bluuebunny/crossref_metadata_2025 huggingface dataset:
Transpiration and stomatal conductance of two wetland macrophytes (Cladium jamaicense and Typha domingensis) in the subtropical Everglades
Authors: Koch Marguerite S. , Rawlik Peter S.
Published: January 2018

In the subtropical Everglades, greater than 85% of water input through atmospheric precipitation, the primary source of water to the ecosystem, is lost through evapotranspiration (ET). Two dominant macrophytes that could influence ET rates through transpiration and stomatal control were investigated in a field study: Cladium jamaicense, presently the species with the greatest distribution (65%–70%); and Typha domingensis, a species increasing in distribution due to eutrophication and hydrological modifications to the ecosystem. Transpiration rates and stomatal conductance of the two species were compared at eutrophic, mesotrophic, and oligotrophic sites throughout an annual wet and dry season of subtropical Florida. Typha domingensis possessed higher transpiration and conductance rates (>; 11 mmol m‐2 sec‐1) than C. jamaicense (<;7 mmol m‐2 sec‐1; P <; 0.01), during the winter and spring months when ambient temperatures and vapor pressure were at a minimum. However, rates for the two species converged and were not significantly different during the summer and fall months. Stomatal conductance of C. jamaicense remained constant over the range of ambient vapor pressures, but significantly increased in T. domingensis with decreasing vapor pressure. Vapor pressure and light were the best predictors of seasonal and diurnal transpiration rates of T. domingensis, whereas temperature explained the most variability in C. jamaicense. Annual transpiration rates for both species were 1 to 2 mmol m‐2 sec‐1 greater at the eutrophic site than at the transitional and oligotrophic sites. Leaf area increased six times in C. jamaicense and twofold in T. domingensis from the control to nutrient‐enriched sites. Results at the leaf scale suggest vegetation shifts and nutrient enrichment have the potential to alter water balances in the Everglades. However, canopy level studies may be necessary to support these conclusions when applied to the larger ecosystem or regional scale.
Pollen wall development in Vigna vexillata I. Characterization of wall layers
Authors: Pérez‐Muñoz Carlos A. , Jernstedt Judith A. , Webster Barbara D.
Published: January 2018

Light and electron microscope observations characterized the layers that comprise Vigna vexillata L. pollen walls, and identified the timing of their development. Exine sculpturings form an unusually coarse ektexinous reticulum. The structure of the ektexine is granular; this differs from the columellate/tectate type of structure typical of most angiosperm pollen. The ektexine overlies a homogeneous‐to‐lamellar, electron‐dense endexine, which in turn surrounds a thick, microfibrillar intine. Pollen grains are triporate and operculate, with Zwischenkörper and thickened intine underlying the apertures. The ektexine forms during the tetrad period of microspore development, the endexine and Zwischenkörper during the free microspore stage, and the intine during the bicelled (pollen) stage. Coarsely reticulate exine sculpturings and the granular structure of the patterned exine wall of the pollen grains are features that make this species suitable for detailed studies of pollen wall pattern formation.
Pollen wall development in Vigna vexillata II. Ultrastructural studies
Authors: Pérez‐Muñoz Carlos A. , Jernstedt Judith A. , Webster Barbara D.
Published: January 2018

Ultrastructural studies to determine the role of cytoplasmic organelles in pollen wall development in Vigna vexillata L. (Fabaceae) showed that plastids, mitochondria, and vacuoles do not directly participate in pollen wall morphogenesis, as inferred from their cytoplasmic distribution during microsporogenesis and pollen development. Spatial and temporal correlations between elements of the endomembrane system and pollen wall development suggest that dictyosomes, the endoplasmic reticulum, and multimembrane inclusions are involved in synthesis, processing, and/or transport of precursors for the various pollen wall layers. Large numbers of dictyosome‐derived vesicles appear during development of the primexine matrix, the patterned primexine, and the apertural Zwischenkörper, suggesting that dictyosomes are involved in development of these layers. Tubules of smooth endoplasmic reticulum, preferentially located under developing primexine ridges and extending to the vicinity of the plasma membrane, support the hypothesis of endoplasmic reticulum involvement in pollen wall pattern formation. Multimembrane inclusions, abundant in the cortical cytoplasm of developing microspores, may be involved in development of the lamellate endexine.
Nuclear size and DNA content of the embryo and endosperm during their initial stages of development in Glycine max (Fabaceae)
Authors: Chamberlin Mark A. , Horner Harry T. , Palmer Reid G.
Published: January 2018

A technique was developed for isolating embryo sacs from ovules of soybean and for separating embryo from endosperm. Image analysis and cytophotometry were used to determine the relative mass of DNA and size of nuclei of endosperm and embryo cells. Analyses were done at the globular through late heart‐shaped embryo stages to correlate ploidy level or nuclear size, and differentiation in these tissues. Mean size of embryo nuclei was fairly constant through all stages studied. Ploidy condition of the embryo was stable, 95%–99% of the nuclei were distributed in a bipolar pattern by relative mass at 2C and 4C. Few embryo nuclei (3%) had ploidy levels above 4C at the late heart‐shaped embryo stage. Variability in size of endosperm nuclei seemed correlated with the morphological state of these nuclei (free‐nuclear vs. cellular). Most endosperm cells did not show significant polyploidy with 84%–92% of nuclei in the expected 3C–6C range, but some nuclei with elevated ploidy levels were noted during endosperm cellularization. Endosperm senescence was correlated with nuclear DNA loss over time. Polyploidy seems to have no direct role in the early differentiation of the soybean embryo and endosperm, but these stable conditions may be necessary for the early establishment of the embryo.
Genome size and environmental factors in the genus Pinus
Authors: Wakamiya Izumi , Newton Ronald J. , Johnston J. Spencer , Price H. James
Published: January 2018

Nuclear 1C DNA content in haploid megagametophyte tissue of 18 North American and one exotic Pinus species was determined using scanning microspectrophotometry. The nuclear DNA content in root meristematic cells of Zea mays L. ssp. mays, inbred line Va35 (4C = 10.31 pg) was used as a standard. DNA content measured by microspectrophotometry was verified using laser flow cytometry with two additional standards, Hordeum vulgare cv. Sultan (2C = 11.12 pg) and P. eldarica (2C = 47.30 pg). DNA values obtained by both methods were significantly correlated (r = 0.987). The 1C nuclear DNA content ranged from 21 pg to 31 pg. The ratio of DNA content in embryo tissue of P. eldarica to that in megagametophyte tissue was 1.72 by scanning microspectrophotometry and 1.74 by laser flow cytometry. To date, this is the most comprehensive data set available for North American Pinus species. Relationships between genome size of 18 North American Pinus species and climatic factors and indices of growth were investigated using regression and correlation analyses. Positive correlations were observed between nuclear DNA content and growth indices, minimum seed‐bearing age, and seed dimensions. Strong negative correlations were observed between nuclear DNA content and two climatic factors, the lowest mean annual and monthly precipitation (excluding January) and the highest mean monthly spring air temperature. These correlations suggest that the large genome size and its variation in Pinus are adapted responses to the habitats of these species.
Fossil bananas (Musaceae): Ensete oregonense sp. nov. from the Eocene of western North America and its phytogeographic significance
Authors: Manchester Steven R. , Kress W. John
Published: January 2018

Fossil seeds of Ensete, a genus presently native to Asia and Africa, have been recovered from the middle Eocene of Oregon, confirming the presence of Musaceae in the North American Tertiary. The seed of Ensete oregonense sp. nov. is operculate, with a well‐defined micropylar collar, a pronounced chalazal chamber, and a wide hilar cavity. A survey of seed morphology in extant Zingiberales provides characters for distinguishing Musaceae from other families of the order, furnishes criteria for distinguishing the three extant genera of Musaceae (Musa, Ensete and Musella), and facilitates critical assessment of fossil seed remains. “Musa” cardiosperma Jain from the Cretaceous/Tertiary boundary Deccan Series of India is excluded from Musaceae (although retained in Zingiberales) on the basis of fruit and seed characters, including the lack of laticifers and absence of a chalazal chamber. We reexamined the musaceous seeds from Colombia that previously were described as Tertiary fossils (Musa enseteformis Berry, 1925) and now believe that they are recent, nonfossil remains, evidently from Ensete ventricosum, which is grown in the region where the specimens were originally obtained. In addition, a reputed fossil banana fruit from the Cretaceous of Colombia was reexamined and determined to be a concretion of nonbiological origin. Ensete oregonense is significant therefore, as the first unequivocal fossil record of Ensete and of Musaceae. Although the Musaceae are currently native only to the Old World tropics, this discovery establishes that the family was present in North America about 43 million years ago.
Ultrastructural features associated with secretion in the salt glands of Frankenia grandifolia (Frankeniaceae) and Avicennia germinans (Avicenniaceae)
Authors: Balsamo Ronald A. , Thomson William W.
Published: January 2018

Using stereological procedures, a detailed analysis was made from thin section electron micrographs of secreting and nonsecreting salt glands of Frankenia grandifolia (Cham. and Schlecht) and Avicennia germinans (L.) Stem. In F. grandifolia secretory cells, vacuolar volume significantly decreased, while the volume of endoplasmic reticulum increased in secreting glands. Numerous minivacuoles were predominantly located along the periphery of secreting secretory cells, some in apparent fusion with the plasma membrane. No difference was found in mitochondrial volume in the secretory cells between secreting and nonsecreting glands. In A. germinans, there was a significant decrease in vacuolar volume in secreting secretory cells. The volume of the endoplasmic reticulum and mitochondria also increased in these cells. However, no evidence of mini‐vacuolar fusion with the plasma membrane was observed. These results indicate that the physical process of secretion may differ between F. grandifolia and A. germinans; in both, however, the ultrastructural observations support the contention that specific structural parameters are correlated with the process of secretion.
Seasonal and diurnal patterns of photosynthetic gas exchange for Lonicera sempervirens and L. Japonica (Caprifoliaceae)
Authors: Schierenbeck Kristina A. , Marshall John D.
Published: January 2018

Photosynthesis, stomatal conductance, and water use efficiency were compared between Lonicera japonica (Japanese honeysuckle), an invasive species in the southeastern United States, and its native congener, Lonicera sempervirens (coral honeysuckle), to determine the role of seasonal patterns of water loss and carbon gain in the invasive ability of the exotic. Diurnal measurements were taken monthly for 1 year under a closed forest canopy and in an open field. There were few significant differences in photosynthetic rates between the two species in either environment. However, at both sites, Lonicera japonica retained its old leaves over winter while old leaves of L. sempervirens senesced. Also, new leaves of L. japonica had significantly higher photosynthetic rates than the emerging leaves of L. sempervirens (6.2 vs. 4.4 μmol m 2sec‐1 under the canopy; 4.4 vs. 3.0 μmol m‐2 sec‐1 in the open). Although differences in conductance and water use efficiency between species were seldom significant, L. japonica tended to have higher maximum values than L. sempervirens. Retention of old leaves by L. japonica during new leaf formation (January–March) as well as higher photosynthetic rates in new leaves contribute to greater annual carbon gain and help explain the invasive ability of Japanese honeysuckle.
Phylogenetic structure in the grass family (Poaceae) as inferred from chloroplast DNA restriction site variation
Authors: Davis Jerrold I , Soreng Robert J.
Published: January 2018

A cladistic analysis of chloroplast DNA restriction site variation among representatives of all subfamilies of the grass family (Poaceae), using Joinvillea (Joinvilleaceae) as the outgroup, placed most genera into two major clades. The first of these groups corresponds to a broadly circumscribed subfamily Pooideae that includes all sampled representatives of Ampelodesmeae, Aveneae, Brachypodieae, Bromeae, Diarrheneae, Meliceae, Poeae, Stipeae, and Triticeae. The second major clade includes all sampled representatives of four subfamilies (Panicoideae [tribes Andropogoneae and Paniceae], Arundinoideae [Arundineae], Chloridoideae [Eragrostideae], and Centothecoideae [Centotheceae]). Within this group (the “PACC” clade), the Panicoideae are resolved as monophyletic and as the sister group of the clade that comprises the other three subfamilies. Within the latter group, Danthonia (Arundinoideae) and Eragroslis (Chloridoideae) are resolved as a stable monophyletic group that excludes Phragmites (Arundinoideae); this structure is inconsistent with the Arundinoideae being monophyletic as currently circumscribed. The PACC clade is placed within a more inclusive though unstable clade that includes the woody Bambusoideae (Bambuseae) plus several disparate tribes of herbaceous grasses of uncertain affinity that are often recognized as herbaceous Bambusoideae (Brachyelytreae, Nardeae, Olyreae, Oryzeae, and Phareae). Among eight most‐parsimonious trees resolved by the analysis, four include a monophyletic Bambusoideae sensu lato (comprising Bambuseae and all five of these herbaceous tribes) as the sister group of the PACC clade; in the other four trees these bambusoid elements are not resolved as monophyletic, and the PACC clade is nested among these tribes. These results are consistent with those of previous analyses that resolve a basal or near‐basal branch within the family between Pooideae and all other grasses. However, resolution by the present analysis of the PACC clade, which includes Centothecoideae, Chloridoideae, and Panicoideae, but excludes Bambusoideae, is inconsistent with the results of previous analyses that place Bambusoideae and Panicoideae in a monophyletic group that excludes Centothecoideae and Chloridoideae.
Prevalence of wood characters in eastern North America: what characters are most promising for interpreting climates from fossil wood?
Authors: Woodcock D. W. , Ignas C. M.
Published: January 2018

The frequency of wood‐anatomical characters in the eastern North America dicotyledonous tree flora shows spatial variance that can be related to climate (40% of the variation in 18 characters is explained by temperature and precipitation). Percent of taxa with rings varies with mean annual temperature, but the relationship is weak and the difficulties in making determinations as to presence or absence of rings make this character a problematic climatic indicator. Significant climate sensitivity is seen among characters pertaining to: a) vessel size and density (in diffuse‐porous woods); 2) vessel arrangement; 3) parenchyma types; and 4) rays. Overall, the anatomical variables can be used to represent 82% of the variance in total precipitation and 91% of the variance in mean annual temperature within the study area. These results demonstrate the possibility of deriving a multivariate representation of the response of wood to climate that will be useful in climate reconstruction and comprise a source of information similar to that obtainable from leaf morphology and permitting estimates of precipitation as well as temperature.
Quantitative survey of sieve tube distribution in foliar terminal veins of ten dicot species
Authors: Horner Harry T. , Lersten Nels R. , Wirth Cassandra L.
Published: January 2018

Quantitative data on sieve tubes in foliar terminal veins (vein endings) were added to the meager published information from only five dicot species. Correlations with other minor vein configurations were also explored. Leaf samples from ten species of dicots (Oxalis nelsonii, O. pes‐capri, O. rubra, O. stricta [Oxalidaceae], Caesalpinia pulcherrima. Glycine max, Trifolium repens [Leguminosae], Ampelamus albidus [Asclepidaceae], Eupatorium rugosum [Asteraceae], and Polygonum convolvulus [Polygonaceae]) were selected for two quantitative procedures: 1) a survey of the arrangement of terminal veins and distribution of sieve tubes in terminal veins in 100 areoles per species using stained leaf clearings; and 2) a search for correlations of sieve tube distribution with number and branching patterns of terminal veins, and with sizes of areoles using image analysis. Two Oxalis species (O. pes‐capri and O. stricta) had the smallest areoles and virtually no sieve tubes in any terminal vein. Polygonum convolvulus, at the other extreme, had sieve tubes extending to the tips of most terminal veins. The other species had various intermediate sieve tube configurations. The data indicate that species with few or no sieve tubes associated with their terminal veins, regardless of the number of terminal veins per areole, have smaller areoles. These results may have implications regarding the entry of leaf photosynthates into the vascular system.
Interspecific allometries of critical buckling height and actual plant height
Authors: Niklas Karl J.
Published: January 2018

Size‐dependent variations in the critical buckling height Hcrit and actual height H of plants were determined for a total of 111 species with self‐supporting stems ranging in diameter between 0.03 cm ≤ D ≤ 3.0m. For each species, experimentally determined values for the physical properties of stems (Young's elastic modulus and bulk tissue density) were used to compute Hcrit. For small species (D < 3 cm), empirically determined critical buckling loads were used to compute Hcrit by means of the Elastica equation and the more traditionally employed Greenhill formula; for larger species (D ≖ 3 cm), Greenhill's formula was used exclusively to estimate Hcrit. Within most of the size‐range examined, the predicted values of Hcrit from the Elastica equation and Greenhill's formula were statistically indistinguishable. Regression analyses showed that the interspecific allometry of Hcrit parallels that of H such that the safety factor against the elastic mechanical failure of stems (i.e., Hcrit/H) under their own biomass was roughly constant. Since the safety factor against elastic buckling is independent of plant size, a general allometric “rule,” Hcrit/H ≈ 4, appears to govern the evolution of plant size.
Disparity of allozyme variation levels in threeMagnolia (Magnoliaceae) species from the southeastern United States
Authors: Qiu Yin‐Long , Parks Clifford R.
Published: January 2018

Allozyme variation at 17 loci encoding ten enzyme systems was examined in 21, 22, and 15 populations across the ranges of Magnolia fraseri, M. macrophylla, and M. tripetala, respectively, in the southeastern United States. All three species have regional distributions, and are insect‐pollinated outcrossing deciduous trees with seeds dispersed by birds, yet strikingly different levels of genetic variability were observed among them. In comparison with other woody angiosperm species, M. fraseri possesses a moderate amount of variation at the population level (A = 1.4, P = 39.2, Ho = 0.111, and He = 0.111), whereas M. macrophylla and M. tripetala are genetically depauperate in their populations (A = 1.2, P = 18.7, Ho = 0.47, and He = 0.055; A = 1.1, P = 11.0, Ho = 0.032, and He = 0.033). Examination of population structure revealed a small amount of inbreeding within populations and extensive intra‐ and interregional differentiation among populations of the latter two species. These two factors are perhaps partly responsible for the low genetic variability in populations of the two Magnolia species. Furthermore, the bottleneck effect caused by extinctions during cold periods of the Quaternary glaciations and human deforestation in the last two centuries as well as the founder effect in postglacial establishment of the populations might have also played significant roles in loss of genetic diversity in M. macrophylla and M. tripetala. We suggest that historical factors are important determinants of genetic variation profile of a species, in addition to life history and ecological characteristics as generally recognized.
Reevaluating the origin of domesticated cotton (Gossypium hirsutum; Malvaceae) using nuclear restriction fragment length polymorphisms (RFLPs)
Authors: Brubaker Curt L. , Wendel Jonathan F.
Published: January 2018

The origin of domestication in Mesoamerican G. hirsutum populations is obscured by several factors, including the absence of a clearly identified wild progenitor, a complex population genetic structure, and many centuries of human‐mediated dispersal and gene flow. Phenetic and phylogenetic analyses of allelic variation at 205 restriction fragment length polymorphism (RFLP) loci were conducted in an effort to unravel this complicated history. The RFLP data, in conjunction with previously published molecular, morphological, and anthropological information, suggest that coastal Yucatan populations are truly wild rather than reestablished feral derivatives. The geographical proximity of these wild coastal populations to agronomically primitive forms of G. hirsutum implicates the Yucatan peninsula as the primary site for the earliest stages of domestication. Agronomically advanced cultigens developed in southern Mexico and Guatemala appear to have been derived from introduced Yucatan peninsular forms, thereby creating the secondary center of diversity that has traditionally been interpreted as the geographical point of origin of domesticated G. hirsutum. The gene pool of modern, improved (Upland) cultivars derives from Mexican highland populations that, in turn, trace their origins to southern Mexico and Guatemala. Gossypium hirsutum is the first tetraploid perennial surveyed for RFLP variation. Levels of RFLP variation in G. hirsutum (HT = 0.048, A = 1.24, and P = 22%) are low relative to other plant taxa, and, in contrast to the few comparable studies, levels of allozyme variation are higher than levels of RFLP variation. Despite assaying 205 loci, only six of the 23 Upland cultivars were found to have unique multilocus genotypes.
Crop/weed microgametophyte competition inCucurbita pepo (Cucurbitaceae)
Authors: Wilson Hugh D. , Payne Jennifer S.
Published: January 2018

Prior studies of crop/weed gene flow in Cucurbita pepo have demonstrated that pollinators can deposit mixed pollen loads. The fate of microgametophytes emerging from these pollen mixtures is unknown. In an effort to define the relationship between pollen mixture composition and progeny composition, experimental plants representing a zucchini cultivar and a cross‐compatible free‐living type were genotyped with an isozyme marker and grown under greenhouse conditions. Weighed mixtures of weed/crop pollen were applied to stigmas of both types in differing ratios. Subsequent fertilizations were tracked by an electrophoretic screen of over 1,600 progeny from 39 fruits. Equal mixtures of weed/crop pollen do not produce a corresponding suite of progeny. Pollen of the pistillate parent is favored, and this advantage increases as the proportion of pollen from the pistillate parent increases. However, increasing the proportion of zucchini pollen does not produce a corresponding increase in fertilization success when the free‐living type is used as pistillate parent. These results indicate that microgametophyte competition in both domesticated and free‐living Cucurbita gynoecia could be a significant component of gene flow dynamics. The nature of this competition can only be defined by experiments that control numerous variables, both paternal and maternal, that might be involved. The tendency for crop/weed hybrids to occur at different portions of the ovary suggests that interactions involving two factors—microgametophyte growth rate and gynoecium structure—might play a significant role.
The “Foliage is the Fruit” hypothesis:Buchloe dactyloides (Poaceae) and the shortgrass prairie of North America
Authors: Quinn James A. , Mowrey Daniel P. , Emanuele Stephen M. , Whalley Ralph D. B.
Published: January 2018

Janzen proposed that foliage of herbaceous plants may serve as the attractant for large herbivore dispersal of seeds. Such herbivore dispersal was envisioned to select for traits enhancing ingestion and passage of viable seeds through the animal. We tested this “Foliage is the Fruit” (FF) hypothesis by collecting and collating appropriate data from Buchloe dactyloides (buffalograss), one of the two dominant grasses of the shortgrass prairie. Passage of buffalograss diaspores through cattle had a positive effect on germination and seedling growth from intact diaspores, damage other than that due to mastication (15%) was minimal, and retention time was 1–5 days. This combination of retention time and migratory herbivores during the northward expansion of shortgrass prairie should have enhanced migration of buffalograss northward to Montana from its area of origin in central Mexico, and our comparisons with its five close dioecious relatives (the “Buchloe group”) showed that buffalograss does possess a suite of distinctive FF traits. Lab analyses of foliage quality and digestibility also confirmed the high quality of its foliage. After reviewing comparable data for Bouteloua gracilis (blue grama), we conclude that buffalograss and blue grama, which dominate major portions of the largest North American steppe Province, provide strong support for the FF hypothesis.
Leaf anatomical responses to light in five tropical moraceae of different successional status
Authors: Strauss‐Debenedetti S. , Berlyn G. P.
Published: January 2018

We characterized the leaf anatomical characteristics and maximum assimilation rates of five neotropical Moraceae of different genera and successional positions. Plants were grown under different light levels and transferred to high light, simulating canopy openings. Total blade thickness increased with irradiance among all species, and thicker blades were developed when plants were switched. However, blade thickness, and the extent to which it was modified, was independent of the species’ successional position and did not predict photosynthetic performance. Palisade thickness was a good predictor of maximum photosynthetic rate, but only on a species‐specific basis. Overall, leaf thickening with increasing irradiance was associated more with structural than with photosynthetic changes. The early successionals Cecropia obtusifolia and Ficus insipida exhibited similarly high photosynthetic plasticity and acclimation values, but differed in their leaf anatomical traits. The late successional Poulsenia armata produced the most anatomically plastic leaves, but failed to acclimate either anatomically or photosynthetically when transferred to higher light levels.
Haustorial synergids: an important character in the systematics of danthonioid grasses (Arundinoideae: Poaceae)?
Authors: Verboom G. Anthony , Linder H. Peter , Barker Nigel P.
Published: January 2018

The mature ovule and megagametophyte of 42 grass species (23 genera), mostly from the taxonomically troublesome subfamily Arundinoideae, was investigated. Haustorial synergids, first described from the Arundineae, are reported for a further 26 species (ten genera) of danthonioid grasses, a group for which they appear to be synapomorphic. The evolution of this character and a suite of associated integument and nucellar characters is discussed. The danthonioid clade, as defined by haustorial synergids, includes Cortaderia (often treated as nondanthonioid) but excludes a number of taxa currently contained in the Arundineae. The full extent of the group remains undetermined, however, since several of its potential members remain unstudied. The data provide some indication of phylogenetic structure within the clade. At least two of the species of Merxmuellera studied appear to occupy a basal position, while three do not, suggesting that this genus may be paraphyletic, or even polyphyletic. Also, the reduction or absence of synergid haustoria in Prionanthium, Pentaschistis, and Pentameris is considered to be secondarily derived and weakly corroborates the monophyly of this generic cluster as indicated by spikelet morphology.
Spontaneous hybridization between oilseed rape (Brassica napus) and weedy B. campestris (Brassicaceae): a risk of growing genetically modified oilseed rape
Authors: J⊘rgensen Rikke B. , Andersen Bente
Published: January 2018

Frequencies of spontaneous hybridization between oilseed rape (Brassica napus L.) and weedy Brassica campesíris ssp. campestris L. were measured in agricultural fields. Hybrids were identified by enzyme electrophoresis, random amplified polymorphic DNA (RAPD) analysis, chromosome counting, morphology, and pollen fertility. When the two species were mixed 1:1, B. campestris produced 13% hybrid seeds and oilseed rape 9%. In two experiments with single plants of the self‐incompatible B. campestris widely spaced within fields of oilseed rape, 56% and 93% hybrid seeds were produced. Analysis of a weedy population of B. campestris in oilseed rape revealed 60% hybrid seeds. Backcrossing of the hybrids to the weedy species seems to occur as supported by the finding in a natural population of two B. campestris‐like plants with a marker specific to oilseed rape. The results suggest that transgenes could be dispersed from oilseed rape to B. campestris.
The effects of density and spatial distribution on selection for emergence time in Prunella vulgaris (Lamiaceae)
Authors: Miller T. E. , Winn A. A. , Schemske D. W.
Published: January 2018

We investigated the effects of both overall density and variation in local density on the relationship between emergence time and final biomass in Prunella vulgaris. The relationship between emergence time and final biomass was used to quantify the pattern of selection on emergence time. Seeds were planted in flats in three different spatial distributions (hexagonal, random, high variance) at each of three overall densities (308, 769, and 3,077 seeds/m2). Individual seedlings were marked upon emergence, and their final biomass was determined after 90 days of growth. With increasing overall density, mean plant biomass decreased, but the coefficient of variation in biomass and the magnitude of directional selection for early emergence increased. Increasing variation in the spatial distribution of the plants had no effect on mean plant biomass but did significantly increase the coefficient of variation in biomass at both low and medium densities. Both the magnitude of directional selection and the curvature in the relationship between emergence time and final biomass tended to increase with increased variation in the spatial distribution. Our results suggest that both overall plant density and the spatial distribution of individuals can affect the pattern of selection on plant traits.
Changes in growth of two C4grasses (Schizachyrium scopariumandPaspalum plicatulum) in monoculture and mixture: influence of soil depth
Authors: Van Auken O. W. , Bush J. K. , Diamond D. D.
Published: January 2018

The growth ofSchizachyrium scoparium(Michx.) Nash (little bluestem) andPaspalum plicatulumMichx. (brownseed paspalum), two C4grasses, was examined in monoculture and in mixed culture in three soil depths. Effects of soil depth and competition were both significant. Growth of both species increased as soil depth increased from 30 to 180 cm in pot experiments. However,P. plicatulumdry mass increased approximately four times more thanS. scopariumas soil depth increased.Schizachyrium scopariumdry mass was always greater in monoculture whileP. plicatulumdry mass was always greater in mixture. Significant interspecific competition was not measured in the shallow soil treatment (30 cm) suggesting equal competition. Significant interspecific competition was measured in the deeper soil treatments (90 and 180 cm), andP. plicatulumdry mass was clearly greater in mixtures in the two deeper soils.Paspalum plicatulumdoes not appear to prevent the growth ofS. scopariumroots in the deeper soil, but seems able to exploit deeper soil resources by proliferating roots at depths whereS. scopariumroots do not seem capable of growth.
Cultivar‐specificity genes of the nitrogen‐fixing soybean symbiont, Rhizobium fredii USDA257, also regulate nodulation of Erythrina SPP.
Authors: Krishnan Hari B. , Pueppke Steven G.
Published: January 2018

Rhizobium fredii USDA257 is a Gram‐negative soil bacterium from China that fixes nitrogen in symbiosis with primitive soybean (Glycine max [L.] Merr.) cultivars such as Peking, but not with advanced cultivars such as McCall. Mutation of either of two bacterial loci, nolBTUVWX or nolC, removes this cultivar‐specificity constraint, allowing the bacterium to nodulate advanced cultivars. We have discovered that USDA257 forms nodules on Erythrina costaricensis M. Micheli, but not on six other species of this genus, which includes trees and shrubs from the tropics. Inactivation of nolBU or nolC broadens the symbiosis to include other Erythrina species. Whereas nolBU‐mutants acquire the capacity to nodulate E. fusca Loureiro, E. variegata L., and E. vespertilio Benth., nolC‐mutants could nodulate only E. variegata. Nodules are determinate and often clustered in root axils near the root crown. E. variegata nodules containing a nolBU‐mutant consist of well‐developed inner and outer cortical layers, as well as a bacteroid zone. The cortical layers are separated from one another by a meristematic region that is associated with large darkly staining cells, and cells of the inner cortex contain numerous starch grains. Histochemical staining of E. variegata roots inoculated with a strain containing a nolB‐lacZ gene fusion confirms that nolB and nolC are expressed during the initial stages of bacterial interaction with the host. R. fredii enters elongated root‐hairs via infection threads, which ramify within root‐hairs and are associated with meristematic activity in the adjacent underlying cortical cells.
Changes in root hydraulic conductivity for two tropical epiphytic cacti as soil moisture varies
Authors: North Gretchen B. , Nobel Park S.
Published: January 2018

The tropical epiphytic cacti Epiphyllum phyllanthus and Rhipsalis baccifera experience extreme variations in soil moisture due to limited soil volumes and episodic rainfalls. To examine possible root rectification, whereby water uptake from a wet soil occurs readily but water loss to a dry soil is minimal, responses of root hydraulic conductivity (Lp) to soil drying and rewetting were investigated along with the underlying anatomical changes. After 30 d of soil drying, Lp decreased 50%–70% for roots of both species, primarily because increased suberization of the periderm reduced radial conductivity. Sheaths composed of soil particles, root hairs, and mucilage covered young roots and helped reduce root desiccation. Axial (xylem) conductance increased during drying due to vessel differentiation and maturation, and drought‐induced embolism was relatively low. Within 4 d of rewetting, Lp for roots of both species attained predrought values; radial conductivity increased for young roots due to the growth of new branch roots initiated during drying and for older roots due to the development of radial breaks in the periderm. The decreases in Lp during drought reduced plant water loss to a dry soil, and yet maximal water uptake and transpiration occurred within a few days of rewetting, helping these epiphytes to take advantage of episodic rainfalls in a moist tropical forest.
Sexual selection of anther trichomes and sexual dimorphism in Ibervillea lindheimeri (Cucurbitaceae: Melothrieae)
Authors: Dieringer Gregg , R. Leticia Cabrera
Published: January 2018

Ibervillea lindheimeri is a dioecious member of the Cucurbitaceae whose male flowers possess a number of sex‐specific characteristics including eglandular trichomes on the anther connective. A 2‐year study (1989 and 1990) was undertaken to assess the potential for sexual selection of anther trichome number as a male floral trait that enhances pollen removal (a male fitness component). Correlation analysis of ten reproductive and floral traits showed that only the mean number of anther trichomes per flower was significantly associated with mean pollen removal per flower. Anther trichomes are two‐celled, consisting of a small, caplike, apical cell and a large, bulbous basal cell. The basal cell is under tension and produces a sticky polysaccharide that is forcefully ejected upward when the apical cell is broken off by visiting bees. The sticky polysaccharide accumulates on the bees and aids in adherence of pollen. We propose that there is directional selection on individual males for number of anther trichomes per flower. The more anther trichomes per flower, the more pollen exported, and the greater the likelihood of siring seeds. Males differed significantly in mean number of anther trichomes per flower and were relatively consistent in their rank order over a 2‐year period; both are prerequisites for sexual selection to operate. Selection coefficients and differentials for 1989 and 1990 were 0.005 and 0.007, and 0.22 and 0.32, respectively, and suggest moderate to strong directional selection on anther trichome number.
Morphogenetic plastid migration and microtubule arrays in mitosis and cytokinesis in the green alga Coleochaete orbicularis
Authors: Brown Roy C. , Lemmon Betty E. , Graham Linda E.
Published: January 2018

This study provides data on cell division in Coleochaete orbicularis, an important taxon in evolutionary theories deriving land plants from green algae. Vegetative growth in discoid species of Coleochaete results from marginal cell division in two planes—radial and circumferential. Like many algae and certain of the simple land plants, Coleochaete is monoplastidic. Prior to mitosis, the single plastid migrates to a position where it will divide and be distributed into the daughter cells. Unlike monoplastidic cell division in hornworts, mosses, and lycopsids; microtubule nucleation is not intimately associated with the plastids. Instead, microtubule organization is associated with centriolar centrosomes throughout the cell cycle, as is common in algae. The cytokinetic apparatus lacks preprophase bands of microtubules, but includes typical phragmoplasts consisting of brushlike arrays of microtubules on either side of a dark zone. However, the origin and role of phragmoplasts is unusual. Phragmoplasts appear to develop among microtubules that emanate from the polar centrosomes rather than from nuclear envelopes and/or plastids. The function of phragmoplasts in Coleochaete is unclear, as the process of cytokinesis is not strictly centrifugal. Some infurrowing occurs in radial division, and cytokinesis appears to be entirely centripetal by infurrowing in circumferential division. The cortical arrays of microtubules differ from those typical of land plants in that they develop as a network in association with centrosomes after mitosis.
Size‐dependent variations in plant growth rates and the “¾‐power rule”
Authors: Niklas Karl J.
Published: January 2018

Size‐dependent variations in morphological and physiological variables adduced to influence growth rate (e.g., cell surface area and volume, chlorophyll a concentration per cell) were determined by reevaluating published data from unicellular and multicellular plants and animals. With respect to cell volume, reduced major axis regression of the available data indicated that cell surface area decreases roughly as the 0.69‐power, the concentration of Chl a decreased roughly as the 0.80‐power, and cell mass decreased as the 0.77‐power. Computer simulations indicated that the scaling exponent for cell surface area was the consequence of size‐dependent variations in cell geometry and aspect ratio (i.e., cell length/width) rather than the result of geometric similitude among cells differing in size. The anisometric relation between cell mass and volume indicated that bulk cell density declines with increasing cell volume. Reanalyses of published data showed that growth rate and weight‐specific growth rate scale as the ¾‐ and negative ¼‐power, respectively, with respect to the body mass of unicellular and multicellular plants and animals. It is speculated that the anisometric relation between the growth rate and mass of unicellular plants is attributable to a “dilution” of metabolically active cellular constituents with increasing cell size in combination with the scaling of surface area with respect to volume (and therefore cell mass). It is further speculated that similar biological scalings may account for the ¾‐power rule obtained for taxonomically and ecologically diverse multicellular plants and animals.
The biosystematics and evolution of the Polyalthia hypoleuca species complex (Annonaceae) of Malesia. III. Floral ontogeny and breeding systems
Authors: Rogstad Steven H.
Published: January 2018

Aspects of floral ontogeny, breeding systems, and hybridization potential for selected members of the monophyletic Polyalthia hypoleuca complex (Annonaceae) of Malesia were investigated. Complete intrafloral dichogamy (protogyny) was found in all five members examined. Further, these five tree species had flowers developing in several serial “cohorts,” the flowers of any one cohort maturing in synchrony resulting in complete intracohort dichogamy. Two modes of the timing of maturation of successive floral cohorts within an individual were observed. In the first (P. hypoleuca and P. sumatrana), the onset of stigma receptivity of successive cohorts was separated by 2 days, resulting in complete intercohort dichogamy within any given individual. This mode of ontogeny probably acts to reduce geitonogamy and stamen‐carpel interference within an individual. Two distinct “sets” of trees existed in these populations. The trees of one set were functionally carpellate at times when the trees of the other set were functionally staminate. Functional status for the two sets was reversed the next day. This pattern of complete intraset dichogamy with temporally shifted sets probably leads to enhanced pollen transfer by beetles between, but not within, the sets. The second mode of successive cohort maturation involved serial cohorts that achieved stigma receptivity day after day such that staminate and carpellate phase flowers were simultaneously present in a given individual. The second mode permits geitonogamy and intraindividual, interfloral stamen‐carpel interference. P. discolor, P. glauca, and P. multinervis exhibited both modes to varying degrees. In addition, autogamy was not detected for P. glauca, P. hypoleuca, and P. sumatrana. Results from manual pollination experiments are consistent with the hypothesis that P. glauca and P. hypoleuca are self‐incompatible, and a bidirectional hybrid cross between these two species yielded no fruit set.
Sexual differences in gas exchange and response to environmental stress in dioecious Silene latifolia (Caryophyllaceae)
Authors: Gehring Janet L. , Monson Russell K.
Published: January 2018

Females of dioecious species usually have higher reproductive effort than males because they produce fruits in addition to flowers. Since females have higher reproductive effort, they are expected to be more negatively affected than males by low resource availability. We tested that assumption by growing females and males of Silene latifolia under low levels of light, water, nitrogen, phosphorus, and potassium. Gas exchange of the sexes did not respond differently to low resource availability; higher female reproductive effort relative to males did not differentially affect their ability to assimilate carbon. However, male photosynthesis rates and stomatal conductances were slightly, but consistently, higher than those of females. The intersexual difference in photosynthesis rate may be a proximate result of reproduction if females translocate nutrients, particularly nitrogen, from their leaves to developing fruits. Alternatively (or perhaps additionally), higher male photosynthesis and stomatal conductances relative to females may be the ultimate result of sexual selection. This could be the case if 1) reproductive effort as estimated by biomass allocation is misleading and males actually invest more in reproduction than females, or 2) females experience stronger selection than males to conserve water late in the growing season, when soil moisture is likely to be low but females need to complete fruit maturation. Our results indicated that females had slightly lower leaf nitrogen but higher photosynthetic water‐use efficiency than males, so it is possible that both proximate and ultimate factors are operating simultaneously to cause lower female photosynthesis rates.
Floral and pollinator divergence in two sexually deceptive South African orchids
Authors: Steiner Kim E. , Whitehead V. B. , Johnson S. D.
Published: January 2018

Two sister species in Disa section Disa were studied to evaluate the effect that minor differences in floral color, shape, and scent have on pollination. D. atricapilla and D. bivalvata have overlapping distributional ranges, occupy similar habitats, flower at the same time, and often occur sympatrically. Observations at several sites indicate that each species is pollinated almost exclusively by male wasps. D. atricapilla is pollinated by Podalonia canescens (Sphecidae), while D. bivalvata is pollinated mainly by Hemipepsis hilaris Smith (Pompilidae). Both wasp genera appear to exhibit mate‐seeking behavior when approaching and visiting flowers. This together with the absence of a floral reward suggests that D. atricapilla and D. bivalvata are pollinated through sexual deception. Pollination success often appears low, but because of long floral life spans, overall fruiting success is generally high. The occasional presence of hybrids in areas of sympatry is attributed to secondary beetle pollinators. The rarity of these hybrids indicates that prefertilization barriers between the species are usually strong. This is the first report of pollination through sexual deception for southern Africa.