Interaction of pollen-specific actin-depolymerizing factor with actin

We have examined the interaction of recombinant lily pollen ADF, LlADF1, with actin and found that whilst it bound both G- and F-actin, it had a much smaller effect on the polymerization and depolymerization rate constants than the maize vegetative ADF, ZmADF3. An antiserum specific to pollen ADF, antipADF, was raised and used to localize pollen ADF in daffodil--a plant in which massive reorganizations of the actin cytoskeleton have been seen to occur as pollen enters and exits dormancy. We show, for the first time, an ADF decorating F-actin in cells that did not result from artificial increase in ADF concentration. In dehydrated pollen this ADF : actin array is replaced by actin : ADF rodlets and aggregates of actin, which presumably act as a storage form of actin during dormancy. In germinated pollen ADF has no specific localization, except when an adhesion is made at the tip where actin and ADF now co-localize. These activities of pollen ADF are discussed with reference to the activities of ZmADF3 and other members of the ADF/cofilin group of proteins.     

Pollen pool heterogeneity in shortleaf pine, Pinus echinata Mill

Pollen is the dominant vector of gamete exchange for most temperate tree species. Because pollen movement influences the creation, maintenance and erosion of genetic structure in adult populations, it is important to understand what factors influence the process of pollen movement. Isolation by distance in pollen donor populations can create highly structured pollen polls by increased sampling of local fathers. Extrinsic factors, such as the intervening vegetative structure and local pollen donor densities, can also influence the genetic composition of local pollen pools. Using paternally inherited chloroplast microsatellite markers, we examined the structure and diversity of pollen pools in Pinus echinata Mill. in southern Missouri, USA. Our analysis is based on a multivariate AMOVA analysis of stands ( approximately 1 ha; six per region) nested within regions (approximately 800 ha; four each). Significant multilocus structure of the pollen pool within regions (phiSR = 0.095), but not among regions (phiRT = 0.010), indicates that pollen movement is relatively restricted. Furthermore, the significant correlation between pairwise genetic and physical distances (Mantel correlation; rho = 0.32) provided support for the isolation by distance hypothesis. Our results indicated that availability of pollen donors did not affect diversity of the pollen pool, measured by the number of unique multilocus genotypes at each stand. However, pollen pool diversity was negatively associated with vegetative structure, measured as total forest tree density. Our findings indicated that on-going pollen movement within continuous forest is relatively restricted as a result of both isolation by distance and vegetative structure.     

The relationship between airborne pollen and fungal spore concentrations and seasonal pollen allergy symptoms in Cracow in 1997–1999

The investigation of airborne pollen and fungalspore concentrations was carried out in Cracowbetween 1997–1999. For this study thevolumetric method has been employed (Burkard).At the same time the clinical diagnosis ofpollen allergy in 40 patients was obtained onthe basis of an interview, positive skin pricktests with pollen extracts and increasedspecific IgE level. An increase in seasonalallergy symptoms in all patients occurred fromthe middle of May to the middle of August.Eighty eight percent of the patients (35 out of40) were sensitive to Poaceae pollen and about50% of them were additionally sensitive totree and herb pollen excluding grasses. Forpatients with additional allergy to tree pollenthe seasonal symptoms started at the end ofMarch (Betula) while for patients withadditional allergy to herb pollen it wasextended to the middle of September (Artemisia).Five people out of 40 revealed positive skinreactions to Alternaria spores and anincrease in specific IgE level. Positive skinreaction to Cladosporium spores with noincrease in specific IgE level occurred in 2patients. The increase in seasonal allergysymptoms in people sensitive to Alternariaspores noted in July and August could becaused not only by these spores but also byPoaceae pollen.     

Complex patterns of mating revealed in a Eucalyptus regnans seed orchard using allozyme markers and the neighbourhood model

The neighbourhood model apportions offspring of individual mother plants to self-fertilization, outcrossing to males within a circumscribed area around the mother plant (the neighbourhood), and outcrossing to males outside the neighbourhood. Formerly the model was applied only to haploid pollen gametes in the offspring of conifers, but is extended so that it can be used with genotypic data from diploid offspring of both angiosperms and gymnosperms. In addition, it is shown that the mating parameters can be estimated without independent estimates of allele frequencies in the pollen pools outside the neighbourhood; thus the model might be applied effectively to natural populations exposed to unknown external pollen sources. Parameters of the neighbourhood mating model were estimated for a 10-year-old seed orchard population of the insect-pollinated tree, Eucalyptus regnans, in southeast Australia, which contained a mixture of two geographical provenances (Victoria and Tasmania). The mating patterns revealed were complex. Crosses between trees of the same provenance occurred three times more often than crosses between trees of different provenances. Levels of self-fertilization and patterns of mating within neighbourhoods were influenced by provenance origin, crop fecundity and orchard position (central vs. edge) of mother trees. Gene dispersal, however, was extensive, with approximately 50% of effective pollen gametes coming from males more than 40 m away from mother trees (average distance between neighbouring trees was 7.4 m). Thus, insect pollinators are efficient promoters of cross-fertilization in this orchard, with the result that the effective number of males mating with each female is large.     

Presence and behaviour of B-chromosomes in Acanthophyllum laxiusculum (Caryophyllaceae)

Two karyotypic variants were recognized in populations of Acanthophyllum laxiusculum Schiman-Czeika. Variant A had 2N = 30 and variant B showed the presence of 0 to 3 B-chromosomes in addition to 2N = 30 chromosomes. Analysis of chromosome behaviour at meiosis showed that the presence of B-chromosomes increases chiasma frequency in A-chromosomes; this effect was higher for plants with odd numbers of B-chromosomes compared with plants with even numbers of B-chromosomes. Comparisons of variants A and B, suggests that B-chromosomes have an effect pollen stainability and seed production. It seems that the presence of B-chromosomes may increase pollen stainability and seed production in variant B.     

Fertilization in Arabidopsis thaliana wild type: developmental stages and time course

We describe some previously uncharacterised stages of fertilization in Arabidopsis thaliana and provide for the first time a precise time course of the fertilization process. We hand-pollinated wild type pistils with wild type pollen (Columbia ecotype), fixed them at various times after pollination, and analysed 600 embryo sacs using Confocal Laser Scanning Microscopy. Degeneration of one of the synergid cells starts at 5 Hours After Pollination (HAP). Polarity of the egg changes rapidly after this synergid degeneration. Karyogamy is then detected by the presence of two nucleoli of different diameters in both the egg and central cell nuclei, 7-8 HAP. Within the next hour, first nuclear division takes place in the fertilized central cell and two nucleoli can then be seen transiently in each nucleus produced. In a second set of experiments, we hand-pollinated wild type pistils with pollen from a transgenic promLAT52::EGFP line that expresses EGFP in its pollen vegetative cell. Release of the pollen tube contents into the synergid cell could be detected in living material. We show that the timing of synergid degeneration and pollen tube release correlate well, suggesting that either the synergid cell degenerates at the time of pollen tube discharge or very shortly before it. These observations and protocols constitute an important basis for the further phenotypic analysis of mutants affected in fertilization.     

New pollen-specific receptor kinases identified in tomato,maize and Arabidopsis: the tomato kinases show overlapping but distinct localization patterns on pollen tubes

We previously characterized LePRK1 and LePRK2, pollen-specific receptor kinases from tomato (Muschietti et al., 1998). Here we identify a similar receptor kinase from maize, ZmPRK1, that is also specifically expressed late in pollen development, and a third pollen receptor kinase from tomato, LePRK3. LePRK3 is less similar to LePRK1 and LePRK2 than either is to each other. We used immunolocalization to show that all three LePRKs localize to the pollen tube wall, in partially overlapping but distinct patterns. We used RT-PCR and degenerate primers to clone homologues of the tomato kinases from other Solanaceae. We deduced features diagnostic of pollen receptor kinases and used these criteria to identify family members in the Arabidopsis database. RT-PCR confirmed pollen expression for five of these Arabidopsis candidates; two of these are clearly homologues of LePRK3. Our results reveal the existence of a distinct pollen-specific receptor kinase gene family whose members are likely to be involved in perceiving extracellular cues during pollen tube growth.     

A novel pollen-specific α-tubulin in sunflower: structure and characterization

We describe here a new -tubulin isoform from sunflower we named -tubulin. -tubulin is the most divergent higher-plant -tubulin described so far, having an unusual deletion in the H1/B2 loop and a glutamine-rich C-terminus. We constructed a three-dimensional model and discuss its implications. Using specific antibodies, we show that -tubulin expression is restricted to the male gametophyte. -tubulin mRNA represents 90% of -tubulin mRNA and a small percentage of total pollen mRNA. Among the plants tested, -tubulin was only detected in sunflower and in Cosmos. Since both plants are Asteraceae, we propose that -tubulin is specific to this family. Our results suggest that -tubulin can inhibit tubulin assembly in pollen. This hypothesis is reinforced by the fact that -tubulin is found in a complex with -tubulin in mature sunflower pollen.     

Phytoseiid predators suppress populations of Bemisia tabaci on cucumber plants with alternative food

Phytoseiids are known to attack whiteflies, but it is an open question whether they can be used for biological control of these pest insects. Preselection experiments in the laboratory showed that two out of five phytoseiid species tested, Euseius scutalis and Typhlodromips swirskii, stood out in terms of their ability to develop and reproduce on a diet of Bemisia tabaci immatures. In this paper, we show that both predators are able to suppress whitefly populations on isolated cucumber plants in a greenhouse. Predatory mites were released 2 weeks in advance of the release of B. tabaci. To enable their survival and promote their population growth, they were provided weekly with alternative food, that is, Typha sp. pollen. A few weeks after whitefly introduction, the numbers of adult whiteflies on plants with predators were consistently lower than on plants without predators, where B. tabaci populations grew exponentially. After 9 weeks, this amounted to a 16- to 21-fold difference in adult whitefly population size. This shows that the two phytoseiid species are promising biocontrol agents of B. tabaci on greenhouse cucumber. This revised version was published online in July 2006 with corrections to the Cover Date.