bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of extended exposure to hypersaline conditions on the germination of five inland halophyte species
Authors: Keiffer Carolyn Howes , Ungar Irwin A.
Published: April 2006

In order to determine how salinity and exposure time affect seed viability and germination, seeds of five halophytes, Atriplex prostrata, Hordeum jubatum, Salicornia europaea, Spergularia marina, and Suaeda calceoliformis were exposed to 3.0, 5.0, and 10.0% NaCl solutions for 30, 60, 90, 365, and 730 d. Recovery experiments in distilled water indicated significantly different species responses to salinity over time. Percentage germination and rate of germination in H. jubatum were dramatically reduced following extended exposure and all seeds exposed to 10% NaCl for > 1 yr failed to germinate. Spergularia marina seeds were stimulated following short‐term exposure to 3% NaCl; however, germination was delayed and overall germination was significantly reduced with exposure time in the two higher salinity levels. Percentage germination in A. prostrata decreased over time, but salinity level was not related to this reduction. Germination of S. europaea and S. calceoliformis, the most salt‐tolerant species being tested, was stimulated by exposure to high salinity. Both species had a significant increase in percentage germination and in the germination rate when compared to seeds germinated in distilled water. Baseline germination data from seeds placed in 0, 1, 2, and 3% NaCl solutions indicated that S. europaea and S. calceoliformis were the only species to germinate in the 3% NaCl solution. Spergularia marina failed to germinate in the 2% NaCl treatment, and germination of A. prostrata and H. jubatum was significantly reduced at this salinity level. It is concluded that prolonged exposure to saline solutions can inhibit or stimulate germination in certain species, and the resulting germination and recovery responses are related to the duration and intensity of their exposure to salt in their natural habitats.
Hybridization between introduced smooth cordgrass (Spartina alterniflora; Poaceae) and native California cordgrass (S. foliosa) in San Francisco Bay, California, USA
Authors: Daehler Curtis C. , Strong Donald R.
Published: April 2006

Introduced Spartina alterniflora (smooth cordgrass) is rapidly invading intertidal mudflats in San Francisco Bay, California. At several sites, S. alterniflora co‐occurs with native S. foliosa (California cordgrass), a species endemic to California salt marshes. In this study, random amplified polymorphic DNA markers (RAPDs) specific to each Spartina species were identified and used to test for hybridization between the native and introduced Spartina species in the greenhouse and in the field. Greenhouse crosses were made using S. alterniflora as the pollen donor and S. foliosa as the maternal plant, and these crosses produced viable seeds. The hybrid status of the crossed offspring was confirmed with the RAPD markers. Hybrids had low self‐fertility but high fertility when back‐crossed with S. foliosa pollen. Hybrids were also found established at two field sites in San Francisco Bay; these hybrids appeared vigorous and morphologically intermediate between the parental species. Field observations suggested that hybrids were recruiting more rapidly than the native S. foliosa. Previous work identified competition from introduced S. alterniflora as a threat to native S. foliosa. In this study, we identify introgression and the spread of hybrids as an additional, perhaps even more serious threat to conservation of S. foliosa in San Francisco Bay.
Morphological and molecular variation among populations of octoploid fragaria virginiana and F. chiloensis (rosaceae) from North America
Authors: Harrison Richard E. , Luby James J. , Furnier Glenn R. , Hancock James F.
Published: April 2006

Relationships among 37 North American octoploid strawberry populations were studied by evaluating 44 morphological traits and 36 randomly amplified polymorphic DNA (RAPD) markers. Both data sets were analyzed by principal components analysis and UPGMA clustering based on genetic distances. Morphological data defined five groups: east of the Missouri River (Fragaria virginiana ssp. virginiana), the Black Hills (F. virginiana ssp. virginiana and ssp. glauca), from the eastern Cascades to the eastern Rocky Mountains (F. virginiana ssp. glauca), the western Cascades and Olympic Peninsula (F. virginiana ssp. platypetala), and the Pacific coast (F. chiloensis). Canonical discriminant analysis clearly discriminated populations into these provenances, suggesting that these groups are morphologically distinct. RAPD data defined three groups, one with F. virginiana ssp. virginiana and ssp. glauca, another with F. chiloensis, and a third with F. virginiana ssp. platypetala. The latter was more similar to F. chiloensis than F. virginiana, suggesting it is likely a subspecies of F. chiloensis. All octoploid North American strawberries have likely derived from a common ancestor and have differentiated into F. chiloensis and F. virginiana by adapting to moister and drier environments, respectively.
Reexamination of series relationships of South American wild potatoes (Solanaceae: Solanum sect. Petota): evidence from chloroplast DNA restriction site variation
Authors: Spooner David M. , T. Raul Castillo
Published: April 2006

Chloroplast DNA (cpDNA) restriction enzyme site analysis was used to test hypotheses of series and superseries affiliations of 76 taxa, representing 11 of the 13 South American series (material unavailable for two series) of wild potatoes (Solanum sect. Petota) recognized in the latest classification by Hawkes. The cladistic results, combined with those from earlier cpDNA studies of 30 taxa of the Mexican and Central American species (representing eight series; ser. Conicibaccata and ser. Tuberosa have representatives in Mexico and in South America), support four main clades for 17 of the 19 series examined in sect. Petota: (1) the Mexican and Central American diploid species, exclusive of S. bulbocastanum, S. cardiophyllum, and S. verrucosum, (2) S. bulbocastanum and S. cardiophyllum (ser. Bulbocastana, ser. Pinnatisecta), (3) South American diploid species constituting all of ser. Piurana, but also members of ser. Conicibaccata, ser. Megistacroloba, ser. Tuberosa, and ser. Yungasensia, (4) all Mexican and Central American polyploid species (ser. Longipedicellata, ser. Demissa), S. verrucosum (diploid Mexican species in ser. Tuberosa), and South American diploid and polyploid members of ser. Acaulia, ser. Circaeifolia, ser. Commersoniana, ser. Conicibaccata, ser. Cuneoalata, ser. Lignicaulia, ser. Maglia, ser. Megistacroloba, ser. Tuberosa, and ser. Yungasensia. Each of these clades contains morphologically and reproductively very diverse species, and there are no evident morphological features that unite members within a clade to therefore distinguish them. These results strongly suggest a need for a reevaluation of the series and superseries classifications of sect. Petota.
Decline of photosynthetic capacity with leaf age in relation to leaf longevities for five tropical canopy tree species
Authors: Kitajima Kaoru , Mulkey Stephen S. , Wright S. Joseph
Published: April 2006

The effect of leaf aging on photosynthetic capacities was examined for upper canopy leaves of five tropical tree species in a seasonally dry forest in Panama. These species varied in mean leaf longevity between 174 and 315 d, and in maximum leaf life span between 304 and 679 d. The light‐saturated CO2 exchange rates of leaves produced during the primary annual leaf flush measured at 7–8 mo of age were 33–65% of the rates measured at 1–2 mo of age for species with leaf life span of < 1 yr. The negative regression slopes of photosynthetic capacity against leaf age were steeper for species with shorter maximum leaf longevity. In all species, regression slopes were less steep than the slopes predicted by assuming a linear decline toward the maximum leaf age (20–80% of the predicted decline rate). Maximum oxygen evolution rates and leaf nitrogen content declined faster with age for species with shorter leaf life spans. Statistical significance of regression slopes of oxygen evolution rates against leaf age was strongest on a leaf mass basis (r2 = 0.49–0.87), followed by leaf nitrogen basis (r2 = 0.48–0.77), and weakest on a leaf area basis (r2 = 0.35–0.70).
A Survey of Anther Glands in the Mimosoid Legume Tribes Parkieae and Mimoseae
Authors: Luckow Melissa , Grimes James
Published: April 2006

In a broad survey of anther glands in the mimosoid legume tribes Mimoseae and Parkieae, representatives from 30 genera with anther glands were studied using scanning electron microscopy. Four kinds of anther glands could be distinguished. The Piptadenia‐type gland, found in all but four of the genera surveyed, is usually spherical to ellipsoid in shape and often borne on a stipe. The cells making up the gland vary in size among species and are often sculptured. Six different kinds of sculpturing can be recognized: smooth, reticulate, striate, rugulate, scabrate, and papillate. The Gagnebina‐type gland is the least specialized, consisting of a simple extension of the connective with irregularly projecting cells. The Prosopis africana‐type gland is borne ventrally between the thecae, the connective extending hump‐like over the apex of the anther. The Pentaclethra‐type gland, found only in the genus Pentaclethra, is distinguished by a median dorsal furrow and a ventral conical structure similar to a food body or osmophore. Anatomical sections revealed two different subtypes within the Piptadenia‐type gland. Some glands are composed of a homogeneous matrix of isodiametric cells, whereas others have two layers: a peripheral layer of large radially elongated cells, and a central sphere of smaller isodiametric cells and large air spaces. Some characters of anther glands have clear taxonomic significance, and more detailed surveys within genera will undoubtedly provide additional taxonomic markers.
The structure and function of RuBisCO and their Implications for Systematic Studies
Authors: Kellogg Elizabeth A. , Juliano Nickolas D.
Published: April 2006

As “the most abundant protein in the world,” ribulose‐1,5‐bisphosphate carboxylase (RuBisCO) attracts the attention of genetic engineers and plant phylogeneticists. The active site, which is responsible for almost all carbon fixation on earth, is in the large subunit (LSU). Over 30% of the 476 amino acids in the LSU are involved in intermolecular associations. Using available sequence data, we find that 105 (22%) of the residues are absolutely conserved across 499 seed plants, with an additional 110 demonstrating only one change. Our analyses show that conserved domains are not fully explained by current structural data. This has several implications for systematic studies. First, the number of potentially variable sites is likely to be slightly over 1000, rather than 1428. Second, rates of change can vary greatly across the molecule; functional constraints on amino acids and codon biases greatly increase the potential for homoplasy. Third, some changes are correlated, and thus might be down‐weighted accordingly. Fourth, some of the variation in RuBisCO may be adaptive and present insights into the nature of evolutionary change in response to the environment.
The mating system of the tropical understory shrub Ardisia escallonioides (Myrsinaceae)
Authors: Pascarella John B.
Published: April 2006

Electrophoretic analysis of progeny arrays was used to determine whether Ardisia escallonioides (Myrsinaceae), a self‐compatible tropical understory shrub in south Florida, exhibits a mixed‐mating system. Ten seedlings from seven to 16 maternal plants from four populations were analyzed using five polymorphic enzyme systems. Multilocus population outcrossing rates ranged from 0.39 to > 1, with three populations showing high levels of selfing. Both single and multilocus inbreeding coefficients (F) indicated excess homozygosity in seedlings but not adults for three of the four populations. Population outcrossing rate was not positively correlated with increased numbers of flowering plants. The importance of annual variation in population outcrossing rates is discussed with regard to the high temporal variability in seedling recruitment in this species.
Mating system of Carapa procera (Meliaceae) in the French Guiana tropical forest
Authors: Doligez Agnès , Joly Héèlène I.
Published: April 2006

The mating system of the tropical rainforest tree Carapa procera was studied for a population located within a sylvicultural trial in French Guiana. We used the mixed‐mating model with the genotypes of 47 open‐pollinated progenies at ten polymorphic loci, obtained through isozyme analysis. Seeds were collected on both logged and unlogged (control) plots, which were interspersed. A high multilocus outcrossing rate (0.78) was found for the global population, and there was indirect evidence for nonrandom mating for outcrosses. It is argued that this may be due to some kind of positive assortative mating, probably biparental inbreeding. Correlation of selfing between sibs was not significantly different from zero, and the proportion of full‐sibs among outcrossed sib‐pairs was significant but low (0.16). We found significant differences between outcrossing rates when computing separate estimates for the 14 trees located on logged plots (tm = 0.63) and the 33 trees located on undisturbed plots (tm = 0.85). It is argued that the decrease in density is probably not the only cause of the decrease in outcrossing rate on logged plots. Lastly, several points concerning the reliability of the estimation are outlined. In particular, the downward bias due to ignoring null alleles during genetic interpretations of zymograms is quantified in a few cases by simulating artificial populations.
Effects of mycorrhizae on plant growth and Dynamics in Experimental Tallgrass Prairie Microcosms
Authors: W Gail W. T. , Hartnett David C.
Published: April 2006

Experimental microcosms (40 ° 52 ° 32 cm) containing an assemblage of eight tallgrass prairie grass and forb species in native prairie soil were maintained under mycorrhizal (untreated control) or mycorrhizal‐suppressed (fungicide‐treated) conditions to examine plant growth, demographic, and community responses to mycorrhizal symbiosis. The fungicide benomyl successfully reduced mycorrhizal root colonization in the fungicide‐treated microcosms to only 6.4% (an 83% reduction relative to mycorrhizal controls). Suppression of mycorrhizas resulted in a 31% reduction in total net aboveground plant production and changes in the relative production of C4 and C3 plants. The C4 tallgrasses Andropogon gerardii and Sorghastrum nutans produced less plant biomass in the fungicide‐treated microcosms, and had a greater ratio of reproductive to vegetative biomass. Cool‐season C3 grasses, Koeleria pyramidata and Poa pratensis, accumulated more biomass and were a significantly greater proportion of total community biomass in mycorrhizal‐suppressed microcosms. Forbs showed variable responses to mycorrhizal suppression. The two legumes Amorpha canescens and Dalea purpurea had significantly lower survivorship in the fungicide‐treated microcosms, relative to the controls. The results confirm the high mycorrhizal dependency and growth responsiveness of dominant prairie grasses, and indicate that differential growth and demographic responses to mycorrhizal colonization among species may significantly affect plant productivity and species relative abundances in tallgrass prairie.
Genetics of adaptive radiation in Hawaiian and Cook Islands species of Tetramolopium (Asteraceae; Astereae). I. Nuclear RFLP marker diversity
Authors: Okada Miki , Whitkus Richard , Lowrey Timothy K.
Published: April 2006

Thirty‐three nuclear RFLP (restriction fragment length polymorphism) probes were used to study genetic diversity in Hawaiian and Cook Islands species of Tetramolopium for comparison with previous morphological and isozyme studies and to provide greater resolution of the events associated with adaptive radiation in the genus. Levels of RFLP diversity are greater than those reported for isozymes, yet are still low in comparison to continental species. Genetic differentiation is greatest among species in sections rather than among sections and is concordant with the hypothesis of phyletic sorting of initial variability as suggested for morphological traits. Hypothesized introgression between T. lepidotum and T. filiforme is supported, but the evidence suggests bidirectional gene flow. Systematic relationships derived from the data agree with hypotheses based on morphology in the placement of populations within their respective species and the recognition of three main lineages within Hawaii. Inclusion of the Cook Islands species, however, renders section Tetramolopium paraphyletic, contradicting morphological, ecological, and crossing evidence. Interpreting these results in light of evidence from previous studies, the genetic diversity and relationships seen among species and sections of Hawaiian and Cook Islands Tetramolopium reflect the recent and rapid evolution of this group, limited addition of new variability, and phyletic sorting.
Effect of salinity on growth, ion content, and cell wall chemistry in Atriplex prostrata (Chenopodiaceae)
Authors: Wang Li‐Wen , Showalter Allan M. , Ungar Irwin A.
Published: April 2006

Atriplex prostrata Boucher, a facultative halophyte, exhibits significant reduction in height and biomass and in the width of the cortex and vascular tissue under saline conditions. Therefore, the goal of this investigation was to determine the effect of salinity on plant growth as well as on the patterns of lignification, peroxidase activity, and extensin deposition. Biomass, leaf area, internode length, water potential, photosynthesis, transpiration, and ion content were measured. In addition, lignin, peroxidase, and extensin were, respectively, examined via phloroglucinol staining, peroxidase staining, and immunostaining with extensin antibody on tissue prints of free‐hand stem sections. Length of internodes and leaf area significantly decreased with increased salinity, and net photosynthesis declined dramatically as well. There was a significant accumulation of Na+ in organs when plants were grown in saline solutions, while the concentration of K+, Ca2+, and Mg2+ decreased. The signals in tissue prints showed that soluble peroxidase and extensin accumulated in the first three internodes of A. prostrata grown under saline conditions. In contrast, lignification was reduced under saline growth conditions in the third and fourth internodes. These results indicate that extensin may replace lignin in providing mechanical support for cells, while stems remain in a juvenile stage because of growth retardation caused by salinity.
The Flora of the Early Miocene Brandon Lignite, Vermont, USA. VIII. Caldesia (Alismataceae)
Authors: Haggard Kristina K. , Tiffney Bruce H.
Published: April 2006

Caldesia, a genus of aquatic monocotyledons, is represented by four living species, which are widely distributed in the temperate and tropical Old World. The genus has an extensive Oligocene through Pleistocene fossil record in Eurasia. We survey the morphology of the extant and fossil fruits of the Alismataceae, and provide a detailed review of the morphology and anatomy of living and fossil Caldesia fruits. The latter exhibit substantial similarity, making the recognition of separate species on the basis of fruit morphology difficult. We erect the new species Caldesia brandoniana from the Early Miocene Brandon Lignite of Vermont primarily on the basis of its geographic isolation; careful revision of all fossil fruiting material of Caldesia might require placement of the Brandon specimens in a more inclusive form species. Together with leaves of Caldesia from the Miocene Clarkia flora of Idaho, this occurrence indicates that Caldesia was in the New World as recently as the Early Miocene.
Relationships in the Caryophyllales as Suggested by Phylogenetic Analyses of Partial chloroplast DNA ORF2280 Homolog Sequences
Authors: Downie Stephen R. , Katz‐Downie Deborah S. , Cho Kyung‐Jin
Published: April 2006

Phylogenetic relationships within the angiosperm order Caryophyllales were investigated by comparative sequencing of two portions of the highly conserved inverted repeat (totaling some 1100 base pairs) coinciding with the region occupied by ORF2280 in Nicotiana, the largest gene in the plastid genomes of most land plants. Data were obtained for 33 species in 11 families within the order and for one species each of Plumbaginaceae, Polygonaceae, and Nepenthaceae. These data, when analyzed along with previously published ORF (open reading frame) sequences from Nicotiana, Spinacia, Epifagus, and Pelargonium using parsimony, neighbor‐joining, and maximum likelihood methods, reveal that: (1) Amaranthus, Celosia, and Froelichia (all Amaranthaceae) do not comprise a monophyletic group; (2) Amaranthus may be nested within a paraphyletic Chenopodiaceae; (3) Sarcobatus (Chenopodiaceae) is allied with Nyctaginaceae + Phytolaccaceae (the latter family excluding Stegnosperma but including Petiveria); and (4) Caryophyllaceae (with Corrigiola basal within the clade) are sister group to Chenopodiaceae + Amaranthaceae. Basal relations within the order remain obscure. Sequence divergence values in pairwise comparisons across all Caryophyllales taxa ranged from 0.1 to 5% of nucleotides. However, despite these low values, 23 insertion and deletion events were apparent, of which five were informative phylogenetically and bolstered several of the relationships listed above. A polymerase chain reaction (PCR) survey for ORF homolog length variants in representatives from 70 additional angiosperm families revealed major deletions, of ° 100 to 1400 base pairs, in 19 of these families. Although the ORF is located within the mutationally retarded inverted repeat region of most angiosperm chloroplast DNAs, this gene appears particularly prone to length mutation.
Effects of thermoperiod on recovery of seed Germination of Halophytes from Saline Conditions
Authors: Khan M. Ajmal , Ungar Irwin A.
Published: April 2006

Recovery of seed germination from NaCl salinity of desert shrubs (Haloxylon recurvum and Suaeda fruticosa, and the herbs Zygophyllum simplex and Triglochin maritima was studied under various thermoperiods. The percentage of ungerminated seeds that recovered when they were transferred to distilled water varied significantly with variation in species and thermoperiods. Zygophyllum simplex had little recovery from all NaCl concentrations in all thermoperiods. Haloxylon recurvum, S. fruticosa, and T. maritima showed substantial recovery. Percentage recovery was highest in S. fruticosa, followed by T. maritima, and H. recurvum. Thermoperiodic effects varied with the species investigated. There was little thermoperiodic effect on the percentage recovery of S. fruticosa, except in the higher salinity treatment at higher thermoperiods. Variation in thermoperiod appears to play an important role in recovery of germination of halophytes from salt stress when seeds are transferred to distilled water.
The genetic control of plastid division in higher plants
Authors: Pyke Kevin A.
Published: April 2006

The division of plastids is an important part of plastid differentiation and development and in distinct cell types, such as leaf mesophyll cells, results in large populations of chloroplasts. The morphology and population dynamics of plastid division have been well documented, but the molecular controls underlying plastid division are largely unknown. With the isolation of Arabidopsis mutants in which specific aspects of plastid and proplastid division have been disrupted, the potential exists for a detailed knowledge of how plastids divide and what factors control the rate of division in different cell types. It is likely that knowledge of plant homologues of bacterial cell division genes will be essential for understanding this process in full. The processes of plastid division and expansion appear to be mutually independent processes, which are compensatory when either division or expansion are disrupted genetically. The rate of cell expansion appears to be an important factor in initiating plastid division and several systems involving rapid cell expansion show high levels of plastid division activity. In addition, observation of plastids in different cell types in higher plants shows that cell‐specific signals are also important in the overall process in determining not only the differentiation pathway of plastids but also the extent of plastid division. It appears likely that with the exploitation of molecular techniques and mutants, a detailed understanding of the molecular basis of plastid division may soon be a reality.
Comparative floral development and evolution in tribe Caesalpinieae (Leguminosae: Caesalpinioideae). Haematoxylum
Authors: Tucker Shirley C. , Kantz Katherine E.
Published: April 2006

Floral organogenesis and development of the tropical legume trees Haematoxylum campechianum (logwood) and H. brasiletto (brazilwood) were studied using scanning electron microscopy. The aims were to compare ontogenies, and to elucidate the relationships of Haematoxylum with other genera of Caesalpinieae, the basal tribe of Caesalpinioideae. Flowers of Haematoxylum are in racemes or fascicles, lack bracteoles, and are pentamerous, hermaphroditic, and either actinomorphic or zygomorphic. Whorls arise in acropetal order except for the carpel, which arises concurrently with the outer stamens. Sepal order is bidirectional (a rare condition) within the whorl in both. Petals and outer stamens are initiated bidirectionally in H. campechianum, and unidirectionally in H. brasiletto. Inner stamens are initiated unidirectionally in both. In H. campechianum, time of petal initiation overlaps with that of outer stamens, and initiation of the two stamen whorls overlap. In both, the gynoecium becomes stipitate, and a hypanthium forms late in development. Both show many plesiomorphic states at anthesis; H. brasiletto alone shows several specialized states (expressed late in development), including a fused, gibbous calyx cup, a zygomorphic corolla, lightly aggregated filaments held together by hairs, and fenestrations in the stamen column. Ontogenetic divergence late in ontogeny characterizes differences at anthesis between related species.
Submarine pollination in the marine angiosperm Zostera marina (Zosteraceae). I. The influence of floral morphology on fluid flow
Authors: Ackerman Josef Daniel
Published: April 2006

An understanding of the process of submarine pollination should provide insight into the evolutionary and reproductive ecology of the marine angiosperms (seagrasses). The flow around the reproductive organs of the seagrass Zostera marina L. (Potamogetonales) was, therefore, examined in a flow chamber. The phenological emergence of flowers during (1) pollen capture and (2) pollen release, and by fruit during (3) seed release, led to a reduction in flow rate toward the inflorescence. This change in flow due to floral emergence was associated with a 50% increase in the fluid shear stress [τ = (2.2 ± 0.3) × 10−−3 Pa for an immature flower vs. τ = (3.1 ± 0.5) × 10−−3 Pa for a receptive flower]. The Reynolds number (Re) and fluid shear stress around inflorescences and infructescences were comparable, indicating a dynamic similarity in the processes of pollen capture and fruit dehiscence [Re = 47 ± 5, τ = (1.6 ± 0.3) × 10−−3 Pa for inflorescences; Re = 38 ± 5, τ = (1.3 ± 0.1) × 10−−3 Pa for infructescences]. These results indicate that the emergence of reproductive organs leads to changes in fluid shear stress, which will affect the release, transport, and capture of particles including pollen. Theoretical considerations of these observations using aerosol‐filtration theory suggest that pollen capture in Z. marina occurs through direct interception of pollen by stigmas.
Self‐incompatibility RNases from three plant families: homology or convergence?
Authors: Richman Adam D. , Broothaerts Wim , Kohn Joshua R.
Published: April 2006

In the Rosaceae, Scrophulariaceae, and Solanaceae, the stylar product of the self‐incompatibility (S‐) locus is an RNase. Using protein sequence data from 34 RNase genes (three fungal RNases, seven angiosperm non‐S RNases, 11 Rosaceae S‐alleles, three Scrophulariaceae S‐alleles, and ten Solanaceae S‐alleles) we reconstructed the genealogy of angiosperm RNases using the neighbor joining method and two distance metrics in order to assess whether use of S‐RNases in these families is the result of homology or convergence. Four monophyletic groups of angiosperm RNases were found: the S‐RNases of each of the three families and a group comprising most of the angiosperm non‐S RNases. The S‐RNases of the Scrophulariaceae and Solanaceae were found to be homologous but strong inference concerning the homology or convergence of S‐RNases from the Rosaceae with those of the other families was not possible because of uncertain placement of both the root and two of the angiosperm non‐S RNases. The most recent common ancestor of the Rosaceae and both the Scrophulariaceae and Solanaceae is shared by ~80% of dicot families. If the ‐RNases of the Rosaceae are homologous to those of the Scrophulariaceae and Solanaceae, then many other dicot families might be expected to share RNases as the mechanism of gametophytic self‐incompatibility.
Phylogenetic relationships of the Raphidophyceae and Xanthophyceae as inferred from nucleotide sequences of the 18s ribosomal RNA gene
Authors: Potter Daniel , Saunders Gary W. , Andersen Robert A.
Published: April 2006

Some earlier studies suggested an evolutionary relationship between the Raphidophyceae (chloromonads) and Xanthophyceae (yellow‐green algae), whereas other studies suggested relationships with different algal classes or the Öomycete fungi. To evaluate the relationships, we determined the complete nucleotide sequences of the 18S ribosomal RNA gene from the raphidophytes Vacuolaria virescens, Chattonella subsalsa, and Heterosigma carterae, and the xanthophytes Vaucheria bursata, Botrydium stoloniferum, Botrydiopsis intercedens, and Xanthonema debile. The results showed that the Xanthophyceae were most closely related to the Phaeophyceae. A cladistic analysis of combined data sets (nucleotide sequences, ultrastructure, and pigments) suggested the Raphidophyceae are the sister taxon to the Phaeophyceae—Xanthophyceae clade, but the bootstrap value was low (40%). The raphidophyte genera were united with high (100%) bootstrap values, supporting a hypothesis based upon ultrastructural features that marine and freshwater raphidophytes form a monophyletic group. We examined the relationship between Vaucheria, a siphoneous xanthophyte alga, and the Öomycetes, and we confirmed that Vaucheria is a member of the class Xanthophyceae. Partial nucleotide sequences of the 18S rRNA gene from eight xanthophytes (including Bumillariopsis filiformis, Heterococcus caespitiosus, and Mischococcus sphaerocephalus) produce a phylogeny that is not congruent with the current morphology‐based classification scheme.
Geographic parthenogenesis in a tropical forest tree
Authors: Thomas Sean C.
Published: April 2006

As evidenced by embryological studies, certain tropical tree species can reproduce asexually via seed; however, it has generally been assumed that such apomictic reproduction is facultative. Here I report the existence of a population of the lowland Malaysian rain forest tree Garcinia scortechinii King that consists entirely of pistillate individuals (40 female trees and no male trees recorded within a 25‐ha area). This constitutes the first documented observation of a geographically segregated, obligately asexual population among wild tropical trees. Six additional Garcinia species showed a trend toward female bias relative to other dioecious tree species studied, an observation that is consistent with facultative apomixis. The more surprising result for G. scortechinii runs counter to the generalization that obligate apomicts occur only in environments in which the absence of competitors might enable persistence of taxa that lack genetic recombination through mixis.
Evolution of extreme xeromorphic characters in wood: a study of nine evolutionary lines in Cactaceae
Authors: Mauseth James D. , Plemons‐Rodriguez Brandon J.
Published: April 2006

Vessels of xeric‐adapted woods have been predicted to be narrower than those of mesic‐adapted woods, to occur at higher densities, to occur in larger clusters, and to have a greater percentage of them in clusters. These predictions were tested by comparing wood structure of several evolutionary lines of xeric‐adapted cacti to that of mesic‐adapted Pereskia, which probably resembles the ancestral cacti. Although derived cacti occur in habitats with water stress ranging from mild (rain forests) to severe (open deserts with little vegetation other than cacti), as long as plants retain wood with an ordinary fibrous matrix, wood characters are remarkably uniform and not correlated with habitat aridity. However, in several evolutionary lines, novel wood types occur with characters that fulfill the predictions for xeric‐adapted woods listed above. However, conductive area (fraction of wood transverse‐sectional area occupied by conduits) and estimated specific conductance (conductance per square millimetre) are correlated with shoot height (the need for mechanical support from xylary fibers) rather than with habitat aridity: tall plants transport water through relatively few, wide vessels, permitting much of the wood volume to consist of fibers. Small plants with little wood use large numbers of narrow vessels rather than small numbers of wide ones, thereby achieving conductive safety.
Clonal analysis of leaf development in cotton
Authors: Dolana Liam , Poethig R. Scott
Published: April 2006

Clonal analysis has been used to describe the cellular parameters of leaf development in American Pima cotton (Gossypium barbadense). Sectors (clones) induced before leaf initiation indicate that the leaf primordium arises from ~100 cells on the flank of the shoot meristem. An analysis of sector frequency during the period of leaf expansion suggests that the rate of cell division is fairly uniform throughout the length of the leaf, but is lower at the margin of the lamina than in intercalary regions. The shapes of marginal sectors indicate that the orientation of cell division (as defined by the orientation of the new cell wall) in this region is more often parallel to the margin than perpendicular to it, although the degree of polarization varies along the length of the margin. There is a slight gradient in the duration of cell division along the length of of the lamina late in development, with cell division ceasing progressively from the lamina tip to the base over two cell cycles. The parameters of cell division in cotton are therefore similar to those described for tobacco with the notable exception of the behavior of cells at the leaf margin.
Pollinator preferences and the persistence of crop genes in wild radish populations (Raphanus raphanistrum, Brassicaceae)
Authors: Lee Ted N. , Snow Allison A.
Published: April 2006

Crop–weed hybridization can potentially influence the evolutionary ecology of wild populations. Many crops are known to hybridize with wild relatives, but few studies have looked at the long‐term persistence of crop genes in the wild. This study investigated one factor in the hybridization process in radish: differential pollinator visitation to wild radish (Raphanus raphanistrum) vs. crop–wild F1 hybrids (R. sativus × R. raphanistrum). Wild genotypes had yellow flowers, a recessive single‐locus trait, whereas hybrids always had white or pale pink flowers. In experimental arrays in northern Michigan, total pollinator visitation was significantly biased toward wild plants when the frequencies of wild and hybrid plants were equal. Syrphid flies, the most frequent visitors, preferred wild plants while bumble bees showed no preference. This pattern was also observed when hybrid plants were overrepresented in the array (12 hybrid: 2 wild). In contrast, when hybrid plants were rare (2 hybrid: 12 wild), neither morph was preferred by any pollinator group. Later in the summer, pollinators were also observed in a large experimental garden with nearly equal frequencies of wild and hybrid plants. Cabbage butterflies (Pieris rapae) strongly overvisited wild plants, while bumble bees showed a slight preference for hybrids. Taken together, these studies suggest that F1 hybrids may not be at a disadvantage with regard to pollinator visits when they occur at low frequencies or when bumble bees are frequent flower visitors. Thus, variation in the proportion of white‐flowered morphs among wild radish populations could be influenced by different histories of crop‐to‐wild hybridization, as well as by variation in the composition of local pollinator taxa.
Factors limiting seed production of Taxus Brevifolia (Taxaceae) in Western Oregon
Authors: DiFazio Stephen P. , Wilson Mark V. , Vance Nan C.
Published: April 2006

Seed production of Pacific yew (Taxus brevifolia), an understory conifer, was studied at four sites in western Oregon over 2 yr. The effects of pollen supplementation, overstory canopy, and predator exclusion on ovule attrition were examined. Supplemental hand‐pollination of ten trees at two sites resulted in significantly increased rates of ovule development and a doubling of seed efficiency (ratio of seeds to ovules). However, seed efficiency still averaged <15% on branches receiving supplemental pollen, so pollination was not a primary factor limiting seed production. The number of developing ovules was positively associated with overstory openness, but seed production was not. Seed efficiency was negatively associated with overstory openness. Branches bagged to exclude vertebrate seed predators had higher seed production than unbagged branches at three of four sites for 2 yr. In contrast to unbagged branches, seed production on bagged branches was positively associated with overstory openness, as was the effectiveness of bagging. Therefore, both vertebrate predation and overstory were important in limiting seed production, and these factors interacted. Factors limiting seed production varied in importance among the four sites and between years, illustrating the importance of examining multiple limiting factors over several sites and years.
Does self‐pollination provide reproductive Assurance in Aquilegia Canadensis (Ranunculaceae)?
Authors: Eckert Christopher G. , Schaefer Amy
Published: April 2006

The ability to produce seeds when pollinators or potential mates are scarce is thought to be one of the main advantages of self‐fertilization in flowering plants. However, whether autonomous selfing increases seed set in natural populations has seldom been tested, and even fewer studies have evaluated the advantage of selfing across a gradient of pollen availability. This study examines the fertility consequences of autonomous selfing in Aquilegia canadensis (Ranunculaceae), a short‐lived, spring‐flowering perennial typically found in small, patchy populations on rock outcrops. We used a pollinator exclusion experiment to confirm reports that A. canadensis has a well‐developed capacity for autonomous selfing resulting from incomplete protogyny and close proximity of stigmas and anthers during dehiscence. Flowers excluded from pollinators set 87% as many seeds per carpel (̄ ± 1 SE = 7.1 ± 1.4 seeds) as hand‐pollinated flowers (8.1 ± 1.3 seeds), and seed production in unpollinated flowers correlated negatively with the distance between stigmas and anthers (r = –0.46). Autonomous selfing could be potentially valuable in providing reproductive assurance because only 2.7 ± 0.5 pollen grains were deposited on each stigma before anther dehiscence, compared to 134.1 ± 17.9 pollen grains by the end of anther dehiscence. However, prevention of autonomous selfing by anther removal before dehiscence did not decrease seed set, even for plants at low plant densities where outcross pollen may have been in short supply. Emasculated flowers set as many seeds per carpel (9.3 ± 0.9) as intact flowers (8.4 ± 1.1), indicating that sufficient cross pollen is deposited for full seed set. These results do not support the hypothesis that autonomous selfing by A. canadensis has been selected because it provides reproductive assurance.
Allozyme and RAPD analysis of the genetic diversity and geographic variation in wild populations of the american chestnut (Fagaceae)
Authors: Huang gwen , Dane Fenny , Kubisiak Tom L.
Published: April 2006

Genetic variation among 12 populations of the American chestnut (Castanea dentata) was investigated. Population genetic parameters estimated from allozyme variation suggest that C. dentata at both the population and species level has narrow genetic diversity as compared to other species in the genus. Average expected heterozygosity was relatively low for the population collected in the Black Rock Mountain State Park, Georgia (He = 0.096 ± 0.035), and high for the population in east central Alabama (He = 0.196 ± 0.048). Partitioning of the genetic diversity based on 18 isozyme loci showed that ~10% of the allozyme diversity resided among populations. Cluster analysis using unweighted pair‐group method using arithmetric averages of Rogers’ genetic distance and principal components analysis based on allele frequencies of both isozyme and RAPD loci revealed four groups: the southernmost population, south‐central Appalachian populations, north‐central Appalachian populations, and northern Appalachian populations. Based on results presented in this study, a conservation strategy and several recommendations related to the backcross breeding aimed at restoring C. dentata are discussed.
Hormone transport and action in the green shoot: long‐term studies of a clonal stock of Coleus blumei (Labiatae)
Authors: Jacobs William P.
Published: April 2006

A decades‐long study of hormone production, transport, developmental actions, and hormonal interactions in the green shoots of mature plants has exploited a clone of Coleus blumei. To obtain data both quantitative and reproducible, we greatly increased sample size over the classical anatomical models, initiated round‐the‐clock collections, and countered that increased workload by clearing and staining organs rather than by embedding and serially sectioning them. Major developmental events occurred at night. The control of the normal differentiation and regeneration of tracheary cells and sieve‐tube members by indole‐3‐acetic acid (IAA) and cytokinins and of fibers by IAA and gibberellic acid have been major findings from this approach. IAA from the leaf blade controls the timing of leaf abscission. As the leaf ages, the ability of the petiole to transport IAA from the blade to the abscission zone declines, with abscisic acid (ABA) decreasing IAA transport down the petiole and concomitantly increasing the conjugation of IAA with aspartic acid. Evidence for transport barriers was found at nodes and abscission zones.
Evolution of interspersed repetitive elements in Gossypium (Malvaceae)
Authors: Hanson Robert E. , Zhao Xin‐ping , Islam‐Faridi M. Nurul , Paterson Andrew H. , Zwick Michael S. , Crane Charles F. , McKnight Thomas D. , Stelly David M. , Price H. James
Published: April 2006

Very little is known regarding how repetitive elements evolve in polyploid organisms. Here we address this subject by fluorescent in situ hybridization (FISH) of 20 interspersed repetitive elements to metaphase chromosomes of the cotton AD‐genome tetraploid Gossypium hirsutum and its putative A‐ and D‐genome diploid ancestors. These elements collectively represent an estimated 18% of the G. hirsutum genome, and constitute the majority of high‐copy interspersed repetitive elements in G. hirsutum. Seventeen of the elements yielded FISH signals on chromosomes of both G. hirsutum subgenomes, while three were A‐subgenome specific. Hybridization of eight selected elements, two of which were A‐subgenome specific, to the A2 genome of G. arboreum yielded a signal distribution that was similar to that of the G. hirsutum A‐subgenome. However, when hybridized to the D5 genome of G. raimondii, the putative diploid ancestor of the G. hirsutum D‐subgenome, none of the probes, including elements that strongly hybridized to both G. hirsutum subgenomes, yielded detectable signal. The results suggest that the majority, although not all, G. hirsutum interspersed repetitive elements have undergone intergenomic concerted evolution following polyploidization and that this has involved colonization of the D‐subgenome by A‐subgenome elements and/or replacement of D‐subgenome elements by elements of the A‐subgenome type.
Pollen donor performance can be consistent across maternal plants in wild radish (Raphanus sativus, Brassicaceae): a necessary condition for the action of sexual selection
Authors: Marshall Diane L.
Published: April 2006

The possibility that sexual selection has played a role in the evolution of plant reproductive characters remains interesting, but controversial. One reason is that clear demonstration of the necessary conditions for sexual selection is lacking. For sexual selection to occur, differences in pollen donor performance must be consistent across maternal plants and not be due to mechanisms such as self‐incompatibility that produce interactions between maternal plants and pollen donors. Here, I performed two experiments with wild radish to test whether differences in pollen donor performance are consistent across maternal plants and not due to subtle effects of the incompatibility system. In the first, all maternal and paternal lineages had different S‐alleles. There were 16 maternal plants, four in each of four lineages and four pollen donors, one in each of four lineages. Rank order of pollen donor performance, in terms of number of seeds sired after mixed pollination, was highly consistent across maternal plants and maternal lineages. In addition, maternal stress treatment had an effect on mating success of pollen donors, but the effect was subtle and did not affect the rank order of seeds sired by the four pollen donors. In the second experiment, pollinations were performed on both mature and immature stigmas. Immature stigmas allowed some self seed set, so the incompatibility system was compromised. There was some nonrandom seed paternity on both mature and immature stigmas. However, the amount of nonrandom mating was less on immature stigmas. Taken together, these experiments show that the kind of consistent nonrandom mating necessary for sexual selection occurs in wild radish, but that the incompatibility system and the mechanisms for sorting among compatible mates may overlap in time of development or in some pathways.
The features of cotyledon areoles in Leguminosae and their systematic utility
Authors: Endo Yasuhiko , Ohashi Hiroyoshi
Published: April 2006

The cotyledon areole, which is a spot with granular projections of epidermal cells, appears on the abaxial surface and on the midvein of some legume seed cotyledons. The distribution and systematic utility of cotyledon areoles were studied by observation of 132 legume species, which represent 100 genera and are classified into 34 tribes of three subfamilies, i.e., Caesalpinioideae, Mimosoideae, and Papilionoideae. The cotyledon areole is found in many species of Papilionoideae but not in the other two subfamilies. Presence of a cotyledon areole is presumed to be an apomorphic character state in Papilionoideae from the outgroup rule.