Abstract: GAMETOPHYTIC self-incompatibility is a genetically based system of cellular recognition in plants1. It prevents fertilization by pollen bearing an S-allele identical to either of the two S-alleles present in the female sporophytic tissues. Self-incompatibility in the Solanaceae has been especially well studied and several S-allele specific style glycoproteins identified2–6. In addition, complementary DNAs for nine style S-glycoproteins have been sequenced7–10 and have homology with two fungal ribonucleases. Recently five Nicotiana alata S-glycoproteins were shown to be RNases (S-RNases)11. We now report that S-allele specific degradation of pollen RNA occurs in vivo. After incompatible, but not after compatible pollinations, pollen RNA becomes degraded. This specificity cannot be demonstrated in vitro using isolated S-RNases and pollen RNAs. Our results support a model in which the gametophytic self-incompatibility system in N. alata acts through a cytotoxic mechanism directed against pollen RNA.

Abstract: Mean pollen production and mean nearest neighbor distance were recorded for several populations of Taxus canadensis and correlated with the proportion of ovules pollinated and seed set. Distance and pollen production together explained 86% of the variation in pollination success, each variable significantly adding to the regression when adjusting for the other. Seed set was correlated significantly with pollen production and nearest neighbor distance separately, but the multiple regression including the latter two variables was not significant. Seed set was correlated most strongly with pollination success and mean ovule production (R2 = 0.71), suggesting that variation in seed set among Taxus populations was a combination of differences in pollen and resource availability.

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

Abstract: Pollen movement is often restricted in natural populations, and insufficient pollination is a potential constraint on sexual reproduction in outcrossing species. Seed-set should decrease with increased distance from the pollen source in outcrossing plants. This prediction was tested using females of the clonal, gynodioecious herb Glechoma hederacea in three natural populations. In controlled pollinations, both hermaphrodites and females had similar high percentages of fruit-set and seed-set. In a natural population where a female clone was isolated from the nearest hermaphroditic clone by c. 100 m, fruit-set was low (1%). In another population where hemaphroditic clones were rare and female clones had a patchy distribution, fruit-and seed-set in females were pollen-limited and decreased with increased distance from the nearest pollen source. The estimated mean pollen dispersal distance was 5.9 m when calculated on fruit-set and 5.3 m when calculated on seed-set. The most frequent pollinators were bumblebees. The mean and median distances moved by pollinators between ramets were 0.13 m and 0.05 m. In a third population where female clones were isolated from the nearest hermaphrodites by more than 200 m, fruit-set was 0%. After introduction of 16 hermaphroditic ramets in the center of the female clone, fruit-set varied between 0% and 100% in individual female ramets. Fruit-set decreased with increased distance from the pollen source. The mean and median pollen movement distances were 1.06 m and 0.54 m.

Abstract: I examined effects of pollination intensity on fruit, seed and seedling characteristics in Campsis radicans, and joint effects of pollen donor and pollination intensity on fruit production. Large pollen loads were more likely to initiate fruit production than small pollen loads, and the former fruits contained more seeds and a greater total seed mass. No further increases in seed number or mass occurred for pollen loads above 4,000 grains. The weight of individual seeds was unaffected by pollen load. Effects of pollen donor were generally larger than effects of pollen load, and fruit production from small loads of pollen from one donor were sometimes equal to fruit production from larger pollen loads from another donor. The ratio of pollen grains deposited to resultant seeds increased with pollen load, and several explanations are proposed. Seeds from heavy pollinations emerged better than seeds from light pollinations, but did not differ in speed of germination or in the performance of seedlings up to 126 days. The emergence differences are probably due to differing intensities of pollen tube competition.

Abstract: We compared the rate of pollen tube growth following self- and cross-pollinations both among and within flowers of two clones of Dianthus chinensis L For among-flower comparisons, both styles of a flower were pollinated with either self- or cross-pollen Within-flower comparisons were made between the two styles of the same flower, one of which was self-pollinated and the other cross-pollinated Comparisons between flowers indicated that self-pollen grew slower than cross-pollen in both clones However, differences in the growth rate of pollen tubes from selfand cross-pollinations were greater when comparisons were made between the two styles of the same flower than when pollinations were made in different flowers These results suggest the existence of interstyle interactions in pollen tube growth

Abstract: Previous research on the Black Beauty bush cv. of zucchini has documented a strong positive relationship between the size of the pollen load and the vigor (performance) of the progeny. Here we report the results of three studies designed to test the hypothesis that the previously observed differences in progeny vigor are heritable. Two studies examined the transmission of the pollen load effect to subsequent generations through the ovules (female role). The third study determined if there is genetic variation for pollen performance and if the pollen load effect could be transmitted to a subsequent generation through the pollen (male role). In each of these studies the vigor of the progeny from the subsequent generation was evaluated in the greenhouse and/or the field. The results of these studies reveal (1) that the ability to sire seeds does respond to selection imposed by high pollen loads, (2) that only 23 of the 35 total traits that we measured in the three studies of transmission to subsequent generations changed in the direction predicted by the pollen competition hypothesis, (3) that only 5 of the 35 traits were significantly affected by the size of the pollen load that produced the previous generation (but all 5 were in the direction predicted by the pollen competition hypothesis), and (4) that only one study produced an overall significant difference (MANOVA) attributable to the size of the pollen load that produced the previous generation (but it too was in the direction predicted by the pollen competition hypothesis). From these experiments we conclude that pollen competition appears to play a real but minor role in the production of differences in vigor between progeny arising from low versus high pollen loads. In Black Beauty bush cv. of zucchini, maternal effects, pollen-pistil interactions, or nonrandom patterns of seed abortion must play important roles as well.

Abstract: The mean volume of pollen grains and total pollen production varied both within and among plants of Erythronium grandiflorum. The second flowers of two-flowered plants tended to produce smaller and fewer grains than first flowers, but there was no overall relationship between mean pollen grain size and production per flower. I evaluated the effects of pollen size differences within and among plants on two components of male reproductive success: pollen tube growth and postfertilization siring ability. Pollen tubes grown in media were longer for second flowers, but were not correlated with the mean size of pollen grains, suggesting that (1) internal resource content of pollen (i.e., carbohydrates plus lipids) was not associated with the hydrated size of pollen, and that (2) pollen from second flowers contained more resources. I analyzed the growth rate and the fertilization ability of pollen growing in styles. Growth rate differed among donors and recipients, but no effects of pollen or donor characters (i.e., pollen production, grain size, and flower position) were detected. In single donor pollinations, pollen size was negatively correlated with fertilization ability across donors, and positively correlated with postfertilization siring ability of donors. A second experiment used pairs of donors; within-plant differences in pollen size and flower position had effects similar to the single donor experiment on fertilization ability, but among-plant differences were not significant. The results corroborate earlier experiments that suggest that the growth of pollen tubes in the style is probably controlled by the recipient, since donor characters had minimal effects on pollen fertilization ability. Postfertilization siring ability was not affected by within-plant differences in mean grain size and production. For among-donor differences, the number of seeds set for each donor was positively correlated with the mean grain volume, and when a donor producing large pollen fertilized ovules in an ovary, there was increased seed abortion for seeds in the same ovary sired by a second donor. In addition, the total number of seeds produced by a fruit was decreased when both donors had large pollen, apparently due to increased postfertilization abortion. Postfertilization processes appear to be influenced by paternal differences that are expressed through competition among developing seeds for maternal resources.

Abstract: Publisher Summary The angiosperms are distinguished from all gymnosperms by their angiospermy, the inclusion of the developing seeds (the ovules) in carpels. As a consequence, the pollen grains do not germinate directly on the ovule but on the outer surface of the carpel (on the stigma) and the pollen tubes reach the ovules only inside the ovary. The carpel not only provides protection to the ovules—a trait that is also present in various gymnosperms by other means—but it also opens new possibilities for fine-tuned interactions between the male and the female gametophytes. Intraspecific incompatibility systems that function in the stigma and the pathway to the ovules are important new acquisitions of the angiosperms. They prevent fertilization of egg cells by sperm cells with too similar genotypes. At the same time, the intervention of the style enhances pollen tube selection among the entire pollen portion that has been transferred to the stigma in the process of pollination, and therefore, fertilization by the most vigorous male gametophytes. Comparative studies of living plants indicate that members of the Magnoliidae retain the largest number of primitive floral characters among extant angiosperms. This has subsequently been reinforced by the fossil record of angiosperms. This chapter considers selected families of the Magnoliidae to illustrate floral organization and diversity within the group.

Abstract: When the dehydrated pollen grain of Brassica oleracea L. alights on a receptive stigma the pollen coat flows out from the exine to form an appresoria-like 'foot' and, within a matter of some 30 min, gross ultrastructural changes become visible both within the protoplast and in the foot itself. These changes are interpreted as reflecting the limited movement of water, and presumably other materials, from the stigma to the grain. The compatible pollen grain then continues to take up water, whilst undergoing other cytoplasmic changes and eventually producing the pollen tube. The tube grows from the colpus towards the point of contact with the stigma, beneath which the outer layer of the papillar wall has become more loosely packed. The pollen tube enters the wall at this point and, as a consequence of its rapid extension, the grain is frequently lifted away from the papilla. The tube then grows between two layers of the pectocellulosic papillar wall into the stigmatic parenchyma, where it follows an intercellular route. These events are discussed in terms of current views of the relationship between male and female cells at these early stages of the pollen stigma interaction.

Abstract: Zinc deficiency decreased pollen viability in maize (Zea mays L. cv. G2) grown in sand culture. On restoring normal zinc supply to zinc-deficient plants before the pollen mother cell stage of anther development, the vegetative yield of plants and pollen fertility could be recovered to a large extent, but the recovery treatment was not effective when given after the release of microspores from the tetrads. If zinc deficiency was induced prior to microsporogenesis it did not significantly affect vegetative yield and ovule fertility, but decreased the fertility of pollen grains, even of those which visibly appeared normal. If the deficiency was induced after the release of microspores from the tetrads, not only vegetative yield and ovule fertility but pollen fertility also remained unaffected.

Abstract: Homogeneous populations of developing microspores and pollen from anthers of lily (Lilium longiflorum Thumb.) and tobacco (Nicotiana tabacum L.) show a continuous production of biomass, reaching a maximum in young pollen. The rate of RNA synthesis was 460 fg · h−1 in young binucleate cells, 138 fg · h−1 in late binucleate cells and 56 fg · h−1 in microspores. The mRNA population in developing pollen can be separated into three groups. In the first group, certain types of mRNAs are present at a constant level during all stages of development. A second group is characteristic of young pollen and increases quantitatively until anthesis. A third group is seen transiently; to this belong mRNAs present only before mitosis or at a distinct cell stage after mitosis. Some of the translation products of this latter group of mRNAs showed similarities between lily and tobacco on two-dimensional gels in respect of molecular weight and isolectric point, indicating that those mRNAs and proteins play a role in the regulation of pollen development.

Abstract: A postembedding method has been developed for localizing water soluble allergens in rye-grass pollen This uses dry fixation in glutaraldehyde vapour, followed by 2,2-dimethoxypropane, prior to a 100% ethanol series leading into embedment in LR Gold This has allowed the attachment of specific monoclonal antibodies to the allergen, which are themselves probed with specific immunogold labels to the antibodies Wall and cytoplasmic sites have been identified, representing an improvement of fixation and localization of allergens over previous studies employing polyclonal, broad spectrum antibodies Rye-grass allergens are labelled in mature pollen grains in the exine (tectum, nexine and central chamber), and in the electron opaque areas of the cytoplasm, especially mitochondria The allergens are absent from the intine, polysaccharide (P) particles, amyloplasts, Golgi bodies and endoplasmic reticulum IgE antibodies derived from humans allergic to rye-grass pollen, bind to similar sites in the cytoplasm but only to the outer surface of the pollen grain wall This method now provides a valuable tool for further developmental studies on the pollen grains, in order to establish the site/s of synthesis of the allergens

Abstract: The nectar of Hibiscus rosa-sinensis L. shows an increase in amino acid concentration with the aging of the flowers, correlated with an increase in the number of detectable amino acids. The amino acid concentration of the nectar increased drastically after pollen addition both in Hibiscus and in the two other species investigated. The main amino acid responsible for this increase was proline. After puncturing or otherwise injuring a flower, the amino acid composition of the nectar is altered. In this case, the increase is due mainly to asparagine. Although contamination of nectar by pollen may be a common and natural event in many flowers, especially in those pollinated by butterflies, such an alteration in nectar constituents should be carefully discussed when considering amino acid concentration or composition in relation to pollinator—plant coevolutionary lines.

Abstract: Rice (Oryza sativa L.) subjected to water deficit during anthesis shows pollination abnormalities resulting in low grain yields. To understand the mechanism of stress-induced poor grain filling in relation to disturbed pollination, upland-adapted cultivars were grown under controlled conditions. A 7-day irrigation-withholding period (Exp. 1) induced −1.7 and −2.0 MPa flag leaf water potentials (Ψ) in ‘Kinandang Patong’ and 63–83, respectively. A stress protocol for 7 d at anthesis achieved stress intensities of −0.4, −0.8, −1.1, −1.4, −1.7, −2.0, −2.3, −2.5, and −2.8 MPa in 63–83 and IRAT13 (Exp. 2). On the last day of the water-deficit stress period, anther dehiscence of spikelets, pollen shedding, viability, germination, and spikelet sterility (at plant maturity) were measured. In each upland cultivar tested, low Ψ reduced pollen shedding capacity and germination. Dehiscence of anthers correlated with flag leaf Ψ (R² = 0.944** [significant at P = 0.01] [IRAT13] and 0.987** [63–83]). Up to a stress intensity of Ψ1.4 MPa, more than 80% of anthers dehisced. Below Ψ2.0 MPa, more than 60% of pollen grains did not dehisce. Pollen shed, total pollen per spikelet, and spikelets with more than 20 pollen were all directly related to Ψ. Pollen germination in vivo and germination per spikelet correlated linearly with water stress intensity. Significant deleterious effects on pollen viability at low water potentials were noted. All measured pollination traits accounted significantly for increases in unfilled spikelets at severe stress intensities. Thus, to ensure pollination success and spikelet fertility, responses of upland rice genotypes to a water deficit at anthesis could be evaluated using anther dehiscence, pollen shedding, and pollen germination in controlled conditions. Joint contribution of Agronomy Dep., IRRI, P.O. Box 933, Manila, Philippines, and Dep. of Agronomy, Cornell Univ., Ithaca, NY 14853.

Abstract: Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) ovules were used to study the method of pollen tube formation and penetration of the nucellus, the movement of the body cell down the pollen tube and development of the archegonia. No pollination drop forms but nucellar tip cells produce a minute secretion that may initiate pollen tube formation. Pollen tubes penetrate the nucellus causing degeneration of nucellar cells in contact with the pollen tube tip. The body cell becomes highly lobed and the tube cytoplasm forms thin sheets between the lobes. This may be the mechanism by which the large body cell is pulled down the narrow pollen tube. Body cell plastids and mitochondria remain unaltered during pollen tube growth, whereas tube cell organelles show signs of degeneration. The pollen tube penetrates the megaspore wall and settles in the archegonial chamber. During pollen elongation and pollen tube growth the egg matured. Egg cell plastids were transformed into large inclusions which filled the periphery of the egg while mitochondria migrated to the perinuclear zone. The neck cells, ventral canal cell and archegonial jacket cells are described. The significance of the body cell and egg cell ultrastructure is discussed in light of recent restriction fragment length polymorphism studies of plastid and mitochondrial inheritance in the Pinaceae.

Abstract: Delphinium nelsonii Greene is a spring-flowering perennial of the Rocky Mountains of North America. Its blue flowers conform to a classical «bee pollination syndrome», but in western Colorado they are visited by hummingbirds (mostly in the first half of the flowering season) as well as bumble bee queens (mostly in the second half of the season). Experiments with potted plants showed that a bee deposits about 10 times as much pollen while visiting a flower as does a bird, and causes about la times as many seeds to be set. In contrast, bees and birds appear similar in the «quality» of pollen they deliver, e. g., in its outcrossing distance. At the level of entire pollinator populations, hummingbird visitation rates may be over 10 times as great as those or bumble bees, in part because birds visit flowers more quickly. Thus the two visitor classes should deliver similar pollen quantities overall, which is confirmed by similar pollen loads of flowers early and late in the season, and should contribute about equally to seed set, which is confirmed by several experiments and observations. Exact relative contributions probably depend on pollinator population sizes, which in the case of hummingbirds appear to have varied 2.5 fold across 14 years. The similar contributions or birds and bees lo seed set shows that individual pollination efficiency must be distinguished from population-level effectiveness. and that the «pollination syndrome» of a flower may not indicate present-day effectiveness of its visitors.

Abstract: Pollen grains of 49 species of Gramineae, most of them from the Venezuelan Andes, were studied. All the species, except one, have the characteristic grass pollen type. The pollen grain size ranges from 17.5 to 60.6 um (maximum diameter). Small differences in ornamentation together with size of grains enabled to distinguish groups or single species within the grass pollen type. Pollen of Pariana stenolemma (herbaceous bamboo) differs from all the others in having an areolate sexine and no annulus.

Abstract: Parthenogenetic development of seeds after pollination with irradiated pollen was studied in the dioecious species Actinidia deliciosa (kiwifruit). In total, 479 pollinations were made involving three recipient female cultivars, with five male and two hermaphrodite pollen donors. Pollen was irradiated with doses of 0.5, 0.7 and 0.9 kGy, all three doses produced parthenogenetic seeds. The 0.7 kGy dose yielded the highest number of germinating seeds (708 of a total of 723), of which 609 developed into seedlings, and 334 survived to grow into plants. Ploidy level was evaluated by cytological studies and stomatal guard cell size. In a total of 416 seedlings and plants evaluated, 332 plants were hexaploid (‘diploid’ 2n=170) and 84 plants were triploids (‘haploids’ 2n=85).