STRUCTURE AND AFFINITIES OF ATHROTAXITES BERRYI BELL,AN EARLY CRETACEOUS CONIFER

Compressions and impressions of leafy twigs, pollen cones, and seed cones of Athrotaxites berryi are abundant in certain layers of the Kootenai Formation (Aptian) in Montana and the Lower Blairmore Formation in adjacent Alberta. The twigs are densely covered by helically arranged leaves that are about 2 mm long and wide. Pollen cones are borne laterally on ultimate branch segments. Some are sessile, while others terminate a minute lateral branch. The cones are 3–4 mm in diam and about 10 mm long. Each sporophyll has a stalk that is about 0.7 mm long and an upturned laminar tip that is 1–1.5 mm long by 1 mm wide. At least two pollen sacs are attached to the abaxial side of each sporophyll. Seed cones are borne terminally on lateral branches that are often curved. These cones are about 10 mm at their widest diameter and about 15 mm long. Each bract and associated ovuliferous scale are fused to form a wedge-shaped complex that is 4–5 mm long. The complex is 0.7 mm wide at its base and expands to about 2.5 mm wide and thick near its apex. The tip of the complex narrows abruptly to a point and terminates in a spine that is about 0.5 mm long. At least one seed occurs on the adaxial side of each complex. Athrotaxites berryi belongs to the Taxodiaceae. It resembles modern Athrotaxis cupressoides but differs from it in too many aspects to be included in the modern genus.     

Differential localization of the LIM domain protein PLIM-1 in microspores and mature pollen grains from sunflower

 PLIM-1 is a LIM domain protein specifically expressed in pollen grains. Using two PLIM-1-specific monoclonal antibodies we studied its expression and intracellular location at various developmental stages of sunflower (Helianthus annuus L.) pollen. Our studies show that the protein appears at the microspore stage in a limited number of cytoplasmic bodies, becomes undetectable in bicellular pollen, and reappears in tricellular pollen grains in cortical patches particularly concentrated in the F-actin-enriched germination cones of the vegetative cell. The developmental stage-dependent, different location of the protein suggests a dual function during pollen development. While this function in microspore development remains obscure, the high concentration of PLIM-1 in the germination cones of mature pollen suggests that it participates in the germination process as well as in pollen tube growth. Received: 11 August 1998 / Revision accepted: 15 December 1998     

Turonian Pinaceae of the Raritan Formation, New Jersey

 Fossil vegetative and reproductive structures from deposits of the Raritan Formation in New Jersey (Turonian, Upper Cretaceous, ∼90 MYBP) include ferns, gymnosperms, and angiosperms. Gymnosperms collected from this formation have been known since the beginning of the 20th century. Fossil leaves, wood and seed cones have been are identified as belonging to the Cupressaceae, Pinaceae, and Taxodiaceae. In the present contribution, we describe a series of fossil dwarf shoots, leaves and a pollen cone belonging to the family Pinaceae. Fossils are charcoalified with preserved three-dimensional structure and excellent cellular detail. The dwarf shoots are assigned to a new species Prepinus crossmanensis sp. nov. and to the previously described Pinus quinquefolia Jeffrey. The new species Prepinus crossmanensis differs in size, shape, presence of hypodermis, sclerenchyma and stomata in the cataphylls, and number and shape of needle leaves from previously known species. Also, isolated leaves were found that were assigned to the new species, Prepinus raritanensis sp. nov. The new species is differentiated by the size and shape of stomata, the presence of number of layers of the hypodermis; and the cell-shape and number of layers of the mesophyll and transfusion tissue. A previously undescribed male cone, Amboystrobus cretacicum gen. and sp. nov., has an axis with spirally attached microsporophylls, each bearing two abaxial ovoid microsporangia. The pollen grains are monosulcate and bisaccate (eusaccate), with an elliptical corpus, granulate exine sculpture, and honeycomb-like wall structure. Received March 21, 2000 Accepted November 13, 2000     

The developmental fate of angiosperm pollen is associated with a preferential decrease in the level of histone H1 in the vegetative nucleus

In angiosperm pollen, the vegetative cell is assumed to function as a gametophytic cell in pollen germination and growth of the pollen tube. The chromatin in the nucleus of the vegetative cell gradually disperses after microspore mitosis, whereas the chromatin in the nucleus of the other generative cell remains highly condensed during the formation of two sperm nuclei. In order to explain the difference in chromatin condensation between the vegetative and generative nuclei, we analyzed the histone composition of each nucleus in Lilium longiflorum Thunb. and Tulipa gesneriana immunocytochemically, using specific antisera raised against histones H1 and H2B of Lilium. We found that the level of histone H1 decreased gradually only in the vegetative nucleus during the development of pollen within anthers and that the vegetative nucleus in mature pollen after anther dehiscence contained little histone H1. By contrast, the vegetative nucleus contained the same amount or more of histone H2B than the generative nucleus. The preferential decrease in the level of histone H1 occurred in anomalous pollen with one nucleus (uninucleate pollen) or with two similar nuclei (equally divided pollen), which had been induced by treatment with colchicine. The nuclei in the anomalous pollen resembled vegetative nuclei in terms of structure and staining properties. The anomalous pollen was able to germinate and extend a pollen tube. From these results, it is suggested that the preferential decrease in level of histone H1 in pollen nuclei is essential for development of the male gametophytic cell through large-scale expression of genes that include pollen-specific genes, which results in pollen germination and growth of the pollen tube. Received: 9 May 1998 / Accepted: 4 June 1998     

THE MOTION OF WINDBORNE POLLEN GRAINS AROUND CONIFER OVULATE CONES: IMPLICATIONS ON WIND POLLINATION

Comparisons are presented between the three-dimensional airflow patterns created around and by a scale model of a conifer ovulate cone and the trajectories of windborne pollen grains around Picea, Larix, and Pinus ovulate cones. Three general components of the airflow pattern around an ovulate cone model are 1) doldrum-like eddies, rotating over the adaxial surfaces of cone scales and directed toward attached ovules, 2) airflow spiralling around the cone axis along cone scale orthostichies and parastichies, and 3) a complex pattern of vortices (“umbilicus”) directed toward the leeward surface of the ovulate cone. The observed trajectories of pollen grains around cones of Picea, Larix, and Pinus conform to two of these three airflow components: 1) pollen grains are seen to roll along cone scales toward the distal scale margin and to become reentrained in airflow directed backward toward attached ovules, and 2) pollen grains passing around the cone are deflected into the “umbilicus” airflow pattern, where they either settle on or impact with cone scales (approach trajectories), or where they approach the leeward cone surface but are deflected away by airflow passing under the cone (Z-shaped trajectories). Vectoral analyses of pollen grain motion reveal a complex pattern of trajectories influenced by boundary layer conditions defined by ovulate cone geometry and ambient airflow speed. Wind tunnel studies of ovulate cones subtended by leaves and stem indicate that leaves circumscribing the cone act as a snowfence, deflecting windborne pollen toward the cone. Vectoral analyses of airflow patterns and pollen grain trajectories close to ovulate cones indicate that wind pollination in conifers is a non-stochastic aerodynamic process influenced by cone-leaf morphology and the behavior of pollen grains as windborne particles.     

SILICIFIED PINUS REMAINS FROM THE MIOCENE OF WASHINGTON

Silicified leaves, dwarf shoots, pollen cones, and seed cones of Pinus from a Late Miocene chert bed within the Yakima Basalt Formation near Yakima, Washington are interpreted as coming from a single new species, P. foisyi. The needles and dwarf shoots are those of a three-needle pine. The needles contain two to four medial resin canals, a biform hypodermis, and endodermal cells with uniformly thickened walls. The pollen cones are ellipsoidal and about 1 cm long, and many contain bisaccate pollen grains. The seed cones are at least 6 cm long and are slightly asymmetrical. The cone axis has a broad sclerotic outer cortex, and the seed wing extends from a thick parenchymatous base. The scale apex bears a conspicuously swollen projection. The foliage and seed cones are identifiable with the Subgenus Pinus, Section Pinus, Subsection Oocarpae independently of one another, and together indicate a fossil species related to the modem Californian closed cone pines. Pinus foisyi represents one of the earliest occurrences of cone asymmetry associated with this group. However, cone serotiny characteristic of the modem species appears to have evolved after the Late Miocene.     

Host-plant influence on the population ecology of the jack pine budworm, Choristoneura pinus (Lepidoptera: Tortricidae)

Abstract.

• 1 Newly-emerged, second-instar jack pine budworm (Choristoneura pinus Freeman) establish spring feeding sites preferentially in the pollen cones of their host tree, Pinus banksiana Lamb.
• 2 Laboratory studies showed that the rate of establishment and survival of jack pine budworm on pollen cones was high throughout the entire spring emergence period of the insect.
• 3 In contrast, the rate of establishment and survival of jack pine budworm on vegetative buds was very poor early in the spring. Vegetative buds were only acceptable as feeding sites to the jack pine budworm for a relatively brief period in late spring.
• 4 Field studies showed that the change in population density of jack pine budworm during the spring emergence stage, as expressed by k-values, was a function of the abundance of pollen cones in the stand. Population reduction was greatest in those stands with the fewest pollen cones.
• 5 Direct measurement of spring dispersal by jack pine budworm showed that dispersal and consequent losses to the budworm population were greatest in stands with the fewest pollen cones.
• 6 We conclude that changes in the density of jack pine budworm are strongly influenced by production of pollen cones in the host stand. Because pollen cone production is related to previous years of defoliation by the jack pine budworm, we propose that pollen cones act as a density-dependent factor governing the density of early-stage jack pine budworm.
• 7 The resulting dynamics are compared to those of other budworm species and used to explain observed regional and temporal patterns of jack pine budworm outbreaks.

     

A NEW STRUCTURALLY PRESERVED PENNSYLVANIAN CORDAITEAN POLLEN ORGAN

Permineralized specimens of the pollen organ Gothania (Hirmer) consist of a primary axis bearing pollen cones in the axils of bracts that are four ranked. The bilaterally symmetrical primary axis consists of a uniform parenchymatous pith surrounded by up to 15 endarch-mesarch axile bundles. The cortex is two-parted and consists of an inner zone of subepidermal fibers. Bract traces arise from the ends of the ellipsoid stele. Traces to the cones are derived from the open ends of the stele, and at higher levels form a centrarch-medullated vascular system. Each pollen cone is constructed of up to 25 helically arranged scales, each vascularized by a single trace that may dichotomize. Scales are elongate and broad, and histologically composed of mesophyll parenchyma and fibrous layers. Stomata are restricted to the adaxial surface between rows of fibers. Up to 10 distal scales may be fertile, each with 4 elongate pollen sacs at the tip. Large monosaccate grains of the Felixipollenites-type are densely packed in each pollen sac. The well-preserved specimens of Gothania provide an opportunity to compare this genus with pollen cones assigned to the genus Cordaianthus, and to relate isolated plant organs to the Cordaitales.     

Insect Pollination in the Cycad Genus Bowenia Hook, ex Hook. f. (Stangeriaceae)1

All confirmed records of entomophilic pollination in cycads are for species in the Zamiaceae. This paper presents details of entomophily in both species of Bowenia in the Stangeriaceae. Seed set in female cones from which wind and water‐borne pollen, but not insects, was excluded, indicates that pollination is obligately entomophilous. The pollination vectors are Miltotranes weevils and the relationships are species‐specific and possibly coevolutionary.     

Evolution of seed dispersal in North American <Emphasis Type="Italic">Ephedra</Emphasis>

Related plants often produce seeds that are dispersed in very different ways, raising questions of how and why plants undergo adaptive shifts in key aspects of their reproductive ecology. Here we analyze the evolution of seed dispersal syndromes in an ancient group of plants. Ephedra (Gymnospermae; Gnetales; Ephedraceae) is a genus containing ≈50 species in semiarid ecosystems worldwide and with three distinct types of cones. We collected mature cones and seeds of ten species of Ephedra in southwestern United States and measured nine morphological traits for each species. Principal component analysis and other data characterized three types of Ephedra cones and seeds. Species with dry, winged cone bracts are dispersed by wind (i.e., E. torreyana and E. trifurca), those with succulent, brightly-colored cone bracts are dispersed by frugivorous birds (i.e., E. antisyphilitica), and those with small, dry cone bracts and large seeds are dispersed by seed-caching rodents (e.g., E. viridis and E. californica). Two species (E. funerea and E. nevadensis) have cone and seed morphologies intermediate between two seed dispersal syndromes. Seed and cones traits were mapped onto two recent phylogenies to help reveal the evolutionary history of seed dispersal syndromes. Bird dispersal is thought to be the ancestral form of seed dispersal in ephedras as it is common in the Old World where Ephedra originated, but the three North American species dispersed by birds are not monophyletic. The two wind dispersed species in North America also do not cluster together, suggesting separate origins. Seed dispersal by seed-caching rodents is common in North America and appears to have evolved several times, but this syndrome is absent form other continents. The evolutionary history of Ephedra in North America suggests that the means of seed dispersal has been malleable. Evolutionary shifts were likely linked to changes in ecological conditions.     

DEVELOPMENTAL CYCLES IN SHOOT GROWTH OF MALE CYCAS CIRCINALIS

Cycles of development in several male shoots of Cycas circinalis were studied by counting sequences of foliage leaves, scale leaves, and cones by observation of either their scar patterns or vascular remains. Although male cones are always produced subsequent to a cycle of foliage leaves and are fairly regularly spaced there is no obvious correlation between their presence and the previous cycles of leaves. Ratios of foliage leaves to scale leaves in each cycle are variable. The primary diameter of the axis is obconical, but a conical stem form results from secondary growth. The result of concentric development of xylem and phloem is positively correlated with stem diameter rather than stem age.     

AtTMEM18 plays important roles in pollen tube and vegetative growth in Arabidopsis

In flowering plants, pollen tube growth is essential for delivery of male gametes into the female gametophyte or embryo sac for double fertilization. Although many genes have been identified as being involved in the process, the molecular mechanisms of pollen tube growth remains poorly understood. In this study, we identified that the Arabidopsis Transmembrane Protein 18 (AtTMEM18) gene played important roles in pollen tube growth. The AtTMEM18 shares a high similarity with the Transmembrane 18 proteins (TMEM18s) that are conserved in most eukaryotes and may play important roles in obesity in humans. Mutation in the AtTMEM18 by a Ds insertion caused abnormal callose deposition in the pollen grains and had a significant impact on pollen germination and pollen tube growth. AtTMEM18 is expressed in pollen grains, pollen tubes, root tips and other vegetative tissues. The pollen‐rescued assays showed that the mutation in AtTMEM18 also caused defects in roots, stems, leaves and transmitting tracts. AtTMEM18‐GFP was located around the nuclei. Genetic assays demonstrated that the localization of AtTMEM18 around the nuclei in the generative cells of pollen grains was essential for the male fertility. Furthermore, expression of the rice TMEM18‐homologous protein (OsTMEM18) driven by LAT52 promoter could recover the fertility of the Arabidopsis attmem18 mutant. These results suggested that the TMEM18 is important for plant growth in Arabidopsis.     

罗汉松雄球花及其雄配子体发育的形态结构

该研究采用光学显微镜和扫描电镜,观察罗汉松雄球花、小孢子及其配子体发育过程的形态结构特征,以揭示罗汉松小孢子的发生和雄配子体的发育规律,为罗汉松的生殖和杂交组合提供胚胎学证据。结果发现：(1)罗汉松花芽于每年的7月开始分化,至次年5月花粉成熟散粉,雄球花由单生的卵圆形转为2~3个葇荑花序并生,小孢子叶螺旋状着生于圆柱状的花序轴上,每一小孢子叶远轴面基部并列着生2个小孢子囊。(2)小孢子囊壁发育过程中由外及里出现各由1层薄壁细胞组成的表皮、药室内壁、中层和绒毡层,至散粉前,后两者基本被分解吸收。(3)同一小孢子囊内的造孢细胞发育在时间上存在差异,小孢子母细胞减数分裂后形成的四分体有四面体型和十字交叉型两种排列方式,成熟的雄配子体包括生殖细胞和粉管细胞,发育过程中出现的第一和第二原叶细胞大部分被分解消失。(4)电镜下罗汉松花粉粒为典型的松花型花粉,两侧各具1个气囊,远极面具一萌发沟,花粉粒表面具纹理或皱褶。     

Pollination in vitro: effects on the growth of pollen tubes,seed set and gametophytic self-incompatibility in Trifolium pratense L. and T. repens L.

Summary Growth of pollen tubes and seed set were compared after hand pollination in situ and in vitro in two self-incompatible species, Trifolium pratense and Trifolium repens. Adhesion of pollen grains to the stigma was greater in vitro for both species. After cross-pollination, in vitro culture gave a significant increase in the cumulative growth of pollen tubes in pistils of T. pratense compared to in situ conditions. After selfing in T. repens, pollen tube growth was significantly increased by in vitro culture of florets. Seed set after crossing in situ and in vitro was similar for both species. Seed set after selfing in vitro was not increased in T. pratense. Several genotypes of T. repens were classified as very good, good and poor selfers based on their capacity for seed set following selfing in situ. In vitro pollination increased self seed formation by 1.7-, 18.0- and 31.0-fold for each class, respectively. Ovules located nearest to the style were fertilized more often after selfing than after crossing.     

A histological comparison of the development of pollen and female gametophytes in fertile and sterile Cryptomeria japonica

To determine a possible mechanism causing male and female sterility in Cryptomeria japonica male and female cones were collected from a C. japonica, tree, ShinDai2, that lacks pollen release and fertile seeds and specimens were processed to examine the development of pollen and female gametophytes using light microscopy and field emission scanning electron microscopy. Pre-meiotic development proceeded normally, but the formation of aberrant meiotic products was observed in cones of both sexes. In sterile microsporangia, heterogeneous microspore populations ranging from monads to polyads gave rise to mature pollen grains of non-uniform size. These pollen grains were covered with an amorphous layer and adhered to each other. In addition, they remained in the microsporangia and were not released even after the onset of pollen dissemination from fertile trees. In the ovules of sterile female cones, megaspores with abnormal shapes, numbers, and sizes formed, and the development of female gametophytes was arrested at the free nuclear or archegonium formation stages. These gametophytes collapsed, and no fertile embryo was generated. Results indicate that meiotic defects are important in the sterility mechanism.     

Attractive Spring-food for willow grouse (Lagopus lagopus subsp. lagopus L.) studied using plant macrofossils and pollen in faeces: a methodological discussion

While macrofossil remains of herbs and flowers have disintegrated beyond identification, pollen survives the digestive process and can be identified, sometimes to species level, and is hence an important tool in determining and reconstructing animal diets.

This study compares macroscopic plant parts and pollen remains in faeces from grouse. While macroscopic remains reflect the quantity of bark, twigs, berries and leaves in the birds' food, the pollen also reflects other food, such as catkins, flower buds with developed pollen, flowers and pollen attached to leaves.

Both techniques reflect that Betula and Salix are the most important food for grouse in early Spring. Pollen analysis shows that later in Spring, after snow-melt, the birds are attracted to different plants, firstly, it is taxa within the Ericales and their fruits from the previous year. The nutrient value of food in periods with more or less snow cover is based on the environmental conditions of the previous year. Later on, different herbs, including insect-pollinated plants rich in nectar/sugar, are recorded in the pollen but are not reflected in the macro study, and are therefore lost in most calculations and not discussed. Nutrient content calculations based on Spring and Summer flowers need to be compared with the environmental and climate conditions of the current year.     

Derepression of the cell cycle by starvation is involved in the induction of tobacco pollen embryogenesis

Summary Microspectrophotometry following Feulgen staining and autoradiography following (³H)-thymidine labelling were used to study cell-cycle events during pollen development in tobacco (Nicotiana tabacum L.). During normal gametophytic pollen development in the anther and in vitro the generative nucleus passes through the S phase to the G₂ phase soon after microspore mitosis, while the vegetative nucleus remains arrested in G₁ (=G₀). During embryogenie induction by an in vitro starvation treatment of immature pollen ongoing DNA replication in the generative nucleus is completed and followed by DNA replication in the vegetative cell in a large fraction of the pollen grains. Addition of the DNA replication inhibitor hydroxyurea to the starvation medium postpones S phase entry until the pollen is transferred to a rich medium and does not affect embryo formation. These results demonstrate that one of the crucial events of embryogenic induction is the derepression of the G₁ arrest in the cell cycle of the vegetative cell.     

Reconstruction of the Jurassic conifer Sewardiodendron laxum (Taxodiaceae)

Compressed seed cones and pollen cones of Sewardiodendron laxum are described from the Middle Jurassic of Yima, Henan, central China. They are either organically attached to or associated with leafy shoots. Seed cones are terminally borne. Each cone is ovate to elongated, up to 6.5 cm long and 3.5 cm wide, and consists of a stout axis and numerous helically arranged bract-scale complexes. The bract protrudes beyond and is partially fused with the reduced ovuliferous scale. The ovuliferous scale bears approximately six inverted, small, and flattened seeds. Pollen cones are borne in terminal clusters. Microsporophylls are helically arranged, each bearing three abaxial, basally fused pollen sacs. Pollen is assaccate, rounded, and with an inconspicuous pore. Morphological, structural, and cuticular features of seed cones, pollen cones, and leafy shoots of S. laxum are compared with those of fossil and extant conifers. S. laxum is included in Taxodiaceae and believed to have its closest affinities with a Mesozoic conifer Elatides and a group of Cunninghamia-like conifers. It is reconstructed as a half-evergreen tree that lived in a humid, warm-temperate climate.