatus. P . × zizii supported proportionately more free-ranging scrapers, such as the chironomid Thienemanniella vittata . than did P. pectinatus while the reverse was true for filter-feeders. These patterns are discussed in relation to habitat structure and behavioural characteristics.     

ent-Labdane glycosides from the aquatic plant Potamogeton lucens and analytical evaluation of the lipophilic extract constituents of various Potamogeton species

Two new ent-labdane glycosides, one known furano-ent-labdane and a new hydroxylated fatty acid were isolated from the dichloromethane extract of the freshwater aquatic plant Potamogeton lucens. The new compounds were assigned the structures of beta-d-glucopyranosyl-8(17),13-ent-labdadien-16,15-olid-18-oate, 18-beta-d-glucopyranosyloxy-8(17),13-ent-labdadien-16,15-olide and 13(R)-hydroxy-octadeca-(9Z,11E,15Z)-trien-oic acid by spectroscopic means. The algicidal activity of these compounds was tested against Raphidocelis subcapitata. Based on our previous study of Potamogeton pectinatus, other constituents were identified in P. lucens by LC-UV-MS, LC-NMR and GC-MS. The lipophilic extract profiles of both species are presented. Two other species, Potamogeton perfoliatus and P. crispus, were also investigated by analytical comparison of their non-polar extracts. The distribution of ent-labdanes characterized in Potamogeton is summarized.     

蓖齿眼子菜繁殖多样性研究

 繁殖是影响水生植物生存竞争、分布以及群落结构动态变化的关键因素。通过野外观察和室内试验,较详细地介绍了蓖齿眼子菜(Potamogeton pectinatus)的繁殖策略。研究结果表明:蓖齿眼子菜有性繁殖中具有水表和水下气泡两种传粉方式;种子发生量较大,但种子发芽率低,不到6%,种子繁殖对种群恢复贡献不大,其主要作用在于远程传播和保持持久的种子库。蓖齿眼子菜具有广泛而高效的无性繁殖系统,可以通过断株、根状茎、地上块茎、地下块茎、地上茎节以及叶腋基部进行繁殖,其中最重要的是地下块茎和根状茎,次年种群恢复主要来自于地下块茎和根状茎。此外,对采用蓖齿眼子菜进行沉水植被恢复与重建提出了建议。     

Reproductive ecology of three ocypodid crabs II. Incubation sites and egg mortality

Mortality of eggs during incubation was estimated for three ocypodid crabs,Scopimera globosa, Ilyoplax pusillus andMacrophthalmus japonicus, and the influence of incubation sites was discussed. These crabs all lived in isolated burrows and fed on sediments during day time low tide.S. globosa andI. pusillus inhabited the upper intertidal sandflats, whereasM. japonicus inhabited the lower intertidal mudflats. Females of bothS. globosa andI. pusillus remained in their plugged burrows without feeding throughout incubation and the mortality of eggs was low despite large broods relative to body size. On the other hand, females ofM. japonicus fed actively on surface mud during incubation and the mortality of eggs was high despiite small broods relative to body size. InS. globosa andI. pusillus, the ovaries of ovigerous females were small until egg-hatching, whereas inM. japonicus, the ovaries grew rapidly during incubation and females were able to produce consecutive broods. I conclude that incubation of eggs in burrows may be advantageous in species which inhabit the upper interidal sandflats, even though the crabs cannot forage during incubation, since otherwise their eggs would be exposed to strong heat stress and desication during the summer. Furthermore, such species may produce few large broods because of less frequent interruption of feeding than that associated with production of many small broods.     

水体无机碳条件对常见沉水植物生长和生理的影响

为了解水华引起的水体无机碳变化对沉水植物生长的影响,对8种沉水植物:金鱼藻、穗花狐尾藻、篦齿眼子菜、光叶眼子菜、微齿眼子菜、伊乐藻、菹草和黑藻在不同无机碳浓度下的生物量、株高、叶绿素以及光合和呼吸速率进行了比较研究.结果表明8种沉水植物均能利用HCO3-作为光合无机碳源,在1.5 mmoL/L外源HCO3-浓度下能促进金鱼藻、菹草和伊乐藻的生长,提高其光合速率;在2.5 mmol/L外源HCO3-浓度下能促进狐尾藻、光叶眼子菜、黑藻、微齿眼子菜和蓖齿眼子菜的生长,提高其光合速率.在CO32-为优势碳源时,8种沉水植物表现出不同的适应性,发现微齿眼子菜、篦齿眼子菜和黑藻在整个实验范围内生长未受抑制,且在不同浓度下表现生长和光合速率的促进,说明这三种沉水植物对[HCO3-]/[CO32-]比值和pH具有较广适应范围.而当CO32-成为优势碳源时,金鱼藻和伊乐藻的生长受到抑制,狐尾藻、菹草和光叶眼子菜均死亡,表明[HCO3-]/[CO32-]比值和pH是这5种沉水植物生长的重要限制因子.     

Submerged macrophytes in the recently freshened lake system Volkerak-Zoom (The Netherlands), 1987–1991

Extensive biological research has been carried out during the first four years after isolation and freshening of Lake Volkerak-Zoom, a former part of the marine-tidal Oosterschelde. Freshening took place in 8 months. Research on submerged macrophytes has been an important part of the investigation because the aim of the water management was to establish a clear and stable freshwater ecosystem, despite high nutrient loading.In the first year after closure the marine Zostera noltii vanished. and the brackish water Ruppia maritima colonized the lake. In subsequent years, several freshwater species colonized the lake (e.g. Potamogeton pusillus, P. pectinatus, Zannichellia palustris, Callitriche sp. and Chara sp.). The total area in the shallow zone (0.5–5.0 m) covered by submerged macrophytes, increased from less than 1% in 1987 to 22.5% in 1991.Characteristics (height, flowering and fruiting) of the main species (P. pusillus, P. pectinatus, Z. palustris, R. maritima) were closely related to water temperature and secchi depth.Waterfowl consumed about half of the production of the submerged macrophytes.     

Mitochondrial and nuclear DNA diversity within six species ofPhytophthora

The extent of intraspecific mitochondrial DNA (mtDNA) diversity was investigated in isolates ofPhytophthora capsici,P. citricola, P. citrophthora, P. megakarya, P. palmivora, andP. parasitica that represented a wide range of host plants and geographic origins. Phenograms were constructed following the analysis of restriction fragment patterns that were generated by several endonucleases. The six species showed different degrees of mtDNA diversity. Restriction fragment patterns inP. palmivora andP. parasitica were very uniform. Distinct subgroups could be distinguished inP. megakarya andP. citrophthora that correlated with the geographic origin or the host plant, respectively. These subgroups did not seem to be closely related to each other. High degrees of diversity were also evident inP. citricola andP. capsici. Although some isolates ofP. capsici had identical mtDNA patterns, no distinct subgroups were found that could be correlated with either a specific host plant or geographic origin. InP. capsici andP. parasitica variation in nuclear DNA was much more pronounced as compared to mtDNA. InP. capsici both types of analysis correlated well. Because of very limited variation of mtDNA inP. parasitica a comparison between the two phenograms was difficult.     

Study of the genus Plectus Bastian, 1865 (Nematoda: Plectidae) from Iran

Three species of Plectus Bastian, 1865 viz., P. aquatilis and P. pusillus from Kerman province and P. velox from Alborz province, Iran are described and illustrated. Partial sequences of 18S region of ribosomal DNA gene were amplified for P. aquatilis and P. pusillus. The Blast results of population of P. aquatilis from Iran showed 8–10 nucleotides differences with populations of the same species (AF036602; GQ892827; AY284700) reported from the UK, Belgium and The Netherlands, respectively. Whereas Iranian population of P. pusillus showed 14–16 nucleotides differences with P. cf. pusillus (AY284705; AY284704) reported from The Netherlands. Molecular analysis revealed close relationship of the Iranian plectids with P. cf. parvus (AY284699) reported from The Netherlands. Phylogenetic relationships with other related species in the genus Plectus and closely related genera that are available in the GenBank are given.     

Competition between two submersed aquatic macrophytes, Potamogeton pectinatus and Potamogeton gramineus, across a light gradient

Competitive abilities of Potamogeton pectinatus L. and Potamogeton gramineus L. were estimated using additive series experiments at across a gradient of total daily irradiance ranging from 1.2 to 9.7 mol m⁻² day⁻¹. Results for P. gramineus showed that its mean weight per plant was reduced more by the presence of other P. gramineus plants than by changes in the density of P. pectinatus. However, the difference was statistically significant only at the higher light levels examined. In the case of P. pectinatus, P. gramineus exerted a stronger impact on P. pectinatus plants than did other P. pectinatus plants. Coefficients representing interspecific competition were significantly greater than those representing intraspecific competition at higher light levels. These results indicate that P. gramineus was a stronger competitor when light levels were high. They further indicate that at low light levels, there was little evidence that competition was a strong force in determining either species performance. These results support a theory offered by Grime. However, it was possible to predict that P. gramineus would be a stronger competitor based on its light compensation point which was lower than the one for P. pectinatus. This demonstrates the utility of the R* approach proposed by Tilman. Aspects of both approaches may aid ecologists in understanding community structure.     

Endozoochory of Mediterranean aquatic plant seeds by teal after a period of desiccation: Determinants of seed survival and influence of retention time on germinability and viability

The capacity of eight wetland seeds to be internally dispersed by common teal (Anas crecca L.) after a dry period typical of natural Mediterranean wetlands was experimentally quantified. These plant taxa (Chara spp., Echinochloacrus-galli (L.) P. Beauv., Eleocharis palustris (L.) Roem. & Schult, Polygonum lapathifolium L., Potamogeton nodosus Poir., Potamogeton pusillus L., Schoenoplectus mucronatus (L.) Palla, Scirpus maritimus L.) were frequently ingested by teal in the field. Captive teal were fed with known quantities of dry seeds and faecal samples were collected at intervals of 1-2 h for 48 h. The proportion of seeds retrieved after gut passage that germinated varied between taxa from 3% to 83%. From 2% to 63% of the seeds ingested were recovered intact, and 18-95% of these were still viable. Therefore, an overall 32% of the seeds ingested were evacuated in a viable condition, ranging from 0.2% for Chara spp. to 54% for S. mucronatus. Mean seed retention time was 3-5 h. Overall, 94% of seeds were evacuated within 12 h, but 2% were recovered after more than 24 h. Seed viability was reduced at longer retention times, although viable seeds of all taxa except Chara spp. were recovered 44-48 h after the experiment began. Germinability was increased by gut passage, although for some species this effect was only significant after stratification, indicating that they exhibit both mechanical and physical dormancy. Seed germination was accelerated by gut passage, especially at longer retention times. Gut passage increased the proportion of viable seeds, suggesting selective digestion of non-viable ones. Endozoochorous transport by teal appears to be a widespread dispersal mechanism among wetland plants.     

Release of developmental constraints on tetrad shape is confirmed in inaperturate pollen of Potamogeton

Background and Aims

Microsporogenesis in monocots is often characterized by successive cytokinesis with centrifugal cell plate formation. Pollen grains in monocots are predominantly monosulcate, but variation occurs, including the lack of apertures. The aperture pattern can be determined by microsporogenesis features such as the tetrad shape and the last sites of callose deposition among the microspores. Potamogeton belongs to the early divergent Potamogetonaceae and possesses inaperturate pollen, a type of pollen for which it has been suggested that there is a release of the constraint on tetrad shape. This study aimed to investigate the microsporogenesis and the ultrastructure of pollen wall in species of Potamogeton in order to better understand the relationship between microsporogenesis features and the inaperturate condition.

Methods

The microsporogenesis was investigated using both light and epifluorescence microscopy. The ultrastructure of the pollen grain was studied using transmission electron microscopy.

Key Results

The cytokinesis is successive and formation of the intersporal callose wall is achieved by centrifugal cell plates, as a one-step process. The microspore tetrads were tetragonal, decussate, T-shaped and linear, except in P. pusillus, which showed less variation. This species also showed a callose ring in the microsporocyte, and some rhomboidal tetrads. In the mature pollen, the thickening observed in a broad area of the intine was here interpreted as an artefact.

Conclusions

The data support the view that there is a correlation between the inaperturate pollen production and the release of constraint on tetrad shape. However, in P. pusillus the tetrad shape may be constrained by a callose ring. It is also suggested that the lack of apertures in the pollen of Potamogeton may be due to the lack of specific sites on which callose deposition is completed. Moreover, inaperturate pollen of Potamogeton would be better classified as omniaperturate.Key words: Alismatales, callose, microsporogenesis, pollen aperture, Potamogeton illinoensis, P. polygonus, P. pusillus, tetrad shape     

A histologic survey of diencephalic circumventricular organs in teleosts with special reference to osteoglossomorphs

Diencephalic circumventricular organs of various teleosts were studied histologically. Special attention was paid to osteoglossomorphs. The neurohypophysis of osteoglossomorphs (Arapaima, Notopterus, Xenomystus, andGymnarchus) is well differentiated into the median eminence and the neural lobe. The pituitary organization of these species is an intermediate between that of holosteans and of more advanced teleosts. The saccus vasculosus is absent inPantodon andGymnarchus, but it is well developed inNotopterus andXenomystus. The light microscopically discernible pineal is absent inGymnarchus: this may be the only species that lacks the pineal among teleosts. The paraphysis is found in various species including most osteoglossomorphs and some perciforms. In advanced teleosts such as gobiids and tetraodontids, the saccus dorsalis and velum transversum are absent, but the diencephalic choroid plexus is well developed instead. Some evolutionary trends are apparent in the occurrence and organization of these circumventricular organs among teleosts.     

A critical comparison ofGracilaria chilensis andG. sordida (Rhodophyta,Gracilariales)

Gracilaria chilensis Bird, McLachlanet Oliveira from Chile andG. sordida Nelson from New Zealand have been compared with respect to reproductive anatomy, chromosome number, interfertility, and organellar DNA restriction profiles. No differences were found in reproductive anatomy, which in these species is distinguished by deeptextorii-type spermatangial conceptacles and prominent tubular nutritive cells directed only to the floor of the cystocarp. The species share a chromosome number ofn = 24 and are readily interfertile. Electrophoretic profiles of organellar DNA digested with four different restriction endonucleases were virtually identical between the species except for bands that represented accompanying plasmids. However, previous research has indicated that the four plasmid bands inG. chilensis and the single one inG. sordida have a common origin. On these groundsG. chilensis andG. sordida are