Abstract: Temperate plants show high correlations between life history strategies (e.g., along the r-K continuum), mating systems (in terms of pollen: ovule, seed: ovule, and fruit: flower ratios), and genet...

Abstract: Virus transmission through seed and pollen has been reviewed or summarized in various reports (3, 5, 10, 23, 24, 34, 37, 63, 78, 81, 99, 102-105, 117, 120, 121, 125, 142, 147, 148). Some of these reviews include viruses with general lists of seedbome pathogens (3, 5,121), while others focus on specialized groups of viruses such as those transmitted by nematodes (99, 117) or those that affect specific crops (78). Eleven reviews provide comprehensive lists of viruses and viroids that are transmitted through seed and pollen (Table 1). Although many reviews focus on the interaction between viruses and seed, aspects of virus-pollen interactions are also examined (10, 103, 142). At least four reviews concentrate on virus interactions with pollen (34, 81, 104, 105). Given the recent interest in both pollen and seed transmission, and the fact that several workers were examining these areas shortly after the tum of the century (49, 134), the first cited review (147) of seed transmission of viruses was, surprisingly, only published in 1951. Between 1951 and 1988, however, there were at least 22 reviews on the subject; nine of these were published between 1981 and 1988. The appearance of 22 reviews on seed and pollen transmission within 37 years probably speaks as much for overall interest in the subject as for advancements being made in the field at the time. Nevertheless, the number of viruses listed as seedor pollen-

Abstract: and ovule abortion in Oxalis magnifica. American Journal of Botany 73:246-253. Hainsworth, F. R., L. L. Wolf, and T. Mercier. 1985. Pollen limitation in a monocarpic species, Ipomopsis aggregate. Journal of Ecology 73:263-270. Harper, J. L. 1977. Population biology of plants. Academic Press, London, England. Hollander, M., and D. A. Wolfe. 1973. Nonparametric statistical methods. John Wiley & Sons, New York, New York, USA. Inoue, K. 1985. Reproductive biology of two Platantherans (Orchidaceae). Japanese Journal of Ecology 35:77-83. Johnston, M. 0. 199 la. Pollen limitation of female reproduction in Lobelia cardinalis and L. siphilitica. Ecology 72: 1500-1503. 1 991 b. Natural selection on floral traits in two species of Lobelia with different pollinators. Evolution 45:14681479. Lubbers, A. E., and M. J. Lechowicz. 1989. Effects of leaf removal on reproduction vs. belowground storage in Trillium grandiflorum. Ecology 70:85-96. Paton, D. C., and V. Turner. 1985. Pollination of Banksia ericifolia: birds, mammals and insects as pollen vectors. Australian Journal of Botany 33:271-286. SAS. 1985. SAS user's guide: statistics. Version 5. SAS Institute, Cary, North Carolina, USA. Schemske, D. W., and C. Fenster. 1983. Pollen-grain interactions in a neotropical Costus: effects of clump size and competitors. Pages 405-410 in D. L. Mulcahy and E. Ottaviano, editors. Pollen biology: basic and applied aspects; implications for plant breeding. Elsevier, New York, New York, USA. Schmitt, J. 1983. Individual flowering phenology, plant size, and reproductive success in Linanthus androsaceus, a California annual. Oecologia (Berlin) 59:135-140. Snow, A. 1986. Pollination dynamics in Epilobium canum (Onagraceae): consequences for gametophytic selection. American Journal of Botany 73:139-151. Webb, C. J., and K. S. Bawa. 1983. Pollen dispersal by hummingbirds: a comparative study of two lowland tropical plants. Evolution 37:1258-1270. Weller, S. G. 1980. Pollen flow and fecundity in populations of Lithospermum caroliniense. American Journal of Botany 67:1334-1341. Werner, P. A. 1975. Predictions of fate from rosette size in teasel (Dipsacus fullonum L.). Oecologia (Berlin) 20:197201. Young, H. J., and T. P. Young. 1992. Alternative outcomes of natural and experimental high pollen loads. Ecology 73: 639-647. Zimmerman, J. K., and T. M. Aide. 1989. Patterns of fruit production in a neotropical orchid: pollinator vs. resource limitation. American Journal of Botany 76:67-73.

Abstract: To determine the effects of soil nitrogen on pollen production, pollen size, and pollen performance, two cultivars of zucchini (Cucurbita pepo) were grown under two nitrogen regimes in an experimental garden. The two cultivars were true breeding for alternative alleles for a one gene trait, ovary color. The soil nitrogen treatment had a significant effect on most measures of reproductive output through the female function. The nitrogen treatment did not affect the number of staminate flowers per plant but did have an effect on the number of pollen grains per staminate flower and the mean pollen grain size. A pollen mixture experiment revealed that pollen produced by plants in the high nitrogen treatment sired significantly more seeds than pollen from low nitrogen plants. Moreover, we found that the high nitrogen pollen sired even a greater percentage of seeds in the region of the fruit (ovary) previously shown to be fertilized by the fastest growing pollen tubes, Thus, the difference in the number of seeds sired by pollen from the two nitrogen treatments is due to differences in pollen performance. We conclude that spatial heterogeneity in soil nitrogen can influence the paternity of seeds in a plant population.

Abstract: It is difficult to visualize how pollen can trigger an attack of asthma, since airborne pollen grains are too large to be respirable [1.2]. However, pollen allergens, as distinct from the grains, are known to occur naturally in the environment associated with much smaller particles [3]. How do these particles originate in the environment? This review addresses this question, in the light of new evidence. This has come from two sources; careful observations over 4 years of thunderstorm-associated epidemics of asthma in Melbourne [4] and molecular cloning of rye-grass pollen allergens [5,6].

Abstract: To determine the effects of soil nitrogen on pollen production, pollen size, and pollen performance, two cultivars of zucchini (Cucurbita pepo) were grown under two nitrogen regimes in an experimental garden. The two cultivars were true breeding for alternative alleles for a one gene trait, ovary color. The soil nitrogen treatment had a significant effect on most measures of reproductive output through the female function. The nitrogen treatment did not affect the number of staminate flowers per plant but did have an effect on the number of pollen grains per staminate flower and the mean pollen grain size. A pollen mixture experiment revealed that pollen produced by plants in the high nitrogen treatment sired significantly more seeds than pollen from low nitrogen plants. Moreover, we found that the high nitrogen pollen sired even a greater percentage of seeds in the region of the fruit (ovary) previously shown to be fertilized by the fastest growing pollen tubes, Thus, the difference in the number of seeds sired by pollen from the two nitrogen treatments is due to differences in pollen performance. We conclude that spatial heterogeneity in soil nitrogen can influence the paternity of seeds in a plant population.

Abstract: In this study we reinvestigated the kinetics of allergen release from birch pollen (Betula verrucosa) and timothy grass pollen (Phleum pratense) using different protein extraction procedures, immunoblotting with specific antibodies and immune electron microscopy. Pollen allergens such as the major birch pollen allergen, Bet v I, the major timothy grass pollen allergens, Phl p I and Phl p V, group-II/III allergens from timothy grass and profilins were released rapidly and in large amounts from hydrated pollen. Within a few minutes pollen allergens could be detected in aqueous supernatants prepared from birch and grass pollen with serum IgE or specific antibodies. In parallel the allergen content in the pollen pellet fractions decreased. A nonallergenic protein such as heat shock protein 70 can be extracted in sufficient amounts only with harsh extraction procedures. Immune electron microscopy of dry and rehydrated birch pollens showed that after short hydration, the major birch pollen allergen, Bet v I, migrated into the exine and to the surface of intact pollen grains, whereas profilin, against which a lower percentage of patients is sensitized, was retained in the pollen grain. Comparing the amino acid composition and hydrophilicity of the tested allergens with a nonallergenic protein such as heat shock protein 70, no significant difference was noted. In agreement with earlier observations we conclude that the allergenic properties of proteins are rather linked to the amount and speed of solubility from airborne particles than to intrinsic properties.

Abstract: Secondary pollen presentation is the developmental relocation of pollen from the anthers onto another floral organ which then functions as the pollen presenting organ for pollination. Nine different types have been identified in sixteen angiosperm families according to which organ is used for presentation, whether the pollen is exposed or concealed within a structure and how pollen is loaded onto the presenting surface: (1) Enveloping bloom presenters (Araceae); (2) Perianth presenters with exposed pollen presentation (Epacridaceae); (3) Androecial presenters (Santalaceae); (4) Terminal stylar presenters with passive pollen placement and concealed stigmas (Rubiaceae and Proteaceae); (5) Terminal stylar presenters with passive pollen placement and sub-terminal stigmas (Marantaceae and Polygalaceae); (6) Terminal stylar presenters with active pollen placement (Asteraceae, Calyceraceae and Lobeliaceae); (7) Sub-terminal stylar presenters (Campanulaceae, Cannaceae, Fabaceae and Myrtaceae); (8) Exposed stigmatic presenters (Rubiaceae); (9) Indusial stigmatic presenters (Goodeniaceae and Brunoniaceae). Secondary pollen presentation occurs in three monocotyledon and thirteen dicotyledon families. The presentation types appear to have been independently derived indicating that secondary pollen presentation is a character with a selective advantage. In all but the enveloping bloom type of secondary pollen presentation, developmental relocation of pollen requires simultaneous, introrse anther dehiscence and a close association of the presenting organ to the anthers prior to anthesis. The various secondary pollen presentation systems may be modified to promote xenogamy or autogamy and this can even change during anthesis. Most plants which have secondary pollen presentation, display reduced herkogamy within the flower to facilitate pollination. Increased risk of self-pollination due to this may be overcome through dichogamy, herkogamy within inflorescences, dry stigmas, self-incompatibility systems and passive or active control over pollinator behaviour. Enhanced male function of the flowers of secondary pollen presenting plants is also evident through extension of the male phase by the protection, controlled release and precise placement and receipt of pollen. Plants displaying secondary pollen presentation are almost always protandrous.

Abstract: The record of daily average grass pollen concentrations monitored at St Mary's Hospital, Paddington, London, U.K. since 1961 is the longest duration pollen data set in Europe. Analysis of the results identifies the trends and characteristics of grass pollen seasons over three decades. During this time seasonal allergic rhinitis has increased significantly in Britain. The annual start dates, length of season and severity are examined in relation to the main meteorological variables of cumulated temperatures above 5.5 degrees C and precipitation measured at one site within London and two in the surrounding rural areas. Land-use changes are also considered. Significant decreases have taken place in both the duration and severity of the seasons, particularly between the 1960s and the early 1970s but also through the last 20 yr. This is largely a result of a decrease in pollen abundance in the region. The decline in pollen counts has slowed in recent years due to the increase in flowering grasses caused by the set-aside policy and by uncut verges. Grass pollen seasons have tended to start later over the last two decades, despite an increase in the cumulated temperature profiles during late winter and spring. Empirical models have been developed using multiple regressions to incorporate meteorological and pollen data for the last 20 yr in order to forecast the start dates, duration and severity of the grass pollen seasons. These models were applied successfully using the data for 1991 and 1992. Predictions of the main characteristics of the pollen seasons can be obtained relatively early in the year through the use of these models by employing the monthly weather forecasts in conjunction with long-term average weather profiles.

Abstract: S. Blackmore & S.H. Barnes: Palynological diversity R.C. Brown & B.E. Lemmon: Sporogenesis in simple land plants U. Fanning, J.B. Richardson & D. Edwards: A review of in situ spores in Silurian land plants J. Gray: Tetrahedralites, Nodospora, and the 'cross' tetrad: an accretion of myth G.A. van Uffelen: The control of spore wall formation J.H.A. van Konijnenburg van Cittert: Diversification of spores in fossil and extant Schizaeaceae M.E. Collinson: Diversification of modern heterosporous pteridophytes W.G. Chaloner & A.R. Hemsley: Heterospory: cul-de-sac or pathway to the seed? J.A. Doyle & C. L. Hotton: Diversification of early angiosperm pollen in a cladistic context E-M. Friis, P.R Crane & K. Rraunsgaard Pedersen: Stamen diversity and in situ pollen of Cretaceous angiosperms M.M. Harley, M.H. Kurmann & I.K. Ferguson: Systematic implications of comparative morphology in selected Tertiary and extant pollen from the Palmae and Sapotaceae M.S. Zavada: Determining character polarities in pollen N.I. Gabarayeve: Patterns of development in gymosperm and angiosperm pollen R. Scotland: A systematic analysis of pollen morphology of Acanthaceae genera with contorted corollas E.L. Vezey, J.J. Skvarla & S.S. Vanderpool: Characterizing pollen sculpture of three closely related Cappareceae species using quantitive image analysis of scanning electron micrographs E. Pacini & G.G. Franchi: Diversification and evolution of the tepetum G. El-Ghazaly & S. Nilsson: Development of tapetum and orbicules of Catharanthus roseus (Apocynaceae) J. Heslop-Harrison & Y. Heslop-Harrison: Structural and functional variation in pollen intines R.B. Knox & S.C. Ducker: The evolution of gametes - from motility to double fertilization P.A. Knox, S. Cromer & T. Jarvis: Underwater pollination, three-dimensional search, and pollen morphology: predictions from a supercomputer analysis.

Abstract: Summary The pistil of flowers is a specialized organ which contains the female gametophytes and provides the structures necessary for pollination and fertilization. Pollen deposited on the stigmatic surface of a compatible plant germinates a pollen tube which penetrates the stigmatic papillae and grows intercellularly through the style towards the ovules in the ovary. Pollen tube growth is largely restricted to the transmitting tissue in the style. Therefore the stylar transmitting tissue is extremely important for the migration of the pollen cell towards the ovary. We have isolated two related cDNAs, transmitting tissue-specific (TTS)-1 and TTS-2, derived from two proline-rich protein (PRP)-encoding mRNAs that accumulate specifically in the transmitting tissue of tobacco. The deduced PRP sequences share similarities with proline-rich cell wall glycoproteins found in a variety of plants. TTS-1 and TTS-2 mRNAs are induced in very young floral buds, accumulate most abundantly during the later stages of flower development when style elongation is the most rapid, and remain at relatively high levels at anthesis. These mRNAs become undetectable in maturing green fruits. In situ hybridization shows that TTS-1 and TTS-2 mRNA accumulation is restricted to the transmitting tissue of the style. The possible roles that these transmitting tissue-specific PRPs may play in maintaining the structural integrity of the style or in the function of this organ is discussed.

Abstract: The perfume syndrome and pollination by fragrance-collecting euglossine bees in the neotropic solanaceous genusCyphomandra was confirmed by field observations. In SE Brazil,C. sciadostylis was visited byEufriesea violaceae, andC. diploconos byEuglossa mandibularis; C. hartwegii was pollinated byEulaema meriana in Costa Rica. The primary attractant, fragrant droplets that ooze from the dorsally bulged connectives, is mopped up by the males with the forebasitarsi. Thereby, the poricidal thecae are inadvertently pushed causing the dry pollen to dust the bee's sternum. The number and direction of the pollen jets are related to pollinator size and stigma structure. The flowers are homogamous, selfsterile, and last three days. The androecium is optically non-contrasting or has cryptic colour. Flowers ofC. sciadostylis andC. diploconos undergo a colour change and an almost three-fold increase in corolla size when scent production and visits cease. The dorsal papillar epidermis of the connective is underlain by a glandular parenchyma typical of osmophores. GC techniques revealed germacrene D as the main component in the mentholic scent ofC. sciadostylis, ipsdienol, heneicosane, and tricosane as dominant in the nutmeg-like scent ofC. diploconos, and benzyl acetate and benzyl alcohol in the sweet fragrance ofC. hartwegii. In all cases, these were accompanied by numerous minor components of heterogeneous chemical nature.—Pollen release by means of a peculiar pneumatic bellows mechanism appears as a necessary and probably ubiquitous feature ofCyphomandra. Even a slight pressure exerted upon the thin, elastic thecal walls blows pollen jets through the pores. Unusual anatomic changes accompany anther maturation. Initially voluminous parenchymatic locular intumescences (placentoids) contract completely during meiosis, then expand once more when the pollen is ripe, pushing the grains against the locular wall, and contract a second time, allowing air to enter the thecae.—Cyphomandra pinetorum was found to be exceptional in exhibiting a pollen flower syndrome, and not cryptical but optically contrasting yellow anthers, as known forSolanum.

Abstract: The phenology, major floral characteristics, fruiting levels, and breeding system ofCistus ladanifer L. (Cistaceae), a common western Mediterranean shrub species, were studied in a southern Spanish population. The white, large (64 mm in diameter) flowers of this shrub appear during spring (March–May) and produce abundant pollen and nectar. In the year of study, flowers lasted up to three days, during which they were visited by a diverse array of insects including beetles, flies, and bees. Hand-pollinations revealed that flowers do not set any seed unless cross pollen is applied to the stigma. Microscopical observations indicate that self pollen tubes grow down the stigma but invariably fail to induce fruit maturation. At the plant level, all estimates of fecundity investigated (number of seeds per capsule, proportion of ovules developing into seed, and proportion of flowers setting fruit) were highly dependent on nearest neighbour distance, with isolated plants setting as little as 0% fruit. In contrast, plants within a clump often transformed into fruit as much as 90% of the flowers. At the population level, seed output was estimated to range between 3,000 and 270,000 seeds per plant during 1991.

Abstract: Publisher Summary The chapter examines the application of fossil pollen analysis to the study of plant invasions and the report progress made while reconstructing range expansion, population growth, and competitive interactions. The chapter also outlines important uncertainties that exist in the use of fossil pollen for these purposes. Fossil pollen records have provided important insight into the population biology of invading plant species that are unavailable from any other source. In respect to the strong leptokurtic nature of pollen dispersal gradients, the relationship between plant population growth and pollen deposition is likely to be dependent on the spatial characteristics of the invasion. The analysis of large sample sets from many lakes of similar size in similar settings allows the calculation of average rates of population growth from pollen records. The presence of macrofossils of invading plants in these lakes provides critical evidence regarding the presence of plant species in low densities during period when pollen abundance is very low. Such evidence would be useful in testing the hypothesis that exponential and logistic increases in pollen represent the growth of local populations from very low densities. In view of the uncertainties outlined in this chapter, particular care should be taken when using rates and areas of geographic spread, rates of population growth, and competition coefficients derived solely from fossil pollen data to parameterize or test mathematical models of plant invasion.

Abstract: We used an F1 hybrid of zucchini and its wild progenitor to examine the effects of pollen competition on progeny performance. We experimentally varied the intensity of pollen competition by depositing large or small pollen loads onto stigmas. To separate the effects of pollen competition from maternal effects, we excised the styles of flowers receiving the large pollen loads after only the fastest pollen tubes had entered the ovary. The styles from flowers receiving small pollen loads were excised after both fast- and slow-growing tubes had entered the ovary. Consequently, the mature fruits from the two treatments were similar in seed number and weight. Because our previous studies had revealed that fast- and slow-growing pollen tubes fertilize ovules in different regions (locations) within the ovary (fast into region I and slow into region 3), we examined the vigor of the progeny produced in regions I and 3 from both large and small pollen loads. The results revealed that the progeny from large pollen lo...

Abstract: Tristylous populations of the annual aquatic Eichhornia paniculata have high levels of outcrossing and intermorph mating despite being fully self- and intramorph compatible. Experi- mental studies of pollen germination, pollen-tube growth, and pollinations with mixtures of ge- netically marked pollen were used to determine whether postpollination processes contribute to the observed mating patterns. Differences in pollen germination were small and did not contribute to differences in pollen siring ability. The fraction of pollen tubes first entering the ovary, however, was greater for legitimate outcross pollen than for either of the other two pollen types (self or outcross illegitimate pollen) in all recipient morphs. Moreover, legitimate pollen had higher siring success when in competition with illegitimate pollen types (self or outcross) in each recipient style morph. The ranking of pollen performance for different pollen-style combinations was the same for both the pollen-tube growth and marker-gene experiments indicating that differences in pollen- tube growth rate are the principal cause of differences in pollen siring ability. Cryptic incompatibility in E. paniculata may represent a weak heteromorphic incompatibility system because the observed patterns of pollen-tube growth parallel pollen-tube growth and seed-set patterns that occur in related species with strong trimorphic incompatibility. The ability to produce mostly outcrossed progeny when pollinators are abundant, but to reliably produce seed under a variety of environmental and demographic conditions may be favored in E. paniculata because of its colonizing life history and occurrence in ephemeral habitats. Cryptic incompatibility may be more likely to occur in species subject to wide fluctuations in population size and levels of pollinator service.

Abstract: Light, pollen, and leaf area were manipulated to examine the role of each of these as determinants of reproductive success in the understory shrub Lindera benzoin. Fruit set was significantly greater in the sun than in the shade, and was reduced in both habitats by shading branches. Supplemental pollination added significantly more viable pollen to stigmas, but plants never responded with increased fruit set, even under conditions of high light availability. Treatments had no effect on fruit and seed mass, but there was a significant maternal effect on these variables. Treatments did result in a significant reduction in per branch flower production in the following year, especially on fruit-bearing branches in shaded sites and on artificially shaded branches (...)

Abstract: We investigated the effect of self-pollination on fruit- and seed-set in Asclepias exaltata, a self-incompatible milkweed. A total of 1,380 hand-pollinations were performed on 138 flowers in each of five treatments. In each treatment, two pollinia were placed in adjacent stigmatic chambers, which transmitted pollen tubes to the same ovary. Treatments 1 and 2 involved simultaneous placement of two self-pollinia (treatment 1) or two cross-pollinia (treatment 2) into adjacent stigmatic chambers. No fruits were produced after self-pollinations, but 23% of the cross-pollinated flowers matured fruits. The three remaining experimental pollination treatments were self-pollination preceding cross-pollination by 24 hr (treatment 3), simultaneous self- and cross-pollination (treatment 4), and cross-pollination preceding self-pollination by 24 hr (treatment 5). Compared with that in flowers receiving only cross-pollen, fruit-set in treatments 3-5 was reduced 81%, 49%, and 29%, respectively. Seed-set was also significantly reduced in flowers receiving self-pollen 24 hr in advance of the cross-pollen. Using genetic markers, we observed that only 0.6% of seeds resulted from self-pollination. Our data strongly suggest that self-pollination in milkweeds not only wastes pollen but also greatly reduces the number of ovules and ovaries that might otherwise mature fruits and seeds after cross-pollination. Hermaphroditic flowering plants employ a tremendous diversity of mechanisms to increase outcrossing and to decrease interference between male (pollen donating) and female (pollen receiving) functions. These mechanisms include, for example, both separation of pollen release and stigma receptivity either temporally (dichogamy) or spatially (herkogamy) (Lloyd and Webb, 1986; Webb and Lloyd, 1986) and genetic self-incompatibility systems, which lead to the rejection of self-pollen (Barrett, 1988; Barrett and Eckert, 1990). These mechanisms, however, may not reduce overall levels of geitonogamy for plants with large floral displays. For example, in distylous Jepsonia heterandra, in which genetic barriers preclude selffertilization, 49.4% of the pollen on pin stigmas was found to be self-pollen (Ganders, 1974).

Abstract: The incidence of self-compatibility in 742 almond trees, resulting from 25 inter-cultivar crossings in which at least one of the parents is self-compatible (Genco and Tuono), was determined by means of microscopic observation of the pollen tube growth in the pistil. The data obtained are consistent with the assumption that self-incompatibility in the genus Prunus is controlled by a single, multi-allelic gene whose expression in the pollen is gametophytic. The 100 per cent occurrence of self-compatible specimens in the cross where the Ferragnes cultivar is the female parent is due to the existence of an allele shared with the self-compatible cultivars used. The high number of progeny examined and the method used to ascertain the self-compatibility make the results very reliable, as opposed to other less precise methodologies or tests with few seedlings.

Abstract: A chimeric toxic gene consisting of the diphtheria toxin A chain gene fused to a promoter previously shown to direct pistil- and anther-specific expression was used to genetically target cell killing in transgenic Arabidopsis. Flowers of Arabidopsis transformants that carried the toxic gene fusion had distinct structural defects. The papillar cells at the stigma surface were stunted and were biosynthetically inactive. Anther development was also impaired by toxic gene expression, leading to abnormalities in anther dehiscence, pollen morphology, and pollen germination. The combined defects of pistil and anther rendered transformants that carried the toxic gene fusion self-sterile. However, the transformants were cross-fertile with untransformed plants: the viable pollen of ablated plants was rescued by wild-type stigmas, and, strikingly, the ablated papillar cells allowed the growth of wild-type pollen.

Abstract: The present invention is related to isolated purified DNA sequences isolated from maize which can act as pollen-specific promoters and which play a role in the expression of genes in pollen. The present invention also relates to a method for conferring pollen-specificity on genes not normally expressed in pollen.