In vitro synthesis of Pisolithus-Eucalyptus ectomycorrhizae: synchronization of lateral tip emergence and ectomycorrhizal development

 A simple and reproducible in vitro system is described for the synthesis of Pisolithus-Eucalyptus grandis ectomycorrhizae. Hyphal discs from actively growing colonies were placed in large petri dishes containing minimum nutrient agar overlaid with cellophane and allowed to grow for 7 days. Seeds were then surface sterilized and placed above the expanding fungal colonies and the plates slanted. Seedlings that germinated and grew in the presence of fungal hyphae had twice as many lateral root tips as seedlings that germinated before they were transferred onto hyphal mats. In addition, the lateral root tips of inoculated seedlings had a faster maturation rate and emerged closer to the primary root apex than non-inoculated seedlings. All lateral tips emerged in contact with fungal hyphae and the differentiation of ectomycorrhizae was followed by examining lateral tips basipetally along a single primary root. Typical ectomycorrhizae had formed on 4-day-old lateral tips, i.e. a mantle, radially elongated epidermal cells and a Hartig net commencing about 0.3 mm behind the lateral root apex. Thereafter, the mantle continued to thicken and the apical meristem diminished. The Hartig net often surrounded the apex of 11- to 12-day-old lateral root tips. This model system will facilitate detailed studies on synchronized ectomycorrhizal development and associated molecular and biochemical changes. Accepted: 12 January 1996     

Reproduction and population density affect humoral immunity in bank voles under field experimental conditions

Density dependence is a common feature in the dynamics of animal populations. Availability of food resources critical to immunity is likely to be one of the mechanisms mediating the effect of population density on individual fitness. The ability to mount an immune response to an antigen is also affected by levels of immunosuppressive hormones associated with reproduction or mediating the response to ecological and social stress. We assessed variation in condition and intensity of humoral immune response to a T-cell-dependent antigen in bank voles (Clethrionomys glareolus) by experimentally altering population density before immunisation. Consistent with our prediction, males had lower humoral immunocompetence in the breeding than in the non-breeding season. Contrary to our expectation, males did not show enhanced immunocompetence and females showed depressed humoral immune response under experimentally lowered population density. Variation of immune response in relation to population density depended on sex, with females but not males showing lower immune response under experimentally reduced density. We conclude that humoral immunity of bank voles was affected by reproduction and social environment rather than by population density. Received: 2 November 1999 / Accepted: 22 March 2000     

The mycorrhizal status of Phragmites australis in several polluted soils and sediments of an industrialised region of Northern Portugal

Roots of Phragmites australis from three polluted soils and sediments (a periodically flooded stream bank containing organic pollutants, a high-pH drying sedimentation pond and an acidic, periodically flooded sand polluted by industrial effluents) were sampled over a 1-year cycle of plant growth to assess the degree of colonisation by arbuscular mycorrhizal fungi (AMF). At the dry sedimentation pond, root samples of Juncus effusus and Salix atrocinerea were also taken to assess the presence of AMF throughout the year. Root colonisation was low (<5% root length colonised) but arbuscule presence peaked in P. australis during the spring and autumn prior to flowering. These changes in arbuscule abundance were also seen in a parallel greenhouse trial using seed taken from one of the sites. Roots of J. effusus contained mainly vesicular colonisation but arbuscule activity peaked during the winter months (December–March). S. atrocinerea roots were found to be ectomycorrhizal throughout the year but the fine feeder roots were colonised by AMF. The results confirm that semi-aquatics, like P. australis, can become arbuscular mycorrhizal but that this status changes during the year depending on soil moisture content and plant phenology. The influence of AMF in these polluted soils is uncertain but the potential exists to establish a more diverse plant ecosystem during the landscaping of these areas (phytostabilisation) by management of adapted plant and AMF ecotypes. Accepted: 6 November 2000     

The Ecological Relation Between Pinus taiwanensis and Fungi in the Process of Ectomycorrhizae Synthesis

The root samples of Pinus taiwanensis from seedlings to large trees of Mt. Huangsban were studied under light microscope(LM) and scanning electron microscope(SEN). It is obvious that ectomycorrhizae from extensively between the pine roots and the fungi. Isolation and pure culture of the samples of sporocarps were carried out, of which six strains were inoculated to the dissinfected seedlings were under laboratory condition. Pisolithus tinctorius was introduced to inoculate the pine seedlings too. Studies on the development of dichotomous mycorrhizae and the early stage of ectomycorrhizae formation were specially emphasized. Three types of the process of hyphae infection and the ontogeny of ectomycorrhizae synthesis, development and subsequent degeneration were described. Some ecological effects of ectomycorrhizae, which increase the growth of pine trees were also mentioned. Finally the authors sugge. st that the success inoculation of Pisolithus tinctorius to the pine trees will offer a new device for the formation and development of the ectomycorrhizae in terms to promote their growth.     

Some properties of a pheromone allowing individual recognition, from the scats of an Australian lizard, Egernia striolata

  The Australian lizard, Egernia striolata, can distinguish its own scats from those of unfamiliar conspecific individuals. This appears to be unrelated to diet, because there is no difference in the response to scats from unfamiliar lizards fed on diets that are the same or different from the test lizard. The signal that induces the response is not a visual or tactile property of scat structure, because test lizards respond equally to crushed and intact scats. We suggest that a pheromone is secreted onto the scat as it is produced. Water solutions of scats did not contain signal components that allowed lizards to distinguish their own scats from others. However, solutions of scats in dichloromethane (DCM) retained unique characteristics, and test lizards responded more strongly to the solution from scats of an unfamiliar lizard that to the solution from their own scats. Further fractionation of the DCM solution in pentane and in methanol led to loss of the unique signals needed for individual recognition, but those were restored when the pentane and methanol fractions were recombined. We infer that these lizards can distinguish between scats of different individuals on the basis of signals they receive from a complex combination of chemicals. Received: 14 December 1998 / Received in revised form: 9 April 1999 / Accepted: 12 April 1999     

Ectomycorrhizae of Tomentella albomarginata (Thelephoraceae) on Scots pine

 The ectomycorrhizae of Tomentella albomarginata are comprehensively described and compared to ectomycorrhizae of other Tomentella species and to ectomycorrhizae of some members of Thelephoraceae ss. Stalpers and Bankeraceae ss. Stalpers. The ectomycorrhizae of T. albomarginata are characterized by a hyphal net lying on a pseudoparenchymatous mantle surface, by tubular outgrowths of irregularly angular mantle cells, and by clamp-bearing emanating hyphae. Accepted: 15 July 1995     

Index of unidentified ectomycorrhizae

 This latest instalment of the index of unidentified ectomycorrhizae lists binomials and reference specimen characterizations of ectomycorrhizae first described in 1995–1997. Accepted: 14 May 1998     

Allozyme polymorphisms of maize populations from southwestern China

Maize (Zea mays L.) is one of the most-important food crops in southwestern China. The diversity of maize populations from southwestern China has been evaluated on the basis of agronomic and morphological data, but not on marker data. Our objectives were to evaluate the allozyme polymorphism of these populations, and group the populations on the basis of allozyme data. We analyzed 27 maize populations from southwestern China and two populations [BS13(S)C2 and Lancaster] from the USA for genetic variation at 18 allozyme loci. We found a total of 69 alleles at 18 allozyme loci with an average of 3.8 alleles per locus. Compared with inbreds, hybrids, and populations from the U.S. Corn Belt, the 27 Chinese populations had a significantly higher (p<0.01) number of allozyme alleles per locus. Maize populations from southwestern China have accumulated abundant genetic diversity, and might be valuable germplasm for broadening the genetic base of U.S. Corn Belt breeding germplasm. The analyses of allele-frequency distributions and the expected heterozygosity also reflected the differences between the Chinese and the U.S. germplasm. The Chinese populations might be valuable germplasm for complementing U.S. Corn Belt breeding germplasm. The analysis of gene diversity showed that 77% of the allozyme variation resided within populations and 23% between populations. This result suggested that breeders should identify one or a few Chinese populations with the best agronomic performance, and exploit the genetic variation within these selected populations. Cluster analysis classified the 29 populations into four main groups. Groupings based on allozyme data could be useful for classifying the populations into different heterotic groups and, consequently, exploiting them in hybrid breeding. Received: 12 October 2000 / Accepted: 13 March 2001     

Suppression of an elicitor-induced oxidative burst reaction in Nicotiana tabacum and Medicago sativa cell cultures by corticrocin but not by mycorradicin

The biological activities of mycorradicin, the major component of the yellow pigment formed in maize and other grasses upon colonization by arbuscular mycorrhizal fungi, and corticrocin from the ectomycorrhizal fungus Piloderma croceum were analysed in cell cultures of tobacco (Nicotiana tabacum L.) and alfalfa (Medicago sativa L.). Tobacco and alfalfa suspension cell cultures react to elicitor treatment by alkalinization of the culture medium and generation of activated oxygen species, the so-called oxidative burst. In the present study, the addition of corticrocin suppressed the elicitor-induced oxidative burst reaction but not the alkalinization. The suppression of the oxidative burst by corticrocin was dose dependent. Mycorradicin in either its methylated or free form had no effect on the oxidative burst or the alkalinization. Accepted: 20 March 2001     

Predicting days of high allergenic risk during Betula pollination using weather types

The aim of this study was to build up a picture of the influence of meteorological conditions on pollen and pollinosis, taking account of weather types, pollen concentrations in the air and pollinosis symptoms, with the aim of preventing allergic responses. The study took place in Burgundy from 1996 to 1998, during the pollination of the birch (Betula), which is the most important arborean allergen in this region. We used daily pollen data from four Hirst volumetric traps, identified weather types by Bénichou’s classification, and obtained data on the occurrence of rhinitis, conjunctivitis, asthma and coughing from a sample of 100 patients. These data were analysed by multiple-component analysis. The results show that pollen dispersal is favoured by windy conditions, low relative humidity, precipitation below 2 mm and temperatures above 6°C. Such weather also favours pollinosis, but other particular meteorological situations, even if they do not assist pollen dispersal, can act directly on the development of symptoms: a decrease of temperature (3°C) led to the development of rhinitis and conjunctivitis, while strong winds were associated with many cases of conjunctivitis and asthma, owing to the irritant effect of cold or wind; asthma was favoured by temperature inversions with fog, probably because such weather corresponds to high levels of pollution, which act on bronchial hyperreactivity. Because the weather types favouring pollination and pollinosis are predicted by the meteorological office, this can constitute a tool for reducing the effect of high-risk allergenic days. Received: 12 December 2000 / Revised: 24 April 2001 / Accepted: 9 May 2001     

Salinity effects on germination,growth, and seed production of the halophyte Cakile maritima

The growth ofEucalyptus regnans seedlings in forest soil is enhanced when it has been air-dried. In undried forest soil seedlings grow poorly and develop purple coloration in the foliage, indicating P deficiency. This paper reports the results of pot experiments designed to investigate the relationship between growth and P acquisition, ectomycorrhizal infection and age of seedlings grown in air-dried and undried soil. The effect on seedling growth of their inoculation with air-dried or undried soil or with ectomycorrhizal roots from plants growing in air-dried or undried soil was also investigated. Ectomycorrhizal root tips were detected in 3-week-oldE. regnans seedlings in both air-dried and undried soil, and from then on the frequency of ectomycorrhizal root tips increased rapidly. In air-dried soil, seedlings were fully ectomycorrhizal at 9 weeks, and the occurrence of maximum ectomycorrhizal infection coincided with enhanced P acquisition and the initiation of rapid seedling growth. In undried forest soil, seedling growth remained poor, even though the seedlings had well-developed ectomycorrhizae and the incidence of ectomycorrhizal root tips was the same as in air-dried soil. The dominant ectomycorrhizae in airdried soil were associated with an ascomycete fungus, whereas in undried, undisturbed soil they were commonly associated with basidiomycete fungi. Inoculation of sterile soil/sand mix with washed ectomycorrhizal roots from air-dried soil increased the P acquisition and growth of the seedlings significantly compared with controls, whereas ectomycorrhizal inocula from undried soil had no effect on seedling growth, although both inocula resulted in a similar incidence of ectomycorrhizal root tips. Similarly, addition of a small amount of air-dried soil into sterile soil/sand mix resulted in a significantly greater increase in the P content and dry weight of the seedlings, compared with the control, than addition of undried soil. In both treatments, the incidence of ectomycorrhial root tips was similar. As (i) the differentiation in seedling growth between air-dried and undried soil occurred after seedlings became ectomycorrhizal, (ii) the dominant ectomycorrhizae in air-dried soil were different from those in undried soil, and (iii) inocula from air-dried soil, but not from undried soil, stimulated seedling growth in sterile soil/sand mix, it is concluded that development of particular ectomycorrhizae may be involved in seedling growth stimulation and enhanced P acquisition associated with air drying of forest soil.     

Sexual reproduction in the cork oak (Quercus suber L). II. Crossing intra- and interspecific barriers

Intraspecific barriers promote outcrossing while interspecific mechanisms may contribute to the isolation of species; both control the exchange of genes between plants. In this paper we establish that post-pollination mechanisms promote outcross and act at different temporal and spatial levels to control seed set and quality in Quercus species. Controlled pollinations were performed to investigate intraspecific crossing barriers in Q. suber and pollen-pistil interactions following interspecific pollinations with some simpatric Quercus species. Cytological data of intraspecific crosses in Q. suber and Q. ilex have shown different kinetics on pollen tube growth after self and outcross pollination, but pollen tubes were able to reach the base of the styles in both species and seed set was successful. Although some pre-zygotic interaction is occurring at the style, the most important interaction takes place at ovary. The cross between Q. ilex and Q. suber is possible only in one direction, revealing a case of unilateral incongruity. We show that the lack of seed set observed in the cross Q. suber×Q. ilex is due to the inability of pollen tubes to penetrate the transmitting tissue after germination. With Q. suber mainly as female parent, pollinations with other simpatric Quercus species have shown different levels of constraint on pollen tube progression at stigma and style levels. Eventual hybridisation between Quercus species will depend on the compatibility of pollen-pistil interactions, on the competitive ability of pollen genotypes, and, most important, on the overlapping of geographical, phenological and ecological factors. Differences in seed set and seed allocation was evident in all crosses, and was particularly outstanding in interspecific and in self intraspecific crosses, determining the ultimate level of seed production and quality in Quercus species. Received: 4 April 2001 / Accepted: 8 May 2001     

Mechanisms of primordium formation during adventitious root development from walnut cotyledon explants

 In walnut (Juglans regia L.), an otherwise difficult-to-root species, explants of cotyledons have been shown to generate complete roots in the absence of exogenous growth regulators. In the present study, this process of root formation was shown to follow a pattern of adventitious, rather than primary or lateral, ontogeny: (i) the arrangement of vascular bundles in the region of root formation was of the petiole type; (ii) a typical root primordium was formed at the side of the procambium within a meristematic ring of actively dividing cells located around each vascular bundle; (iii) the developing root apical meristem was connected in a lateral way with the vascular bundle of the petiole. This adventitious root formation occurred in three main stages of cell division, primordium formation and organization of apical meristem. These stages were characterized by expression of LATERAL ROOT PRIMORDIUM-1 and CHALCONE SYNTHASE genes, which were found to be sequentially expressed during the formation of the primordium. Activation of genes related to root cell differentiation started at the early stage of primordium formation prior to organization of the root apical meristem. The systematic development of adventitious root primordia at a precise site gave indications on the positional and biochemical cues that are necessary for adventitious root formation. Received: 30 July 1999 / Accepted: 16 February 2000     

MS32-regulated timing of callose degradation during microsporogenesisin Arabidopsis is associated with the accumulation of stacked rough ER in tapetal cells

  In the male sterile32(ms32)mutant in Arabidopsis thaliana, pollen development is affected during meiosis of pollen mother cells (PMCs). In normal wild-type (WT) anthers, callose is deposited around PMCs before and during meiosis, and after meiosis the tetrads have a complete callose wall. In ms32, PMCs showed initial signs of some callose deposition before meiosis, but it was degraded soon after, as was part of the cellulosic wall around the PMCs. The early dissolution of callose in ms32 was associated with the occurrence of extensive stacks of rough ER (RER) in tapetal cells. The stacks of RER were also observed in the WT tapetum, but at a later stage, i.e., after the tetrads were formed and when callose is normally broken down for release of microspores. Based on these observations it is suggested that: (1) callose degradation around developing microspores is linked to the formation of RER in tapetal cells, which presumably synthesize and/or secrete callase into the anther locule, and (2) mutation in MS32 disrupts the timing of these events. Received: 27 April 1999 / Revision accepted: 21 June 1999     

Socialization in spectacled parrotlets (Forpus conspicillatus): how juveniles compensate for the lack of siblings

  Socialization, that is, the process of the integration of an individual into the social system and the acquisition of basic social traits, has been studied in a variety of vertebrate species. Deprivation experiments have shown that the lack of early affiliative relationships has negative long-term effects on social behaviour and reproduction. Most studies emphasized the importance of the mother-infant relationship. However, it soon became evident that peer relationships to like-aged conspecifics, such as siblings and unrelated juveniles of nearly the same age, are also important for socialization. Whether individuals, deprived of one of these important social components, are able to compensate for this lack is not known. Here I tested the hypothesis that in spectacled parrotlets (Forpus conspicillatus), singletons (i.e., those that grew up without siblings) were able to compensate for this social lack by establishing and strengthening other relationships. In spectacled parrotlets socialization depends on the formation of long-lasting sibling groups. However, singletons without nest mates are quite common (about 6%), both in captivity and in nature. In this study I analysed the affiliative interactions with other group members of five singletons in comparison to eight siblings, from fledging to the 36th week after fledging, within a group of adult and juvenile conspecifics. In contrast to siblings, the singletons prolonged the relationships with their parents. Then they established a ”host sibling group” with other like-aged individuals. All singletons became well integrated into the group and established exclusive pair bonds. It is concluded that juvenile singletons of spectacled parrotlets are able to compensate for the lack of siblings by the development of alternative socialization tactics. Received: 12 December 1998 / Received in revised form: 17 May 1999 / Accepted: 7 June 1999     

An integrative approach to sex change: social, behavioural and neurochemical changes in Lythrypnus dalli (Pisces)

This study examined three aspects of protogynous sex change in Lythrypnus dalli (Gobiidae): (1) social influences on the rate of sex change, (2) the sequence of behavioural changes, and (3) neuroendocrine changes. Social groups consisted of either four females, or four females with a male who was subsequently removed. Sex change occurred most rapidly in male- removed groups when the sex changer was larger than other females. Sex changers in female only groups and sex changers not larger than other females in male-removed groups changed sex at similar rates. These differences may be explained by two factors that affect dominance: prior knowledge of the social group and greater size. Sex changers were dominant to other females prior to male removal, and larger sex changers increased displacement rates three-fold immediately after male removal. Sex changers in the other groups did not show this increase in displacements. This early establishment of dominance accounts for the overall difference in the rate of sex change. Prior to spawning, however, all sex changers increased displacements and performed male-typical displays. Arginine vasotocin-immunoreactive forebrain cells of sex changers were similar in size to field-collected males, and larger than field-collected females. Previously nesting males also changed sex in male-only groups, but at slow rates. These data are combined with those of existing studies to generate an integrative model of sex change in this goby. Received: 17 March 1999 / Received in revised form: 15 May 1999 / Accepted: 28 May 1999     

Programmed proteome response for drought avoidance/tolerance in the root of a C(3) xerophyte (wild watermelon) under water deficits

Water availability is a critical determinant for the growth and ecological distribution of terrestrial plants. Although some xerophytes are unique regarding their highly developed root architecture and the successful adaptation to arid environments, virtually nothing is known about the molecular mechanisms underlying this adaptation. Here, we report physiological and molecular responses of wild watermelon (Citrullus lanatus sp.), which exhibits extraordinarily high drought resistance. At the early stage of drought stress, root development of wild watermelon was significantly enhanced compared with that of the irrigated plants, indicating the activation of a drought avoidance mechanism for absorbing water from deep soil layers. Consistent with this observation, comparative proteome analysis revealed that many proteins induced in the early stage of drought stress are involved in root morphogenesis and carbon/nitrogen metabolism, which may contribute to the drought avoidance via the enhancement of root growth. On the other hand, lignin synthesis-related proteins and molecular chaperones, which may function in the enhancement of physical desiccation tolerance and maintenance of protein integrity, respectively, were induced mostly at the later stage of drought stress. Our findings suggest that this xerophyte switches survival strategies from drought avoidance to drought tolerance during the progression of drought stress, by regulating its root proteome in a temporally programmed manner. This study provides new insights into the complex molecular networks within plant roots involved in the adaptation to adverse environments.     

Ectomycorrhizal syntheses with Picea abies and three fungal species: a case study on the use of an in vitro technique to identify naturally occurring ectomycorrhizae

Ectomycorrhizal syntheses between Picea abies and the fungal associates Scleroderma citrinum, Boletus luridus, and Tricholoma vaccinum were carried out using Melin's Erlenmeyer flask technique. The symbioses of S. citrinum were characterized by a mantle composed of an outer prosenchymatous and an inner synenchymatous layer. The mantles of B. luridus and T. vaccinum were solely prosenchymatous. Rhizomorphs were produced in all treatments, but only in association with S. citrinum were they differentiated with additional, enlarged hyphae. All synthesized ectomycorrhizae were white or whitish to light orange and greyishorange. On large-scale root sampling in two differing Picea abies forests in Switzerland, nine out of a total of 22 morphological types of ectomycorrhizae were white or yellow in colour and were, therefore, comparable with the synthesized ectomycorrhizae. These nine natural types generally had distinct mantle features (irregular synenchyma, gelatinous matrix, cystides, thick-walled hyphae), but mostly lacked clamp connections. Synthesized ectomycorrhizae, on the other hand, lacked distinct mantle characteristics and always had clamp connections. Natural and synthesized white or yellow ectomycorrhizae did not coincide morphologically and thus identification of the fungal partners of natural symbioses by means of in vitro-synthesis with potential ectomycorrhizal fungi was not possible in the present study.     

Is supernumerary chromatin involved in gametophytic apomixis of polyploid plants?

Gametophytic apomixis, or unreduced embryo sac development that results in asexual reproduction through seeds, occurs in several families of angiosperms and must be polyphyletic in origin. The molecular mechanisms underlying gametophytic apomixis have not been discovered and are the subject of intense investigation. A common feature of almost all apomicts is their polyploid nature. From genetic mapping studies in both monocots and dicots, there is low genetic recombination associated with a single (rarely two), dominant locus for either aposporous or diplosporous embryo sac formation. In Pennisetum squamulatum and Cenchrus ciliaris, some DNA sequences mapping to the apospory locus are unique to apomictic genotypes and apparently hemizygous. This sequence divergence at the apomixis locus could be a consequence of genome rearrangements and isolation from genetic recombination, both of which may have contributed to the definition of a chromosomal region as supernumerary. The possible involvement of supernumerary chromatin, formed as a result of interspecific hybridization, in the origin of apomixis, is explored here. Received: 26 October 2000 / Revision accepted: 5 April 2001