bluuebunny/crossref_metadata_2025 huggingface dataset:
Isoflavonoids in root and hypocotyl of soybean seedlings (Glycine max, Fabaceae)
Authors: Grady Haiyan , Palmer Reid G. , Imsande John
Published: January 2018

Isoflavonoids, some of which are highly fluorescent, are produced by soybean [Glycine max (L.) Merr.] and serve as chemical signals for certain aspects of nitrogen fixation and microbial resistance. This study was conducted to determine whether soybean mutants with nonfluorescent roots contained abnormal concentrations of isoflavonoids. Isoflavonoids were extracted from the root and hypocotyl of 4‐d‐old wild‐type soybean seedlings (cv. Hark) having fluorescent roots and from four nonallelic mutant, near isogenic lines of Hark having nonfluorescent roots. In addition, isoflavonoids were extracted from the root and hypocotyl of 4‐d‐old seedlings of near isogenic lines of Hark harboring two pairs of the mutant alleles for nonfluorescent roots. Malonyl daidzin, daidzin, malonyl genistin, and genistein were the most abundant isoflavonoids extracted from either the root or hypocotyl of seedlings with either fluorescent or nonfluorescent roots. Extracted malonyl daidzin, malonyl genistin, and malonyl glycitin decomposed readily, yielding daidzin, genistin, and glycitin, respectively. The concentrations of malonyl genistin and genistein, two highly fluorescent compounds, were similar in both fluorescent and nonfluorescent roots. Thus, root fluorescence was not correlated with abundance per se of fluorescent isoflavonoids in roots. In addition, the abundance of isoflavonoids extractable from the hypocotyl did not correlate with root fluorescence.
Two new male‐sterile mutants ofZea mays (Poaceae) with abnormal tapetal cell morphology
Authors: Loukides Cynthia A. , Broadwater Anne H. , Bedinger Patricia A.
Published: January 2018

Two new recessive male‐sterile mutants of Zea mays (Poaceae), or maize, were studied to identify the timing of pollen abortion and to examine the involvement of anther wall cell layers. The results of test crosses indicated that these mutants were not allelic with any known male‐sterile mutants of maize. Light and transmission electron microscopy were used to compare pollen development in homozygous male‐sterile mutants to that in fertile heterozygous siblings. In both mutants, microspores abort soon after release from the meiotic tetrad. However, the two mutations have strikingly different phenotypes. Large lipid bodies accumulate in the tapetal cells as the microspores vacuolate and die in the mutant ms25. Large vacuoles appear in both the tapetal cells and the young microspores as they begin to disintegrate in the mutant ms26. Because abnormal tapetal cell morphology is detected in both mutants, it is possible that both of these mutations affect the expression of genes in tapetal cells.
Phylogenetic relationships in tribe Cardueae (Asteraceae) based on ITS sequences
Authors: Susanna Alfonso , Jacas Nuria Garcia , Soltis Douglas E. , Soltis Pamela S.
Published: January 2018

The Cardueae pose vexing systematic problems at several taxonomic levels. Tribal delimitation is controversial, with views ranging from a broadly defined Cardueae comprising subtribes Echinopsidinae, Carlininae, Carduinae, and Centaureinae to a more restrictive Cardueae (comprising only Carduinae and Centaureinae) with tribal rank also given to Echinopsideae (or Echinopeae) and Carlineae. Furthermore, the circumscription of groups within a broad Cardueae is also controversial, with divergent views emphasizing differences in floral or achene morphology; the distinction between Carduinae and Centaureinae is particularly weak. The generic limits of Centaurea, comprising 500–600 species and great diversity in both chromosome number and pollen morphology, are also unclear. Patterns of morphological, chromosomal, and pollen diversity in Centaurea do not completely support either the current taxonomy or any of the proposed modifications. Clearly, the Cardueae in general and Centaurea in particular require a phylogenetic approach to resolve problems of taxonomic circumscription and rank and to understand patterns of pollen and chromosomal evolution. We therefore analyzed DNA sequences of the internal transcribed spacers (ITS) of the nuclear ribosomal RNA genes (rDNA) of 35 taxa to reconstruct the phylogeny of Cardueae and assess 1) the positions of Echinopsidinae and Carlininae, 2) the circumscription of the Carduinae‐Centaureinae complex, and 3) the limits of Centaurea and related genera. Phylogenetic analysis of ITS sequence variation strongly supports the monophyly of Cardueae relative to outgroup taxa from Mutisieae and Cichorieae. Both Carlininae and Echinopsidinae occupy basal branches in Cardueae. Carduinae are paraphyletic, forming a basal grade in the tribe. The Centaureinae, however, form a well‐supported clade. As typically circumscribed, Centaurea is paraphyletic, comprising species of several other genera in addition to those currently recognized as Centaurea. Proposed evolutionary trends in pollen morphology and, to a lesser extent, base chromosome numbers are largely supported by the ITS phylogeny for Cardueae.
Narrow hybrid zone between two subspecies of big sagebrush,Artemisia tridentata(Asteraceae). III. Developmental instability
Authors: Freeman D. Carl , Graham John H. , Byrd David W. , McArthur E. Durant , Turner William A.
Published: January 2018

Stable hybrid zones are believed to occur because gene dispersal is opposed by selection, but the nature of this selection remains unclear. The dynamic equilibrium model postulates that hybridization disrupts coadapted gene complexes, leading to alterations in development and subsequent hybrid unfitness. Alternatively, the bounded hybrid superiority model assumes that selection is due to exogenous factors. Here, we examine the developmental instability of sagebrush across a narrow hybrid zone. The results show no difference among the parental and hybrid taxa for the majority of comparisons examined. When significant differences in developmental instability were observed, one of the parental taxa (mountain big sagebrush) was typically the least developmentally stable. Hybrids were found to be the least developmentally stable for only two of the 28 comparisons studied. Interestingly, for some comparisons, hybrids were themostdevelopmentallystable.These results contradict predictions of the dynamic equilibrium model. The sagebrush hybrid zone does not appear to be maintained by endogenous selection, as there is little indication that development is disrupted by hybridization.
Chloroplast DNA and isozyme analysis of the progenitor‐derivative species relationship betweenSenecio nebrodensisandS. viscosus (Asteraceae)
Authors: Kadereit Joachim W. , Comes Hans Peter , Curnow David J. , Irwin Judith A. , Abbott Richard J.
Published: January 2018

A comparison of chloroplast DNA (cpDNA) and isozyme diversity in Senecio nebrodensis L., a species restricted to certain mountain ranges in Spain, and S. viscosus L., a widespread ruderal species in Europe, revealed that S. viscosus possessed the more common of two cpDNA haplotypes resolved in S. nebrodensis and contained only a small subset of the alleles found in S. nebrodensis at enzyme coding loci. The two species shared one restriction length mutation and one site mutation in their cpDNA, which distinguished them from other European Senecio species examined previously. Taken overall, these results support the hypothesis that S. nebrodensis and S. viscosus are related as a progenitor‐derivative pair of species. The fact that no novel alleles were found in S. viscosus would suggest a relatively recent origin of the species, most probably in late glacial or postglacial times.
DEVELOPMENTALLY VARIABLE, POLYMORPHIC WOODS IN CACTI
Authors: Mauseth James D. , Plemons Brandon J.
Published: January 2018

Sixteen genera of cacti were discovered to have polymorphic wood, that is, the plants produce one type of wood while young but a different type when older. The polymorphisms are: fibrous wood (with vessels and scanty paratracheal parenchyma) followed by parenchymatous wood (with vessels but few or no fibers) (Hylocereus venezuelensis, Dendrocereus nudiflorus, Borzicactus humboldtii, Haageocereus australis, Morawetzia sericata, Stephanocereus leucostele, Trichocereus schickendantzii); WBT wood (with wide‐band tracheids, vessels, and apotracheal parenchyma but few or no fibers) followed by fibrous wood (Buiningia aurea, Oreocereus celsianus, Vatricania guentheri); WBT wood followed by parenchymatous wood (Echinopsis tubiflora, Gymnocalycium marsoneri, G. oenanthemum, Notocactus warasii, Parodia maassii); trimorphic wood in which WBT wood is followed by fibrous wood, which is followed by parenchymatous wood (Melocactus intortus, Arrojadoa braunii). The different phases within each plant may differ in vessel cluster size, percentage of the vessels that are solitary, diameter of vessels, and lignification of ray cells. Several of these genera are not closely related to the others, so wood polymorphism may have arisen several times.
EFFECTS OF COMPETITION AND DISTURBANCE ON THE RESPROUTING PERFORMANCE OF THE MEDITERRANEAN SHRUB ERICA MULTIFLORA L. (ERICACEAE)
Authors: Vilà Montserrat , Terradas Jaume
Published: January 2018

Two field experiments were designed to evaluate the importance of competition, fire, repeated disturbance, and their interactions on the vegetative and reproductive performance of the Mediterranean shrub Erica multiflora over a 2.5‐yr period. In a burn experiment, fire was applied to the ground‐level stumps of previously clipped 13‐yr‐old plants with a propane torch and competition was diminished by removal of neighboring plants. Fire resulted in a reduction of sprout vigor and biomass of flowers; mature neighbors also reduced E. multiflora sprout vigor and flowering. The interaction between fire and competition was nonsignificant. In a stand burned by a wildfire we studied the effects of regenerating neighbors on target plants by removing all neighbors or only Quercus coccifera, the most dominant species in the burned stand. In this stand we also simulated herbivory by repeatedly clipping the sprouts of E. multiflora. Regenerating neighbors did not affect target plant sprout vigor after the wildfire, but did cause a decrease in the biomass of flowers per plant. Survival decreased after repeated clipping but was not affected by neighborhood treatment. The results suggest that the importance of competition on resprouting vigor was temporally variable. Variables related to plant size rather than species determined competitive superiority: resprouting neighbors did not affect resprouting performance of target plants, but mature neighbors did. In nature, fire may directly reduce vegetative and reproductive biomass by the heating effect. But it may have an indirect positive effect on biomass, by reducing competition among plants. Frequent disturbances that removed aboveground biomass of E. multiflora had a detrimental effect on target plant survival independent of neighborhood effect.
A CLADISTIC ANALYSIS OFPARKIA(LEGUMINOSAE: MIMOSOIDEAE)
Authors: Luckow Melissa , Hopkins Helen C. F.
Published: January 2018

A cladistic analysis of the tropical mimosoid genusParkiawas undertaken to examine relationships among the 31 species and to test the monophyly of the three recognized sections. The implications of the cladogram to the evolution of bat‐pollination and biogeography were also explored. The analysis, based on 52 morphological characters, resulted in 408 most parsimonious trees. A consensus tree supports the monophyly of sectionsParkiaandPlatyparkia, but sectionSphaeroparkiais paraphyletic. The latter section is distinguished by a capitulum of all fertile flowers, a plesiomorphic attribute in this analysis. Characters supporting the monophyly of sectionPlatyparkiainclude an inflorescence with distal nectar flowers having exserted styles, and fruits with seeds in two rows. SectionParkiais characterized by having sterile basal flowers with nectar flowers just above them, and calyx lobes included in bud. Bat‐pollination was mapped onto one of the most parsimonious cladograms to examine the evolution of pollination syndromes within the genus. Our phylogeny is consistent with a single origin of bat‐pollination and indicates that entomophilous species ofParkiaare basal rather than secondarily derived. SectionsPlatyparkiaandParkiaare separate lineages within the bat‐pollinated clade and have independently developed capitulum types adapted to chiropterophily. Characters that are associated with chiropterophily include specialized nectar‐producing flowers and basifixed anthers. Several characters, including presence of a staminodial fringe, a nectar ring, and pollen with verrucate sculpturing on the exine, probably represent increasing specialization for bat‐pollination. The cladogram supports a South American origin forParkiabut is not consistent with a Gondwanan vicariance event as is usually hypothesized to explain its amphi‐Atlantic distribution.
GENETIC VARIATION IN TRAGOPOGON SPECIES: ADDITIONAL ORIGINS OF THE ALLOTETRAPLOIDS T. MIRUS AND T. MISCELLUS (COMPOSITAE)
Authors: Soltis Pamela S. , Plunkett Gregory M. , Novak Stephen J. , Soltis Douglas E.
Published: January 2018

Genetic diversity in the introduced diploids Tragopogon dubius, T. porrifolius, and T. pratensis and their neoallotetraploid derivatives T. mirus and T. miscellus was estimated to assess the numbers of recurrent, independent origins of the two tetraploid species in the Palouse region of eastern Washington and adjacent Idaho. These tetraploid species arose in this region, probably within the past 50–60 yr, and provide one of the best models for the study of polyploidy in plants. The parental species of both T. mirus and T. miscellus have been well documented, and each tetraploid species has apparently formed multiple times. However, a recent survey of the distributions of these allotetraploids revealed that both tetraploid species have expanded their ranges considerably during the past 50 yr, and several new populations of each species were discovered. Therefore, to evaluate the possibility that these recently discovered populations are of recent independent origin, a broad analysis of genetic diversity in T. mirus, T. miscellus, and their diploid progenitors was conducted. Analyses of allozymic and DNA restriction site variation in all known populations of T. mirus and T. miscellus in the Palouse and several populations of each parental diploid species revealed several distinct genotypes in each tetraploid species. Four isozymic multilocus genotypes were observed in T. mirus, and seven were detected in T. miscellus. Tragopogon mirus possesses a single chloroplast genome, that of T. porrifolius, and two distinct repeat types of the 18S‐26S ribosomal RNA genes. Populations of T. miscellus from Pullman, Washington, have the chloroplast genome of T. dubius; all other populations of T. miscellus have the chloroplast DNA of T. pratensis. All populations of T. miscellus combine the ribosomal RNA repeat types of T. dubius and T. pratensis, as demonstrated previously. When all current and previously published data are considered, both T. mirus and T. miscellus appear to have formed numerous times even within the small geographic confines of the Palouse, with estimates of five to nine and two to 21 independent origins, respectively. Such recurrent polyploidization appears to characterize most polyploid plant species investigated to date (although this number is small) and may contribute to the genetic diversity and ultimate success of polyploid species.
Woodland canopy structure and the light response of juvenileQuercus lobata(Fagaceae)
Authors: Holmes Tyson H.
Published: January 2018

I investigated competition for light between canopy plants and juvenile valley oaks (Quercus lobataNee) in a mixed‐broadleaf woodland of California's northern Coast Ranges. Canopy effects on understory light supply were separated among the overlying adult valley oak, the adult's woody understory, and neighboring trees and shrubs through a series of light sampling surveys and measurements of the number, size, and spatial distribution of neighboring plants. Light supply in the understory was primarily influenced by neighboring plants, with no detectable effect of the overlying adult valley oak. Light supply in the understory averaged 25% full sun due to a high frequency of canopy gaps and a typically open understory. Seedling response to understory light supply was investigated in an experimental sunfleck gradient (10%, 19%, and 100% full sun). Between 10% and 100% full sun, seedling growth increased by 90% and the shoot:∗∗∗root ratio changed from 1.561 to 0.607. Shade seedlings were also taller and produced fewer, larger, and thinner leaves than seedlings grown in full sun. A field survey of the spatial distribution and crown morphology of saplings and young adults found 1) the distance between young valley oaks and neighboring overstory trees to increase with neighbor size, and 2) crowns of the young oaks to be skewed away from neighbors. Although shading by the canopy was only moderate, canopy effects on understory light supply may restrict juvenile recruitment of valley oak in this woodland.
HELIOTROPIC LEAF MOVEMENT RESPONSE TO H+/ATPase activation, H+/ATPase inhibition, AND K+ CHANNEL INHIBITION IN VIVO
Authors: Cronlund Sarah L. , Forseth Irwin N.
Published: January 2018

The pulvinus, located at the base of soybean leaflets, is both the light perception and motor organ for heliotropic leaf movements. Our objective was to investigate the role of plasma membrane H+/ATPase and TEA‐sensitive K+ channels in mediating pulvinar response to light. The plasma membrane H+/ATPase activator, fusicoccin, plasma membrane H+/ATPase inhibitors, vanadate and erythrosin‐B, and the K+ channel blocker TEA were introduced to the intact pulvinus through the transpiration stream. The pulvinus was illuminated by a vertical light beam of 1,400 μmol m‐2 s‐1 to stimulate leaf movement. Leaf orientation was measured every 5 min for 60 min of illumination. All compounds tested inhibited pulvinar bending, but concentration and uptake time required for inhibition varied: 12.5 μM fusicoccin reduced leaf movement after 3 hr uptake, 2 mM vanadate reduced leaf movement after 6 hr uptake, 100 μM erythrosin‐B reduced leaf movement after 3 hr uptake, and 15 mM TEA reduced leaf movement after 6 hr uptake. In all cases final leaf angle was reduced by higher concentrations and/or increased time for uptake of the chemical into the pulvinus. Results support the hypothesis that the proximal mechanism of heliotropic movement is similar to that of nyctinastic movements.
Auxin metabolism in representative land PLANTS
Authors: Sztein A. Ester , Cohen Jerry D. , Slovin Janet P. , Cooke Todd J.
Published: January 2018

The plant hormone auxin (indole‐3‐acetic acid, IAA) appears to control many plant developmental processes, and studies performed in seed plants suggest that IAA conjugation is the critical mechanism to regulate free IAA concentration. The purpose of this investigation is to characterize the biochemical ability of one charophyte and 23 land plants ranging from liverworts to angiosperms to produce IAA conjugates, and to study the complexity of their conjugation patterns. Actively growing tissue was incubated with 14C‐IAA, after which labeled IAA conjugates were separated using thin‐layer chromatography. The conjugates were analyzed using radioimaging techniques and their tentative identity assigned by co‐chromatography and/or by differential hydrolysis. The charophyte and the liverworts appear unable to conjugate IAA. The mosses and the hornwort are able to conjugate IAA into a few amide and ester conjugates. The tracheophytes examined synthesize several conjugates unique to the vascular plants, indole‐3‐acetyl‐aspartic acid (‐glutamic acid) and/or indole‐3‐acetyl‐β‐1‐O‐glucose, as well as a variety of other amide and ester conjugates. These three conjugation patterns are correlated to the type of conducting tissue characteristic of the plants analyzed. These biochemical differences may be indicative of significative differences in the hormonal regulation in these plant groups, thus suggesting that changes in IAA regulation accompanied the major evolutionary events in land plants.
The effects of natural variation in pollinator visitation on rates of pollen removal in wild radish, Raphanus raphanistrum (Brassicaceae)
Authors: Rush Scott , Conner Jeffrey K. , Jennetten Peter
Published: January 2018

Pollen removal from flowers is an important component of male fitness, but the effects of natural variation in visitation rates on pollen removal are poorly understood. We measured pollen removal over 2 yr in experimental field populations of wild radish, Raphanus raphanistrum. Pollen removal and pollinator visitation over 1‐hr periods were measured on previously unvisited flowers. The effects of pollen production and visitation by different insect taxa on pollen removal were determined using multiple regression. Pollen removal rates were extremely high; a median of 84% of pollen produced was removed in 1 hr. Pollen production was far more important than visitation in determining the number of pollen grains removed. Pollen removal increased with increasing numbers of visits by honey bees and small native bees, but increased numbers of syrphid fly visits had no effect. Average visit duration had no effect on pollen removal in 1991, and a marginally negative effect in 1992.
Ecological constraints on fruit initiation by Calyptrogyne ghiesbreghtiana (Arecaceae): FLORAL HERBIVORY, POLLEN AVAILABILITY, AND VISITATION BY POLLINATING BATS
Authors: Cunningham Saul A.
Published: January 2018

Failure of a flower to initiate fruit can be attributed to an insufficiency of resources, genetic incompatibilities, or ecological constraints on pollination. Flower visitors can increase fruit initiation by pollinating flowers, or decrease fruit initiation by damaging them. If, however, resources limit fruit initiation, variation in visitation may be relatively unimportant. Visitors to Calyptrogyne ghiesbreghtiana, a rain forest understory palm, leave a record of their activity by feeding on floral tissue. I recorded variation in inflorescence visitation, floral display, and fruit initiation during 7 mo over two field seasons. On average, bats visited 50‐60% of flowers; katydids and scarab beetles visited and damaged the remaining 40‐50%. Four species of bat (Phyllostomidae) captured near inflorescences were found to be carrying C. ghiesbreghtiana pollen. Approximately 18% of flowers visited by bats and not damaged by insects initiated fruit, whereas insect‐damaged flowers set a negligible number. Some variation in fruit initiation was explained by nightly variation in the proportion of inflorescences at each site that were potential pollen donors (male‐phase inflorescences). Visitors responded to variation in floral display; katydids damaged more flowers on taller inflorescences, and in one season bats visited a greater proportion of flowers on inflorescences with many flowers. However, floral display only explained a small amount of variation in visitation. A similar amount of variation in flower visitation was explained by the degree to which inflorescences were obstructed by surrounding vegetation. I used path analysis to summarize the overall effect of floral display on visitation by both pollinators and florivores and the effect of visitation and site sex ratio on fruit initiation. Because almost all flowers were visited by bats or damaged by katydids, the amount of bat visitation was strongly negatively correlated with katydid damage. In spite of the low fruit set from bat‐visited flowers, variation in bat visitation explained 27‐37% of the variation in fruit initiation.
Molecular divergence in the eastern Asia– eastern North America disjunct section Rytidospermum of Magnolia (Magnoliaceae)
Authors: Qiu Yin‐Long , Parks Clifford R. , Chase Mark W.
Published: January 2018

Molecular divergence in the eastern Asia—eastern North American disjunct section Rytidospermum of Magnolia was investigated by allozyme electrophoresis, chloroplast DNA (cpDNA) restriction site analysis, and gene sequencing. We calculated Nei's genetic identities between two Asian species, M. officinalis var. biloba and M. hypoleuca, and three American species, M. tripetala, M. fraseri var. fraseri, and M. macrophylla var. macrophylla, by using gene frequency data from 17 nuclear‐encoded allozyme loci in 67 populations. We then estimated cpDNA sequence divergence between the five species by examining restriction site variation for ten endonucleases over the entire genome. Finally, nucleotide sequences of the chloroplast gene rbcL were compared between M. hypoleuca, M. tripetala, and M. macrophylla var. macrophylla. All three methods consistently yielded low divergence values between the American species M. tripetala and its Asian sister taxa, M. officinalis var. biloba and M. hypoleuca (Nei's I = 0.712 and 0.809, respectively; D‐cpDNA = 0.083% for both pairs; D‐rbcL = 0.000% between M. tripetala and M. hypoleuca). The other two American species, M. fraseri var. fraseri and M. macrophylla var. macrophylla, neither of which is sister to the Asian taxa, exhibited much higher divergence from the Asian taxa. We interpreted the low divergence between M. tripetala and its Asian sister taxa as a result of recent separation (the late Miocene to early Pliocene), based on time estimates from molecular data as well as geological and paleoclimatic evidence. A comparison of our results with those of the earlier studies revealed a diverse array of levels of divergence between several eastern Asian and eastern North American species pairs. Though different extinction patterns and variation in molecular evolutionary rates may be partly responsible, this heterogeneous pattern of divergence is best explained by different times of disjunction in different taxa, which in turn suggests that the floristic similarity between the two continents was most likely attained by multiple migrations via both Bering and North Atlantic land bridges, or possibly even with involvement of dispersal.
Effects of atmospheric CO2 enrichment and foliar methanol application on net photosynthesis of sour orange tree (Citrus aurantium; Rutaceae) leaves
Authors: Idso Sherwood B. , Idso Kieth E. , Garcia Richard L. , Kimball Bruce A. , Hoober J. Kenneth
Published: January 2018

Foliar spray applications of 40% aqueous methanol were made to sunlit leaves of sour orange trees that had been grown continuously in clear‐plastic‐wall open‐top enclosures maintained out‐of‐doors at Phoenix, Arizona, for over 5.5 years in ambient air of approximately 400 μmol mol‐1 CO2 and in air enriched with CO2 to a concentration of approximately 700 μmol mol‐1. No unambiguous effects of the methanol applications were detected in net photosynthesis measurements made on foliage in either of the two CO2 treatments. The 75% increase in CO2, however, raised the upper‐limiting leaf temperature for positive net photosynthesis by approximately 7 C, which resulted in a 75% enhancement in net photosynthesis at a leaf temperature of 31 C, a 100% enhancement at a leaf temperature of 35 C, and a 200% enhancement at 42 C.
Reproductive significance of indirect pollen‐tube growth in Dalechampia (Euphorbiaceae)
Authors: Armbruster W. Scott , Martin Phillip , Kidd Janet , Stafford Ruth , Rogers Denise G.
Published: January 2018

Most species of Dalechampia have expanded stigmatic surfaces that extend from the stylar tip part way down the sides of the elongated styles. Pollen grains landing at the stylar tip grow tubes directly down the style to the ovary. Pollen grains landing on the lateral stigmatic surfaces, however, exhibit indirect pollen‐tube growth: the tubes grow first to the stylar tip, bend 180°, and then grow to the ovary. Indirect pollen‐tube growth appears to be reproductively important: more than half the arriving pollen lands on the lateral stigmatic surfaces, and virtually all of these grains produce tubes that grow indirectly to the ovary; pollen on the lateral surface fertilizes seeds about as effectively as pollen at the tip (with direct tube growth). Indirect pollen‐tube growth may be the result of a correlated response to selection for expanded stigmatic surfaces in Dalechampia, or it may be an adaptation to increase the intensity of pollen competition.
Inflorescence development in the “standard exotic” maize, Argentine popcorn (Poaceae)
Authors: Sundberg Marshall D. , LaFargue Christopher , Orr Alan R.
Published: January 2018

Argentine popcorn is an exotic race considered by some to be similar to the earliest cultivated maize. We used scanning electron microscopy to examine inflorescence development in both the tassel and ear. In our material, and under our conditions, both two‐ranked central tassel spikes and two‐ranked ears were observed as well as more typical four‐ranked structures. Subsequent development of spikelets and florets was similar to that observed in other varieties of maize and in their close relatives—the teosintes. We suggest that the switch from two‐ranked to four‐ranked inflorescences (a key trait difference between teosinte and maize) may be due to a change in developmental timing allowing an additional meristem bifurcation of axillary branch primordia prior to the initiation of spikelet pair primordia.
Pollen aperture heteromorphism is not due to unreduced gametophytes
Authors: Dajoz Isabelle , Mignot Agnès , Hoss Caroline , Till‐Bottraud Irène
Published: January 2018

Variations in ploidy level of the sporophyte are usually acknowledged as the main cause of polymorphism in pollen aperture number and pollen size. In heteromorphic species (two or more pollen morphs in all flowers of all plants) the different pollen types could thus be due to the presence of reduced and unreduced gametes. But data from the fossil record indicate that pollen aperture number has increased, suggesting that this trait may have evolved through selection. Our studies ofViola diversifoliahave shown that the different aperture morphs have different selective values, also indicating that this character could have evolved and is not always due to ploidy level variations. To test this hypothesis, we measured DNA content of the reproductive nucleus as a test of gametophytic reduction in four heteromorphic species ofViolaand in diploid and tetraploid individuals of aPetunia hybridaclone (which also served as a control to test for accuracy of the measurements). Our results show that aperture polymorphism is not due to gametophytic ploidy variations within plants and that variations in the proportions of the different pollen morphs are not correlated with variations of the amount of DNA in the sporophyte.
C3 photosynthesis in the gametophyte of the epiphytic CAM fern Pyrrosia longifolia (Polypodiaceae)
Authors: Martin Craig E. , Allen Mitchell T. , Haufler Christopher H.
Published: January 2018

Sporophytes of some epiphytic species in the fern genus Pyrrosia exhibit Crassulacean acid metabolism (CAM), generally considered to be a derived physiological response to xeric habitats. Because these species alternate between independent sporophytic and gametophytic generations yet only the sporophyte has been characterized physiologically, experiments were conducted to determine the photosynthetic pathways present in mature sporophytes, immature sporophytes, and gametophytes of Pyrrosia longifolia. Diurnal CO2 exchange and malic acid fluctuations demonstrated that although the mature sporophytes exhibited CAM, only C3 photosynthesis occurred in the gametophytes and young sporophytes. Consideration of the above results and those from previous studies, as well as the life cycle of ferns, indicates that the induction of CAM probably occurs at a certain developmental stage of the sporophyte and/or following exposure to stress. Elucidation of the precise mechanisms underlying this C3‐CAM transition awaits further research.
Population genetics ofCordia alliodora(Boraginaceae), a neotropical tree. 1. Genetic variation in natural populations
Authors: Chase Michael R. , Boshier David H. , Bawa Kamauit S.
Published: January 2018

We provide an estimate of genetic differentiation within and among 11 populations ofCordia alliodora, an economically important timber treeCordia alliodorais a widespread species that is distributed throughout Central and South America. Our survey of isozyme variation was conducted on material gathered for international provenance trials over approximately 1,000 km in Central America. Results from provenance trials indicate that there are significant differences between Atlantic and Pacific coast provenances for quantitative characters. Genetic data support some of these findings. Populations ofC. alliodorashow significant differences in allele frequency at various loci. Significant differences in multilocus allele frequencies occur at 13 of the 55 possible combinations. Eight of these 13 populations are situated on opposite coasts. This physical separation corresponds well with the results of provenance trials that indicate differentiation among the Atlantic and Pacific populations in quantitative morphological traits. We also found a significant negative correlation between levels of heterozygosity and the amount of rainfall, indicating that populations from the drier zone are genetically more heterogenous than populations from the wet zone. Our study indicates that in situ and ex situ conservation should accord high priority to the dry zone populations; furthermore, conservation of this widespread species would require preservation of multiple populations.
Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae). II. Selection gradients and hybrid fitness
Authors: Graham John H. , Freeman D. Carl , McArthur E. Durant
Published: January 2018

The dynamic equilibrium hypothesis proposes that hybrid zones are stabilized by a balance between dispersal and selection against hybrids. A key prediction of this hypothesis is that hybrids should have lower fitness than either parental taxon, regardless of habitat. Hybrid big sagebrush (Artemisia tridentatassp.tridentata× ssp.vaseyana) in two narrow hybrid zones do show greatly decreased recruitment. Hybrids in one zone also show increased browsing by grasshoppers, while those in the other zone have increased numbers of aphids. Overall herbivore loads, however, are not greater on the hybrids than on the parental subspecies. Browsing by mule deer is greatest on ssp.vaseyanain both hybrid zones. Incidence of galls is also greatest on ssp.vaseyanain one hybrid zone. Moreover, browsing by Artemisia weevils is greatest on ssp.tridentatain one hybrid zone. Hybrids produce more flowers than either ssp.tridentataor ssp.vaseyana, while seed production rates of hybrids do not differ from those of the parental taxa. Finally, hybrid seeds germinate as well as those of ssp.tridentataand better than those of ssp.vaseyana. Thus, our data do not support the dynamic equilibrium hypothesis.
The structure of phenotypic variation in gender and floral traits within and among populations of Spergularia marina (Caryophyllaceae)
Authors: Delesalle Véronique A. , Mazer Susan J.
Published: January 2018

We sampled four wild populations of the highly autogamous Spergularia marina (Caryophyllaceae) in California to detect and to measure the magnitude of within‐ and among‐population sources of phenotypic variation in gender and floral traits. From flowers and fruits collected from field and greenhouse‐raised plants, we measured ovule number, seed number, mean seed mass, pollen production (greenhouse families only), mean pollen grain volume (greenhouse families only), anther number, anther/ovule ratio, pollen/ovule ratio (estimated using different flowers for pollen than for ovules; greenhouse families only), petal number, and petal size. Using greenhouse‐raised genotypes, variation among maternal families nested within populations was evaluated for each trait to determine whether populations differ in the degree of maternally transmitted phenotypic variation. For each population, we used 15 greenhouse‐raised maternal families to estimate the broad‐sense heritability and genetic coefficient of variation of each floral trait. The magnitude and statistical significance of broad‐sense heritability estimates were trait‐ and population‐specific. Each population was characterized by a different combination of floral traits that expressed significant maternally transmitted (presumably genetic) variation under greenhouse conditions. Flowers representing two populations expressed low levels of maternally transmitted variation (three or fewer of nine measured traits exhibited significant maternal family effects on phenotype), while flowers representing the other two populations exhibited significant maternal family effects on phenotype for five or more traits. Our ability to detect statistically significant differences among the four populations depended upon the conditions under which plants were grown (field vs. greenhouse) and on the floral trait observed. Field‐collected flowers exhibited significant differences among population means for all traits except anther number. Flowers sampled from greenhouse‐raised maternal families differed among populations for all traits except ovule number, seed number, and petal size. We detected negligible evidence that genetic correlations constrain selection on floral traits in Spergularia marina.
Wood specific gravity and anatomy inHeliocarpus appendiculatus(Tiliaceae)
Authors: McDonald Suzanne S. , Williamson G. Bruce , Wiemann Michael C.
Published: January 2018

Specific gravity exhibits extremely large radial increases with distance from the pith inHeliocarpus appendiculatusTurcz. (Tiliaceae), a pioneer of neotropical wet forests. To determine some of the wood anatomical changes associated with this increase, wood samples taken at breast height from three trees were divided into 1.0‐cm‐long segments from pith to bark. Measurements were made of fiber wall thickness, fiber lumen diameter, and percentages of fibers, axial parenchyma, ray parenchyma, and vessels on sections prepared from each segment. The extreme radial increases in specific gravity were associated with increases in fiber wall thickness, decreases in fiber diameter, decreases in fiber lumen diameter, and changes in the relative proportions of fibers and parenchyma. The increase in percent fiber concomitant with a decrease in axial parenchyma was the most important contributor to the increase in specific gravity in this species. The best predictor of specific gravity was percent fibers (r= 0.91, 0.92, 0.94) or percent axial parenchyma (r= ‐0.92, ‐0.91, ‐0.95), two variables that were highly intercorrelated (r= ‐0.95, ‐0.98, ‐0.99).
Chloroplast DNA variations in sect. Cyclachaena of Iva (Asteraceae)
Authors: Miao Bomao , Turner Billie L. , Mabry Tom J.
Published: January 2018

Much argument has been occasioned by questions having to do with generic concepts in the tribe Heliantheae, subtribe Ambrosiinae, especially involving the genus Iva. Some workers recognize five genera (e.g., Leuciva, Chorisiva, Oxytenia, Cyclachaena, and Iva s. str.), while others recognize only a single genus Iva s. 1. Although chemical, pollen ultrastructure, and other morphological data have challenged the latter concept, relationships among the segregate taxa are still unclear. The current study used cladistic analyses of chloroplast DNA variation to investigate evolutionary relationships within Iva s. l., especially within the controversial section Cyclachaena. Nuclear rDNA was also utilized to test for hybrid origin of selected taxa. The results support the dismemberment of Iva s. l. and recognition of Iva s. str., largely because Iva s. l. is shown to be paraphyletic. Most members of the section Cyclachaena were found to have relatively close interspecific relationships. Nevertheless, cpDNA data strongly support two lineages within Cyclachaena. One lineage, including I. xanthifolia, I. acerosa, I. nevadensis, and I. dealbata, has a close relationship with the genus Euphrosyne. The second lineage includes only one species, I. ambrosiaefolia, which is closely related to Dicoria. The origin of I. ambrosiaefolia was shown to be monophyletic, not involving hybridization.
The role of hybridization in evolution: old wine in new skins
Authors: Rieseberg Loren H.
Published: January 2018

Perhaps no one has had a greater influence on the development of hybridization theory than Dr. Ledyard Stebbins. However, his contributions have not been restricted to his writings or lectures alone. Many of you have marveled at the great authority with which Dr. Stebbins identified the hybrid status, parentage, and ploidal level of plants in the field or on herbarium sheets. He didn't seem to need all the modern techniques that the current generation of botanists is both blessed and burdened with. For example, I remember a short field trip with Dr. Stebbins in the fall of 1984 to look at some sunflower hybrids near Davis. The plants were dead, only a few dried leaves, stalks, and floral heads remained, yet he confidently identified parental, hybrid, and backcrossed generations. Ironically, after 2 yr of careful molecular studies, I essentially confirmed his initial observations (Rieseberg, Soltis, and Palmer, 1988). Thus, I came to the conclusion that he was able to see things in plants that escaped less careful or less knowledgeable observers such as myself.
Temperature influences on root growth for Encelia farinosa (Asteraceae), Pleuraphis rigida (Poaceae), and Agave deserti (Agavaceae) under current and doubled CO2 concentrations
Authors: Drennan Philippa M. , Nobel Park S.
Published: January 2018

To help evaluate root distribution patterns, elongation rates of individual roots were measured as a function of soil temperature for Encelia farinosa (a C3 species), Pleuraphis rigida (C4), and Agave deserti (CAM), sympatric codominants in the northwestern Sonoran Desert. Measurements were made at current and doubled CO2 concentrations under winter and summer conditions of air temperature (day/night temperatures of 17 C/10 C and 33 C/22 C, respectively). The three species had different optimal temperatures for root elongation (Topt) under winter conditions (25 C for E. farinosa, 35 C for P. rigida, and 30 C for A. deserti); Topt increased by 2‐3 C under summer conditions for all three species. The limiting temperatures for elongation also acclimated from winter to summer conditions. The rate of root elongation at Topt was higher under summer than winter conditions for E. farinosa (9 vs. 6 mm d−1) and P. rigida (20 vs. 14 mm d−1), reflecting conditions for maximum photosynthesis; no difference occurred for A. deserti (9 vs. 10 mm d−1). Decreased elongation rates at extreme temperatures were associated with less cell division and reduced cell extension. The doubled CO2 concentration increased average daily root elongation rates for A. deserti under both winter (7%) and summer (12%) conditions, reflecting increased cell extension, but had no effect for the other two species. Simulations of root elongation as a function of soil temperatures showed that maximum elongation would occur at different depths (16‐20 cm for E. farinosa, 4‐8 cm for P. rigida, and 0‐4 cm for A. deserti) and during different seasons (winter to spring for E. farinosa, spring to summer for P. rigida, and all year for A. deserti), contributing to their niche separation. Shading of the soil surface moderated daily variations in soil temperature, reducing seasonal root elongation for winter and spring and increasing elongation for summer. Shading also altered root distribution patterns, e.g., optimal rooting depth for A. deserti and especially P. rigida increased for a hot summer day.
Localization of ubiquitin to differentiating vascular tissues
Authors: Stephenson Paul , Collins Beth A. , Reid Philip D. , Rubinstein Bernard
Published: January 2018

The selective degradation of proteins, an essential process of any developmental program, may entail conjugation of the protein to be destroyed to the polypeptide ubiquitin. Experiments were designed to localize ubiquitin as a first step in determining whether this molecule is crucial for certain developmental processes in plant tissues and cells. Antibodies to ubiquitinated protein were detected on tissue prints of cross sections of bean petioles (Phaseolus vulgaris, Fabaceae), cotton hypocotyls (Gossypium hirsutum, Malvaceae), and Coleus stems (Coleus x hybridus, Lamiaceae). For most of the material investigated, there appears to be an accumulation of ubiquitin antibodies in vascular tissues, but not preferentially in the abscission zone of bean petioles. Vascular localization was confirmed using immunohistochemical methods on fixed and sectioned internodal tissues of Coleus. Antibodies to ubiquitin are detected in parenchyma cells of the cortex and pith, but are most concentrated in the xylem, especially secondary xylem, and in the cambial region, and in the phloem. Thus, ubiquitin accumulates in certain vascular tissues, some of which may be undergoing programmed cell death. Ubiquitin can also be detected in nondifferentiating cells, and its level is elevated in rapidly dividing cambial cells.
Biomass and density responses in tallgrass prairie legumes to annual fire and topographic position
Authors: Towne E. Gene , Knapp Alan K.
Published: January 2018

Annually burned tallgrass prairie is purported to be a nitrogen‐limited system, especially when compared to unburned prairie. To test the hypothesis that legumes, potential nitrogen‐fixers, would increase in relative abundance in annually burned sites, we assessed their density and biomass for two seasons on upland and lowland soils in annually burned and unburned watersheds. Total legume density was significantly higher in burned (8.0 ± 1.0 [SE] stems/m2) than in unburned watersheds (3.0 ± 0.3 stems/m2). Species with higher (P < 0.05) densities in burned than in unburned prairie included Amorpha canescens, Dalea candida, Dalea purpurea, Lespedeza violacea, Psoralea tenuiflora, and Schrankia nuttallii. Desmodium illinoense was the only legume that responded negatively to annual fire. Total legume biomass did not differ between burned (11.3 ± 1.3 g/m2) and unburned prairie (10.5 ± 0.9 g/m2). Biomass productions of Dalea candida and Psoralea tenuiflora were higher (P < 0.05) in burned than in unburned sites, but biomasses of other legumes were similar between burn treatments. Average individual stem masses of Amorpha canescens and Baptisia bracteata were significantly greater in unburned than in burned prairie. Legumes were affected differentially by topographic location. Total legume density was higher (P < 0.05) on lowland soils (6.6 ± 1.0 stems/m2) than on upland soils (4.3 ± 0.5 stems/m2). However, total legume biomass was not different between lowland soils (12.0 ± 1.2 g/m2) and upland soils (9.9 ± 1.0 g/m2). Densities and biomasses of Amorpha canescens, Desmodium illinoense, and Lespedeza capitata were higher on lowland sites than on upland sites, whereas densities and biomasses of Baptisia bracteata and Dalea purpurea were higher on upland than on lowland soils. Most legume species are either fire tolerant or exhibit a positive response to fire and their persistence in annually burned prairie suggests that they may play an important role in the nitrogen budget of this ecosystem.