Pollen Research Articles

Proximal aperture in Cephalanthera longifolia (L.) Fritsch (Orchidaceae) pollen: a rare germination site for angiosperms.

The pollen dispersal unit of the epidendroid species, Cephalanthera longifolia, is a soft pollinium consisting of loosely connected tetrads that are agglutinated by elastoviscin. With scanning electron microscopy, the reticulate exine is visible on the outer pollen grains of outer tetrads of a pollinium. The pollen grains are mostly arranged in planar-tetragonal tetrads or decussate tetrads and easily disintegrate into monads. Contrary to the inaperturate pollen in members of subfamily Epidendroideae known so far, C. longifolia exhibits ulcerate pollen. When pollen grains are attached in tetrads within a pollinium the apertures are obscured, as they are located on the proximal side of the pollen grains. The ulcus can only be observed when tetrads disintegrate, freeing the monads and exposing the proximal side of pollen grains for investigation by light and scanning electron microscopy. Proximal aperture configurations are rare among angiosperms and currently known only from few other species of flowering plants. This is the first report of an ulcerate proximal aperture within Orchidaceae.

Exploring the influences of resource limitation and plant aging on pollen development in Azorella nivalis Phil. (Apiaceae), a long-lived high-Andean cushion plant.

Angiosperm pollen, the male gametophyte, plays a crucial role in facilitating fertilization by protecting and transporting male sperm cells to the female pistil. Despite their seemingly simple structure, pollen grains undergo intricate development to produce viable sperm cells capable of fertilizing the egg cell. Factors such as resource limitation and plant aging can disrupt normal pollen development and affect pollen performance. We investigated the influence of plant resources and aging on pollen developmental failure in Azorella nivalis Phil., an exceptionally long-lived high-Andean species that grows in a stressful alpine environment. Leveraging the modular nature of plants, we aimed to identify intra-individual sources of variation in pollen developmental failure. By using pollen viability and variation in viable pollen grain size as indicators of pollen developmental performance, we assessed whether proxies of plant resource availability and aging influenced these pollen traits at the inter-individual, inter-flower and intra-flower levels. Our findings revealed decreased pollen viability in putative resource-depleted flowers and in shoots that experienced higher levels of meristematic divisions from the zygote (i.e., greater cell depth). Additionally, we observed increased variability in the size of viable pollen grains in resource-depleted anthers. Our study suggests that resource availability and shoot aging are critical determinants shaping pollen development in long-lived plants at the intra-individual level. These findings contribute to our understanding of how differences in male fitness can arise in plants, with implications for their evolutionary trajectory.

Palynotaxonomy of Neotropical species of Paullinia L. (Sapindaceae)

Paullinia is the second-largest genus within the Sapindaceae, with approximately 200 species. It predominantly comprises lianas that inhabit humid forests, mainly the Amazon and Atlantic forests in Brazil. This study aimed to characterize the pollen morphology of 60 species of Paullinia, examining the potential of pollen characters as morphological markers to support the systematics of the genus. The pollen material was obtained from exsiccatae of flower buds from major herbaria. Pollen grains were acetolyzed, measured, described, and illustrated using light microscopy. Scanning electron microscopy was used for accurate descriptions of surface features. The analyzed characters included pollen shape, size, aperture type and number, and exine ornamentation. The similarity of pollen characters between species was analyzed using hierarchical cluster analysis and principal component analysis. The results showed that pollen grains of Paullinia species are shed in monads, heteropolar in most species and isopolar in some others, medium or large in size, oblate or suboblate, and 3- or 3-4-porate, with perforate sexine ornamentation in most species and microreticulate in some others. Multivariate analyses revealed that pollen morphology is informative and holds taxonomic potential, enabling grouping based on the similarity of the unique pollen characters of the genus. Species dispersion on the PCA biplot showed that the five clusters formed by HCA were robust, suggesting that quantitative and qualitative pollen characters exhibit consistency with regard to the similarity species. The palynological findings presented here contribute to enhancing our understanding of the morphological characters, aiding in the taxonomy and systematics of the genus.

Pollen inventory in urban remnants of Cerrado in midwest Brazil

Studies focusing on plant-pollinator interactions in urban environments aim to understand how the anthropized landscape affects interactions and, consequently, the reproductive success of plants. In these studies, the identification of plant species visited can be performed through focal observations and the analysis of pollen loads carried by vectors. Therefore, pollen inventories are essential for assisting in studies focused on the analysis of pollen grains carried by pollinators and palynological studies, favoring the scientific interpretation of the biodiversity in each area. Data was collected over 12 months in 14 remnants of different physiognomies of the Cerrado domain within the urban perimeter of Campo Grande, Mato Grosso do Sul. In these places, the 118 plant species distributed in 39 families that received visits from pollinating insects had their pollen grains photographed and characterized. The families with the highest number of species were Asteraceae, with 19 species (22.42%); Fabaceae, with 15 species (17.7%), and Malvaceae, with nine species (10.62%). The high representation of Asteraceae can be explained as its being the largest botanical family among Angiosperms, being adapted to various types of environments, and being very common in anthropized areas. This pollen guide can support future studies focused on plant-pollinator interactions, mostly in urban remnants of the Cerrado.

Pollen and Leaf Micromorphological Characteristics of Spiny Almonds (Prunus subgenus Amygdalus) in Iran.

This study investigates the micromorphological characteristics of pollen grains and leaf epidermal cells from 20 accessions across four species of spiny almonds using scanning electron microscopy. Thirteen quantitative traits of pollen grains, including exine sculpturing, were analyzed alongside qualitative features such as shape, exine sculpture type, and aperture type. Additionally, four quantitative and five qualitative features of the leaf epidermis were examined, focusing on cuticular ornamentation patterns, types of epicuticular wax, and stomatal measurements. The pollen grains were found to be isopolar monads, radially symmetric, medium-sized, varying from prolate spheroidal to prolate, and exhibiting 3-colporate to 3-colpate structures. The exine sculpturing was generally striate with short and long ridges, with or without perforations, and could be classified into three types. Notably, in the Isfahan population of Prunus lycioides and the North Khorasan population of Prunus spinosissima, the exine sculpture types were distinctly different, being rugulate and reticulate, respectively. Multivariate statistical analysis identified equatorial diameter, colpus length and width, and ridge width as key diagnostic markers for species identification within spiny almonds. Principal component analysis and hierarchical clustering further highlighted the significance of stomatal length, cuticular ornamentation patterns, and epicuticular wax types in differentiating among taxa. We conclude that groupings recognized in recent classifications of the subgenus Amygdalus (spiny almonds) remain challenging to delineate solely based on palynological data, as diverse pollen types are present across different clades and subclades. Furthermore, micromorphological leaf traits proved valuable in distinguishing certain spiny almond taxa, and the traits of epidermal cells may reflect the ecological adaptations of spiny almond species.

AIpollen: An Analytic Website for Pollen Identification Through Convolutional Neural Networks

With the rapid development of artificial intelligence, deep learning has been widely applied to complex tasks such as computer vision and natural language processing, demonstrating its outstanding performance. This study aims to exploit the high precision and efficiency of deep learning to develop a system for the identification of pollen. To this end, we constructed a dataset across 36 distinct genera. In terms of model selection, we employed a pre-trained ResNet34 network and fine-tuned its architecture to suit our specific task. For the optimization algorithm, we opted for the Adam optimizer and utilized the cross-entropy loss function. Additionally, we implemented ELU activation function, data augmentation, learning rate decay, and early stopping strategies to enhance the training efficiency and generalization capability of the model. After training for 203 epochs, our model achieved an accuracy of 97.01% on the test set and 99.89% on the training set. Further evaluation metrics, such as an F1 score of 95.9%, indicate that the model exhibits good balance and robustness across all categories. To facilitate the use of the model, we develop a user-friendly web interface. Users can upload images of pollen grains through the URL link provided in this article) and immediately receive predicted results of their genus names. Altogether, this study has successfully trained and validated a high-precision pollen grain identification model, providing a powerful tool for the identification of pollen.

Trees Are a Major Foraging Resource for Honeybees in the City.

Large cities are typically characterized by a mosaic of green spaces that hold a remarkable variety of native and "exotic" plants. Urban beekeeping has gained increasing popularity. In order to characterize the "urban" in the honey, pollen diversity in 50 honey samples from 18 apiary locations in Vienna, Austria, was microscopically analyzed. The relative abundances of each plant taxon were determined by counting out 500 individual pollen grains per sample. In total, 202 taxa could be identified, with a median of 46 per sample. Taxa richness and diversity differed significantly across three years but did not so between urban and suburban apiaries. Despite trees comprising only roughly a quarter of all taxa, the amount of tree pollen was disproportionally high. The invasive Ailanthus altissima was predominant in 15 out of 50 samples. Other important non-native and/or ornamental trees included Sophora japonica, Gleditsia triacanthos, Castanea sativa, Koelreuteria paniculata, and Liriodendron tulipifera. Urban honey from Central Europe may typically comprise pollen taxa from Europe, East Asia, and North America alike. The results of this study show that intentionally planted, managed urban green spaces can support stable foraging resources for pollinators in cities.

Digest: Scarce pollen resources and asymmetric reproductive isolation.

What mechanisms cause asymmetries in reproductive success in crosses between closely related species that differ in floral style length? Feller et al. (2024) found that in five Phlox species, short-styled species produced smaller pollen grains than long-styled species. The smaller pollen of short-styled species lacked the resources to grow pollen tubes long enough to reach the ovules of long-styled species. This asymmetric pollen-style-length incompatibility may considerably affect patterns of gene flow among species.

Multiporate Poaceae pollen grains observed in the recent fossil record from the Greater Serengeti Ecosystem and Lake Victoria region

Multiporate Poaceae pollen grains observed in the recent fossil record from the Greater Serengeti Ecosystem and Lake Victoria region

ORBICULES IN SOUTH AMERICAN BALANOPHORACEAE: ANALYSIS OF ITS POSSIBLE ROLE AND ITS TAXONOMIC VALUE IN THE FAMILY

Balanophoraceae are root parasites, lacking both chlorophyll and typical cormophytic organization. There have been few studies of pollen dispersal mechanisms in Balanophoraceae, and no studies on structures accompanying pollen, such as orbicules. Anthers were analyzed in five South American taxa of Balanophoraceae (Langsdorffia hypogaea, Lophophytum pyramidale, L. mirabile. subsp. bolivianum, Ombrophytum subterraneum and Helosis cayennensis), in order to: (1) determine the presence of orbicules, characterize them and relate their presence with the tapetum type, characteristics of the anther wall and dehiscence, and the pollination mode; (2) and analyze its possible taxonomic value in relation to the phylogeny of the family Balanophoraceae. In three genera (Lophophytum, Langsdorffia and Ombrophytum), the anthers were found to be dithecous, tetrasporangiate with longitudinal dehiscence. In these taxa the endothecium is present and is responsible for dehiscing the anthers. In Helosis the pollen sacs are welded in a synandrium with apical groves and lacking an endothecium. In all species, a secretory tapetum is responsible for nourishing the pollen grains during their formation. The presence of orbicules is variable among the species studied: it is found in Lophophytum and Langsdorffia, and is absent in Ombrophytum and Helosis. In Lophophytum the orbicules appear as small and spheroidal corpuscles with smooth surfaces. In Langsdorffia hypogaea the orbicules are conspicuous spherical, ellipsoid to ovoid forms. This study shows that there is no relationship between layers present in mature anthers, dehiscence type, pollination mode and orbicules presence. We report for the first time the presence of orbicules in the holoparasitic family Balanophoraceae belonging to the order Santalales, in which there is scarce information available regarding the presence of orbicules. Given the intergeneric variations and the consistency at generic level observed in the taxa here analyzed, orbicules may have predictive value and potential for systematically oriented research questions.

Enhanced pollen tube performance at high temperature contributes to thermotolerant fruit and seed production in tomato.

Rising temperature extremes during critical reproductive periods threaten the yield of major grain and fruit crops. Flowering plant reproduction depends on the ability of pollen grains to generate a pollen tube, which elongates through the pistil to deliver sperm cells to female gametes for double fertilization. We used tomato as a model fruit crop to determine how high temperature affects the pollen tube growth phase, taking advantage of cultivars noted for fruit production in exceptionally hot growing seasons. We found that exposure to high temperature solely during the pollen tube growth phase limits fruit biomass and seed set more significantly in thermosensitive cultivars than in thermotolerant cultivars. Importantly, we found that pollen tubes from the thermotolerant Tamaulipas cultivar have enhanced growth invivo and invitro under high temperature. Analysis of the pollen tube transcriptome's response to high temperature allowed us to define two response modes (enhanced induction of stress responses and higher basal levels of growth pathways repressed by heat stress) associated with reproductive thermotolerance. Importantly, we define key components of the pollen tube stress response, identifying enhanced reactive oxygen species (ROS) homeostasis and pollen tube callose synthesis and deposition as important components of reproductive thermotolerance in Tamaulipas. Our work identifies the pollen tube growth phase as a viable target to enhance reproductive thermotolerance and delineates key pathways that are altered in crop varieties capable of fruiting under high-temperature conditions.

In vitro studies on the pollen viability and germination of Impatiens cordata Wight. an endemic species of the Southern-Western Ghats

Impatiens cordata is an endemic balsam in the southern Western Ghats. The present work aimed to study pollen morphology, fertility, viability, cytology, and in vitro pollen germination studies of I. cordata. The study also focused on finding a relationship between pollen viability and germination. The results revealed that the I. cordata pollen grains are elliptical and quadrangular. The pollen grains are bicellular, mainly tetracolpate, with some tricolpate occurrences, and have reticulate exine ornamentation. Brew baker’s medium supplemented with 5% sucrose had the most remarkable ability to germinate in vitro. The stain and the number of days significantly affect germination. The peak of pollen viability was observed on the day of anthesis. The results of the Alexander stain were more strongly correlated with in vitro germination and suggested that for pollen viability studies, the Alexander stain is considered the best stain compared to others.

Mining Candidate Genes for Maize Tassel Spindle Length Based on a Genome-Wide Association Analysis

Maize tassel spindle length is closely related to the number of pollen grains and the duration of the flowering stage, ultimately affecting maize yield and adaptations to stress conditions. In this study, 182 maize inbred lines were included in an association population. A genome-wide association study was conducted on maize tassel spindle length using the Q + K model. With p ≤ 1.0 × 10−4 applied as the significance threshold, 240 SNPs significantly associated with tassel spindle length were detected, which were associated with 99 quantitative trait loci (QTLs), with 21 QTLs detected in two or more environments. Moreover, 51 candidate genes were detected in 21 co-localized QTLs. A KEGG enrichment analysis and candidate gene expression analysis indicated that Zm00001d042312 affects plant hormone signal transduction and is highly expressed in maize tassels. A haplotype analysis of Zm00001d042312 revealed three main haplotypes, with significant differences between Hap1 and Hap2. In conclusion, we propose that Zm00001d042312 is a gene that regulates maize tassel spindle length. This study has further elucidated the genetic basis of maize tassel spindle length, while also providing excellent genetic targets and germplasm resources for the genetic improvement of maize tassel spindle length and yield.

Floral Developmental Morphology and Biochemical Characteristics of Male Sterile Mutants of Lagerstroemia indica.

Male sterility is a common phenomenon in higher plants and often plays an important role in the selection of superior offspring. 'Xiang Yun' is a mutant of Lagerstroemia indica that does not bear fruit after flowering, and its flowering period is significantly longer than that of normal L. indica. To explore the timing and molecular mechanisms of sterility in 'Xiang Yun', this study determined the period of sterility through anatomical observation and compared the content of nutrients and the activity of antioxidative enzymes at different stages of flower development. Finally, sequence alignment and qPCR were used to analyze the differences in pollen development genes between 'Xiang Yun' and 'Hong Ye'. The results showed that the anthers of 'Xiang Yun' dispersed pollen normally, but the pollen grains could not germinate normally. Observations with scanning electron microscopy revealed that the pollen grains were uneven in size and shriveled in shape. Further observation of anther sections found that abnormal development of the microspores began at the S2 stage, with the callose wall between microspores of 'Xiang Yun' being thicker than that of 'Hong Ye'. In addition, during the flower development of 'Xiang Yun', the contents of soluble sugar, soluble protein, free proline, and triglycerides were deficient to varying degrees, and the activities of POD, SOD, and MDA were lower. Sequence alignment and qPCR showed that there were several mutations in EFD1, TPD1, and DEX1 of 'Xiang Yun' compared with 'Hong Ye', and the expression levels of these genes were abnormally elevated in the later stages of development. Our results clarified the timing and phenotype of male sterility in 'Xiang Yun'. This provides solid and valuable information for further research on the molecular mechanism of sterility in 'Xiang Yun' and the genetic breeding of crape myrtle.

Nanoengineering Spikey Surfaces: Investigation of Reversible Organizational Control of Surface-Tethered Polypeptide Brushes.

Nature serves as an important source of inspiration for the innovation and development of micro- and nanostructures for advanced functional surfaces and substrates. One example used in nature is a spikey surface ranging from micrometer-sized spikes on pollen grains down to the nanometer-scale protein spikes found on viruses. This study explored the realization of such highly textured surfaces via the nanoengineering of self-assembled poly(γ-benzyl-l-glutamate) "nanospikes", exploiting solvent-induced chain organization, controlled surface chemical functionality, and enhanced stability in the form of polymer brushes. The reversible solvent-responsive behavior of these polymer chains and the aggregation behavior of the chain-ends were investigated via fluorescence characterization and studied through molecular simulations. Vapor-based solvent treatments were developed for orientation control with in situ analysis to understand film response and brush organizational behavior under different selected conditions. The effect of sub-100 nm nanopatterning on surface morphology and chain organization was examined via an integrated approach of experimental and computational studies. The methodologies established in this study present opportunities for engineering sophisticated nanoscale spikey surfaces with high customizability by means of nanolithography combined with solvent-assisted treatments.

Archaic sap beetles (Coleoptera: Nitidulidae) as Cretaceous pollinators

Kateretidae have been considered a family of generalist (as a whole) fossil pollinator beetles after the description of many fossil species in this taxon from the Upper Cretaceous Kachin amber together with pollen grains from their host plant. But the placement of this group of fossils in Kateretidae remained tentative because some definite characters to be observed in the fossils (e.g., maxillae and genitalia) were almost inaccessible by conventional methods. A recent paper proposed to include most of these fossil “kateretid” genera and species in the newly erected family Apophisandridae among Cucujoidea. The description of the two new genera and species Diopsiretes corniger gen. et sp. nov. and Cornuturetes elaphus gen. et sp. nov. from the same deposit, and the use of synchrotron light to describe the first cited species, combined with the examination of new photographic material of the type of Apophisandra ammytae, allowed us to better define this peculiar group of fossils. We attempt to demonstrate their placement in an extinct basal subfamily in Nitidulidae (Apophisandrinae stat. nov.), with some partially shared plesiomorphic characters of both Kateretidae and Nitidulidae: Epuraeinae, and with a series of convergent morphological characters also shared with other extant anthophagous nitidulids including Nitidulinae: Mystropini and Meligethinae. As such, all the fossil species from the Kachin amber initially described in Kateretidae and recently moved to Apophisandridae, should be included in Nitidulidae: Apophisandrinae.

MIKC*-type MADS transcription factors control JINGUBANG expression and the degree of pollen dormancy in Arabidopsis.

While pollen dormancy has been proposed to play a necessary role in sexual reproduction, it remains poorly understood. Here, we used traditional pollen germination assays to characterize dormancy. Our results underscore variation in the degree of dormancy between individual pollen grains. In addition, we provide evidence that JINGUBANG (JGB), previously defined as a negative regulator of pollen germination in Arabidopsis (Arabidopsis thaliana), is responsible for the uneven degrees of pollen dormancy, as asynchronous pollen germination in vitro reflected varied expression levels of JGB. We identified five cis-acting elements, including four CArG-boxes and the previously uncharacterized element ERE7, as essential for the initiation and enhancement of JGB expression. A 10-bp sequence between CArG-box 3 and ERE7, likely the result of an inverse DNA loop formed between CArG-box 3 and CArG-box 4, was required for robust gene expression. In addition, the pollen-specific AtMIKC*-type MADS transcription factors AGAMOUS-LIKE 30 (AGL30), AGL65, AGL66, AGL94, and AGL104 activated JGB transcription. Notably, the transactivation levels differed among the obligate AtMIKC* heterodimers tested. Our results indicate that distinct AtMIKC* complexes formed in individual pollen grains direct pollen dormancy to uneven degrees, which is likely an adaptive trait that ensures broader pollen dispersal under adverse environmental conditions.

Morphology, pollen viability, and meiotic index of nance (Byrsonima cydoniifolia [A.] Juss)

Byrsonima cydoniifolia (nance), a forest species from the Malpighiaceae family, is widely distributed across Brazil, predominantly in the North, Northeast, and Central-West regions. This study aimed to analyze pollen morphology, viability, and the meiotic index in different native populations of nance in the eastern region of Mato Grosso state. For each population, five individuals were selected, and floral buds were collected during various developmental stages. The morphological characterization of pollen grains was conducted using the acetolysis protocol, followed by photography, measurement, and classification based on size, shape, ornamentation, and polar area index. The meiotic index was determined by counting post-meiotic products. Pollen grains were found to be spheroidal, small, 3-colporate, with a colpus, identified as tricolporate grains with a large polar area. The exine in the polar area was microreticulate. The meiotic index varied among populations and individuals, exceeding 95%. Pollen viability tests effectively distinguished between viable and non-viable pollen, with viability rates over 90%. The pollen grains contained starch and lipids as reserve substances. The species demonstrated high stability and meiotic regularity. The findings from this study contribute to our understanding of the ecology, conservation, dispersal, and propagation potential of nance, which supports the reproductive success of the species.

Pollen micromorphology and ultrastructure between two isolated species of Colchicum L. in Iran

Pollen micromorphology and ultrastructure of Colchicum kotschyi and Colchicum robustum with palynological isolated position in a previous research were examined by Light Microscopy (LM), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The observations showed that all quantitative characters of pollen micromorphology varied in the studied taxa. Although, pollen grains in both species were oblate. Two pollen types, two major exine ornamentations in the equatorial surface of pollen grain with two kinds of pore intine ornamentation were seen during this research. Regarding sporoderm data, the thickness of the pollen wall layer, state of the endexine layer, and number of intine layers of C. kotschyi were different from C. robustum. Sporoderm characters strongly supported the unique position of C. robustum resulting from previous palynological research.

An evaluation rule to manage productivity properties performance of male date palms

ABSTRACT Male palm trees almost prominently display minute morphological variations; however, date palm growers rely on readily available pollen from unproven male genotypes without giving correct type selection any thought, which may result in low productivity and/or poor fruit quality. This study sought to develop an evaluation rule by calculating an evaluation index for managing the productivity characteristics performance of nine male date palms, which were examined for their pollen productivity, nutritional status and morphological traits from their leaves, pinnae and spathes. The findings showed that the evaluation rule for a male date palm should depend on pollen grains productivity and germination percentage traits with a weight of 5, spathe morphological traits with a weight of 4, pinnae morphological traits with a weight of 3, leaf morphological traits with a weight of 2 and leaf nutritional status with a weight of 1. The best productivity characteristics performance of male date palms was male No. 8 ‘M8’ due to its high evaluation index. The proposed evaluation index criterion will contribute to better information and analytical support for management of the date palm industry to maximise the effectiveness of germplasm conservation and exploitation, as well as procedural and methodological aspects of the analysis.