bluuebunny/crossref_metadata_2025 huggingface dataset:
PARAVEINAL MESOPHYLL IN CALLIANDRA TWEEDII AND C. EMARGINATA (LEGUMINOSAE; MIMOSOIDEAE)
Authors: Lersten Nels R. , Curtis John D.
Published: January 2018

Paraveinal mesophyll (PVM) in Leguminosae, subfamily Mimosoideae, was first reported in 1894 but never described in detail before now. We cleared, and sectioned in resin, leaflets of Calliandra tweedii and C. emarginata (Tribe Ingeae). Lamina anatomy in both species is very similar: one palisade layer, two to three spongy layers, and the horizontal veinal network with its interconnected PVM in between. PVM is a unistratose cellular lacework extending between veins and attached medianly along each flank of all veins. PVM cells have a normal complement of typical chloroplasts similar to other mesophyll cells. Most veins are ensheathed by fibers except for an extended lateral slit along each flank where the PVM is attached; a parenchymatous bundle sheath is therefore lacking. All vein endings lack phloem, although the tracheary elements of some vein endings are flanked by one or two long, slender, seemingly undifferentiated cells. Occasional small gaps occur between the PVM cell wall and adjacent tracheary elements, which expose xylem directly to mesophyll intercellular space. PVM anatomy of Calliandra, including its physical relationship to the various vein orders, differs in some important respects from PVM of the few other leguminous and nonleguminous species studied anatomically in any detail.
CALCIUM DELAYS THE ONSET OF CELL DIVISION AND RHIZOID ELONGATION IN GEMMAE OF THE CALCIFUGE FERN, VITTARIA GRAMINIFOLIA
Authors: Sabba Robert P. , Miller John H.
Published: January 2018

Vittaria graminifolia gametophytes reproduce asexually by linear six‐celled propagules known as gemmae. It has been shown previously that asymmetric cell division and rhizoid elongation in gemmae are inhibited by millimolar concentrations of Ca+ +. The present paper shows that millimolar Ca+ + delays the onset of cell division at a point prior to mitosis, without affecting the maximal rate of cell division. Ca+ + is most effective in delaying cell division when it is present during the first 24 hours of culture, 2 or 3 days before the initiation of cell division. Millimolar Ca+ + inhibits rhizoid elongation by delaying its onset, while also reducing its maximal rate. Ca+ + is also most effective in delaying rhizoid elongation during the first 24 hours of culture. Culture of gemmae on Ethylglycol‐bis‐(aminoethyl ether)‐N,N,N‘,N‘‐tetraacetic acid‐buffered media shows that the maximum frequency of cell division occurs at pCa 7, while for the initiation of rhizoid elongation, it occurs at pCa 5.
CONE DEVELOPMENT IN LIBOCEDRUS (CUPRESSACEAE)—PHENOLOGICAL AND MORPHOLOGICAL ASPECTS
Authors: Tomlinson P. B. , Takaso T. , Cameron E. K.
Published: January 2018

Cones in Libocedrus plumosa are initiated in New Zealand in February (late summer) and continue to develop through winter. The ultimate pair of bracts protrude and continue extension growth while the apex remains flat. Ovules are initiated in two pairs in July on the cone apex (i.e., are axial in origin), alternate with the upper two pairs of bracts. Ovule differentiation proceeds rapidly to the stage of pollination; the cone apex may develop further as a short columella. Soon after ovule initiation an adaxial ligulelike outgrowth of each member of the upper two pairs of bracts is initiated, that of the ultimate pair being broader than that of the lower pair. By intercalary growth of each ligule base an enlarged structure is developed, displacing the bract into a lateral position and forming the four scales that enclose the developing seeds in a valvate manner. Cone and seed maturation follows with seed dispersal in March, approximately 1 year after cone initiation. The results show that there is no morphologically discrete ovuliferous scale, and there is no ontogenetic fusion of discrete separate structures. The vascular system of the scale complex develops after the ovules are initiated and forms a single series of vascular bundles with inversely oriented xylem and phloem; this and other histological changes are the result of the activity of the intercalary growth process and do not relate to primary structures. The results are discussed in relation to existing knowledge of cone development in Cupressaceae, in which axially borne ovules are common.
SEED SIZE AND SEED PACKAGING VARIATION IN BAPTISIA LANCEOLATA (FABACEAE)
Authors: Mehlman David W.
Published: January 2018

Pods and seeds of field‐collected Baptisia lanceolala plants were analyzed to partition seed weight and seed packaging trait variance among and within plants and to detect relationships between these traits. Packaging traits studied were: pod weight, seed weight per pod, number of seeds per pod, mean weight of seeds per pod, proportion seed weight of total pod weight, and pod weight per seed. Significant among‐plant variation was found for seed weight and all packaging traits. Within plants, positive correlations were found between number of seeds per pod and pod dry weight and between the proportion seed weight of total pod weight and number of seeds per pod. Pod weight per seed was negatively correlated with number of seeds per pod. Most plants had a negative correlation between mean seed weight and number of seeds per pod. When compared with an equality of slopes test, slopes of regressions of the above pairs of traits were found to differ among plants. Among plants, the same relationships were found, except for the latter two traits, which were not correlated. These within‐plant patterns may represent constraints on seed weight variance imposed by the seed package. This view is supported by a positive correlation between packaging trait variance and seed weight variance. Packaging‐related constraints could have an effect on seed weight in this and other species. If these phenotypic constraints have a genetic basis, then selection on seed packaging could change seed weight in a way different from that which might be predicted by considering seed weight alone.
A FURTHER CONTRIBUTION TO CLOSED‐CONE PINE (OOCARPAE) HISTORY
Authors: Axelrod Daniel I. , Cota Joseph
Published: January 2018

A new record of a fossil Monterey pine (Pinus radiata D. Don) is recorded from rocks of the Plio‐Pleistocene age, southern California, and the affinities of other presumed fossil closed‐cone pines are revised. This has led to the recognition of two new pine species, Pinus storeyana Axelrod of subsect. Oocarpae and Pinus verdiana Axelrod of subsect. Ponderosae. Geologic evidence indicates that forerunners of the present California and Mexican species of Oocarpae were in proximity in Mexico during the Miocene. They were isolated following opening of the Gulf of California, the northward movement of Baja and Alta California on the San Andreas fault system, and the spread of desert climate. New populations of Pinus radiata developed during the Pliocene (5–2 million years) and later as environmental diversity increased. This also enabled Pinus remorala Mason and P. muricata D. Don, which the fossil record suggests were distinct into the Late Pleistocene, to hybridize in the new topographic‐climatic Holocene environments.
SITE‐SPECIFIC SEED DORMANCY IN SPARTINA ALTERNIFLORA (POACEAE)
Authors: Plyler Daniel B. , Carrick Kevin M.
Published: January 2018

Seed dormancy in Spartina alterniflora was studied with regard to: 1) the specific site of the dormancy mechanism, and 2) the influence of three growth‐regulating substances: gibberellic acid, fusicoccin, and abscisic acid. The site of the mechanism was determined by assessing the germinability of surgically altered dormant seeds. Effects of the growth substances were determined by assessing the germinability of seeds incubated in their presence. Results revealed that dormancy could be broken surgically by altering the scutellum or chemically by applying fusicoccin. Dormancy could be restored by abscisic acid in the former case but not the latter. It is concluded that the dormancy mechanism is located in the scutellum, that it consists of at least two sequential steps, and that it involves a leachable chemical inhibitor.
HETEROCHRONY AND HETEROBLASTIC LEAF DEVELOPMENT IN TWO SUBSPECIES OF CUCURBITA ARGYROSPERMA (CUCURBITACEAE)
Authors: Jones Cynthia S.
Published: January 2018

To date, reports of paedomorphosis at the whole plant or shoot level have been loosely based on whole plant form or on the sequence of leaf shapes produced along the shoot (heteroblasty). However, interpreting the significance of heterochrony in the evolutionary loss or gain of heteroblasty based on mature leaf forms assumes that all leaves with the same shape arose through very similar modes of organogenesis. This study examines this assumption in two subspecies of Cucurbita argyrosperma, one that is wild and heteroblastic and a second that is cultivated and not markedly heteroblastic. All leaves of the cultivar are visually similar to early leaves of the wild subspecies. The cultivar is considered to be the progenitor of the wild subspecies. Scanning electron microscopy and allometry of developing leaves showed that at early nodal positions along the primary shoot, leaf development in both subspecies was similar. At later nodal positions, very young leaves of both subspecies were more similar to each other than to leaves at earlier nodal positions within the same plant at the same stage of development. This early similarity was masked in the mature shapes of later leaves due to subsequent differences in allometric growth. Thus a simple hypothesis of paedomorphosis in which the early leaf form in the progenitor is simply reiterated at later nodal positions in the cultivar is not supported by patterns of leaf development.
Fertility variation in Pinus sylvestris: A TEST OF SEXUAL ALLOCATION THEORY
Authors: Savolainen Outi , Kärkkäinen Katri , Harju Anni , Nikkanen Teijo , Rusanen Mari
Published: January 2018

Sexual allocation theory assumes trade‐offs and negative genetic correlations between male and female allocation in hermaphrodite plants. We tested this assumption by studying variation in male and female fertility in two experimental populations of Pinus sylvestris. In these populations, the genotypes have been vegetatively replicated, which allowed separation of the genetic and environmental components of variation. The genetic components of variation accounted for 36% of the total variation in pollen production in the two populations, and for 54% of cone production. As assumed by sexual allocation theory, the genetic correlation of pollen and cone production was negative in both populations (‐0.59 and ‐0.15). However, positive environmental correlations between these traits (0.43 and 0.45) resulted in no phenotypic correlation in one population and a positive phenotypic correlation in the other.
Molecular evolution and phylogenetic implications of internal transcribed spacer sequences of Ribosomal DNA in Winteraceae
Authors: Suh Youngbae , Thien Leonard B. , Reeve Helena E. , Zimmer Elizabeth A.
Published: January 2018

The internal transcribed spacers and the 5.8S coding region of nuclear ribosomal DNA were sequenced and analyzed to address questions of generic relationships in Winteraceae. The molecular data generated a single tree that is congruent with one based on morphological data. The sequences of ITS 1 in the family range from 235 to 252 bases in size and of ITS 2 from 213 to 226 bases. The size of the 5.8S coding region is 164 bases. The range of ITS 1 and ITS 2 sequence divergence between pairs of genera within Winteraceae is relatively low in comparison to other plant families. Two types of ITS 1 and ITS 2 sequences were observed in the same individual for some taxa. Sequence variations between the two arrays are 4.7%–6.3% for ITS 1 and 5.1%–7.0% for ITS 2. Both arrays of sequences, however, generate the same phylogenetic relationships. Rates of nucleotide substitutions for the internal transcribed spacers are 3.2–5.2 × 10‐10 substitution per site per year estimated in ITS 1 and 3.6–5.7 × 10‐10 in ITS 2.
Patterns of allozyme variation and clonal diversity in Carex lasiocarpa and C. pellita (Cyperaceae)
Authors: McClintock Katherine A. , Waterway Marcia J.
Published: January 2018

We compared genetic variability and clonal diversity in the closely related sedges Carex lasiocarpa and C. pellita using allozyme markers at 12 loci. Both species produce spreading rhizomes, occur in open habitats, and can form large clones; C. lasiocarpa primarily along lakeshores, or in bogs, fens, or marshes, and C. pellita more commonly along riverbanks and ditches or in wet meadows. Polymorphism was high in both species, similar to that of other rhizomatous Carex and to other species with comparable growth forms and life histories. Total gene diversity was higher for C. lasiocarpa (HT = 0.266) than for C. pellita (HT = 0.248), but the coefficient of differentiation among populations was lower. Rare alleles usually occurred as heterozygotes rather than homozygotes, and significant deviations from Hardy‐Weinberg equilibrium were found at few loci, suggesting that both species are predominantly outcrossing. Mean clone size, diversity, and evenness were not significantly different between the two species, although populations varied from monoclonal to those where nearly every sampled shoot belonged to a different clone. No significant differences in genetic variation or clone size of C. pellita were found when comparisons were made between groups based on climate (warmer vs. cooler) or successional stage (pioneer vs. established). However, within C. lasiocarpa, genetic variability decreased and clone size increased in cooler climates and at established sites.
The role of nodal regions in growth of Xanthium (Compositae) stem
Authors: Maksymowych Roman , Orkwiszewski Joseph A. J.
Published: January 2018

Vegetative Xanthium plants grown under noninductive conditions were marked with India ink along the stem and photographed at three consecutive time intervals. Relative elemental rates (d[dX/dt]/dX) of stem elongation were estimated from displacement of marks during stem elongation. Young internodes elongated with constant relative elemental rates of 0.2 day‐1. Older internodes displayed an acropetal pattern of elongation in which the basal segments of an internode stopped elongating first and the apical portion last. Nodal regions elongated with very small relative elemental rates of 0.05 day‐1. Rates decreased as the age of the internodes and nodes increased and stopped shortly after Leaf Plastochron Index 9.
Photosynthetic and stomatal responses of Avena sativa (poaceae) to a variable light environment
Authors: Fay Philip A. , Knapp Alan K.
Published: January 2018

The net photosynthetic (A), stomatal conductance to water vapor (g), water use efficiency (WUE = A/transpiration), and leaf water potential (ψ) responses of cultivated oats (A vena saliva) were determined under an experimental regime of alternating full sun (photosynthetic photon flux density, PPFD > 1,700 μmol · m‐2‐sec‐1) and shade (300‐400 μmol · m‐2 · sec‐1 PPFD). Less extensive measurements were made on winter wheat (Triticum aestivum) to test the generality of crop species' responses. The rates of stomatal opening/closing after changes in PPFD in A vena and Triticum were compared with previously determined rates for native grasses and forbs to assess how domestication might have altered stomatal dynamics. Characteristics of Avena under alternating sun and shade were 1) rapid fluctuations in A between full sun (~27 μmol · m‐2 · sec‐1) and shade rates (~12 ‐13 μmol · m 2sec 1); 2) slower changes in g, causing progressive stomatal closure during the measurement sequence and possible stomatal limitation of A; 3) no change in leaf ψ; and 4) a net reduction in WUE. Triticum had similar sun/shade A, g, and WUE dynamics, except that Triticum stomata returned to full‐sun g between shade periods. The rates of change of g in Avena and Triticum were lower than for some desert and subalpine native species, but were similar to rates for species in adjoining native habitat. The basic stomatal dynamics of Avena and Triticum may typify many cultivated C, species, and these data indicate that crop stomatal behavior has not diverged significantly from that of native species.
Flower development in the organ number mutant clavata1‐1 of Arabidopsis thaliana (Brassicaceae)
Authors: Crone Wilson , Lord Elizabeth M.
Published: January 2018

Flowers of the organ number (meristic) mutant clavata1‐1 of Arabidopsis thaliana (Brassicaceae) were studied to examine timing and patterns of floral organogenesis as compared to the wild type. All clavata1‐1 flowers examined had four‐ instead of two‐loculed gynoecia; half showed increased numbers of stamens; and 10% formed increased numbers of sepals. An inflorescence plastochron index was used to establish the timing of developmental events during flower organogenesis. clavata1‐1 flowers initiate faster but grow more slowly than in the wild type. The stages of sepal and stamen initiation were prolonged compared to those of the wild type. Although gynoecial initiation was not prolonged, the preceding stage was and it was characterized by a proliferation of meristematic cells above the initiating stamens. The clavata1‐1 flower apex did not become wider than that of the wild type until after the establishment of the gynoecium. We propose that clavata1‐1 is a heterochronic mutant, where flower organ number increases are due partly to prolongation of organ initiation stages.
The megagametophyte in Anarthria (Anarthriaceae, Poales) and its implications for the phylogeny of the Poales
Authors: Linder H. P. , Rudall P. J.
Published: January 2018

The development and structure of the megagametophyte of Anarthria (Anarthriaceae), Aphclia, and Centrolepis (Centrolepidaceae) are described. Anarthriaceae has tenuinucellate ovules and the Polygonum type of megagametophyte development, both characters typical of the Poales. However, it lacks the anticlinally elongated nucellar epidermis and numerous large starch bodies observed in the megagametophyte of Centrolepidaceae, both characters also present in Restionaceae. This relatively generalized megagametophyte structure is consistent with data from the chloroplast genome, which suggest that Anarthriaceae are not as closely related to Restionaceae as previously assumed. New data from the megagametophyte are analyzed cladistically together with other available information on the poalean families. The results show that there are two possible positions for Anarthriaceae: either as sister to Poaceae. Joinvilleaceae, Restionaceae, Ecdeiocoleaceae, and Restionaceae, or as sister to only the latter three families. The new data also allow a critical reevaluation of the phylogenetic position of Centrolepidaceae, which is either basal to the poalean clade (based on microgametophyte data), or embedded in the Restionaceae (based on anther structure and megagametophyte data).
Structure and mating system of the graminicolous fungal epibiont Echinodothis tuberiformis (Clavicipitales)
Authors: White James F.
Published: January 2018

The developmental morphology and mating system of the epibiont Echinodothis tuberiformis is investigated. The structure of conidial stromata, conidia, perithecial stromata, asci, and ascospores is documented. Crosses involving transfer of conidia between stromata resulted in formation of perithecia, indicating a heterothallic mating system. Comparisons are made to other members of the Clavicipitales that are presently classified in the tribe Balansieae. It is suggested that this epibiont bears a closer relationship to the grass endophytes classified in the genus Epichloë (Fr.) Tul. than to several other members of the Balansieae.
Polyploidy and the evolution of domesticated plants
Authors: Hilu K. W.
Published: January 2018

Polyploidy and domestication are common features of plant evolution. A number of selective advantages conferred by polyploidy appear relevant to domestication. Surprisingly, the correlation between the two has not previously been examined. Anderson (Plants, man and life. University of California Press, Berkeley, CA, 1969) asserted that we do not yet know exactly what percentage of cultivated plants and weeds are polyploid, but it must be high. Heiser (Seeds to civilization, the story of food, 2d ed., W. H. Freeman, San Francisco, CA, 1981) stated that a large number of the major food crops are polyploids, giving wheat, sugar cane, potatoes, sweet potatoes, and bananas as examples. In this study, the distribution of polyploidy in 244 crop species was compared to the estimates of polyploidy in their respective higher categories. The proportion of polyploidy in crop plants was considered in relation to taxonomic origin, habitat, and reproductive strategies of the crops. The study showed that the crop species were a random selection as far as ploidy level is concerned and that domestication did not appear to have favored polyploid over diploid genomes or vice versa. Vegetative, seed, and tree crops were statistically homogenous in their polyploid composition. The distribution of polyploidy in annual and perennial crops did not differ statistically. The data imply that polyploid genomic constitution neither facilitated nor hindered the ability of wild species for domestication.
The evolution of theStreptanthus glandulosuscomplex (Cruciferae): genetic divergence and gene flow in serpentine endemics
Authors: Mayer Michael S. , Soltis Pamela S. , Soltis Douglas E.
Published: January 2018

An analysis of the levels and distribution of allozyme variation in the Streptanthus glandulosus species complex was undertaken to test paradigms of speciation processes in the context of serpentine endemism. Electrophoretic analysis of 21 putative enzyme loci in 1,224 individuals representing 56 populations revealed extensive intrapopulational variation and interpopulational divergence. Estimates of gene flow among populations within taxa are typically lower than is theoretically needed to counteract the effects of genetic drift (i.e., Nm values are below 0.5), suggesting that drift may play a significant role in the evolution of the complex. A cluster analysis of genetic identities between populations using UPGMA demonstrates geographically structured groupings, some of which include neighboring populations of different taxa. Moreover, the genetic identity between two populations is correlated with the distance by which they are separated. The results are consistent with a hypothesis of a paleoendemic origin of the complex. The ancestor of the complex (perhaps S. glandulosus ssp. glandulosus) probably was formerly distributed more continuously across serpentine and nonserpentine habitat throughout its range. Elimination of the nonserpentine populations allowed regional and population‐level divergence, following a model of geographic speciation.
The expression of andromonoecy inSolanum hirtum (Solanaceae): phenotypic plasticity and ontogenetic contingency
Authors: Diggle Pamela K.
Published: January 2018

Sex expression (the proportions of staminate and hermaphrodite flowers produced) in andromonoecious Solarium hirtum is phenotypically plastic, and there is genetic variation for sex expression plasticity. Changes in sex expression phenotype are inherently the result of altered development. However, the underlying developmental components of sex expression plasticity and of differences in plasticity among genotypes are unknown. This study takes an explicitly genetic and developmental approach to the study of phenotypic plasticity and examines changes in sex expression of ten clonally replicated genotypes at three levels of organization: among inflorescences, within inflorescences, and at the level of developing floral meristems. Changes in sex expression of individuals and differences among individuals are the result of a predictable interplay of resource, architectural, and floral level response within the hierarchical construction of the shoot system. Phenotypic plasticity of whole plant sex expression is ultimately due to sexual lability of individual developing flowers: floral sex is not determined until a primordium size of 9–10 mm. Until that time, sex expression remains labile and developing floral primordia can respond to changes in plant resource status. This flower level developmental lability, however, is expressed within the constraints set by the architecture and ontogenetic history of the organism. Only those floral primordia produced in distal portions of each inflorescence are labile, capable of developing into either a staminate or hermaphrodite flower, whereas those primordia in basal positions invariably develop as hermaphrodite flowers. The genotypes differ with respect to the architectural components of phenotypic plasticity and it is this architectural variation that results in differences in plasticity among genotypes. The phenomenon, in which the developmental fate of a primordium depends upon where and when it is produced within the architecture of an organism and what events have preceded it during ontogeny, can be termed “ontogenetic contingency.”
Selective fruit abortion inPrunus mahaleb (Rosaceae)
Authors: Guitian Javier
Published: January 2018

In Prunus mahaleb (Rosaceae), only a small proportion of those flowers that initially develop give rise to fruits, and the probability of producing fruit differs between flowers. The results of this study indicate that the probability of producing fruit is about 60% for the first (i.e., most proximal) flower to develop in each inflorescence, but very low for the last (i.e., most distal). This pattern is maintained regardless of between‐inflorescence differences in flowering phenology, suggesting that each inflorescence can be viewed as an independent subunit with respect to allocation of resources for reproduction. These results are compatible with the ovary reserve and selective abortion hypotheses for the adaptive value of low fruit set in P. mahaleb.
Symbiosis in cycads: the origin and development of coralloid roots inMacrozamia communis (Cycadaceae)
Authors: Ahern Charmian P. , Staff Ian A.
Published: January 2018

Coralloid roots of Macrozamia have more apparent developmental stages than those of many other cycad genera, providing an ideal study vehicle for obtaining a better understanding of the growth and development of symbiotic cycad coralloid roots. In M. communis L. Johnson, the process begins with initiation of young apogeotropic, papillose roots called “precoralloids” and involves phases of maturation, cyanobacterial invasion, coralloid formation, senescence, and regeneration. Active precoralloid apices continue to produce papillose tissue, but during precoralloid maturation, the prominent papillose sheath is gradually replaced by a thin, dermal layer with scattered lenticels. Cyanobacterial invasion has been observed at different stages of precoralloid maturation and stimulates further, irreversible development of precoralloids into coralloids. Newly invaded precoralloids in the process of transition may be readily identified by their distinctive apical lenticels. Coralloid development involves transformation of the original, apogeotropic precoralloid tissue as well as production of new coralloid tissue by apical meristems. Although continuous, these two coralloid regions may be recognized by their external morphology. New coralloid growth involves cessation of papillose sheath production, change in gravitropic response, proliferation of lenticels, and early differentiation of a conspicuous cyanobacterial zone. Three mechanisms enabling continuity of the coralloid root system are: 1) production of new precoralloids and coralloids from bases of existing roots of the same kind; 2) initiation of atypical roots from within the internal tissues of degenerating coralloids; and 3) development of internal secondary periderm during decortication of aging coralloid tissue.
Root tubercles in apostasiad orchids
Authors: Stern William Louis , Warcup John H.
Published: January 2018

Tubercles are swollen, stalked, warty branches arising from the main elongated roots of species in the terrestrial orchid genus Apostasia (subfamily Apostasioideae). Generalized anatomy resembles that of the main roots, except tubercles lack a velamen and conductive strands are few. There are multinucleate cortical cells, and stomata occur in the epidermis. Pores of stomata appear to be permanently open and thus may enhance the interchange of gases between root tissues and soil under the moist conditions in which apostasias grow. Multicellular warts seem to function as holdfasts and are points of entry for mycorrhizal fungi.
Clonal repeatability of in vitro pollen tube growth rates in Oenothera organensis (Onagraceae)
Authors: Havens Kayri
Published: January 2018

The concept that pollen selection is an important force driving angiosperm evolution has received a lot of attention in recent years. In order for pollen competition to have evolutionary significance, heritable variation for pollen tube growth rate must exist. In this study, I tested the clonal repeatability, a measure of broad‐sense heritability, of in vitro pollen tube growth rate in Oenothera organensis. Although I found significant phenotypic differences in pollen tube growth rate, the calculated clonal repeatability value of 9.4% indicates that heritability of pollen tube growth rate in this species is quite low. In contrast, both flower identity and plant identity had highly significant effects on pollen tube growth rate, suggesting that the environment may be more important than genotype in determining pollen performance in this species.
Extensive variation in the levels of genetic diversity and degree of relatedness among five species of Cypripedium (Orchidaceae)
Authors: Case Martha A.
Published: January 2018

An electrophoretic analysis of allozyme variation from 14 loci in Cypripedium calceolus, C. candidum, C. arietinum, C. acaule, and C. reginae was conducted to address evolutionary conclusions reached in prior studies on the Orchidaceae. The following specific questions were examined: 1) Do the allozyme data suggest that C. arietinum be transferred to the genus Criosanthes? 2) Do Cypripedium populations contain unusually low levels of genetic variation relative to other angiosperms with comparable life histories? and 3) Is the distribution of genetic variation among populations consistent with the idea that evolutionary processes produce higher levels of among‐population differentiation in the Orchidaceae? Very low Nei's genetic identities (0.000–0.285) were found for most species comparisons; however, C. arietinum was not the most genetically distinct taxon and should be retained in the genus Cypripedium. Although most Cypripedium populations contain very low levels of expected heterozygosity, C. calceolus contains unusually high levels in all populations examined. Most species examined here have below average levels of variation distributed among populations. This result indicates that evolutionary processes produce relatively lower, not higher, levels of genetic differentiation among Cypripedium populations compared to other flowering plants. Historical events that could have influenced the observed genetic patterns are discussed.
Environmental contribution to floral trait variation in Chamaecrista fasciculata (Fabaceae: Caesalpinoideae)
Authors: Frazee Joan E. , Marquis Robert J.
Published: January 2018

Although intraspecific variation in plant floral traits has been documented for a number of plant species, the causes of such variation are largely unknown. We first quantified floral trait variation in an Illinois prairie population of Chamaecrista fasciculata Michx. We then used a field experiment to determine the contribution of leaf herbivory to this variation and a greenhouse experiment to determine the contribution of leaf herbivory, and variable soil nutrient and water content to floral trait variation. Variation in environmental factors explained a significant portion of the naturally occurring variation in corolla width, ovule number, ovule size, and anther length. In the field, manual removal of 25% or more leaf area reduced ovule size and anther length (and by inference, pollen production), and delayed flowering. In the greenhouse, plants from which we removed 25% or more of their leaf area or which were given limited water produced fewer ovules than control plants. Addition of nutrients interacted with soil moisture to affect corolla diameter and ovule number. Despite our demonstration of significant environmental impacts on reproductive traits, these impacts were relatively much smaller than those on plant size, suggesting that floral traits are buffered against variable resource availability.
Self‐sterility in Epilobium obcordatum (Onagraceae)
Authors: Seavey Steven R. , Carter Sarah K.
Published: January 2018

Greenhouse pollinations among 23 field‐collected plants and their progeny revealed a high and variable degree of self‐sterility in Epilobium obcordatum. Field‐collected plants averaged 5% seed‐set when selfed and 43% seed‐set in crosses; greenhouse progeny 11% and 49%, respectively. In two of three pollen chase tests, previously or simultaneously applied self‐pollen reduced seed‐set to that resulting from pure self‐pollination. Based on the relative survivorship of self‐ and outcross embryos, the mean number of lethal equivalents was determined to be 11.0 (range 2.9 to 17.6) in the field‐collected plants, and 7.1 (range 0.62 to 21.8) in the greenhouse progeny. Pollinations among 91 individuals showed a significant negative correlation between seed‐set and inbreeding coefficients of the resulting zygotes. Intrapopulation crosses yielded significantly fewer seeds than interpopulation crosses. Early embryonic mutational load, in combination with some level of biparental inbreeding, appears to be responsible for the level of self‐sterility in natural populations of this species. A pollen dosage test for an interpopulation cross resulted in a maximum seed set of 47% at 16 tetrads. Additional unmeasured characteristics govern the probability of ovules becoming mature seeds.
Fate of plants from buried seeds on Volcano Usu, Japan, after the 1977–1978 eruptions
Authors: Tsuyuzaki Shiro
Published: January 2018

The eruptions of 1977–1978 on Mount Usu in northern Japan resulted in the almost complete destruction of vegetation by a 1–3‐m‐thick accumulation of volcanic deposits. Erosion created gullies that removed these deposits and frequently exposed the old original soil. I previously confirmed that seedlings of 14 species (eight annual and six perennial herbs) emerged from seeds buried in the original topsoil. To clarify the role of the seed bank on volcanic succession, I monitored seedlings of seed bank species from 1983 to 1992. Nearly all the annuals, such as Polygonum longisetum and Rorippa islandica, originated from the seed bank. However, seed supply from the seed bank declined with time. Because seedling mortality was extremely high and reproductive success was low, due mostly to the instability of ground surface, these annuals emerged for several years but disappeared after 1989. The nitrogen‐fixing and stoloniferous perennials, Trifolium repens and Lotus corniculatus var. japonicus, were derived only from the seed bank. They have gradually increased in cover and have become large enough to flower. The other perennials derived from the seed bank, most of which produce short rhizomes, did not increase in cover annually and thus contributed less to revegetation than nitrogen‐fixing stoloniferous species. The fate of perennials seems to be dependent on the types of rhizome and stolon systems. Although recruitment from the seed bank was restricted to gullies, the seed bank was the major source of annuals and of nitrogen‐fixing perennials in the gullies. Succession in the gullies was substantially different from that which occurred outside the gullies where plants mostly originated from seed immigration and vegetative reproduction from surviving plants, and annual and nitrogen‐fixing plants were absent.
Occurrence and phylogenetic significance of glucose utilization by charophycean algae: glucose enhancement of growth in Coleochaete orbicularis
Authors: Graham Linda E. , Graham James M. , Russin William A. , Chesnick Joby M.
Published: January 2018

Two critical innovations had a profound influence upon the evolutionary history of plants: the nutritionally dependent embryo and apoplastic phloem loading processes. Both depend upon the ability of the plant cell membrane to transport sugars. The evolutionary origin of sugar transport by plants is, therefore, of special phylogenetic importance. Recent evidence suggests that hexoses such as glucose are the main form of sugar transported apoplastically across the placental junction between gametophyte and sporophyte of the moss Polytrichum (Renault et al., 1992, Plant Physiology 100: 1815–1822). There is also considerable evidence that hexose transport may be involved in apoplastic phloem loading in Arabidopsis and other flowering plants. Results of numerous molecular, biochemical, immunofluorescence, and ultrastructural studies indicate that bryophytes and charophycean algae are related to the ancestors of vascular plants. This report demonstrates that the charophyte Coleochaete orbicularis exhibits enhanced growth in the presence of glucose under conditions in which inorganic carbon sources are limiting. Computer image analysis was used to demonstrate that nonaerated cultures of C. orbicularis grown for 7 weeks in an inorganic medium supplemented with 1% glucose produce as much as 13.6 times the biomass of clonal cultures grown for the same length of time in the same medium without glucose. Furthermore, addition of 1% glucose to nonaerated cultures yielded chlorophyll a concentration 20 times higher after 4 weeks growth than cultures grown under the same conditions without added glucose. This and other evidence derived from comparative growth measurements strongly suggest that Coleochaete takes up (or loads) glucose. Experimental results also suggest that hexose uptake by charophytes (such as Coleochaete) that typically grow in low alkalinity waters might provide a supplementary source of organic carbon when dissolved carbon dioxide levels are low. This capability could have served as an evolutionary precursor to hexose import by plant embryos, as well as leptom and phloem loading in bryophytes and vascular plants.
Pollination ofRavenala madagascariensis(Strelitziaceae) by lemurs in Madagascar: evidence for an archaic coevolutionary system?
Authors: Kress W. John , Schatz George E. , Andrianifahanana Michel , Morland Hilary Simons
Published: January 2018

Investigations of the floral biology of the traveler's tree (Ravenala madagascariensis) and the ecology of the ruffed lemur (Varecia variegata), both endemic to the island of Madagascar, suggest a plant‐pollinator relationship.Ravenalaexhibits many specializations for visitation by large nonflying animals: inflorescences placed below the crown of the plant and easily accessible to arboreal animals; large flowers enclosed in tough, protective bracts that require a strong pollinator to open; stiff, rodlike styles that withstand the rough handling of the visitors; and copious, sucrose‐dominant nectar that provides a renewable reward for a sizable animal for a long time period. Our observations in the field also show thatVarecia variegata:consistently and almost exclusively visit the flowers ofRavenala; carry pollen on their fur between flowers on the same plant and between conspecific plants; do not destroy the flowers while obtaining the nectar; and appear to be highly dependent on nectar as a food source during specific times of the year. The basal phylogenetic position ofRavenalain the family Strelitziaceae, as indicated by molecular sequence data, and the distribution of reproductive traits in the three extant genera are consistent with the hypothesis that pollination by nonflying mammals is an archaic system, whereas bird and bat pollination are derived.
Floral phenology and morphology of black cottonwood,Populus trichocarpa(Salicaceae)
Authors: Boes Teresa K. , Strauss Steven H.
Published: January 2018

Seasonal changes in the development of reproductive structures are documented forPopulus trichocarpaTorr. and Gray. Buds were collected and studied from several trees for a 2‐yr period, but to maintain a congruous phenology, representative structures from only one male and one female tree are presented. Collected tissues were fixed, dehydrated, embedded in wax, sectioned, and differentially stained. The development of reproductive meristems begins early in the spring, before leaves emerge. However, the anatomy of male and female flowers is virtually indistinguishable until late spring. The structures of the gynoecium develop in about 2 wk, then continue to enlarge through the summer and autumn until the trees become dormant. The unilocular ovary consists of usually three, but sometimes four carples. Stamen development begins in the center of a disk‐shaped meristematic region and proceeds centrifugally. Megasporogenesis and microsporogenesis take place late in the winter, approximately 2 wk before anthesis. Dissection of mature flowers revealed 30–50 seeds per capsule on female trees and 40–60 stamens on male trees. When compared to most otherPopulusspecies,P. trichocarpahas a relatively large number of reproductive structures.
Whole‐plant gas exchange responses of Spartina alterniflora (Poaceae) to a range of constant and transient salinities
Authors: Hwang Yuan‐Hsun , Morris James T.
Published: January 2018

A two‐chamber‐system was used to study whole‐plant gas exchange responses of Spartina alterniflora to long‐term and transient salinity treatments over the range of 5 to 40 ppt NaCl. Lower photosynthetic rates, leaf water vapor conductances, belowground respiration rates, and higher aboveground respiration rates in plants adapted to 40 ppt NaCl were observed. Area‐specific leaf weight increased with salinity, although the salt content of leaf tissues did not. A reduced rate of gross photosynthesis and higher aboveground respiration rate in 40‐ppt NaCl plants significantly lowered the net whole‐plant CO2 gain below that of 5‐ppt NaCl plants, while the net CO2 gain of 25‐ppt NaCl plants was intermediate. Within 6 hr of increasing the salinity of 5‐ and 25‐ppt NaCl plants by 20 and 15 ppt NaCl, S. alterniflora responded by reducing leaf water vapor conductance, which in turn reduced the photosynthetic rate. This response was reversed by returning the plants to their original salinity, which indicates that S. alterniflora adjusts water loss and gas exchange in response to transient salinity stress by regulating stomatal aperture. On the other hand, decreasing salinity of the growth media of plants cultured at 25 and 40 ppt NaCl had little or no effect on gas exchange characteristics. This suggests that S. alterniflora adapts to constant salinity through fixed, salinity‐dependent structural modifications, such as stomatal density.
The connective base and filament of Acicarpha tribuloides (Calyceraceae)
Authors: Pesacreta Thomas C. , Sullivan Victoria I. , DeVore Melanie
Published: January 2018

The structural and autofluorescent properties of the staminal connective base of Acicarpha tribuloides (Juss.) clearly distinguish it from the filament. The abaxial and lateral connective base epidermal walls have secondary thickenings and are autofluorescent. The filament walls lack these characteristics. Also, the wrinkled or bulbous cuticular surface of the filament epidermis is distinct from that of the connective base which is smooth and relatively flat. In regard to these characteristics, A. tribuloides strongly resembles Cirsium horridulum (Michx.), a species in the Asteraceae. A. tribuloides differs from C. horridulum in that the cytoplasm in both the connective base and the free filament cells becomes severely disorganized and some of the walls collapse during anthesis in the former species. Thus, while the staminal tissues of these two species have some similar structural and biochemical features, they have significantly different functional roles. The presence of a connective base in the Calyceraceae significantly broadens the known range of this feature, and can be used as evidence to support the hypothesis that this feature is plesiomorphic within the Asteraceae.
Carpellary outgrowth development in the endocarp of grapefruit, Citrus paradisi (Rutaceae)
Authors: Burns Jacqueline K. , Achor Diann S. , Echeverria Ed
Published: January 2018

The development and function of the carpellary outgrowth was investigated in grapefruit. Carpellary outgrowths were initiated 3 d postanthesis. By 7 d postanthesis, enlarged globose cells developed that were subtended by a parenchymatous stalk. Numerous Golgi, Golgi‐derived vesicles, endoplasmic reticulum, mitochondria, and thickened cell walls present in globose cells from 7 d to 3 mo postanthesis suggest that the carpellary outgrowth was secretory in nature. Lectin‐gold complex binding indicated that the secreted product contained galactose and arabinose. Cessation of secretory activity, marked by protoplast degeneration, occurred between 3 and 5 mo postanthesis.
Analyses of mutants of three genes that influence root hair development in Zea mays (Gramineae) suggest that root hairs are dispensable
Authors: Wen Tsui‐Jung , Schnable Patrick S.
Published: January 2018

Root hairs are specialized epidermal cells that are thought to play an important role in plant nutrition by facilitating the absorption of water and nutrients. Three maize mutants with abnormal root hair morphologies (rthl, rth2, and rth3) have been isolated from Mutator transposon stocks. All three root hair mutant phenotypes are controlled by single recessive alleles. The rthl mutant initiates normal‐looking root hair primordia that fail to elongate. The normal‐looking root hair primordia of the rth2 mutant elongate to only approximately one‐fifth to one‐fourth the length of wild type root hairs. Like rth1 primordia, rth3 primordia undergo little elongation. However, unlike the relatively normal‐looking rth1 primordia, rth3 primordia are distinctly abnormal when viewed through a scanning electron microscope. The rth1 mutant exhibits pleiotropic nutrient deficiencies, while the rth2 and rth3 mutants grow vigorously. This finding suggests that under some environmental conditions, root hairs are less important to plant growth than has been previously thought. The rthl, rth2, and rth3 genes have been mapped to chromosomes 1L, 5L, and 1S, respectively, via crosses with BA translocation stocks. The rth2 allele exhibits reduced transmission through the male gametophyte, but a normal rate of transmission through female gametophytes; rth1 and rth3 are transmitted at normal rates.