bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the short needle phenomenon in red spruce
Authors: Klein Richard M. , Adams Gregory T. , Liedeker Heiko , Perkins Timothy D.
Published: January 2018

Red spruce trees (Picea rubens Sarg.) occasionally produce short twigs bearing short needles. The frequency of short needle cohorts is positively correlated with both elevation and defoliation and they are found in greater numbers on trees that regularly experience winter injury. Short needles are smaller, have lower fresh and dry weights, and reduced volumes compared with normal needles. They have reduced cross‐sectional areas due to smaller areas of stelar and mesophyll tissue systems. Individual mesophyll cells, however, have the same cross‐ and longitudinal sectional areas. On a weight or volume basis, both short and normal needles contain similar amounts of chlorophyll and carotenoid pigments. When pigment concentration was calculated on a unit needle or a needle area base, short needles contain more pigment than normal needles. Short needles appear to have a greater photosynthetic efficiency as determined by fluorescence measurements.
The effect of accelerated sand accretion on growth, carbohydrate reserves, and ethylene production in Ammophila breviligulata (Poaceae)
Authors: Seliskar Denise M.
Published: January 2018

In a 3‐yr field study Ammophila breviligulata responded positively to sand accretion by maintaining plant height above a rising sand surface. Vertical growth for treated plants was approximately 80 cm over 3 yr. Bunch size did not differ between treated and control plants in the first or second year. But by Year 3, bunch circumference, number of stems per bunch, and plant height above the sand surface were significantly greater in plants receiving accelerated sand accretion. During the first year, treated plants flowered significantly less than controls. The greater vertical growth necessary for the treated plants may have depleted the energy reserves of a young rhizome system otherwise used for inflorescence production. The percent of the total nonstructural carbohydrates in rhizomes in the form of sugar was greater in plants in the accelerated sand accretion treatment, perhaps sustaining the necessary rapid vertical growth. To determine whether ethylene plays a role in stimulating stem elongation, endogenous ethylene accumulation was measured in plants in the field and seedlings in the greenhouse exposed to sand accretion. Treated plants responded by accumulating higher levels of ethylene in their stems, after 10 and/or 30 d, than did control plants. However, plants treated with exogenous ethylene exhibited growth and elongation inhibition.
Characterization of a rice pollen‐specific gene and its expression
Authors: Zou Ji‐tao , Zhan Xiao‐yan , Wu Hen‐ming , Wang g , Cheung Alice Y.
Published: January 2018

Pollen development requires a large number of genes expressed in both sporophytic and gametophytic tissues. We have isolated a pollen‐specific gene, PS1, from rice. PS1 is a unique gene in the rice genome and encodes a 164 amino acid long protein. RNA blot analysis shows that PS1 mRNAs accumulate specifically in rice anthers. When introduced into rice tissues by microprojectile bombardment, the PS1 promoter drives expression of a marker gene, β‐glucuronidase, specifically in rice pollen. The PS1 gene and the deduced amino acid sequence of the PS1 protein share significant levels of homology with another monocot pollen‐specific gene—the maize Zm‐13 gene and its deduced protein, respectively. PS1 also shows some homology with the dicot tomato anther‐specific gene LAT‐52. Interestingly, the structure of the PS1 gene is more similar to that of the LAT‐52 gene than to Zm‐13. The coding regions of both PS1 and LAT‐52 are interrupted by a single intron, and the positions of the introns are conserved in these genes. Moreover, there is considerable sequence homology in the introns of the PS1 and LAT‐52 genes in regions immediately upstream of the 3' splice sites. The upstream regulatory sequences of the PS1 gene show several regions of homology with other pollen‐ or anther‐specific genes from a number of plant species. The conservation of coding sequences of PS1 from rice, Zm‐I3 from maize, and LAT‐52 from tomato suggests a functional conservation of their gene products. Similarities in the regulatory regions of PS1 and other anther‐ or pollen‐specific genes among monocotyledonous and dicotyledonous species indicate that at least some regulatory features controlling gene expression in male reproductive tissues are conserved. This is supported by the preservation of pollen‐specific expression from the rice PS1 promoter when it is introduced into tobacco plants by Agrobacterium Ti plasmid‐mediated transformation.
Antheridiogen, dark spore germination, and outcrossing mechanisms in Bommeria (Adiantaceae)
Authors: Haufler Christopher H. , Welling Christopher B.
Published: January 2018

Isozymic analyses of the patterns of genetic variability in sporophyte populations have demonstrated that most fern species have outcrossing breeding systems. However, because fertilization takes place during the ephemeral, diminutive gametophyte generation, direct observation of breeding systems in nature has not been possible. Recent discoveries of soil‐bound spore banks suggested that genetic diversity could be stored beneath the surface and subsequently released by appropriate chemical cues. Previous studies demonstrated that Bommeria sporophytes are the product of outcrossing, that their gametophytes carry high levels of genetic load, and that they produce and respond to antheridiogen. Research reported here demonstrated that Bommeria spores can survive long‐term storage but will not germinate in the dark. Antheridiogen, however, will release spores from this light requirement and stimulate germination. Higher concentrations of antheridiogen result in higher germination rates. Gametophytes grown in the dark on antheridiogen‐enriched agar form antheridia and release actively swimming sperms. Thus, spores housed beneath the soil surface could remain dormant until stimulated to germinate by antheridiogen secreted by surface‐dwelling, archegoniate gametophytes. Sperm released from these subterranean gametophytes could fertilize eggs on the surface. Because spores housed in the soil are likely to be genetically different than those at the surface, heterozygous sporophytes would be more likely to result. Discovering that Bommeria species contain all of the prerequisites for this proposed outcrossing mechanism provides an explanation for the maintenance of genetic diversity in some fern populations.
Plesiomorphic and apomorphic pollen structure characteristics of anthemideae (Asteroideae: Asteraceae)
Authors: Vezey Edward L. , Watson Linda E. , Skvarla John J. , Estes James R.
Published: January 2018

Anthemideae (Asteroideae: Asteraceae) pollen grains have basal columellae, a structural type called “anthemoid” in earlier publications. To survey structure variation in Anthemideae pollen, we examined freeze‐sectioned grains from 45 species within 23 representative genera using scanning electron microscopy (SEM). From resulting data and a literature review, we concluded that: 1) pollen of Anthemideae taxa is qualitatively identical except forUrsinia(grains essentially lack basal columellae) and theArtemisiagroup (branches of basal columellae are complex and interwoven); 2) the double tectum (a term introduced in this study) is a synapomorphy of Asteroideae and plesiomorphic in Anthemideae; 3) apomorphies of Anthemideae grains include large basal columellae, a thick foot layer, and absence of internal foramina; and 4) Anthemideae pollen is qualitatively different from similar pollen in Lactucoideae, a distinction we recognized by restricting “anthemoid” to Anthemideae grains.Ursiniagrains have occasional basal columellae and features resembling rolled‐up columellae; we consider these vestiges of a reversal to the plesiomorphic condition. To assess quantitative structural variation, 2,200 image‐analysis measurements were taken from 73 SEM micrographs. Intrageneric variation was analyzed by standard deviation, and intergeneric variation by principal components analysis. Compared to other Anthemideae taxa, the structural elements ofArtemisiagrains have reduced dimensions and variability. Otherwise, structural radiation of Anthemideae pollen has produced a phenetic continuum.
Ontogeny of the vascular bundles and contiguous tissues in the maize leaf blade
Authors: Bosabalidis Artemios M. , Evert Ray F. , Russin William A.
Published: January 2018

The patterns of initiation and early development of the minor and major veins in the flat portion of the leaf blade of maize (Zea mays L.) follow similar patterns. The veins and their associated bundle sheath cells commonly arise from cell assemblages derived from a single cell lineage, or longitudinal file of cells, rather than from two “half vein units” derived from different cell lineages. In addition, apparently, none of the vascular cells derived from the procambium is directly related ontogenetically to a bundle sheath cell. In veins derived from larger cell assemblages, the lateral bundle sheath cells are more closely related ontogenetically to the mesophyll cells, which are derived from the ground meristem, than to the vascular cells, which are derived from procambium. The bundle sheath cells, accordingly, are interpreted as being ground meristem in origin.
A cytogenetic study of Eriophyllum confertiflorum (Compositae, Helenieae)
Authors: Mooring John S.
Published: January 2018

Meiotic analyses of 176 plants from 130 populations of Eriophyllum confertiflorum var. confertiflorum showed that diploids (n = 8) and tetraploids were about equally frequent and that hexaploids and octoploids were rare. Supernumerary chromosomes were found in 14% of the individuals; other meiotic aberrations were uncommon. Eriophyllum confertiflorum var. tanacetiflorum is octoploid. Migration from southwest North America, tolerance of aridity, and spontaneous origin of polyploids may explain the nonrandom distribution of cytotypes in E. confertiflorum var. confertiflorum. Artificial intravarietal crosses of E. confertiflorum var. confertiflorum yielded vigorous, bivalent‐forming progeny with mean pollen stainabilities of 41%‐96% and 88%‐90% at the diploid and tetraploid levels, respectively. Tetraploid x diploid crosses gave triploids in one case and tetraploids in another. The progenies of some artificial crosses between distant populations of E. confertiflorum var. confertiflorum had significantly lower rates of germination and pollen viability.
Genetic variation associated with chronic water and nutrient stress in pinyon pine
Authors: Cobb Neil S. , Mitton Jeffry B. , Whitham Thomas G.
Published: January 2018

We examined how genotypic variation at the glycerate dehydrogenase (GLY) locus in pinyon pine might be affected by environmental stress and herbivory. We compared GLY allelic and genotypic frequencies among mature and juvenile trees growing in stressful cinder soil and adjacent sandy‐loam soil. While no association was found with herbivory, three lines of evidence support the hypothesis that GLY slow homozygotes (SS) are selected for under conditions of environmental stress. 1) We found no differences at the GLY locus between juvenile and mature trees growing in sandy‐loam soil. 2) However, in the stressful cinder soil we found a lower frequency of SS homozygotes in juvenile trees than in mature trees, suggesting that selection has occurred in one generation. 3) Using biomass as a measure of fitness, SS homozygotes were superior to other GLY genotypes in cinder soil. Two lines of evidence were inconsistent with the hypothesis of selection for SS homozygotes in stressful environments. 1) SS homozygote frequency between habitats was not significantly different, suggesting that too few generations have passed for differentiation to occur, and/or insufficient selection pressure. 2) The low frequency of SS homozygote juvenile trees growing in cinder soil suggests that counterbalancing selection may prevent SS homozygotes from increasing in the population.
Conservation biology of a rare plant species,Eriocaulon kornickianum(Eriocaulaceae)
Authors: Watson Linda E. , Uno Gordon E. , McCarty Newell A. , Kornkven Amy B.
Published: January 2018

Historical and current ecological and genetic factors were examined in western popultions ofEriocaulon kornickianumto determine the cause and consequence of rarity in this disjunct species and to assess its extinction vulnerability. Reproductive biology was examined, which included an examination of breeding systems, seed set, and pollen viability. Recruitment into and maintenance of the populations was evaluated using seed bank estimates. A disturbance study was conducted that examined the effects of competing vegetation and associated species, and included clipping, burning, and artificial seeding. Enzyme electrophoresis was used to measure genetic variation in an effort to examine gene flow within and among populations. Many factors are contributing to the decline of the western populations of this species and include an annual or weak perennial life history, no vegetative reproduction, low seed set, little seed bank contribution to population growth and maintenance, genetic homogeneity, a restricted habitat, and poor competitive abilities. Continuing studies of genetic variation are being used to examine historical factors that may have resulted in a genetic bottleneck observed in the western populations.
Chloroplast DNA systematics: a review of methods and data analysis
Authors: Olmstead Richard G. , Palmer Jeffrey D.
Published: January 2018

The field of plant molecular systematics is expanding rapidly, and with it new and refined methods are coming into use. This paper reviews recent advances in experimental methods and data analysis, as applied to the chloroplast genome. Restriction site mapping of the chloroplast genome has been used widely, but is limited in the range of taxonomic levels to which it can be applied. The upper limits (i.e., greatest divergence) of its application are being explored by mapping of the chloroplast inverted repeat region, where rates of nucleotide substitution are low. The lower limits of divergence amenable to restriction site study are being examined using restriction enzymes with 4‐base recognition sites to analyze polymerase chain reaction (PCR)‐amplified portions of the chloroplast genome that evolve rapidly. The comparison of DNA sequences is the area of molecular systematics in which the greatest advances are being made. PCR and methods for direct sequencing of PCR products have resulted in a mushrooming of sequence data. In theory, any degree of divergence is amenable to comparative sequencing studies. In practice, plant systematists have focused on two slowly evolving sequences (rbcL and rRNA genes). More rapidly evolving DNA sequences, including rapidly changing chloroplast genes, chloroplast introns, and intergenic spacers, and the noncoding portions of the nuclear ribosomal RNA repeat, also are being investigated for comparative purposes. The relative advantages and disadvantages of comparative restriction site mapping and DNA sequencing are reviewed. For both methods, the analysis of resulting data requires sufficient taxon and character sampling to achieve the best possible estimate of phylogenetic relationships. Parsimony analysis is particularly sensitive to the issue of taxon sampling due to the problem of long branches attracting on a tree. However, data sets with many taxa present serious computational difficulties that may result in the inability to achieve maximum parsimony or to find all shortest trees.
The stigmatic orifice in Cassia, Senna, and Chamaecrista (Caesalpiniaceae): morphological variation, function during pollination, and possible adaptive significance
Authors: Dulberger Rivka , Smith Mary B. , Bawa Kamal S.
Published: January 2018

In species of Cassia, Senna, and Chamaecrista an orifice leading into a stigmatic cavity is present at the tip of the style. The size of the orifice, the occurrence and morphology of surrounding trichomes or papillae, and the occurrence of a drop of secretion at its outlet were recorded in 17 species belonging to the three genera of the subtribe Cassiinae. Much of the observed variation in these characters apparently reflects different modes of pollen capturing and varying degrees of secretion exposure. In some of the species studied no secretion was noticeable at the entrance to the stigmatic cavity. The unusual type of stigma in the Cassiinae does not fit into any of the recognized main groups of angiosperm stigmas. It is conjectured that in the buzz‐pollinated Cassiinae species with small stigmatic orifices, the secretory material is retained within the stigmatic cavity, to be extruded by vibratory movements of the style induced by a buzzing bee. It is also hypothesized that in the wet tropics, concealment of secretory materials within a cavity prevents their washing away or dilution by rain. Furthermore, in the Cassiinae, the considerable variation in features of the style and of the stigma may function as mechanisms isolating between sympatric, visitor‐sharing, concurrently blooming species.
Morphology and phylogenetic interrelationships of the Asteraceae, Calyceraceae, Campanulaceae, Goodeniaceae, and related families (Asterales)
Authors: Gustafsson Mats H. G. , Bremer Kåre
Published: January 2018

In search for the sister group of the Asteraceae, morphological evidence was assembled for investigating the relationship between the Asteraceae and those families most frequently considered to be their closest relatives, in particular the Calyceraceae, Campanulaceae (along with the frequently included Lobeliaceae, Cyphiaceae, Cyphocarpaceae, and Nemacladaceae), and Goodeniaceae (and the sometimes included Brunoniaceae). Several other families that have been associated with this group of families, the “Asterales‐Campanulales‐complex,” were also considered: Pentaphragmataceae, Sphenocleaceae, Stylidiaceae, Donatiaceae, Menyanthaceae, and Argophyllaceae. In order to delineate the complex more precisely, another eight putatively related families were also included in the analysis. Cladistic parsimony analysis of 46 morphological and chemical characters for the 23 families was undertaken. Stability of the branches was estimated by the number of extra steps necessary to lose the group, as well as by the number of reweighted extra steps (using rescaled consistency indices) necessary to lose the group (a new approach). The results indicate that there is a monophyletic group of 14 families comprising those of the Asterales‐Campanulales‐complex as well as Pentaphragmataceae, Sphenocleaceae, Stylidiaceae, Donatiaceae, and Menyanthaceae; this group is recognized as the order Asterales. Within the order, the Asteraceae, Calyceraceae, Brunoniaceae, and Goodeniaceae form one comparatively well‐supported clade and the five families of the Campanulaceae sensu lato form another well‐supported clade.
When figs wait for pollinators: the length of fig receptivity
Authors: Khadari Bouchaib , Gibernau Marc , Anstett Marie‐Charlotte , Kjellberg Finn , Hossaert‐McKey Martine
Published: January 2018

In plant species with an obligate species‐specific pollinator, gamete encounter is a critical phase in the success of reproductive strategies. One of the key factors in the success of gamete encounter, the length of female receptivity, has been rarely studied experimentally. In Ficus species (Moraceae), each exclusively associated with its specific pollinating wasp, the receptive female phase of individual syconia was believed to last only a few days. This estimate, based on field observations of pollinator arrivals, neglected the possibility that unpollinated syconia may remain receptive for a prolonged period. In two distantly related fig species (F. carica and F. aurea), we measured experimentally the duration of receptivity of individual syconia protected from pollinator visits. For these two species, receptivity lasted from 2 to 3 wk. Syconia pollinated at any time during this period of receptivity are capable of setting seeds. Furthermore, it has been assumed that female syconium receptivity stops quickly after pollinator visitation. Our experiments showed that syconia of both species are able to extend their receptive period for a few days longer when visited only by a single wasp. The demonstration of a long duration of female receptivity has important consequences for understanding the maintenance of the fig‐wasp mutualism.
Estimating volume flow rates through xylem conduits
Authors: Lewis Ann M. , Boose Emery R.
Published: January 2018

We discuss the errors in common approximations of the volume flow rate for laminar flow through conduits with noncircular transverse sections. Before calculating flow rates, ideal geometric shapes are chosen to represent the noncircular transverse sections. The Hagen–Poiseuille equation used with hydraulic diameter underestimates the volume flow rate for laminar flow through conduits even with such ideal shapes. Correction factors that have been proposed for the Hagen–Poiseuille equation also lead to underestimates of the volume flow rate for those shapes. The exact solutions are sometimes difficult to attain, but rates calculated using the exact solutions for the ideal shapes may be as much as five times higher than the approximated rates for common transversely elongated shapes. Either the exact solutions or the approximations may be used to calculate volume flow rates through the xylem of plants. Both of these methods actually approximate flow through the original conduits because the shapes used are approximations of the conduits’ transverse sections. We recommend using the exact solutions whenever possible; they should be closer to the real solution than other approximations. We give tables of correction factors for use in the cases where calculating volume flow rate from the approximate solution, the Hagen–Poiseuille equation, is more feasible. Obtaining theoretical volume flow rates that are larger than previously thought highlights the need to clarify the causes of differences between the theoretical rates and the smaller measured volume flow rates in plant xylem.
Assessment of pollen viability in hand‐pollination experiments: a review
Authors: Stone Judy L. , Thomson James D. , Dent‐Acosta Sara J.
Published: January 2018

Pollen viability is known to decline, sometimes rapidly, with age and exposure to environmental stresses. Because of the potential impact of nongenetic factors on the ability of pollen to fertilize ovules, researchers conducting hand‐pollinations should attempt to control the freshness or viability of pollen used. We surveyed hand‐pollination experiments published in seven major journals from 1980 until mid‐1994, collecting data on the purpose of the experiment, the degree of care taken to ensure pollen viability, and the degree of care taken to ensure stigmatic receptivity. Fewer than one‐third of the papers reported any consideration of pollen freshness or viability, whereas over one‐half made some mention of stigmatic receptivity. Pollen freshness or age was mentioned more frequently for some types of experiments than for others. Experiments attempting to compare performance of different donors are especially susceptible to error when donor pollen is not treated equally or otherwise controlled for viability. We discuss strengths and weaknesses of tests to measure pollen viability, and experimental protocols to reduce differences in pollen condition across donors.
SIMULATION ANALYSIS OF CROP ROTATION EFFECTS ON WEED SEEDBANKS
Authors: Jordan Nicholas , Mortensen David A. , Prenzlow Danielle M. , Cox K. Curtis
Published: January 2018

A population‐projection model was developed for a depth‐structured weed seed population (employing transition matrices to model seed survival, germination, and vertical movement) and plant survival and seed production. Abutilon theophrasti and Setaria viridis seedbank dynamics were simulated in continuous corn and in two crop rotations (corn‐soybean and oat/clover‐corn‐soybean‐corn). Results suggest that crop rotation can nearly eliminate S. viridis seedbanks, while A. theophrasti seedbanks are less affected. Sensitivity analysis indicated that variation in seed survivorships over winter influenced population dynamics most strongly. Other seed survivorships were also highly influential, while plant survivorships and per‐plant seed production had smaller effects. These results highlight the potential value of weed control measures aimed at seed.
DISTURBANCE, LIFE HISTORY STRATEGIES, AND SEED FATES IN ALPINE HERBFIELD COMMUNITIES
Authors: Chambers Jeanne C.
Published: January 2018

Species responses to disturbance are governed primarily by their life history and physiological traits and by the characteristics of the disturbance. Species reproductive traits are especially important in determining the potential of species to establish and to persist following disturbance. Herein, I review available literature on relationships among disturbance, species life histories, and seed fates in tundra environments. Research conducted on these relationships in alpine herbfield vegetation on the Beartooth Plateau, Montana, over the past 9 yr by my colleagues and myself is synthesized. In tundra environments, species reproductive capacities are often similar to those in more temperate environments, but short, cool growing seasons constrain seed production and reduce seedling growth and survival. Highly variable growing season conditions result in large differences in seed production and seedling establishment among years. On disturbed sites, disturbance characteristics determine the seed and seedling environment and influence rates of establishment. In these windy environments, relationships among soil surface characteristics and seed morphological attributes determine both the horizontal and vertical movement of seeds on exposed soils. Once seeds are incorporated into the soil, soil physical and chemical properties determine temperature and nutrient regimes and have the greatest effects on seed germination and seedling growth and survival. Examining the seed fates of herbfield species with varying life histories illustrates that the identities of species that establish following disturbance are largely predictable from their reproductive traits. Disturbance characteristics determine the success of different reproductive strategies and significantly influence community structure.
DIFFERENTIAL STAINING WITH ORCEIN, GIEMSA, CMA, AND DAPI FOR COMPARATIVE CHROMOSOME STUDY OF 12 SPECIES OF AUSTRALIAN DROSERA (DROSERACEAE)
Authors: Sheikh Shamimul Alam , Kondo Katsuhiko
Published: January 2018

Differential stainings with orcein, Giemsa, CMA, and DAPI were compared in 12 species of Western Australian Drosera. Chromosome numbers of D. roseana, D. barbigera, D. leioblasta, D. oreopodion, D. mannii, D. walyunga, D. sewelliae, D. helodes, and D. echinoblasta are reported here for the first time. A marked difference regarding chromosome number was observed in Drosera dichrosepala (2n = 12) from that of the previous report (2n = 18). The karyotypes of the species showed commonly that degree of asymmetry in chromosome length was directly proportional to the mean chromosomal length whereas the number of chromosomes was inversely proportional. Bimodal karyotypes were observed in D. oreopodion, D. walyunga, D. barbigera, and D. echinoblasta, which perhaps resulted from interspecific hybridization of the former two and fragmentation in the latter two. Sat‐chromosomes found in D. falconeri, D. sewelliae, D. helodes, and D. echinoblasta responded differently in differential staining. The C and fluorescent bands at the mostly terminal region revealed that maximum C‐positive heterochromatin‐rich segments, GC‐rich segments, and AT‐rich segments were accumulated at the ends of Drosera chromosomes. Some chromosomes could be identified by their specific staining property. On the basis of chromosome number and C‐ and fluorescent‐banding pattern, we suggest that D. helodes and D. sewelliae are closely related.
Vessels in the roots of Barclaya rotundifolia (Nymphaeaceae)
Authors: Schneider Edward L. , Carlquist Sherwin
Published: January 2018

Scanning electron microscope (SEM) studies of paraffin‐sectioned material of stems and roots of Barclaya rotundifolia Hotta revealed perforations on tracheary elements of roots, but not on those of stems. End walls of vessels are identical with lateral walls except for the presence of perforations. Perforations can only be clearly revealed with SEM, and this method is advocated for further study of tracheary elements of Nymphaeaceae in particular, and primary xylem of ∗∗∗angiosperms in general. Vessel presence may be related to the habitat of this species, which unlike other members of the Nymphaeaceae (sensu stricto) has only aerial leaves and a rhizomatous system that is not inundated for prolonged periods.
Exceptional seed longevity and robust growth: ancient Sacred Lotus from China
Authors: Shen‐Miller J. , Mudgett Mary Beth , Schopf J. William , Clarke Steven , Berger Rainer
Published: January 2018

A 1,288 ± 271‐yr‐old (1,350 ± 220 yr BP, radiocarbon age) seed of Sacred Lotus (Nelumbo nuciferaGaertn.) from an ancient lake bed at Pulantien, Liaoning Province, China, has been germinated and subsequently radiocarbon dated. This is the oldest demonstrably viable and directly dated seed ever reported, the preserved relict of one of the early crops of lotus cultivated by Buddhists at Pulantien after introduction of the religion into the region prior to 372 A.D. A small portion of the dry pericarp of a second lotus fruit from the same locale has been dated as being 332 ± 135‐yr‐old (270 ± 60 yr BP, radiocarbon age) by accelerator mass spectroscopy at the Lawrence Livermore National Laboratory. This polycentenarian seed not only germinated but is still growing (since March, 1994). Of six old lotus fruits tested, two‐thirds germinated, almost all in fewer than 4 d, as rapidly as fruits harvested from the progeny of Pulantien Sacred Lotus plants (under cultivation by the National Park Service in Washington, DC), and more rapidly than fresh fruits of Yellow Lotus [N. lutea(Willd.) Pers.]. Growth of the old lotus is robust: rhizome formation and leaf emergence at rhizome nodes are more rapid than those of the Pulantien progeny, although the leaf width is smaller. Activity of the protein‐repair enzyme L‐isoaspartyl methyltransferase in the old lotus seed is persistent during germination and is as robust as that in the progeny, and the degree of aspartyl racemization in proteins of the two groups of plants is minimal and essentially identical. The six dated ancient Sacred Lotus fruits range in age from 95 to 1,288 yr (with a mean age of 595 ± 380 yr), evidently reflecting their production, deposition, and preservation at varying times during the intervening millennium.
Restriction fragment length polymorphisms reveal considerable nuclear divergence within a well‐supported maternal clade in allium section Cepa (Alliaceae)
Authors: Bradeen James M. , Havey Michael J.
Published: January 2018

Maternal phylogenies estimated by restriction fragment length polymorphisms (RFLPs) in the chloroplast DNA (cpDNA) delineated a well‐supported clade containing Allium altaicum, A. cepa (bulb onion), A. fistulosum (Japanese bunching onion), A. galanthum, and A. vavilovii. Few polymorphic restriction‐enzyme sites were detected among the wild and cultivated species within this clade, and relationships could not be confidently estimated. Random nuclear RFLPs revealed considerable variation among these species and three distinct groups were identified (Altaicum, Cepa, and Galanthum). Relationships were estimated using principal components and cluster analyses of the Jaccard's similarity matrix. For five out of six analyses, nuclear phylogenies estimated by UPGMA and neighbor joining of the Jaccard's similarity matrix produced a weakly supported monophyletic lineage for A. altaicum, A. fistulosum, and A. galanthum, disagreeing with maternal phylogenies that produced a weakly supported monophyletic lineage for A. altaicum, A. fistulosum, A. cepa, and A. vavilovii. Allium oschaninii was closely related to A. galanthum and these two species may represent the progenitor types. Overall, restriction‐enzyme analyses of the nuclear and cpDNA produced few synapomorphies among closely related species in Allium section Cepa.
In situ plastid and mitochondrial DNA determination: Implication of the observed MINIMAL PLASTID GENOME NUMBER
Authors: Maguire Mark J. , Goff Lynda J. , Coleman Annette W.
Published: January 2018

The total loss of plastid DNA has never been reported for any alga or plant cell line, with the sole exception of the protozoanEuglena,yet plastid distribution at mitosis is apparently stochastric (Birky and Skavaril,Journal of Theoretical Biology,vol. 106, pp. 441–447, 1984) and accidental loss might be expected. It is not obvious how stem cells of photosynthetic eukaryotes avoid this problem. The chrysophyte algaOchromonas danica,described as having but one or two plastids, can proliferate indefinitely without the benefit of photosynthesis. Under such conditions its plastid genome copy number per cell might drop to the absolute minimum compatible with maintaining its inheritance. In situ quantitation ofOchromonasplastid DNA in both photosynthetic and enriched mixotrophic growth, and in heterotrophic growth in prolonged darkness, suggests that plastids are capable of very wide variation (7 to >;200 genomes/plastid) in their DNA content, and likewise, cells can vary from one to >;8 plastids per cell, with total genomes numbers from 7 to >;1,000 per cell. Among many growth conditions tested, the smallest plastids were found in rapidly dividing cells grown in the dark, many of which contained but one plastid. The inability to find plastids with fewer than seven plastid genome equivalents of DNA, even in these rapidly multiplying cells grown in total darkness for months, suggests that multiple copies of the plastid genome may be very carefully maintained, even in the prolonged absence of photosynthesis. This implies that multiple copies are important for reasons other than photosynthetic capability; two possibilities are the biosynthetic steps necessary for eukaryote cell survival known to occur solely within a plastid, and/or the potential that multiple plastid genome copies provide to escape the effects of Muller's ratchet.
Ten‐year seed bank and vegetation dynamics of a tidal freshwater marsh
Authors: Leck Mary Allessio , Simpson Robert L.
Published: January 2018

A decade‐long examination was made of recruitment and establishment in a tidal freshwater high marsh along the Delaware River. Over the 10 yr of the study, seed bank, field seedlings, and vegetation showed variable patterns and significant year‐to‐year fluctuations. Patterns of each species were unique, perhaps the result of specific germination and/or establishment requirements and seedling morphology. For a given species there was little correlation among seed bank, seedling, and vegetation patterns, and germination success did not guarantee establishment. Species diversity showed significant year‐to‐year fluctuation, but there was no trend, and perennials did not change in importance during the 10‐yr period. Because four annual species (Bidens laevis, Cuscuta gronovii, Impatiens capensis, and Polygonum arifolium) composed over 90% of the seed bank and field seedlings, and 58‐89% ( = 70 ± 4) of the cover, community dynamics were dependent on seedling recruitment. For a given species life history stages (seed bank, field seedlings, and vegetation) were not predictable over the temporal scale of a decade. It is predicted, however, that if hydrology remains unchanged, the same suite of species will persist. The importance of the parasite Cuscuta gronovii is noteworthy.
A fully fertile intergeneric hybrid derivative from Argyroxiphium sandwicense SSP. macrocephalumDUBAUTIA MENZIESII(Asteraceae) and its relevance to plant evolution in the Hawaiian Islands
Authors: Carr Gerald D.
Published: January 2018

Achenes collected from natural putative F1 intergeneric hybrids involving Argyroxiphium sandwicense DC. ssp. macrocephalum (A. Gray) Meyrat and Dubautia menziesii (A. Gray) Keck were germinated and grown in cultivation. One of these apparent B1 hybrids that approached D. menziesii in morphology exhibited greatly increased fertility over the F1 (79% vs. 9% pollen stainability), and was used as a female parent to generate a B2 progeny by backcrossing a second time to D. menziesii. The B2 was surprisingly uniform. One individual that flowered was fully fertile (99% pollen stainability). Its floral and vegetative features were extremely similar to those of the recurrent parent, D. menziesii. Observations suggest that plants of similar origin may exist under natural conditions and that the close relatives, D. platyphylla (A. Gray) Keck and D. dolosa (Degener & Sherff) G. Carr, may have originated from the same or a similar intergeneric hybrid combination. Because many other analogous situations occur in the silversword alliance and elsewhere in the Hawaiian flora, it is concluded that hybridization is an evolutionarily important phenomenon, especially in unstable geological systems. Although the Hawaiian archipelago is a premier example of such instability, continents are not immune to natural perturbations. Therefore, hybridization, as a mechanism that greatly extends the size of gene pools available for recombination, should also be expected to play an important evolutionary role in continental floras.
Stomatal characteristics, conductance ratios, and drought‐induced leaf modifications of semiarid grassland species
Authors: Hardy Joyce Phillips , Anderson Val Jo , Gardner John S.
Published: January 2018

Seventeen greenhouse‐grown grasses from the Nebraska Sandhills region were surveyed for foliar stomatal density and distribution, closed guard cell lengths, open stomatal apertures, and surface characteristics (using scanning electron microscopy), surface conductance (using a steady‐state porometer), and drought‐induced leaf modifications. Leaves of C3species exhibited a proclivity toward being amphistomatic or hyperstomatic, while C4species tended to be more hypostomatic. Leaf modification, when it occurred, resulted in the enshrouding of the adaxial surface. Conductance data showed functional amphistomaty in most species, revealing differential functioning of adaxial and abaxial stomata. Conductance patterns were not closely related to stomatal aperture per unit area leaf surface or to stomatal distribution patterns. Lowered adaxial: abaxial conductance ratios, increased stomatal density, reduced stomatal size, and less drought‐induced leaf modification were seen in C4grasses as compared with C3grasses. C3range and C3meadow species did not differ in conductance ratios, density ratios, or stomatal size, although meadow species exhibited much greater drought‐induced leaf modification. Postulations involving correlation of adaxial: abaxial conductance ratios to stomatal distribution patterns, and assumptions of stomatal distribution based upon habitat and/or photosynthetic pathway may be erroneous. These characteristics may be of limited usefulness as morphological indicators in the search for drought‐tolerant ecotypes of prairie grasses.
The haustorium of the root parasiteTriphysaria(Scrophulariaceae), with special reference to xylem bridge ultrastructure
Authors: Heide‐Jørgensen Henning S. , Kuijt Job
Published: January 2018

Haustoria ofTriphysaria pusillaandT. versicolorsubsp. faucibarbatafrom a natural habitat were analyzed by light and electron microscopy. Secretory trichomes (root hairs) participate in securing the haustorium to the surface of the host root. The keel‐shaped intrusive part of the secondary haustorium penetrates to the depth of the vascular tissue of the host. Some of the epidermal interface cells differentiate into xylem elements. A significant number of haustoria do not differentiate further, but in most haustoria one to five of the epidermal xylem elements terminate a similar number of xylem strands. The strands mostly consist of vessel members and they connect host xylem or occasionally host parenchyma to the plate xylem adjacent to the stele of the parasite root. Each strand of this xylem bridge is accompanied by highly protoplasmic parenchyma cells with supposed transfer cell function. Increased surface area of the plasmalemma occurs in these cells as it does in interface parenchyma cells. Graniferous tracheary elements are restricted to the haustorium and occur most frequently in the plate xylem. The plate xylem is also accompanied by highly protoplasmic parenchyma cells. Hyphae of mycorrhizal fungi of the host root occasionally penetrate into the distal part of the xylem bridge. We combine structural observations and physiological facts into a hypothesis for translocation of water and nutrients between host and parasite. Some evolutionary aspects related to endogeny/exogeny of haustoria are discussed, and it is argued that theTriphysariahaustorium represents a greatly advanced and/or reduced condition within Scrophulariaceae.
Circumscription of Myrtales and their relationships to other rosids: evidence fromrbcL sequence data
Authors: Conti Elena , Litt Amy , Sytsma Kenneth J.
Published: January 2018

Despite intensive morphological and chemical studies on the Myrtales, the circumscription of the order remains poorly defined. To test the monophyly of Myrtales sensu Dahlgren and Thorne (Annals of the Missouri Botanical Garden71: 633‐694, 1984), determine the relationships of some controversial families, and identify the most likely sister group of Myrtales, we conducted parsimony analyses on 80rbcL sequences representing 36 taxa from families traditionally included in Myrtales and 44 taxa from other Rosidae. The consensus tree resulting from these analyses supports the monophyly of Myrtales and is substantially congruent with the circumscription of the order proposed by Dahlgren and Thorne (Annals of the Missouri Botanical Garden71: 633‐694, 1984), with one notable exception: in therbcL tree Vochysiaceae are placed in Myrtales. A reanalysis of morphological attributes of Vochysiaceae revealed that the inclusion of the family in Myrtales is also supported by the combined occurrence of two typical myrtalean features of the wood: vestured pits and bicollateral vascular bundles. Furthermore, our analyses excluded Thymelaeaceae, Lecythidaceae, Haloragaceae, and Gunneraceae from Myrtales, suggesting that the association of these families with Myrtales, as previously proposed by other authors, may not reflect common ancestry. Finally, our analyses support a sister group relationship between the order Myrtales and a clade formed by an expanded Malvales, Sapindales, and an expanded Capparales.
Temporal patterns of seed set and decelerating fitness returns on female allocation in Zigadenus paniculatus (Liliaceae), an andromonoecious lily
Authors: Emms Simon K.
Published: January 2018

I describe temporal patterns of seed production in the andromonoecious lily Zigadenus particulatus. Fruit set per flower and seed set per fruit declined through time within plants. Hand pollination experiments showed that this was not due to increasing pollen limitation. Nutrient supplementation had little effect on seed output, but leaf clipping reduced seed production, especially in late‐blooming flowers, and removal of early‐blooming flowers increased seed set by later flowers. Thus, the temporal pattern of seed output was due to declining availability of photosynthates. Plants with larger bulbs produced larger inflorescences, a greater proportion of hermaphrodite flowers, more fruits per hermaphrodite flower, and more seeds per fruit, but lost a greater fraction of their initial bulb mass as a consequence of fruiting. After controlling for the effects of bulb mass, plants with larger inflorescences produced a greater proportion of male flowers, and plants with more hermaphrodite flowers produced fewer fruits per hermaphrodite flower and fewer seeds per fruit. Thus, the female fitness gain curve was decelerating. The temporal decline in seed output provides a partial explanation for the parallel decline in allocation to pistils. However, a complete explanation for the pattern of gamete packaging requires an understanding of factors controlling male, as well as female, fitness.
Ovule fates in Epilobium obcordatum (Onagraceae)
Authors: Seavey Steven R. , Carter Sarah K.
Published: January 2018

We investigated the fates of ovules following self‐ and cross‐pollination of the variably self‐sterile Epilobium obcordatum by observing thin sections of ovaries 4, 5, and 10 d postpollination (PP). Three types of unfertilized ovules were observed: apparently normal ovules not entered by pollen tubes, nonfunctional ovules with a nucellus but lacking an embryo sac, and empty ovules with integuments but lacking a nucellus. The average frequencies for all three types were not different for selfs and crosses. Fertilization frequencies did not differ among pollination treatments, averaging 61.4% of the total sample of 4 and 5 d PP ovules. The phenotypes of failing postfertilization ovules at 4 and 5 d PP included those containing preglobular and globular embryos lacking endosperm, ovules with endosperm but no embryo present, and failing embryos in the presence of endosperm. Self‐ and cross‐fertilized 10 d PP ovules also possessed heart‐stage and torpedo‐stage failing embryos. Early embryo failures (5 d PP) were distributed throughout the length of the ovary, as expected if failures are the consequence of factors intrinsic to each ovule. The sizes of normally developing self‐ and cross‐fertilized embryos were not different at 4 d PP. The 5 d PP cross embryos were larger than selfs. A comparison of 10 d samples was not possible due to attrition of self embryos. Although ovular position did not affect the probability of early embryo failure, it did affect the size of normally developing embryos at 4, 5, and 10 d PP, with embryos at the stylar end larger than those at the basal end.
Effects of Rht‐dosage on the breaking strength of wheat seedling leaves
Authors: Paolillo Dominick J. , Niklas Karl J.
Published: January 2018

We report the effect of the reduced‐height alleles Rht1 and Rht2 on the breaking strength and breaking stress of the first foliage leaves of wheat seedlings. Transverse size variables such as blade transverse area and blade width were positively related to the breaking strength and breaking stress of leaves, as was the total wall area of the principal fiber strands. A negative correlation was found for the Rht‐dosage with respect to the breaking strength. Because Rht plants had greater transverse dimensions and equal amounts of principal fiber strands compared to wild type, we posit that Rht may affect the mechanical quality of leaf tissues per se. Rht may serve as an example of a simple genetic system that profoundly affects plant morphology, development, and biomechanics.
Wind pollination in high‐mountain populations of Hormathophylla spinosa (Cruciferae)
Authors: Gómez José M. , Zamora Regino
Published: January 2018

In this paper we study aspects of the breeding system of Hormathophylla spinosa (Crucifcrae) to identify the factors responsible for seed production in the absence of insect pollinators. The pollinator‐exclusion experiments show that H. spinosa, under natural conditions, does not produce seed by apomixis or spontaneous autogamy. H. spinosa appears to be self‐incompatible but slightly geitonogamous. Thus, this plant species needs pollen vectors for reproduction. The results of the wind‐exclusion experiments performed during two different years in two populations of H. spinosa support the hypothesis that the wind acts as a pollen vector; flowers excluded from the wind had a lower fruit set and female fertility than flowers excluded from all pollinator insects (winged and wingless). This generalist pollination system (insects and wind) permits this species to colonize and sustain viable populations in high mountains, where this species is the only woody shrub living above 3000 m above sea level in the Sierra Nevada.