Floral development and molecular phylogeny support the generic status of Tasmannia (Winteraceae)

The taxonomic status of and evolutionary relationship between Tasmannia and Drimys (Winteraceae) have been subjects of controversy for many years. In this paper, a molecular phylogenetic analysis of the family with sequences of previously unpublished Tasmannia and Drimys species confirms earlier conclusions that Tasmannia and Drimys do not form a monophyletic group, despite the fact that they appear to share distinctive inflorescence and floral morphological attributes. Examination of alternative hypotheses of relationships with likelihood-ratio tests and parametric bootstrapping supports the separation of Tasmannia and Drimys. A detailed analysis of floral development in Tasmannia lanceolata and T. xerophila indicates that timing and position of sepal initiation differs between them, but that the position of subsequent organ initiation predictably follows from sepal position. This is in contrast to Drimys winteri, where a prolonged delay between sepal and petal initiation leads to the production of many phyllotactic patterns. The prolonged period of calyx tube growth leading to the formation of a calyptra in Tasmannia and Drimys probably evolved in parallel in the two lineages.     

The Pollen Tube Pathway in Tasmannia insipida (Winteraceae): Homology of the Male Gametophyte Conduction Tissue in Angiosperms

Abstract: The pathway of the pollen tube in Tasmannia insipida (Winteraceae), an archaic angiosperm, is described. Visual observations and measurements of percentage sugar content from stigmatic exudate and the calyptra droplet were made. The droplet that forms on the calyptra of unopened flowers was artificially pollinated, but no pollen tubes appeared to grow through it to the gynoecium of female flowers. Calyptra droplets occur on both female and male (having reduced female structures) flowers of this dioecious plant. It is considered unlikely that a drop pollination mechanism, analogous to that found in some gymnosperms, is at work in T. insipida, and it is proposed that one possible droplet function is as a "reward" to potential pollinators in advance of flower opening. Pollen tubes were observed to grow almost exclusively along epidermal cells. Early thoughts on angiosperm transmission tissue are re-examined and built upon. It is proposed that the male gametophyte conduction tissue in angiosperms is homologous with epidermal tissue, and that pollen tube passage occurred originally solely along the surface of specialized epidermal cells, or possibly for short distances along unspecialized regions covered with exudate derived from these cells. Some earlier attempts to explain transmitting tissue homology and evolution are discussed.     

Chloroplast evidence for geographic stasis of the Australian bird‐dispersed shrub Tasmannia lanceolata (Winteraceae)

Few chloroplast‐based genetic studies have been undertaken for plants of mesic temperate forests in the southern hemisphere and fossil‐based models have provided evidence of vegetation history only at the broadest scales in this region. This study investigates the chloroplast DNA phylogeography of Tasmannia lanceolata (Winteraceae), a fleshy‐fruited, bird‐dispersed shrub that is widespread in the mountains of southeastern Australia and Tasmania. Thirty haplotypes were identified after sequencing 3206 bp of chloroplast DNA in each of 244 individuals collected across the species’ range. These haplotypes showed unexpectedly strong phylogeographic structuring, including a phylogeographic break within a continuous part of the species’ range, with the distribution of four major clades mostly not overlapping, and geographic structuring of haplotypes within these clades. This strong geographic patterning of chloroplast DNA provided evidence for the survival of T. lanceolata in multiple putative wet forest refugia as well as evidence for additional wet forest species refugia in southeastern Australia. In western Tasmania lower haplotype diversity below the LGM tree line compared to above the LGM tree line suggests that glacial refugia at high altitudes may have been important for T. lanceolata. The level of geographic structuring in T. lanceolata is similar to gravity dispersed southern hemisphere plants such as Nothofagus and Eucalyptus. Behavioural traits of the birds transporting seed may have had a strong bearing on the limited transport of T. lanceolata seed, although factors limiting establishment, possibly including selection, may also have been important.     

Hardly a relict: freezing and the evolution of vesselless wood in Winteraceae

The Winteraceae are traditionally regarded as the least-specialized descendents of the first flowering plants, based largely on their lack of xylem vessels. Since vessels have been viewed as a key innovation for angiosperm diversification, Winteraceae have been portrayed as declining relicts, limited to wet forest habitats where their tracheid-based wood does not impose a significant hydraulic constraints. In contrast, phylogenetic analyses place Winteraceae among angiosperm clades with vessels, indicating that their vesselless wood is derived rather than primitive, whereas extension of the Winteraceae fossil record into the Early Cretaceous suggests a more complex ecological history than has been deduced from their current distribution. However, the selective regime and ecological events underlying the possible loss of vessels in Winteraceae have remained enigmatic. Here we examine the hypothesis that vessels were lost as an adaptation to freezing-prone environments in Winteraceae by measuring the responses of xylem water transport to freezing for a diverse group of Winteraceae taxa as compared to Canella winterana (Canellaceae, a close relative with vessels) and sympatric conifer taxa. We found that mean percent loss of xylem water transport capacity following freeze-thaw varied from 0% to 6% for Winteraceae species from freezing-prone temperate climates and approximately 20% in those taxa from tropical (nonfreezing) climates. Similarly, conifers exhibit almost no decrease in xylem hydraulic conductivity following freezing. In contrast, water transport in Canella stems is nearly 85% blocked after freeze-thaw. Although vessel-bearing wood of Canella possesses considerably greaterhydraulic capacity than Winteraceae, nearly 20% of xylem hydraulic conductance remains, a value that is comparable to the hydraulic capacity of vesselless Winteraceae xylem, if the proportion of hydraulic flow through vessels (modeled as ideal capillaries) is removed. Thus, the evolutionary removal of vessels may not necessarily require a deleterious shift to an ineffective vascular system. By integrating Winteraceae's phylogenetic relationships and fossil history with physiological and ecological observations, we suggest that, as ancestors of modern Winteraceae passed through temperate conditions present in Southern Gondwana during the Early Cretaceous, they were exposed to selective pressures against vessel-possession and returned to a vascular system relying on tracheids. These results suggest that the vesselless condition is advantageous in freezing-prone areas, which is supported by the strong bias in the ecological abundance of Winteraceae to wet temperate and tropical alpine habitats, rather than a retained feature from the first vesselless angiosperms. We believe that vesselless wood plays an important role in the ecological abundance of Winteraceae in Southern Hemisphere temperate environments by enabling the retention of leaves and photosynthesis in the face of frequent freeze-thaw events.     

Analysis of the Contents of Oil Cells in Tasmannia lanceolata(Poir.) A. C. Smith (Winteraceae)

The simple, robust oil cells found in leaves of Tasmannia lanceolata(Poir.)A. C. Smith (Winteraceae) are shown to contain a preponderanceof the bioactive compound polygodial using both direct samplingand GCMS analysis of cell contents and Fourier Transform infraredspectroscopy. The implications of this for comparison of plantmaterial on the basis of extracts and essential oils are discussed.Copyright 2000 Annals of Botany Company Tasmannia lanceolata, Winteraceae, polygodial, direct sampling, FTIR spectrometry, oil cell, idioblast, antifeedant     

Reproductive biology of a primitive angiosperm,Pseudowintera colorata (Winteraceae), and the evolution of pollination systems in theAnthophyta

Stigmatic exudate-eating chironomid flies (Smittia) and pollen-eating halodid beetles are the most common visitors to flowers ofPseudowintera colorata. Plants are self-incompatible. After selfing pollen tubes penetrate the nucellus; chase pollination experiments show that the incompatibility reaction occurs before fertilization. When pollen is applied to stigmas, the exudate dries rapidly and does not usually reappear. A review of anthophytes suggests that their common ancestor around 200 mya was bisexual and pollinated at least in part by nectar-seeking insects, possibly including flies. The angiosperm stigma appears to have evolved from a pollination drop mechanism via an adaxial stigmatic surface.Dedicated with pleasure to ProfessorW. R. Philipson on the occasion of his 80th birthday.     

Xylem sap flow and stem hydraulics of the vesselless angiosperm Drimys granadensis (Winteraceae) in a Costa Rican elfin forest

For decades, botanists have considered Winteraceae as the least modified descendents of the first angiosperms primarily because this group lacks xylem vessels. Because of a presumed high resistance of a tracheid‐based vascular system to water transport, Winteraceae have been viewed as disadvantaged relative to vessel‐bearing angiosperms. Here we show that in a Costa Rican cloud forest, stem hydraulic properties, sapwood area‐ and leaf area‐specific hydraulic conductivities of Drimys granadensis L. (Winteraceae) are similar to several co‐occurring angiosperm tree species with vessels. In addition, D. granadensis had realized midday transpiration rates comparable to most vessel‐bearing trees. Surprisingly, we found that D. granadensis transpired more water at night than during the day, with actual water loss being correlated with wind speed. The failure of stomata to shut at night may be related to the occlusion of stomatal pores by cutin and wax. Our measurements do not support the view that absence of xylem vessels imposes limitations on water transport above those for other vesselled plants in the same environment. This, in turn, suggests that a putative return to a tracheid‐based xylem in Winteraceae may not have required a significant loss of hydraulic performance.     

Evidence for ovarian self-incompatibility as a cause of self-sterility in the relictual woody angiosperm,Pseudowintera axillaris (Winteraceae)

Species within the genus Pseudowintera exhibit high rates of self-sterility. Self-sterility in the genus has been previously posited-but not confirmed-to be the result of late-acting ovarian self-incompatibility (OSI) functioning within nucellar tissue of the ovule to prevent self pollen tubes from entering the embryo sac. Structural and functional aspects of pollen-carpel interactions and early seed development following cross- and self-pollination were investigated in P. axillaris to determine the site, timing and possible mechanisms of self-sterility. No significant differences were observed between pollen tube growth, ovule penetration and double fertilization following cross- and self-pollination. Pollen tubes exhibited phasic growth in an extracellular matrix composed of proteins and carbohydrates, as well as arabinogalactans/arabinogalactan proteins. A uniform failure in embryo sac development prior to division of the zygote was apparent within 15 d following double fertilization by self gametes. Results indicate that SI mechanisms in P. axillaris do not prevent double fertilization from occurring. Instead, mechanisms of self-sterility affect post-zygotic development of the embryo sac. Although self-sterility may be attributed to inbreeding depression, given the post-zygotic nature of failure in embryo sac development, the possibility of late-acting OSI is discussed.     

The structure and evolution of angiosperm nuclear genomes

Despite several decades of investigation, the organization of angiosperm genomes remained largely unknown until very recently. Data describing the sequence composition of large segments of genomes, covering hundreds of kilobases of contiguous sequence, have only become available in the past two years. Recent results indicate commonalities in the characteristics of many plant genomes, including in the structure of chromosomal components like telomeres and centromeres, and in the order and content of genes. Major differences between angiosperms have been associated mainly with repetitive DNAs, both gene families and mobile elements. Intriguing new studies have begun to characterize the dynamic three-dimensional structures of chromosomes and chromatin, and the relationship between genome structure and co-ordinated gene function.     

The early evolution of the angiosperm flower

An unexpected variety of new fossil flowers from the Lower and mid-Cretaceous and new results on the structure, development and biology of the flowers of extant primitive angiosperms are leading to modifications of earlier concepts of early flower evolution. Most fossil flowers conform best to those of the angiosperm subclass Magnoliidae, diverse though they may be. The unusual variety in organ number and organ arrangement patterns is a characteristic not only of the fossils but also of the extant Magnoliidae. It is a feature of the still 'open' organization of the flower (without intricate synorganization of parts) at this evolutionary level, and not an expression of only distant phylogenetic relationship. On the other hand, many other predominant features of modern angiosperms are lacking in both earliest fossils and most extant Magnoliidae.     

被子植物翅果的多样性及演化

翅果能够依靠风力进行传播, 可能是被子植物快速散布和物种分化的一个重要因素。狭义的翅果是指果皮延伸成翅且不开裂的干果; 广义的翅果则包括果皮、花被片或苞片形成果翅的所有果实。根据果翅形态及其生长方式的不同, 广义的翅果可分为单侧翅果、周位翅果(圆翅果与蝶翅果)、棱翅果、披针翅果、翼状萼翅果、叶状苞翅果6种类型, 其空中运动方式有自旋式(单侧翅果、翼状萼翅果)、波浪式(周位翅果、叶状苞翅果)、翻滚自旋式(周位翅果)、直升机式(披针翅果、翼状萼翅果)和滚筒式(棱翅果)。棱翅果与圆翅果在被子植物基部类群樟目就有发生, 并同时出现在单子叶植物和双子叶植物中, 可能是最早出现的翅果类型。翅果的演化过程呈现出果翅数量增加、果翅偏向单侧和果翅负荷(果实质量与果翅面积之比)降低的趋势, 以利于适应较小的风并增加传播距离。果翅除了促进果实与种子的风力传播外, 还具有物理防御、调节种子萌发和促进二次传播等作用。泛热带分布的金虎尾科有着极其丰富的翅果类型, 与其多次跨洋长距离扩散密切相关, 可以作为研究翅果适应与演化的一个模式类群。结合生态和演化-发育生物学方法, 研究不同类型翅果在适应风力传播方面的差异、萼片或苞片发育成翅的分子与遗传机制、翅果不同类型的演化历史及其对被子植物物种多样性的影响等是今后值得探讨的重要问题。     

Diversity and evolution of samara in angiosperm

翅果能够依靠风力进行传播, 可能是被子植物快速散布和物种分化的一个重要因素。狭义的翅果是指果皮延伸成翅且不开裂的干果; 广义的翅果则包括果皮、花被片或苞片形成果翅的所有果实。根据果翅形态及其生长方式的不同, 广义的翅果可分为单侧翅果、周位翅果(圆翅果与蝶翅果)、棱翅果、披针翅果、翼状萼翅果、叶状苞翅果6种类型, 其空中运动方式有自旋式(单侧翅果、翼状萼翅果)、波浪式(周位翅果、叶状苞翅果)、翻滚自旋式(周位翅果)、直升机式(披针翅果、翼状萼翅果)和滚筒式(棱翅果)。棱翅果与圆翅果在被子植物基部类群樟目就有发生, 并同时出现在单子叶植物和双子叶植物中, 可能是最早出现的翅果类型。翅果的演化过程呈现出果翅数量增加、果翅偏向单侧和果翅负荷(果实质量与果翅面积之比)降低的趋势, 以利于适应较小的风并增加传播距离。果翅除了促进果实与种子的风力传播外, 还具有物理防御、调节种子萌发和促进二次传播等作用。泛热带分布的金虎尾科有着极其丰富的翅果类型, 与其多次跨洋长距离扩散密切相关, 可以作为研究翅果适应与演化的一个模式类群。结合生态和演化-发育生物学方法, 研究不同类型翅果在适应风力传播方面的差异、萼片或苞片发育成翅的分子与遗传机制、翅果不同类型的演化历史及其对被子植物物种多样性的影响等是今后值得探讨的重要问题。     

Anatomical wood variation of Buddleja cordata (Buddlejaceae) along its natural range in Mexico

Buddleja cordata is an evergreen species of wide distribution in Mexico that is represented by shrubs and trees. Wood variability of B. cordata was evaluated in relation to plant size as well as latitude, altitude, soils, and climatic data. Canonical correlation analysis (CCA) showed that two canonical correlations are significant (Wilks' λ, p<0.0001) and explained 76% of total variance. Redundancy analysis revealed that the first pair of canonical variates are significant, thus the canonical variate, named distribution, represents a gradient of maximum temperature of the warmest period, annual temperature range, and latitude in its area of distribution; whereas the canonical variate named wood represents vessel density, fiber length, and plant size, best associated to the environmental gradient. Vessel density expressed by its distribution in latewood and porosity type showed that ring-porosity is common in individuals from high latitudes. Temperatures below zero or lack of rainfall during several months might induce porosity variability in B. cordata as suggested by CCA, but was not related to phenology since the species is evergreen along its latitudinal range. Plant size was also influenced by extreme temperature and rainfall. Shorter plants are distributed in the northern population or driest sites located in north-central Mexico, and in addition, fiber length followed an allometric relation with individuals' height. Wood characters in B. cordata as for simple perforation plate, helical thickenings, type of intervascular and vessel-ray pits, scanty paratracheal parenchyma, and heterogeneous type IIB rays were not correlated with plant size, climate, and soil parameters or species distribution. These features are common with other species of Buddleja.An erratum to this article can be found at     

The evolution of angiosperm seed proteins: A methionine-rich legumin subfamily present in lower angiosperm Clades

Analysis of legumin-encoding cDNAs fromDioscorea caucasica Lipsky (Dioscoreaceae) and fromAsarum europaeum L. (Aristolochiaceae) shows that there is an especially methionine-rich legumin subfamily present in the lower angiosperm clades including the Monocotyledoneae. It is characterized by a methionine content of 3–4 mol% which is roughly triple the methionine proportion of most other legumins. These “MetR” legumins, if present, still have to be detected in the higher angiosperms including the important seed crops. Evolutionary analysis suggests that the MetR legumins are the result of a gene duplication allowing the differentiation of legumin genes according to their sulfur content. The duplication event must have taken place before the split into mono- and dicotyledonous plants but probably after the separation of angiosperms and gymnosperms. Correspondence to: H. Fischer     

The nucleobase-ascorbate transporter (NAT) family: genomics, evolution, structure-function relationships and physiological role

This review summarizes knowledge concerning a ubiquitous plasma transmembrane protein family that mediates nucleobase or ascorbate secondary active transport (NAT). We show that prototype bacterial and mostly fungal members have become unique model systems to unravel structure-function relationships and regulation of expression, using classical and reverse genetics, as well as biochemical approaches. We discuss the importance of NAT-mediated ascorbate transport in mammals and how changes in substrate specificity, from different nucleobases to ascorbate, might have evolved at the molecular level. Finally, we also discuss how modelling NAT-purine interactions might constitute a step towards the use of NAT proteins as specific gateways for targeting pathogenic microbes.     

Structure and function in angiosperm pollen wall evolution

Observations and measurements from angiosperm species in more than 150 genera from 15 monocotyledonous and 69 dicotyledonous families show that harmomegathy, changes in size, shape, and volume of pollen grains as a result of water loss or intake are characteristic for flowering plants. Size changes as measured from the exterior wall surfaces average 46%. No particular pollen types or kinds or arrangements of apertures seem to be superior for providing mechanisms to accomodate these volumetric changes and the associated stress. As water is lost from a grain, contractions and invaginations of thinner areas of the wall establish geometric forms related to the positions and numbers of germinal apertures, and to internal and sculptural elements of the exine. As a result of these invaginations and accompanying flexion and arcuation (arching) of interapertural wall sections, configurations are created that permit the grain to develop and withstand enormous stress without breaking. The stress is a measure of negative wall pressure that helps establish a water deficit within the grain that brings the living substance of the protoplast into equilibrium with the desiccating forces of the atmosphere. Stress is accommodated through the inherent strength and resiliency of sporopollenin, enhanced by cellularization (baculation, lamination, plication, and alveolation), and by strutting and reinforcement systems involving massive deposits of sporopollenin at special bearing and stress points, such as costal and oral margins, or the poles. Architectural features that distribute and bear the stress include mechanisms for tension, arcuation, and suspension that carry stress to bearing points. The effect of these accommodations is to permit the pollen grain to arrive at the stigma alive and in condition to respond and grow quickly. It is hypothesized that evolution of structural features that meet harmomegathal stress requirements provides the principal explanation for pollen wall form, composition, organization, and architecture.     

The timing and the mode of evolution of wild grapes (Vitis)

Wild grapes are woody climbers, found mostly in temperate regions of the northern hemisphere, comprising the genus Vitis. Despite its importance, the evolutionary history of Vitis is still contentious. Past studies have led to conflicting hypotheses about the phylogeny, speciation events, and biogeographic history of the genus. Here we investigate the evolutionary history of Vitis using data from four chloroplast spacers (trnH-psbA, trnK-rps16, trnF-nahJ, and rpl32-trnL) and the nuclear gene RPB2-I, and we explore mechanisms that could have shaped the observed distribution of current species. Maximum likelihood and Bayesian analyses provided similar results, strongly supporting the presence of two subgenera and suggesting a species clustering within subgenus Vitis that mainly mirrors the disjunction between the Old and New World. Vitis vinifera subsp. sylvestris was found to be sister to the Asian species while three major clades were found in the American species. A network approach confirmed the main geographic groups and highlighted different chloroplast haplotype patterns between Asian and American species. Molecular dating analysis provided the time boundaries to discuss our results. Our study shows wild grape diversification to be a continuous and complex process that concerned the Tertiary as well as the Quaternary, most likely involving both geographical and climatic forces. Local variations in extent and timing of these forces were discussed based on observed differences between groups. In the context of the Tertiary–Quaternary debate, we provide evidence in favor of the “continuous hypothesis” to explain present diversity. Finally, two directions for future research are highlighted: (i) was the earliest grape American or Asian? and (ii) are all modern grape species real?     

Distribution of starch and lipids in reaction wood of some angiosperm trees

Distribution of starch and lipids has been studied in upper and lower parts of tilt branches and vertical branches of Azadirachta indica A. Juss., Mangifera indica L. and Polyalthia longifolia (Sonn.) Thw. Starch grains in tiltwood are smaller than in vertical wood. Their accumulation is considerably lower in upper tiltwood than in lower tiltwood and vertical wood. The rays and axial parenchyma contiguous to vessels show the highest lipid content in the upper tiltwood of A. indica and P. longifolia. The accumulation of lipids in axial and ray parenchyma of upper tiltwood is smaller than in lower tiltwood and vertical wood. Since we found that not only the upper wood but also the lower part of the tilt wood is different from normal wood, we would like to suggest that the entire new wood of a leaning stem should be considered to be reaction wood.     

Leaf morphological and genetic divergence in populations of Drimys (Winteraceae) in Chile

The genus Drimys is distributed in Chile from semi-arid zones to sub-Antarctic forests; there are three species of this tree, D. andina, D. confertifolia and D. winteri, the latter with varieties chilensis and winteri. Northern populations are found in small disjunct natural refuges, specifically mountain cloud forests and the bottom of ravines. The size and continuity of populations are greater in the south, where wetter conditions prevail. Morphological differences between populations have been observed, particularly between the northern populations of Fray Jorge and Talinay. This observation, led to the following questions: a) what is the level of morphological and genetic divergence among the populations of Drimys in Chile? and b) do the populations from Fray Jorge/Talinay, currently classified as D. winteri var. chilensis, differ genetically from the other populations of this variety? To answer these questions, we collected leaf samples from 37 populations of all Chilean Drimys, performed leaf morphology analysis and estimated genetic divergence using RAPD markers. We found a high degree of leaf morphological and genetic divergence between the populations of Fray Jorge/Talinay and the other Chilean species of Drimys. The morphological and genetic divergence among varieties of D. winteri was greater than that among the species of Drimys, which may indicate problems with their taxonomic classification.