bluuebunny/crossref_metadata_2025 huggingface dataset:
Interspecific nutrient transfer in a tallgrass prairie plant community
Authors: Walter Laura E. Fischer , Hartnett David C. , Hetrick Barbara A. D. , Schwab A. Paul
Published: January 2018

Interplant nutrient transfer may be an important ecological process in grasslands, and may significantly influence plant neighborhood interactions. We investigated the potential for phosphorus transfer between the dominant grass Andropogon gerardii and several neighboring plant species in tallgrass prairie via a field 32PO4 labelling experiment. The mean amount of 32P received from donor shoots differed significantly among neighboring species and decreased with increasing distance from the donor. In general, forbs and cool‐season C3 grasses received more labelled 32P than warm‐season C4 grasses. Phosphorus transfer occurred over distances up to 0.5 m. The effects of species and distance on movement of phosphorus changed with increasing time after labelling. The relative mass of receiver and donor shoots did not affect amounts of 32P transfer. A benomyl fungicide treatment, applied to suppress mycorrhizal activity, likely did not affect existing vegetative hyphae and did not affect the amount of 32P transferred. These studies demonstrate that: (1) phosphorus is transferred among neighboring species in tallgrass prairie plant communities, (2) phosphorus may be transferred over significantly greater distances than reported in other grasslands, and (3) there is differential transfer among co‐occurring species. Hypothesized mechanisms accounting for these patterns in tallgrass prairie include mycorrhizal hyphal interconnections and/or extensive and differential root and rhizosphere overlap among neighboring species.
Morphological studies in Zygophyllaceae. II. The floral development and vascular anatomy ofPeganum harmala
Authors: Decraene L. P. Ronse , Laet J. De , Smets E. F.
Published: January 2018

Floral development and vascular anatomy are investigated inPeganum harmala, emphasizing its unusual androccium with 15 stamens. Sepals arise successively; petals emerge simultaneously with five antesepalous stamens. The five stamen pairs arise in the space between the petals and the antesepalous stamens. The gynoecium arises from three carpel primordia with evidence of two reduced carpels. Placentae are axile and each bears two double rows of ovules. A weakly developed nectary surrounds the base of the ovary. The antepetalous stamen traces diverge from a common supply to petals and sepal laterals, independent of the antesepalous stamen traces. The androecium ofPeganumis described as a derived obdiploste‐monous form, differing from the complex haplostemonous androecium ofNitraria.“Congenital dédoublement” cannot adequately explain the origin of the paired antepetalous stamens; two stamens can arise either by the splitting of a common primordium or independently, and both ways of inception are best understood as extremes of a gradation. The systematic position ofPeganumis discussed in relation to other Zygophyllaceae using a cladistic analysis withPtelea(Rutaceae) andQuassia(Simaroubaceae) as outgroups. The basal division in the Zygophyllaceae is betweenPeganumand the rest of the family.
Isozyme characterization of genetic diversity in Minnesota populations of purple loosestrife,Lythrum salicaria(lythraceae)
Authors: Strefeler Mark S. , Darmo Elizabeth , Becker Roger L. , Katovich Elizabeth J.
Published: January 2018

Starch gel electrophoresis of plant proteins was used to identify purple loosestrife (Lythrumspp.) cultivars and weedy populations. Preliminary determinations were made as to what degree weedy loosestrife populations were related (or genetically similar) to populations ofL. alatum, L. virgatum, and horticultural cultivars. Cluster analysis of the data indicated that nativeL. alatumwas genetically different from all populations of purple loosestrife and cultivars examined. TheL. salicariaandL. virgatumcultivars, as groups, were not genetically distinguishable from the weedy populations analyzed. Seven cultivars ofL. salicariaorigin analyzed as a group were not distinguishable from the eight cultivars ofL. virgatumorigin, indicating that separation by cultivar origin may not be feasible. While the two “groups” were not distinguishable, most individual cultivars could be distinguished from one another by isozyme phenotype. Genetic variation was high within populations of weedy purple loosestrife but low among populations, which is characteristic of polyploid, perennial plant species that are widely distributed. Geographic location did not consistently correlate with genetic similarity.
A Comparative Analysis of in vitro cellulose synthesis from cell‐free extracts of mung bean (Vigna radiata, Fabaceae) And Cotton (Gossypium hirsutum, Malvaceae)
Authors: Kudlicka Krystyna , Lee Jong H. , Brown R. Malcolm
Published: January 2018

A comparison of cellulose synthesized in vitro from primary walls of etiolated mung bean (Vigna radiata) seedlings and secondary walls of cotton fibers (Gossypium hirsutum) was made by applying conditions found to be essential for in vitro cellulose I assembly from cotton (Kudlicka et al., 1995, Plant Physiology, vol. 107, pp. 111–123). Mung bean fractions including the plasma membrane (PM), the first solubilized fraction (SE1), and the second solubilized fraction (SE2), incorporated more radioactive UDP‐Glc into the total product than the same fractions from secondary walls. A significant difference was found with the mild digitonin solubilized fraction (SE1), which produced eight times more total product than the SE1 fraction of cotton. However, the SE1 fraction from cotton produced a larger quantity of cellulose (32.1%) than from mung bean (6.9%). Treatment of the in vitro product by acetic/nitric acid reagent (AN) for varying periods of time demonstrated that cellulose synthesized in vitro from mung bean was more easily degraded than cellulose from cotton fibers. This would suggest that cellulose I produced in vitro from the cotton SE1 fraction may have a higher crystallinity and DP than cellulose I produced in vitro from mung bean. The fibrils of cellulose produced by the SE, fraction of mung bean were loosely associated and not arranged into a compact bundle as in case of cellulose I synthesized by the cotton SE1 fraction. The electron diffraction patterns (ED) of both products show reflections characteristic for cellulose I. Products from the SE2 fraction of mung bean and cotton reveal similarities with the cellulose II allomorph synthesized, as well as abundant β‐1,3‐glucan.
Timing of morphological and histological development in premeiotic anthers of Nicotiana tabacum cv. Xanthi (Solanaceae)
Authors: Hill Jeffrey P. , Malmberg Russell L.
Published: January 2018

The tobacco stamen has been the object of many developmental studies, and the organ has more recently become a model for molecular genetic studies of anther differentiation. However, the spatial and temporal details of cellular differentiation of early anther development have never been thoroughly characterized. In the present study, the age of 15 tobacco flowers from plants grown under constant light and temperature was estimated using growth analysis. Prior to tissue fixation for light microscopy, moulds of stamen and anther primordia were made with a dental impression polymer so morphological and histological observations could be made on each tissue sample. Flower ages spanned an 8‐d interval during which petal and stamen initiation occurred, and sporogenous cells reached the leptonema stage of meiosis. The initial development of the tetrasporangiate anther shape largely preceded periclinal division of archesporial initials. Anatomically, periclinal divisions in the hypodermal ∗∗∗(l2) layer were observed before archesporial initials began to divide. These data indicate differences in the cellular basis of tobacco anther development compared to earlier clonal analyses of Datura. The pattern of mitotic cell division associated with microsporangial development suggested modal peaks in division over time. The ability to estimate developmental time in the tobacco anther has implications for future studies directed at understanding mechanisms of anther evolution via heterochrony.
Limited effects of soil nutrient heterogeneity on populations ofAbutilon theophrasti(Malvaceae)
Authors: Casper Brenda B. , Cahill James F.
Published: January 2018

An experiment was conducted to determine if spatial nutrient heterogeneity affects mean plant size or size hierarchies in experimental populations of the weedy annualAbutilon theophrastiMedic. (Malvaceae). Heterogeneity was imposed by alternating 8 × 8 × 10 cm blocks of low and high nutrient soil in a checkerboard design, while a homogeneous soil treatment consisted of a spatially uniform mixture of the two soil types (mixed soil). Populations were planted at three densities. The effect of soil type on the growth of individuals was determined through a bioassay experiment using potted plants. The high nutrient, low nutrient, and mixed soil differed in their ability to support plant growth as indicated by differences in growth rates and final aboveground biomass. Concentrations of N, K, P, and Mg, measured at the end of the growing season in the experimental plots, also differed among all three soil types. Nevertheless, nutrient heterogeneity had little effect at the population level. Mean maximum leaf width measured at midseason was greater for populations on heterogeneous soil, but soil treatment did not affect midseason measurements of plant height, total number of leaves per plant, or canopy width. Population density affected all these parameters except plant height. When aboveground biomass was harvested at the end of the growing season, soil treatment was found to have no main effect on mean plant biomass, total population biomass, the coefficient of variation in plant biomass, or the combined biomass of the five largest plants in the population, but mean plant biomass was greater for populations on heterogeneous soils at the intermediate planting density. Mean plant biomass, total population biomass, and the coefficient of variation in plant biomass all varied with planting density. Mortality was low overall but significantly higher on homogeneous soil across all three densities. Soil heterogeneity had its strongest effect on individuals. In heterogeneous treatments plant size depended on the location of the plant stem with respect to high and low nutrient patches. Thus, soil nutrient heterogeneity influenced whether particular individuals were destined to be dominant or subordinate within the population but had little effect on overall population structure.
Isozyme analysis of intercontinental disjuncts within Styrax (Styracaceae): implications for the Madrean —Tethyan hypothesis
Authors: Fritsch Peter
Published: January 2018

Various hypotheses have been put forward to explain the presence of sclerophyllous plant disjuncts between western North America and the Mediterranean region. The Madrean–Tethyan hypothesis postulates that the two regions were floristically connected in the Early to Middle Tertiary by way of a low‐latitude migration route. Others deny the possibility of such a route, and instead postulate convergence to xerophytic conditions from more widespread mesophytic ancestors, or suggest long‐distance dispersal scenarios. One example of a “Madrean–Tethyan link” between the two regions is composed of four species within the genus Styrax: S. officinalis subsp. officinalis from the Mediterranean region, S. officinalis subsp. redivivus and subsp. fulvescens from California, and three closely related species in Texas and northeastern Mexico (S. texanus, S. platanifolius, and S. youngiae). This group was examined with isozymes to assess whether patterns of genetic variation are consistent with those predicted by the Madrean–Tethyan hypothesis. Ten populations from California, six from the Mediterranean region, and three from Texas were sampled. Pairwise comparisons revealed mean genetic identity (I) estimates of 0.581 between Mediterranean and California populations, 0.470 between Mediterranean and Texas populations, and 0.640 between California and Texas populations. Two populations of a species thought by many to be the closest relative of S. officinalis on morphological grounds (S. jaliscanus) exhibited low I (0.299–0.321) relative to all other group comparisons. Intercontinentally disjunct populations of S. officinalis possessed an I value that warrants species status for the Californian and Mediterranean groups. Divergence time estimates between Madrean and Tethyan Styrax range from 5.0 to 13.8 Mya, too recent to be consistent with the Madrean–Tethyan hypothesis. However, alternative explanations for this disjunction are suboptimal in that they require the invocation of either long‐distance dispersal, which appears unlikely in this group, or extinction. Nonetheless, the evidence presented here and in other recent studies casts substantial doubt on the Madrean–Tethyan hypothesis as a general explanation for the presence of Madrean and Tethyan taxa similar in overall appearance. More plants with Madrean–Tethyan distributions must be sampled before definitive conclusions regarding this aspect of Madrean and Tethyan vegetation can be reached.
Ultrastructure of the spermatozoid of Lycopodium obscurum (Lycopodiaceae)
Authors: Maden Angel R. , Renzaglia Karen Sue , Whittier Dean P.
Published: January 2018

Ultrastructural observations reveal that the spermatozoid of Lycopodium obscurum is crescent shaped and contains two posteriorly directed flagella that are inserted at the front of the cell. The nucleus is broad and elongated with a narrow posterior projection or nuclear diverticulum. Spline microtubules (MTs) number 180 at their maximum and provide the framework for the cell. These MTs extend from the anterior of the locomotory apparatus and along the outermost surface of the nucleus, with a central shank of 14–17 MTs encircling the cell for at least one‐third gyre beyond the nucleus. The two basal bodies are slightly staggered and positioned at the front of the cell over a highly elongated multilayered structure (MLS). The MLS extends laterally around the cell anterior and curves posteriorly over the nucleus. One large anterior mitochondrion is situated subjacent to the MLS, while numerous small mitochondria are scattered near or among the lobes of the single plastid. The plastid rests on the inner nuclear surface and contains numerous large starch grains. This cell differs from that of L. cernuum, the only other species of Lycopodium examined to date, in that it is more elongated and has an anterior‐posterior orientation of the nucleus, basal bodies, MLS, and spline. Comparisons with coiled gametes of bryophytes and Selaginella suggest that some degree of coiling and cell streamlining may be ancestral in archegoniate spermatozoids.
Phylogenetic inferences in Antennaria (Asteraceae: Gnaphalieae: Cassiniinae) based on sequences from Nuclear Ribosomal DNA internal transcribed spacers (ITS)
Authors: Bayer Randall J. , Soltis Douglas E. , Soltis Pamela S.
Published: January 2018

The phylogenetic relationships among sexually reproducing species of Antennaria (Asteraceae) are poorly understood. An earlier cladistic analysis based on morphology did not fully resolve the phylogeny of these taxa and therefore a different approach using molecular data was explored. The internal transcribed spacer regions (ITS‐1 and ITS‐2) of nuclear ribosomal DNA were sequenced for 30 species of Antennaria and one species from each of the outgroup genera Anaphalis, Ewartia, Leontopodium, and Pseudognaphalium. The ITS‐1 sequence in Antennaria ranged from 253 to 260 base pairs (bp) in length, and the proportion of nucleotide differences between pairs of species of Antennaria ranged from 1 to 14%. For ITS‐2, the divergence between pairs of species of Antennaria ranged from 0 to 8%. ITS‐2 is shorter than ITS‐1, ranging from 213 to 219 bp. Phylogenetic analysis indicates that, relative to the outgroups included, Antennaria is a well‐supported monophyletic group. Based on the genera surveyed, Leontopodium appears to be the sister genus of Antennaria. The general topology of the molecular trees agrees with that based on previous morphological analyses and indicates that Antennaria is composed of six clades of equal rank, corresponding to the traditionally recognized informal groups, the Geyeriae, Argenteae, Arcuatae, Dimorphae, Pulcherrimae, and Catipes. Sequence and morphological data indicate that the Alpinae and Dioicae are unnatural, polyphyletic units that should be abandoned and redefined as the monophyletic Catipes group. Phylogenetic analysis of ITS sequences also suggests the dissociation of A. stenophylla from the Dimorphae, where it is traditionally placed, and its affiliation with the Argenteae, as well as the placement of A. arcuata in its own group.
Morphological side effects of using gibberellic acid to induce germination: consequences for the study of seed dormancy
Authors: Evans Ann S. , Randall J. Mitchell , Cabin Robert J.
Published: January 2018

To assess the evolutionary significance of persistent seed banks, phenotypes of naturally germinating seeds must be compared with those that remain dormant under the same environmental conditions. Dormant seeds can often be induced to germinate by application of gibberellic acid (GA). However, this method is valid only if there are no phenotypic “side effects” of GA that could confound comparisons between dormant and naturally germinating seeds. We examined this assumption in Lesquerella fendleri, a short‐lived perennial mustard of the desert Southwest. We exposed 3840 seeds from 16 maternal sibships to two different GA treatments (0 or 1 g/L GA) in two different germination environments (greenhouse and growth chamber), and measured germination and postgermination traits. As expected, application of GA increased germination. GA also had strong and long‐lasting effects on seedling morphology. Seeds that received GA developed into seedlings that were taller, with fewer but longer leaves, than seeds that did not receive GA. Effects of GA on both dormancy and postgermination traits varied among maternal sibships. Our results indicate that for this species and this concentration of GA, morphological effects can be substantial. Further study is required to determine whether such side effects are found for lower concentrations of GA, or under conditions that encourage faster seedling growth. Nonetheless, the present results illustrate the importance of testing potential confounding effects of GA in studies of the evolution of seed dormancy and its influence on postgermination traits.
Effect of enhanced UV‐B radiation on pollen quantity, quality, and seed yield in Brassica rapa (Brassicaceae)
Authors: Demchik Sophie M. , Day Thomas A.
Published: January 2018

We conducted three experiments to examine the influence of ultraviolet‐B radiation (UV‐B; 280–320 nm) exposure on reproduction in Brassica rapa (Brassicaceae). Plants were grown in a greenhouse under three biologically effective UV‐B levels that simulated either an ambient stratospheric ozone level (control), 16% (“low enhanced”), or 32% (“high enhanced”) ozone depletion levels at Morgantown, WV, USA in mid‐March. In the first experiment, we examined whether UV‐B level during plant growth influenced in vivo pollen production and viability, and flower production. Pollen production and viability per flower were reduced by ≈50% under both enhanced UV‐B levels relative to ambient controls. While plants under high‐enhanced UV‐B produced over 40% more flowers than plants under the two lower UV‐B treatments, whole‐plant production of viable pollen was reduced under high‐enhanced UV‐B to 17% of that of ambient controls. Whole‐plant production of viable pollen was reduced under low‐enhanced UV‐B to 34% of ambient controls. In the second experiment, we collected pollen from plants under the three UV‐B levels and examined whether source‐plant UV‐B exposure influenced in vitro pollen germination and viability. Pollen from plants under both enhanced‐UV‐B treatments had initially lower germination and viability than pollen from the ambient level. After in vitro exposure to the high‐enhanced UV‐B levels for 6 h, viability of the pollen from plants grown under ambient UV‐B was reduced from 65 to 18%. In contrast, viability of the pollen from plants grown under both enhanced UV‐B treatments was reduced to a much lesser extent: only from ≈43 to 22%. Thus, ambient source‐plant pollen was more sensitive to enhanced UV‐B exposure. In the third experiment, we used pollen collected from source plants under the three UV‐B levels to fertilize plants growing under ambient‐UV‐B levels, and assessed subsequent seed production and germination. Seed abortion rates were higher in plants pollinated with pollen from the enhanced UV‐B treatments, than from ambient UV‐B. Despite this, seed yield (number and mass) per plant was similar, regardless of the UV‐B exposure of their pollen source. Our findings demonstrate that enhanced UV‐B levels associated with springtime ozone depletion events have the capacity to substantially reduce viable pollen production, and could ultimately reduce reproductive success of B. rapa.
Fertility differences among floral morphs following selfing in tristylous Eichhornia paniculata (Pontederiaceae): inbreeding depression or partial incompatibility?
Authors: Manicacci Domenica , Barrett Spencer C. H.
Published: January 2018

Reduction in seed set following self‐ vs. cross‐pollination in flowering plants can result from abortion of selfed offspring owing to inbreeding depression and/or partial self‐incompatibility. Previous studies on tristylous Eichhornia paniculata (Pontederiaceae) indicate that reduced seed set following self‐pollination generally occurs in the short‐ (S), but not the long‐(L) or mid‐styled (M) morphs. To determine whether this pattern results from morph‐specific differences in inbreeding depression owing to the sheltering of deleterious alleles at the S locus and/or partial self‐incompatibility, we conducted controlled hand‐pollinations of the floral morphs and measured seed set and levels of seed abortion. There were no significant differences in fertilization success and seed set following self‐, illegitimate, and legitimate pollinations in the L and M morphs. In contrast, in the S morph self‐, intramorph and intermorph illegitimate pollinations resulted in significant reduction in seed set in comparison with legitimate pollination. This indicates that the reduced seed set observed in self‐pollination is the result of partial incompatibility rather than inbreeding depression. Significantly reduced fertilization success and low levels of ovule abortion in illegitimate pollinations of S plants also supported this conclusion. Reduced fertility in the S morph may have implications for the observed loss of this morph from natural populations and the evolutionary breakdown of tristyly.
The allometry of root production and loss in seedlings of Acer rubrum (Aceraceae) and Betula papyrifera (Betulaceae): implications for root dynamics in elevated CO2
Authors: Berntson Glenn M. , Bazzaz F. A.
Published: January 2018

Total root production (∑P), total root loss (∑L), net root production. (NP), and biomass production were determined for seedlings of Betula papyrifera and Acer rubrum in ambient and elevated CO2 environments. ∑P, ∑L, and NP were calculated from sequential, independent observations of root length production through plexiglass windows. Elevated CO2 increased ∑P, ∑L, and NP in seedlings of Betula papyrifera but not Acer rubrum. Root production and loss were qualitatively similar to whole‐plant growth responses to elevated CO2. Betula showed enhanced ∑P, ∑L, and biomass with elevated CO2 but Acer did not. However, the observed effects of CO2 on root production and loss did not alter the allometric relationship between root production and root loss for either Acer or Betula. Thus, in this experiment, elevated CO2 did not affect the relationship between root production and root loss. The results of this study have important implications for the potential effects of elevated CO2 on root dynamics. Elevated CO2 may lead to increases in root production and in root loss (turnover) where the changes in root turnover are largely a function of the magnitude of root production increases.
Multiple paternity in common bean (Phaseolus vulgaris L., Fabaceae)
Authors: Ibarra‐Perez Francisco J. , Ellstrand Norman C. , Waines J. Giles
Published: January 2018

We report on two field experiments that were conducted in 1991 and 1992 at the South Coast Extension and Research Center, Irvine, CA, to study the incidence of multiple paternity in the common bean (Phaseolus vulgaris L.). Hypocotyl color and shikimate dehydrogenase (Skdh) isozymes were used as genetic markers. The white‐seeded cultivar ‘Ferry Morse 53’ (FM 53) was used as the female parent. This cultivar is homozygous recessive (pp) for hypocotyl color. The pollen source parents were three homozygous dominant (PP) purple‐hypocotyled, black‐seeded cultivars. Three cultivars, ‘ICA Pijao,’ G4459, and the maternal parent FM 53, are of Mesoamerican origin and homozygous for the fast (F) allele at the Skdh locus. The other cultivar, Black Valentine, is of Andean origin and is homozygous for the slow (S) allele at the Skdh locus. Overall, 6 125 pods were obtained from 57 and 111 plants harvested individually in 1991 and 1992, respectively. All progeny, 28938 seeds, were scored for hypocotyl color at the seedling stage. The purple‐hypocotyled seedlings were genotyped for the Skdh locus to identify their pollen parents. Multiple paternity was identified in all the pods with hybrid seeds (i.e., those of intercultivar crosses) at 5.8% and 8.1% in 1991 and 1992, respectively. All multiply sired pods produced both nonhybrid and hybrid seeds. As many as three successful fathers per pod were identified, but the number of markers limited measuring higher levels of multiple paternity. Most multiply sired pods (≈70%) were filled by nonhybrid seeds plus a single hybrid seed. Ovule position effect within multiply sired pods was inferred from the nonrandom distribution of hybrid seeds within a pod. On average, hybrid seeds occurred more frequently in ovules in position 7 (most basal) and in position 1 (most stylar) than in ovules in the middle positions of the pod.
A quantitative study of tissue dynamics in Venus's flytrap Dionaea muscipula (Droseraceae). II. Trap reopening
Authors: Fagerberg Wayne R. , Howe Douglas G.
Published: January 2018

Changes in normalized cell length (NCL) and tissue volume densities (Vv) of five trap tissues were studied during reopening of fully closed traps of Venus's flytrap (Dionaea muscipula Ellis). Four trap‐reopening stages were identified based on morphological changes observed in time‐lapse video: (1) Sealed—the last stage of trap closure before the trap began to reopen; (2) Deappressed—characterized by a convex bulge in the upper region of the trap; (3) Release—in which the bulge region moved closer to the trap margins initiating lobe separation while the marginal tynes remained interdigitated; (4) Fully opened—the trap lobes assumed a morphology similar to that of a nonstimulated trap. Morphological changes associated with trap reopening occurred as a series of relatively fast (l‐5h) and slow (10‐15 h) movements and appeared to be a reversal of the morphologies observed during trap closure. However, comparison of changes in NCL of trap tissues during closure and reopening showed very little statistical correlation indicating that the tissue dynamics associated with trap closure were not simply reversed during reopening. Although the precise cell movements that provided driving force for trap morphological change were not delineated in this study, comparison of NCL data suggested that tissues in the trap lobe were alternately “active” and “quiescent” in temporally and regionally complex patterns. Changes in the NCL of analogous tissues on opposite sides of the mid‐trap tissues within a trap region showed high positive correlation values, which indicated the possibility of coordinated activity in opposing tissues.
Weedy adaptation in Setaria spp. IV. Changes in the germinative capacity of S. faberii (poaceae) embryos with development from anthesis to after abscission
Authors: Dekker Jack , Dekker Beatrix , Hilhorst Henk , Karssen Cees
Published: January 2018

Studies were conducted evaluating germinability states in giant foxtail (Setaria faberii) embryos, as well as surrounding tissues (hull, caryopsis), with germination assays. Further, seed age, fascicle arrangement, flowering patterns, and elongation in the inflorescence were evaluated. Both qualitatitive and quantitative morphological observations of the hull and the caryopsis were revealed by precisely determined fertilized spikelet age from anthesis until after seed abscission. Red coloration of the placental pad at ≈ 11 d after anthesis is probably a morphological indicator of physiological maturity. Germinability of giant foxtail embryos changed with development. Four qualitatively different types of embryo germination were observed during development of the seed: early disorganized callus growth at the basal, coleorhizal end of the embryo; germination of immature embryos with shortened and thickened axes; germination of the scutellum; and germination and growth of the coleoptile and coleorhiza in embryos aged 7 d after anthesis and older. Axis‐specific embryo germinability was also observed. Inhibition of the embryo could be localized to the coleoptile, the coleorhiza, or both. These studies provide evidence for a complex model of germinability regulation based on the independent, asynchronous actions of the embryo, caryopsis, and hull compartments, as well as on their dependent, synchronous action. These studies provide evidence for a dynamic, developmental model of giant foxtail germinability regulation resulting in phenotypes with a wide range of germinability shed from an individual panicle. These diverse germinability phenotypes are found at all stages of development, but particularly when the seed is shed and the soil seed bank is replenished.
Water relations parameters and tissue development in somatic and zygotic embryos of three pinaceous conifers
Authors: Dumont‐BéBoux Nicole , Mazari Alicia , Livingston Nigel J. , von Aderkas Patrick , Becwar Michael R. , Percy Robin E. , Pond Sharon E.
Published: January 2018

There is increasing interest in using somatic embryogenesis to meet the demand for high quality seedlings. However, in vitro production of propagules on a large scale depends on the optimization of the maturation and germination steps promoted by desiccation and subsequent imbibition of the embryo, respectively. It is therefore important to characterize zygotic and somatic embryos in terms of their water relations. Bound water, elastic modulus, osmotic potential at full turgor, and relative water content at turgor loss point were determined for somatic and zygotic embryos of western larch and loblolly pine and somatic embryos of white spruce at two developmental stages. These water relations parameters were derived from water‐release curves obtained by suspending tissue samples in sealed vials over unsaturated NaCl solutions of known water potential. There was little difference in water relations parameters among species but marked stage dependency for bound water and elastic modulus. The amount of bound water was lowest in western larch somatic embryos (0.02‐0.07) and highest in zygotic loblolly pine embryos (0.10‐0.18). Elastic modulus ranged from 2.5 to 6.2 MPa in somatic embryos but varied between 1.4 and 1.8 MPa in zygotic embryos. The osmotic potential was lower in somatic embryos than in their zygotic counterparts. Our results show that water relations parameters are remarkably conservative across species but that, within a given species, these parameters are stage specific. It would seem, therefore, that desiccation protocols might be developed for a given developmental stage and applied across a range of species without the confounding effects of differences in water relations parameters.
Na and k accumulation and salt tolerance of Atriplex canescens (Chenopodiaceae) genotypes
Authors: Glenn Edward , Pfister Rachael , Brown J. Jed , Thompson T. Lewis , O'Leary James
Published: January 2018

Sixteen accessions of the xerohalophyte, Atriplex canescens (Pursh.) Nutt., differing in tendency to accumulate Na or K in leaf tissues, were compared for salt tolerance in a greenhouse study. Plants were grown along a salinity gradient from 72 to 2017 mol/m3 NaCl measured in the root zone. Growth rates (RGR) were negatively affected by salinity for all accessions. Initial leaf levels of Na (measured before exposing plants to saline solutions) were positively correlated with subsequent RGR's of accessions on the salinity gradient (r = 0.60 ‐ 0.88, P < 0.05 across salinity levels), whereas initial leaf K levels were negatively correlated (r = ‐0.68 to ‐0.85, P < 0.01 across salinity levels). Varieties linearis (S. Wats.) Munz and grandidentatum Stutz & Sanderson had greater tendency for Na accumulation, lower tendency for K, and higher growth rates on saline solutions than var. occidentalis (Torr. & Frem.) Welsh & Stutz accessions. Within var. occidentalis accessions, RGRs were negatively correlated with initial leaf levels of K but not Na. Postexposure leaf Na and K levels were not strongly correlated with RGR's. All accessions responded to salinity by increasing their uptake of Na, which is the primary mechanism of osmotic adjustment to salinity in this species. It is suggested that differences in tendency to accumulate Na or K among A. canescens genotypes are related to their specialization for saline or xeric habitats, respectively.
Genetic structure of two endangered pitcher plants,Sarracenia jonesiiandSarracenia oreophila(sarraceniaceae)
Authors: Godt Mary Jo W. , Hamrick J. L.
Published: January 2018

Sarracenia jonesiiandS. oreophilaarc insectivorous perennial plants of the southeastern United States. Both pitcher plant taxa arc rare and endangered. Allozyme diversity was assessed for eight of the ten extant populations ofS. jonesiiand 14 of the 35 remainingS. oreophilapopulations. Genetic diversity was low and comparable for both species (Hes= 0.086 and 0.082 forS. jonesiiandS. oreophila, respectively). Mean population genic diversity(Hep)was 0.061 forS. jonesiiand 0.060 forS. oreophila.Estimates of genetic diversity were typical of those commonly associated with endemic species. Small populations of each species and geographically disjunct populations tended to maintain less genetic diversity. Indirect estimates of gene flow were comparable forS. oreophila (Nm= 1.62) andS. jonesii (Nm= 1.07).
Genetic diversity in micronesian island populations of the tropical treecampnosperma brevipetiolata(anacardiaceae)
Authors: Sheely Deborah L. , Meagher Thomas R.
Published: January 2018

Tropical plant species have been the focus of considerable attention in regard to their potential economic and social importance in the face of rapidly diminishing biodiversity in the tropics. Pacific Island species represent an even more fragile resource because different island populations are widely scattered and overall population sizes are small. We examined the distribution of genetic variation inCampnosperma brevipetiolata(Anacardiaceae), an upland rainforest tree species that is of potential use for both lumber and reforestation efforts in the Federated States of Micronesia (FSM). Seeds were collected from multiple populations on four island groups in the Caroline Islands (Kosrae, Pohnpei, and Yap in the FSM; and the Republic of Palau) and subjected to an electrophoretic analysis involving four polymorphic genetic loci. We hypothesized that variation on these islands would decrease with increasing distance from the presumed Indo‐Malayan source of these island floras. Indeed, we found a trend of decreasing variation from west to east indicated by the mean number of alleles per locus(A =1.50‐1.33), effective number of alleles per locus(Ae=1.14‐1.12) and mean genetic diversity(He=0.123‐0.107). We also found little genetic differentiation among the islands (Fpt= 0.174) and among subpopulations within islands (Fsp= 0.047), indicating that either there are high levels of gene flow among the islands by seed dispersal or that these populations have not been established long enough for divergence to have occurred. The lack of divergence among islands observed forCampnosperma brevipetiolatasuggests that germplasm sampled from any one island population would be a suitable starting point for plant breeding or reforestation efforts.
Pollination genetics of hybridization in sympatric populations of asclepias exaltata and a. syriaca (asclepiadaceae)
Authors: Broyles Steven B. , Vail Christopher , Sherman‐Broyles Susan L.
Published: January 2018

Enzyme electrophoresis of pollinia and seeds was used to identify pollinia on pollinators, interspecific pollinations, and hybrid seed production in sympatric populations of Asclepias exaltata and A. syriaca. The frequency of mixed pollinia loads on pollinators was low. Only 4.1% (N= 169 pollinia) and 8% (N= 244 pollinia) of the pollinia collected from pollinators of A. syriaca and A. exaltata, respectively, were identified as pollinia from the other species. Natural levels of interspecific pollination, 3.6% (N = 166 pollinia) on A. syriaca and 3.1% (N = 228 pollinia) on A. exaltata, were typically lower than the number of foreign pollinia carried by pollinators. Hybrid seeds were identified in only two of 208 A. syriaca fruits and one of 178 A. exaltata fruits. Hybrid seeds were largely underdeveloped in the single A. exaltata fruit. High fruit set (34.7%) and near normal seed set following hand‐pollination of A. syriaca with A. exaltata pollinia suggest that hybridization is more likely between these taxa when A. syriaca is the maternal parent. Our findings indicate that the likelihood of hybridization between A. exaltata and A. syriaca is remote. Nevertheless, introgressive hybridization has been documented in these species, which suggests that hybridization remains a strong evolutionary force even for species that infrequently interbreed.
Genetic load, nutrient limitation, and seed production in Lupinus texensis (Fabaceae)
Authors: Helenurm Kaius , Schaal Barbara A.
Published: January 2018

The interaction of mating system and nutrient limitation in determining seed production was investigated in the annual, self‐compatible plant Lupinus texensis (Fabaceae). Abortion of developing seeds is a major factor limiting seed production in natural populations (17‐28%). Selfing rates are generally low (0.02‐0.21), suggesting that deleterious recessive genes may be maintained at significant levels in natural populations. The average inbreeding depression associated with seed development is δ = 0.24. Nutrient limitation reduced seed output across experimental treatments by a factor of 0.22 through decreased production of inflorescences, flowers, and ovules, and by a factor of 0.29 through increased abortion of fruits and of seeds within fruits. Competition for resources among fruits increased the frequency of seed abortion. Moreover, a greater proportion of selfed seeds were aborted as the overall abortion rate increased. Estimates of genetic load may therefore only be appropriate if undertaken in the field, and inbreeding depression may vary from year to year simply due to changes in environmental conditions rather than to underlying genetic changes in populations. The existence of inbreeding depression and the high frequency of abortions suggest that selective abortion favoring outcrossed progeny occurs in natural populations of L. texensis.
Genetic variation in some plants of Florida scrub
Authors: McDonald David B. , Hamrick J. L.
Published: January 2018

Genetic diversity in three genera of perennial plants found in the sand pine, oak scrub in peninsular Florida was examined by allozyme electrophoresis. These plants vary greatly in terms of geographic range, population size, pollination ecology, and seed dispersal mechanisms. Ceratiola ericoides (Empetraceae) is a shrub that occurs throughout scrub and other sandy habitats in Florida and neighboring states. In contrast, Eryngium cuneifolium (Apiaceae) is a Federally endangered herbaceous perennial, limited to the southern end of the Lake Wales Ridge, site of a proposed National Wildlife Refuge that would be the first designed primarily to protect plant diversity. Four species of endangered woody perennial Dicerandra (Labiatae) are part of a monophyletic group endemic to Florida sand pine scrubs; Dicerandra frutescens and D. christmanii are found on the southern end of the Lake Wales ridge, D. cornutissima is found in north‐central Florida, and D. immaculata occurs in a small area along Florida's Atlantic coast. Allozyme electrophoresis of 17 loci for C. ericoides indicated that 64.7% of the loci were polymorphic (Ps), that there were 2.55 alleles per polymorphic locus (APs), and that the mean gene diversity (Hes) was 0.141. The proportion of genetic diversity among the four populations (GST) was 0.059. For the 31 loci analyzed in E. cuneifolium, Ps was 32.3%, APS was 2.1, and Hes was 0.104. GST was 0.106. The woody Dicerandra species complex (four species) was analyzed for 17 loci. Ps was 64.7%, APs was 3.1, and mean gene diversity was 0.219. The mean GST value across the species complex was 0.137. Taken together these results suggest that considerable genetic variation is still present in the relict populations of the rare scrub taxa (Eryngium and Dicerandra), but that to preserve current levels of genetic variation will require protecting areas in each of several different scrub regions along a 350‐km stretch of peninsular Florida.
The ultrastructure of somatic embryo development in pearl millet (Pennisetum glaucum; Poaceae)
Authors: Taylor Mark G. , Vasil Indra K.
Published: January 2018

The ultrastructure, morphology, and histology of somatic embryogenesis in pearl millet (Pennisetum glaucum) were examined using light and electron microscopic techniques. Somatic embryogenesis was initiated from zygotic embryo explants cultured 8 d after pollination. Formation of a ridge of tissue began 3–4 d after culture (DAC) by divisions in the epidermal and subepidermal cells of the scutellum. Ridge formation was accompanied by a decrease in vacuoles, lipid bodies, and cell size, and an increase in endoplasmic reticulum (ER). Proembryonic cell masses (proembryoids) formed from the scutellar ridge by 10 DAC. Proembryoid cells had abundant Golgi bodies and ER while the amounts of lipids and starch varied. Somatic embryos developed from the proembryonic masses 13 DAC and by 21 DAC had all the parts of mature zygotic embryos. Although shoot and root primordia of somatic embryos were always less differentiated than those of zygotic embryos, scutellar cells of somatic and zygotic embryos had similar amounts of lipids, vacuoles, and starch. Somatic scutellar epidermal cells were more vacuolated than their zygotic counterparts. In contrast, somatic scutellar nodal cells were smaller and not as vacuolated as in zygotic embryos. Somatic embryogenesis was characterized by three phases of cell development: first, scutellar cell dedifferentiation with a reduction in lipids and cell and vacuole size; second, proembryoid formation with high levels of ER; and third, the development of somatic embryos that were functionally and morphologically similar to zygotic embryos.
Genetic diversity and population structure in the outcrossing populations of Equisetum arvense and E. hyemale (Equisetaceae)
Authors: Korpelainen Helena , Kolkkala Mikko
Published: January 2018

An allozyme examination was conducted to study the mating systems and genetic differentiation of populations of Equisetum arvense and E. hyemale. The study revealed that the rate of intragametophytic selfing in these homosporous pteridophytes is very low, i.e., on average 0.020 and 0.019, respectively, despite the potential hermaproditism and selfing of the gametophytes. Most populations consisted of numerous genotypes, and the average heterozygosities of E. arvense and E. hyemale equalled 0.092 and 0.134, respectively. The commonly observed excess of the heterozygote genotypes indicates that there are interclonal differences in the frequency of vegetative reproduction. The level of genetic divergence among populations was considerable even within a limited geographic area. It is suggested that the life history of Equisetum, characterized by the inefficiency of spore germination and gametophyte reproduction in noncolonizing situations, limits the level of gene flow and leads to a great genetic divergence between populations.
Spatial models of foraging in clonal plant species
Authors: Cain Michael L. , Dudle Dana A. , Evans Jonathan P.
Published: January 2018

Ramets of some clonal plant species alter their internode lengths or their frequency of lateral branching in response to their immediate microenvironment. Such “plant foraging” responses are thought to allow clones to concentrate in favorable portions of their environment. Despite widespread interest among ecologists in plant foraging, few realistic models have been developed to examine conditions under which plant foraging responses are likely to provide clones with ecological benefit. In this paper, we develop spatially explicit, stochastic simulation models to examine consequences of both empirical and hypothetical plant foraging responses. We construct a hierarchical series of models in which we incorporate effects of resource heterogeneity on spacer lengths, angles of growth, and lateral branch production. We also vary the number, size, and arrangement of patches, and the presence or absence of ramet mortality. Simulations based on hypothetical data demonstrated the potential importance of shortening spacer lengths in favorable habitat. In these simulations, ramet crowding increased significantly, implying a potential cost to plant foraging responses whose magnitude is large enough to cause ramets to concentrate in favorable patches. Models calibrated with empirical data suggest that when clonal plants were able to concentrate in favorable habitat, this was usually caused by increased daughter ramet production in the favorable habitat. Variation in clonal growth angles had little impact on the ability of ramets or clones to locate favorable patches, but did increase the ability of clones to remain in favorable patches once found. Alterations in the number and size of patches strongly influenced the effectiveness of the foraging response. The spatial arrangement of patches also was important: clumped distributions of patches decreased the success with which plants located favorable patches, especially at the genet level and when the number of patches was low. Finally, when ramet mortality varied with patch quality, there was an increase in the percentage of ramets located in favorable patches; differential ramet mortality also lessened the impact of other effects, such as the decreased success of clones when patches are clumped. Overall, our models indicate that the effectiveness of plant foraging responses is variable and is likely to depend on a suite of environmental conditions.