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PubMed1989

Genetic analysis of an interspecific hybrid swarm of Populus: occurrence of unidirectional introgression.

Restriction fragment length polymorphisms were used to distinguish genotypes of two species of Populus, P. fremontii ('Fremont') and P. angustifolia ('narrowleaf'). Both inter- and intraspecific polymorphisms were detected in these cottonwood trees. The interspecific variation was much greater than the intraspecific variation. This permitted identification of parental genotypes within individual trees of a hybrid swarm which exists in an overlap zone between the two species. Within this hybrid swarm, individual trees are either F1 hybrids or backcrosses with a pure 'narrowleaf' parent; no progeny were found that could be attributed to crossing between F1 hybrid trees, or to backcrossing between F1 hybrid trees and 'Fremont'.

Crosses, Genetic↗

PubMed1995

Molecular genetics of growth and development in populus. IV. Mapping QTLs with large effects on growth, form, and phenology traits in a forest tree.

We have mapped quantitative trait loci (QTLs) for commercially important traits (stem growth and form) and an adaptive trait (spring leaf flush) in a Populus F2 generation derived from a cross between interspecific F1 hybrids (P. trichocarpa x P. deltoides). Phenotypic data were collected over a 2-year period from a replicated clonal trial containing ramets of the parental, F1, and F2 trees. Contrary to the assumptions of simple polygenic models of quantitative trait inheritance, 1-5 QTLs of large effect are responsible for a large portion of the genetic variance in each of the traits measured. For example, 44.7% of the genetic variance in stem volume after 2 years of growth is controlled by just two QTLs. QTLs governing stem basal area were found clustered with QTLs for sylleptic branch leaf area, sharing similar chromosomal position and mode of action and suggesting a pleiotropic effect of QTLs ultimately responsible for stem diameter growth.

Chromosome Mapping↗

PubMed2000

Quantitative trait loci and candidate gene mapping of bud set and bud flush in populus.

The genetic control of bud phenology in hybrid poplar was studied by mapping quantitative trait loci (QTL) affecting the timing of autumn bud set and spring bud flush. The founders of the mapping pedigree were collected from widely separated latitudes to maximize segregating variation for dormancy-related traits in the F(2) generation-the female Populus trichocarpa parent is from Washington State (48 degrees N) and the male P. deltoides parent is from Texas (31 degrees N). Bud set and bud flush timing were measured on the F(2) generation in a replicated clonal field trial. Using a linkage map constructed of AFLP and microsatellite markers, three QTL controlling bud set and six QTL controlling bud flush were detected. Additionally, five candidate genes believed to be involved in perception of photoperiod (PHYB1, PHYB2) or transduction of abscisic acid response signals (ABI1B, ABI1D, and ABI3) were placed on the QTL map. PHYB2 and ABI1B were found to be coincident with QTL affecting bud set and bud flush.

Base Sequence↗

PubMed2002

Light-regulated leaf expansion in two Populus species: dependence on developmentally controlled ion transport.

Leaf growth responses to light have been compared in two species of Populus, P. deltoides and P. trichocarpa. These species differ markedly in morphology, anatomy, and dependence on light during leaf expansion. Light stimulates the growth rate and acidification of cell walls in P. trichocarpa but not in P. deltoides, whereas leaves of P. deltoides maintain growth in the dark. Light-induced growth is promoted in P. deltoides when cells are provided 50-100 mM KCl. In both species, light initially depolarizes, then hyperpolarizes mesophyll plasma membranes. However, in the dark, the resting E(m) of mesophyll cells in P. deltoides, but not in P. trichocarpa, is relatively insensitive to decade changes in external [K+]. Results suggest that light-stimulated leaf growth depends on developmentally regulated cellular mechanisms controlling ion fluxes across the plasma membrane. These developmental differences underlie species-level differences in growth and physiological responses to the photoenvironment.

Cell Wall↗

PubMedDate not supplied

RAPD variation within and among natural populations of trembling aspen (Populus tremuloides Michx.) from Alberta.

This article described the population structure of trembling aspen (Populus tremuloides Michx.) in Alberta, a dioecious tree with continuous and wide distribution, and with a primary mode of reproduction through suckering. We studied random amplified polymorphic DNA (RAPD) variation in 249 trees from eight natural populations. Trees within a population were a minimum of 200 m apart to decrease the risk of sampling ramets of a single ortet. Of a total of 28 amplified RAPD products (bands) from five random oligonucleotide primers, the frequencies at seven (25%) were heterogeneous across populations and the percentage of polymorphism averaged 90.2 per population. Estimates of Shannon's phenotypic diversity index ranged between 0.58 and 0.69 among populations, averaging 0.65. There were 246 multiband phenotypes among the 249 trees; three were each shared by two trees from different populations and the remaining 243 were unique. Thus, trees within populations probably were different clones. Analysis of molecular variance partitioned the RAPD variation into the among- and within-population components. The within-population component accounted for 97.4% of the variation and was significantly different from zero at the 2% level of probability. The among-population component, although accounting for only 2.6% of the variation, was significantly different from zero at the 1% level of probability. Pairwise tests for the homogeneity of the RAPD variance between populations suggested significant divergences among 18 of the 28 (64%) population pairs.

Alberta↗

PubMed1986

Ribulose-1,5-bisphosphate carboxylase activity of Populus tremuloides Michx. bark tissues.

Ribulose-1,5-bisphosphate (RubP) carboxylase was isolated from bark tissue of Populus tremuloides Michx. by a one-step Sephadex G l00-120 column chromatography procedure. The peak fraction had specific activity of 1.3 micromol CO(2) mg(-1) chlorophyll min(-1). The bark RubP carboxylase activity was comparable to that of leaf tissues. Thus, young corticular tissues are photosynthetically competent and contain sufficient RubP carboxylase to account for the reported rates of photosynthesis.

Journal Article↗

PubMed1986

Leaf growth characteristics of fast-growing poplar hybrids Populus trichocarpa x P. deltoides.

Fast-growing hybrid poplar trees (Populus trichocarpa Torr. & A. Gray x P. deltoides Bartr. ex Marsh.) were compared with slower-growing parental types in both field and laboratory experiments to determine physiological components of leaf growth that could be closely related to biomass production. Stem volume was correlated with individual leaf area (r = 0.81) and leaf growth rate (r = 0.82). Hybrids had a greater total leaf area, not because they produced more leaves, but because they had larger leaves than either parental type. The greater leaf size of the hybrids may be explained by inheritance of larger cell number from P. deltoides and larger cell size from P. trichocarpa. Rates of enlargement of isolated leaf discs in liquid culture were approximately 50% of those observed in intact leaves of field-grown plants.

Journal Article↗

PubMed1992

Loss of hydraulic conductivity due to water stress in intact juveniles of Quercus rubra and Populus deltoides.

Despite many studies of the percent loss of hydraulic conductivity in excised branches, there is doubt as to whether cutting stems in air introduces unnatural embolism into the xylem at the cut surface. To address this question, hydraulic conductivity was measured in seedlings of northern red oak (Quercus rubra L.) and rooted scions of eastern cottonwood (Populus deltoides Bartr. ex Marsh.) that had been droughted in pots. Results indicate that in situ dehydration produced a very similar vulnerability curve (% loss of conductivity versus water potential) to those previously obtained by bench-top dehydration of excised branches of eastern cottonwood and red oak. In eastern cottonwood cuttings, conductivity loss increased sharply below water potentials of -1.0 MPa, with 100% loss of conductivity occurring by -2.0 MPa, whereas conductivity loss in red oak seedlings was more gradual, i.e., increasing below -1.5 MPa and sustaining 100% loss of conductivity by about -4.0 MPa.

Journal Article↗

PubMed1993

Restriction map and polymorphisms of nuclear ribosomal genes of Populus balsamifera.

Balsam poplar (Populus balsamifera) clones from five populations, which were collected along a transect from northern Wisconsin to the northern tree line, were evaluated for polymorphisms in nuclear ribosomal DNA. For this purpose, a restriction map was constructed using four six-cutter enzymes in single and double digests of genomic DNA. After electrophoretic separation on agarose gels and Southern transfer, blots were hybridized to non-radioactively labeled heterologous rDNA probes of soybean. Among populations, variation was detected in the length of the intergenic spacer between the tandem repeats of the coding regions and in the degree of methylation of one restriction enzyme recognition site. Based on a comparison of the derived restriction map of balsam poplar and other poplars, high homology was evident in the rDNA coding regions among species, whereas the intergenic spacer varied slightly in both length and number of restriction sites.

Journal Article↗

PubMed1994

ELISA Quantitation and GC-MS identification of abscisic acid in stigma, ovary and pedicel of pollinated poplar flowers (Populus nigra L.).

A method of fractionation, quantitation and identification of abscisic acid (ABA) in poplar flowers is presented in the context of intra- and interspecific pollination studies in Populus nigra x P. nigra and P. nigra x P. deltoides, respectively. Poplar flowers were dissected into stigma, ovary and pedicel. Abscisic acid concentrations were measured at receptivity and 5 days after pollination in each part of the flower. Abscisic acid was fractionated by reverse-phase HPLC followed by an enzyme-linked immunosorbent assay (ELISA) with anti-ABA polyclonal antibody and GC-MS identification of the immunoreactive ABA fractions. Samples were fractionated and ABA was identified by the presence of a cross-reactive metabolite of ABA in the extracts. The interspecific cross (P. nigra x P. deltoides) had a high concentration of ABA in the pedicel, where abscission occurred, whereas in the intraspecific cross, ABA concentration in the pedicel was low. The results are discussed with reference to the control ABA exerts on the abscission of poplar flowers after interspecific incompatible pollinations.

Journal Article↗

PubMed1994

Organic solute accumulation and dehydration tolerance in three water-stressed Populus deltoides clones.

The relationship between osmotic potential, water-soluble organic solutes and electrolyte leakage was investigated in three greenhouse-grown eastern cottonwood (Populus deltoides Bartr.) clones. The Ohio Red (from southern Ohio) and Platte (from eastern Nebraska) clones were selected because they differ in dehydration tolerance, gas exchange and osmotic potential. A third clone, Wildcat (from western Nebraska) was included because of its origin in a very dry area. Plants were either watered daily (control) or watered every 4-6 days (preconditioned). A third group of plants was watered daily until it was water-stressed at the end of the experiment (nonconditioned). Leaves for osmotic potential and water-soluble solute determinations were sampled at predawn after plants were rewatered. All clones showed osmotic adjustment ranging from 0.23 to 0.48 MPa. Organic solutes contributed up to 48% of the total osmotic adjustment. The solutes that contributed at least -0.05 MPa each to leaf osmotic potential in any clone were sucrose, malic acid, glucose, fructose, myoinositol and salicin. Fructose and glucose concentrations were unchanged or declined in preconditioned Ohio Red and Platte but increased in Wildcat. The Ohio Red clone had the highest sucrose concentration in both well-watered and preconditioned plants, and a lower injury index (more membrane stability) than Wildcat in the preconditioned plants, whereas nonconditioned Platte displayed the greatest electrolyte leakage of all clones and treatments. Cell membrane stability was correlated to osmotic potential and sucrose concentration only in Ohio Red.

Journal Article↗

PubMedDate not supplied

First-order root development from cuttings of Populus trichocarpa x P. deltoides hybrids.

We studied first-order root development of field-grown plants of 44 F(1) Populus trichocarpa x P. deltoides hybrids as well as 15 clones of P. trichocarpa (T) and 20 clones of P. deltoides (D) during their first growing season. The cuttings were planted in the field on May 11-12, 1988 and destructively sampled in July, August and September. By September 12, hybrids had an average of 50 first-order roots per cutting (range = 32 to 85) with an average of 25% dead roots (range = 10 to 51%). The longest roots of hybrids averaged 107 cm (range = 58 to 182 cm) and originated at the base of the cutting. Roots originating at the side of the cutting averaged 54 cm in length (range = 12 to 96 cm). For most aboveground and root parameters measured, the values for hybrids exceeded those for both parent species clones. For all clones, aboveground weights were positively correlated with weights of collected roots (R(2) = 0.66 to 0.86). In contrast, aboveground weights were negatively (but poorly) correlated with root/shoot ratios (R(2) = 0.08 to 0.21). Roots differed allometrically depending on their location on the cutting. Total weight of roots originating along the sides of the cutting was not correlated with aboveground weight (R(2) = 0.001 to 0.27), whereas total weight of roots originating at the base of the cutting was correlated with aboveground weight (R(2) = 0.52 to 0.80). Basal roots dominated the first-order root systems of most clones in terms of maximum length and total mass, but not in total numbers of roots.

Journal Article↗

PubMed1995

Characterization of BspA, a major boiling-stable, water-stress-responsive protein in aspen (Populus tremula).

We identified a novel 66 kDa boiling-stable protein (BspA) in cultured shoots of aspen (Populus tremula L.) which was highly expressed in response to gradual water stress. The BspA protein, which was highly expressed as early as 1 h after initiation of a drought treatment, accumulated during progressive water stress, decreased on rehydration, and was expressed in response to abscisic acid (ABA) application, as detected by SDS-PAGE protein analysis and Western blotting. Anti-BspA antibodies also cross-reacted with a 119 kDa protein. The 119 kDa protein was also induced by water stress, but it was detected only in the total protein fraction and not in the heat-stable fraction. The BspA protein cross-reacted with antibodies raised against a water-stress-responsive protein isolated from the African resurrection plant Craterostigma plantagineum Hochst. The N-terminal amino acid sequence of BspA was determined and exhibited high homology with the wheat germins GF-2.8 and GF-3.8. The BspA protein was the only major, water-stress-responsive boiling-stable protein detected in aspen.

Journal Article↗

PubMed1995

Changes in respiration and chemical content during autumnal senescence of Populus tremuloides and Quercus rubra leaves.

Changes in respiration rate, chemical content and chemical concentration were measured in leaves of field-grown Populus tremuloides Michx. and Quercus rubra L. trees throughout the growing season and autumnal senescence. Chlorophyll, soluble sugar, N, P, K and Mg contents and concentrations all declined during leaf senescence, whereas Ca content and concentration increased. Leaf dry mass per area declined 24 and 35% in P. tremuloides and Q. rubra, respectively, during senescence. In leaves of both species, respiration rates peaked during leaf expansion in the spring and then declined, as a result of reduced cytochrome-mediated respiration, to reach relatively constant rates by midsummer. In senescing P. tremuloides leaves, respiration rates remained relatively constant until mid-October and then declined rapidly. In senescing Q. rubra leaves, respiration rates increased in late September, as a result of the appearance of residual respiration that could not be reduced by respiratory inhibitors, and then declined quickly in early November. No changes in alternative pathway respiratory activity were observed in leaves of either species during senescence until late autumn when rates declined. Because respiration rates were correlated with both leaf sugar and nitrogen content during leaf senescence, we conclude that respiration rates were maintained or increased during leaf senescence to supply energy for degradation and mobilization of chemical constituents.

Journal Article↗

PubMed1995

Evaluation of sampling schemes for estimating instantaneous whole-tree photosynthesis in Populus clones: a modeling approach.

We evaluated several sampling schemes for estimating instantaneous whole-tree photosynthesis of 1-year-old Populus clones. Growth of two clones was simulated under varying weather conditions and leaf orientation scenarios providing photosynthetic data on a leaf-by-leaf basis throughout the growing season. Simple random sampling, stratified random sampling and a series of physiologically based sampling schemes were evaluated using either whole-leaf photosynthesis or photosynthetic rate (i.e., photosynthesis per unit leaf area) as the sampling attribute. Ratio and regression estimators with leaf area as an auxiliary variable were also studied. On the basis of their bias and accuracy in estimating instantaneous whole-tree photosynthesis (mg CO(2)), the physiologically based sampling schemes were superior for all combinations of clone type, weather condition and leaf orientation. Aspects of extending the sampling process to estimate daily and seasonal photosynthesis are also elaborated.

Journal Article↗

PubMedDate not supplied

First- and second-year aboveground growth and productivity of two Populus hybrids grown at ambient and elevated CO(2).

Two hybrid poplar (Populus) clones (the fast-growing clone Beaupré (P. trichocarpa Torr. and Gray x P. deltoides Bartr. ex Marsh.) and the slow-growing clone Robusta (P. deltoides Bartr. ex Marsh. x P. nigra L.)) were grown from hardwood cuttings for one or two growing seasons (1993-1994) in either ambient or elevated (= ambient + 350 micro mol mol(-1)) CO(2) in open-top chambers at the University of Antwerpen. Both clones responded positively to the elevated CO(2) treatment with increased stem volume and aboveground biomass production; however, the clones exhibited different response strategies to the elevated CO(2) treatment, and the responses varied with cutting age and duration of exposure. Clone Beaupré responded to the elevated CO(2) treatment with increases in leaf area and leaf area index during both the first and second growing seasons, but little increase in height growth. Clone Robusta exhibited increased height growth, leaf biomass and total leaf nitrogen content in response to elevated CO(2), but no increase in leaf area index. The elevated CO(2) treatment increased the total number of branches and total branch biomass in both clones during both growing seasons. At the end of the first growing season, woody stem biomass of the fast- and slow-growing clones was increased by 38 and 55%, respectively. At the end of the second growing season, stem volume was increased by 43% in clone Beaupré and by 58% in clone Robusta. The increase in stem volume was a result of the stimulation of both height and diameter growth in the slow-growing clone, whereas only height growth was stimulated in the fast-growing clone. In the fall of the first growing season, the average date of bud set in clone Robusta was advanced by 4 days in the elevated CO(2) treatment; there were no other significant effects of the elevated CO(2) treatment on bud set. The elevated CO(2) treatment enhanced leaf C/N ratios in both clones in both years.

Journal Article↗

PubMed1997

Growth, leaf anatomy, and physiology of Populus clones in response to solar ultraviolet-B radiation.

We compared the physiological and morphological responses of rooted cuttings of Populus trichocarpa Torr. & Gray and P. trichocarpa x P. deltoides Bartr. ex Marsh. grown in either near-ambient solar ultraviolet-B (UV-B; 280-320 nm) radiation (cellulose diacetate film) or subambient UV-B radiation (polyester film) for one growing season. Midday biologically effective UV-B radiation was 120.6 and 1.6 mJ m(-2) s(-1) under the cellulose diacetate and polyester films, respectively. Gas exchange, leaf chlorophyll, light harvesting efficiency of photosystem II, and foliar UV-B radiation-absorbing compounds (i.e., flavonoid derivatives) were measured in expanding (leaf plastochron index (LPI) 5), nearly expanded (LPI 10), and fully expanded mature (LPI 15) leaves of intact plants of plastochron index 30 to 35. Plants were then harvested and height, diameter, biomass allocation and leaf anatomical attributes determined. Net photosynthesis, transpiration, and stomatal conductance were significantly greater in mature leaves exposed to subambient UV-B radiation than in mature leaves exposed to near-ambient UV-B radiation. Concentrations of UV-B radiation-absorbing compounds (measured as absorbance of methanol-extracts at 300 nm) were significantly greater in mature leaves exposed to near-ambient UV-B radiation than in mature leaves exposed to subambient UV-B radiation. The UV-B radiation treatments had no effects on chlorophyll content or intrinsic light harvesting efficiency of photosystem II. Height, diameter, and biomass were not significantly affected by UV-B radiation regime in either clone. Leaf anatomical development was unaffected by UV-B radiation treatment in P. trichocarpa x P. deltoides. For P. trichocarpa, leaf anatomical development was complete by LPI 10 in the near-ambient UV-B radiation treatment, but continued through to LPI 15 in the subambient UV-B radiation treatment. Mature leaves of P. trichocarpa were thicker in the subambient UV-B radiation treatment than in the near-ambient UV-B radiation treament as a result of greater development of palisade parenchyma tissue. We conclude that exposure to near-ambient UV-B radiation for one growing season caused shifts in carbon allocation from leaf development to other pools, probably including but not limited to, UV-B absorbing compounds. This reallocation curtailed leaf development and reduced photosynthetic capacity of the plants compared with those in the subambient UV-B radiation treatment and may affect growth over longer periods of exposure.

Journal Article↗

PubMed1997

Influence of rewatering and time of sampling on solute accumulation of two Populus deltoides clones.

We investigated effects of rehydration and time of sampling on solute accumulation in plants of two greenhouse-grown Populus deltoides Bartr. clones (Ohio Red and Platte) subjected to multiple cycles of water stress. Osmotic potential of leaves at full turgor was measured at predawn on well-watered (control) and water-stressed (conditioned) plants that had been rewatered the previous afternoon. Water-soluble organic solutes (carbohydrates, phenolic glucosides and organic acids) were determined at both predawn and midday, before and after rewatering. Conditioning resulted in solute accumulation; however, rewatering of conditioned plants decreased the predawn concentration of glucose by 19-35% and the total solute concentration by 14-15%, relative to values before rewatering. There was a 52% increase in salicin concentration in response to rewatering in conditioned plants of the Platte clone. In conditioned plants of both clones, the concentration of glucose was generally lower at midday than at predawn (16-47%), whereas the concentration of sucrose was higher at midday than at predawn (46-133%). Time of sampling was an important factor in determining whether conditioning resulted in accumulation of glucose and fructose. Compared with control plants, there was a significant accumulation of glucose and fructose at predawn and either no accumulation or a significant reduction of these solutes at midday both before and after rewatering of conditioned plants. Sampling time also affected the amount of solute that accumulated in response to conditioning.

Journal Article↗