bluuebunny/crossref_metadata_2025 huggingface dataset:
Drought tolerance in the alpine dandelion,Taraxacum ceratophorum(Asteraceae), its exotic congenerT. officinale, and interspecific hybrids under natural and experimental conditions
Authors: Brock Marcus T. , Galen Candace
Published: February 2008

We compared water relations and adaptations to drought stress in native and invasive exotic dandelions,Taraxacum ceratophorumandT. officinale. Photosynthesis (A), transpiration (E), and water use efficiency (WUE; carbon gained/water lost) were measured for the two species under extreme drought in the alpine tundra of Colorado, USA. We also subjected both species and F1hybrids to a dry‐down experiment to determine how relative physiological performance varied with water availability. Photosynthesis and transpiration in the field were low and did not differ betweenTaraxacumcongeners; however, nativeT. ceratophorumhad higher WUE thanT. officinale. After 6 days of greenhouse drought, photosynthesis and transpiration were reduced inT. officinalecompared toT. ceratophorum.Taraxacum ceratophorummaintained high WUE under control and drought treatments. Conversely, WUE inT. officinalewas highly plastic between watered (low WUE) and dry‐down (high WUE) treatments. Hybrids did not exhibit heterosis; instead, they were similar toT. officinaleinAandEand intermediate to the parental species in WUE. Overall, results suggest that native dandelions are more drought tolerant than invasive congeners or their hybrids, but have less plasticity in WUE. Arid habitats and occasional drought in mesic sites may provide native dandelions with refugia from negative interactions with invasives.
Molecular phylogenetic analysis of uniovulate Euphorbiaceae (Euphorbiaceae sensu stricto) using plastid RBCL and TRNL‐F DNA sequences
Authors: Wurdack Kenneth J. , Hoffmann Petra , Chase Mark W.
Published: February 2008

Parsimony and Bayesian analyses of plastidrbcLandtrnL‐FDNA sequence data of the pantropical family Euphorbiaceae sensu stricto (s.s.) are presented. Sampling includes representatives of all three subfamilies (Acalyphoideae, Crotonoideae, and Euphorbioideae), 35 of 37 tribes and 179 of the 247 genera of uniovulate Euphorbiaceae sensu lato (s.l.). Euphorbiaceae s.s. were recovered as a monophyletic group with no new adjustments in circumscription. Two clades containing taxa previously placed in Acalyphoideae are found to be successive sisters to all other Euphorbiaceae s.s. and are proposed here at subfamilial rank as Peroideae and Cheilosoideae. The remainder of the family fall into seven major lineages including Erismantheae and Acalyphoideae s.s. (parts of Acalyphoideae), Adenoclineae s.l., Gelonieae, articulated crotonoids and inaperturate crotonoids (parts of Crotonoideae), and Euphorbioideae. Potential synapomorphies and biogeographical trends are suggested for these clades. Acalyphoideae s.s., inaperturate crotonoids, and Euphorbioideae tribe Hippomaneae each have two major subclades that represent novel groupings without apparent morphological synapomorphies. Two subfamilies, 14 tribes, and 10 genera were found to be para‐ or polyphyletic. Noteworthy among these, Omphaleae are embedded in Adenoclineae, Hureae + Pachystromateae in Hippomaneae,DittainTetrorchidium, andSapiums.s. inStillingia.
Leaf architecture and direction of incident light influence mesophyll fluorescence profiles
Authors: Johnson Daniel M. , Smith William K. , Vogelmann Thomas C. , Brodersen Craig R.
Published: February 2008

Light propagation and distribution inside leaves have been recognized as important processes influencing photosynthesis. Monochromatic light absorption across the mesophyll was measured using chlorophyll fluorescence generated from illumination of the cut edge (epi‐illumination), as well as the adaxial or abaxial surfaces of the leaf. Species were selected that had basic leaf types: laminar leaf with adaxial palisade layer (Rhododendron catawbiense), needle with palisade (Abies fraseri), and needle without palisade (Picea rubens). Fluorescence was more evenly distributed across the mesophyll for adaxially illuminated leaves with a palisade cell layer, as well as for the needles (cylindrical) without palisade, when compared to fluorescence generated by abaxial illumination. Moreover, fluorescence from green light illumination remained high across the mesophyll of adaxially illuminated R. catawbiense, indicating a possible influence of mesophyll structure on internal light distribution beyond that of chlorophyll levels. These data support the idea that light propagation within the mesophyll is associated with asymmetric mesophyll structure, in particular the presence of palisade cell layers. In addition, we propose that the evolution of a more cylindrical leaf form, such as found in conifer species, may be a structural solution to excessive sunlight that replaces the highly differentiated mesophyll found in most laminar‐leaved species.
An extinct calycanthoid taxon,Jerseyanthus calycanthoides, from the Late Cretaceous of New Jersey
Authors: Crepet William L. , Nixon Kevin C. , Gandolfo Maria A.
Published: February 2008

A new fossil genus and species,Jerseyanthus calycanthoides, is described from the Late Cretaceous (Turonian, ∼90 MYBP) Raritan Formation of New Jersey. Flowers have cupulate receptacles bearing imbricately arranged tepals that subtend a series of recurved tepals near the cup margin. Recurved tepal subtends a “stamen‐staminode” pair, that includes a laminar stamen with ramified connective extensions, and an outer staminode. Outer staminodes are geniculate and incurved, and in aggregate their inner extremities define a circular area above the carpels and carpellodes. Each “stamen‐staminode” pair apparently subtends (is opposite to) an inner tepal. Pollen is rounded and disulculate, with tectate columellate wall structure. Carpels are located at the center of the receptacle and have elongate styles that extend to and beyond the opening defined by the staminodal organs. Carpels are surrounded by tomentose carpellodes. Carpels include one marginally ridged seed. While these fossils do not match exactly any living species in morphology, they share numerous characters with extant members of Calycanthaceae and can be unequivocally placed within that family. Affinities ofJerseyanthusandVirginianthuswere evaluated by including them in a combined analysis for the Laurales.Jerseyanthusis placed within Calycanthaceae as a sister taxon to the modern genusCalycanthus.
Molecular phylogenetics of the giant genus Croton and tribe Crotoneae (Euphorbiaceae sensu stricto) using ITS and TRNL‐TRNF DNA sequence data
Authors: Berry Paul E. , Hipp Andrew L. , Wurdack Kenneth J. , Van Ee Benjamin , Riina Ricarda
Published: February 2008

Parsimony, likelihood, and Bayesian analyses of nuclear ITS and plastid trnL‐F DNA sequence data are presented for the giant genus Croton (Euphorbiaceae s.s.) and related taxa. Sampling comprises 88 taxa, including 78 of the estimated 1223 species and 29 of the 40 sections previously recognized of Croton. It also includes the satellite genus Moacroton and genera formerly placed in tribe Crotoneae. Croton and all sampled segregate genera form a monophyletic group sister to Brasiliocroton, with the exception of Croton sect. Astraea, which is reinstated to the genus Astraea. A small clade including Moacroton, Croton alabamensis, and C. olivaceus is sister to all other Croton species sampled. The remaining Croton species fall into three major clades. One of these is entirely New World, corresponding to sections Cyclostigma, Cascarilla, and Velamea sensu Webster. The second is entirely Old World and is sister to a third, also entirely New World clade, which is composed of at least 13 of Webster's sections of Croton. This study establishes a phylogenetic framework for future studies in the hyper‐diverse genus Croton, indicates a New World origin for the genus, and will soon be used to evaluate wood anatomical, cytological, and morphological data in the Crotoneae tribe.
Molecular phylogeny of Oryzeae (Poaceae) based on DNA sequences from chloroplast, mitochondrial, and nuclear genomes
Authors: Guo Ya‐Long , Ge Song
Published: February 2008

The phylogeny and evolutionary history of the rice tribe (Oryzeae) were explored using sequences of five DNA fragments (matK, trnL, nad1, Adh2, and GPA1) from chloroplast, mitochondrial, and nuclear genomes. Results indicate that (1) Oryzeae is monophyletic and falls into two main clades corresponding to the traditionally recognized subtribes; (2) previous recognition of three monotypic genera (Hydrochloa, Porteresia, and Prosphytochloa) is not justified; and (3) close affinities of the monoecious genera are not supported, suggesting the possibility of multiple origins of unisexual florets. Based on the magnitude of matK and GPA1 sequence divergence, we suggest that Oryza and Leersia branched off from the remaining genera of Oryzeae ∼20 million years ago (mya), and separated from each other ∼14 mya. A divergence time of ∼9 mya is obtained for the most basal split within Oryza. These estimates suggest that Oryzeae diverged during the Miocene, and thus imply that long‐distance dispersal appears to be one of the important factors in the diversification of the tribe.
Phylogenetic relationships among the “spiny solanums” (Solanum subgenus Leptostemonum, Solanaceae)
Authors: Levin Rachel A. , Myers Nicole R. , Bohs Lynn
Published: February 2008

Species of Solanum subgenus Leptostemonum comprise almost one third of the genus and are distributed worldwide. Members of this group are defined by their sharp epidermal prickles; thus, they are commonly referred to as the “spiny solanums.” This subgenus includes a number of economically important species such as the Old World eggplants, as well as locally cultivated New World species such as the naranjilla and cocona. Given the size and importance of this group we have examined phylogenetic relationships across subgenus Leptostemonum, including a large sampling of species from previously defined species groups within the subgenus. Evolutionary relationships were inferred using DNA sequence data from two nuclear regions (ITS and the granule‐bound starch synthase gene [GBSSI or waxy]) and one chloroplast spacer region (trnS‐trnG). Results suggest that Solanum subgenus Leptostemonum is monophyletic when the S. wendlandii and S. nemorense species groups are excluded. We have defined 10 clades within subgenus Leptostemonum, some of which correspond to previously circumscribed species groups or sections. Most of the Old World species of subgenus Leptostemonum belong to a single species‐rich clade. Sharp prickles and/or stellate hairs evolved more than once in Solanum, and floral heterandry originated multiple times within the “spiny solanums.”
Experimental approaches used to quantify physical parameters at cellular and subcellular levels
Authors: Geitmann Anja
Published: February 2008

From a mechanical point of view, plant and hyphal cells are more complex than their animal counterparts because the variety of structural components determining cellular architecture is broader. In addition to cytoskeletal elements and the plasma membrane, the cell wall and turgor pressure equip plant and hyphal cells with structures analogous to an exoskeleton and a hydroskeleton, respectively. To quantify the physical properties of plant and hyphal cells, researchers have developed a plethora of experimental methods. This review provides an overview of experimental approaches that have been used to measure turgor pressure and to determine the mechanical properties of the plant cell wall at the subcellular level. It is completed by a glimpse into the arsenal of techniques that has been used to characterize the physical properties of cytoskeletal elements. These have mostly been used on animal cells, but we hope they will find their way into plant cell research. Finally, assays and tests to measure the generation of forces by cells and subcellular structures are discussed.
Comparison of mechanical properties of four large, wave‐exposed seaweeds
Authors: Harder Deane L. , Hurd Catriona L. , Speck Thomas
Published: February 2008

Seaweeds have a simple structural design compared to most terrestrial plants. Nonetheless, some species have adapted to the severe mechanical conditions of the surf zone. The material properties of either tissue sections or the whole stipe of four wave‐exposed seaweeds,Durvillaea antarctica,D. willana,Laminaria digitata, andL. hyperborea, were tested in tension, bending, and torsion.Durvillaeahas a very low modulus of elasticity in tension (Etension= 3–7 MN·m−2) and in bending (Ebending= 9–12 MN · m−2), torsion modulus (G= 0.3 MN · m−2) and strength (σbrk= 1–2 MN · m−2), combining a compliable and twistable stipe “material” with a comparatively high breaking strain (εbrk= 0.4–0.6). In comparison, the smaller stipes ofLaminariahave a higher modulus of elasticity in tension (Etension= 6–28 MN·m−2) and in bending (Ebending= 84–109 MN·m−2), similar strength (σbrk= 1–3 MN·m−2), and a higher torsion modulus (G= 0.7–10 MN·m−2), combined with a lower breaking strain (εbrk= 0.2–0.3) thanDurvillaea. Time‐dependent, viscoelastic reactions were investigated with cycling tests. The tested species dissipated 42–52% of the loading energy in tension through plastic‐viscoelastic processes, a finding that bears important ecological implications. Overall, there seems to be no correlation between single material properties and the size or habitat position of the tested seaweed species.
Wood for sound
Authors: Wegst Ulrike G. K.
Published: February 2008

The unique mechanical and acoustical properties of wood and its aesthetic appeal still make it the material of choice for musical instruments and the interior of concert halls. Worldwide, several hundred wood species are available for making wind, string, or percussion instruments. Over generations, first by trial and error and more recently by scientific approach, the most appropriate species were found for each instrument and application. Using material property charts on which acoustic properties such as the speed of sound, the characteristic impedance, the sound radiation coefficient, and the loss coefficient are plotted against one another for woods. We analyze and explain why spruce is the preferred choice for soundboards, why tropical species are favored for xylophone bars and woodwind instruments, why violinists still prefer pernambuco over other species as a bow material, and why hornbeam and birch are used in piano actions.
A unified hypothesis of mechanoperception in plants
Authors: Telewski Frank W.
Published: February 2008

The perception of mechanical stimuli in the environment is crucial to the survival of all living organisms. Recent advances have led to the proposal of a plant‐specific mechanosensory network within plant cells that is similar to the previously described network in animal systems. This sensory network is the basis for a unifying hypothesis, which may account for the perception of numerous mechanical signals including gravitropic, thigmomorphic, thigmotropic, self‐loading, growth strains, turgor pressure, xylem pressure potential, and sound. The current state of our knowledge of a mechanosensory network in plants is reviewed, and two mechanoreceptor models are considered: a plasmodesmata‐based cytoskeleton–plasma membrane–cell wall (CPMCW) network vs. stretch‐activated ion channels. Post‐mechanosensory physiological responses to mechanical stresses are also reviewed, and future research directions in the area of mechanoperception and response are recommended.
Plant biomechanics in an ecological context
Authors: Read Jennifer , Stokes Alexia
Published: February 2008

Fundamental plant traits such as support, anchorage, and protection against environmental stress depend substantially on biomechanical design. The costs, subsequent trade‐offs, and effects on plant performance of mechanical traits are not well understood, but it appears that many of these traits have evolved in response to abiotic and biotic mechanical forces and resource deficits. The relationships between environmental stresses and mechanical traits can be specific and direct, as in responses to strong winds, with structural reinforcement related to plant survival. Some traits such as leaf toughness might provide protection from multiple forms of stress. In both cases, the adaptive value of mechanical traits may vary between habitats, so is best considered in the context of the broader growth environment, not just of the proximate stress. Plants can also show considerable phenotypic plasticity in mechanical traits, allowing adjustment to changing environments across a range of spatial and temporal scales. However, it is not always clear whether a mechanical property is adaptive or a consequence of the physiology associated with stress. Mechanical traits do not only affect plant survival; evidence suggests they have downstream effects on ecosystem organization and functioning (e.g., diversity, trophic relationships, and productivity), but these remain poorly explored.
Pruning‐induced tylose development in stems of current‐year shoots ofVitis vinifera(Vitaceae)
Authors: Sun Qiang , Rost Thomas L. , Matthews Mark A.
Published: February 2008

Tyloses form in xylem vessels in response to various environmental stimuli, but little is known of the kinetics or regulation of their development. Preliminary investigations indicated that wounds seal quickly with tyloses after pruning of grapevine shoots. In this study, tylose development was analyzed qualitatively and quantitatively at different depths and times from pruning cuts along current‐year shoots of grapevines at basal, middle, and apical stem regions. Tyloses developed simultaneously within a single vessel but much separated in time among vessels. Pruning caused prodigious tylosis in vessels of grape stems, extending to approximately 1 cm deep and to 7 d after wounding, but about half of the vessels did not become completely occluded. The fraction of vessels forming tyloses was greatest in basal (85%) and least in apical (50%) regions. The depth of maximum density of tyloses was 4 mm from the cut in the basal region and 2 mm from the cut in the middle and apical regions. Tylose development was faster in the basal and middle than in the apical region. The pattern of tylose development is discussed in the context of wound repair and pathogen movement in grapevines.
Bordered pit structure and function determine spatial patterns of air‐seeding thresholds in xylem of Douglas‐fir (Pseudotsuga menziesii; Pinaceae) trees
Authors: Domec Jean‐Christophe , Lachenbruch Barbara , Meinzer Frederick C.
Published: February 2008

The air‐seeding hypothesis predicts that xylem embolism resistance is linked directly to bordered pit functioning. We tested this prediction in trunks, roots, and branches at different vertical and radial locations in young and old trees of Pseudotsuga menziesii. Dimensions of bordered pits were measured from light and scanning electron micrographs, and physiological data were from published values. Consistent with observations, calculations showed that earlywood tracheids were more resistant to embolism than latewood tracheids, mainly from earlywood having stretchier pit membranes that can distend and cover the pit aperture. Air seeding that occurs in earlywood appears to happen through gaps between the torus edge and pit border, as shown by the similar calculated pressures required to stretch the membrane over the pit aperture and to cause embolism. Although bordered pit functioning was correlated with tracheid hydraulic diameter, pit pore size and above all pit aperture constrained conductivity the most. From roots to branches and from the trunk base to higher on the trunk, hydraulic resistance of the earlywood pit membrane increased significantly because of a decrease in the size of the pit aperture and size and number of margo pores. Moreover, overall wood conductivity decreased, in part due to lower pit conductivity and a decrease in size and frequency of pits. Structural and functional constraints leading to the trade‐off of efficiency against safety of water transport were also demonstrated at the individual pit level, with a positive correlation between pit membrane resistance on an area basis and the pressure differential required to cause membrane stretching, a characteristic that is essential for pit aspiration.
Low clouds and cloud immersion enhance photosynthesis in understory species of a southern Appalachian spruce–fir forest (USA)
Authors: Johnson Daniel M. , Smith William K.
Published: February 2008

High‐altitude forests of the southern Appalachian Mountains (USA) are frequently immersed in clouds, as are many mountain forests. They may be particularly sensitive to predicted increases in cloud base altitude with global warming. However, few studies have addressed the impacts of immersion on incident sunlight and photosynthesis. Understory sunlight (photosynthetically active radiation, PAR) was measured during clear, low cloud, and cloud‐immersed conditions at Mount Mitchell and Roan Mountain, NC (USA) along with accompanying photosynthesis in four representative understory species. Understory PAR was substantially less variable on immersed vs. clear days. Photosynthesis became light‐saturated between ∼100 and 400 μmol · m−2 · s−1 PAR for all species measured, corresponding closely to the sunlight environment measured during immersion. Estimated daily carbon gain was 26% greater on clear days at a more open canopy site but was 22% greater on immersed/cloudy days at a more closed canopy site. Fv/Fm (maximum photosystem II efficiency) in Abies fraseri seedlings exposed to 2.5 min full sunlight was significantly reduced (10%), indicating potential reductions in photosynthesis on clear days. In addition, photosynthesis in microsites with canopy cover was nearly 3‐fold greater under immersed (2.6 mmol · m−2 · h−1) vs. clear conditions (0.9 mmol · m−2 · h−1). Thus, cloud immersion provided more constant PAR regimes that enhanced photosynthesis, especially in shaded microsites. Future studies are needed to predict the survival of these refugial forests under potential changes in cloud regimes.
Oil bodies in leaf mesophyll cells of angiosperms: overview and a selected survey
Authors: Lersten Nels R. , Czlapinski Albert R. , Curtis John D. , Freckmann Robert , Horner Harry T.
Published: February 2008

Neutral (storage) oil bodies occur in leaf mesophyll cells of many angiosperms, but their literature has been largely forgotten. We review this literature and provide a survey of 302 species and hybrids from mostly north‐central US species representing 113 families. Freehand cross sections of fresh leaves stained with Sudan IV verified the presence of oil. In 71 species from 24 families we observed 1–15 oil bodies per mesophyll cell. The eudicot families Asteraceae, Caprifoliaceae, Lamiaceae, and Rosaceae had the highest number of species with oil bodies, whereas few or no species in the Apiaceae, Betulaceae, Fabaceae, and Scrophulariaceae had them. Only three of 19 monocot species sampled had oil bodies. Repeat sampling of a Malus (crabapple) cultivar and a Euonymus species showed conspicuous oil bodies in mid‐summer and also in mid‐autumn in both attached and recently shed leaves. Oil bodies in leaf mesophyll cells are conspicuous (visible in hand cross sections using moderate magnification in unstained water mounts) in numerous species, and they occur throughout the growing season in at least some species. Neutral oil bodies in leaf mesophyll cells are not mentioned in contemporary textbooks and advanced works, but they deserve recognition as significant cellular components of many taxa, in which they may be significant sources of commercial oils.
Delayed fertilization and pollen‐tube growth in pistils ofFagus japonica(Fagaceae)
Authors: Sogo Akiko , Tobe Hiroshi
Published: February 2008

In contrast to most angiosperms, in which fertilization occurs 1 or 2 days after pollination, in some plant orders, including the Fagales, fertilization is delayed from 4 days to more than 1 year, raising questions regarding why fertilization is delayed and where and how pollen tubes remain in the pistil during the delay. To answer these questions, we investigated pollen‐tube growth in pistils ofFagus japonica(Fagaceae), which are tricarpellate and have six ovules, using light, fluorescence, and scanning electron microscopy. The ovules were immature at the time of pollination and required 5 weeks to become fully developed. During this 5 weeks, pollen tubes grew from the stigma to the embryo sac in association with the development of ovules and intermittently in three steps with two growth‐cessation sites, i.e., on the funicle and near the micropyle. The number of pollen tubes was gradually reduced from many to one at the two growth‐cessation sites, and fertilization occurred in one ovule that apparently developed earlier than the others in the pistil. Thus, delayed fertilization plays an important role in gametophyte competition and selection leading to nonrandom fertilization. Intermittent pollen‐tube growth is also likely widespread in angiosperms because it is known in other Fagales and an unrelated order Garryales.
Ecological correlates of secondary sexual dimorphism in Salix glauca (Salicaceae)
Authors: Dudley Leah S.
Published: February 2008

The ecological causation hypothesis for secondary sexual dimorphism was tested in Salix glauca, a dioecious willow shrub. Plants growing in a Colorado Rocky Mountain (USA) krummholz mosaic of mesic and xeric patches were monitored for four consecutive years. Ecological causation is predicated on unique resource demands associated with sexual function. In S. glauca, seeds have twofold higher N and P concentrations compared to pollen. P, but not N, allocation costs differed between sexes at plant and flower scales. Ecological causation also predicts spatial segregation of sexes along underlying habitat gradients. In five populations of S. glauca, sexes displayed significant spatial segregation. The theory also predicts that sexes differ in performance across gradients of environmental stress or resource availability. Consistent with this hypothesis, females had lower drought tolerance than males under years of extreme aridity. Furthermore, over 10 years, annual shoot growth for females was greatest in mesic habitat patches, while males grew at a consistent rate regardless of habitat aridity. Because current shoot growth is correlated with future catkin production, habitat specialization likely provides a fitness payoff in females. Overall, this long‐term study provides some of the strongest evidence to date for ecological causation of secondary sexual dimorphism in plants.
Self‐incompatibility and floral parameters inHypochaerissect.Hypochaeris(Asteraceae)
Authors: Ortiz Maria Ángeles , Talavera Salvador , Garcia‐Castaño Juan Luis , Tremetsberger Karin , Stuessy Tod , Balao Francisco , Casimiro‐Soriguer Ramón
Published: February 2008

We studied the relationships between self‐incompatibility mechanisms and floral parameters in the genusHypochaerisL. sect.Hypochaeris(consisting ofH. glabra,H. radicata,H. arachnoidea, andH. salzmanniana). We assessed at intra‐ and interspecific levels (1) the self‐incompatibility (SI) mechanism and its distribution among populations, (2) the relationship between SI and floral parameters, and (3) the relationship of SI to reproductive success.Hypochaeris salzmannianais semi‐incompatible,H. glabrais self‐compatible, andH. arachnoideaandH. radicataare self‐incompatible. Floral parameters differed among populations ofH. salzmanniana: plants in self‐compatible populations had fewer flowers per head, a smaller head diameter on the flower, and a shorter period of anthesis than self‐incompatible populations. We also detected this pattern within a semi‐compatible population ofH. salzmanniana, and these differences were also found between species with different breeding mechanisms. Fruit to flower ratio in natural populations was generally high (>60%) in all species, regardless of breeding system. It is hypothesized that self‐compatibility may have arisen through loss of allelic diversity at theSlocus due to bottleneck events and genetic drift.
Failure of reproductive assurance in the chasmogamous flowers of Polygala lewtonii (Polygalaceae), an endangered sandhill herb
Authors: Weekley Carl W , Brothers Amanda
Published: February 2008

Hypothetically, a species with both cleistogamous (CL) flowers and delayed selfing chasmogamous (CH) flowers should display high levels of reproductive assurance because, over time, obligate selfing by CL flowers should reduce inbreeding depression and delayed selfing in CH flowers should compensate for the absence of outcross pollen. We used pollinator‐exclusion experiments to investigate reproductive assurance in the CH flowers of Polygala lewtonii, an herb with a mixed mating system. We followed CH flowers from bud‐break to flower/fruit abscission to quantify fruit initiation and maturation and rates of floral development. We also evaluated the efficacy of the selfing mechanism, conducted pollinator watches to assess the likelihood of pollinator limitation, and performed regression analysis to determine the effect of flower position on fruit production. Pollinator exclusion significantly reduced fruit initiation and maturation. Investigation of floral development demonstrated that the selfing mechanism is largely dysfunctional in CH flowers, indicating the failure of reproductive assurance. Low observed rates of insect visitation appear to contradict high rates of CH fruit production in open‐pollinated plants, particularly given the rarity of delayed selfing. In both treatments, flower position significantly affected fruit initiation, suggesting a role for resource limitation in both pollinator‐excluded and open‐pollinated flowers.
Self‐sterility in Ipomopsis aggregata (Polemoniaceae) is due to prezygotic ovule degeneration
Authors: Sage Tammy L , Price Mary V , Waser Nickolas M
Published: February 2008

Based on previous studies, extreme (>99%) self‐sterility in scarlet gilia (Ipomopsis aggregata) appears to be involved in late‐acting ovarian self‐incompatibility (OSI). Here, we confirm this suggestion by comparing structural events that follow from cross‐ vs. self‐pollinations of I. aggregata. Growth of cross‐ and self‐pollen tubes in the style at 11 h and growth in the ovary at 24 h was equivalent. Nonetheless, by 24 h, cross‐pollen effected a significantly higher percentage of both ovule penetration and fertilization. Ovules in self‐pollinated flowers showed pronounced changes, including an absence of embryo sac expansion and reduced starch in the integument, by 11 h post‐pollination, well before pollen tube entry into the ovary. In addition, the integumentary tapetum and adjacent 1–3 cell layers exhibited abnormal cell division, pronounced deposition of thick, pectin‐rich cell walls, and cellular collapse. Ovules and embryo sacs from cross‐pollinated flowers rarely showed such features. Developmental changes in ovules from self‐pollinated flowers eventually resulted in integument and embryo sac collapse, a process not observed in ovules of unpollinated flowers. We suggest that OSI involves long‐distance signaling between self‐pollen or self‐pollen tubes and carpel tissue that reduces availability of receptive ovules for fertilization before pollen tubes arrive in the ovary.
A highly differentiated glomeromycotean association with the mucilage‐secreting, primitive antipodean liverwort Treubia (Treubiaceae): clues to the origins of mycorrhizas
Authors: Duckett Jeffrey G. , Carafa Anna , Ligrone Roberto
Published: February 2008

Thallus anatomy in three species of the primitive liverwort genus Treubia (Metzgeriidae, Treubiales) was studied by light and electron microscopy. The thallus exudes copious mucilage, a feature shared elsewhere in liverworts only with the mycotrophic subterranean axes of the allied genus Haplomitrium. The central strand in the thallus midrib has a unique histological organization and harbors an intra‐ and intercellular infection by a glomeromycotean fungus that is far more highly differentiated than most of the glomeromycotean associations described to date. The fungus enters the thallus via clefts in the ventral epidermis along the midrib and colonizes the parenchyma above, forming intracellular coils and prominent, relatively short‐lived, hyphal swellings. Above the zone with intracellular colonization is a tissue area containing mucilage‐filled intercellular spaces; here the fungus is entirely intercellular and forms abundant pseudoparenchymatous structures and, in more mature parts of the thalli, large hyphae with thick multistratose walls. Mucilage in Treubia differs in histochemistry and origin from that produced by apical papillae, via hypertrophied Golgi, in all other bryophytes. Remarkable parallels between fungal associations in Treubia, Haplomitrium, and Lycopodium, all members of very ancient lineages, suggest that these associations epitomize very early stages in the evolution of glomeromycotean symbioses.
Population divergence for heteroblasty in the Canary Island pine (Pinus canariensis, Pinaceae)
Authors: Climent José , Chambel Maria Regina , López Rosana , Mutke Sven , Alía Ricardo , Gil Luis
Published: February 2008

A heteroblastic (or vegetative phase) change is an abrupt manifestation in the general heteroblastic development during the ontogeny of plants. The Canary Island pine undergoes an especially marked and delayed heteroblastic change, including both the formation of secondary needles on dwarf shoots and the onset of preformed growth. To assess genetic and environmental effects on the heteroblastic change in this species, we followed plants from 19 populations at a dry site and a wetter site. Comparing juvenile and adult needles from the same individuals, the adult had a significantly lower rate of water loss and higher leaf mass per area. Pooling data from all seed sources, the heteroblastic change took place when plants reached a critical height, on average, at 4 years of age at the dry site and 1 year earlier at the wet site. Within a subsample of individuals of equal size, mortality was significantly higher in juvenile plants than in mature plants. However, the juvenile phase was longer in plants from dry regions when compared to plants from highly productive, wet regions. This apparent contradiction might be explained through differential resource allocation and the cost of sclerophylly and resprouting ability. Considering the life strategy of the Canary Island pine, we interpret the prolonged juvenile phase as an unavoidable trade‐off for the high tolerance of adults to harsh environments.
Vascular pathways constrain 13C accumulation in large root sinks of Lycopersicon esculentum (Solanaceae)
Authors: Orians Tara M. Bledsoe and Colin M.
Published: February 2008

While carbon transport and partitioning is largely determined by phloem source–sink relationships, it may be constrained by vascular connections. Tomato (Lycopersicon esculentum) plants exhibit a high degree of sectoriality, with restricted movement of nutrients from particular roots to orthostichous leaves. In this experiment we investigated the manner in which sectoriality influences source–sink phloem partitioning from shoots to roots in tomatoes and whether the size of the sink (root) modifies the pattern of carbon movement outside sectored pathways. Using 13C, we determined that shoot‐to‐root carbon transport in tomatoes is sectored even from upper leaves. Sink size also influenced carbon partitioning. Specifically, when a lateral root was grown in isolation (using a split‐pot technique), it grew more and acquired significantly more 13C from an orthostichous, exposed leaf than did any other single root. Vascular constraints were evident. 13C accumulation in a large, isolated lateral root was very low when a leaf opposite the isolated lateral root was exposed. Thus sink size did not overcome vascular constraints. Because carbon assimilates are needed for nutrient acquisition and assimilation, these vascular constraints may affect the ability of sectored plants to utilize heterogeneously distributed soil resources. If so, future studies should compare species that differ in sectoriality to determine whether vascular constraints affect competitive hierarchies when soil resource availability is patchy.
A stochastic population model for Lepidium papilliferum (Brassicaceae), a rare desert ephemeral with a persistent seed bank
Authors: Meyer Susan E. , Quinney Dana , Weaver Jay
Published: February 2008

Population viability analysis (PVA) is a valuable tool for rare plant conservation, but PVA for plants with persistent seed banks is difficult without reliable information on seed bank processes. We modeled the population dynamics of the Snake River Plains ephemeral Lepidium papilliferum using data from an 11‐yr artificial seed bank experiment to estimate age‐specific vital rates for viability loss and germination. We related variation in postgermination demographic parameters to annual variation in precipitation patterns and used these relationships to construct a stochastic population model using precipitation driver variables. This enabled us to incorporate realistic levels of environmental variability into the model. A model incorporating best estimates for parameter values resulted in a mean trajectory for seed bank size that remained essentially stable through time, although there was a measurable risk of extinction over a 100‐yr period for the study population under this scenario. Doubling the annual seed viability loss rate resulted in near‐certain extinction, as did increasing first‐year germination to 100%, showing the importance of the persistent seed bank. Interestingly, increasing environmental variance substantially decreased the risk of extinction, presumably because this plant relies on extremely good years to restock the persistent seed bank, while extremely bad years have little impact. If every year were average in this desert environment, the species could not persist. Simulated effects of livestock trampling resulted in greatly increased extinction risk, even over time frames as short as 15 years.
Fruit production in cranberry (Ericaceae: Vaccinium macrocarpon): a bet‐hedging strategy to optimize reproductive effort
Authors: Brown Adam O. , McNeil Jeremy N.
Published: February 2008

In the cultivated cranberry (Vaccinium macrocarpon), reproductive stems produce 1–3 fruit even though they usually have 5–7 flowers in the spring. We undertook experiments to test the hypothesis that this was an adaptive life history strategy associated with reproductive effort rather than simply the result of insufficient pollination. We compared fruit production on naturally pollinated plants with those that were either manually pollinated or that were caged to exclude insects. Clearly, insects are necessary for the effective pollination of cranberry plants, but hand pollination of all flowers did not result in an increase in fruit number. Most of the upper flowers, which had significantly fewer ovules than did the lower flowers, aborted naturally soon after pollination. However, when the lower flower buds were removed, the upper flowers produced fruit. This suggests that the upper flowers may serve as a backup if the earlier blooming lower ones are lost early in the season. Furthermore, the late‐blooming flowers may still contribute to the plant's reproductive success as visiting pollinators remove the pollen, which could serve to sire fruit on other plants. These results are discussed in the context of their possible evolutionary and proximate causes.
A biomechanical perspective on the role of large stem volume and high water content in baobab trees (Adansoniaspp.; Bombacaceae)
Authors: Chapotin Saharah Moon , Razanameharizaka Juvet H. , Holbrook N. Michele
Published: February 2008

The stems of large trees serve in transport, storage, and support; however, the degree to which these roles are reflected in their morphology is not always apparent. The large, water‐filled stems of baobab trees (Adansoniaspp.) are generally assumed to serve a water storage function, yet recent studies indicate limited use of stored water. Through an analysis of wood structure and composition, we examined whether baobab morphology reflects biomechanical constraints rather than water storage capacity in the six Madagascar baobab species. Baobab wood has a high water content (up to 79%), low wood density (0.09–0.17 g · cm−3), high parenchyma content (69–88%), and living cells beyond 35 cm into the xylem from the cambium. Volumetric construction cost of the wood is several times lower than in more typical trees, and the elastic modulus approaches that of parenchyma tissue. Safety factors calculated from estimated elastic buckling heights were low, indicating that baobabs are not more overbuilt than other temperate and tropical trees, yet the energy investment in stem material is comparable to that in temperate deciduous trees. Furthermore, the elastic modulus of the wood decreases with water content, such that excessive water withdrawal from the stem could affect mechanical stability.
Fine‐scale genetic structure of the common Primula elatior (Primulaceae) at an early stage of population fragmentation
Authors: Van Rossum Fabienne , Triest Ludwig
Published: February 2008

Many rare species are threatened by habitat fragmentation; however, less is known about effects of fragmentation on common species, despite their potential role in ecosystem productivity and functioning. We identified key factors and processes influencing gene flow in a large population of Primula elatior, a common distylous perennial herb, at an early stage of the fragmentation process, i.e., when fragmentation is taking place. Using 19 allozyme loci, we investigated genetic variation and fine‐scale spatial genetic structure (SGS) at seedling and adult life stages in relation to fragmentation history (recent bottlenecks), selection, clonal propagation, sexual reproduction (seed and pollen dispersal, distyly), and patchy structure (patch size, plant density, and morph ratio). The main factors contributing to the strong SGS are seed and (to a lesser extent) pollen dispersal, through a spatial Wahlund effect and biparental inbreeding. Significant differences in allele frequencies between seedlings and adults indicate a temporal Wahlund effect. Patch plant density and biased morph ratio also affect the genetic patterns. Our results show that if P. elatior populations evolve into patchworks of small, isolated remnants, genetic erosion, reduced gene flow, and increased inbreeding can be expected, suggesting that such common plant species might require large population sizes to remain viable.
Reproductive effort and costs of reproduction do not explain female‐biased sex ratios in the moss Pseudocalliergon trifarium (Amblystegiaceae)
Authors: Bisang Irene , Ehrlén Johan , Hedenäs Lars
Published: February 2008

A fundamental assumption in life‐history theory is that reproduction is costly. Higher reproductive investment for fruits than for flowers may result in larger costs of reproduction in females than in males, which is often used to explain male‐skewed sex ratios in unisexual seed plants. In contrast, bryophytes have predominantly female‐biased sex ratios, suggested to be a product of a higher average cost of sexual reproduction in males. Empirical evidence to support this notion is largely lacking. We investigated sex‐specific reproductive effort and costs in the unisexual moss Pseudocalliergon trifarium that has a female‐dominated expressed sex ratio and rarely produces sporophytes. Annual vegetative segment mass did not differ among male, female, and non‐expressing individuals, indicating that there was no threshold‐size for sex expression. Mean and annual mass of sexual branches were higher in females than in males, but branch number per segment did not differ between sexes. Prefertilization reproductive effort for females was significantly greater (11.2%) than for males (8.6%). No cost for sexual branch production in terms of reduced relative vegetative growth or decreased investment in reproductive structures in consecutive years was detected. A higher realized reproductive cost in males cannot explain the unbalanced sex ratio in the study species.
Molecular phylogeny and dating reveals an Oligo‐Miocene radiation of dry‐adapted shrubs (former Tremandraceae) from rainforest tree progenitors (Elaeocarpaceae) in Australia
Authors: Crayn Darren M. , Rossetto Maurizio , Maynard David J.
Published: February 2008

To better understand the historical biogeography of the southern hemisphere and evolutionary responses of plants to aridity, we undertook a detailed phylogenetic study of the predominantly southern family Elaeocarpaceae sensu lato (including Tremandraceae). Plastid trnL‐trnF and nuclear ITS sequence data were analyzed using parsimony and Bayesian methods and molecular evolutionary rates calibrated using the Oligocene fossil record of Elaeocarpus mesocarps to estimate the minimum divergence dates. The results indicate the monophyly of all recognized genera and a placement for the former Tremandraceae (three genera and about 49 species of shrubby, dry‐adapted Australian plants) within the widespread predominantly rainforest tree family Elaeocarpaceae (nine genera, over 500 species). The former Tremandraceae clade diverged from its sister (Aceratium + Elaeocarpus + Sericolea) during the Paleocene, after which it underwent a marked acceleration in evolutionary rate. Furthermore, this lineage diversified during the late Miocene, coincident with widespread aridification in Australian environments and extensive radiations of several sclerophyllous groups. The role of dispersal in explaining the current geographical distribution of Elaeocarpaceae is illustrated by Aristotelia. This genus, whose distribution was previously thought to reflect Gondwanan vicariance, is shown to have arrived in New Zealand from Australia at least 6–7 million yr ago.
Amyloplast to chromoplast conversion in developing ornamental tobacco floral nectaries provides sugar for nectar and antioxidants for protection
Authors: Horner H. T. , Healy R. A. , Ren G. , Fritz D. , Klyne A. , Seames C. , Thornburg R. W.
Published: February 2008

Tobacco floral nectaries undergo changes in form and function. As nectaries change from green to orange, a new pigment is expressed. Analysis demonstrated that it is β‐carotene. Plastids undergo dramatic changes. Early in nectary development, they divide and by stage 9 (S9) they are engorged with starch. About S9, nectaries shift from quiescent anabolism to active catabolism resulting in starch breakdown and production of nectar sugars. Starch is replaced by osmiophilic bodies, which contain needle‐like carotenoid crystals. Between S9 and S12, amyloplasts are converted to chromoplasts. Changes in carotenoids and ascorbate were assayed and are expressed at low levels early in development; however, following S9 metabolic shift, syntheses of β‐carotene and ascorbate greatly increase in advance of expression of nectar redox cycle. Transcript analysis for carotenoid and ascorbate biosynthetic pathways showed that these genes are significantly expressed at S6, prior to the S9 metabolic shift. Thus, formation of antioxidants β‐carotene and ascorbate after the metabolic shift is independent of transcriptional regulation. We propose that biosynthesis of these antioxidants is governed by availability of substrate molecules that arise from starch breakdown. These processes and events may be amenable to molecular manipulation to provide a better system for insect attraction, cross pollination, and hybridization.