Abstract: Background: The haploid male gametophyte generation of flowering plants consists of two- or three-celled pollen grains. This functional specialization is thought to be a key factor in the evolutionary success of flowering plants. Moreover, pollen ontogeny is also an attractive model in which to dissect cellular networks that control cell growth, asymmetric cell division and cellular differentiation. Our objective, and an essential step towards the detailed understanding of these processes, was to comprehensively define the male haploid transcriptome throughout development. Results: We have developed staged spore isolation procedures for Arabidopsis and used Affymetrix ATH1 genome arrays to identify a total of 13,977 male gametophyte-expressed mRNAs, 9.7% of which were male-gametophyte-specific. The transition from bicellular to tricellular pollen was accompanied by a decline in the number of diverse mRNA species and an increase in the proportion of male gametophyte-specific transcripts. Expression profiles of regulatory proteins and distinct clusters of coexpressed genes were identified that could correspond to components of gametophytic regulatory networks. Moreover, integration of transcriptome and experimental data revealed the early synthesis of translation factors and their requirement to support pollen tube growth. Conclusions: The progression from proliferating microspores to terminally differentiated pollen is characterized by large-scale repression of early program genes and the activation of a unique late gene-expression program in maturing pollen. These data provide a quantum increase in knowledge concerning gametophytic transcription and lay the foundations for new genomic-led studies of the regulatory networks and cellular functions that operate to specify male gametophyte development.

Abstract: Stamens are the male reproductive organs of flowering plants. They consist of an anther, the site of pollen development, and in most species a stalk-like filament, which transmits water and nutrients to the anther and positions it to aid pollen dispersal. Within the anther, male sporogenous cells

Abstract: Pollen analysis of honey, or melissopalynol-ogy, is of great importance for quality control.Honey always includes numerous pollen grains(mainly from the plant species foraged by honeybees) and honeydew elem ents (like wax tubes,algae and fungal spores) that altogether providea good fingerprint of th e environment where thehoney comes from. Pollen analysis can thereforebe useful to determine and control the geograph-ical and botanical origin of honeys even if sen-sory and physico-chemical analyses are alsoneeded for a correct dia gnosis of botanical ori-gin. Moreover, pollen analysis provides someimportant information about honey extractionand filtration, fermentation (Russmann, 1998),some kinds of adulteration (Kerkvliet et al

Abstract: High temperature stress (HTS), during flowering, decreases seed production in many plants. To determine the effect of a moderate HTS on flowering, fruit and seed set in Brassica napus, plants were exposed to a HTS (8/16 h dark/light, 18 degrees C night, ramped at 2 degrees C h-1, over 6 h, to 35 degrees C for 4 h, ramped at 2 degrees C h-1 back to 23 degrees C for 6 h) for 1 or 2 weeks after the initiation of flowering. Although flowering on the HTS-treated plants, during both the 1 week and 2 week HTS treatments, was equal to that of control-grown plants, fruit and seed development, as well as seed weight, were significantly reduced. Under HTS, flowers either developed into seedless, parthenocarpic fruit or aborted on the stem. At the cessation of the HTS, plants compensated for the lack of fruit and seed production by increasing the number of lateral inflorescences produced. During the HTS, pollen viability and germinability were slightly reduced. In vitro pollen tube growth at 35 degrees C, from both control pollen and pollen developed under a HTS, appeared abnormal, however, in vivo tube growth to the micropyle appeared normal. Reciprocal pollination of HTS or control pistils with HTS or control pollen indicated that the combined effects of HTS on both micro- and megagametophytes was required to knock out fruit and seed development. Expression profiles for a subset of HEAT SHOCK PROTEINs (HSP101, HSP70, HSP17.6) showed that both micro- and megagametophytes were thermosensitive despite HTS-induced expression from these genes.

Abstract: Despite much recent activity in the field of pollination biology, the extent to which animal pollinators drive the formation of new angiosperm species remains unresolved. One problem has been identifying floral adaptations that promote reproductive isolation. The evolution of a bilaterally symmetrical corolla restricts the direction of approach and movement of pollinators on and between flowers. Restricting pollinators to approaching a flower from a single direction facilitates specific placement of pollen on the pollinator. When coupled with pollinator constancy, precise pollen placement can increase the probability that pollen grains reach a compatible stigma. This has the potential to generate reproductive isolation between species, because mutations that cause changes in the placement of pollen on the pollinator may decrease gene flow between incipient species. I predict that animal-pollinated lineages that possess bilaterally symmetrical flowers should have higher speciation rates than lineages possessing radially symmetrical flowers. Using sister-group comparisons I demonstrate that bilaterally symmetric lineages tend to be more species rich than their radially symmetrical sister lineages. This study supports an important role for pollinator-mediated speciation and demonstrates that floral morphology plays a key role in angiosperm speciation.

Abstract: AtMYB32 gene is a member of the R2R3 MYB gene family coding for transcription factors in Arabidopsis thaliana. Its expression pattern was analysed using Northern blotting, in situ hybridization and promoter-GUS fusions. AtMYB32 is expressed in many tissues, but most strongly in the anther tapetum, stigma papillae and lateral root primordia. AtMYB32-GUS was induced in leaves and stems following wounding, and in root primordia by auxin. T-DNA insertion populations were screened and two insertion mutants were identified, both of which were partially male sterile, more than 50% of the pollen grains being distorted in shape and lacking cytoplasm. AtMYB4 is closely related to AtMYB32 and represses the CINNAMATE 4-HYDROXYLASE gene. Distorted pollen grains were produced in both AtMYB4 insertion mutant and overexpression lines. In an AtMYB32 insertion mutant, the transcript levels of the DIHYDROFLAVONOL 4-REDUCTASE and ANTHOCYANIDIN SYNTHASE genes decreased while the level of the CAFFEIC ACID 0-METHYLTRANSFERASE transcript increased. Change in the levels of AtMYB32 and AtMYB4 expression may influence pollen development by changing the flux along the phenylpropanoid pathways, affecting the composition of the pollen wall.

Abstract: Preface Acknowledgements 1. Introduction 2. The biogeographical setting 3. Autecology and pollen representation 4. Full-glacial refugia 5. Eastern Canada - fossil record and reconstruction 6. The Western interior 7. Pacific-Cordilleran region 8. Vegetation reconstruction and palaeoenvironments Appendix References Index.

Abstract: In this paper we use a simulation approach to explore the effect of variation in taxon parameters and landscape patterning on relevant source area of pollen. We use the Prentice-Sugita model, assume constant atmospheric conditions and basin morphology, and take a reductionist approach to explore the behaviour of pollen dispersal and deposition in a simple landscape scenario. Individual factors within the scenario (pollen fall speed, relative pollen productivity, size of basic unit in the landscape mosaic, patch size, rarity of individual taxa and overall number of taxa present in the landscape) are varied while all other parameters are kept constant, thus permitting exploration of the role of different components of the system. These simulations suggest that, for basins of given size under fixed atmospheric conditions, the relevant source area of pollen is primarily an expression of the patterning of the different vegetation elements within the landscape. This has important implications for the interpretation of palaeoecological records and reconstruction of past environments. Reconstruction, especially quantitative reconstruction, requires some estimate of past relevant source area of pollen. If, as our results suggest, vegetation patterning is an important determinant of this, then it must also be taken into account when attempting to reconstruct past vegetation communities.

Abstract: This paper reviews current knowledge on the occurrence of several types of pollen grains in the sediments of honey samples, propolis and bee loads of Apiinae and Meliponinae in Brazil. After a short historical introduction about research activities in Melissopalynology using Brazilian samples, bee products were analyzed in respect to the greater Brazilian regions (South, Southeast, Northeast and North), emphasizing monofloral honeys and the green propolis. Numerous bibliographic references and a short glossary of the technical terms used is presented.

Abstract: Recently, we have provided evidence that the polymorphic self-incompatibility (S) locus-encoded F-box (SLF) protein AhSLF-S2 plays a role in mediating a selective S-RNase destruction during the self-incompatible response in Antirrhinum hispanicum. To investigate its role further, we first transformed a transformation-competent artificial chromosome clone (TAC26) containing both AhSLF-S2 and AhS2-RNase into a self-incompatible (SI) line of Petunia hybrida. Molecular analyses showed that both genes are correctly expressed in pollen and pistil in four independent transgenic lines of petunia. Pollination tests indicated that all four lines became self-compatible because of the specific loss of the pollen function of SI. This alteration was transmitted stably into the T1 progeny. We then transformed AhSLF-S2 cDNA under the control of a tomato (Lycopersicon esculentum) pollen-specific promoter LAT52 into the self-incompatible petunia line. Molecular studies revealed that AhSLF-S2 is specifically expressed in pollen of five independent transgenic plants. Pollination tests showed that they also had lost the pollen function of SI. Importantly, expression of endogenous SLF or SLF-like genes was not altered in these transgenic plants. These results phenocopy a well-known phenomenon called competitive interaction whereby the presence of two different pollen S alleles within pollen leads to the breakdown of the pollen function of SI in several solanaceaous species. Furthermore, we demonstrated that AhSLF-S2 physically interacts with PhS3-RNase from the P. hybrida line used for transformation. Together with the recent demonstration of PiSLF as the pollen determinant in P. inflata, these results provide direct evidence that the polymorphic SLF including AhSLF-S2 controls the pollen function of S-RNase–based self-incompatibility.

Abstract: For pollination to succeed, pollen must carry sperm through a variety of different floral tissues to access the ovules within the pistil. The pistil provides everything the pollen requires for success in this endeavor including distinct guidance cues and essential nutrients that allow the pollen tube to traverse enormous distances along a complex path to the unfertilized ovule. Although the pistil is a great facilitator of pollen function, it can also be viewed as an elaborate barrier that shields ovules from access from inappropriate pollen, such as pollen from other species. Each discrete step taken by pollen tubes en route to the ovules is a potential barrier point to ovule access and waste by inappropriate mates. In this review, we survey the current molecular understanding of how pollination proceeds, and ask to what extent is each step important for mate discrimination. As this field progresses, this synthesis of functional biology and evolutionary studies will provide insight into the molecular basis of the species barriers that maintain the enormous diversity seen in flowering plants.

Abstract: Small populations of reward-producing plants are likely to be less attractive to animal pollinators than large populations. As a result, both the quantity and the proportion of compatible pollen d ...

Abstract: Pollen tube growth requires a Ca 21 gradient, with elevated levels of cytosolic Ca 21 at the growing tip. This gradient’s magnitude oscillates with growth oscillation but is always maintained. Ca 21 influx into the growing tip is necessary, and its magnitude also oscillates with growth. It has been widely assumed that stretch-activated Ca 21 channels underlie this influx, but such channels have never been reported in either pollen grains or pollen tubes. We have identified and characterized stretch-activated Ca 21 channels from Lilium longiflorum pollen grain and tube tip protoplasts. The channels were localized to a small region of the grain protoplasts associated with the site of tube germination. In addition, we find a stretch-activated K 1 channel as well as a spontaneous K 1 channel distributed over the entire grain surface, but neither was present at the germination site or at the tip. Neither stretch-activated channel was detected in the grain protoplasts unless the grains were left in germination medium for at least 1 h before protoplast preparation. The stretch-activated channels were inhibited by a spider venom that is known to block stretch-activated channels in animal cells, but the spontaneous channel was unaffected by the venom. The venom also stopped pollen tube germination and elongation and blocked Ca 21 entry into the growing tip, suggesting that channel function is necessary for growth.

Abstract: Ca2+ dynamics in the growing pollen tube have been well documented in vitro using germination assays and Ca2+ imaging techniques. However, very few in vivo studies of Ca2+ in the pollen grain and papilla cell during pollination have been performed. We expressed yellow cameleon, a Ca2+ indicator based on green fluorescent protein, in the pollen grains and papilla cells of Arabidopsis (Arabidopsis thaliana) and monitored Ca2+ dynamics during pollination. In the pollen grain, [Ca2+]cyt increased at the potential germination site soon after hydration and remained augmented until germination. As in previous in vitro germination studies, [Ca2+]cyt oscillations were observed in the tip region of the growing pollen tube, but the oscillation frequency was faster and [Ca2+]cyt was higher than had been observed in vitro. In the pollinated papilla cell, remarkable increases in [Ca2+]cyt occurred three times in succession, just under the site of pollen-grain attachment. [Ca2+]cyt increased first soon after pollen hydration, with a second increase occurring after pollen protrusion. The third and most remarkable [Ca2+]cyt increase took place when the pollen tube penetrated into the papilla cell wall.

Abstract: Endo-β-mannanase (EC 3.2.1.78) is involved in cell wall disassembly and the weakening of plant tissues by degrading mannan polymers in the cell walls. Endo-β-mannanase genes are expressed in tomato (Lycopersicon esculentum) seeds (LeMAN1 and LeMAN2) and fruits (LeMAN3 and LeMAN4). A novel endo-β-mannanase gene (termed LeMAN5) was found in the tomato genome by genome-walking PCR and bacterial artificial chromosome library screening. The 5′-upstream region of this endo-β-mannanase gene contained four copies of the pollen-specific cis-acting elements POLLEN1LELAT52 (AGAAA). A GUS-reporter gene driven with the putative LeMAN5 promoter (-543 to +38) was activated in anthers and pollen of transgenic Arabidopsis, with the highest β-glucuronidase activity detected in pollen. β-Glucuronidase expression was detected in mature pollen retained in sporangia, discharged pollen, and elongating pollen tubes in transgenic Arabidopsis. Consistently, expression of LeMAN5 mRNA and endo-β-mannnanase activity was detected in tomato anthers and pollen. In anthers, the highest mRNA expression and endo-β-mannanase activity were detected during late stages of anther development, when pollen maturation occurred. Endo-β-mannanase activity was present in discharged pollen, which was easily eluted in a buffer, indicating that the enzyme proteins are probably secreted from, and deposited on, the surface of pollen. These data suggest that the LeMAN5 endo-β-mannanase is associated with anther and pollen development.

Abstract: In long-lived organisms, it is often difficult to determine which environmental factors will have the largest effects on population dynamics. In this study, I incorporated the results of short-term experiments and observations into a demographic matrix model to determine the effects of both herbivory and pollen limitation on the dynamics of a declining population of the perennial herb Trillium grandiflorum. While pollen supple- mentation experiments in both 1999 and 2000 revealed that plants produce fewer seeds as a result of pollen limitation, this pollen limitation had almost no effect on the growth rate of the population. White-tailed deer (Odocoileus virginianus) consumed nearly half of the reproductive plants in this population in 2000 and 2001. Herbivory causes reproductive and large nonreproductive plants to regress in stage and have lower fecundity. In the absence of herbivory, demographic projections suggest that the population would shift from de- clining to growing, the proportional representation of new recruits would rise, and plants in larger stage classes would have higher reproductive values. Such shifts in the reproductive values and stable stage distribution result in shifts in elasticities. A life table response experiment demonstrated that, while herbivory affected six vital rates, two of these con- tributed disproportionately to the change in the population growth rate: reproductive plants remaining reproductive and large nonreproductive plants remaining nonreproductive. In this population, herbivores contribute more to its decline than pollinators. Thus, active long-term management of deer populations appears necessary for the conservation of un- derstory herbs such as Trillium grandiflorum.

Abstract: As pollen tubes grow through the pistil they are thought to perceive and respond to diverse signals. The tomato pollen-specific receptor kinases LePRK1 and LePRK2 might participate in signaling during pollen tube growth. We previously showed that the extracellular domain of LePRK2 interacts with a pollen protein, LAT52, before but not after pollen germination. To determine whether LePRK2 might have different binding partner(s) after pollen germination, we characterized two more proteins that, like LAT52, were identified in yeast two-hybrid screens using the extracellular domains of LePRK1 and LePRK2 as baits. We show that LeSHY, a leucine-rich repeat protein from pollen, and LeSTIG1, a small cysteine-rich protein from pistil, can bind the extracellular domains of both LePRK1 and LePRK2 in vitro. In vitro binding assays with the extracellular domain of LePRK2 suggested that LeSTIG1 could displace binding of LAT52, consistent with the idea that LePRK1 and LePRK2 might interact with different ligands at different stages of pollen tube growth. Exogenous LeSTIG1 promotes pollen tube growth in vitro. The interaction of these pollen kinases with LeSTIG1 supports the notion that LePRK1 and LePRK2 are involved in mediating pollen-pistil interactions.

Abstract: There is an increasing concern about the preservation of genetic identity of conventional maize (Zea mays L.) and of distance required to segregate non-genetically modified (non-GM) from GM grain production since the introduction of Bacillus thuringiensis (Bt) and other transgenic events into commercial hybrids. Field experiments were conducted at three sites in Ottawa, Canada, for 3 yr to determine (i) the extent of cross-fertilization of a maize genotype by foreign pollen of neighboring hybrids and (ii) the practical distance required to isolate conventional maize hybrids from neighboring GM maize fields. At each site, yellow-kernel Bt maize was planted in the center (27 by 27 m) of a field surrounded in all directions by the distance equivalent to 24 or 48 rows (37 m) of white-kernel maize, and a 200-m non-maize crop was maintained in all directions. Phenology and weather conditions were closely monitored during the tasseling and silking period. At maturity, a thorough examination on the cross-fertilization was conducted in the white maize population. Our results showed that the rate of cross-fertilization in maize was dependent upon the distance from the pollen source, wind direction and synchronization of silking and pollen shedding of the two genotypes involved. Up to 82% out-cross was measured in the first row adjacent to the Bt maize. The level of out-cross was <1% beyond the 37th border row (28 m) downwind and the 13th row (10 m) upwind in all site-years. An exponential decline model was fitted well (P < 0.01) to the cross-fertilization data as a function of distance from the yellow maize pollen source with R 2 up to 0.64. Our data suggested that it is possible to produce non-GM maize grains by removing the outside rows of non-GM maize plants (about 30 m) neighboring the GM maize field in concern if the acceptance level is set at ≤1% out-cross. The generally recommended 200-m distance between two genotypes (inbreds, populations, hybrids, and wild relatives) appears to be appropriate for Bt or other GM maize, as well.

Abstract: Cytosolic free Ca2+ and actin microfilaments play crucial roles in regulation of pollen germination and tube growth. The focus of this study is to test the hypothesis that Ca2+ channels, as well as channel-mediated Ca2+ influxes across the plasma membrane (PM) of pollen and pollen tubes, are regulated by actin microfilaments and that cytoplasmic Ca2+ in pollen and pollen tubes is consequently regulated. In vitro Arabidopsis (Arabidopsis thaliana) pollen germination and tube growth were significantly inhibited by Ca2+ channel blockers La3+ or Gd3+ and F-actin depolymerization regents. The inhibitory effect of cytochalasin D (CD) or cytochalasin B (CB) on pollen germination and tube growth was enhanced by increasing external Ca2+. Ca2+ fluorescence imaging showed that addition of actin depolymerization reagents significantly increased cytoplasmic Ca2+ levels in pollen protoplasts and pollen tubes, and that cytoplasmic Ca2+ increase induced by CD or CB was abolished by addition of Ca2+ channel blockers. By using patch-clamp techniques, we identified the hyperpolarization-activated inward Ca2+ currents across the PM of Arabidopsis pollen protoplasts. The activity of Ca2+-permeable channels was stimulated by CB or CD, but not by phalloidin. However, preincubation of the pollen protoplasts with phalloidin abolished the effects of CD or CB on the channel activity. The presented results demonstrate that the Ca2+-permeable channels exist in Arabidopsis pollen and pollen tube PMs, and that dynamic actin microfilaments regulate Ca2+ channel activity and may consequently regulate cytoplasmic Ca2+.

Abstract: Prevailing ambient temperature during the reproductive phase is one of several important factors for seed and fruit set in different plant species, and its consequences on reproductive success may increase with global warming. The effect of temperature on pollen performance was evaluated in sweet cherry (Prunus a'iumn L.). comparing as pollen donors two cultivars that differ in their adaptation to temperature. 'Sunburst' is a cultivar that originated in Canada with a pedigree of cultivars from Northern Europe. while 'Cristobalina' is a cultivar native to southeast Spain. adapted to warmer conditions. Temperature effects were tested either in controlled-temperature chambers or in the field in a plastic cage. In both genotypes, an increase in temperature reduced pollen germination, but accelerated pollen tube growth. However, a different genotypic response. which reflected the overall adaptation of the pollen donor, was obtained for pollen tube dynamics, expressed as the census of the microgametophyte population that successfully reached the base of the style. While both cultivars performed similarly at 200C. the microgametophyte population was reduced at 30'C for Sunburst and at 100C for Cristobalina. These results indicate a differential genotypic response to temperature during the reproductive phase. which could be important in terms of the time needed for a plant species to adapt to rapid temperature changes.

Abstract: The antioxidant activities of total extracts of a mixture of honeybee-collected pollen and its six constituent pollens were determined by lipid peroxidatio

Abstract: The sensitivity of pollen as an indicator of elevation in neotropical lowland and Andean forests was measured using modern pollen samples collected from moss-polsters along a transect between 340 m and 3530 m elevation and from surface sediments in lowland swamps (240 m) of Madre de Dios, Peru. A blind study, using samples collected from the same transect in the following year, provided a test of reproducibility. The results show (1) clear elevational distribution patterns and (2) the ability of calibration data to predict the altitude of the blind samples. Characteristic associations of pollen taxa are found under differing hydrologies and elevations. The floodplain pollen assemblages are characterized by abundant Mauritia, Sloanea, Ficus, Iriartea and Arecaceae pollen types. At higher elevations, these lowland types decrease or are absent. Alchornea ,U rticaceae/Moraceae, Bignoniaceae and Cecropia are dominant components of the pollen rain of the low-elevation zone (< 1000 m). Acalypha, Alchornea, Cecropia ,R ubiaceae and Urticaceae/Moraceae are important between 1000 m and 1600 m elevation. Pollen of Hedyosmum, Alnus ,P oaceae and Combretaceae/Melastomataceae are abundant between 1600 m and 2000 m. Cecropia pollen dominates samples from low- to mid-elevation disturbed forests. Alnus pollen is most abundant, and Poaceae becomes rare, between 2000 and 2700 m. At high elevations above 2700 m, Asteraceae, Poaceae, Polylepis, Muehlenbeckia-type and Myrsine pollen are dominant. Statistical analysis of the data set using Detrended Correspondence Analysis (DCA) shows a precise correlation between community composition and elevation. The DCA axis 1 values are strongly correlated with sample elevation, exhibiting a linear relationship (r 2 = 0.904). The results provide an estimate of the sensitivity of pollen analysis in the Neotropics as a proxy for measuring elevation and, by inference, temperature.

Abstract: The successful establishment of angiosperms on land is in part determined by their floral design. Because plants cannot move to find the ideal mate, they have developed a great variety of flowers to provide different mechanisms of pollen release, pollen transfer, and deposition of the pollen from

Abstract: Most models of floral specialization assume that adaptations to a particular type of pollinator incur a fitness trade-off in reduced effectiveness of others. To examine this assumption and characterize the form of trade-offs, I manipulated floral form in Dudleya greenei (Crassulaceae), a species that is pollinated by hummingbirds, bumble bees, and other insects. Existing pollination literature predicts that pollination by hummingbirds should favor narrower flowers than pollination by bumble bees. When hummingbirds alone visited experimental populations, narrow flowers indeed performed best by most measures. Hummingbirds showed a slight preference for flowers of intermediate width but deposited more pollen per visit and more pollen overall, and they exported more dye (a pollen analogue) as corolla flare decreased. Bees were more effective than birds at pollinating wide flowers but did not generate overall performance trade-offs. Bees also preferred flowers of intermediate width and deposited more pollen per visit and more pollen overall as corolla flare decreased, but the overall efficiency with which bumble bees exported dye was independent of corolla flare. This demonstrates that phenotypic specialization for hummingbirds might evolve without trading-off the effectiveness of bumble bees. However, both birds and bees tended to transfer dye most efficiently between like phenotypes, suggesting that the form of selection and presence of trade-offs may be frequency dependent in natural populations.