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Summary: The N6‐methyladenosine (m6A) mRNA modification is crucial for plant development and stress responses. In rice, the male sterility resulting from the deficiency of OsFIP37, a core component of m6A methyltransferase complex, emphasizes the significant role of m6A in male fertility. m6A is reversible and can be removed by m6A demethylases. However, whether mRNA m6A demethylase regulates male fertility in rice has remained unknown. Here, we identify the mRNA m6A demethylase OsALKBH9 and demonstrate its involvement in male fertility regulation. Knockout of OsALKBH9 causes male sterility, dependent on its m6A demethylation activity. Cytological analysis reveals defective tapetal programmed cell death (PCD) and excessive accumulation of microspores exine in Osalkbh9‐1. Transcriptome analysis of anthers shows up‐regulation of genes involved in tapetum development, sporopollenin synthesis, and transport pathways in Osalkbh9‐1. Additionally, we demonstrate that OsALKBH9 demethylates the m6A modification in TDR and GAMYB transcripts, which affects the stability of these mRNAs and ultimately leads to excessive accumulation of pollen exine. Our findings highlight the precise control of mRNA m6A modification and reveal the pivotal roles played by OsALKBH9‐mediated m6A demethylation in tapetal PCD and pollen exine accumulation in rice. [ABSTRACT FROM AUTHOR]

The flowering and fruit set of grapevines are determined by many morphological, physiological, and environmental factors. Although the elemental composition of pollen grains plays a crucial role in the fruit set, there is still a considerable gap in our knowledge. To date, no study has been conducted on the elemental composition of Vitis vinifera subsp. sylvestris (hereafter V. sylvestris) pollen grains. The aim of this work was to investigate the elemental composition of pollen grains of V. sylvestris using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). The pollen grains of ten V. sylvestris individuals (eight male and two female) and one hermaphrodite cultivar 'Plavac mali crni' were analyzed. SEM-EDX analysis revealed the presence of eight elements (carbon—C, oxygen—O, magnesium—Mg, phosphorus—P, potassium—K, calcium—Ca, molybdenum—Mo, and aluminum—Al) in the pollen grains. Interestingly, aluminum was detected exclusively in the pollen of the cultivated grape cultivar 'Plavac mali crni', while it was not present in the genotypes of V. sylvestris. No significant differences between genotypes were found for oxygen and phosphorus, while significant differences were found for other elements. Pollen dimorphism was not associated with differences in element composition, although principal component analysis separated the genotypes into two distinct groups, with two female individuals (Pak10 and Pak12) and one male (Im19) tending to form separate clusters. This study is the first report on the elemental composition of pollen grains of V. sylvestris genotypes and provides valuable insights for further studies on pollen functionality. [ABSTRACT FROM AUTHOR]

The grasses are one of the most diverse plant families on Earth. However, their classification and evolutionary history are obscured by their pollen stenopalynous (similar) morphology. A combination of high‐resolution imaging of pollen surface ornamentation and computational analysis has previously been proposed as a promising tool to classify grass taxonomic boundaries. In this study, we test this hypothesis by studying Poaceae pollen across the phylogeny from plants collected in northern South America and also from published literature across the globe. We assessed if morphotypes that we establish using descriptive terminology are supported by computational analysis, if they vary along six (a)biotic variables and vary across the phylogeny. Based on this analysis, we constructed a reference framework for pollen surface ornamentation morphotypes. Our results showed that there is a wide variation of grass pollen surface ornamentation. We identified nine new and confirmed six known morphotypes, establishing a data set for 223 species (243 individual plant specimens) that represent 11 subfamilies. Computational analysis showed that our morphotypes are well‐supported by two quantitative features of pollen sculptural elements (size and density). The specific data set and mapping of the phylogeny confirmed that pollen morphological sculpture is unrelated to (a)biotic variables and is diverse across the phylogeny. [ABSTRACT FROM AUTHOR]

The flowering plant family Asteraceae is diverse and its constituent species are common in many habitats worldwide. However, its pollen, although widely available, is rarely collected by generalist bee species, suggesting it possesses properties that deter these bees from over-exploiting it. Previous studies have proposed that the conspicuous spines on Asteraceae pollen grains might serve as a deterrent against exploitation, but these studies have not separated the effects of pollen morphology from those of pollen chemical composition. Here, we assessed whether Asteraceae pollen spines are detrimental to generalist bees independently of any effects of pollen chemistry. To do so, we administered three pollen diet treatments to queenless bumble bee microcolonies: one treatment incorporated sporopollenin exine "shells" extracted from spinous (echinate) sunflower pollen; a second incorporated chemically identical shells from non-spinous mixed pollen; and the third was a control diet with no added exine. We found that the presence of pollen spines in the diet significantly reduced larval growth, beyond the reduction caused by adding exine to the diet. However, we observed no effect of pollen spines on the survival of adult workers or larvae, nor did we find substantially increased intestinal damage in adults. Our results show that Asteraceae pollen spines impair larval development of generalist bumble bees, but further investigation is required to elucidate the mechanism behind this phenomenon. [ABSTRACT FROM AUTHOR]

The insufficiency of vitamin D, resulting from inadequate exposure to sunlight and/or insufficient dietary intake, remains a major public health concern on a global scale. In this study, vitamin D2 and D3 were microencapsulated using sporopollenin exine microcapsules extracted from Cedrus libani pollens. After loading vitamin D into the microcapsules, they were coated with chitosan, an edible, biocompatible, and mucoadhesive polysaccharide, and alginate (a food additive agent coded E401). Exine microcapsules were extracted by microwave irradiation-assisted chemical method, and structural and morphological examination of exine structures was performed by FT-IR, TGA, SEM, and SEM-EDX analyses. After loading vitamin D into microcapsules in an ethanol medium, the loaded microcapsules were immobilised into the alginate matrix in a calcium chloride solution. D2 and D3 were loaded into 100 mg of sporopollenin exine microcapsules, resulting in loading efficiencies of 31.5 mg and 16.0 mg, respectively. The vitamin D release performance of the microcapsules was examined depending on time and temperature after they were coated with a thin chitosan layer. The release of the highest amount of vitamin D2 and D3 occurred at a temperature of 37°C. Encapsulating vitamin D molecules in chitosan and alginate creates a barrier against degrading environmental conditions, which helps prevent the loss of vitamin D biological activity. This can improve vitamin D dietary supplements' storage, preservation, and marketing requirements. [ABSTRACT FROM AUTHOR]

The exine ultrastructure of 18 species of Anisopappus (Anisopappinae, Athroismeae, Asteraceae) and three species of Duhaldea (Inuleae, Asteraceae) was studied using transmission electron microscopy (TEM). Two ultrastructural patterns were identified: senecioid and helianthoid. The senecioid pattern is characteristic of the species included in the basal clades of the phylogenetic tree of Anisopappus, as published in earlier studies. The helianthoid pattern is restricted to the taxa placed in the derived clades, including the core group of species of Anisopappus in which A. chinensis, the type species, is included. The observed ultrastructural differences seem to suggest that a future splitting of Anisopappus into several different genera should not be disregarded and that the helianthoid pattern represents, within this genus, the derived condition. The ultrastructure of the exine supports the inclusion, suggested by previous authors, of the species Duhaldea stuhlmannii, but not that of Philyrophyllum schinzii, in Anisopappus. In contrast, the three studied species of Duhaldea (D. cappa, D. nervosa, D. revoluta) present an exine with a senecioid pattern, which is characteristic of the tribe Inuleae, in which they are included. The ectoaperture, mesoaperture, and endoaperture of all studied Anisopappinae and of Duhaldea respectively intersect the tectum plus columellae, the foot layer and the outer part of the endexine, and the inner part of the endexine. This feature seems to characterize, in a consistent way, the 'Heliantheae alliance', and is also present in all the studied Asteroideae (except Anthemideae), Dicomoideae, and Carduoideae. [ABSTRACT FROM AUTHOR]

Cryptomeria japonica D. Don is a model plant for studying male sterility in conifers. To date, five male sterile loci have been identified by crossing tests. When at least one of these loci is homozygote of a recessive male sterile allele, male sterility is induced. Cytological studies have been performed for ms1 to ms4 mutants, but there have yet to be such investigations of ms5 mutants. This study newly showed that ms2 mutants lack callose and exhibit different phenotypes for each microsporangium. Furthermore, we found the leakage of cellular contents and the appearance of amorphous substances in ms3 mutants. We also detected leakage of cellular contents in ms4 mutants. On the other hand, abnormal pollen development in ms5 mutants was found to begin at the tetrad stage. This abnormality was characterized by the maintenance of abnormal tetrads and uneven spores, abnormal pollen wall formation, covered with amorphous substances, disappearance of the nucleus, and central nuclear positioning during the binuclear microspore stage. These results were clearly different from those of ms1 to ms4 mutants. Abnormal meiosis in pollen mother cells, the abnormal pollen wall, and abnormal mitosis during pollen development may be closely associated with male sterility caused by mutation of MS5. [ABSTRACT FROM AUTHOR]

Pollen micromorphology of nine species of the genus Tulipa (including three subgenera Tulipa, Clusiana, and Eriostemones) and one species from the genus Amana were examined using light microscopy (LM) and scanning electron microscopy (SEM). Moreover, the pollen wall ultrastructure of five selected taxa from the studied species of Tulipa and one species of Amana were examined by transmission electron microscopy (TEM). Pollen micromorphology (especially exine ornamentation, sulcus margin and sulcus membrane ornamentation, operculum ornamentation) and pollen wall ultrastructure (sporoderm thickness, tectum/foot layer ratio, number of intine layers in sulcus membrane region) varied in the studied taxa. A dendrogram of the pollen micromorphological characteristics (obtained from LM and SEM observations) distinguished three pollen types and six subtypes. Amana edulis (subtype A) and Tulipa biebersteiniana (subtype B) were placed in pollen type 1. Tulipa tetraphylla (subgenus Eriostemones) with Tulipa urumiensis and Tulipa kolpakowskiana (subgenus Tulipa) were placed in pollen type 2. Tulipa clusiana (subgenus Clusiana) and Tulipa suaveolens (subgenus Tulipa) belonged to pollen type 3. Information from pollen wall ultrastructure provided better differentiation of these taxa for better taxonomical resolution. Pollen micromorphology along with ultrastructure can be useful for better understanding the systematic affinities of the species in the genus Tulipa and its relation with the genus Amana and for establishing subgenus rank for T. biebersteiniana and T. clusiana. [ABSTRACT FROM AUTHOR]

Many parks and green spaces in Tehran are located in polluted areas in order to reduce some air pollution; however, sometimes the plants themselves are damaged which cannot be easily recognized.The studied ornamental plants were collected, their pollen were separated from the anthers, and their purification was done by Erdtman's acetolysis method. They were stained with methylene blue and Lugol's solution and the pollens prepared for microscopic observations. Morphological changes of pollens with regional depressions (shrinking), changes in the size of the space between the exine and intine, tearing, asymmetry and deformation of pollen were observed. In the anatomical results: some pollen grains were vacuolated and larger than normal, and some others were starchy and contained accumulations of contaminated particles. All these changes damage the pollen performance. Dahlia variabilis Dest. 97% and Tagetes patula L. 83% experienced the most anatomical damages and Rosa hibrida L. 46% and Datura innoxia Miller 24% underwent the most morphological damages. [ABSTRACT FROM AUTHOR]

Abstract The spore wall of Riccia plano-biconvexa, R. fruchartii, R. cavernosa, R. stenophylla, and R. curtisii was analyzed using light microscopy. The study involved cytochemical analysis to distinguish the different layers of the sporoderm and assess their chemical composition. In all the species studied, the sporoderm was found to have a tri-layered exine, consisting of a lamellar exine 1 that forms ridges and depressions, an intermediate exine 2, and a thick and generally discontinuous exine 3. Cytochemical studies indicated that exine 1 and 2 are composed of sporopollenin, while exine 3 is a mixture of sporopollenin and polysaccharides. The intine, on the other hand, is the only layer that is purely cellulosic and contains pectins. Based on the chemical composition and structural organization, exine 1 and 2 can be categorized as ectexine while exine 3 corresponds to an endexine. We emphasize the importance of using cytochemical tests to study the spore wall in liverworts and other bryophytes.

This study aimed to examine the pollen and pollinia morpho-structure of 18 horticultural Apocynaceous species. Advanced light and scanning electron microscopy (LM and SEM) were used to elaborate on and examine the systematic importance of pollen and pollinia micromorphology. Pollen grains were first acetolysed, which was followed by visualisation of their sculpturing features. The quantified data were subjected to statistical tools to elucidate dendrogram clustering and principal component analysis to reveal pollen/pollinia morphotypes. The size of pollen is variable, ranging from 113.45 μm in Cascabela thevetia to 23.4 μm in Alstonia scholaris. The study revealed tetrad, tetraporate, and tricolporate grains. Sculpturing (exine ornamentation) varies from reticulate perforate to reticulate. Pollinum shape was observed to be narrow oblong, obovate, orbicular, and reniform. Reticulate-psilate sculptural features were prominent among pollinia surfaces. Based on examination, it was ascertained that the minimum exine thickness in Periploca aphylla was 4.9 μm, whereas the corresponding number in Cryptolepis dubia was 1.35 μm. Taxonomic identification keys were constructed separately based on pollen/pollinia characters to identify the Apocynaceous taxa. In the presented study, seven pollen shapes were observed: from oblate to per prolate. The findings confirm that morphopollinic traits differ amongst genera of Apocynaceous species. However, these features can be used to distinguish the Apocynaceous taxa. The results show that structural characteristics of pollen and pollinia can help accurately identify Apocynaceous species.

The flowering and fruit set of grapevines are determined by many morphological, physiological, and environmental factors. Although the elemental composition of pollen grains plays a crucial role in the fruit set, there is still a considerable gap in our knowledge. To date, no study has been conducted on the elemental composition of Vitis vinifera subsp. sylvestris (hereafter V. sylvestris) pollen grains. The aim of this work was to investigate the elemental composition of pollen grains of V. sylvestris using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). The pollen grains of ten V. sylvestris individuals (eight male and two female) and one hermaphrodite cultivar ‘Plavac mali crni’ were analyzed. SEM-EDX analysis revealed the presence of eight elements (carbon—C, oxygen—O, magnesium—Mg, phosphorus—P, potassium—K, calcium—Ca, molybdenum—Mo, and aluminum—Al) in the pollen grains. Interestingly, aluminum was detected exclusively in the pollen of the cultivated grape cultivar ‘Plavac mali crni’, while it was not present in the genotypes of V. sylvestris. No significant differences between genotypes were found for oxygen and phosphorus, while significant differences were found for other elements. Pollen dimorphism was not associated with differences in element composition, although principal component analysis separated the genotypes into two distinct groups, with two female individuals (Pak10 and Pak12) and one male (Im19) tending to form separate clusters. This study is the first report on the elemental composition of pollen grains of V. sylvestris genotypes and provides valuable insights for further studies on pollen functionality.

Based on molecular phylogenetic and morphological studies, the new genera Sedobassia Freitag & G. Kadereit and Spirobassia Freitag & G. Kadereit were described in the tribe Camphorosmeae (Chenopodiaceae/Amaranthaceae sensu APG IV). Palynomorphological peculiarities are often used in taxonomy as additional diagnostic features. Pollen grains from 26 herbarium specimens belonging to 13 taxa of Bassia, Sedobassia, Spirobassia and Neokochia genera in Eurasia and North America were acetolyzed and studied using both light microscopy and scanning electron microscopy. Dry pollen grains were also studied. The structure of the columellae of pollen grains was analyzed for the first time in the current study. The aim of this research was to provide data on their pollen characteristics and to evaluate the taxonomic value of these data for generic and species-specific identification. The pollen grains are pantoporate, spheroidal in shape, circular in outline, slightly undulate, undulate or straight on the edges; and medium- or small-sized. Pores are circular, with distinct or indistinct margins. Exine sculpture is nanoechinate; tectum psilate or psilate-perforate. Pore membranes with nanoechini. Taxonomic relevance of the most important characters of pollen grains is discussed (pollen diameter, pore number, pore diameter, distance between pores and between pore centers, pollen diameter(C)/distance between pore centers(D) value, nanoechini density, presenсe/absence of perforations, structure of columellae, number of nanoechini on pore membranes). Pollen morphology proved to be an important additional source of information for species-specific identification. This study provides new data and analyzes the morphological features of pollen grains of Bassia (in the currently accepted circumscription), palynomorphological similarities, and differences between taxa of the genera Bassia, Sedobassia, Spirobassia, and Neokochia. [ABSTRACT FROM AUTHOR]

Recent molecular phylogenetic studies of Camphorosmoideae (Chenopodiaceae) demonstrated that Camphorosma is monophyletic. Palynomorphological peculiarities are used in taxonomy as additional diagnostic features and pollen analysis. Pollen morphology was studied using light and scanning electron microscopy, based on 13 specimens belonging to four species ( C. annua , C. lessingii , C. monspeliaca and C. songorica ). The aim of this research was to provide new data on pollen characteristics of the above mentioned species and to evaluate their taxonomic value. The results obtained show that pollen grains are pantoporate, spheroidal, circular in outline, undulate or slightly undulate on the edges; small or medium-sized. Pores are circular, with distinct margins. Exine sculpture is nanoechinate, tectum psilate or psilate-perforate. Pore membranes are nanoechinate. Taxonomic relevance of the most important characters of pollen grains (pollen diameter, pore number, pore diameter, distance between pores and between pore centres, C/D value, nanoechini density, presence/absence of perforations, number of nanoechini on pore membranes, structure of columellae) is discussed. The exine structure of pollen grains of all species was analysed for the first time in the current study. Pollen morphology proved to be an important additional source of information for taxonomy for species-specific identification and pollen analysis within Camphorosma . Palynomorphological data are interpreted in the existing phylogenetic framework.

Because of its significance for plant male fertility and, hence, direct impact on crop yield, pollen exine development has inspired decades of scientific inquiry. However, the molecular mechanism underlying exine formation and thickness remains elusive. In this study, we identified that a previously unrecognized repressor, ZmMS1/ZmLBD30, controls proper pollen exine development in maize. Using an ms1 mutant with aberrantly thickened exine, we cloned a male-sterility gene, ZmMs1 , which encodes a tapetum-specific lateral organ boundary domain transcription factor, ZmLBD30. We showed that ZmMs1/ZmLBD30 is initially turned on by a transcriptional activation cascade of ZmbHLH51-ZmMYB84-ZmMS7, and then it serves as a repressor to shut down this cascade via feedback repression to ensure timely tapetal degeneration and proper level of exine. This activation-feedback repression loop regulating male fertility is conserved in maize and sorghum, and similar regulatory mechanism may also exist in other flowering plants such as rice and Arabidopsis. Collectively, these findings reveal a novel regulatory mechanism of pollen exine development by which a long-sought master repressor of upstream activators prevents excessive exine formation. The causal gene of the first discovered maize male sterility mutant ms1 was identified, which encodes a LOB domain transcription factor, ZmLBD30. A transcriptional activation cascade, ZmbHLH51-ZmMYB84-ZmMS7, initially turns on the expression of ZmMs1/ZmLBD30 , which in turn shuts down the cascade via feedback repression to ensure timely tapetal degeneration and proper level of exine. This negative-feedback repression of a transcriptional activation cascade represents a novel regulatory mechanism of pollen development. [ABSTRACT FROM AUTHOR]

Pollen micromorphology and sporoderm ultrastructure of 10 species of the genus Gagea sensu lato (including Lloydia) were examined by light microscopy, scanning electron microscopy, and transmission electron microscopy. The results showed variation in all quantitative characters of pollen micromorphology. In terms of qualitative characters, oblate pollen shape and two pollen types (medium and large) were seen. Exine ornamentation of the equatorial surface differed from that of the sulcus margin region. Intine ornamentation in the sulcus region was similar in all taxa. Furthermore, the situation of the furrow among cristates and granulates in muri differed, as did the lumina connections. The qualitative and quantitative characters of the pollen sporoderm, such as the presence or absence of endexine, number of intine layers in the sulcus region, and sporoderm thickness, also varied. A dendrogram of all qualitative and quantitative palynological characters, created by the unweighted pair group method with arithmetic mean (UPGMA) based on Euclidean distances, identified six pollen types. Palynological types strongly supported the transfer of Lloydia to Gagea. However, the palynological dendrogram did not support reducing the number of sections in these taxa. A dichotomous key is also presented based on pollen micromorphology and ultrastructure. [ABSTRACT FROM AUTHOR]

Summary: Sporopollenin is one of the most structurally sophisticated and chemically recalcitrant biopolymers. In higher plants, sporopollenin is the dominant component of exine, the outer wall of pollen grains, and contains covalently linked phenolics that protect the male gametes from harsh environments. Although much has been learned about the biosynthesis of sporopollenin precursors in the tapetum, the nutritive cell layer surrounding developing microspores, little is known about how the biopolymer is assembled on the microspore surface.We identified SCULP1 (SKS clade universal in pollen) as a seed plant conserved clade of the multicopper oxidase family. We showed that SCULP1 in common wheat (Triticum aestivum) is specifically expressed in the microspore when sporopollenin assembly takes place, localized to the developing exine, and binds p‐coumaric acid in vitro.Through genetic, biochemical, and 3D reconstruction analyses, we demonstrated that SCULP1 is required for p‐coumaroylation of sporopollenin, exine integrity, and pollen viability. Moreover, we found that SCULP1 accumulation is compromised in thermosensitive genic male sterile wheat lines and its expression partially restored exine integrity and male fertility.These findings identified a key microspore protein in autonomous sporopollenin polymer assembly, thereby laying the foundation for elucidating and engineering sporopollenin biosynthesis. [ABSTRACT FROM AUTHOR]

Premise of research. The genus Echinops is unique among the Cardueae tribe of Asteraceae for presenting two distinctive features, both related to reproductive structures: a syncephalium (=secondary capitulum) and an impressively large pollen grain with a triangular section and probably the thickest of all plant cell walls. While the syncephalium constitutes a synapomorphy for the genus, recent evidence suggests that some Echinops species have pollen similar to that of other Cardueae. This study therefore seeks to contribute insights into the spatiotemporal frame of pollen evolution within the genus. Methodology. Micromorphological characterization was provided for 35 specimens from 28 Echinops species using light and scanning electron microscopy. Pollen counts were carried out for two Echinops species and Cardopatium corymbosum. Pollen data are discussed in the context of a dated Echinops phylogeny. For comparison purposes, new and published pollen data of 622 Cardueae species and 303 taxa of Vernonieae, another tribe where syncephaly has evolved, were collated. Pivotal results. The "Perennial" Echinops pollen type of huge size and triangular section likely derived from the "Annual" Echinops pollen type, more similar in shape, size, and exine structure to that of other Cardueae. Pollen type transition took place in the genus long after syncephaly evolved. Pollen size increase did not occur at the expense of pollen quantity and could respond to warmer environmental conditions and increased male competition. Conclusions. This study of Echinops pollen evidenced the evolutionary exploration of novel phenotypic space in the genus, most certainly in response to the climatic context in which the species have diversified. [ABSTRACT FROM AUTHOR]

Recent molecular phylogenetic studies of Camphorosmoideae (Chenopodiaceae) demonstrated that Camphorosma is monophyletic. Palynomorphological peculiarities are used in taxonomy as additional diagnostic features and pollen analysis. Pollen morphology was studied using light and scanning electron microscopy, based on 13 specimens belonging to four species (C. annua, C. lessingii, C. monspeliaca and C. songorica). The aim of this research was to provide new data on pollen characteristics of the above mentioned species and to evaluate their taxonomic value. The results obtained show that pollen grains are pantoporate, spheroidal, circular in outline, undulate or slightly undulate on the edges; small or medium-sized. Pores are circular, with distinct margins. Exine sculpture is nanoechinate, tectum psilate or psilate-perforate. Pore membranes are nanoechinate. Taxonomic relevance of the most important characters of pollen grains (pollen diameter, pore number, pore diameter, distance between pores and between pore centres, C/D value, nanoechini density, presence/absence of perforations, number of nanoechini on pore membranes, structure of columellae) is discussed. The exine structure of pollen grains of all species was analysed for the first time in the current study. Pollen morphology proved to be an important additional source of information for taxonomy for species-specific identification and pollen analysis within Camphorosma. Palynomorphological data are interpreted in the existing phylogenetic framework. [ABSTRACT FROM AUTHOR]

Two Balkan species of the Campanula pyramidalis complex, respectively Campanula montenegrina and Campanula austroadriatica were analyzed based on comparative methodology for their palynomorphological features, and provided the evidence of similarities and differences of palynological features between them. Palynomorphological features of these species were described for the first time. Pollen grains of two species resulted to be triporate with circular pores, isopolar with radial symmetry, spheroidal shape in polar view and wide oval in equatorial one. The exine sculpture of pollen grains appeared echinate in all studied subpopulations, and it was accompanied by spinules in pollen grains of C. austroadriatica and pollen grains of C. montenegrina. The largest sizes of the pollen grains were identified at C. austroadriatica population collected near Perast, for the length of pores were identified at in pollen grains of Shirokë-Zogaj and Petrovac populations and for the width was identified in pollen grains of Shkalla e Tujanit and Kruja Castle populations. As for the exine, it was thicker at pollen grains of C. austroadriatica populations of Shirokë-Zogaj, Petrovac and near Perast localities. The smallest sizes for length of pollen grains and length of pores were found in C. austroadriatica collected at Shirokë-Zogaj, while for the width of pollen grains were found in pollen grains of C. austroadriatica collected in Montenegro populations and C. montenegrina of Albanian localities. The smallest width of pores was observed in pollen grains of C. austroadriatica collected in Petrovac. The exine was thinner in all populations of C. austroadriatica collected in Albanian localities. [ABSTRACT FROM AUTHOR]

Our aim was to unravel the underlying mechanisms of pollen wall development in Cymbalaria muralis. By determining the sequence of developing substructures with TEM, we intended to compare it with that of other taxa and clarify whether physical processes of self-assembly and phase separation were involved. In parallel, we tried to simulate in vitro the substructures observed in Cymbalaria muralis exine development, using colloidal mixtures, to determine whether purely physical self-assembly processes could replicate them. Exine ontogeny followed the main stages observed in many other species and was initiated by phase separation, resulting in heterogeneity of the homogeneous contents of the periplasmic space around the microspore which is filled with genome-determined substances. At every stage, phase separation and self-assembly come into force, gradually driving the substances through the sequence of mesophases: spherical micelles, columns of spherical micelles, cylindrical micelles arranged in a layer, laminate micelles. The final two of these mesophases define the structure of the columellate ectexine and lamellate endexine respectively. Structures obtained in vitro from colloidal mixtures simulated the developing exine structures. Striking columella-like surface of some abnormal tapetal cells and lamella-like structures in the anther medium confirm the conclusion that pattern generation is a feature of colloidal materials, after genomic control on material contents. Simulation experiments show the high pattern-generating capacity of colloidal interactions. [ABSTRACT FROM AUTHOR]

Juniperus is one of the few conifers in Iran, which has six species and forms mostly sparse forests with scattered trees. Among them, Juniperus polycarpos and J.excela are more widespread than the other species. Due to the great similarity in their phenotypes, it is difficult to distinguish the two species from each other. In this study, pollinological, anatomical, and molecular indicators were evaluated to identify and differentiate these two Juniper species in the Chahar-Bagh region of Gorgan province, Iran. Using nrDNA ITS nuclear marker, molecular relationships between the two species were investigated. Phylogeny analyzes showed that two species are monophyletic and the populations were subdivided into unresolved subclades I and II. Pollen grains of the two species, J. polycarpos and J. excelsa, were examined using light (LM) and scanning electron (SEM) microscopes. The results showed that all pollen grains were monad, ulcurate, asymmetric, and small in size. In terms of shape, both species were spheroidal (prolate spheroidal) with granular exine ornamentations. The general shape of the pollens in the LM was circular with a smooth surface and no fovea, but the pollen grains examined under SEM were irregular and had fovea. The results of the anatomical studies of the stems also showed little difference, and it was not possible to distinguish and identify the two species. The results indicate that one species is probably distributed in the Chahar-Bagh region and these two taxons are synonymous. [ABSTRACT FROM AUTHOR]

In order to have proper identification of Iris species, many scientific works are referring to the morphological features of pollen grains as adequate sources of information about the origin and variability concerning the different populations of Iris. According to several taxonomic works, in Romania are 17 (18) species of Iris. There is a lack of information about the morphology of pollen in Iris species from our country. SEM analyses of pollen from five populations of Iris species from the Botanical Garden of the University of Agronomic Science and Veterinary Medicine of Bucharest revealed that four of them had reticulated exine, respectively Iris germanica, I. pseudacorus, I. variegate, and I. suaveolens and one had gemmated exine - Iris pumila. The pollen morphological description presented in this study may be of systematic significance to Iris species, enabling species distinction. [ABSTRACT FROM AUTHOR]

Although the evolution of spores was critical to the diversification of plants on land, sporogenesis is incompletely characterized for model plants such as Physcomitrium patens. In this study, the complete process of P. patens sporogenesis is detailed from capsule expansion to mature spore formation, with emphasis on the construction of the complex spore wall and proximal aperture. Both diploid (sporophytic) and haploid (spores) cells contribute to the development and maturation of spores. During capsule expansion, the diploid cells of the capsule, including spore mother cells (SMCs), inner capsule wall layer (spore sac), and columella, contribute a locular fibrillar matrix that contains the machinery and nutrients for spore ontogeny. Nascent spores are enclosed in a second matrix that is surrounded by a thin SMC wall and suspended in the locular material. As they expand and separate, a band of exine is produced external to a thin foundation layer of tripartite lamellae. Dense globules assemble evenly throughout the locule, and these are incorporated progressively onto the spore surface to form the perine external to the exine. On the distal spore surface, the intine forms internally, while the spiny perine ornamentation is assembled. The exine is at least partially extrasporal in origin, while the perine is derived exclusively from outside the spore. Across the proximal surface of the polar spores, an aperture begins formation at the onset of spore development and consists of an expanded intine, an annulus, and a central pad with radiating fibers. This complex aperture is elastic and enables the proximal spore surface to cycle between being compressed (concave) and expanded (rounded). In addition to providing a site for water intake and germination, the elastic aperture is likely involved in desiccation tolerance. Based on the current phylogenies, the ancestral plant spore contained an aperture, exine, intine, and perine. The reductive evolution of liverwort and hornwort spores entailed the loss of perine in both groups and the aperture in liverworts. This research serves as the foundation for comparisons with other plant groups and for future studies of the developmental genetics and evolution of spores across plants.

Abstract Background Sesame is a great reservoir of bioactive constituents and unique antioxidant components. It is widely used for its nutritional and medicinal value. The expanding demand for sesame seeds is putting pressure on sesame breeders to develop high-yielding varieties. A hybrid breeding strategy based on male sterility is one of the most effective ways to increase the crop yield. To date, little is known about the genes and mechanism underlying sesame male fertility. Therefore, studies are being conducted to identify and functionally characterize key candidate genes involved in sesame pollen development. Polyketide synthases (PKSs) are critical enzymes involved in the biosynthesis of sporopollenin, the primary component of pollen exine. Their in planta functions are being investigated for applications in crop breeding. Results In this study, we cloned the sesame POLYKETIDE SYNTHASE A (SiPKSA) and examined its function in male sterility. SiPKSA was specifically expressed in sesame flower buds, and its expression was significantly higher in sterile sesame anthers than in fertile anthers during the tetrad and microspore development stages. Furthermore, overexpression of SiPKSA in Arabidopsis caused male sterility in transgenic plants. Ultrastructural observation showed that the pollen grains of SiPKSA-overexpressing plants contained few cytoplasmic inclusions and exhibited an abnormal pollen wall structure, with a thicker exine layer compared to the wild type. In agreement with this, the expression of a set of sporopollenin biosynthesis-related genes and the contents of their fatty acids and phenolics were significantly altered in anthers of SiPKSA-overexpressing plants compared with wild type during anther development. Conclusion These findings highlighted that overexpression of SiPKSA in Arabidopsis might cause male sterility through defective pollen wall formation. Moreover, they suggested that SiPKSA modulates vibrant pollen development via sporopollenin biosynthesis, and a defect in its regulation may induce male sterility. Therefore, genetic manipulation of SiPKSA might promote hybrid breeding in sesame and other crop species.

• Pollen morphology of eight coconut accessions differed in origin, stature, breeding behaviour and tolerance to abiotic stresses were characterised with scanning electron microscope. • Variations in pollen size, shape and exine ornamentation pattern was observed between the coconut genotypes. • Pollen physiological features such as pollen viability, germination and pollen tube length and pollen nutrient composition were evaluated for the eight coconut genotypes. • The results obtained revealed differences in pollen morphological features which can potentially be used for cultivar identification and the information on pollen viability, germination and pollen mineral contents amongst genotypes can support conservation and crop improvement studies of the genotypes. The micro-morphological characteristic of the pollen grain is one of the most important diagnostic traits use for identification and characterization of plants even to the accession levels. In this study, pollen grains characterization of eight different coconut (Cocos nucifera L.) accessions were carried out. Morphometric observations and structure analysis of the pollen grains were performed using light and scanning electron microscopy. The variation in length and width observed ranged from 55.06 -71.25 µm and 24.38 -36.27 µm amongst the accessions. The pollen grains exhibited an ellipsoidal to elliptical shape with the exine ornamentation ranging from granulate to reticulate. Pollen viability, germination and pollen tube length were significantly different amongst the tested accessions. While pollen viability varied from 92.35 to 96.5%, germination rate and pollen tube length (after 2 h) ranged from 16.05 - 31.59% and 234.95 μm to 414.96 μm respectively. Pollen mineral composition from different accessions also varied significantly with Malayan Orange Dwarf (MOD) recording higher phosphorus (0.93%), calcium (0.64%) and magnesium (0.38%) content while highest potassium (1.01%), sodium (0.71%), iron (149.35 ppm) zinc (119.59 ppm) and boron (45.05 ppm) content was noticed in San Ramon Tall (SNRT). This investigation highlights the fact that these pollen morphological features could be potentially used for differentiating the selected accessions thereby supporting their conservation and crop improvement studies. [ABSTRACT FROM AUTHOR]

The pollen morphology of 150 species representing 33 genera of Zingiberaceae was examined using light (LM) and scanning electron microscopy (SEM) as part of a comprehensive survey of this family. The pollen grains of the species studied are inaperturate, with a thin exine and thick intine, and with diverse ornamentation. This variation in the pollen suggests it may be a useful source of characters for future phylogenetic analyses based on combined datasets. [ABSTRACT FROM AUTHOR]

SUMMARY: Pollen development includes a series of biological events that require precise gene regulation. Although several transcription factors (TFs) have been shown to play roles in maintaining pollen fertility, the major regulatory networks underlying tapetum development and pollen wall formation are largely unknown. Herein, we report that ABERRANT MICROSPORE DEVELOPMENT1 (AMD1), a protein annotated previously as unknown protein, is required for tapetum development and pollen exine patterning in rice (Oryza sativa L.). AMD1 encodes a grass‐specific protein exhibiting transactivation activity in the nucleus and is spatiotemporally expressed in the tapetum and microspores during pollen development. Further biochemical assays indicate that AMD1 directly activates the transcription of DEFECTIVE POLLEN WALL (DPW) and POLYKETIDE SYNTHASE2 (OsPKS2), which are both implicated in sporopollenin biosynthesis during exine formation. Additionally, AMD1 directly interacts with TAPETUM DEGENERATION RETARDATION (TDR), a key TF involved in the regulation of tapetum degradation and exine formation. Taken together, we demonstrate that AMD1 is an important regulatory component involved in the TDR‐mediated regulatory pathway to regulate sporopollenin biosynthesis, tapetum degradation, and exine formation for pollen development. Our work provides insights into the regulatory network of rice sexual reproduction and a useful target for genetic engineering of new male‐sterile lines for hybrid rice breeding. [ABSTRACT FROM AUTHOR]

The N 6 -methyladenosine (m 6 A) mRNA modification is crucial for plant development and stress responses. In rice, the male sterility resulting from the deficiency of OsFIP37, a core component of m 6 A methyltransferase complex, emphasizes the significant role of m 6 A in male fertility. m 6 A is reversible and can be removed by m 6 A demethylases. However, whether mRNA m 6 A demethylase regulates male fertility in rice has remained unknown. Here, we identify the mRNA m 6 A demethylase OsALKBH9 and demonstrate its involvement in male fertility regulation. Knockout of OsALKBH9 causes male sterility, dependent on its m 6 A demethylation activity. Cytological analysis reveals defective tapetal programmed cell death (PCD) and excessive accumulation of microspores exine in Osalkbh9-1. Transcriptome analysis of anthers shows up-regulation of genes involved in tapetum development, sporopollenin synthesis, and transport pathways in Osalkbh9-1. Additionally, we demonstrate that OsALKBH9 demethylates the m 6 A modification in TDR and GAMYB transcripts, which affects the stability of these mRNAs and ultimately leads to excessive accumulation of pollen exine. Our findings highlight the precise control of mRNA m 6 A modification and reveal the pivotal roles played by OsALKBH9-mediated m 6 A demethylation in tapetal PCD and pollen exine accumulation in rice., (© 2024 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.)

In flowering plants, male reproductive function is determined by successful development and performance of stamens, pollen grains, and pollen tubes. Despite the crucial role of highly glycosylated arabinogalactan-proteins (AGPs) in male gamete formation, pollen grain, and pollen tube cell walls, the underlying mechanisms defining these functions of AGPs have remained elusive. Eight partially redundant Hyp-galactosyltransferases (named GALT2-GALT9) genes/enzymes are known to initiate Hyp- O -galactosylation for Hyp-arabinogalactan (AG) production in Arabidopsis thaliana. To assess the contributions of these Hyp-AGs to male reproductive function, we used a galt2galt5galt7galt8galt9 quintuple Hyp-GALT mutant for this study. Both anther size and pollen viability were compromised in the quintuple mutants. Defects in male gametogenesis were observed in later stages of maturing microspores after meiosis, accompanied by membrane blebbing and numerous lytic vacuoles. Cytological and ultramicroscopic observations revealed that pollen exine reticulate architecture and intine layer development were affected such that non-viable collapsed mature pollen grains were produced, which were devoid of cell content and nuclei, with virtually no intine. AGP immunolabeling demonstrated alterations in cell wall architecture of the anther, pollen grains, and pollen tube. Specifically, the LM2 monoclonal antibody (which recognized β-GlcA epitopes on AGPs) showed a weak signal for the endothecium, microspores, and pollen tube apex. Pollen tube tips also displayed excessive callose deposition. Interestingly, expression patterns of pollen-specific AGPs, namely AGP6, AGP11, AGP23, and AGP40, were determined to be higher in the quintuple mutants. Taken together, our data illustrate the importance of type-II AGs in male reproductive function for successful fertilization. [ABSTRACT FROM AUTHOR]

Fertilization is a key event for sexually reproducing plants. Pollen–stigma adhesion, which is the first step in male–female interaction during fertilization, requires proper pollen wall patterning. Callose, which is a β-1.3-glucan, is an essential polysaccharide that is required for pollen development and pollen wall formation. Mutations in CALLOSE SYNTHASE 5 (CalS5) disrupt male meiotic callose accumulation; however, how CalS5 activity and callose synthesis are regulated is not fully understood. In this paper, we report the isolation of a kompeito-1 (kom-1) mutant defective in pollen wall patterning and pollen–stigma adhesion in Arabidopsis thaliana. Callose was not accumulated in kom-1 meiocytes or microspores, which was very similar to the cals5 mutant. The KOM gene encoded a member of a subclass of Rhomboid serine protease proteins that lacked active site residues. KOM was localized to the Golgi apparatus, and both KOM and CalS5 genes were highly expressed in meiocytes. A 220 kDa CalS5 protein was detected in wild-type (Col-0) floral buds but was dramatically reduced in kom-1. These results suggested that KOM was required for CalS5 protein accumulation, leading to the regulation of meiocyte-specific callose accumulation and pollen wall formation. [ABSTRACT FROM AUTHOR]

Premise: The sporoderm of seed‐plant pollen grains typically has apertures in which the outer sporopollenin‐bearing layer is relatively sparse. The apertures allow regulation of the internal volume of the pollen grain during desiccation and rehydration (harmomegathy) and also serve as sites of pollen germination. A small fraction of angiosperms undergo pollination in water or at the water surface, where desiccation is unlikely. Their pollen grains commonly lack apertures, though with some notable exceptions. We tested a hypothesis that in some angiosperm aquatics that inhabit water of unstable salinity, the pollen apertures accommodate osmotic effects that occur during pollination in such conditions. Methods: Pollen grains of the tepaloid clade of the monocot order Alismatales, which contains ecologically diverse aquatic and marshy plants, were examined using light microscopy and scanning electron microscopy. We used Ruppia as a model to test pollen grain response in water of various salinities. Pollen aperture evolution was also analyzed using molecular tree topologies. Results: Phylogenetic optimizations demonstrated an evolutionary loss and two subsequent regains of the aperturate condition in the tepaloid clade of Alismatales. Both of the taxa that have reverted to aperturate pollen (Ruppia, Ruppiaceae; Althenia, Potamogetonaceae) are adapted to changeable water salinity. Direct experiments with Ruppia showed that the pollen apertures have a role in a harmomegathic response to differences in water salinity. Conclusions: Our results showed that the inferred regain of pollen apertures represents an adaptation to changeable water salinity. We invoke a loss‐and‐regain scenario, prompting questions that are testable using developmental genetics and plant physiology. [ABSTRACT FROM AUTHOR]

Background: Sesame is a great reservoir of bioactive constituents and unique antioxidant components. It is widely used for its nutritional and medicinal value. The expanding demand for sesame seeds is putting pressure on sesame breeders to develop high-yielding varieties. A hybrid breeding strategy based on male sterility is one of the most effective ways to increase the crop yield. To date, little is known about the genes and mechanism underlying sesame male fertility. Therefore, studies are being conducted to identify and functionally characterize key candidate genes involved in sesame pollen development. Polyketide synthases (PKSs) are critical enzymes involved in the biosynthesis of sporopollenin, the primary component of pollen exine. Their in planta functions are being investigated for applications in crop breeding. Results: In this study, we cloned the sesame POLYKETIDE SYNTHASE A (SiPKSA) and examined its function in male sterility. SiPKSA was specifically expressed in sesame flower buds, and its expression was significantly higher in sterile sesame anthers than in fertile anthers during the tetrad and microspore development stages. Furthermore, overexpression of SiPKSA in Arabidopsis caused male sterility in transgenic plants. Ultrastructural observation showed that the pollen grains of SiPKSA-overexpressing plants contained few cytoplasmic inclusions and exhibited an abnormal pollen wall structure, with a thicker exine layer compared to the wild type. In agreement with this, the expression of a set of sporopollenin biosynthesis-related genes and the contents of their fatty acids and phenolics were significantly altered in anthers of SiPKSA-overexpressing plants compared with wild type during anther development. Conclusion: These findings highlighted that overexpression of SiPKSA in Arabidopsis might cause male sterility through defective pollen wall formation. Moreover, they suggested that SiPKSA modulates vibrant pollen development via sporopollenin biosynthesis, and a defect in its regulation may induce male sterility. Therefore, genetic manipulation of SiPKSA might promote hybrid breeding in sesame and other crop species. [ABSTRACT FROM AUTHOR]

In flowering plants, male reproductive function is determined by successful development and performance of stamens, pollen grains, and pollen tubes. Despite the crucial role of highly glycosylated arabinogalactan-proteins (AGPs) in male gamete formation, pollen grain, and pollen tube cell walls, the underlying mechanisms defining these functions of AGPs have remained elusive. Eight partially redundant Hyp-galactosyltransferases (named GALT2-GALT9) genes/enzymes are known to initiate Hyp-O-galactosylation for Hyp-arabinogalactan (AG) production in Arabidopsis thaliana. To assess the contributions of these Hyp-AGs to male reproductive function, we used a galt2galt5galt7galt8galt9 quintuple Hyp-GALT mutant for this study. Both anther size and pollen viability were compromised in the quintuple mutants. Defects in male gametogenesis were observed in later stages of maturing microspores after meiosis, accompanied by membrane blebbing and numerous lytic vacuoles. Cytological and ultramicroscopic observations revealed that pollen exine reticulate architecture and intine layer development were affected such that non-viable collapsed mature pollen grains were produced, which were devoid of cell content and nuclei, with virtually no intine. AGP immunolabeling demonstrated alterations in cell wall architecture of the anther, pollen grains, and pollen tube. Specifically, the LM2 monoclonal antibody (which recognized β-GlcA epitopes on AGPs) showed a weak signal for the endothecium, microspores, and pollen tube apex. Pollen tube tips also displayed excessive callose deposition. Interestingly, expression patterns of pollen-specific AGPs, namely AGP6, AGP11, AGP23, and AGP40, were determined to be higher in the quintuple mutants. Taken together, our data illustrate the importance of type-II AGs in male reproductive function for successful fertilization.

In this research, pollen micromorphology and ultrastructure of eight species belonging to genera including Alrawia, Bellevalia, Fessia, Muscari, Othocallis, Prospero, Puschkinia, and Zagrosia were investigated by light microscopy, scanning electron microscopy, and transmission electron microscopy. The pollen size varied among the studied species. Othocallis monanthos and Muscari neglectum had the largest and smallest pollen grains, respectively. Based on the Polar axis/Equatorial axis (P/E) ratio, Bellevalia saviczii had peroblate pollen shape and the rest were oblate. Exine ornamentation on the equatorial surface, sulcus margin exine ornamentation, and intine ornamentation in the sulcus membrane region of the pollen grains varied among the selected species of all genera. The exine layer in all genera had semitectate tectum, simplicolumellate infratectum, and discontinuous foot layer. There was discontinuous endexine in M. neglectum, Prospero autumnale, and Zagrosia persica. Alrawia bellii, P. autumnale, and Puschkinia scilloides had three intine layers in the sulcus membrane region, O. monanthos had two, and the rest of the species had one. Also, in those species with three layers in the sulcus membrane region, the outer intine layer had many channels. A dendrogram of the palynological characters grouped them into three pollen types and six pollen subtypes. The pollen types verified the phylogenetic relationships among the studied genera, whereas the pollen subtypes partly supported these relationships. [ABSTRACT FROM AUTHOR]

Background. Learning about morphological and biological features of pollen is very important to make correct estimations of plant productivity and breeding efficiency.Materials and methods. The viability of black currant pollen was analyzed in 2019 at the Laboratory for Long-Term Storage of Plant Genetic Resources, N.I. Vavilov All-Russian Institute of Plant Genetic Resources (VIR). Eleven black currant cultivars of various ecogeographic and genetic origin maintained at Pushkin and Pavlovsk Laboratories of VIR served as the material for the research. Pollen viability was tested on an artificial medium with 10% sucrose and 0.8% agar. Morphological studies were carried out using light and confocal laser scanning microscopy at the Palynology Laboratory and the Core Centrum of Cell and Molecular Technologies in Plant Science housed by the Komarov Botanical Institute (BIN).Results and conclusion. The prevailing adverse weather conditions in 2019 produced a negative impact on the process of male generative structure formation. The level of pollen viability, depending on the cultivar, ranged from 17.98 to 58.60%. After exposure to liquid nitrogen (–196°C) for 6 months, the number of germinated pollen grains increased 1.1 to 3.2 times in all the studied cultivars, except one (‘Pozdnyaya poslevoennaya’, k-7652). A palynomorphological study revealed that reduced pollen viability in some cultivars (‘Krasnoyarskaya 1018’, k-7607; ‘Tsema’, k-25900; ‘Pozdnyaya poslevoennaya’, k-7652) was associated with morphological deviations in the sporoderm structure (small pollen grains, exine thickening and formation of verrucate mesoporium surfaces). A low positive correlation was observed between the level of pollen viability and the diameters of the pore (r = 0.43) and pollen grain (r = 0.27). An insignificant negative correlation was apparent between the level of viability and the exine thickness (r = –0.33).

We are still far from being able to predict organisms' shapes purely from their genetic codes. While it is imperative to identify which encoded macromolecules contribute to a phenotype, determining how macromolecules self‐assemble independently of the genetic code may be equally crucial for understanding shape development. Pollen grains are typically single‐celled microgametophytes that have decorated walls of various shapes and patterns. The accumulation of morphological data and a comprehensive understanding of the wall development makes this system ripe for mathematical and physical modeling. Therefore, pollen walls are an excellent system for identifying both the genetic products and the physical processes that result in a huge diversity of extracellular morphologies. In this piece, I highlight the current understanding of pollen wall biology relevant for quantification studies and enumerate the modellable aspects of pollen wall patterning and specific approaches that one may take to elucidate how pollen grains build their beautifully patterned walls. Research Highlights: The patterned pollen surface is an ideal system for uncovering pattern formation mechanisms. Relevant developmental steps and genes involved in pollen pattern formation are summarized, and mathematical and physical applications are proposed. [ABSTRACT FROM AUTHOR]

Studies have shown that Acacia Mill. sensu lato consists of seven genera (Acacia sensu stricto, Acaciella Britton & Rose, Mariosousa Seigler & Ebinger, Senegalia Raf., and Vachellia Wight & Arnott) but does not constitute a monophyletic group. The Senegalia sensu lato clade, which corresponds to the genera Acaciella, Mariosousa, and Senegalia sensu stricto, likewise does not constitute a monophyletic group. The pollen morphology of a total of 22 species of Senegalia that occur in Brazil, and that of representatives of the genera Acaciella, Parasenegalia, Mariosousa, and Vachellia, is analyzed here. Pollen material was obtained from exsiccata deposited at some herbaria of Brazil. The pollen was acetolyzed and analyzed using both light and scanning electron microscopy. The dispersal units (polyads) were generally medium to large sized. All of the Senegalia species studied had apolar pollen grains organized in polyads comprising 16 pollen grains. The number of pollen grains in polyads is a synapomorphic character for recognizing those genera. Acaciella polyads have eight pollen grains; Parasenegalia and Mariosousa polyads have 16 pollen grains, and Vachellia polyads have more than 32 pollen grains that are irregularly arranged. The sexine and nexine had identical thickness in most of the species analyzed. Exine ornamentation varied from rugulate to rugulate-perforated to psilate-perforated. [ABSTRACT FROM AUTHOR]

Bee-pollen is a product of the hive which has had a growth in consumption in recent years due to the recognition of its nutritional and bioactive potential. However, several reports have shown that the external structure of the grain limits the absorption of nutrients in the human gastrointestinal tract. A structural modification could be achieved through fermentative processes, favoring the release of compounds found inside this food, in addition to obtaining a product with potential probiotic characteristics. The objective of this work was to evaluate how fermentation through the inclusion of yeasts of the species Saccharomyces cerevisiae, bacteria of species Lactobacillus plantarum or a commercial culture Choozit® affeccted such parameters as Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), phenolic compounds, flavonoids and antioxidant activity. The results found that the use of consortia between yeast and lactic acid bacteria significantly increased in such characteristics as total phenolics and antioxidant activity by 31% and 39% respectively. The analysis by DSC showed an increase in the heat flow of the fermented products compared to fresh bee-pollen, which could indicate structural modification caused by the activity of microorganisms, a fact made visible through micrographs obtained by Scanning Electron Microscopy.

Despite the large amount of knowledge accumulated, a precise understanding of the morphogenesis of the intricate and complex pollen walls (exines) is incomplete. A new factor (simple physico-chemical interactions) is shown to be involved in exine development. The stages of exine development in many species show remarkable similarity with successive micellar self-assembling mesophases of a colloidal system. Currently, > 100 genes have been reported to play a role in exine deposition, but nothing contradicts the view that specific patterns of exines are based on physico-chemical principles of space-filling operations taking place after genomic control of the concentrations of the source materials. On the examples of Chloranthus japonicus , magnoliids and other early-diverging angiosperms we show that exine development unfolds by two physico-chemical processes (phase separation and self-assembly) after genomic control, revealing an interplay between genomic and physical processes. [ABSTRACT FROM AUTHOR]

Juncaceae, a cosmopolitan family, belong to the cyperid clade of Poales together with Cyperaceae and Thurniaceae. Pollen grain of Juncaceae, as in Thurniaceae, is dispersed in a permanent tetrad, and knowledge about the ontogeny of its wall is still incipient, based on data from only one species. This study aims to analyze the formation of the pollen wall of seven Juncus species in order to characterize the timing and the ontogenetic events that lead to the cohesion of the four pollen grains in a permanent tetrad. Anthers at different developmental stages were submitted to techniques of light microscopy and transmission electron microscopy; dehiscent anthers with mature pollens were also analyzed in scanning electron microscopy. In all the species here studied, callose deposits around each microsporocyte, with dissolution prior to meiosis. Microspore wall starts at the end of the second meiotic division with formation of primexine. Exine comprises tectum, columellae, and foot layer. During cytokinesis, cell plates form the internal wall of the pollen tetrad. Mature permanent tetrad is enveloped externally by both the exine and intine and internally by the intine and the foot layer, which forms the continuous internal wall. Callose was detected in the early stages of microsporocytes, although reported to be absent in Juncaceae. Our data confirm the variation in Juncaceae cytokinesis and the occurrence of simple cohesion due to the presence of a continuous tectum along the pollen tetrad. [ABSTRACT FROM AUTHOR]

The present study was carried out on scanning electron microscopic‐based palynological characterization of selected 20 Euphorbiaceae taxa. In this study, important pollen qualitative and quantitative features of selected Euphorbiaceae species such as polar diameter, equatorial diameter, P/E ratio, sculpturing of pollen, exine thickness, intine thickness, presence or absence of colpi and length of colpi, and pollen fertility were examined. Remarkable variations in these pollen characters had been observed among these species. In both polar and equatorial views, Riccinus communis L. exhibited the highest pollen size (polar = 264.1 μm, Equatorial = 270 μm), while Acalypha wilkesiana Mull Arg. showed lowest pollen size (Polar = 17 μm, Equatorial = 18.5 μm). Most of the pollen varied from oblate to spheroidal in shape. With regard to the P/E ratio, Sapium sebiferum L. Roxb showed the highest ratio while Bischofia javanica Blume showed minimum, that is, 1.18 and 0.85, respectively. Intine and exine thickness also varied. Most of the pollen grains were monade. Tricolporate, tricolpate, monocolpate, pentaporate, and polyporate pollen aperture types have been observed. Most of the plants showed regular, reticulate, and echinate pollen sculpturing. Pollen fertility also varied from species to species but most of the plant showed pollen fertility between 70 and 80%. Through this work, it has been concluded that quantitative and qualitative pollen features are helpful at the specific level as well as the generic level and can provide a fruitful taxonomic solution. [ABSTRACT FROM AUTHOR]

Key message: IEF, a novel plasma plasma membrane protein, is important for exine formation in Arabidopsis. Exine, an important part of pollen wall, is crucial for male fertility. The major component of exine is sporopollenin which are synthesized and secreted by tapetum. Although sporopollenin synthesis has been well studied, the transportation of it remains elusive. To understand it, we analyzed the gene expression pattern in tapetal microdissection data, and investigated the potential transporter genes that are putatively regulated by ABORTED MICROSPORES (AMS). Among these genes, we identified IMPERFECTIVE EXINE FORMATION (IEF) that is important for exine formation. Compared to the wild type, ief mutants exhibit severe male sterility and pollen abortion, suggesting IEF is crucial for pollen development and male fertility. Using both scanning and transmission electron microscopes, we showed that exine structure was not well defined in ief mutant. The transient expression of IEF-GFP driven by the 35S promoter indicated that IEF-GFP was localized in plasma membrane. Furthermore, AMS can specifically activate the expression of promoterIEF:LUC in vitro, which suggesting AMS regulates IEF for exine formation. The expression of ATP-BINDING CASSETTE TRANSPORTER G26 (AGCB26) was not affected in ief mutants. In addition, SEM and TEM data showed that the sporopollenin deposition is more defective in abcg26/ief-2 than that of in abcg26, which suggesting that IEF is involved in an independent sporopollenin transportation pathway. This work reveal a novel gene, IEF regulated by AMS that is essential for exine formation. [ABSTRACT FROM AUTHOR]

Sporopollenin is often said to be one of the toughest biopolymers known to man. The shift in dormancy cell wall deposition from around the diploid zygotes of charophycean algae to sporopollenin around the haploid spores of land plants essentially imparted onto land plants the gift of passive motility, a key acquisition that contributed to their vast and successful colonization across terrestrial habitats. 1,2 A putative transcription factor controlling the land plant mode of sporopollenin deposition is the subclass II bHLHs, which are conserved and novel to land plants, with mutants of genes in angiosperms and mosses divulging roles relating to tapetum degeneration and spore development. 3,4,5,6,7 We demonstrate that a subclass II bHLH gene, Mp bHLH37 , regulates sporopollenin biosynthesis and deposition in the model liverwort Marchantia polymorpha. Mp bhlh37 sporophytes show a striking loss of secondary wall deposits of the capsule wall, the elaters, and the spore exine, all while maintaining spore viability, identifying Mp bHLH37 as a master regulator of secondary wall deposits of the sporophyte. Localization of Mp bHLH37 to the capsule wall and elaters of the sporophyte directly designates these tissue types as a bona fide tapetum in liverworts, giving support to the notion that the presence of a tapetum is an ancestral land plant trait. Finally, as early land plant spore walls exhibit evidence of tapetal deposition, 8,9,10,11,12 a tapetal capsule wall could have provided these plants with a developmental mechanism for sporopollenin deposition. [Display omitted] • Mp bHLH37 regulates secondary cell wall deposits in M. polymorpha sporophytes • Mp bHLH37 is exclusively expressed in the elaters and the capsule wall • The capsule wall and elaters could therefore be acting as a tapetum in liverworts • Subclass 2 bHLHs expressed by a tapetum may be ancestral in land plant sporogenesis Spore production is a key innovation behind the successful colonization of land by plants. Levins et al. show that in the liverwort Marchantia polymorpha , a bHLH transcription factor and a tapetum are essential in spore production. The conservation of these traits across land plants lends us insight into the evolution of the land plant sporangium. [ABSTRACT FROM AUTHOR]

Fertilization is a key event for sexually reproducing plants. Pollen–stigma adhesion, which is the first step in male–female interaction during fertilization, requires proper pollen wall patterning. Callose, which is a β-1.3-glucan, is an essential polysaccharide that is required for pollen development and pollen wall formation. Mutations in CALLOSE SYNTHASE 5 (CalS5) disrupt male meiotic callose accumulation; however, how CalS5 activity and callose synthesis are regulated is not fully understood. In this paper, we report the isolation of a kompeito-1 (kom-1) mutant defective in pollen wall patterning and pollen–stigma adhesion in Arabidopsis thaliana. Callose was not accumulated in kom-1 meiocytes or microspores, which was very similar to the cals5 mutant. The KOM gene encoded a member of a subclass of Rhomboid serine protease proteins that lacked active site residues. KOM was localized to the Golgi apparatus, and both KOM and CalS5 genes were highly expressed in meiocytes. A 220 kDa CalS5 protein was detected in wild-type (Col-0) floral buds but was dramatically reduced in kom-1. These results suggested that KOM was required for CalS5 protein accumulation, leading to the regulation of meiocyte-specific callose accumulation and pollen wall formation.

Abstract Background The pollen wall, which protects male gametophyte against various stresses and facilitates pollination, is essential for successful reproduction in flowering plants. The pollen wall consists of gametophyte-derived intine and sporophyte-derived exine. From outside to inside of exine are tectum, bacula, nexine I and nexine II layers. How these structural layers are formed has been under extensive studies, but the molecular mechanisms remain obscure. Results Here we identified two osabcg3 allelic mutants and demonstrated that OsABCG3 was required for pollen development in rice. OsABCG3 encodes a half-size ABCG transporter localized on the plasma membrane. It was mainly expressed in anther when exine started to form. Loss-function of OsABCG3 caused abnormal degradation of the tapetum. The mutant pollen lacked the nexine II and intine layers, and shriveled without cytoplasm. The expression of some genes required for pollen wall formation was examined in osabcg3 mutants. The mutation did not alter the expression of the regulatory genes and lipid metabolism genes, but altered the expression of lipid transport genes. Conclusions Base on the genetic and cytological analyses, OsABCG3 was proposed to transport the tapetum-produced materials essential for pollen wall formation. This study provided a new perspective to the genetic regulation of pollen wall development.