The potential role of polyploidy and hybridisation in the further evolution of the highly invasive <Emphasis Type="Italic">Fallopia</Emphasis> taxa in Europe

Japanese knotweed s.l. comprises Fallopia japonica, F. sachalinensis, F. × bohemica and any F2s or backcrosses. The parental taxa were introduced from the East to the West as garden ornamentals in the nineteenth century, and soon spread beyond the confines of the garden to become widespread and persistent weeds. Since only female F. japonica var. japonica was introduced, its impressive spread has occurred solely by vegetative means. However, the initial lack of genetic variability has been complemented by an extensive series of hybridisations in the adventive range. We examine the history, spread, reproductive biology and ecological impact of these species in the West. The role and importance of polyploidy and hybridisation in their invasion of the West is discussed, as are the implications of these factors for the potential further evolution of the group.     

Correlation between physico-chemical properties of quaternary ammonium salts of heptacaine and their inhibitory activity against photosynthesizing organisms

Photosynthesis inhibition in algae (Chlorella) and plant (spinach) chloroplasts by quaternary ammonium salts of heptacaine {N-[2-(2-heptyloxyphenylcarbamoyloxy)-ethyl]-N-alkylpiperidinium bromides} depended on the alkyl chain length of the alkyl substituent and showed good correlations with theoretical hydrophobic fragment constants as well as with experimentally determined physico-chemical parameters, namely extraction constants and surface activities. Communicated by. Z. ŠESTáK     

Chemical quenching of singlet oxygen by plastoquinols and their oxidation products in Arabidopsis

Prenylquinols (tocochromanols and plastoquinols) serve as efficient physical and chemical quenchers of singlet oxygen (¹O₂) formed during high light stress in higher plants. Although quenching of ¹O₂ by prenylquinols has been previously studied, direct evidence for chemical quenching of ¹O₂ by plastoquinols and their oxidation products is limited in vivo. In the present study, the role of plastoquinol‐9 (PQH₂‐9) in chemical quenching of ¹O₂ was studied in Arabidopsis thaliana lines overexpressing the SOLANESYL DIPHOSPHATE SYNTHASE 1 gene (SPS1oex) involved in PQH₂‐9 and plastochromanol‐8 biosynthesis. In this work, direct evidence for chemical quenching of ¹O₂ by plastoquinols and their oxidation products is presented, which is obtained by microscopic techniques in vivo. Chemical quenching of ¹O₂ was associated with consumption of PQH₂‐9 and formation of its various oxidized forms. Oxidation of PQH₂‐9 by ¹O₂ leads to plastoquinone‐9 (PQ‐9), which is subsequently oxidized to hydroxyplastoquinone‐9 [PQ(OH)‐9]. We provide here evidence that oxidation of PQ(OH)‐9 by ¹O₂ results in the formation of trihydroxyplastoquinone‐9 [PQ(OH)₃‐9]. It is concluded here that PQH₂‐9 serves as an efficient ¹O₂ chemical quencher in Arabidopsis, and PQ(OH)₃‐9 can be considered as a natural product of ¹O₂ reaction with PQ(OH)‐9. The understanding of the mechanisms underlying ¹O₂ chemical quenching provides information on the role of plastoquinols and their oxidation products in the response of plants to photooxidative stress.     

Photosynthetic Traits in Wheat Grown under Decreased and Increased CO2 Concentration, and after Transfer to Natural CO2 concentration

Wheat plants were grown from sowing to day 18 in 26-dm³ chambers at three different CO₂ concentrations: 150 (-CO₂), 350 (C, control), 800 (+CO₂) mol mol^-1. Afterwards, plants of the three variants were grown at the same natural CO₂ concentration. Plant characteristics were measured just before the transfer (0 days after CO₂ treatment, DAT), and at 5 – 8 DAT on the 1^st leaf, and at 12 – 22 DAT on the 4^th leaf. Decreased or increased CO₂ concentrations caused acclimations which persisted after transplantation to natural CO₂ concentration. At 5 – 8 DAT, stomatal density, stomatal conductance (g_s), CO₂ saturated net photosynthetic rate (P_Nsat0), radiation saturated net photosynthetic rate (P_Nsat1), and carboxylation efficiency () were higher in -CO₂ plants and lower in +CO₂ plants than in C plants. As compared with C plants, the photochemical efficiency () was lower in -CO₂ and higher in -CO₂ plants, however, chlorophyll (Chl) a, Chl b, Chl a–b and carotenoid contents were lower in both -CO₂ and +CO₂ plants. On the 4^th leaf, which emerged on plant after finishing CO₂ treatments, at 12 – 22 DAT, no differences in stomatal density and g, between treatments were observed. In -CO₂ plants, pigment content and P_Nsat0 were higher, was lower, and P_Nsat1 and were not different from C plants. In contrast, in +CO₂ plants, pigment content, P_Nsat1 and were lower, and P_Nsat0 and were unchanged. Leaf area, dry mass, and tiller development increased in +CO₂ plants and decreased in -CO₂ plants. In the interval between 8 and 22 DAT, lower net assimilation rate in +CO₂ than in -CO₂ plants was observed.     

Beech forest management does not affect the infestation rate of the beech scale Cryptococcus fagisuga across three regions in Germany

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Habitat requirements, short-term population dynamics and coexistence of native and invasive Impatiens species: a field study

The genus Impatiens (Balsaminaceae) includes three widespread species in the Czech Republic, central Europe: the native I. noli-tangere, and two invasive species, I. parviflora and I. glandulifera, differing in the dynamics of invasion. They all occur in similar habitats and share basic life-history characteristics, which make them a suitable model for studying species traits associated with invasiveness. In this study we investigated differences in habitat requirements of these Impatiens species, their coexistence and short-term population dynamics in the field. We established 84 1 × 1 m permanent plots in five localities where all three species co-occurred. In each plot vascular plant species were determined, their cover estimated and all individuals of Impatiens species counted. Site characteristics including tree canopy cover, soil moisture, nitrogen and carbon content, and slope were measured directly. Nutrients, light, humidity and soil reaction were estimated using Ellenberg indicator values. The presence of I. noli-tangere was strongly correlated with high soil moisture, that of I. parviflora with high tree canopy cover and low soil moisture. Impatiens glandulifera exhibited a unimodal response to tree canopy cover, avoiding both very shaded and fully open sites. The current-year abundances of all species were negatively related to those of congeneric species. These results suggest that the coexistence of Impatiens species in the same habitat is due to microsite differentiation. Further spread of I. glandulifera to new habitats, and reduction of the native I. noli-tangere niche, can be expected in areas where the latter species co-occurs with competitively strong invasive congeners.     

Molecular Variability and Evolution of the Pectate Lyase (<Emphasis Type="Italic">pel</Emphasis>-2) Parasitism Gene in Cyst Nematodes Parasitizing Different <Emphasis Type="Italic">Solanaceous</Emphasis> Plants

While pectate lyases are major parasitism factors in plant-parasitic nematodes, there is little information on the variability of these genes within species and their utility as pathotype or host range molecular markers. We have analysed polymorphisms of pectate lyase 2 (pel-2) gene, which degrades the unesterified polygalacturonate (pectate) of the host cell-wall, in the genus Globodera. Molecular variability of the pel-2 gene and the predicted protein was evaluated in populations of G. rostochiensis, G. pallida, G. “mexicana” and G. tabacum. Seventy eight pel-2 sequences were obtained and aligned. Point mutations were observed at 373 positions, 57% of these affect the coding part of the gene and produce 129 aa replacements. The observed polymorphism does not correlate either to the pathotypes proposed in potato cyst nematodes (PCN) or the subspecies described in tobacco cyst nematodes. The trees reveal a topology different from the admitted species topology as G. rostochiensis and G. pallida sequences are more similar to each other than to G. tabacum. Species-specific sites, potentially applicable for identification, and sites distinguishing PCN from tobacco cyst nematodes, were identified. As both G. rostochiensis and G. pallida display the same host range, but distinct from G. tabacum, which cannot parasitize potato plants, it is tempting to speculate that pel-2 genes polymorphism may be implicated in this adaptation, a view supported by the fact that no active pectate lyase 2 was found in G. “mexicana”, a close relative of G. pallida that is unable to develop on cultivated potato varieties.