Pollen Ovule Research Articles

Flower opening dynamics, pollen-ovule ratio, stigma receptivity and stigmatic pollen germination (in-vivo) in Chaenomeles speciosa (Sweet) Nakai

Although Chaenomeles is widely used in horticulture, traditional Chinese medicine and landscape greening, insufficient research has hindered its breeding and seed selection. This study investigated the floral phenology, floral organ characteristics, palynology, and breeding systems of Chaenomeles speciosa (Sweet) Nakai. The floral characteristics of C. speciosa were observed both visually and stereoscopically. The microstructures of the flower organs were observed using scanning electron microscopy. Pollen stainability was determined using triphenyl tetrazolium chloride staining. Stigma receptivity was determined using the benzidine-H2O2 method and the post-artificial pollination pollen germination method. The breeding system was assessed based on the outcrossing index and pollen–ovule ratio. The flowers of C. speciosa were bisexual with a flowering period from March to April. The flowering periods of single flowers ranged from 8 to 19 d, and those of single plants lasted 18–20 d. The anthers were cylindrical, with the base attached to the filament, and were split longitudinally to release pollen. The flower had five styles, with a connate base. The ovaries had five carpels and five compartments. The inverted ovules were arranged in two rows on the placental axis. The stigma of C. speciosa was dry and had many papillary protrusions. In the early flowering stage (1–2 d of flowering), the pollen exhibited high stainability (up to 84.24%), but all stainability was lost at 7 d of flowering. Storage at – 20 °C effectively delayed pollen inactivation. The stigma receptivity of C. speciosa lasted for approximately 7 days, and the breeding system was classified as outcrossing with partial self-compatibility.

Dependency of Crops on Pollinators and Pollination Deficits: An Approach to Measurement Considering the Influence of Various Reproductive Traits

Pollinators provide crucial ecosystem services, i.e., pollination, which determines crops’ reproductive fitness and yield. As pollinators decline, flowering crops might face pollination-deficit stress depending on their dependence on pollinators and pollinator availability. Here, we assessed the dependency of some crops (belonging to diverse plant families) on biotic pollinators based on their maximum reproductive potential in a supplementary pollination treatment and minimum reproductive success in a pollinator exclusion treatment. Additionally, we determined the pollen transfer limitation of the crops in open field conditions. We also determined the influence of the different reproductive traits with the index of dependency of crops on pollinators (IDP) and the coefficient of pollination deficit (D). Based on the values of IDP, members of Cucurbitaceae are obligatorily dependent on pollinators for their fruit set. Members of Brassicaceae and Rutaceae are highly reliant on pollinators. A few crops, like Lablab purpureus and Nigella sativa, are less dependent on pollinators. In open field conditions, most crops have a low pollination deficit, some without pollen transfer limitations, and only a few crops (Citrus × limon and Citrus maxima) show a higher pollination deficit. The IDP is negatively influenced by the pollen–ovule ratio, which also negatively affects the pollination deficit of the crops. This study will be useful in understanding and mitigating the effects of pollinator losses, as well as in choosing crops (those under pollination deficit stress and largely dependent on pollinators for fruit set) for supplemental pollination services to increase agricultural production.

Phenotypic Selection in Halenia elliptica D. Don (Gentianaceae), an Alpine Biennial with Mixed Mating System.

The transition from outcrossing to selfing is a common evolutionary trend in flowering plants, and floral traits change significantly with the evolution of selfing. Whether or not plant traits are subjected to selection remains an open question in species with mixed mating systems. We examined phenotypic selection in two populations of Halenia elliptica with different selfing rates. We found that the pollen–ovule ratio, seed size, plant height, spur length, and pollinator visitation rate in the population with the higher selfing rate were lower than those in the population with the lower selfing rate. Selfing provides reproductive assurance for populations when pollinator service is low, and the floral traits that are associated with selfing syndrome are evident in populations with a higher selfing rate but are subjected to weak selection in each of the two populations with different selfing rates. Directional selection for an early flowering time indicated that late blooming flowers could experience a risk of seed development in alpine environments, and for large plants, selection indicated that seed production could be limited by the available resources. The floral traits that are associated with pollinator attraction and specialization could be subjected to weak selection at the plant level as selfing evolves, and the selective pressures that are independent of pollinators might not change significantly; highlighting the selective biotic and abiotic pressures that shape the morphological traits of plant species and their independence from the mating system.

Intraspecific breakdown of self-incompatibility in Physalis acutifolia (Solanaceae).

Variation in mating systems is prevalent throughout angiosperms, with many transitions between outcrossing and selfing above and below the species level. This study documents a new case of an intraspecific breakdown of self-incompatibility in a wild relative of tomatillo, Physalis acutifolia. We used controlled greenhouse crosses to identify self-incompatible (SI) and self-compatible (SC) individuals grown from seed sampled across seven sites across Arizona and New Mexico. We measured 14 flower and fruit traits to test for trait variation associated with mating system. We also quantified pollen tube growth in vivo and tested for the presence of the S-RNase proteins in SI and SC styles. We found that seed from six of the seven sites produced SI individuals that terminated self-pollen tubes in the style and showed detectable S-RNase expression. By contrast, seed from one Arizona site produced SC individuals with no S-RNase expression. These SC individuals displayed typical selfing-syndrome traits such as smaller corollas, reduced stigma–anther distances, and a smaller pollen–ovule ratio. We also found plasticity in self-incompatibility as most of the SI individuals became SC and lost S-RNase expression roughly after 6 months in the greenhouse. While fixed differences in mating systems are known among the SI wild species and the often SC domesticated tomatillos, our study is the first to demonstrate intraspecific variation in natural populations as well as variation in SI over an individual’s lifespan.

Longevity and germination of Juniperus communis L. pollen after storage

Pollen storage belongs among the most important activities associated with pollen handling. It overcomes the differences in pollen shedding and ovule receptivity during controlled pollination experiments. It is especially important for species like common juniper (Juniperus communis L.) with an extremely low quality of seeds due to pollination failure. Additionally, it is a substantial part of germplasm preservation programmes in pollen banks. In the present paper, the effect of short-term storage of pollen was studied using pollen samples from five shrubs in an in vitro germination test. Two temperature regimes were tested. The pollen viability of freshly collected pollen varied considerably between individual shrubs, exhibiting 67.3–88.6% germination rate and 248.0–367.3 µm of pollen tubes. Storage at + 4 °C for four months was accompanied by a profound decline in pollen viability. The germination percentage was reduced to 49.2–75.2% and the pollen tube length to 32.5–69.0%, depending on individual shrubs. The corresponding decline in pollen viability characteristics during storage at − 20 °C was only negligible in two of the tested shrubs. In the remaining three shrub samples, an increase in germination percentage was observed. Pollen tube growth responded more sensitively to freezing, but, on average, the decrease in length was lower than that at + 4 °C. The rate of reduction in pollen tube length varied between 11.5 and 45.4%. Cytological events accompanying in vitro germination of freezer-stored pollen exhibited some delay in releasing the exine from pollen grains during the early stages of germination as compared with freshly collected pollen. In conclusion, short-term storage of the common juniper pollen in a freezer is better for the preservation of its viability than storage at + 4 °C.

Floral Structure and Breeding Systems of Manglietia conifera Dandy (Magnoliaceae)

Manglietia conifera Dandy is a fast-growing tree species that has been introduced to China from Vietnam, which has great potential for commercial planting. However, plantation development is hindered by a lack of seed material, due to low natural seed-set in locally grown trees. Thus, we investigated the morphological characteristics of male and female flower organs, and conducted controlled pollination to understand the breeding systems of the species. The individual flower of M. conifera is bisexual, and the stamen group is polymerized at the base of the receptacle. Pollen is symmetrically distributed on both sides. Controlled pollination suggests that apomixis does not occur in M. conifera. Results from the flower structure, pollen–ovule ratio, outcrossing index, and controlled pollination indicated that the breeding system in M. conifera was outcrossing (partially self-compatible, pollinators required), and self-incompatibility occurred in a later stage of embryonic development. Moreover, the self-incompatibility phenomenon was revealed by the abnormal germination of pollen on the stigma. This paper provides a basis for controlled pollination programs of M. conifera.

The Grouping of Species Saurauia Willd. in West Sumatera Based on Morphometric Analysis and Pollination System

Saurauia Willd. is a genus of perennial plant or bush which usually found in highland forest or as rheophyte in rocky areas along the river bed. There are 12 species of this genus found in West Sumatera. The purpose of this research is to analyze the grouping of Saurauia species based on morphometric analysis and determine the pollination system based on pollen-ovule (P/O) ratio. The research has been conducted since September 2014 until December 2015 by using the self-collected specimen and Herbarium ANDA specimen. Morphometric analysis was applied to all 12 species which consist of 21 morphological characters and pollen–ovule (P/O) ratio was applied to 10 species. The results of this research are: generally the euclidian distance is ranged 7.35-14.73. The shortest one is S. cerea and S. laxa which d point is 7.35 and the longest one is S. cerea and Saurauia sp. which the d point is 14.73. Saurauia sp. is closely related with S. leprosa and S. bracteosa which are belonged to same sub cluster and having the same character which are glabrous leaf surface, acuminate apex and 5 similar sepals. Pollen-ovule (P/O) ratio determined the pollination system of Saurauia is xenogami.

P/O(花粉数/胚珠数)比より推定したカワゴケソウ科数種の送粉様式

P/O(花粉数/胚珠数)比より推定したカワゴケソウ科数種の送粉様式

Pollen–ovule ratios are strongly correlated with floral reciprocity, in addition to sexual system, in Mussaenda (Rubiaceae)

Heterostyly is a floral polymorphism that increase inter‐morph pollen transfer and promote disassortative mating. Breakdown of heterostyly has happened many times, either leading to dioecy or monomorphism. Mussaenda is a genus with diverse sexual systems including distyly, dioecy, floral monomorphism, and homostyly, making it an ideal system to study the evolution of floral traits and their relationship with sexual system shifts. Here, floral traits and pollen–ovule (P/O) ratios were estimated and used to test hypotheses about the relationships among P/O ratios, floral trait evolution, and sexual system shifts. Our results revealed that there is no significant difference of reciprocity in upper level sexual organs between species with different sexual systems. The reciprocity indices of the lower level sexual organs, however, are smaller in species with functional dioecy than in those with distyly. P/O ratios in dimorphic Mussaenda species were relatively lower than in monomorphic outcrossing species, but did not differ significantly between species with distyly and functional dioecy. Populational P/O ratios were negatively correlated with reciprocity index in the dimorphic species. We suggest that the loss of function in lower level organs in species with functional dioecy has resulted from less strict reciprocity. The relationship between P/O ratios and reciprocity indices strongly support that efficient disassortative pollination of distylus flowers may have promoted evolution towards low P/O ratios.

Neutral hybridization can overcome a strong Allee effect by improving pollination quality

Small populations of plant species can be susceptible to demographic Allee effects mainly due to pollen limitation. Although sympatry with a common, co-flowering species may somewhat alleviate the problem of pollinator visitation (pollination quantity), the interspecific pollen transfer, IPT, (pollination quality) may remain a barrier to reproduction in small populations such as new introductions. However, if the two species are crosscompatible, our hypothesis is that neutral hybridization can help the small founding population overcome the Allee effect by improving the quality of pollination. We tested this hypothesis by using a novel modelling approach based on the theory of kinetic reactions wherein pollinators act as enzymes to catalyse the reaction between the two substrates: pollen and unselfed ovule. Using a single locus, two-allele genetic model, we developed a generic model that allows for hybridization between the invading and the native genotypes. Analysing the stability properties of the trivial equilibria in hybridization model as compared with the single genotype invasion model, we found that hybridization can either remove or reduce the Allee effect by making an otherwise stable trivial equilibrium unstable. Our study suggests that hybridization can be neutral but still be the key driver of a successful invasion by mediating pollen limitation. Conservation programmes should therefore account for this cryptic role that hybridization could play in plant invasions.

Relationship between herkogamy, incompatibility and reciprocity with pollen–ovule ratios in Melochia (Malvaceae)

Heterostyly is a floral polymorphism that increases pollination efficiency by promoting cross-pollination and reducing pollen wastage. Efficiency in pollination has been related to plant investment in gamete production and to the pollen to ovule ratio (P/O), which has been proposed as an indication of the likelihood of enough pollen grains reaching the stigmas to result in maximum reproductive success. In heterostylous species, cross-pollination is promoted by the reciprocal position of sexual organs between morphs and a heteromorphic incompatibility system, which precludes selfing and fertilizations among plants of the same morph. Morphological features like reciprocity (between morphs) and herkogamy (within morph) together with the breeding system are thought to influence pollination quality. Therefore, a close relationship between the pollination efficiency, morphological characteristics, and incompatibility would be expected. Pollination treatments and morphological measurements were carried out to describe the breeding system, herkogamy, and reciprocity of six Melochia species. Afterward, the relation between the P/O (as a surrogate of the efficiency in pollination), and reciprocity, herkogamy and incompatibility was evaluated. Monomorphic M. nodiflora and distylous M. pyramidata are self-compatible species, whereas the rest of the species are self- and morph-incompatible. There was a positive relationship between the P/O value and the degree of herkogamy and incompatibility. However, P/O values appear to increase when higher reciprocity is found in the populations. As expected, the lower values of P/O are associated with lower levels of herkogamy and compatibility in the Melochia species studied. The relationship between the factors is discussed under different scenarios of the pollinators’ predictability.

Rhipsalis(Cactaceae): loss and gain of floral rewards is mirrored in range sizes and distribution patterns of species

Autogamous species are usually distinguishable from xenogamous relatives by smaller flowers, fewer or even no floral rewards and lower pollen–ovule (P/O) ratios. Many Rhipsalis spp. are small flowered, selfing and include the most widespread species in Cactaceae. However, Rhipsalis also includes a large number of narrowly endemic species and is most diverse in the Atlantic rainforests of Brazil. To investigate the evolution of floral function and the correlation between floral function and range size, we analysed display size, floral reward and P/O ratios of Rhipsalis and its closest relatives, reconstructed ancestral traits and related these patterns to the distributions and range sizes of the species. Display size and sugar amount are reduced in subgenera Goniorhipsalis and Rhipsalis and secondarily increased in Phyllarthrorhipsalis, whereas the P/O ratio is decreased in subgenera Rhipsalis and Phyllarthrorhipsalis. We interpret this pattern as a switch from a predominantly xenogamous to an autogamous reproductive system, followed by a return to a predominantly xenogamous system. None of the floral parameters shows significant correlations with range size, except for display size. Nevertheless, those species with the smallest flowers, lowest sugar amounts per flower and lowest P/O ratios occur either outside southeastern Brazil and/or have comparatively large distribution ranges. Almost all Rhipsalis spp. occurring outside the Atlantic rainforests are restricted to the clade formed by subgenera Rhipsalis and Phyllarthrorhipsalis. Thus, we believe that the evolution of an autogamous reproduction system enabled this lineage of Rhipsalis to diversify and spread in the Atlantic rainforests, in the rest of the Neotropics and even spread to the Old World, where it is the only member of the family.

Studies on the Morphology and In Vitro Seed Germination of Polypleurum stylosum var. laciniata (Podostemaceae)

Polypleurum stylosum var. laciniata of the family Podostemaceae, is an endemic aquatic angiosperm, which grows on rocks in fast flowing rivers and streams in Kerala (India). The plant body is thalloid and it lacks the conventional differentiation into root and shoot and is attached to the rocks with the help of rhizoids. Vegetative growth occurs in submerged conditions and lowering of water table triggers flowering. Flower buds appear along the thallus margin enclosed by a spathella and sustained by two or three pairs of bracts. The ovary lacks a distinct style and the stigma is characteristically bifid. There are two stamens with their filaments fused, which keep on elongating and mingle with the stigma at maturity. High pollen–ovule and ovule–seed ratio indicate the high probability of plant establishment. Nearly 205 minute seeds are produced in a fruit. The embryo lacks plumule and radicle. In tissue culture, the seeds germinate and produce a green radical which sticks to the hard substratum by means of the epidermal outgrowths. The main thalloid plant body originates from the hypocotyl region as a bulge and grows into a prostrate branched thallus.

EMBRYOLOGIC MECHANISMS OF STERILITY IN TRIPLOID LOQUAT

Anther structure, anther dehiscence characteristics, pollen viability, pollen germination, pollen tube growth and ovule structure of triploid loquat (Eriobotrya japonica Lindl.) were studied. Most anthers were immature, and a few anthers, though mature, could not dehisce on time. Connective parenchyma cells were thick, the anther chamber was small, the amount of pollen was very small, and most pollen (up histo 83.7%) was abnormal. All this resulted in a high degree of male sterility in triploid loquat. Pollen germination and pollen tube growth were generally altered, indicating that the pre-fertilization barrier was strong in triploid loquat. Anatomical observations showed an atypical structure of most ovules, including small embryo sac, stigma and degeneration of style, embryo sac, and ovule. This resulted in a high degree of female sterility in triploid loquat. Fertilization and embryo development did not occur regularly in abnormal ovules of triploid loquat, which resulted in very low fruit set after cross-pollination, and no fruit production under open pollination and self-pollination probably as a result of lack of hormones from seeds.

Variation in pollen–ovule ratio of southern African Periplocoideae (Apocynaceae): Evolutionary implications

Variation in pollen–ovule ratio of southern African Periplocoideae (Apocynaceae): Evolutionary implications

Range-wide genetic analysis reveals limited structure and suggests asexual patterns in the rare forbSenecio macrocarpus

Genetic diversity and recombination underlie the long-term persistence and evolution of species and are strongly influenced by population size, breeding system and plant longevity. Here, we study genetic structure in the rare Senecio macrocarpus in southeastern Australia to guide current conservation practices. Thirteen neutral microsatellite markers and two chloroplast regions were used to survey the 20 known S. macrocarpus populations and one sympatric S. squarrosus population, a morphologically similar species. All markers showed severe excess or deficit of heterozygotes and linkage disequilibrium was significant. Microsatellite markers revealed 100 multi-locus genotypes (MLGs) from 523 S. macrocarpus individuals and a further 4 MLGs from 27 S. squarrosus individuals. MLGs varied in frequency and distribution. At the extremes, one MLG was found 108 times across the sampling region and 66 MLGs were found once. The MLGs of all 38 seedlings genotyped were identical to their seed parents implying an asexual origin. Chloroplast regions showed little variation within S. macrocarpus but differed from S. squarrosus. Chromosome counts for S. macrocarpus revealed the same ploidy level as S. squarrosus (2n = 6x = 60) and pollen–ovule ratios were typical of erechthitoid Senecio species showing self-compatibility. Results suggest that establishment of small populations occur primarily from one extensive source population with indications that both apomixis and selfing may be contributing to its reproduction cycle. We suggest that this species may contribute to future evolutionary processes despite limited genotypic variation and restricted distribution. Its conservation will safeguard evolutionary processes that might occur through occasional outcrossing and hybridization events between sympatric species. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115, 256–269.

Comparative reproductive biology of Apocynum venetum L. in wild and managed populations in the arid region of NW China

Apocynum venetum L. (dogbane) is one of the ecologically important species in the arid region of Northwest China. To select plants with higher flowering rate and fruit production, we investigated the following characteristics of A. venetum in wild and managed populations: flowering dynamics, pollen viability, pollen limitation, floral visitors and breeding system. We found that the species showed four reproductive characteristics. First, the flower production period and flowering peak were different between the wild and managed populations, longer in the managed. Second, A. venetum was pollen-limited, and pollen limitation was more intense in the wild population than in the managed. Third, in the wild, Apis mellifera L. was found to be frequent pollinator, Ophion luteus L. being the most frequent and effective visitor in the managed. Finally, the pollen ovule rate was 36.2. Self-pollination was dominant and played an important role to assure production in the breeding system. Differences in flower production influenced by artificial selection and pollinator type explain different fruit production in managed and wild populations, further, proper management could promote re-vegetation or restoration of degraded A. venetum in this region.

Pollinator sharing and low pollen–ovule ratio diminish reproductive success in two sympatric species of Portulaca (Portulacaceae)

We studied the breeding systems, phenology, pollination, and reproductive success of Portulaca grandiflora and P. hirsutissima (Portulacaceae) at Parque Nacional do Catimbau in the Brazilian Caatinga. The species flowered synchronously, exhibited similar floral morphology, offered pollen as the sole floral resource and shared the same bee species as pollinators. They visited flowers of both Portulaca species at similar frequencies, and their visitation peaks occurred at the same time of day. The pollinators made no distinction between the species during foraging. Both plant species are self-compatible, but produce fewer fruits and seeds after self-pollination than after cross-pollination. Comparing the reproductive success in areas where both species co-occur to that of areas with only one of them, seed set of P. grandiflora decreased by 25% and of P. hirsutissima by 36%. This is likely due to diminished flow of conspecific pollen grains, as the pollen–ovule ratio was extraordinarily small.

Homogalacturonan deesterification during pollen-ovule interaction in Larix decidua Mill.: an immunocytochemical study.

Studies on angiosperm plants have shown that homogalacturonan present in the extracellular matrix of pistils plays an important role in the interaction with the male gametophyte. However, in gymnosperms, knowledge on the participation of HG in the pollen–ovule interaction is limited, and only a few studies on male gametophytes have been reported. Thus, the aim of this study was to determine the distribution of HG in male gametophytes and ovules during their interaction in Larix decidua Mill. The distribution of HG in pollen grains and unpollinated and pollinated ovules was investigated by immunofluorescence techniques using monoclonal antibodies that recognise high methyl-esterified HG (JIM7), low methyl-esterified HG (JIM5) and calcium cross-linked HG (2F4). All studied categories of HG were detected in the ovule. Highly methyl-esterified HG was present in the cell walls of all cells throughout the interaction; however, the distribution of low methyl-esterified and calcium cross-linked HG changed during the course of interaction. Both of these categories of HG appeared only in the apoplast and the extracellular matrix of the ovule tissues, which interact with the male gametophyte. This finding suggests that in L. decidua, low methyl-esterified and calcium cross-linked HG play an important role in pollen–ovule interaction. The last category of HG is most likely involved in adhesion between the pollen and the ovule and might provide an optimal calcium environment for pollen grain germination and pollen tube growth.

Interspecific variation in pollen–ovule ratio is negatively correlated with pollen transfer efficiency in a natural community

The pollination efficiency hypothesis has long been proposed as an explanation for interspecific variation in pollen-ovule (P:O) ratios. However, no empirical study on P:O ratios has directly and quantitatively measured pollen transfer efficiency (PE). Here, we use a PE index, defined as the proportion of pollen grains removed from anthers that are subsequently deposited on conspecific stigmas, as a direct and quantitative measure of PE. We investigated P:O ratios, pollen removal and pollen deposition in 26 plant species in an alpine meadow, over three consecutive years. Our community survey showed that nearly 5% of removed pollen was successfully deposited on conspecific stigmas. The PE index ranged from 0.01% up to 78.56% among species, and correlated negatively with the P:O ratio across years. This correlation was not changed by controlling for phylogenetic relationships among species, suggesting that the interspecific variation in P:O ratios can be attributed to the probability of pollen grains reaching a stigma. The results indicate that the pollination efficiency hypothesis can help to explain interspecific variation in P:O ratios.