Translocation and Metabolism of Picloram and 2,4-D in Populus tremula

Translocation and metabolism of 4-amino-3,5,6-trichloropicolinic acid (picloram) and 2,4-dichlorophenoxyacetic acid (2,4-D) in small plants of aspen (Populus tremula L.) were studied. In most experiments ¹⁴C-carboxyl-labelled herbicides were used. Considerable quantities of both herbicides were retained in the treated leaf. Translocation was mainly upwards into the growing shoot tip. Only minute quantities were found in the roots. Injection of the herbicides through a cut stem surface increased the translocation into the roots very little. One of the reasons for the limited downward translocation is considered to be a ready transfer of the herbicides between the phloem and the xylem. Both herbicides were incorporated into complexes from which the active herbicides could be released. However, this complex formation can only partly account for the retention of the herbicides in the treated leaves. The differences in metabolism found between 2,4-D and picloram cannot explain the considerable difference in toxicity between the compounds.     

Chromosome number of Icelandic Populus tremula

Aspen ( Populus tremula ) from two locations in Iceland, representing the north and the east populations, were examined for its chromosome number. The plants all have diploid chromosome number (2n=2x=38), as with most other aspen populations of this species in Europe. No previous record of chromosome count on the Icelandic material is available. The significance of such chromosome study is discussed. — Flora Nordica Notes no. 22.     

Growth Regulators in Populus tremula

Shoots grown out from aspen root sections in light or in darkness were extracted and the content of growth-regulating substances in various fractions was determined with the Avena coleoptile straight-growth assay. The most obvious difference was obtained for the inhibitor β fraction. This was about ten times more active in the light-grown than in the dark-grown shoots. Some indications of more growth inhibitory material in ether-insoluble fractions of light-grown plants were also obtained. The stimulation obtained at the Rf of indol-3-yl-acetic acid was somewhat lower in the etiolated shoots than in the light-grown ones.     

Growth Regulators in Populus tremula

The seasonal variation in capacity to form suckers and in auxin level in bark and wood was determined in root segments of aspen (Populus tremula L.). Auxin occurred in the roots from May to October but not in November. The highest auxin level was found during the period of shoot growth. During this period the capacity of root segments to form suckers was low. Auxin level decreased in isolated root segments during the first 24 hours after excision and was low during the period of sucker induction. The relation of endogenous auxin level to control of sucker formation is discussed. The experiments do not exclude the possibility that the auxin effect is mediated through inhibitors.     

Adaptive evolution of the Populus tremula photoperiod pathway

Perennial plants monitor seasonal changes through changes in environmental conditions such as the quantity and quality of light and genes in the photoperiodic pathway are known to be involved in controlling these processes. Here, we examine 25 of genes from the photoperiod pathway in Populus tremula (Salicaceae) for signatures of adaptive evolution. Overall, levels of synonymous polymorphism in the 25 genes are lower than at control loci selected randomly from the genome. This appears primarily to be caused by lower levels of synonymous polymorphism in genes associated with the circadian clock. Natural selection appears to play an important role in shaping protein evolution at several of the genes in the photoperiod pathways, which is highlighted by the fact that approximately 40% of the genes from the photoperiod pathway have estimates of selection on nonsynonymous polymorphisms that are significantly different from zero. A surprising observation we make is that circadian clock-associated genes appear to be over-represented among the genes showing elevated rates of protein evolution; seven genes are evolving under positive selection and all but one of these genes are involved in the circadian clock of Populus.     

Dependence of Root Growth on Photosynthesis in Populus tremula

Hoot elongation of rooted cuttings of aspen, Populus tremula L., was followed on moist filter paper. The time course of root growth during treatments which decrease or interrupt the supply of carbohydrates to the roots was studied. At light intensities below 4000 lux the rate of root elongation was found to berelated to the light intensity over the leaves. In the dark, root growth decreased within 24 hours and the roots stopped growing completely during the second or third day. Excision of the leaves or steam-killing of the tissue in a stem section below the leaves was followed by root growth stoppage within 24 hours. These results imply that the rate of root growth under certain conditions is determined by the supply of carbohydrates from the leaves.     

Die vegetative Vermehrung von Aspen (Populus tremula)

Ohne Zusammenfassung     

Fading of wound-induced volatile release during Populus tremula leaf expansion

Journal of Plant Research - The release of stress-driven volatiles throughout leaf development has been little studied. Therefore, we subjected poplar leaves during their developmental stage (from...     

Responses of Populus tremula to Picloram and Other Translocated Herbicides

Whole aspen plants and isolated aspen root segments were three to ten times more sensitive to the growth-inhibitory and toxic effects of picloram than to those of 2,4-D, 2,4,5-T and dicamba. The activity of picloram in the inhibition of root growth was about ten times higher than that of 2,4-D and dicamba when tbe substances were added to the nutrient solution. Epinastic responses indicated a very rapid translocation of picioram from the roots to the growing shoot parts. When the herbicides were applied to the mature leaves dicamba rapidly caused a complete inhibition of root growth indicating a rapid translocation of this compound from the leaves to the root tips. Leaf-applied picloram, 2,4-D and 2,4,5-T affected root growth considerably more slowly. Dicamba, 2,4-D and 2,4,5-T rapidly killed the directly treated leaf tissue due to high acute toxicity while picloram did not show this type of toxicity. It is concluded that the higher activity of picloram in killing the plant and in inhibition of root and shoot growth can only partly be explained as a result of greater uptake and translocation of this compound.     

Response of Populus tremula to heterogeneous B distributions in soil

Background

Poplars accumulate inordinate amounts of B in their leaves and are candidate plants for the remediation of B contaminated soil. We aimed to determine the effect of heterogeneous B distribution in soil by comparing the growth and B accumulation of young Populus tremula trees growing in soil with heterogeneous and homogeneous B distributions.

Methods

The first of two experiments focused on the tolerance and B accumulation of P. tremula under heterogeneous soil B distributions, while the second was designed to study fine root growth under such conditions in detail.

Results

Growth and B accumulation of P. tremula were unaffected by the spatial distribution of B. Root and shoot growth were both reduced simultaneously when leaf B concentrations increased above 800 mg kg^?1. In the heterogeneous soil B treatments, root growth was more reduced in spiked soil portions with B concentrations >20 mg kg^?1. Fine root length growth was stronger inhibited by B stress than secondary growth.

Conclusions

The root growth responses of P. tremula to B are primarily a systemic effect induced by shoot B toxicity and local toxicity effects on roots become dominant only at rather high soil B concentrations. Local heterogeneity in soil B should have little influence on the phytoremediation of contaminated sites.     

Multilocus patterns of nucleotide polymorphism and the demographic history of Populus tremula

I have studied nucleotide polymorphism and linkage disequilibrium using multilocus data from 77 fragments, with an average length of fragments of 550 bp, in the deciduous tree Populus tremula (Salicaceae). The frequency spectrum across loci showed a modest excess of mutations segregating at low frequency and a marked excess of high-frequency derived mutations at silent sites, relative to neutral expectations. These excesses were also seen at replacement sites, but were not so pronounced for high-frequency derived mutations. There was a marked excess of low-frequency mutations at replacement sites, likely indicating deleterious amino acid-changing mutations that segregate at low frequencies in P. tremula. I used approximate Bayesian computation (ABC) to evaluate a number of different demographic scenarios and to estimate parameters for the best-fitting model. The data were found to be consistent with a historical reduction in the effective population size of P. tremula through a bottleneck. The timing inferred for this bottleneck is largely consistent with geological data and with data from several other long-lived plant species. The results show that P. tremula harbors substantial levels of nucleotide polymorphism with the posterior mode of the scaled mutation rate, = 0.0177 across loci. The ABC analyses also provided an estimate of the scaled recombination rate that indicates that recombination rates in P. tremula are likely to be 2-10 times higher than the mutation rate. This study reinforces the notion that linkage disequilibrium is low and decays to negligible levels within a few hundred base pairs in P. tremula.     

A Novel Metabolic Pathway for Indole-3-Acetic Acid in Apical Shoots of Populus tremula (L.) x Populus tremuloides (Michx.)

Metabolism of indole-3-acetic acid (IAA) in apical shoots of Populus tremula (L.) x Populus tremuloides (Michx.) was investigated by feeding a mixture of [12C]IAA, [13C6]IAA, and [1[prime]-14C]IAA through the base of the excised stem. HPLC of methanolic plant extracts revealed eight major radiolabeled metabolites after a 24-h incubation period. Comparison between feeds with [5-3H]IAA and [1[prime]-14C]IAA showed that all detectable metabolites were nondecarboxylative products. The purified radiolabeled HPLC fractions were screened by frit-fast atom bombardment liquid chromatography-mass spectrometry for compounds with characteristic fragment pairs originating from the application with 12C and 13C isotopes. Samples of interest were further characterized by gas chromatography-mass spectrometry. Using this procedure, oxindole-3-acetic acid (OxIAA), indole-3-acetyl-N-aspartic acid (IAAsp), oxindole-3-acetyl-N-aspartic acid (OxIAAsp), and ring-hydroxylated oxindole-3-acetic acid were all identified as IAA metabolites. Furthermore, a novel metabolic pathway from IAA via IAAsp and OxIAAsp to OxIAA was established on the basis of refeeding experiments with the different IAA metabolites.     

Genetic linkage mapping in aspen (Populus tremula L. and Populus tremuloides Michx.)

A large number of simple sequence repeat (SSR) marker-containing genetic maps are available for several Populus species. For aspen however, no SSR-containing map has been published so far. In this study, genetic linkage mapping was carried out with an interspecific mapping pedigree of 61 full-sib hybrids of European × quaking aspen (Populus tremula L. × Populus tremuloides Michx.), using the two-way pseudo-testcross strategy. Amplified fragment-length polymorphism (AFLP) and SSR markers were used for mapping, resulting in the first SSR-containing genetic linkage maps for aspen. The maps allow comparisons with a Populus consensus map and other published genetic maps of the genus Populus. The maps showed good collinearity to each other and to the Populus consensus map and provide a direct link to the Populus trichocarpa genomic sequence. Sex as a morphological trait was assessed in the mapping population and mapped on a non-terminal position of linkage group XIX on the male P. tremuloides map.     

Clone identification and clonal structure of the European aspen (Populus tremula)

The European aspen (Populus tremula) is thought to reproduce mostly asexually. Thus aspen forms clones, in which several ramets belong to one genetically defined genet. We compared the clonal structure of aspen in old-growth and managed forests in southern and northeastern Finland. Clones were identified using morphological characters and nine microsatellite loci originally developed for Populus tremuloides. There were more clones identified by microsatellites than morphotypes both in old-growth and managed forest. The average size of the clones was only 2.3 ramets and most clones (70%) consisted of just one ramet. The size of the clones showed no difference between managed and old-growth forests or between northeastern and southern Finland. The small size of the clones suggests that most of them are relatively young. Therefore, sexual reproduction may be more common than previously thought. There was an aggregated spatial genetic structure as measured by Moran's I (0-10 m) and by co-ancestry (rho(ij), 0-20 m). Low level of co-ancestry can be explained by relatively unrestricted gene flow, the important role of disturbance in reproduction, and/or local selection.     

Transgenic Populus tremula: a step-by-step protocol for its Agrobacterium-mediated transformation

In recent years, Populus species have acquired an important place in basic and applied research of woody plants. The practical role of Populus species in world forestry and their importance to research as a woody-plant model have led to increasing interest in tissue-culture and molecular techniques, as well as the development of transformation procedures for this genus. A simple technical procedure is described here step-by-step, for the first time, as a routine method for transforming Populus tremula using a disarmed Agrobacterium tumefaciens hypervirulent strain. The procedure begins with the inoculation of stem explants with bacterial suspension, followed by a short period of co-cultivation on a highly regenerative medium. Transformed shoots are selected on regeneration medium containing antibiotics and the presence of the inserted target genes is checked using a rapid and efficient PCR test. Selected shoots are transferred to a rooting medium, under the same selection pressure, and propagated via stem cuttings. Selected plants can be hardened and transferred to the green-house within 4 months of inoculation. The method has proven efficient for several gene constructs, selection on Kan or Hyg, and three different Agrobacterium strains.     

Natural phenological variation in aspen (Populus tremula): the SwAsp collection

The genus Populus is currently the main model system for genetic, genomic, and physiological research in trees. Phenotypic variation in aspen (Populus tremula) populations growing in different environments across Sweden is expected to reflect genetic variation that is important for local adaptation. To analyze such natural phenotypic and genetic variation, the Swedish Aspen (SwAsp) Collection was established. Trees were taken from 12 different populations across Sweden, from 56° to 66° latitude north and planted in two common gardens in Ekebo (55.9°N) and Sävar (63.4°N). Data related to phenological and growth traits were collected during the second year of growth. Some traits like the date of bud set and leaf area duration showed strong clinal variation patterns with latitude in both field trials, but the date of bud flush did not change along a latitudinal cline. The phenological traits showed moderate within-populations heritabilities, although growth traits showed weaker clinal patterns and lower heritabilities than the phenological traits. This research forms the starting point for the development of the SwAsp collection, a resource facilitating analysis of the natural genetic variation in aspen, the elucidation of the structure and dynamics of aspen populations, and the future identification of the genes controlling adaptive traits using association mapping of selected candidate genes.     

MLO-Associated Decline of Alnus glutinosa, Populus tremula and Crataegus monogyna

In the Heidelberg area of southwestern Germany declining trees of Alnus glutinosa (L.) Gaertn. and Populus tremula L. as well as stunting shrubs of Crataegus monogyna Jacq. were observed. In all 3 species mycoplasmalike organisms, which appear to be the causal agents of the disorders, were detected by fluorescence and electron microscopy. The diseases of alder and aspen seem to be lethal while the hawthorn apparently is less affected.