Exine Pattern Research Articles

EPAD1 Orthologs Play a Conserved Role in Pollen Exine Patterning.

The pollen wall protects pollen during dispersal and is critical for pollination recognition. In the Poaceae family, the pollen exine stereostructure exhibits a high degree of conservation with similar patterns across species. However, there remains controversy regarding the conservation of key factors involved in its formation among various Poaceae species. EPAD1, as a gene specific to the Poaceae family, and its orthologous genes play a conserved role in pollen wall formation in wheat and rice. However, they do not appear to have significant functions in maize. To further confirm the conserved function of EPAD1 in Poaceae, we performed an analysis on four EPAD1 orthologs from two distinct sub-clades within the Poaceae family. The two functional redundant barley EPAD1 genes (HvEPAD1 and HvEPAD2) from the BOP clade, along with the single copy of sorghum (SbEPAD1) and millet (SiEPAD1) from the PACMAD clade were examined. The CRISPR-Cas9-generated mutants all exhibited defects in pollen wall formation, consistent with previous findings on EPAD1 in rice and wheat. Interestingly, in barley, hvepad2 single mutant also showed apical spikelets abortion, aligning with a decreased expression level of HvEPAD1 and HvEPAD2 from the apical to the bottom of the spike. Our finding provides evidence that EPAD1 orthologs contribute to Poaceae specific pollen exine pattern formation via maintaining primexine integrity despite potential variations in copy numbers across different species.

Pollen Morphology in Bignoniaceae in Relation to Taxonomy

Palonological investigation of 49 species of the family Bignoniaceae distributed over 32 genera has been made. There is a great diversity in pollen morphological characters. The pollen grains may be united in tetrad as in Chilopsis saligna or free as in rest of the species.The pollen grains may be atreme 3,4,7 zonocolpate, 3 zonocolporoidate, 3,4, zonocolporate, parasyncolpate, monoporate, pantoporate, pantocolpate or anomotreme. Similarly the exine pattern varies from obscure to reticulate with occasional occurrence of retipilate, baculate types. Taking aperture as major and exine pattern as subsidiary characters as many as twelve distinct pollen types have been recognised.

Pollen Morphology of Polygala L. (Polygalaceae) from Turkey and its Taxonomic Implications

Pollen morphology of Polygala taxa from the family Polygalaceae in Turkey is presented in this study. Pollen features of 18 species along with one undescribed species in the section Polygala were examined with light and scanning electron microscopy, 11 of which were studied and defined for the first time. Cluster analysis and principal components analysis were conducted to determine informative palynological characters and to discover similarities among the studied taxa. Based on qualitative and quantitative variables in the phenogram, the studied taxa were divided into three major clusters. Multivariate analyses revealed that apocolpium characters, including a psilate apocolpium, the presence of apocolpial lumens with granules and small depressions with psilate or rugulate walls are the most distinct features for discriminating Polygala taxa. Intraspecific variations in some pollen characters, such as the exine pattern and aperture membrane features, are reported for several taxa. Pollen morphological data obtained in the present study are compared with those from previous studies for a number of species, and the results are evaluated. In addition, the aperture number and its probable significance in the Turkish Polygala are considered for some taxa, with emphasis on their known pollination strategies.

Xylan clustering on the pollen surface is required for exine patterning.

Xylan is a crosslinking polymer that plays an important role in the assembly of heterogeneous cell wall structures in plants. The pollen wall, a specialized cell wall matrix, exhibits diverse sculpted patterns that serve to protect male gametophytes and facilitate pollination during plant reproduction. However, whether xylan is precisely anchored into clusters and its influence on pollen wall patterning remain unclear. Here, we report xylan clustering on the mature pollen surface in different plant species that is indispensable for the formation of sculpted exine patterns in dicot and monocot plants. Chemical composition analyses revealed that xylan is generally present at low abundance in the mature pollen of flowering plants and shows plentiful variations in terms of substitutions and modifications. Consistent with the expression profiles of their encoding genes, genetic characterization revealed IRREGULAR XYLEM10-LIKE (IRX10L) and its homologous proteins in the GT47 family of glycosyltransferases as key players in the formation of these xylan micro-/nano-compartments on the pollen surface in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa). A deficiency in xylan biosynthesis abolished exine patterning on pollen and compromised male fertility. Therefore, our study outlines a mechanism of exine patterning and provides a tool for manipulating male fertility in crop breeding.

The Role of Physical Processes in Pollen Wall Morphogenesis: Hypothesis and Experimental Confirmation

The review is devoted to the analysis and generalization of modern knowledge about the mechanisms underlying the ontogeny of the male gametophyte envelope. New and earlier data on exine development аre discussed, and recurrent phases in the development of exine of phylogenetically distant plant species are emphasized. Though exine formation has been shown to be dependent on plenty of genes, the reiteration of exine patterns in different plant species (e. g. columellate, granular, “white-lined” lamellae) suggests that these patterns are based on some non-biological principles of space-filling operations. However, mechanisms involved remained obscure until it became clear that the sequence of structures observed during exine development coincided with the sequence of self-assembling micellar mesophases. It was discovered later that another physical-chemical process – phase separation – participated in exine formation. To confirm that exine-like patterns are capable of generating in vitro by simple physical processes, and their formation does not require regulation at the genome level, some our and other authors’ in vitro experiments were undertaken; the data obtained are discussed. Several series of our new experiments on modeling exine development with mixtures of urface-active substances resulted in some patterns simulating the main types of natural exine. Transmission electron microscopy analysis of the samples has shown that patterns simulating the full range of exine types were obtained by joint action of phase separation and micellar self-assembly. The reconsideration and analysis of our and other authors’ morphogenetic and modeling data revealed that molecular-genetic mechanisms and physical forces work in tandem, with considerable input of physical processes.

Putting the brakes on pollen wall development: A conserved negative feedback loop regulates pollen exine formation in flowering plants

Pollen grains are covered by a complex multi-layered structure, the pollen wall. Exine, the outermost layer of this wall, is made from the biopolymer sporopollenin that exhibits remarkable physical and chemical stability. In different plants, exine, which shields pollen from harsh environmental stresses, has very diverse morphologies and forms different patterns (Wang and Dobritsa, 2018). It also contributes to pollination, pollen-stigma interaction, pollen hydration, and eventual release of the pollen tube. Formation of exine begins after male meiosis when four microspores are arranged in a tetrad configuration and enclosed by the callose wall (Ariizumi and Toriyama, 2011). At this stage, microspores secrete primexine, the precursor of exine that accumulates between the microspore plasma membrane and the callose wall, providing a scaffold for exine patterning (Wang et al., 2021). As the callose wall gradually gets degraded, sporopollenin is secreted by the nearby tapetal cells and deposited onto the primexine template to form mature exine. This process requires coordination of activities between microspores and the surrounding tapetum.

Pollen morphological investigation of selected species of family Asteraceae from Pakistan by using light and scanning electron microscopy.

A light and scanning electron microscopy technique was conducted to investigate the palynological features of 19 species belonging to 15 genera of the family Asteraceae. The species under investigation yielded pollen in a range of shapes, including spheroidal, prolate, and subprolate. Trizoncolporate, Tricolporate, and Tetracolporate are the three types of pollen apertures observed in examined species. Except for Gazania rigens, which has reticulate ornamentation under SEM, the exine pattern in all studied species is echinate. The majority of the species had isopolar polarity, whereas some members were apolar and heteropolar. The quantitative parameters that are polar to equatorial diameter, P/E ratio, length of colpi, width of colpi, length of the spine, width of spine, and exine thickness was measured by using light microscopy. The Coreopsis tinctoria had the lowest mean polar 19.75 μm to mean equatorial diameter 18.25 μm while the Silybum marianum had the highest polar 44.7μm to equatorial 48.2μm value. The value for colpi length/width was highest in Cirsium arvensis and lowest in C. tinctoria, measuring 9.7/13.2μm and 2.7/4.7μm, respectively. The spine length varied from 0.5μm in Sonchus arvensis to 5.5μm in Calendula officinalis. Verbesina encelioides had the highest exine thickness measurement (3.3μm), whereas S. arvensis had the lowest (0.3μm). The pollen surface of Tagetes erectus, has the highest number (65) whereas the lowest spines number (20) is found in S. arvensis. A taxonomic key based on pollen traits is provided for quick identification of the species. Significant implications for the systematics of the Asteraceae family can be drawn from the reported pollen's quantitative and qualitative data. RESEARCH HIGHLIGHTS: SEM and LM technique was used to study the palynological features of pollen grains. Quantitative and qualitative pollen features of 19 species of family Asteraceae are described. Morphological traits of pollen grains are important for the systematics of family Asteraceae.

Targeted expression of bgl23-D, a dominant-negative allele of ATCSLD5, affects cytokinesis of guard mother cells and exine formation of pollen in Arabidopsis thaliana.

Targeted expression of bgl23-D, a dominant-negative allele of ATCSLD5, is a useful genetic approach for functional analysis of ATCSLDs in specific cells and tissues in plants. Stomata are key cellular structures for gas and water exchange in plants and their development is influenced by several genes. We found the A. thaliana bagel23-D (bgl23-D) mutant showing abnormal bagel-shaped single guard cells. The bgl23-D was a novel dominant mutation in the A. thaliana cellulose synthase-like D5 (ATCSLD5) gene that was reported to function in the division of guard mother cells. The dominant character of bgl23-D was used to inhibit ATCSLD5 function in specific cells and tissues. Transgenic A. thaliana expressing bgl23-D cDNA with the promoter of stomata lineage genes, SDD1, MUTE, and FAMA, showed bagel-shaped stomata as observed in the bgl23-D mutant. Especially, the FAMA promoter exhibited a higher frequency of bagel-shaped stomata with severe cytokinesis defects. Expression of bgl23-D cDNA in the tapetum with SP11 promoter or in the anther with ATSP146 promoter induced defects in exine pattern and pollen shape, novel phenotypes that were not shown in the bgl23-D mutant. These results indicated that bgl23-D inhibited unknown ATCSLD(s) that exert the function of exine formation in the tapetum. Furthermore, transgenic A. thaliana expressing bgl23-D cDNA with SDD1, MUTE, and FAMA promoters showed enhanced rosette diameter and increased leaf growth. Taken together, these findings suggest that the bgl23-D mutation could be a helpful genetic tool for functional analysis of ATCSLDs and manipulating plant growth.

Membrane-processed honey samples for pollen characterization with health benefits

Better processing techniques must be utilized widely due to the rising demand for honey. The most common honey processing techniques are applied to melissopalynomorphs to check the quality and quantity of valuable honey using microporous ultrafiltration membranes. It is essential to have the ability to selectively filter out sugars from honey using ultrafiltration. This study authenticated 24 honey samples using membrane reactors ultrafiltration protocol to describe the pollen spectrum of dominant vegetation. The purpose of this study was also to explore nutritional benefits as well as the active phytochemical constituents of honey samples. Honey samples were collected and labeled Acacia, Eucalyptus, and Ziziphus species based on plant resources provided by local beekeepers. A variety of honeybee flora was collected around the apiaries between 2020 and 2021. Honey analysis revealed that the pollen extraction of 24 bee foraging species belonging to 14 families. The honey membrane technology verified the identities of honey and nectar sources. Also, pollen identified using honey ultrafiltration membranes revealed dominant resources: Acacia spp. (69%), Eucalyptus spp. (52%) and Ziziphus spp. Honey filtration using a membrane technology classified 14 samples as unifloral, represented by six dominant pollen types. The absolute pollen count in the honey sample revealed that 58.33% (n = 14) belong to Maurizio's class I. Scanning ultrasculpturing showed diverse exine patterns: reticulate, psilate, scabrate-verrucate, scabrate-gemmate, granulate, perforate, microechinate, microreticulate, and regulate to fossulate for correct identification of honey pollen types. Honey ultrafiltration should be utilized to validate the botanical sources of honey and trace their biogeographic authenticity. Thus, it is imperative to look at the alternative useful method to identify the botanical origin of filtered honey. It is critical to separate honey from adulteration by a standardized protocol. Membrane technology has yielded significant outcomes in the purification of honey.

Exploration of pollen traits and their taxonomic relevance in selected taxa of the subfamily Papilionoideae from Hainan Island, China

The Papilionoideae is one taxonomically complex subfamily with high economic and medicinal potential. The pollen micro-morphology and taxonomic relevance of this subfamily are still poorly known in the island. Therefore, this study aims to provide new palynological information to correctly identify and define species boundaries within the subfamily. The species were collected from different geographical regions of Hainan Island. Both light and scanning electron microscopic techniques were used to observe pollen traits. Additionally, principal component analysis was performed to elucidate the variation among the taxa. A significant variation was found in exine sculpturing i.e. most of the taxa have reticulate type pollen while Desmodium triflorum has a psilate exine pattern. Variations were found on the surface of the reticula that can help to delimit the species from one another. Pollen type was observed as tricolporate and rarely tricolpate. Similarly, the colpus surface membrane morphology may also vary significantly from species to species i.e. scabrate, verrucate, gemmate, rugulate patterns. Besides, the mergo having various sculpturing found in Canavalia rosea, Desmodium triflorum, D. microphyllum Glycine max, Macroptilium atropurpureum, Erythrina crista-galli and Zornia gibbosa should be considered as a potential taxonomic trait for the subfamily. The maximum P/E ratio was found in Zornia gibbosa (2.24). Similarly, the maximum pollen size was found in Alysicarpus vaginalis (34.64 × 33.99 µm). Our study explored the pollen morphological traits and can be helpful to correctly identify the species and define species boundaries within Papilionoideae at various taxonomic levels. This study strengthens and supports the taxonomic position of the subfamily and will provide bases for further phylogenetic and molecular studies of Papilionoideae.

Identification of prominent airborne pollen in a city situated in foot-hills of Himalayas, Chandigarh, India.

Pollen allergy is considered one of the important critical thrust areas, as 20-30% of the world population suffers from allergic rhinitis. The increase in global surface temperature directly affects pollen physiological (e.g., pollen production) and morphological parameters and indirectly affects the distribution pattern, the allergenic potential of pollen, and plant species. Therefore, periodic sampling and pollen studies of a region have become necessary to assess the status of change in species and its morphological characteristics of different taxa. The current study is conducted to identify the airborne pollen based on studying their unique and distinctive morphological characters to serve as a reference pollen guide for future research. The airborne pollens were trapped using the Burkard volumetric sampler at three different locations in Chandigarh from 2018 to 2020 and analyzed under Leica DM5500B-Automated Upright Microscope System. The study investigated various pollen features such as shape, size, aperture type, and exine/surface pattern for taxonomic classification of plant groups. The majority of LM-analyzed pollen grains were prolate-spheroidal or oblate, whereas the aperture types were 3-zonocolporate, 3-colpate, and 3-zonocolporate. Exine patterns were predominantly psilate, reticulate, and straite and were easily discernible. Nonetheless, the vast majority of airborne pollen belonging to both arboreal and non-arboreal was quite small and fall into small pollen size classes, i.e., 10-24μm. The exine pattern was readily apparent and were predominantly psilate, reticulate, and straight. The current study improved the knowledge on airborne pollen biodiversity, which will help to understand the regional distribution, long-range transport, and construct the current status of morphological features of species/taxa.

Pollen Morphological Study of Some Selected Flowering Plants within Adekunle Ajasin University Main Campus, Akungba-Akoko, Ondo State, Nigeria

On the Adekunle Ajasin University Main campus, Akungba-Akoko, Ondo State, Nigeria, the pollen morphological study of seven (7) flowering plant species representing three (3) angiospermic plant Families (Asteraceae, Euphorbiaceae, and Fabaceae sub-family Caesalpinoideae) was examined, analyzed, and studied palynologically to determine the morphological features and attributes as an aid in the identification and classification of its members within each family. Pollen grains from fresh polleniferous materials were extracted using acetolysis methods. Detailed morphological evaluations were performed at x100 magnification. Results showed similarities and differences between species in the same genera, as well as differences between species in other families. Pollen study of these species revealed several similarities between species within the same family. Aperture type, forms, pollen grain size, sculpturing pattern, pollen dimension, and exine pattern were all studied for differences and similarities. Euphorbia hirta L and Euphorbia heterophylla L, both Euphorbiaceae species, have tricolpate apertures, are prolate in shape, reticulate, and contain small to medium pollen sizes. Asteraceae has tricolporate apertures, prolate spheroidal shapes, spinate, short and long spines, and pollen sizes ranging from microscopic to enormous (Ageratum conyzoides L, Tithonia diversifolia, and Tridax procumbens). Pollen from the family Fabaceae subfamily Caesalpinioideae (which includes Caesalpinia pulcherrima (L.) Swartz. and Senna alata (Linn.) Roxb) were found to be subprolate, coarsely reticulate, tricolporate, and with pollen sizes ranging from medium to large. Aperture measures such as number and diameter, pollen size, and spine height were suggestive in all of the species studied. Because all of the species studied exhibited comparable form and symmetry, they were grouped together and assigned to the same family.

Grass‐specific ABERRANT MICROSPORE DEVELOPMENT 1 is required for maintaining pollen fertility in rice

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.

Morphological Characterization of Pollen in Some Varieties of Walnut (Juglans regia)

ABSTRACT In this study carried out to determine the pollen characteristics of walnut, Bilecik, Chandler, Fernette, Fernor, Kaman 1, Pedro, Şebin, and Şen 1 varieties were used as material. As a result of scanning electron microscopy (SEM) examination it was stated that the pollen shapes were oblate spheroidal for all the walnut varieties. The pollen of the varieties exhibited diversity in pollen length (37.54–40.52 µm), width (41.10–45.02 µm), pori diameter (2.45–3.61 µm), distance between pori (11.28–14.41 µm) and spinules (0.54–0.73 µm), pore (16.40–23.00) and spinules (20.50–43.50) number, spinule width (0.18–0.26 µm) and length (0.09–0.28 µm). Results showed that in particular, the Fernor had the largest pore diameter, so their number per unit area was low. In contrast, Bilecik had the smallest pore diameter. Distance between pori of this variety was the least. Therefore, a large number of pori was observed on the surface. In addition, spinules sizes were determined to be larger in Şen 1, but smaller in Chandler variety than the others. In particular, these morphological properties of pollen can be used for identification of different varieties. Also, the pollen shape and exine patterning of the varieties studied were illustrated by SEM images.

Systematic palynology in Korean Piperales with special focus on its exine surface ornamentation and orbicule morphology

The pollen and orbicule morphology of the Korean Piperales (Aristolochia, Asarum, Houttuynia, Piper, and Saururus) were investigated via scanning electron microscopy. Piperales pollen is a monad, its size ranging from very small to large (P = 7.78–51.4 μm, E = 6.68–43.1 μm), and having a mainly circular to sub-circular shape. The aperture type is constant in the genus [inaperturate (Aristolochia), tri to pentaporate (Asarum), and monosulcate (Houttuynia, Piper, and Saururus)]. There are four distinct types of exine ornamentation: Fossulate with perforate, microreticulate with gemmae, microperforate with granula, and microechinate. The orbicules (minute sporopollenin granules) were observed in all studied taxa and thus, may be a possible symplesiomorphic characteristic of Piperales. Further, the observed orbicule surface ornamentation was similar to pollen exine patterns, for example muri, gemmae, or granula. This resemblance between orbicule and pollen exine ornamentation may imply a similar biosynthesis pattern of sporopollenin of pollen exine and orbicules. The phenogram resulting from a cluster analysis using palynological characters was generally consistent with the known molecular phylogeny of Piperales. This initial study will help understand the palynological diversity and provide detailed information of pollen and orbicule characteristics in Piperales.

Authentication of the therapeutic Lamiaceae taxa by using pollen traits observed under scanning electron microscopy.

Herbal medicines are gaining popularity worldwide for human healthcare because of their therapeutic potential. However, adulteration and use of unauthentic raw herbals as substitutes have become a major issue for the local communities and industry for reasons of safety and efficacy. Therefore, the authentication of medicinal plants before their use in herbal medicines is a need of time. Hence, the present study was designed with an aim, to authenticate the therapeutic Lamiaceous taxa by using pollen traits observed under scanning electron microscopy. Pollen micro-morphological studies solve the problem through discrimination and correct identification of the Lamiaceae species from the adulterants. Based on pollen features, Lamiaceae were further divided into two sub-families Lamioideae (tricolpate) and Nepetoideae (hexa-colpate). The pollen grains of Lamioideae were found as small to medium-sized, tricolpate, radially/bilateral symmetrical, sub-spheroidal and oblate shape. Besides, exine patterns bireticulate, reticulate and micro-reticulate, colpus surface sculpturing as psilate, gemmate, scabrate, and verrucate have also been reported. A significant variation was found in the pattern of the reticulum, thickness, and the number of secondary lumina per primary lumen. Similarly, Nepetoideae has a hexa zono-colpate pollen but tri and tetra zono-colpate pollen have also been observed. Hence, this study contributes to the authentication and correct identification of medicinally important Lamiaceae taxa by using scanning electron microscopic techniques and can help to solve the adulteration problem. Highlights Authentication of medicinally important Lamiceous taxa was carried out through scanning electron microscopic techniques. Chemotaxonomic characterization was used for the accurate identification of the therapeutic taxa. The medicinal, palynological and phytochemical significance of Lamiaceae taxa were evaluated. A significant variation was seen in the palynological traits that help in the determination and authentication of the therapeutic Lamiaceous species. Based on the chemotaxonomic characterization, our study can help to solve the adulteration problem for the reason of safety and efficacy.

DCET1 Controls Male Sterility Through Callose Regulation, Exine Formation, and Tapetal Programmed Cell Death in Rice.

In angiosperms, anther development comprises of various complex and interrelated biological processes, critically needed for pollen viability. The transitory callose layer serves to separate the meiocytes. It helps in primexine formation, while the timely degradation of tapetal cells is essential for the timely callose wall dissolution and pollen wall formation by providing nutrients for pollen growth. In rice, many genes have been reported and functionally characterized that are involved in callose regulation and pollen wall patterning, including timely programmed cell death (PCD) of the tapetum, but the mechanism of pollen development largely remains ambiguous. We identified and functionally characterized a rice mutant dcet1, having a complete male-sterile phenotype caused by defects in anther callose wall, exine patterning, and tapetal PCD. DCET1 belongs to the RNA recognition motif (RRM)-containing family also called as the ribonucleoprotein (RNP) domain or RNA-binding domain (RBD) protein, having single-nucleotide polymorphism (SNP) substitution from G (threonine-192) to A (isoleucine-192) located at the fifth exon of LOC_Os08g02330, was responsible for the male sterile phenotype in mutant dcet1. Our cytological analysis suggested that DCET1 regulates callose biosynthesis and degradation, pollen exine formation by affecting exine wall patterning, including abnormal nexine, collapsed bacula, and irregular tectum, and timely PCD by delaying the tapetal cell degeneration. As a result, the microspore of dcet1 was swollen and abnormally bursted and even collapsed within the anther locule characterizing complete male sterility. GUS and qRT-PCR analysis indicated that DCET1 is specifically expressed in the anther till the developmental stage 9, consistent with the observed phenotype. The characterization of DCET1 in callose regulation, pollen wall patterning, and tapetal cell PCD strengthens our knowledge for knowing the regulatory pathways involved in rice male reproductive development and has future prospects in hybrid rice breeding.

Implication of light and scanning electron microscopy for pollen morphology of selected taxa of family Asteraceae and Brassicaceae.

The present study was intended to assess pollen morphological attributes of selected Asteraceous and Brassicaceous species from tehsil Esa Khel (Mianwali), Punjab using scanning electron microscopy (SEM) and light microscopy (LM) techniques for its systematic and taxonomic significance for correct identification. Pollen from 12 different species belongs to two plant families from various distributional localities were collected, acetolyzed and measured. Different palynomorphological features were investigated using LM and SEM techniques. In Asteraceous species, three types of pollen (tricolporate, trizonocolporate, and tetracolporate) were observed. Pollen shape was observed prolate-spheroidal in three species while oblate and oblate-spheroidal were detected in Parthenium hysterophorus and Erigeron bonariensis. While sculpturing pattern of exine were echinate, echinate fenestrate, echinate perforate and scabrate echinate. Mesocolpium measurement was calculated maximum for Sonchus oleraceous (16.6μm). Brassicaceae pollen were circular, lobate, tricolpate and exine show reticulate peculiarities. Whereas dominant shape was oblate-spheroidal followed by prolate-spheroidal and sub-prolate in Lepidium didymum and Sisymbrium irio, respectively. Mesocolpium distance was noted highest in Raphanus raphanistrum (14.4μm). Exine thickness was noted maximum in Erigeron bonariensis (2.9μm) in Asteraceous species and in Brassicaceae; Lepedium didymum exine measurement was 2.7μm. The study showed that pollen micromorphology has important role to accurately identify and classify diverse plants genera belong to different families. Based on these taxonomic palynomorph features, the accurate identification of species from flora of tehsil Esa Khel, Mianwali were elaborated.

Secretory lipid transfer protein OsLTPL94 acts as a target of EAT1 and is required for rice pollen wall development.

The plant pollen wall protects the male gametophyte from various biotic and abiotic stresses. The formation of a unique pollen wall structure and elaborate exine pattern is a well-organized process, which needs coordination between reproductive cells and the neighboring somatic cells. However, molecular mechanisms underlying this process remain largely unknown. Here, we report a rice male-sterile mutant (l94) that exhibits defective pollen exine patterning and abnormal tapetal cell development. MutMap and knockout analyses demonstrated that the causal gene encodes a type-G non-specific lipid transfer protein (OsLTPL94). Histological and cellular analyses established that OsLTPL94 is strongly expressed in the developing microspores and tapetal cells, and its protein is secreted to the plasma membrane. The l94 mutation impeded the secretory ability of OsLTPL94 protein. Further in vivo and in vitro investigations supported the hypothesis that ETERNAL TAPETUM 1 (EAT1), a basic helix-loop-helix transcription factor (bHLH TF), activated OsLTPL94 expression through direct binding to the E-box motif of the OsLTPL94 promoter, which was supported by the positive correlation between the expression of EAT1 and OsLTPL94 in two independent eat1 mutants. Our findings suggest that the secretory OsLTPL94 plays a key role in the coordinated development of tapetum and microspores with the regulation of EAT1.

ESCRT components ISTL1 andLIP5 are required for tapetal function and pollen viability.

Pollen wall assembly is crucial for pollen development and plant fertility. The durable biopolymer sporopollenin and the constituents of the tryphine coat are delivered to developing pollen grains by the highly coordinated secretory activity of the surrounding tapetal cells. The role of membrane trafficking in this process, however, is largely unknown. In this study, we used Arabidopsis thaliana to characterize the role of two late-acting endosomal sorting complex required for transport (ESCRT) components, ISTL1 and LIP5, in tapetal function. Plants lacking ISTL1 and LIP5 form pollen with aberrant exine patterns, leading to partial pollen lethality. We found that ISTL1 and LIP5 are required for exocytosis of plasma membrane and secreted proteins in the tapetal cells at the free microspore stage, contributing to pollen wall development and tryphine deposition. Whereas the ESCRT machinery is well known for its role in endosomal trafficking, the function of ISTL1 and LIP5 in exocytosis is not a typical ESCRT function. The istl1 lip5 double mutants also show reduced intralumenal vesicle concatenation in multivesicular endosomes in both tapetal cells and developing pollen grains as well as morphological defects in early endosomes/trans-Golgi networks, suggesting that late ESCRT components function in the early endosomal pathway and exocytosis.