Modification of stress tolerance by dehydration pretreatment in winter rape hypocotyls

Dehydration of isolated rape hypocotyls (Brassica napus L. var. oleifera L. cv. Górczański) to a water saturation deficít of about 60% resulted in increased tolerance to subsequent desiccation and to prolonged immersion in water. Dehydration pretreatment followed by restoration of tissue turgidity, caused a decrease in leakage of electrolytes, ultraviolet-absorbing materials and ninhydrin-reactive substances from the desiccated or water immersed hypocotyl tissue. A hardening effect of tissue dehydration is supposed to be related to an improved stability of cell membranes.     

Phylogenetic relationships and neotenic evolution of Metzgeriopsis (Lejeuneaceae) based on chloroplast DNA sequences and morphology

The systematic position of the enigmatic Asiatic liverwort Metzgeriopsis pusilla (Marchantiophyta), the single thalloid member of the largest family of leafy liverworts, Lejeuneaceae, was investigated based on sequences of the rbc L gene and the trn L-F region of chloroplast DNA, and morphology. Metzgeriopsis is not phylogenetically isolated from other taxa of Lejeuneaceae, as previously suggested, but is nested within Cololejeunea . The two genera share many morphological features, especially in the sporophyte generation, which is newly described. Metzgeriopsis and Cololejeunea are members of the Tuyamaella – Cololejeunea clade, characterized by neotenic features that probably evolved as adaptations to ephemeral habitats in tropical rain forests. Three different types of neoteny occur in this clade, which apparently originated by multiple heterochronic events. Within Lejeuneaceae, protonemal neoteny is unique to Metzgeriopsis and apparently resulted by evolution from a primary neotenic ancestor. The occurrence of protonemal neoteny in bryophytes is briefly reviewed and two types are recognized: species having a persistent thalloid protonema and species having a persistent filamentous protonema. The thalloid type is very rare and exclusive to epiphyllous liverworts, whereas the filamentous type is much more common and is characteristic of many terrestrial bryophytes, including the rare genus Protocephalozia . The new combination Cololejeunea metzgeriopsis (K.I.Goebel) comb. nov. is proposed.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 293–308.     

High-Speed Cell Sorting of Infectious Trophic and Cystic Forms of Pneumocystis carinii

ABSTRACT. The separation of Pneumocystis carinii life-cycle stages while preserving infectivity is a hitherto unresolved challenge. We describe an original, reproducible, and efficient method for separating trophic from cystic forms of P. carinii using a high-speed cell sorter. The large amounts of highly purified (99.6±0.3%) infectious trophic and cystic forms can now be used to elucidate the poorly understood P. carinii life cycle.     

Hydrangea mosaic virus, a new ilarvirus from Hydrangea macrophylla (Saxifragaceae)

A previously unrecognised virus isolated from Hydrangea macrophylla with chlorotic mosaic leaf symptoms in West Sussex was named hydrangea mosaic virus (HydMV). HydMV was mechanically transmitted without difficulty to four of 16 species from three of five families, and was seed transmitted in Chenopodium quinoa, but was not aphid transmitted. Although relatively unstable in vitro, HydMV was purified by clarifying leaf extracts by emulsification with chloroform and acidification with citric acid, followed by differential centrifugation and sucrose density gradient centrifugation. Purified virus incompletely separated on sucrose density gradients into three components (T. M and B) with sedimentation coefficients (s^o_20w) of 86, 97, and 105 S respectively, but all particles had buoyant densities in caesium chloride of 1.37 g/cm³. Virus contained a single polypeptide species (mol. wt 26.4 times 10³), appeared quasiisometric to ovoid or elliptical, and measured c. 28 times 30 (T), 30 times 30 (M) or 30 times 32–38 nm (B). Single-stranded RNA species or mol. wt 1–25, 1–08, 0–83, 0–36 and 0–27 (RNA-1 to 5 respectively) were obtained from virus preparations but mixtures containing RNA-1 to 3 plus either RNA-4 + 5 or the coat protein, were infective. These properties suggest that HydMV has affinities with ilarviruses, but it showed no serological relationship to any of six ilarviruses or 42 other viruses.     

K+Nutrition and Na+Toxicity: The Basis of Cellular K+/Na+Ratios

The capacity of plants to maintain a high cytosolic K⁺/Na⁺ratiois likely to be one of the key determinants of plant salt tolerance.Important progress has been made in recent years regarding theidentification and characterization of genes and transportersthat contribute to the cytosolic K⁺/Na⁺ratio. For K⁺uptake,K⁺efflux and K⁺translocation to the shoot, genes have been isolatedthat encode K⁺uptake and K⁺release ion channels and K⁺carriersthat are coupled to either a H⁺or Na⁺gradient. Although thepicture is less clear for the movement of Na⁺, one pathway,in the form of non-selective ion channels, is likely to playa role in Na⁺uptake, whereas Na⁺efflux and compartmentationare likely to be mediated by H⁺-coupled antiport. In addition,several proteins have been characterized that play prominentroles in the regulation of K⁺and/or Na⁺fluxes. In this BotanicalBriefing we will discuss the functions and interactions of thesegenes and transporters in the broader context of K⁺nutritionand Na⁺toxicity. Copyright 1999 Annals of Botany Company Salinty, K⁺/N⁺ratio, transporter, membrane.     

In comparison with nitrate nutrition,ammonium nutrition increases growth of the frostbite1 Arabidopsis mutant

Ammonium nutrition inhibits the growth of many plant species, including Arabidopsis thaliana. The toxicity of ammonium is associated with changes in the cellular redox state. The cellular oxidant/antioxidant balance is controlled by mitochondrial electron transport chain. In this study, we analysed the redox metabolism of frostbite1 (fro1) plants, which lack mitochondrial respiratory chain complex I. Surprisingly, the growth of fro1 plants increased under ammonium nutrition. Ammonium nutrition increased the reduction level of pyridine nucleotides in the leaves of wild‐type plants, but not in the leaves of fro1 mutant plants. The observed higher activities of type II NADH dehydrogenases and cytochrome c oxidase in the mitochondrial electron transport chain may improve the energy metabolism of fro1 plants grown on ammonium. Additionally, the observed changes in reactive oxygen species (ROS) metabolism in the apoplast may be important for determining the growth of fro1 under ammonium nutrition. Moreover, bioinformatic analyses showed that the gene expression changes in fro1 plants significantly overlap with the changes previously observed in plants with a modified apoplastic pH. Overall, the results suggest a pronounced connection between the mitochondrial redox system and the apoplastic pH and ROS levels, which may modify cell wall plasticity and influence growth.     

Temperature effects on forest herbs assessed by warming and transplant experiments along a latitudinal gradient

Slow‐colonizing forest understorey plants are probably not able to rapidly adjust their distribution range following large‐scale climate change. Therefore, the acclimation potential to climate change within their actual occupied habitats will likely be key for their short‐ and long‐term persistence. We combined transplant experiments along a latitudinal gradient with open‐top chambers to assess the effects of temperature on phenology, growth and reproductive performance of multiple populations of slow‐colonizing understorey plants, using the spring flowering geophytic forb Anemone nemorosa and the early summer flowering grass Milium effusum as study species. In both species, emergence time and start of flowering clearly advanced with increasing temperatures. Vegetative growth (plant height, aboveground biomass) and reproductive success (seed mass, seed germination and germinable seed output) of A. nemorosa benefited from higher temperatures. Climate warming may thus increase future competitive ability and colonization rates of this species. Apart from the effects on phenology, growth and reproductive performance of M. effusum generally decreased when transplanted southwards (e.g., plant size and number of individuals decreased towards the south) and was probably more limited by light availability in the south. Specific leaf area of both species increased when transplanted southwards, but decreased with open‐top chamber installation in A. nemorosa. In general, individuals of both species transplanted at the home site performed best, suggesting local adaptation. We conclude that contrasting understorey plants may display divergent plasticity in response to changing temperatures which may alter future understorey community dynamics.     

Distribution,host specificity,and the potential for cryptic speciation in hoverfly Microdon myrmicae (Diptera: Syrphidae), a social parasite of Myrmica ants

1. In 2002 Microdon myrmicae, a social parasite of Myrmica ants, was taxonomically separated from Microdon mutabilis. The original study in the U.K. found Microdon myrmicae to be specific to one ant species, Myrmica scabrinodis, yet it became apparent that the range of Microdon myrmicae includes at least the western Palaearctic. 2. Current knowledge of the European distributions of both Microdon myrmicae and Microdon mutabilis in Europe is reviewed. Also, in detailed studies of two Polish populations, Microdon myrmicae was found to survive equally well with two Myrmica ant species. We examine, however, the possibility that this reflects the presence of two separate Microdon species, each connected to one species of Myrmica. 3. Forty populations of Microdon myrmicae and 37 populations of Microdon mutabilis are currently known in Europe. All the populations in central and southern Europe that were visited after the separation of the two species were identified as Microdon myrmicae, while Microdon mutabilis’ recognised range is now restricted to the British Isles and Scandinavia. Myrmica scabrinodis was found to host Microdon myrmicae in 26 out of 31 populations investigated. Four other Myrmica species were identified to the host Microdon myrmicae: Myrmica gallienii (eight populations), Myrmica rubra (four), Myrmica vandeli (one), and Myrmica sabuleti (one). Microdon myrmicae occurs in waterlogged grassland habitats, mainly of the ‘Molinietum’ type, resulting in a patchy distribution relative to its host ants. 4. In two populations Myrmica scabrinodis and Myrmica gallienii are both abundant and rear Microdon myrmicae in equal proportions. Microdon myrmicae pupae from Myrmica gallienii nests were heavier and the anterior respiratory organs were of significantly different shape. In contrast, the comparisons of Microdon myrmicae pupae among all other populations showed no significant differences, suggesting only one species throughout the European range.     

Sibling species in the Chrysis ignita complex: molecular,morphological and trophic differentiation of Baltic species,with a description of two new cryptic species (Hymenoptera: Chrysididae)

Cryptic species complexes cause major challenges for taxonomists and alter understanding of species diversity. In Northern Europe, the Chrysis ignita species group is one such complex with numerous sympatric sibling species. The objective of this paper is to assess the taxonomy of 15 species from this group using three different approaches: molecular, morphological and trophic differentiation. The analysed set of molecular markers included a 7400‐bp‐long sequence of the mitochondrial genome covering complete sequences of CO1, CO2, ATP8, ATP6, CO3, ND3, 16S and 12S rRNA, nine tRNAs and a partial sequence of CytB, as well as a 3880‐bp‐long sequence of the nuclear DNA covering a part of 18S rRNA, the ITS1, 5.8S rRNA, ITS2 and a part of 28S rRNA. Discrete diagnostic characters of each species sequence were retrieved using the Characteristic Attribute Organisation System algorithm and a molecular identification key was compiled. The study revealed a higher evolutionary rate of the genes ATP8, ATP6, CO3, ND3 and CytB compared to that of CO1, CO2 and 16S; the studied nuclear markers demonstrated a lower evolutionary rate than the mitochondrial markers. A consensus tree compiled based on the combined mtDNA and nuclear markers with a strongly supported topology resolved the position of the C. schencki – C. parietis sp.n. clade as sister to the C. ignita – C. impressa clade and supported the monophyly of the C. angustula – C. longula clade. We compiled a morphometric species identification key applying linear discriminant equations. The trophic differentiation was assessed using data on host preferences of ten Chrysis species reared from trap‐nests; the analysis demonstrated that most of them are specialists exploiting a single or a few taxonomically related host species. In most cases, all three approaches supported the distinct status of the included species. Moreover, two previously undescribed species were consistently supported by the molecular methods. Therefore, we describe these as new, namely C. horridula sp.n. and C. parietis sp.n. Only C. mediata and C. solida were not clearly distinguished using the molecular phylogeny reconstruction methods. However, based on distinctive niche divergence, the presence of molecular characters and morphometric differences, we consider them as phylogenetically young but distinct species. In view of the weak morphological and molecular differentiation, the widely overlapping distribution areas and often similar habitat preferences and the trophic specialization, the C. ignita complex presents a possible model for studies of sympatric cryptic speciation. This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:1EBAF0E1‐5FB7‐4CF4‐A595‐C11982448360 .     

Anatomy of the vegetative organs and secretory structures of Rhaponticum carthamoides (Asteraceae)

Roots, stems, rhizomes and leaves of Rhaponticum carthamoides (Willd.) Iljin (a Siberian adaptogenic plant, originating from the Altai and Saian Mountains) of different ages were investigated by means of light and electron microscopy. Schizogenous secretory reservoirs occurred in every organ, and were located within the secondary xylem (adventitious roots and rhizome of young plants), at the interface of endodermis/cortical parenchyma (roots and hypocotyl), along phloem and primary xylem (older rhizome), around the vascular bundles (inflorescence stem, petiole and leaf midrib veins) and along phloem (cotyledonary and leaf veins). At the interface of endodermis/inner parenchyma, secretion accumulated in the intercellular spaces prior to the formation of proper epithelial cells. The secretion as observed by transmission electron microscopy comprised three components: soluble (i.e. absent from sections; probably phenolic), insoluble and strongly osmiophilic (probably phenolic) and insoluble, moderately osmiophilic (probably lipidic). Numerous osmiophilic oil droplets, similar to the lipidic secretion inside the reservoirs, local proliferation of rough endoplasmic reticulum and numerous multivesicular bodies characterized epithelial cells in all organs. Leucoplasts (in subterranean organs) with osmiophilic inclusions and peroxisomes with crystalloid inclusions were specific for parenchyma cells. Peltate glandular hairs were formed on leaf blades.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 207–233.