Zur Ultrastruktur und Funktion pollenverbindender Fäden beiEricaceae und anderen Angiospermenfamilien

Viscin threads and other pollen connecting threads of some angiosperm families were investigated, especially those ofEricaceae. According to the definition adopted, viscin threads are ± long exinous processes which consist of exinous material and connect pollen grains or tetrads. Such viscin threads are found within theOnagraceae, Caesalpiniaceae, Ericaceae, andMimosaceae only. While they differ in structure and composition, they always consist of sporopollenin and exhibit a very strong stickiness, even after all viscid substances have been removed by acetolysis. In contrast, the pollen connecting scleroprotein threads ofOrchidaceae and the cellular threads ofStrelitzia reginae Aiton. (Musaceae) are not connected with the exine surface, are destroyed by acetolysis, and thus do not correspond to viscin threads.

     

Late Quaternary vegetation and climatic history of eastern Nepal

The late Quaternary vegetation and climatic history at high altitude in eastern Nepal was studied through stratigraphy, radiocarbon dating and pollen analysis. The Thulo Pokhari lake (27°41′ N, 87°43′ E, ca. 3980 m a.s.l.) is just above the subalpine Abies spectabilis–Betula utilis forest zone and surrounded by Rhododendron scrub. The climate in the studied area is very humid under the influence of the monsoon. Silty sediments suggesting lake conditions prevailed at the lower part of the sediment samples, whereas the upper part consisted mainly of herbaceous peat indicating a mire condition. The pollen record extends back to ca. 11000 yr bp . Although the absence of major changes between the pollen assemblages of the Pleistocene and those in the Holocene was attributed to the situation of the sampling plot above the forest limit, the results suggest the following history. (1) The abundance of Pinus pollen around 11000 yr bp represents expansion of the area unoccupied by late successional trees and/or a drier condition. Significant occurrence of Picea pollen is noteworthy, since this genus is absent in eastern Nepal at present in spite of its wide distribution throughout the neighbouring areas of the Himalayas. (2) The increase in abundance of Quercus pollen and the decline in Pinus pollen in the latest Pleistocene represent climatic amelioration favourable to late successional mesophytes. (3) The climate was most moist and mild in the SP-III, although the absolute age of the pollen zone is not distinct. The percentages of broadleaved trees such as Alnus, Betula, Carpinus and Corylus were increased at the expense of Quercus and coniferous pollen types. Sedimentation was interrupted by lake level decline and/or glacial advance during the period from ca. 11000–1600 yr bp . (4) The increase in abundance of coniferous pollen types such as Pinus, Abies and Tsuga indicates that the climate became drier and cooler, and the present subalpine forest zone composed of A. spectabilis, T. dumosa and Betula utilis was established around 1600 yr bp . The formation of bog or alpine meadow vegetation during the period was shown by the ¹⁴C dates of the peat and the increase in Rosaceae and herbaceous pollen. (5) The increase in abundance of Ericaceae and Alnus pollen in the SP-V indicates that the present alpine Rhododendron scrub zone has been established since ca. 940 yr bp as a result of human influence on the original vegetation. This interpretation is supported by the decline in the proportion of arboreal pollen. Since the age of the initiation of human influence varies with the altitude and region, further study will be necessary to determine the accurate age.     

LATE CRETACEOUS FOSSIL FLOWERS OF ERICALEAN AFFINITY

Fossilized flowers of ericalean affinity are reported from the Turanian (ca. 90 MYBP, million years before present) of New Jersey. The fossils are remarkably well preserved and three-dimensional, and are the oldest known floral remains of Ericales. The series of fossil flower buds, floral fragments, and fruits are not identical to any modern genus of Ericales. The inverted U-shaped anthers with pseudoterminal awns, and the fluted syncarpous ovary of the fossils suggest affinities with basal Ericaceae, probably near extant Enkianthus, a taxon that also shares monadinous pollen with the fossil. Pollen grains were observed clumped on a stigma in one of the fossil flowers. Fossilized acid-resistant strands having characteristics, including similar diameter and sculpture pattern, in common with the muri connect pollen grains and, with scanning electron microscopy, appear continuous with the tectum, supporting the interpretation that they are viscin threads. These are the oldest reported fossilized viscin threads, and the only fossilized viscin threads found in situ in flowers. In modern Ericales and Onagraceae, the presence of viscin threads is associated with highly specific plant-pollinator relationships, raising the possibility that such specific pollinator-plant relationships had developed by the mid-Cretaceous. This is consistent with floral characters in these ericalean fossils, the presence of advanced meliponine bees in slightly younger sediments from the same region, and with the morphology and affinities of other fossil flowers from the same sediments.     

Pollen of Ceratostema (Ericaceae, Vaccinieae): tetrads without septa

The pollen morphology of two species of the Neotropical genus Ceratostema (Ericaceae) was examined by light, scanning and transmission electron microscopy. The Ceratostema species examined have 3-colporate pollen grains united in permanent tetrahedral tetrads that show a common condition encountered in the Ericaceae. But the septal exine was absent between two neighboring grains in each pollen tetrad of Ceratostema. The pollen tetrads without septa are the first report for the Ericaceae as well as other angiosperm families.     

Relationships of pollen size,pistil length and pollen tube growth rates in Rhododendron and their influence on hybridization

Summary Pollen size and pistil length data have been collected for 93 species of Rhododendron (Ericaceae) belonging to a number of different subgeneric taxa. For a sample of eight species in section Vireya, pollen tube growth in the style after selfor interspecific pollination has been quantified. Pollen volume and the time taken for pollen tubes to reach the ovary were both related to pistil length. Pollen-tube growth rates were generally greater for species with longer pistils and larger pollen. Increasing temperature increased the rate of pollen-tube growth. There was no detectable effect of pollen tube density on tube growth rate in the style. After interspecific pollinations tube growth rates in foreign styles could be faster or slower than in self styles. A semisterile individual with two viable pollen grains per tetrad and a plant grafted as scion to a longer-styled stock both showed more rapid pollen-tube growth than expected on the basis of pistil size. Data collected for 26 species in section Vireya showed that where extreme disparity of pollen/pistil size causes failure of interspecific crosses, one or more bridging species with intermediate pollen/pistil size can generally be selected.     

Bumble bee-initiated vibration release mechanism of rhododendron pollen

Although Rhododendron spp. anthers have apical pores and should be expected to be buzz pollinated, bees do not normally sonicate them to release pollen. Stamens were examined to determine their pollen release mechanism; the filaments were shown to have natural vibration modes that cause pollen to be forcibly ejected by vibration, providing the pollen is mature. The first natural vibration mode of the stamens was found to generate centrifugal force sufficient to throw the pollen toward the apical pore and out of the anther, so that it adheres to the anther tip and hangs in the bee's path to the nectaries. These vibrations may be triggered by bees brushing past the long stamens when foraging for nectar, so that the flowers retain their pollen until insect vectors begin foraging on them. The low frequency vibration modes of the viscin threads, which hold the pollen together, may contribute towards the pollen ejection by low frequency stamen vibration. Vibration transmission of dehiscent anthers containing pollen was good from 50 Hz to 850 Hz, suggesting that sonication should be an efficient method of pollen collection, although this rarely occurs. Vibratory ejection occurs at a constant energy level, rather than the constant force levels found in previous research on Actinidia.     

Association of the Generative Cell and Vegetative Nucleus in Pollen Tubes of Rhododendron

Mixed fluorescence/bright field microscopy of Rhododendron pollentubes in the first 72 h after germination reveals a lens-shapedgenerative cell which divides to give two associated spermswithin the original cell boundary. The generative cell is closelyassociated with the vegetative nucleus which precedes it in92 per cent of pollen tubes. Three-dimensional reconstruction from serial thin sections ofa pollen tube fixed 24 h after germination shows that the associationbetween the generative cell and vegetative nucleus is extremelycomplex. Elongated tails of the generative cell physically enfoldthe vegetative nucleus and penetrate into enclaves within it.The association has been clarified by use of the periodic acid-phosphotungsticacid-chromic acid technique to enhance electron contrast ofthe plasma membranes surrounding the generative cell. In thisbicellular system, the male germ unit association is apparentlyinitiated after pollen maturity but prior to generative celldivision. Pollen tube, generative cell, male germ unit, plasma membrane, vegetative nucleus, Rhododendron, Ericaceae     

FUCHSIA POLLEN FROM THE EARLY MIOCENE OF NEW ZEALAND

Fossil pollen of Diporites aspis Pocknall & Mildenhall, from the early Miocene of New Zealand, was examined by combined light, scanning, and transmission electron microscopy, in order to determine its relationship to extant Fuchsia pollen. Based on overall morphology, exine structure, exine surface sculpture, viscin thread morphology, and apertural features, the fossil pollen definitely can be considered to represent Fuchsia. Parallel studies of extant Fuchsia pollen indicate that a more precise identification of the fossils is not possible. With the examination of additional fossil material, it should be possible to learn a great deal about the timing of origin and migration of the genus Fuchsia, but not of its constituent parts.     

Substructure of spore and pollen grain exines in Lycopodium,Alnus, Betula,Fagus and Rhododendron

We have used atomic force microscopy and scanning tunnelling microscopy to extract new information about the substructure of the Alnus, Betula, Fagus, Lycopodium and Rhododendron pollen grain exine. Our scans of exines using atomic force microscopy and scanning tunnelling microscopy reveal somewhat similar substructures for Lycopodium spores and pollen of Alnus, Betula, Fagus and Rhododendron. They show various levels of alignment and clustering of substructure components. Except for Alnus, which showed polygonal clustering of spheroids and weak alignment, there is pronounced alignment of helical units. In Betula, Fagus, Lycopodium and Rhododendron the subunits appear to be helical or perhaps consisting of elongated spheroids, these spheroids are however arranged in a way that suggest that they are part of a helical structure. The diameter of these helical subunits range from 10–15 nm in Fagus, 20–25 nm in Lycopodium, 35–90 nm in Rhododendron up to 70–120 nm in Betula. Our preparations graded from intact or fractured fresh pollen to pollen that was acetolyzed, chemically fixed and epoxy resin embedded. While our knowledge of the exact radial/lateral orientation of most of our scans is less than perfect there were in all cases substructures or cross connections of exine units. We found results from scanning and transmission electron microscopy to be helpful in understanding images from Atomic Force- and Scanning Tunnelling Microscopy.     

贵州30种杜鹃属植物叶背表皮显微形态特征

杜鹃属植物的分类历来都十分重视叶片表皮特征的分类学价值,无论是在各亚属之间还是在种及种下等级的划分中都很强调此类特征的作用。贵州省位于世界现代杜鹃分布中心边缘及向东部散布的过渡地带,省内自然分布的杜鹃种类资源丰富而又独具特色,包括很多尚未深入研究的特有类群。为进一步研究贵州杜鹃属植物的属下系统分类关系,该文对自然分布于贵州的30种杜鹃进行了叶背显微形态特征研究,其中有28种的叶背表皮特征为首次报道。研究材料全部来自采于贵州西北部百里杜鹃自然保护区内的杜鹃属植物,包括杜鹃亚属4种、糙叶杜鹃亚属1种、常绿杜鹃亚属22种、马银花亚属1种及映山红亚属2种,共计30种。研究方法为取成熟叶片处理后在JSM-6490型扫描电镜下对叶背表皮进行观测。叶背鳞片类型的划分方法参照前人工作。结果表明:这30种杜鹃叶片叶背表皮形态特征在电子显微镜下表现出明显的多样性,如有鳞类杜鹃具有鳞片而其他类群则无,叶表面有或无表皮毛,表皮毛排列稀疏或密生,气孔器未见或偶见,散生于乳突状或非乳突状突起之间,或角质层增厚气孔器下陷,内、外拱盖表面粗糙或光滑,气孔器周围有或无间断的条形突起,突起呈环状或羽状等,但在同一亚属或亚组中又呈现出或多或少的一致性。研究讨论表明,叶背表皮显微形态特征在杜鹃属植物的属下系统分类中具有重要的研究价值。     

THE NATURE OF THREADLIKE STRUCTURES AND OTHER MORPHOLOGICAL CHARACTERS IN JACQUESHUBERIA POLLEN (LEGUMINOSAE: CAESALPINIOIDEAE)

Threadlike structures were observed on many pollen grains of Jacqueshuberia amplifoliola, J. purpurea, and J. quinquangulata of the Leguminosae/Caesalpinioideae. Each end was attached to the highly reticulate polar exine surface of different grains. The consistency of this observation, hence, the absence of free thread ends, is interpreted to mean that they should be considered as either exine bridges or exinial connections rather than viscin threads, although, most likely functionally homologous to viscin threads. Other significant morphological characters were the tricolporate apertures and strikingly lamellate foot layer and endexine.     

Antibiotics,Sugars, and Amino Acids in Nectar of Rhododendron and Piptanthus Species from Nepal

Nectars were extracted in Helambu and Langtang Nepal Himalayas from Rhododendron arboreum and Rh. barbatum (Ericaceae), and from Piptanthus nepalensis (Fabaceae), and analyzed for sugars, amino acids, and antibiotic activity. Sugar content in Rhododendron nectar varied from 17 to 65%. In most nectars, G and F were present in a 1:1 ratio. In addition, from a Rh. arboreum nectar, S could be detected. Piptanthus nectar showed a very high sugar content (up to 80%), F and G, or F, G, and S, respectively, being the main sugar constituents. In all Rhododendron nectar amino acids could be found. In Piptanthus nectar there were no traceable amino acids. Neither an evolutionary significance of amino acid contents in floral nectar nor their close correlation with bees, the main pollinators of both genera, could be confirmed from our studies. Rhododendron nectar showed antibiotic activity due to the presence of acetylandromedol. The biological significance of acetylandromedol, the main toxic principle from Rhododendron nectar, seems to be its antibiotic activity, which could possibly compensate for lower sugar contents in preventing bacterial growth.     

Pollen morphology of some selected plant species from Horton Plains,Sri Lanka

The pollen morphology of four species: Gaultheria leschenaultii (Ericaceae), Psychotria zeylanica (Rubiaceae), Rubus leucocarpus (Rosaceae) and Symplocos bractealis (Symplocaceae) from Horton Plains, Sri Lanka was investigated using LM and SEM. Psychotria zeylanica is endemic to Sri Lanka and the other three taxa are common in Horton Plains. Gaultheria leschenaultii has tetrads with 3-colporate, coarsely granular to granulo-rugulate pollen grains; in the polar region and at the colpus margin the exine is smooth with micro-rugulate structure. Psychotria zeylanica has 3- (or 4-) colporate, reticulate-spinulose to granular pollen grains. Rubus leucocarpus has 3-colporate, striate-perforate pollen grains and Symplocos bractealis has 3- (or 4-) colporate pollen grains with a verrucate-perforate exine. Pollen grains of these four species are very indicative of human impact and palaeoclimate.     

Zur Frage der Anheftung des Pollens an blütenbesuchende Insekten mittels Pollenkitt und Viscinfäden

The attachment of pollen grains among themselves, on the loculus wall, and on flower-visiting insects is quite different in entomophilous angiosperms using pollenkitt and those using viscin threads as pollen adhesives. The sticky and viscous pollenkitt makes the pollen grains adhere, while the thin, non-elastic, non-sticky, and flexible viscin fibers fasten them like ropes on insect hairs or bristles. Nectar vomited by honey-bees, sticky stigma secretions or other additional sticky substances further improve the pollen adherence to flower-visiting insects.

Herrn Univ.-Prof. Dr.Walter Leinfellner zum 70. Geburtstag gewidmet.     

Annual variation of airborne pollen in the city of Palencia,Spain, 1990–1992

The aim of this work is to present the atmospheric pollen concentrations of Palencia, Spain. Data were collected for three consecutive years (1990–92). An active volumetric pollen trap, type CAP2, was used. During this time, 88 different pollen types were identified, of which 27 occured at more than 0.15% of the total pollen recorded annually. These types formed the main pollen spectrum of this sampling station. Pollen coming from herbs (Poaceae, Chenopodiaceae, Plantago Urticaceae, etc.) was predominant (53.79%); arboreal pollen (Quercus, Populus Cupressaceae, etc.) represented 42.11%, and pollen from shrubs (Ericaceae, Sambucus etc.) only 4.10%.

May and June was the time of the year with maximum pollen emission to the air. This was due to the quantities of pollen coming from Poaceae and Quercus which together represent 47.25% of the pollen recorded over the three‐year sampling period. Herbaceous pollen appeared throughout the year with maximum concentrations recorded in the spring, coinciding with the maximum levels of arboreal pollen in the atmosphere.

An analysis of multiple regression and one‐way anova test between pollen concentrations and selected meteorological parameters show that relative humidity and average temperature are the meteorological factors most correlated with the concentrations of specific pollen types (Plantago, Ligustrum, Sambucus, Carex). In the same way, when the winds are predominantly from the northeast (second quadrant), there are higher pollen concentrations of Sambucus Ericaceae and Mercurialis.     

Extraction of nitrate reductase from leaves of ericaceae

The inability to obtain active nitrate reductase (E.C. 1.6.6.2) preparations from leaf extracts of Leucothoe and Rhododendron (Ericaceae) was due to a galloyl ester-like compound, similar in nature to tannic acid.     

Pollen morphology and its taxonomic significance of the monotropoideae (Ericaceae)

A palynological survey, including LM, SEM and TEM is presented for eight genera, nine species and 76 samples of the Monotropoideae which is composed of 10 genera and 13 species. On the basis of the aperture number and shape, the following six pollen types are recognized: 1) 3-colp(oroid) ate—Allotropa, 2) 2-colpor(oid)ate—Monotropsis andHemitomes, 3) 4-colpor(oid)ate—Pterospora, Sarcodes andPleuricospora, 4) 2- and 3-colpor(oid)ate—Monotropa hypopitys, 5) 3-colporate and-porate —Monotropa uniflora, 6) 3- to 4- porate—Monotropastrum humile. Relationships among taxa within the Monotropoideae are illustrated on the palynological characters including the aperture type, exine sculpture and structure. Both pollen grains with two and four apertures have evolved independently from pollen grains with three apertures, according to the infraspecific variation of aperture numbers and the usual occurrence of three-aperturate pollen grains in the Ericaceae. 3-colp(oroid)ate pollen ofAllotropa is the most primitive and occupies an isolated position in the subfamily, on the other hand 3- to 4-porate pollen ofMonotropastrum humile is most advanced in the subfamily, probably even in the Ericaceae. A reduced sexine inMonotropastrum humile appears to be a specialized pollen character. Infraspecific geographical difference in palynological characters is revealed in two species ofMonotropa for the first time.M. hypopitys is basically characterized by pollen grains with two apertures in the New World vs. three apertures in the Old World.M. uniflora is basically characterized by 3-porate pollen in the New World vs. 3-colporate in the Old World. In both species pollen grains with more primitive characters usually occur in the Old World.     

Ontogeny of the Calliandra – massulae (Mimosaceae: Ingeae), and the associated viscin body

Polyads, called also massulae, are common in the Mimosaceae. Within this family, only in Calliandra (s. l.) polyads show a remarkable morphological variation: 16-grained lens-shaped massulae in the neotropical Zapoteca (syn. Calliandra p.p.), and highly asymmetric eight-grained massulae in Calliandra (s. str.). As a further specialisation the massulae in Calliandra (s. str.) possess a sticky appendage called a viscin body. The form and ontogeny of this unique two-dimensional construction of the massula is of particular interest. In Calliandra (s. str.) the octad is normally the developmental product of the initiation stage, beginning with one pollen mother cell (PMC). In total, Calliandra (s. str.) possesses eight PMCs in each anther.The dicotyledons are characterised by the simultaneous type of cytokinesis, but wall formation in Calliandra (s. str.) during meiotic division is successive, as common in monocotyledons. The first wall divides the PMC diagonally, and during the tetrad period, two clear variants of tetrads are found. One shows the typical rhomboidal arrangement and the other forms two congruent symmetrical halves. The latter probably results from early fixed, quite inflexible walls. The cells of tetrad do not separate, and four successive mitotic divisions give rise to the eight-celled massula. The direction of growth of the PMC and the massula, the sequence of division, and the position of the walls all show a strict polarity. The normal number of eight cells in each massula is sometimes exceeded without loss of viability.Calliandra (s. str.) lacks a developed “Pollenkitt”, and its asymmetrical massula is combined with the viscin body, which is involved in pollination. This viscin body is located on a specialised pollen grain at the top of the massula. With the viscin body, Calliandra (s. str.) massulae have a mechanism for immediate and persistent attachment to different surfaces. SEM is used to understand the mechanisms of attachment in detail. Furthermore, the relation between pollinators and the massula shape is investigated. Massula transport and the role of the viscin body in pollen–stigma interaction are discussed as well. The stigma of Calliandra (s. str.) is papillate and in the receptive stage, it is characterised by acquisition of a copious exudate.Zapoteca (syn. Calliandra p.p.) massulae could be distinguished histochemically from those of Calliandra (s. str.) by the main components of the “Pollenkitt”. Histochemical and physical properties of the viscin body suggest a waxy nature, including lipids in combination with unsaturated fatty acids. Proteins are present in less amounts and polysaccharides and polyglucans are absent. These results are discussed in relation to analogous phenomena in other families.The term “apex cell” is introduced to indicate the specialisation of the tip-cell of the massula by ontogeny and polarity.     

Pollen harvest by solitary bees (Ptilothrix relata,Hym. Apidae,Emphorini) in the Argentine pampas – preliminary results

In order to determine the plants foraged by solitary Ptilothrix relata, the pollen content of food provisions was identified. The main pollen types confirm foraging by these bees on Malvaceae, Asteraceae and Onagraceae. Pollen sources belonging to Cucurbitaceae, Dipsacaceae and Portulacaceae families enrich the harvesting range of P. relata. According to the preliminary results, these bees can be considered more as narrowly polylectic than oligolectic because they collect pollen from a few unrelated species. Among the most abundant pollen collected, two major morphological types were recognized: (1) pollen with long spines (4–25?μm), many single apertures and large size (115–135?μm of diameter); and (2) tricolporate pollen with viscin threads.