Priming biotic factors for optimal protocorm-like body and callus induction in hybrid Cymbidium (Orchidaceae), and assessment of cytogenetic stability in regenerated plantlets

Protocorm-like bodies (PLBs) and callus were induced in epiphytic hybrid Cymbidium Twilight Moon ‘Day Light’, where induction capacity was strongly explant dependent. Following the use of various explant sources (PLB, leaf tip or base, root tip or base, cell and tissue ‘suspension’), highest PLB formation and callus induction occurred when we used whole PLBs, PLB segments or PLB transverse thin cell layers (tTCLs) or longitudinal TCLs (lTCLs). Plantlet growth and photosynthetic state from whole or bisected PLBs, as well as from tTCLs were not significantly different, after analysis of chlorophyll content. However plantlets generated from lTCLs showed lower values for growth and photosynthetic parameters. All resultant plants were shown to be cytogenetically identical using RAPD and mtDNA analysis despite cytological variation and endopolyploidy occuring between different plant parts. Acclimatization and survival rate was shown to be 100% in the generated plants.     

Influences of Nitrogen Sources on Usnic Acid Production in a Cultured Mycobiont of the Lichen Usnea hirta (L.) Wigg.

Effects of the nitrogen sources in the medium for the production of secondary metabolites in lichens were examined. The usnic acid production by a mycobiont of the lichen Usnea hirta was higher in the liquid medium containing ammonium and nitrate ions than in those containing amino acids.     

Plants and landscape in the Vestfold Hills,Antarctica

Maps are presented showing the recorded distribution and species density of terrestrial plants in the Vestfold Hills. The distribution, biomass and species diversity of terrestrial lithic algae, mosses and lichens is influenced positively by availability of meltwater from drift snow and by additional nutrient supply (probably N and P) near bird nest sites. The terrestrial plants are affected negatively by exposure (including sand blast) and salinity. These four factors are probably the most important environmental characteristics exercising local control over plant distribution and abundance within the limits set by temperature.Large changes in salinity, degree of exposure, water supply and nutrient supply occur across the Vestfold Hills, with the most favourable conditions generally occurring in the eastern half fairly close to the ice sheet.Plant distribution and abundance are also discussed in relation to the length of time that particular areas have been exposed as a result of ice retreat. With increasing time of exposure, plant diversity and abundance rise but subsequently fall sharply as conditions become more arid, saline, or both. This temporal sequence can be explained by considering changes in the important factors that control plant growth.     

Analysis of ploidy in a planarian by flow cytometry

Flow cytometry (flow microfluorimetry) provides a quick means for analysis of ploidy in planarians. Nuclei from homogenized tissues of the freshwater planarian Dugesia japonica japonica Ichikawa et Kawakatsu were stained with propidium iodide and measured with an argon-laser flow cytometer to produce histograms of DNA content. Tissues from sexually mature individuals produced histograms with a 1n (haploid) peak but no 3n peak (triploid peak), whereas those from asexual individuals showed a 2n peak or a 3n peak or both, but no 1n peak. Thus, the 1n peak distinguished sexual individuals. Mixoploid individuals, i.e., mosaics with both diploid and triploid tissues, were identified by the presence of both a 2n peak and a 3n peak. The ratios of the heights of the 2n and 3n peaks from tissues in different parts of a single mixoploid individual were similar, suggesting that the diploid and triploid cells are homogeneously distributed.     

Morphofunctional characterization and ploidy levels of cells in the bivalve digestive gland, with special reference to somatic polyploidy

This study investigates the histological organization and ploidy levels of the digestive gland cells in 29 species of marine, brackish water, and freshwater bivalves belonging to 5 subclasses. In all species studied, the digestive gland epithelium consists of two types of differentiated cells: digestive and basophilic. The nuclei of digestive cells contain the diploid quantity of DNA. Basophilic (secretory) cells often remain diploid also; however, in a number of species all or some of the cells showed an increase in the quantity of DNA per nucleus up to 4c. Tetraploidy of basophilic cells in several species of the subclass Anomalodesmata seems to be due to carnivory. In other species, no apparent correlation was found between selective polyploidy of basophilic cells and environmental conditions or biology traits of the bivalves. Additionally, there was no relationship between the occurrence of polyploid cells and the lifespan of the investigated species. In the bivalve mollusks, somatic polyploidy appears to be an adaptation; it is neither a tissue growth strategy nor a component of the cytodifferentiation program.     

Endopolyploidy in seed plants is differently correlated to systematics, organ, life strategy and genome size

Endopolyploidy is a systemic feature in seed plants. A negative correlation between genome size and endopolyploidization has been claimed previously, assuming that a minimum amount of DNA, necessary for certain cell functions, has to be acquired by endopolyploidization of the corresponding cells in plants with small genomes. This assumption was based on the analysis of only a limited set of data from few species. In the present study the endopolyploidization of several organs of 54 seed plant species belonging to two gymnosperm and 14 angiosperm families was investigated. The results revealed a low negative correlation between genome size and endopolyploidization. However, differences between the families, between the different organs of a given species and between the different life‐cycle types with regard to endopolyploidization became obvious. A three‐way analysis of variance with covariate to quantify the impact of the different factors on the extent of endopolyploidization suggested that taxonomic position is the major factor determining the degree of endopolyploidy within a species, while life cycle, genome size and organ type have a minor but also significant effect on endopolyploidization. The comparison of habitats of 16 investigated Central European species implies that endopolyploidization represents a mean to accelerate the growth of plant species in niches, which require and support fast development.     

Abscisic acid in lichens: variation, water relations and metabolism

For the first time the well known drought stress hormone abscisic acid, which is involved in regulating processes increasing desiccation tolerance in many plant systems, was analysed in lichens. ABA was detected in all 26 species investigated. In contrast to higher plants and liverworts, the ABA content increased after hydration of air dry lichen thalli and decreased in desiccating lichen material. Experiments with Baeomyces rufus (Huds.) Rebent indicated that the mycobiont might be the major site of ABA biosynthesis. After incubation of hydrated lichen thalli with radioactive ABA for up to 72 h no metabolism to phaseic acid and dihydrophaseic acid could be detected. Fluctuations of internal ABA might be a result of ABA release to the external medium.     

High frequency plant regeneration from Eucalyptus globulus Labill. hypocotyls: Ontogenesis and ploidy level of the regenerants

Up to 70% regenerating hypocotyls provided with 5 to 20 buds were obtained on MS medium containing 0.01 or 1 mg l^-1 NAA and 0.2 mg l^-1 BA or 0.2 mg l^-1 BA and 0.2 mg l^-1 TDZ. The ability to regenerate buds was correlated with the presence of oil glands at a stage in germination when oil secretion was not yet occurring. The regeneration of shoot meristems took place from the cells involved in the differentiation of these glands. Such glands could also appear during callus redifferentiation, giving rise to indirect regeneration. Rooting of the regenerants was efficient using a two-step procedure of induction under darkness in the presence of 3 mg l^-1 IBA, followed by root development on medium devoid of growth regulators under a 16-h photoperiod, the medium being solidified with Gelrite. Regenerated plants showed no phenotypic alterations. Nuclear DNA contents in mother-plant material and regenerants were analysed using flow cytometry. There was no evidence of polyploidy in any of the samples, indicating the absence of polyploidisation during cell differentiation and under in vitro conditions. No regeneration was obtained from leaf or stem explants from micropropagated plantlets. This revised version was published online in June 2006 with corrections to the Cover Date.     

Genome size and the nucleolar number as estimators of ploidy level in Dactylis glomeratain the Slovenian Alps

 We studied five natural populations of Dactylis glomerata L. (Poaceae) growing at different altitudes in the south-eastern fringe of the Alps in northern Slovenia to determine the subspecies. The stomatal length, the pollen diameter and chromosome counts were consistent with the tetraploid taxon D. glomerata subsp. glomerata (2n=4x =28). Genome size was measured in 55 individuals. The mean 2C value was 8.6 pg DNA. The mean 2C values of populations growing at different altitudes showed only 2.1% variation, and no correlation was observed between altitude and genome size. In D. nk;glomerata subsp. glomerata eight nucleoli were observed in late telophase, indicating that the nucleolus-organising regions inherited from both diploid parent species are functional. We demonstrate that both genome size and the number of nucleoli may be used to determine the ploidy level as an alternative to chromosome counting. Received May 31, 2001; accepted March 5, 2002 Published online: November 14, 2002 Addresses of the authors: Dr. Barbara Vilhar (e-mail: barbara.vilhar@uni-lj.si), Tatjana Vidic, Nejc Jogan, Prof. Marina Dermastia, University of Ljubljana, Biotechnical Faculty, Department of Biology, Večna pot 111, 1001 Ljubljana, Slovenia.     

Warming reduces the growth and diversity of biological soil crusts in a semi-arid environment: implications for ecosystem structure and functioning

Biological soil crusts (BSCs) are key biotic components of dryland ecosystems worldwide that control many functional processes, including carbon and nitrogen cycling, soil stabilization and infiltration. Regardless of their ecological importance and prevalence in drylands, very few studies have explicitly evaluated how climate change will affect the structure and composition of BSCs, and the functioning of their constituents. Using a manipulative experiment conducted over 3 years in a semi-arid site from central Spain, we evaluated how the composition, structure and performance of lichen-dominated BSCs respond to a 2.4°C increase in temperature, and to an approximately 30 per cent reduction of total annual rainfall. In areas with well-developed BSCs, warming promoted a significant decrease in the richness and diversity of the whole BSC community. This was accompanied by important compositional changes, as the cover of lichens suffered a substantial decrease with warming (from 70 to 40% on average), while that of mosses increased slightly (from 0.3 to 7% on average). The physiological performance of the BSC community, evaluated using chlorophyll fluorescence, increased with warming during the first year of the experiment, but did not respond to rainfall reduction. Our results indicate that ongoing climate change will strongly affect the diversity and composition of BSC communities, as well as their recovery after disturbances. The expected changes in richness and composition under warming could reduce or even reverse the positive effects of BSCs on important soil processes. Thus, these changes are likely to promote an overall reduction in ecosystem processes that sustain and control nutrient cycling, soil stabilization and water dynamics.     

A review of ploidy in the genus Prosopis (Leguminosae)

The genus Prosopis contains 44 species of trees and shrubs, the majority of which originate in the Americas. Most species are reported to be diploid, with a somatic chromosome number of 2 n  = 28. There are rare reports of polyploidy, although it is thought that these may represent polysomaty in root tissues. However, flow cytometry has recently indicated that P. juliflora is entirely tetraploid with a somatic chromosome number of 2 n  = 56. In order to clarify the situation, an extensive review of ploidy in Prosopis was undertaken, the first of its kind. The ploidy levels of 124 samples of Prosopis from 21 countries, including both the natural and introduced ranges, were analysed using flow cytometry. In addition, a comprehensive literature review was carried out, examining 305 published ploidy values and covering 32 of the 44 species of Prosopis . Flow cytometry analysis suggests that P. juliflora is the only tetraploid species, with a somatic chromosome number of 2 n  = 4 x  = 56, whilst the remainder of the species analysed are diploid with 2 n  = 2 x  = 28, including the first report for P. articulata (2 n  = 28). A critical review of published ploidy values shows that all species of Prosopis are reported to be entirely diploid, except P. glandulosa , P. juliflora , and P. koelziana , for which both diploid and tetraploid values have been recorded. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 425–438.     

Cytogeography of Pilosella officinarum (Compositae): altitudinal and longitudinal differences in ploidy level distribution in the Czech Republic and Slovakia and the general pattern in Europe

BACKGROUND AND AIMS: Pilosella officinarum (syn. Hieracium pilosella) is a highly structured species with respect to the ploidy level, with obvious cytogeographic trends. Previous non-collated data indicated a possible differentiation in the frequency of particular ploidy levels in the Czech Republic and Slovakia. Therefore, detailed sampling and ploidy level analyses were assessed to reveal a boundary of common occurrence of tetraploids on one hand and higher ploids on the other. For a better understanding of cytogeographic differentiation of P. officinarum in central Europe, a search was made for a general cytogeographic pattern in Europe based on published data. METHODS: DNA-ploidy level and/or chromosome number were identified for 1059 plants using flow cytometry and/or chromosome counting on root meristem preparations. Samples were collected from 336 localities in the Czech Republic, Slovakia and north-eastern Hungary. In addition, ploidy levels were determined for plants from 18 localities in Bulgaria, Georgia, Ireland, Italy, Romania and Ukraine. KEY RESULTS: Four ploidy levels were found in the studied area with a contrasting pattern of distribution. The most widespread cytotype in the western part of the Czech Republic is tetraploid (4x) reproducing sexually, while the apomictic pentaploids and mostly apomictic hexaploids (5x and 6x, respectively) clearly prevail in Slovakia and the eastern part of the Czech Republic. The boundary between common occurrence of tetraploids and higher ploids is very obvious and represents the geomorphologic boundary between the Bohemian Massif and the Western Carpathians with the adjacent part of Pannonia. Mixed populations consisting of two different ploidy levels were recorded in nearly 11% of localities. A statistically significant difference in a vertical distribution of penta- and hexaploids was observed in the Western Carpathians and the adjacent Pannonian Plain. Hexaploid populations tend to occur at lower elevations (usually below 500 m), while the pentaploid level is more or less evenly distributed up to 1000 m a.s.l. For the first time the heptaploid level (7x) was found on one site in Slovakia. In Europe, the sexual tetraploid level has clearly a sub-Atlantic character of distribution. The plants of higher ploidy level (penta- and hexa-) with mostly apomictic reproduction prevail in the northern part of Scandinavia and the British Isles, the Alps and the Western Carpathians with the adjacent part of Pannonia. A detailed overview of published data shows that extremely rare records on existence of diploid populations in the south-west Alps are with high probability erroneous and most probably refer to the closely related diploid species P. peleteriana. CONCLUSIONS: The recent distribution of P. officinarum in Europe is complex and probably reflects the climatic changes during the Pleistocene and consequent postglacial migrations. Probably both penta- and hexaploids arose independently in central Europe (Alps and Carpathian Mountains) and in northern Europe (Scandinavia, Great Britain, Ireland), where the apomictic plants colonized deglaciated areas. We suggest that P. officinarum is in fact an amphidiploid species with a basic tetraploid level, which probably originated from hybridizations of diploid taxa from the section Pilosellina.     

Molecular phylogeography and cryptic speciation in the mosses, Mielichhoferia elongata and M. mielichhoferiana (Bryaceae)

Nucleotide sequence variation in the ITS1-5.8S-ITS2 region of nuclear ribosomal DNA (nrDNA) from 70 populations of Mielichhoferia elongata and M. mielichhoferiana, plus two outgroup species, was analysed using maximum parsimony and maximum likelihood methods. High levels of nucleotide substitution and numerous insertion-deletion events were detected within and between the two species. M. elongata is monophyletic with regard to nrDNA variation, but M. mielichhoferiana is paraphyletic. (M. elongata is nested within it.) A clade within M. mielichhoferiana provides evidence of vicariance, with North American and Scandinavian sister groups of populations. Two major clades are resolved in M. elongata by sequence data that are completely congruent with previous isozyme work. One clade includes populations from both North America and Europe whereas the other is strictly North American. These two clades, resolved by multiple independent loci, clearly represent cryptic species within the morphologically uniform M. elongata. Certain geographical areas, most notably southwestern Colorado in Ouray and San Juan Counties, harbour diverse populations of M. elongata with distinct phylogenetic and phylogeographical histories. Morphologically indistinguishable but phylogenetically distant populations were detected a few metres apart at one site. In contrast, all populations collected over hundreds of kilometres in California belong to a single clade. Arctic North American populations belong to a clade that includes disjunct populations in Alaska, northern Ellesmere Island, and the northeastern USA, but not subarctic Swedish populations, which are more closely related to plants from the Rocky Mountains. Morphological uniformity belies complex infraspecific phylogenetic patterns within M. elongata and M. mielichhoferiana.     

Open tundra persist,but arctic features decline—Vegetation changes in the warming Fennoscandian tundra

In the forest‐tundra ecotone of the North Fennoscandian inland, summer and winter temperatures have increased by two to three centigrades since 1965, which is expected to result in major vegetation changes. To document the expected expansion of woodlands and scrublands and its impact on the arctic vegetation, we repeated a vegetation transect study conducted in 1976 in the Darju, spanning from woodland to a summit, 200 m above the tree line. Contrary to our expectations, tree line movement was not detected, and there was no increase in willows or shrubby mountain birches, either. Nevertheless, the stability of tundra was apparent. Small‐sized, poorly competing arctic species had declined, lichen cover had decreased, and vascular plants, especially evergreen ericoid dwarf shrubs, had gained ground. The novel climate seems to favour competitive clonal species and species thriving in closed vegetation, creating a community hostile for seedling establishment, but equally hostile for many arctic species, too. Preventing trees and shrubs from invading the tundra is thus not sufficient for conserving arctic biota in the changing climate. The only dependable cure is to stop the global warming.     

The relation between cell size, ploidy level and nitrate concentration in lettuce

In two experiments the relation between cell size, ploidy level and nitrate concentration of genotypes of lettuce ( Lactuca saliva L.) was investigated. Artificial increase of cell size by application of gibberellic acid to young plants decreased the percentage dry weight and the concentration of organic acids in the plant sap and increased the nitrate concentration of the shoot. Application of chlormequat chloride caused the opposite effects. Tetraploid genotypes of lettuce had larger cells, a lower nitrate concentration and a higher concentration of organic solutes than diploid genotypes. Genotypical differences in nitrate concentration could not be explained by differences in cell size, but were consistently related to differences in concentration of organic acids in plant sap. The percentage dry weight of genotypes was positively correlated with the concentration of organic acids in plant sap. However, differences in nitrate concentration were also found among genotypes with comparable dry matter content. These differences could be caused by differences in partitioning of photosynthates over structural components and organic acids in the vacuoles. Mono-saccharides seem to be less important than organic acids for explaining genotypical differences in nitrate level, because the concentration of monosaccharides was much lower than that of organic acids and because a negative relation between the concentration of monosaccharides and of nitrate was not found in every case. Genotypical differences in nitrate accumulation were not related to differences in osmolarity.     

Disentangling the roles of chance,abiotic factors and biotic interactions among epiphytic bryophyte communities in a tropical rainforest (Yunnan,China)

• Epiphytes offer an appealing framework to disentangle the contributions of chance, biotic and abiotic drivers of species distributions. In the context of the stress-gradient theory, we test the hypotheses that (i) deterministic (i.e., non-random) factors play an increasing role in communities from young to old trees, (ii) negative biotic interactions increase on older trees and towards the tree base, and (iii) positive interactions show the reverse pattern.
• Bryophyte species distributions and abiotic conditions were recorded on a 1.1 ha tropical rainforest canopy crane site. We analysed co-occurrence patterns in a niche modelling framework to disentangle the roles of chance, abiotic factors and putative biotic interactions among species pairs.
• 76% of species pairs resulted from chance. Abiotic factors explained 78% of non-randomly associated species pairs, and co-occurrences prevailed over non-coincidences in the remaining species pairs. Positive and negative interactions mostly involved species pairs from the same versus different communities (mosses versus liverworts) and life forms, respectively. There was an increase in randomly associated pairs from large to small trees. No increase in negative interactions from young to old trees or from the canopy to the base was observed.
• Our results suggest that epiphytic bryophyte community composition is primarily driven by environmental filtering, whose importance increases with niche complexity and diversity. Biotic interactions play a secondary role, with a very marginal contribution of competitive exclusion. Biotic interactions vary among communities (mosses versus liverworts) and life forms, facilitation prevailing among species from the same community and life form, and competition among species from different communities and life forms.