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At least 361 records · Page 20Linked to original sources
PubMed2005

Pollen-wall formation in Arum alpinum.

BACKGROUND AND AIMS: Arum alpinum has a quite uncommon pollen wall. A sporopolleninous ektexine is missing. The outermost pollen wall layer is formed by the endexine which is covered by polysaccharidic ornamentation elements. An ontogenetical investigation was accomplished to clarify pollen-wall development, with special reference to callose and pollen-wall development. METHODS: Plants of Arum alpinum grown in their natural habitat were collected once a week within the vegetative period and processed for semi- and ultra-thin sectioning. KEY RESULTS: At any stage of pollen-wall formation callose is missing. Microspores are released from the tetrad by invagination of the amoeboid tapetum. The polysaccharidic wall ornamentations are formed by the tapetum. CONCLUSIONS: There appears to be no truth in the dogma that callose is essential for microspore separation and release from the tetrad. The lack of callose does not influence fertility but could be the reason for the uncommon pollen wall, where a sporopolleninous ektexine is missing.

Arum↗
PubMed2002

Evolution of IgM, IgE and IgG(1-4 )antibody responses in early childhood monitored with recombinant allergen components: implications for class switch mechanisms.

The formation of IgE antibodies against environmental allergens represents the hallmark of type I allergy. Data from in vitro cultured cells and experimental animal models provide controversial evidence for isotype switching from IgM to IgE production via sequential as well as non-sequential (i.e. direct) class switch. We analyzed the evolution of IgE responses in 11 children developing birch pollen and/or grass pollen allergy during the first 7 years of life using purified recombinant allergen molecules (major birch pollen allergen, Bet v 1; major timothy grass pollen allergens, Phl p 1, Phl p 2, Phl p 5). Demographic, clinical and serological data indicated a postnatal sensitization to pollen allergens. A parallel development of IgG(1-4) and IgE responses to recombinant allergen molecules compatible with a strictly sequential class switch to IgE was observed only in one child. The only partly synchronized and dissociated development of allergen-specific antibody responses found in all other cases can be best explained by a partly sequential class switch involving few switch stations or, more likely, by direct class switching. Kinetics and courses of allergen-specific antibody responses (IgM, IgG(1-4), IgE) during the first years of life suggest that, once established, allergen-specific IgE responses are driven by antigen contact rather than by cytokines controlling class switch to IgE.

Age Factors↗
PubMed1986

Effect of pollen extract on the development of experimental atherosclerosis in rabbits.

Our previous studies have shown that the pollen extract, Cernitin, reveals lipid-lowering properties in animals and humans. The present study was designed to investigate the influence of Cernitin on the development of experimental atherosclerosis in rabbits over a period of 12 weeks. Forty male mongrel rabbits were divided into 4 equal groups: (1) controls, (2) animals receiving high-fat diet (HFD) containing cholesterol and coconut oil, (3) HFD + pollen extract, and (4) HFD + clofibrate. The most pronounced reduction in lipid metabolism and in the severity of plaque formation occurred after the pollen extract had been applied. The total cholesterol content in serum and liver homogenate was depressed by 67% and 45%, respectively, while the serum HDL cholesterol and alpha-lipoproteins level was increased by 19% and from 7.73% to 21.73% respectively. The cytochrome P-450 content in the liver microsomes was elevated by 98% (nmol/g liver). Atherosclerotic plaque intensity at 12 weeks, measured planimetrically, averaged 85.5% in HFD-fed animals vs 33.7% in pollen extract-treated rabbits. These findings suggest that Cernitin, in addition to significantly lowering serum lipid levels in rabbits on an experimental diet, may modify lipid deposition in major arteries.

Animals↗
PubMed2006

Disruption of actin filaments by latrunculin B affects cell wall construction in Picea meyeri pollen tube by disturbing vesicle trafficking.

The involvement of actin filaments (AFs) in vesicle trafficking, cell wall construction and tip growth was investigated during pollen tube development of Picea meyeri. Pollen germination and tube elongation were inhibited in a dose-dependent manner by the latrunculin B (LatB) treatment. The fine AFs were broken down into disorganized fragments showing a tendency to aggregate. FM4-64 labeling revealed that the dynamic balance of vesicle trafficking was perturbed due to F-actin disruption and the fountain-like cytoplasmic pattern changed into disorganized Brownian movement. The configuration and/or distribution of cell wall components, such as pectins, callose and cellulose, as well as arabinogalactan proteins changed in obvious ways after the LatB application. Fourier transform infrared (FTIR) analysis further established significant changes in the chemical composition of the wall material. Our results indicate that depolymerization of AFs affects the distribution and configuration of cell wall components in Picea meyeri pollen tube by disturbing vesicle trafficking.

Actins↗
PubMed2004

The MADS box transcription factor ZmMADS2 is required for anther and pollen maturation in maize and accumulates in apoptotic bodies during anther dehiscence.

The maize (Zea mays) late pollen gene ZmMADS2 belongs to the MIKC type of MADS box transcription factor genes. Here, we report that ZmMADS2, which forms a homodimer in yeast (Saccharomyces cerevisiae), is required for anther dehiscence and pollen maturation. Development of anthers and pollen was arrested at 1 d before dehiscence in transgenic plants expressing the ZmMADS2-cDNA in antisense orientation. Temporal and spatial expression analyses showed high amounts of ZmMADS2 transcripts in endothecium and connective tissues of the anther at 1 d before dehiscence and in mature pollen after dehiscence. Transient transformation of maize and tobacco (Nicotiana tabacum) pollen with the luciferase reporter gene under the control of different ZmMADS2 promoter deletion constructs demonstrated the functionality and tissue specificity of the promoter. Transgenic maize plants expressing a ZmMADS2-green fluorescent protein fusion protein under control of the ZmMADS2 promoter were used to monitor protein localization during anther maturation and pollen tube growth. High amounts of the fusion protein accumulate in degenerating nuclei of endothecial and connective cells of the anther. A possible function of ZmMADS2 during anther dehiscence and pollen maturation and during pollen tube growth is discussed.

Antisense Elements (Genetics)↗
PubMed2004

Male germ line development in Arabidopsis. duo pollen mutants reveal gametophytic regulators of generative cell cycle progression.

Male germ line development in flowering plants is initiated with the formation of the generative cell that is the progenitor of the two sperm cells. While structural features of the generative cell are well documented, genetic programs required for generative cell cycle progression are unknown. We describe two novel Arabidopsis (Arabidopsis thaliana) mutants, duo pollen1 (duo1) and duo pollen2 (duo2), in which generative cell division is blocked, resulting in the formation of bicellular pollen grains at anthesis. duo1 and duo2 map to different chromosomes and act gametophytically in a male-specific manner. Both duo mutants progress normally through the first haploid division at pollen mitosis I (PMI) but fail at distinct stages of the generative cell cycle. Mutant generative cells in duo1 pollen fail to enter mitosis at G2-M transition, whereas mutant generative cells in duo2 enter PMII but arrest at prometaphase. In wild-type plants, generative and sperm nuclei enter S phase soon after inception, implying that male gametic cells follow a simple S to M cycle. Mutant generative nuclei in duo1 complete DNA synthesis but bypass PMII and enter an endocycle during pollen maturation. However, mutant generative nuclei in duo2 arrest in prometaphase of PMII with a 2C DNA content. Our results identify two essential gametophytic loci required for progression through different phases of the generative cell cycle, providing the first evidence to our knowledge for genetic regulators of male germ line development in flowering plants.

Arabidopsis↗
PubMed2005

Reversed-phase liquid chromatographic characterization and analysis of air particulates humic (-like) substances in presence of pollens.

Newly developed method for characterisation and analysis of humic substances (HS) and humic-like substances (HULIS) in air dust particles was tested for potential interferences caused by abundant co-sampled pollens (common dandelion, common wormwood-absinth, apple tree). RP-HPLC using 10-step gradient of dimethylformamide (DMF) in a buffered aqueous mobile phase and a wide-pore (30 nm) octadecylsilica column has been applied to the analysis of HS and HULIS using tandem of spectrophotometric (DAD) and fluorimetric detection (FLD). Achieved results suggest that the devised method is reliable for characterisation, fractionation and analysis of terrestrial HS, air dust HS and air particulate HULIS in liquid extracts at a trace concentration levels. Fluorimetric detection (ex. 470 nm/em. 530 nm; LOD, 3.1 microg/ml) enables sensitive, highly selective and interference free determination of HS and HULIS regardless the presence of pollen constituents, whereas spectrophotometric detection is susceptible to interferences in UV region above 260 nm. However, even in this case, the interfering substances can be revealed by both different pattern and shape of their peaks, as well as by spectral features different from HS or HULIS. Analytical procedure based on air sampling, extraction and above-mentioned HPLC method enables characterisation and analysis of HS and/or HULIS at relative concentration levels down to 0.1% (m/m) in 10 mg mass scale of sampled air dust and particulate material.

Air Pollutants↗
PubMed2005

The Arabidopsis plastidic glucose 6-phosphate/phosphate translocator GPT1 is essential for pollen maturation and embryo sac development.

Plastids of nongreen tissues can import carbon in the form of glucose 6-phosphate via the glucose 6-phosphate/phosphate translocator (GPT). The Arabidopsis thaliana genome contains two homologous GPT genes, AtGPT1 and AtGPT2. Both proteins show glucose 6-phosphate translocator activity after reconstitution in liposomes, and each of them can rescue the low-starch leaf phenotype of the pgi1 mutant (which lacks plastid phosphoglucoisomerase), indicating that the two proteins are also functional in planta. AtGPT1 transcripts are ubiquitously expressed during plant development, with highest expression in stamens, whereas AtGPT2 expression is restricted to a few tissues, including senescing leaves. Disruption of GPT2 has no obvious effect on growth and development under greenhouse conditions, whereas the mutations gpt1-1 and gpt1-2 are lethal. In both gpt1 lines, distorted segregation ratios, reduced efficiency of transmission in males and females, and inability to complete pollen and ovule development were observed, indicating profound defects in gametogenesis. Embryo sac development is arrested in the gpt1 mutants at a stage before the fusion of the polar nuclei. Mutant pollen development is associated with reduced formation of lipid bodies and small vesicles and the disappearance of dispersed vacuoles, which results in disintegration of the pollen structure. Taken together, our results indicate that GPT1-mediated import of glucose 6-phosphate into nongreen plastids is crucial for gametophyte development. We suggest that loss of GPT1 function results in disruption of the oxidative pentose phosphate cycle, which in turn affects fatty acid biosynthesis.

Alleles↗
PubMed2002

Fructokinase and hexokinase from pollen grains of bell pepper (Capsicum annuum L.): possible role in pollen germination under conditions of high temperature and CO2 enrichment.

The processes of pollen grain development and germination depend on the uptake and metabolism of pollen sugars. In pepper (Capsicum annuum L.), initial sugar metabolism includes sucrose hydrolysis by invertase and subsequent phosphorylation of glucose and fructose by hexose kinases. The main objective of this study was to investigate changes in fructokinase (EC 2.7.1.4) and hexokinase (EC.2.7.1.1) activities in pepper flowers during their development, and to study the possible roles of these enzymes in determining pollen germination capacity under high temperature and under CO(2) enrichment, previously shown to modify sugar concentrations in pepper pollen (Aloni et al., 2001 Physiologia Plantarum 112: 505-512). Fructokinase (FK) activity was predominant in pepper pollen, and increased during pollen maturation. Pollen hexokinase (HK) activity was low and did not change throughout pollen development. High-temperature treatment (day/night, 32/26 degrees C) of pepper plants reduced the percentage of pollen that germinated compared with that under normal temperatures (26/22 degrees C), and concomitantly reduced the activity of FK in mature pollen. High temperature also reduced FK and HK activity in the anther. Under high ambient CO(2) (800 micro l l(-1)) pollen FK activity was enhanced. The results suggest that pollen and anther FK may play a role in the regulation of pollen germination, possibly by providing fructose-6-phosphate for glycolysis, or through conversion to UDP-glucose (UDPG) to support the biosynthesis of cell wall material for pollen tube growth. High temperature stress and CO(2) enrichment may influence pollen germination capacity by affecting these pathways.

Calcium Chloride↗
PubMed1997

Relevance of pollen-specific IgE levels to the development of Apiaceae hypersensitivity in patients with birch pollen allergy.

A large clinical/serologic study was carried out to determine the prevalence of Apiaceae (carrot, celery, and fennel) hypersensitivity in patients with birch pollen allergy, and to investigate its relationship with apple and hazelnut allergy and with birch pollen-specific IgE levels. A total of 196 birch pollen-hypersensitive patients with oral allergy syndrome (OAS) caused by different vegetable foods were examined in the cross-sectional part of the study. Of this total, 195 patients had apple and/or hazelnut allergy, and 103 had Apiaceae sensitivity; only one patient had Apiaceae allergy alone. Apiaceae-positive patients showed significantly higher birch pollen-specific IgE levels than negative ones (median 13 vs 7 AU/ml; P < 0.0001). The prospective part of the study was performed on 103 birch pollen-hypersensitive patients who were OAS-free at the time of the first visit and were periodically followed-up for OAS. Patients who developed Apiaceae sensitivity showed much higher birch-specific IgE levels than patients who developed apple/hazelnut allergy only (median 15.5 vs 8.5 AU/ml; P < 0.05), whereas those who remained OAS-free showed the lowest specific IgE levels (median 5 AU/ml). This study suggests that most Apiaceae determinants cross-react with apple or hazelnut determinants, whereas only some apple or hazelnut determinants cross-react with Apiaceae-allergenic determinants; moreover, it shows that birch-specific IgE levels heavily influence the onset of OAS as a whole, and probably play a critical role in the development of allergies to distinct vegetable foods as well.

Adolescent↗
PubMed1991

Pollen cultures as a tool to study plant development.

In in vitro cultures, isolated microspores and pollen grains can undergo two fundamentally different types of development. In conditions that simulate the tapetum they continue normal gametophytic development to produce functional pollen. Under stress conditions, they are induced to form haploid embryos and plants (sporophytes). In vitro matured pollen is a "minimal" pollen that lacks substances to enhance its reproductive success. In vitro pollen maturation is presented as an experimental system to study pollen development and its interaction with the tapetum. For young binucleate pollen grains, a starvation treatment is sufficient to induce sporophytic development, for microspores a heat shock treatment is required. During the stress treatments, transcription of specific mRNAs is activated. An important aspect of embryogenic induction of binucleate pollen is the derepression of the cell cycle in the G1-arrested vegetative cell.

Cell Cycle↗
PubMed2004

Field and semifield evaluation of impacts of transgenic canola pollen on survival and development of worker honey bees.

A 2-yr field trial (2001 and 2002) and 1-yr semifield trial (2002) were conducted to evaluate the effect of transgenic herbicide (glyphosate) -tolerant canola Brassica napus L. pollen on larval and adult honey bee, Apis mellifera L., workers. In the field trial, colonies of honey bees were moved to transgenic or nontransgenic canola fields (each at least 40 hectares) during bloom and then sampled for larval survival and adult recovery, pupal weight, and hemolymph protein concentrations. No differences in larval survival, adult recovery, and pupal weight were detected between colonies placed in nontransgenic canola fields and those in transgenic canola fields. Colonies placed in the transgenic canola fields in the 2002 field experiment showed significantly higher hemolymph protein in newly emerged bees compared with those placed in nontransgenic canola field; however, this difference was not detected in the 2001 field experiment. In the semifield trial, bee larvae were artificially fed with bee-collected transgenic and nontransgenic canola pollen and returned to their original colonies. Larval survival, pupal survival, pupal weight, and hemolymph protein concentration of newly emerged adults were measured. There were no significant differences in any of the parameters measured between larvae that were fed transgenic canola pollen and those fed nontransgenic corn pollen. Results from this study suggest that transgenic canola pollen does not have adverse effects on honey bee development and that the use of transgenic canola dose not pose any threat to honey bees.

Animals↗
PubMed2002

Antirrhinum majus microspore maturation and transient transformation in vitro.

The male gametophyte of higher plants represents an excellent system to study gene regulation, cell fate determination and cellular differentiation in plants because of its relative simplicity compared to the sporophyte and its accessibility for cytological and molecular analysis. Unicellular plant microspores are single haploid cells, which can be isolated in large amounts at a defined developmental stage. Microspores cultured in vitro in a rich medium develop into mature pollen grains, which are fertile upon pollination in vivo. It is reported here that isolated Antirrhinum majus microspores when cultured in an optimal medium develop to form mature, fertile pollen. Their development closely resembled that of pollen formed in vivo. Isolated microspores were bombarded with Aquorea victoria Green Fluorescent Protein (GFP), Discosoma Red Fluorescent Protein (dsRFP) and beta-glucuronidase (GUS) reporter genes under the control of various promoters and transient expression was observed throughout pollen development in vitro. Bombarded and not bombarded in vitro-matured pollen grains were able to germinate both in vitro and on receptive stigmas and to set seed. The protocol of maturation, transient transformation and germination of Antirrhinum majus pollen in vitro described here provides a valuable tool for basic and applied research.

Cell Survival↗
PubMed2006

Influence of pollen diet in spring on development of honey bee (Hymenoptera: Apidae) colonies.

The effects of changes in spring pollen diet on the development of honey bee, Apis mellifera L. (Hymenoptera: Apidae), colonies were examined in a 3-yr study (2002-2004). Pollen-supplemented and pollen-limited conditions were created in colonies every spring, and brood rearing and honey yields were subsequently monitored throughout the summer. In all 3 yr, colonies that were supplemented with pollen or a pollen substitute in the spring started rearing brood earlier than colonies in other treatment groups and produced the most workers by late April or early May. In 2002, these initial differences were reflected by a two-fold increase in annual honey yields by September for colonies that were pollen-supplemented during the spring compared with pollen-limited colonies. In 2003 and 2004, differences between treatment groups in the cumulative number of workers produced by colonies disappeared by midsummer, and all colonies had similar annual honey yields (exception: in one year, productivity was low for colonies supplemented with pollen before wintering). Discrepancies between years coincided with differences in spring weather conditions. Colonies supplemented with pollen or a substitute during the spring performed similarly in all respects. These results indicate that an investment in supplementing the pollen diet of colonies would be returned for situations in which large spring populations are important, but long-term improvement in honey yields may only result when spring foraging is severely reduced by inclement weather. Beekeepers should weigh this information against the nutritional deficiencies that are frequently generated in colonies by the stresses of commercial management.

Animal Nutritional Physiological Phenomena↗
PubMed2006

Pollen carbohydrates and water content during development, presentation, and dispersal: a short review.

Pollen accumulates starch reserves during development and the final stage of ripening. Before the anther opens, starch is totally or partially converted to pectins, glucose, fructose, sucrose, and to some unknown polysaccharides. Pollen is exposed to dispersing agents in an arrested developmental state which differs according to pollen water content. Pollen is classified as partially dehydrated or partially hydrated. The final water content may be reached before or after anther opening. Especially during exposure and dispersal, partially dehydrated pollen may interconvert soluble and insoluble reserves, modifying internal turgor pressure and hindering water loss or gain. Partially hydrated pollen is commonly devoid of mechanisms to conserve viability in time but has the advantage of quickly emitting pollen tubes on reaching the stigma.

Carbohydrates↗
PubMedDate not supplied

Morphology of cell injury: An approach to the EDIT programme by the use of tobacco pollen tubes. Evaluation-guided Development of New In Vitro Test Batteries.

Tobacco pollen tubes were used as a standard in vitro system to investigate cell growth aberrations caused by some of the Multicentre Evaluation of In Vitro Cytotoxicity (MEIC) programme chemicals and other toxic compounds. Changes in cytoskeletal pattern were observed in the tube cells by using tubulin immunofluorescence and rhodamin-phalloidin fluorescence for the localisation of microtubules and actin filaments, respectively. Four different types of cell malformation were found: screw-like growth, isodiametric tip swelling, hook formation, and pollen grain enlargement. We suggest that these malformations resulted from an interference by the chemicals with the cytosolic calcium gradient which controls tip growth and the orientation of the pollen tube. The results may contribute to a general understanding of toxicity-based cell malformations.

In Vitro Techniques↗
PubMed1997

Plant reproduction in spaceflight environments.

Because plant reproduction is a complex developmental process there are many possible sites of perturbation by the unusual environments of orbital spacecraft. Previous long-duration experiments on Soviet platforms shared features of slowed development through the vegetative stage of plant growth and aborted reproductive function. Our goal has been to understand how special features of the spaceflight environment impact physiological function and reproductive development. In a series of short-duration experiments in the Shuttle mid-deck we studied early reproductive development in Arabidopsis thaliana. Pollen and ovule development aborted at an early stage in the first experiment on STS-54 which utilized closed plant growth chambers. Post-flight analysis suggested that the plants may have been carbon dioxide limited. Subsequent experiments utilized carbon dioxide enrichment (on STS-51) and cabin air flow-through with an air exchange system (on STS-68). Both modifications allowed pollen and ovule development to occur normally on orbit, and full reproductive development up to the stage of an immature seed occurred on STS-68. However, analysis of plant roots from these experiments demonstrated a limitation in rootzone aeration in the spaceflight material that was not mitigated by these procedures. In the future, additional resources (crew time, upgraded flight hardware, and special platforms) will invite more elaborate, long-duration experimentation. On the ISS, a variable speed centrifuge and upgraded plant habitats will permit detailed experiments on the role of gravity in shaping the plant micro-environment, and what influence this plays during reproduction.

Arabidopsis↗