bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructure of stomatal development in Arabidopsis (Brassicaceae) leaves
Authors: Zhao Liming , Sack Fred D.
Published: April 2006

Stomatal development was studied in wild‐type Arabidopsis leaves using light and electron microscopy. Development involves three successive types of stomatal precursor cells: meristemoid mother cells, meristemoids, and guard mother cells (GMCs). The first two types divide asymmetrically, whereas GMCs divide symmetrically. Analysis of cell wall patterns indicates that meristemoids can divide asymmetrically a variable number of times. Before meristemoid division, the nucleus and a preprophase band of microtubules become located on one side of the cell, and the vacuole on the other. Meristemoids are often triangular in shape and have evenly thickened walls. GMCs can be detected by their roughly oval shape, increased starch accumulation, and wall thickenings on opposite ends of the cells. Because these features are also found in developing stomata, stomatal differentiation begins in GMCs. The wall thickenings mark the division site in the GMC since they overlie a preprophase band of microtubules and occur where the cell plate fuses with the parent cell wall. Stomatal differentiation in Arabidopsis resembles that of other genera with kidney‐shaped guard cells. This identification of stages in stomatal development in wild‐type Arabidopsis provides a foundation for the analysis of relevant genes and of mutants defective in stomatal patterning, cell specification, and differentiation.
Why be a honeyless honey mesquite? Reproduction and mating system of nectarful and nectarless individuals
Authors: Golubov Jordan , Eguiarte Luis E. , Mandujano Mari´a C. , Lo´pez‐Portillo Jorge , Montan~a Carlos
Published: April 2006

Populations of Prosopis glandulosa var. torreyana in the Chihuahuan desert have a fixed dimorphic system of nectar production in which half the individuals produce nectar (are nectarful) and the other half are nectarless. We analyzed the impact of nectar production on different estimates of fitness, comparing nectarful against nectarless individuals in size, mating system, seed traits, and fruit set in a 1‐ha scrubland. Of the reproductive individuals (358), 46% were nectarful and 54% were nectarless. Neither tree size nor flowering phenology differed between nectar morphs. Fixation indices (F) for both progeny (F = −0.2) and adults (F = −0.45) were negative, and high heterozygosities were found in adults and progeny (H = 0.45). No differences were found between nectar morphs for F, H, and single (ts = 1.1) and multilocus (tm = 1.03) outcrossing rates. Controlled pollinations showed differences between selfing and control treatments with no differences between nectar morphs. Nectarless individuals produced significantly more pollen grains than did nectar producers, but all other measured floral traits showed no differences. Nectarful trees were visited by pollinators 21 times more often and had a significantly higher overall fruit set than did nectarless trees. No differences between nectar morphs in seed mass or in percentage seed germination were found, but heavier seeds tended to have higher heterozygosities. Both morphs had similar success as females, but nectarless trees had ∼7% higher male function. We discuss three possible scenarios for the evolution of the fixed dimorphism in nectar production, two involving unstable phases (substitution of one morph by the other, and evolution towards dioecy) and one stable scenario (maintenance of the dimorphic system).
Inbreeding depression and selfing rates in a self‐compatible, hermaphroditic species, Schiedea membranacea (Caryophyllaceae)
Authors: Culley Theresa M. , Weller Stephen G. , Sakai Ann K. , Rankin Anne E.
Published: April 2006

Inbreeding depression and selfing rates were investigated in Schiedea membranacea (Caryophyllaceae), a hermaphroditic species endemic to the Hawaiian Islands. Most theoretical models predict high inbreeding depression in outcrossing hermaphroditic species and low inbreeding depression in inbreeding species. Although high outcrossing rates and high levels of inbreeding depression are characteristic of many species of Schiedea, self‐ fertilization is common among relatives of hermaphroditic S. membranacea, and high selfing rates and low levels of inbreeding depression were predicted in this species. Sixteen individuals grown in the greenhouse were used to produce selfed and outcrossed progeny. Inbreeding depression, which was evident throughout the stages measured (percentage viable seeds per capsule, mean seed mass, percentage seed germination, percentage seedling survival, and biomass after 8 mo), averaged 0.70. Inbreeding depression among maternal families varied significantly for all measured traits and ranged from −0.12 to 0.97. Using isozyme analysis, the multilocus selfing rate varied from 0.13 to 0.38 over 4 yr. Contrary to the initial prediction of high selfing and low inbreeding depression based on phylogenetic relationships within Schiedea, low selfing rates and high levels of inbreeding depression were found in S. membranacea. These results indicate that outcrossing is stable in this species and maintained by high levels of inbreeding depression.
Incongruence between chloroplast and species phylogenies in Eucalyptus subgenus Monocalyptus (Myrtaceae)
Authors: McKinnon Gay E. , Steane Dorothy A. , Potts Bradley M. , Vaillancourt Rene´ E.
Published: April 2006

Seventy‐eight polymorphic cpDNA (chloroplast DNA) characters were found in 13 closely related taxa from Eucalyptus series Amygdalinae (subgenus Monocalyptus) and seven potential outgroup taxa. The strict consensus of six cladograms generated from cpDNA data confirmed monophyly of Monocalyptus. However, cpDNA phylogeny within Monocalyptus was incongruent with taxonomic classification, being more related to geography, even when accessions were from divergent series. Monocalyptus cpDNA formed two major clades. On the island of Tasmania cpDNA was restricted to a single clade, exhibited very little variation, and was phylogenetically related to cpDNA found in central and western Victoria. In contrast, cpDNA of mainland monocalypt taxa was more variable, even within the Amygdalinae. Four out of six Tasmanian Amygdalinae species were polymorphic. The difference between cpDNA of replicates was often greater than differences between species from different series. The low level of cpDNA variation and extensive morphological intergradation between the Tasmanian endemics suggest recent speciation. However, the transfer of cpDNA through hybridization between lineages is the most likely explanation for the observed sharing of cpDNA across series. This study highlights that the geographical pattern to cpDNA variation in Eucalyptus may be an important source of information on past plant distributions in Australia.
Wound‐induced traumatic resin duct development in stems of Norway spruce (Pinaceae): anatomy and cytochemical traits
Authors: Nagy Nina E. , Franceschi Vincent R. , Solheim Halvor , Krekling Trygve , Christiansen Erik
Published: April 2006

Wounding of Norway spruce by inoculation with sterile agar, or agar containing the pathogenic fungus Ceratocystis polonica, induced traumatic resin duct formation in the stem. Visible anatomical responses occurred in the cambium 6–9 d post‐inoculation. Near the inoculation site cellular proliferation, polyphenolic accumulation, and lignification were induced as a wound reaction to seal the damaged area. Five centimetres from the inoculation site cells in the cambial zone swelled and divided to form clusters. By 18 d post‐inoculation, these cells began to differentiate into resin duct epithelial cells surrounding incipient schizogenous lumens. Mature axial traumatic ducts appeared by 36 d as a row of ducts in the xylem centripetal to the cambium. The ducts formed an interconnected network continuous with radial resin ducts. Parenchyma cells surrounding the ducts accumulated polyphenols that disappeared as the cells differentiated into tracheids. These polyphenols appeared to contain fewer sugar residues compared to those accumulating in the secondary phloem, as indicated by the periodic acid—Schiff's staining. The epithelial cells did not accumulate polyphenols but contained immunologically detectable phenylalanine ammonia lyase (EC 4.3.1.5), indicating synthesis of phenolics as a possible resin component. These findings may represent a defense mechanism in Norway spruce against the pathogenic fungus Ceratocystis polonica.
Consequences of phenotypic plasticity vs. interspecific differences in leaf and root traits for acquisition of aboveground and belowground resources
Authors: Ryser Peter , Eek Liina
Published: April 2006

Trade‐offs between acquisition capacities for aboveground and belowground resources were investigated by studying the phenotypic plasticity of leaf and root traits in response to different irradiance levels at low nutrient supply. Two congeneric grasses with contrasting light requirements, Dactylis glomerata and D. polygama, were used. The aim was to analyze phenotypic covariation in components of leaf area and root length in response to above‐ and belowground resource limitation and the consequences of this variation for resource acquisition and plant growth. At intermediate shading (30 and 20% of full sunlight) the plants were able to maintain their total root length, despite a strongly increased total leaf area and a reduced biomass allocation to roots. This was associated with an unaltered or slightly increased nutrient uptake and growth. At 5.5% relative irradiance, growth was severely reduced, especially in the shade‐tolerant D. polygama. The results show that constraints on acquisition capacities for aboveground and belowground resources, caused by biomass allocation, may be alleviated by plasticity in other traits such as tissue‐mass density and thickness of roots and leaves. The results also suggest different adaptive constraints for phenotypic plasticity and for genetically determined interspecific variation. Phenotypic plasticity tends to maximize resource acquisition and growth rate in the short term, whereas the higher tissue‐mass density and the longer leaf life‐span of shade‐tolerant species indicate reduced loss rates as a more advantageous species‐specific adaptation to shade in the long term.
Artocarpus (Moraceae)–gall midge pollination mutualism mediated by a male‐flower parasitic fungus
Authors: Sakai Shoko , Kato Makoto , Nagamasu Hidetoshi
Published: April 2006

A previously undescribed pollination system involving a monoecious tree species, Artocarpus integer (Moraceae), pollinator gall midges, and fungi is reported from a mixed dipterocarp forest in Sarawak, Borneo. The fungus Choanephora sp. (Choanephoraceae, Mucorales, Zygomycetes) infects male inflorescences of A. integer, and gall midges (Contarinia spp., Cecidomyiinae, Diptera) feed on the fungal mycelia and oviposit on the inflorescence. Their larvae also feed on the mycelia and pupate in the inflorescence. The gall midges are also attracted by female inflorescences lacking mycelia, probably due to a floral fragrance similar to that of male inflorescences. Because of the sticky pollen, dominance of Contarinia spp. in flower visitors, and pollen load observed on Contarinia spp. collected on both male and female inflorescences, Artocarpus integer is thought to be pollinated by the gall midges. Although several pathogenic fungi have been reported to have interactions with pollinators, this is the first report on a pollination mutualism in which a fungus plays an indispensable role. The pollination system described here suggests that we should be more aware of the roles fungi can play in pollinations.
Pollen and anther development inNelumbo(Nelumbonaceae)
Authors: Kreunen Sarah S. , Osborn Jeffrey M.
Published: April 2006

The Nelumbonaceae are a small family of aquatic angiosperms comprisingNelumbo nuciferaandNelumbo lutea.Historically, the genus has been considered to be closely related to Nymphaeales, however new systematic work has alliedNelumbowith lower eudicots, particularlyPlatanus.In recent years, studies of pollen development have contributed greatly to the understanding of phylogenetic relationships, but little has been known about these events inNelumbo.In this paper, pollen and anther development are morphologically described for the first time inN. lutea.A comprehensive ontogenetic sequence is documented, including the sporogenous tissue, microspore mother cell, tetrad, free spore, and mature pollen grain stages. The deposition of a microspore mother cell coat and callose wall, the co‐occurrence of both tetrahedral and tetragonal tetrads, the formation of a primexine in tetrads, and primexine persistence into the late free spore stage are shown. The majority of exine development occurs during the free spore stage with the deposition of a tectate‐columellate ectexine, a lamellate endexine, and an unusual granular layer below and intermixed with the endexine lamellae. A two‐layered intine forms rapidly during the earliest mature pollen stage. Major events of anther development documented include the degradation of a secretory‐type tapetum during the free spore stage and the rapid formation of U‐shaped endothecial thickenings in the mature pollen grain stage. The majority of mature pollen grains are tricolpate, however less common monosulcate and diaperturate grains also develop. Co‐occurring aperture types inNelumbohave been suggested to be an important transition in angiosperm aperture number. However, aperture variability inNelumbomay be correlated with the lateness of aperture ontogeny in the genus, which occurs in the early free spore stage. This character, as well as other details of pollen and anther ontogeny inNelumbo,are compared to those of Nymphaeales andPlatanusin an effort to provide additional insight into systematic and phylogenetic relationships. AlthoughNelumbois similar to both groups in several characters, the ontogenetic sequence of the genus is different in many ways.
Phylogenetic relationships of Eurasian pines (Pinus, Pinaceae) based on chloroplast rbcL, MATK, RPL20‐RPS18 spacer, and TRNV intron sequences
Authors: Wang Xiao‐Ru , Tsumura Yoshihiko , Yoshimaru Hiroshi , Nagasaka Kazutoshi , Szmidt Alfred E.
Published: April 2006

The sequence divergence of chloroplast rbcL, matK, trnV intron, and rpl20‐rps18 spacer regions was analyzed among 32 Pinus species and representatives of six other genera in Pinaceae. The total aligned sequence length is 3570 bp. Of the four sequences examined, matK evolved much faster than rbcL in Pinus and in other Pinaceae genera. The two noncoding regions did not show more divergence than the two coding regions, especially within each Pinus subgenus. Phylogenetic analyses based on these four sequences gave consistent results and strongly supported the monophyly hypothesis for the genus Pinus and its two recognized subgenera. Pinus krempfii, the two‐flat‐needle pine endemic to Vietnam, was placed in subgen. Strobus and showed closer affinity to subsect. Gerardianae. The ancient character of sect. Parrya is further confirmed. However, monophyly of the sect. Parrya is not supported by our data. Among the Eurasian pines of subgen. Pinus, Mediterranean pines formed one clade and the Asian members of subsect. Sylvestres formed another. The Himalayan P. roxburghii showed considerable divergence from all the other hard pines from both regions. Pinus merkusii was distinctly separated from all the Asian members of subsect. Sylvestres. The implications of our results for Pinus classification are discussed.
Hybridization among sympatric species of Rhododendron (Ericaceae) in Turkey: morphological and molecular evidence
Authors: Milne Richard I. , Abbott Richard J. , Wolff Kirsten , Chamberlain David F.
Published: April 2006

Rhododendron (Ericaceae) is a large genus in which barriers to hybridization are especially weak, but many species are maintained in sympatry. Hybridization among four species of Rhododendron subsect. Pontica, which occur in sympatry in Turkey, was investigated. Material of R. ponticum, R. smirnovii, R. ungernii, and R. caucasicum and their putative hybrids was collected from the wild. Based on morphology, chloroplast DNA and nuclear ribosomal DNA restriction fragment length polymorphism (RFLP) profiles, each accession was identified as a species or hybrid combination. Five of the six possible hybrid combinations among the four species were detected. Rhododendron ponticum × R. smirnovii was represented by a single individual and R. caucasicum × R. smirnovii by one small group of hybrid plants. The combinations R. ponticum × R. ungernii and R. ungernii × R. smirnovii showed evidence of frequent backcrossing, while R. ponticum × R. caucasicum appeared unusual in that an intermediate hybrid type was abundant, whereas hybrids with phenotypes approaching either parent were rare. Possible explanations of this latter situation are discussed. The results suggest that natural hybridization among Rhododendron species is common and that ecological factors are important in maintaining integrity when species occur in sympatry.
Dominant Wilty mutants of Zea mays (Poaceae) are not impaired in abscisic acidperception or metabolism
Authors: Rock Christopher D. , Ng Patrick P. F.
Published: April 2006

Abscisic acid (ABA) is a plant hormone involved in growth, development, and stress adaptation. It acts via multiple pathways including rapid closure of stomatal pores by ion efflux from guard cells (thereby decreasing water loss) and by slower changes in gene expression. The Wilty2, Wilty3, and Wilty‐2445 mutants are nonallelic members of a class of dominant mutants whose top leaves wilt when plants are subjected to drought conditions. We investigated the ABA responses of the Wi2 mutant by analysis of leaf transpiration rates and RAB17 (Responsive to ABA) gene expression. Wi2 leaves transpired less than those of wild‐type siblings, but the slopes of Wi2 and wild‐type ABA dose‐leaf transpiration curves were identical, suggesting that Wi2 guard cell sensitivity to ABA is normal. Based on total RNA blot analysis, RAB17 transcripts in unstressed and drought‐stressed Wi2 leaves were elevated relative to wild‐type tissue. Wi2 ABA concentrations were also elevated relative to wild type in both unstressed and drought‐stressed leaves. Similar to the Wi2 phenotype, Wilty3 and Wi‐2445 mutants transpired less than their wild‐type siblings and had normal ABA and ABA‐conjugate levels, as measured by gas chromatography‐mass spectrometry. Despite lower leaf transpiration rates, Wi2 mutants lost a greater percentage of fresh mass over time compared to the wild type. The previously characterized recessive mutant wilty1, which has a defect in vascular element development, also had reduced transpiration rates. It is concluded that the dominant Wi2, Wi3, and Wi‐2445 mutants are not impaired in ABA metabolism or signaling. It is hypothesized, based on preliminary data, that the dominant mutants described here are impaired in vascular element development, analogous to the wilty1 mutant.
Meristem growth dynamics and branching patterns in the Cladoniaceae
Authors: Hammer Samuel
Published: April 2006

Branching patterns in the lichen family Cladoniaceae are varied and taxonomically important. Branching occurs on the podetium, the erect secondary thallus that characterizes most species in the Cladoniaceae, and is influenced by growth dynamics of the fungal meristem tissue at the apex of the podetium. Branching is primarily the result of meristem divisions, and branching patterns are modified by meristem enlargement, deformation, and torsion. Branching processes are conserved, and early branch ontogeny provides information from which to determine relationships in the Cladoniaceae. Branching is characterized by two major patterns. In one pattern, branches arise from the relatively late divisions of a large meristem (≥100 μm in diameter), whose shape changes during ontogeny. In a second pattern, branches arise from small meristems (<100 μm in diameter), which split early in ontogeny but whose shape does not change. The trend toward reduced meristems that split early in ontogeny is seen as an evolutionary advance in the Cladoniaceae. Some “small meristem” species retain aspects of the “large meristem” habit in early ontogeny, and this provides a clue to their relationships. Patterns of meristem growth dynamics provide a basis for interpreting phylogeny in mycobionts of the Cladoniaceae. Meristem activities in four genera of the Cladoniaceae were compared in order to determine trends in growth dynamics within the family.
Sex ratios and genetic variation in a functionally androdioecious species, Schizopepon bryoniaefolius (Cucurbitaceae)
Authors: Akimoto Junichi , Fukuhara Tatsundo , Kikuzawa Kihachiro
Published: April 2006

Androdioecy, coexistence of hermaphrodites and males, is an extremely rare breeding system in angiosperms. In the present study, Schizopepon bryoniaefolius (Cucurbitaceae) was confirmed to be functionally androdioecious based on observations of floral and pollen morphology and bagging experiments. Six out of the 11 studied populations consisted of only hermaphrodites, while the other five populations were androdioecious and the frequencies of males were consistently lower than those of hermaphrodites (5.5–28.3%). To understand the consequences of an androdioecious breeding system, genetic variation was estimated using four polymorphic allozyme loci. The degree of genetic differentiation among 11 populations was high (GST = 0.688). Inbreeding coefficients (FIS) for all loci significantly deviated from zero. In particular, the FIS values averaged across the polymorphic loci in hermaphrodite populations were close to unity, suggesting that hermaphrodites are predominantly selfing in the absence of males. A significant negative correlation was found between the frequencies of males and inbreeding coefficients, indicating that outcrossing rates depend on the population sex ratio.
Long‐distance seed dispersal in plant populations
Authors: Cain Michael L. , Milligan Brook G. , Strand Allan E.
Published: April 2006

Long‐distance seed dispersal influences many key aspects of the biology of plants, including spread of invasive species, metapopulation dynamics, and diversity and dynamics in plant communities. However, because long‐distance seed dispersal is inherently hard to measure, there are few data sets that characterize the tails of seed dispersal curves. This paper is structured around two lines of argument. First, we argue that long‐distance seed dispersal is of critical importance and, hence, that we must collect better data from the tails of seed dispersal curves. To make the case for the importance of long‐distance seed dispersal, we review existing data and models of long‐distance seed dispersal, focusing on situations in which seeds that travel long distances have a critical impact (colonization of islands, Holocene migrations, response to global change, metapopulation biology). Second, we argue that genetic methods provide a broadly applicable way to monitor long‐distance seed dispersal; to place this argument in context, we review genetic estimates of plant migration rates. At present, several promising genetic approaches for estimating long‐distance seed dispersal are under active development, including assignment methods, likelihood methods, genealogical methods, and genealogical/demographic methods. We close the paper by discussing important but as yet largely unexplored areas for future research.
Cross‐species amplification of cassava (Manihot esculenta) (Euphorbiaceae) microsatellites: allelic polymorphism and degree of relationship
Authors: Roa Ana C. , Chavarriaga‐Aguirre Paul , Duque Myriam C. , Maya María M. , Bonierbale Merideth W. , Iglesias Carlos , Tohme Joe
Published: April 2006

Microsatellite amplification was performed on cassava (Manihot esculenta) and six other different species (all wild) of the Manihot genus. We used ten pairs of microsatellite primers previously developed from cassava, detecting 124 alleles in a sample of 121 accessions of the seven species. The number of alleles per locus ranged from four to 21 alleles, and allelic diversity was greater in the wild species than in cassava. Seventy‐nine alleles, including unique ones, were detected in the wild species but were not found in the crop. The lower level of heterozygosity in some wild species probably resulted from a combination of fine‐scale differentiation within the species and the presence of null alleles. Overall, microsatellite primers worked across the genus, but, with increasing genetic distance, success in amplifying loci tended to decrease. No accession of M. aesculifolia, M. carthaginensis, and M. brachyloba presented a banding pattern at locus Ga‐140; neither did one appear for M. aesculifolia at locus Ga‐13. Previous work with amplified fragment length polymorphism (AFLP) markers and this microsatellite analysis show that these three wild taxa are the most distant relatives of the crop, whereas the wild forms M. esculenta subsp. flabellifolia and M. esculenta subsp. peruviana appear to be the closest.
Comparative morphology and physiology of fruit and seed development in the two shrubs Rhus aromatica and R. glabra (Anacardiaceae)
Authors: Li Xiaojie , Baskin Jerry M. , Baskin Carol C.
Published: April 2006

Morphology and physiology of fruit and seed development were compared in Rhus aromatica and R. glabra (Anacardiaceae), both of which produce drupes with water‐impermeable endocarps. Phenology of flowering/fruiting of the two species at the study site was separated by ∼2 mo. However, they were similar in the timetable and pattern of fruit and seed development; it took ∼2 mo and ∼1.5 mo for flowers of Rhus aromatica and R. glabra, respectively, to develop into mature drupes. The single sigmoidal growth curve for increase in fruit size and in dry mass of these two species differs from the double‐sigmoidal one described for typical commercial drupes such as peach and plum. Order of attainment of maximum size was fruit and endocarp (same time), seed coat, and embryo. By the time fruits turned red, the embryo had reached full size and become germinable; moisture content of seed plus endocarp had decreased to ∼40%. The endocarp was the last fruit component to reach physiological maturity, which coincided with development of its impermeability and a seed plus endocarp moisture content of <10%. At this time, ∼50, 37, and 13% of the dry mass of the drupe was allocated to the exocarp plus mesocarp unit, endocarp, and seed, respectively. The time course of fruit and seed development in these two species is much faster than that reported for other Anacardiaceae, including Rhus lancea, Protorhus, and Pistacia.
Floral plasticity in an iteroparous plant: the interactive effects of genotype, environment, and ontogeny in Campanula rapunculoides (Campanulaceae)
Authors: Vogler Donna W. , Peretz Shani , Stephenson Andrew G.
Published: April 2006

Phenotypic variation in 11 floral and reproductive traits was studied in cloned plants of Campanula rapunculoides replicated in three discrete environments. Using an ANOVA approach, we determined the relative influence of genotype (G), environment (E), G × E interaction, and ontogeny (position on the raceme) on the 11 traits. Two traits, duration of flowering and pollen size, showed no significant variation. All nine remaining traits had significant genotypic variation, accounting for 21–38% of the total phenotypic variation. Correlations among variant traits in seven genotypes were predominantly positive, but several significant correlations in one environment changed sign or were nonsignificant in another environment. Ovule number was negatively correlated with most male function traits: the negative correlation between ovule and pollen number was particularly strong and consistent across environments. Six traits varied significantly across environments, including number of flowers, number of ovules per flower, and duration of the male phase, but pollen traits did not show a significant environmental main effect. The G × E interaction was significant for flower number, corolla size, nectar quality, duration of the male phase, pollen viability, and ovule number. The contribution of interaction variance to the total phenotypic variation (5–14%) was comparable to that of the environment alone (7–21%). Ovule number decreased in flowers on the upper part of the raceme by nearly 25%, but other traits did not vary significantly by floral position. These results suggest that (1) pollen traits are buffered against environmental change more than ovule number or other floral characters, (2) a male–female trade‐off exists and is complicated by ontogenic factors, (3) G × E interactions are common but may have small effects, and (4) specific correlation patterns among floral traits can be dependent upon the environment under which they develop.
Seedbed and moisture availability determine safe sites for early Thuja occidentalis (Cupressaceae) regeneration
Authors: Cornett Meredith W. , Reich Peter B. , Puettmann Klaus J. , Frelich Lee E.
Published: April 2006

Regeneration of many late‐successional tree species depends on specialized safe sites. The primary objective was to investigate the roles of seedbed and moisture retention as dimensions of safe sites for the early regeneration of drought‐sensitive northern white cedar (Thuja occidentalis). We hypothesized that rates of germination, survival, and growth of T. occidentalis are unlikely to differ among seedbed types under conditions of abundant water, but that differences are likely to emerge as water becomes more limited. In a 67‐d greenhouse experiment, cedar seeds were sown on logs, leaf litter, and soil of cedar and paper birch (Betula papyrifera) canopy origin. Seedbeds were subjected to three water treatments. Among the water treatments, highest germination rates occurred within the high water treatment, although germination on cedar litter was comparable to that of the low water treatment. Higher germination and survival rates occurred on decayed logs than other natural seedbeds for medium (P = 0.001) and low (P < 0.0001) water treatments. Germination on birch logs occurred at higher rates than on cedar logs within the low water treatment (P = 0.04). Seedling growth for the medium water treatment was lower on leaf litter than any other type of seedbed (P < 0.01). Results generally demonstrated that the interplay between seedbed and moisture retention is a component of safe sites for T. occidentalis regeneration.
Floral dimorphism, pollination, and self‐fertilization in gynodioecious GERANIUM RICHARDSONII (Geraniaceae)
Authors: Williams Charles F. , Kuchenreuther Margaret A. , Drew Allison
Published: April 2006

The selective maintenance of gynodioecy depends on the relative fitness of the male‐sterile (female) and hermaphroditic morphs. Females may compensate for their loss of male fitness by reallocating resources from male function (pollen production and pollinator attraction) to female function (seeds and fruits), thus increasing seed production. Females may also benefit from their inability to self‐fertilize if selfing and inbreeding depression reduce seed quality in hermaphrodites. We investigated how differences in floral resource allocation (flower size) between female and hermaphroditic plants affect two measures of female reproductive success, pollinator visitation and pollen receipt, in gynodioecious populations of Geranium richardsonii in Colorado. Using emasculation treatments in natural populations, we further examined whether selfing by autogamy and geitonogamy comprises a significant proportion of pollen receipt by hermaphrodites. Flowers of female plants are significantly smaller than those of hermaphrodites. The reduction in allocation to pollinator‐attracting structures (petals) is correlated with a significant reduction in pollinator visitation to female flowers in artificial arrays. The reduction in attractiveness is further manifested in significantly less pollen being deposited on the stigmas of female flowers in natural populations. Autogamy is rare in these protandrous flowers, and geitonogamy accounts for most of the difference in pollen receipt between hermaphrodites and females. Female success at receiving pollen was negatively frequency dependent on the relative frequency of females in populations. Thus, two of the prerequisites for the maintenance of females in gynodioecious populations, differences in resource allocation between floral morphs and high selfing rates in hermaphrodites, occur in G. richardsonii.
Pollen viability reduction as a potential cost of ant association forAcacia constricta(Fabaceae)
Authors: Wagner Diane
Published: April 2006

Field studies investigating the impact of ants on the reproduction of plants bearing extrafloral nectaries have traditionally focused on seed production, a component of female fitness. The purpose of this study was to test whether ants can affect the pollen viability, a component of male fitness, when they visit flowers of the shrubAcacia constricta. Acacia constrictainflorescences hand‐pollinated with flowers over whichFormica perpilosaants had crawled set significantly fewer seed pods than inflorescences hand‐pollinated by control flowers that had no contact with ants. Many ant species secrete antibiotic substances onto the integument that render pollen inviable, and these secretions are probably the mechanism for reduced pollen viability in this study. The ratio of seed pods produced by self‐pollinated inflorescences to those produced by cross‐pollinated inflorescences was 0.16, indicating thatA. constrictais largely self‐incompatible. BecauseF. perpilosaworkers forage primarily on the acacia tree under which they nest, they are unlikely to serve as efficient vectors of outcrossing. Previous work showed thatA. constrictashrubs withF. perpilosaants produce approximately twice as many seeds as similarly sized plants not so associated. The results indicate that association withF. perpilosacould cause a reproductive trade‐off forA. constricta: benefits to female function may be accompanied by costs to male function. Selection to discourage ant visitation to flowers may have affected the pollination biology of this and other ant‐associated plant species.
Patterns of genetic variation in rare and widespread plant congeners
Authors: Gitzendanner Matthew A. , Soltis Pamela S.
Published: April 2006

Rare species are typically considered to maintain low levels of genetic variation, and this view has been supported by several reviews of large numbers of isozyme studies. Although these reviews have provided valuable data on levels of variability in plant species in general, and rare species in particular, these broad overviews involve comparisons that may confound the effects of rarity with a multitude of other factors that affect genetic variability. Additionally, the statistical analyses employed assume the data to be independent, which is not the case for organisms that share a common phylogenetic history. As the role of evolutionary history and historical constraints has become better understood, more researchers have studied widespread congeners when investigating the genetic diversity of rare species in an effort to control for these effects. We summarize the available data from such studies, comparing for rare and widespread congeners (1) the levels of genetic variability at the population and species levels and (2) measures of population substructuring. At the population level, we summarized data for percentage polymorphic loci (%Ppop), mean number of alleles per locus (Apop), and observed heterozygosity (Ho). Species‐level measures used were percentage polymorphic loci (%Pspp), mean number of alleles per locus (Aspp), and total genetic diversity (HT). Indices of population subdivision (eitherFSTorGST) were also examined. Using Wilcoxon signed rank tests, we found significant, but small, differences between rare and widespread species for all diversity measures exceptHT. However, there does not appear to be a difference between rare and widespread congeners in terms of how genetic variation is partitioned within and among populations. Levels of diversity, for all measures examined, between rare and widespread congeners are highly correlated.
How accessible are receptive megastrobili to pollen? the example of jack pine (Pinus banksiana)
Authors: Roussy Anne‐Marie , Kevan Peter G.
Published: April 2006

We examined the effects of wind speeds on pollen capture by megastrobili of jack pine (Pinus banksiana). We found that, when wind speed increased from 1.3 to 7.5 m/s, the relative capture efficiency (Er) did not change significantly (P ≤ 0.206) and remained below 12%. However, total capture rates increased linearly with wind speed and atmospheric pollen density. Because theoretical models of capture efficiency predict the Er to increase to ∼80% asymptotically, our findings suggest that receptive megastrobili are equally adept at capturing pollen at all naturally occurring wind speeds.
Clonal growth of Lithospermum caroliniense (Boraginaceae) in contrasting sand dune habitats
Authors: Weller Stephen G. , Keeler Kathleen H. , Thomson Barbara A.
Published: April 2006

The occurrence of clonal growth of distylous Lithospermum caroliniense was investigated in a population in the Nebraska Sandhills, an area where sand dunes have been relatively stable for at least 1500–3000 yr, and compared to a population occurring at the Indiana Dunes, an area of active sand dune formation. Spatial autocorrelation analysis indicated the occurrence of significant clonal propagation of genetically based floral morphs at Arapaho Prairie, but not for the Indiana Dunes. Apparent clonal growth in the Sandhills population had no overall negative effect on pollen deposition or fecundity relative to the Indiana population, although in some large clones the proportion of compatible pollen grains on stigmas was lower. Clonal growth may have occurred in the Sandhills population because of the greater age and stability of the Nebraska Sandhills; infrequent establishment of seedlings permits detection of clonal growth using the spatial pattern of floral morphs. At the Indiana dunes, repeated cycles of dune formation provide conditions favoring establishment of seedlings, and sand dune succession results in disappearance of L. caroliniense before the development of clones.
Interactive effects of elevated CO2and temperature on water transport inponderosa pine
Authors: Maherali Hafiz , DeLucia Evan H.
Published: April 2006

Many studies report that water flux through trees declines in response to elevated CO2, but this response may be modified by exposure to increased temperatures. To determine whether elevated CO2and temperature interact to affect hydraulic conductivity, we grew ponderosa pine seedlings for 24 wk in growth chambers with one of four atmospheric CO2concentrations (350, 550, 750, and 1100 ppm) and either a low (15°C nights, 25°C days) or high (20°C nights, 30°C days) temperature treatment. Vapor pressure deficits were also higher in the elevated temperature treatment. Seedling biomass increased with CO2concentration but was not affected by temperature. Root : shoot ratio was unaffected by CO2and temperature. Leaf : sapwood area ratio (AL/AS) declined in response to elevated temperature but was not influenced by CO2. Larger tracheid diameters at elevated temperature caused an increase in xylem‐specific hydraulic conductivity (KS). The increase inKSand decrease inAL/ASled to higher leaf‐specific hydraulic conductivity (KL) at elevated temperature. Stomatal conductance (gS) was correlated withKLacross all treatments. NeitherKS,KL, norgSwere affected by elevated CO2concentrations. HighKLin response to elevated temperature may support increased transpiration or reduce the incidence of xylem cavitation in ponderosa pine in future, warmer climates.
Phylogeny of South African Gnaphalieae (Asteraceae) based on two noncoding chloroplast sequences
Authors: Bayer Randall J. , Puttock Christopher F. , Kelchner Scot A.
Published: April 2006

The Gnaphalieae are a group of sunflowers that have their greatest diversity in South America, Southern Africa, and Australia. The objective of this study was to reconstruct a phylogeny of the South African Gnaphalieae using sequence data from two noncoding chloroplast DNA sequences, the trnL intron and trnL/trnF intergenic spacer. Included in this investigation are the genera of the Gnaphalieae from the African basal groups, members of the subtribes Cassiniinae, Gnaphaliinae, and Relhaniinae, and African representatives from the large Old World genus Helichrysum. Results indicate that two Gnaphaloid genera, Printzia and Callilepis, should be excluded from the Gnaphalieae. In most trees the Relhaniinae s.s. (sensu stricto) and some of the basal taxa comprise a clade that is sister to the remainder of the tribe Gnaphalieae. The Relhaniinae, which are restricted to Africa, are not a monophyletic group as presently circumscribed, nor are the South African members of Helichrysum, the Cassiniinae and Gnaphaliinae. There is general agreement between our molecular analysis and that of morphology, particularly in the terminal branches of the trees.
Reproductive biology and conservation genetics of Goodyera procera (Orchidaceae)
Authors: Wong K. C. , Sun M.
Published: April 2006

Goodyera procera is an endangered terrestrial orchid in Hong Kong. Information on its reproductive biology and pattern of genetic variation is needed to develop efficient conservation strategies. Pollination experiments showed that the species is self‐compatible, but dependent on pollinators for fruit set. Bagged plants produced no fruits. Artificial pollinations resulted in 92% fruit set through selfing, 94% with geitonogamous pollination, and 95% following xenogamous pollination. Fruit set in the open‐pollinated control was 75% at the same sites. Allozyme electrophoresis and random amplified polymorphic DNA (RAPD) were used to evaluate genetic variation and structure of 15 populations of Goodyera procera. Despite its outbreeding system, allozyme data revealed low variation both at the population (P = 21.78%, A = 1.22, and H = 0.073) and species (P = 33%, A = 1.33, and H = 0.15) levels, in comparison with other animal‐pollinated outbreeding plant species. However, RAPD variation was relatively high (P = 55.13% and H = 0.18 at the population level, and P = 97.03% and H = 0.29 at the species level). GST estimates indicated high levels of genetic differentiation among populations (GST = 0.52 and I = 0.909 ± 0.049 based on allozyme data, and GST = 0.39 and I = 0.859 ± 0.038 based on RAPD data), much above the average for outcrossing species, suggesting that gene flow was limited in this species. Based on these data, suitable strategies were developed for the genetic conservation and management of the species.
Light environment, sapling architecture, and leaf display in six rain forest tree species
Authors: Poorter Lourens , Werger Marinus J. A.
Published: April 2006

Architecture and leaf display were compared in saplings of six rain forest tree species differing in shade tolerance. Saplings were selected along the whole light range encountered in a forest environment. Species differed largely in realized height and crown expansion per unit support biomass, but this could not be related to differences in shade tolerance. The results demonstrate that there exist various solutions to an effective expansion of plant height and crown area. It is argued that choice of the study species and the ontogenetic trajectory regarded determine to a large extent the outcome of interspecific comparisons. No evidence was found that pioneers were characterized by a multilayered and shade tolerants by a monolayered leaf distribution. Yet, sun plants had a similar crown area, a deeper crown, and a higher leaf area index compared to shade plants and their leaves were more evenly distributed along the stem. This suggests that differences in leaf layering are found between plants growing in different light environments, rather than between species differing in shade tolerance.
Phylogenetic relationships withinKorthalsella(Viscaceae) based on nuclear ITS and plastidtrnL‐Fsequence data
Authors: Molvray Mia , Kores Paul J. , Chase Mark W.
Published: April 2006

The nuclear encoded internal transcribed spacer (ITS) region and the plastid encodedtrnL‐Fregion were sequenced for 25 populations ofKorthalsella, a genus of reduced, monoecious, Old World misletoes. The molecular study confirms the hypothesis that branch shape and cladotaxy (the arrangement of branches with respect to their parent axis) are unreliable indicators of relationship in the genus and demonstrates that many of the taxa previously recognized are not monophyletic. Both gene regions identify three major subgroups within the genus and find lower level relationships within these subgroups highly correlated with geographic distance. An analysis based upon 18S andrbcLsequences identifiesGinalloaas the sister group toKorthalsella, which together with the branching order within the genus, indicates thatKorthalsellaoriginated in Papuasia and aids in elucidating evolution of the peculiar inflorescence structure. There are problems associated with species delimitation when evolutionary units are more restricted than morphological lineages, and justification is offered for recognizing only morphologically diagnosable monophyletic lineages as species. Varying substitution rates and differing modes of inheritance in ITS andtrnL‐Fresult in complementary utility of the two regions for elucidating infrageneric relationships inKorthalsella.
Studies in Neotropical paleobotany. XIII. An Oligo‐Miocene palynoflora from Simojovel (Chiapas, Mexico)
Authors: Graham Alan
Published: April 2006

A plant microfossil assemblage of 24 identified and five unknown pollen and spore types is reported from the early Miocene La Quinta Formation near Simojovel, Chiapas, Mexico. The taxa group into seven paleocommunities representing versions of the modern mangroves (Pelliciera, Rhizophora), swamp and lowland riparian forest (Ceratopteris, Crudia, Pachira), tropical rain forest (Selaginella, cf. Antrophyum, Pteris, Sphaeropteris/Trichipteris, cf. Aguiaria, Crudia, Guarea, Pachira), lower montane rain forest (Alfaroa/Oreomunnea, possibly Eugenia), evergreen cloud forest [Picea, Pinus, Podocarpus, Ericaceae (possibly Cavendishia/Vaccinium)], evergreen seasonal forest (Hymenaea, Ilex, possibly Eugenia), and tropical deciduous forest (Cedrela). Elements of arid and high‐elevation habitats were absent or few, and northern temperate elements (Picea, Pinus?) were few or rare. Paleoelevations are estimated at 1000–1200 m (present average 2000 m, maximum 3004 m), MAT (mean annual temperature) at least as warm as the present 24°C, and annual rainfall near the present ∼2500 mm but more evenly distributed. The La Quinta (Simojovel) and other Tertiary floras from the region reflect a trend toward higher altitudes, more seasonal rainfall, cooling tempertures, increased introduction of cool‐temperate elements from the north after ∼15 Ma (million years), and increased introduction of tropical elements from the south after completion of the isthmian land bridge ∼3.5 Ma ago.