Pollen Research Articles

Comparing nuclear DNA content, pollen viability, pollen production and seed retention of lavender and lavandin

Lavender (Lavandula spp.) is one of the most widely grown essential oil crops in the world. This study aimed to determine the nuclear DNA contents using flow cytometry, pollen viability using TTC (2,3,5-Triphenyl Tetrazolium Chloride) and IKI (Iodine Potassium Iodide) tests, pollen production quantities using hemacytometric method, and seed retention rates per spike and flower of lavender (L. angustifolia var. Raya) and lavandin (L. intermedia var. Super) grown under ecological conditions in Isparta province of Turkey. The nuclear DNA contents were 2.11 and 2.54 pg 2C-1, respectively in the lavender and lavandin cultivar. The flowers of the lavender cultivar produced abundant pollen grains (average 5800 pollen per flower and 1450 pollen per anther) with high viability (60.65-65.05%) and seed retention rate per spike (91.57% on average). The lavandin cultivar, which had very low pollen viability (1.08-3.32%) and pollen grains (average of 2350 pollen per flower and 587.5 pollen per anther) gave very low seed retention rates per spike (0.60% on average). While each flower had four ovaries with the potential to produce four nutlets, lavandin flowers produced only trace numbers (0.15% on average) of seeds. As a result, the lavandin cultivar had more nuclear DNA content, longer stem and spike, smaller size but more numerous flowers, less and lighter anthers, lower pollen grains and viability, and vey few inviabile seeds compared to the lavender cultivar. It has been observed by eye that honey bees do not visit lavender and lavandin flowers for collecting pollen, but solely for collecting nectar.

A Simple and User-Friendly Method for High-Quality Preparation of Pollen Grains for Scanning Electron Microscopy (SEM).

Pollen is becoming an increasingly important subject for molecular researchers in genetic engineering, plant breeding, and environmental monitoring. To broaden the scope of these studies, it is essential to develop accessible methods for scientists who are not specialized in palynology. The article presents a simplified technical procedure for preparing pollen grains for scanning electron microscopy (SEM). The protocol is convenient for any molecular laboratory due to its small set of reagents, ease of execution, low cost, does not require special equipment, and takes only one hour to complete. The high penetrating ability of formaldehyde and the final delicate dehydration using hexamethyldisilazane (HMDS) instead of critical point drying allow for sufficient preservation of the architecture of the aperture, which is considered a gateway for the passage of biomolecules. The method was successfully applied to pollen grains of representatives of dicotyledons (beetroot, petunia, radish, tomato and tobacco) and monocotyledons (lily, onion, corn, rye and wheat). Species studied included insect-pollinated (entomophilous) and wind-pollinated (anemophilous) species. A comparative analysis of the sizes of fresh living pollen grains under a light microscope and those prepared for SEM showed some shrinkage. Quantitative analysis of the degree of pollen grain shrinkage showed that this process depends on the initial shape of dry pollen grains, and the number and structure of apertures. The results support the theoretical model of the folding/unfolding pathways of pollen grains.

Cytogenics, morphology and viability of Borreria spinosa (Rubiaceae) pollen grains

Introduction: Borreria spinosa is a herbaceous plant considered a weed in agricultural crops, although it also has potential in apiculture. Despite its agronomic importance, its cytogenetic and palynological traits are poorly known. Objective: To do the cytogenetic characterization of B. spinosa, describe the morphology of its pollen grains, and estimate their potential viability. Methods: We collected plant material in Santiago del Estero, Argentina, in May 2017 and used classical methods (8-hydroxyquinoline and Farmer for mitosis and meiosis; viability with Müntzing; pollen morphology with nonacetolysed and acetolysed techniques, and SEM). Results: B. spinosa has a chromosome number of 2n = 56, with a karyotype of 46 m + 10 sm. Meiotic abnormalities mainly include chromosomes outside the equatorial plate, lagging chromosomes, and cytomixis. Pollen grains are small to medium-sized, suboblate to oblate-spheroidal, with a viability of 70%. This is a tetraploid species, most chromosomes are metacentric or submetacentric; and it has irregular meiotic behavior and cytomixis, with concomitant low viability in pollen grains. Conclusion: In B. spinose, pollen grains have similar characteristics to other species of the genus Borreria.

Pollination efficiency and the pollen-ovule ratio.

Pollination presents a risky journey for pollen grains. Pollen loss is sometimes thought to favour greater pollen investment to compensate for the inefficiency of transport. Sex allocation theory, to the contrary, has consistently concluded that postdispersal loss should have no selective effect on investment in either sex function. But the intuitively appealing compensation idea continues to be raised despite the lack of theoretical endorsement. We address the theoretical issue with a model that directly represents pollen loss (and ovule loss through floral demise or loss of receptivity) as rate-dependent dynamical processes. These loss rates can be varied to examine the effect of pollination efficiency on optimal sex allocation. Pollen-ovule ratios follow from the sex allocation based on the resource costs of pollen and ovule production. This model confirms conventional findings that pollen loss should have essentially no effect on sexual resource allocation in large, panmictic populations. Pollen limitation of seed set does not alter this conclusion. These results force us to rethink the empirical association of pollination efficiency with low pollen-ovule ratios. This pattern could arise if efficient pollen transport commonly results in stigmatic deposition of cohorts of related pollen. Empirical evidence of correlated paternity supports this explanation.

ICE1 interacts with IDD14 to transcriptionally activate QQS to increase pollen germination and viability.

In flowering plants, sexual reproductive success depends on the production of viable pollen grains. However, the mechanisms by which QUA QUINE STARCH (QQS) regulates pollen development and how transcriptional activators facilitate the transcription of QQS in this process remain poorly understood. Here, we demonstrate that INDUCER OF CBF EXPRESSION 1 (ICE1), a basic helix-loop-helix (bHLH) transcription factor, acts as a key transcriptional activator and positively regulates QQS expression to increase pollen germination and viability in Arabidopsis thaliana by interacting with INDETERMINATE DOMAIN14 (IDD14). In our genetic and biochemical experiments, overexpression of ICE1 greatly promoted both the activation of QQS and high pollen viability mediated by QQS. IDD14 additively enhanced ICE1 function by promoting the binding of ICE1 to the QQS promoter. In addition, mutation of ICE1 significantly repressed QQS expression; the impaired function of QQS and the abnormal anther dehiscence jointly affected pollen development of the ice1-2 mutant. Our results also showed that the enhancement of pollen activity by ICE1 depends on QQS. Furthermore, QQS interacted with CUT1, the key enzyme for long-chain lipid biosynthesis. This interaction both promoted CUT1 activity and regulated pollen lipid metabolism, ultimately determining pollen hydration and fertility. Our results not only provide new insights into the key function of QQS in promoting pollen development by regulating pollen lipid metabolism, but also elucidate the mechanism that facilitates the transcription of QQS in this vital developmental process.

Fossil pollen data can reconstruct robust spatial patterns of biodiversity in the past

Fossil pollen data are valuable for understanding past spatio-temporal variations in plant diversity. However, deducing robust patterns of fossil pollen-assemblage properties is challenging due to factors related to pollen production, dispersal, and fossilisation; sediment sampling; and nomenclature and taxonomy of the fossil pollen grains reflecting the vegetation that produced them. If the composition pattern of the most recent fossil pollen assemblage concords with those in modern or surface pollen assemblages from the same location(s), the pattern can be regarded as robust.Using recent (50–500 years) fossil pollen and surface pollen assemblages of angiosperms compiled from the same geographic area of Central Asia, we analyse spatial patterns in compositional turnover and phylogenetic dispersion. These are widely used to quantify different aspects of plant diversity.Despite differences in the data regarding spatial coverage, number of pollen records, and number of pollen taxa, the spatial pattern in the modern and fossil pollen-assemblage properties across climate zones is broadly similar. Especially, the latitudinal patterns of pollen-assemblage properties are strikingly similar between both data types. However, the degree of concordance varies according to the diversity metric being analysed, and the magnitudes of the metric may differ between both data types. When the data are compiled, processed, and standardised following consistent criteria and analysed using appropriate metrics and methods, spatial patterns in pollen-assemblage properties of fossil pollen data are as robust as those in surface pollen data (∼modern vegetation). Therefore, regional patterns of compositional turnover and phylogenetic dispersion can be confidently inferred from older fossil assemblages through the Holocene.

New pollen taxon Syncolpraedapollis angolensis nov. gen. sp. nov.: A noteworthy discovery reported in the preliminary investigation of the latest Eocene-latest Oligocene deposits in the Kwanza Basin, Angola

A palynostratigraphic study of the upper Cunga and lower Quifangondo deposits in the Cabo de São Brás section, Kwanza Basin, Angola, has revealed a new pollen named Syncolpraedapollis angolensis nov. gen. sp. nov. This finding was part of a wider survey in the upper Cunga and lower Quifangondo deposits of the Cabo de São Brás section, Kwanza Basin, Angola, covering the latest Eocene to the latest Oligocene.The novel pollen features unique characteristics, notably a 3-syncolporate structure with well-defined and distinctive pores. The pollen grain is adorned with a free but irregular reticulum with an irregular polygonal mesh. Syncolpraedapollis angolensis nov. gen. sp. nov. is sporadically but consistently observed within the latest Eocene-latest Oligocene interval, conspicuously absent in the underlying Eocene sediments (lower Cunga Formation) and occurring infrequently in the latest Oligocene sediments (lower Quifangondo Formation). Thus, it is plausible to infer a limited age range, likely restricted to the latest Eocene-latest Oligocene, as previous studies in the Kwanza Basin have not documented this pollen.

Late Cretaceous thrips (Thysanoptera) from Hti Lin amber

The present study provides a first investigation of fossil thrips from the Late Cretaceous. It deals with two specimens—Avithrips yellae gen. et sp. n. and Campanithrips kyakhei gen. et sp. n.—which are preserved as inclusions in Campanian Hti Lin (or Tilin) amber from Myanmar. Their taxonomic classification in the families Melanthripidae and Stenurothripidae, as well as an adhering pollen grain suggest that both thrips may have been associated with flowers.

STUDIES ON THE POLLEN MORPHOLOGY OF SOME WEEDY FLORA OF NIZAMABAD DISTRICT OF TELANGANA STATE, INDIA

The present work is aimed to study the pollen morphology of weed plants by light microscopy (LM). Polleniferous material of eight weed plants viz., Mimosa pudica, Cleome viscosa, Tribulus terrestris, Lantana camara, Commelina benghalensis, Ziziphus mauritiana, Cardiospermum halicacabum and Datura stramonium were collected from in and around agricultural lands of Nizamabad district, Telangana, India during 2022-2023.The pollen features viz., shape, apertures and the sporoderm pattern was studied. The pollen grains studied showed spheroidal, sub- prolate, eu-oblate, oblate-spheroidal, oblate to per oblate shape. The apertural diversity include tricolporate, triporate, pantoporate and monosulcate condition. The Exine ornamentation is indicated by psilate in three species, striate in two, reticulate in another two species and one species possess microechinate pattern. The diversity in pollen features are helpful in the identification of the taxa at various levels. This study highlights the some of the common weed pollen morphological features useful to distinguish the species of weeds.

THE PHARMACEUTICAL BOTANICAL STUDIES ON THE ENDEMIC Asperula pestalozzae Boiss. (RUBIACEAE)

In this study, endemic Asperula pestalozzae Boiss. (Rubiaceae) was investigated in aspects of pharmaceutical botany. The morphological, anatomical, micromorphological, palynological, and chemical (antioxidant activity and total amount of phenolic substance) characteristics were reported in detail for the first time. Expanded descriptions and images of A. pestalozzae were given. The anatomical description was presented in detail and supported by photographs. The stem is usually angular or orbicular shaped and the leaf is monofacial. Its trichome and pollen micromorphology were examined with a scanning electron microscope (SEM). The pollen grains of A. pestalozzae are monad, radial symmetry, isopolar, and hexacolpate (sometimes heptacolpate). DPPH and ABTS radicals were used to determine antioxidant activity. The DPPH 50% inhibition concentration (IC50) value was found to be 0.0011±0.0002 mg/ml for standard gallic acid and 0.134±0.017 mg/ml for A. pestalozzae extract. 0.1 mg/ml extract calculated 0.022±0.36 Mm TEAC activity; 1.437±0.51 mM TEAC activity was determined in 10 mg/ml extract. The total amount of phenolic substances was calculated as 53 mg gallic acid equivalent (GAE).

Blooming calendar and polliniferous plants in Djuanda Great Forest Park, West Java, Indonesia: Implication for beekeeping management

Abstract. Husodo T, Wulandari I, Saputri Y, Kasmara H, Hermawan W, Kusmoro J, Shanida SS, Khairina F, Haydar MRA, Asyraf MN, Febrian RR. 2024. Blooming calendar and polliniferous plants in Djuanda Great Forest Park, West Java, Indonesia: Implication for beekeeping management. Biodiversitas 25: 3216-3229. Information was unavailable regarding the types of pollinator plants and their blooming periods in Djuanda Great Forest Park, West Java, Indonesia. Information about flower blooming seasons was useful for various purposes. These findings will provide a basis for understanding the importance of Apis cerana Fabricius, 1793 in plant pollination and plant species resources for honey bees so that beekeeping practices can be carried out sustainably. The blossoming period of a plant is determined by its blooming period at the time of observation. The blooming period is observed every month in the second and fourth weeks for six months (December 2021-May 2022). Pollen collection was carried out in August 2021 (dry season). Pollen identification was carried out using the acetolysis method, which involves dissolving the non-pollen components of a sample to reveal the pollen grains, thereby enabling accurate identification. An overview of the observation records revealed the presence of 249 plant species from 82 families. The Asteraceae family has the most abundant species richness. Most plants were identified as pollinator plants (30.52%), nectariferous plants (10.04%), and plants that produce both (18.47%). Flowering plants of melliferous plants for honeybees are available throughout the rest of the year, especially from December to May. Therefore, to optimize honey harvesting, it is important to establish multiple colonies during periods of large honey flows. Honeybees may use alternative sugar sources beekeepers provide, such as fruit juice, during nectar scarcity. We would like to know more about the year-round bloom calendar. Sharing knowledge with farmers about the availability of melliferous plants in certain months will empower them to make decisions for sustainable beekeeping.

The first record of ants as potential pollinators of a Neotropical tree species (Lomatia hirsuta Diels ex J.F.Macbr., Proteaceae)

AbstractWe provide evidence that Camponotus chilensis (Spinola) visit flowers of the Radal tree (Lomatia hirsuta Diels ex J.F.Macbr.), possibly acting as pollinators of this important tree of the Proteaceae family in the Andean Patagonian forests of Argentina. We found several ant workers transporting pollen from different trees during the blooming season. Pollen transported by workers varied in amount, with some individuals observed fully coated with pollen grains. This note constitutes the first observation of ant activity on the flowers of this plant species and also the first potential example of a tree pollinated by ants in the Neotropics. This note highlights the importance of natural history data in the emergent study field of ant‐pollination.

Honey Bee Products as Bio Indicator of Heavy Metals Pollution and Health Risk Assessment Through the Consumption of Multifloral Honey Collected in Azad Kashmir, Pakistan.

The study assessed the health risks associated with heavy metal ingestion and explored the use of honey bee products as a bio-indicator for heavy metal pollution. All honey bee products tested showed heavy metals, but some honey samples had concentrations exceeding permissible limits for Cd, Pb, Ni, and Cr. The mean concentrations of heavy metals (mg/kg) in the honey, propolis, bee wax, and bee pollen were Fe (1.32) > Zn (1.31) > Pb (0.46) > Ni (0.18) > Cr (0.16) > Cu (0.14) > Co (0.12) > Mn (0.05) > Cd (0.03), Fe (8) > Zn (1.13) > Mn (0.59) > Pb (0.13) > Ni (0.07) > Cu (0.06) > Co (0.05) > Cr (0.03) > Cd (0.02), Fe (1.31) > Pb (0.41) > Ni (0.407) > Zn(0.25) > Mn (0.12) > Co(0.10) > Cu (0.07) > Cr (0.05) > Cd (0.002), and Fe (2.2) > Zn (0.75) > Ni (0.25) > Pb (0.16) > Cu (0.05) > Mn (0.045) > Co (0.04) > Cr (0.01) > Cd(0.002), respectively. Similarly, the mean concentration of heavy metals (mg/kg) in the soil, flowers and pine pollen was Fe (539.08) > Zn (89.53) > Mn (66.91) > Ni (58.5) > Co (19.2) > Cr (11.42) > Pb (6.58) > Cu (5.71) > Cd (0.19), Fe (3.12) > Zn (0.95) > Mn (0.72) > Ni (0.29) > Cu (0.16) > Cr (0.14) > Pb (0.059) > Co (0.057) > Cd (0.003) and Fe (2.59) > Zn (1.75) > Mn (0.43) > Pb (0.34) > Co (0.1) > Cr (0.07) > Cu (0.06) > Cd (0.039) > Ni (0.03), respectively. The atomic absorption spectrophotometry procedure was validated through a recovery study and achieved accuracy through the limit of detection (LOD) and limit of quantification (LOQ). The mean Bio concentration factor (BCF) indicated that the transfer from soil to honey was higher than from soil to flower. The metal pollution index (MPI) of the selected indicators was in descending order: soil > honey > flowers > propolis > pine pollen > beeswax > bee pollen. The hazard quotient (HQ) and hazard index (HI) were below one, showing no chronic health risk. The carcinogenic risk (CR) of Cd, Cr, and Ni in honey for children, male and female adults for the consumers exceeds the acceptable level, making Cd, Cr, and Ni the most concerning heavy metals in honey. The study suggests that regular monitoring of heavy metal pollution is essential.

Simultaneous knockout of cytosolic and plastidial disproportionating enzymes disrupts grain setting and filling in rice.

Rice (Oryza sativa) plants contain plastidial and cytosolic disproportionating enzymes (DPE1 and DPE2). Our previous studies showed that DPE2 acts on maltose, the major product of starch degradation in pollens, releasing one glucose to fuel pollen tube growth and fertilization, whereas DPE1 participates in endosperm starch synthesis by transferring maltooligosyl groups from amylose to amylopectin, and removing excess short maltooligosaccharides. However, little is known about their integrated function. Here, we report that the coordinated actions of DPE1 and DPE2 contribute to grain setting and filling in rice. The dpe1dpe2 mutants could not be isolated from the progeny of heterozygous parental plants but were obtained via anther culture. Unlike that reported in Arabidopsis (Arabidopsis thaliana) and potato (Solanum tuberosum), the dpe1dpe2 rice plants grew normally but only yielded a small number of empty, unfilled seeds. In the dpe1dpe2 seeds, nutrient accumulation was substantially reduced, and dorsal vascular bundles were also severely malnourished. Zymogram analyses showed that changes in activities of the major starch-synthesizing enzymes matched well with various endosperm phenotypes of mutant seeds. Mechanistically, DPE1 deficiency allowed normal starch mobilization in leaves and pollens but affected starch synthesis in endosperm, while DPE2 deficiency blocked starch degradation, resulting in substantially decreased levels of the sugars available for pollen tube growth and grain filling. Overall, our results demonstrate the great potential of DPE1-DPE2 as an important regulatory module to realize higher crop yields and present a promising target for regulating nutrient accumulation in cereal crop endosperm.

Phenotypic characteristics of black apricot Prunus × dasycarpa cultivar ‘Shlor-Tsiran’ in Armenia

ABSTRACT ‘Shlor-Tsiran’ (literally called ‘Plum-Apricot’) is an old black apricot cultivar, which is traditionally cultivated in Armenia. Taxonomically, it belongs to Prunus × dasycarpa Ehrh., which is a spontaneous hybrid of apricot and cherry plum (P. armeniaca L. × P. cerasifera Ehrh.). Currently, ‘Shlor-Tsiran’ is considered to be very rare in Armenia and it occurs as single trees in old home orchards of the Ararat Valley. It is characterised by high frost and disease resistance, late flowering and fruiting compared with other cultivated apricots, and is of interest for the development of apricot cultivars displaying delayed fruit ripening and enhanced frost resistance. This study aims to phenotype the cv. ‘Shlor-Tsiran’ taking into consideration 67 quantitative and qualitative characteristics of vegetative and generative organs, growth and development. Morphological description of the cv. ‘Shlor-Tsiran’, comparing with its parent species, P. armeniaca and P. cerasifera, was performed. Data on fertility and viability of pollen grains, biochemical and nutritional properties of fruits and tree productivity are provided. The data obtained should contribute to a wider use and conservation of the black apricot cv. ‘Shlor-Tsiran’ gene pool, which can be used for breeding purposes as well. The article is illustrated with tables and original photographs.

The invertase gene PWIN1 confers chilling tolerance of rice at the booting stage via mediating pollen development.

Pollen fertility is a primary regulator of grain yield and is highly susceptible to cold and other environmental stress. We revealed the roles of rice cell wall invertase gene PWIN1 in pollen development and chilling tolerance. We uncovered its preferential expression in microspores and bicellular pollen and identified its knock-down and knock-out mutants. pwin1 mutants produced a higher proportion of abnormal pollen than wild-type plants. The contents of sucrose, glucose, and fructose were increased, while ATP content and primary metabolism activity were reduced in the mutant pollen. Furthermore, the loss of function of PWIN1 coincided with an increase in SnRK1 activity and a decrease in TOR activity. Under chilling conditions, pwin1 mutants displayed significantly reduced pollen viability and seed-setting rate, while overexpressing PWIN1 notably increased pollen viability and seed-setting rate as compared with the wild-type, indicating that PWIN1 is essential for rice pollen development and grain yield under cold stress. This study provides insights into the molecular mechanisms underlying rice pollen fertility during chilling stress, and a new module to improve chilling tolerance of rice at the booting stage by molecular design.

Exploring the Floral Biology of Salix alba: Insights into Reproductive Dynamics, Pollen Production and Pollen Morphology in Kashmir Himalayas

This study investigates the floral phenology, pollen production and pollen characteristics of Salix alba (white willow) over the years 2022 and 2023, highlighting inter-annual and individual tree variations. In 2022, male catkins began flowering between March 8 and March 10, while female catkins initiated between March 14 and March 22. Flowering for male catkins lasted until mid-May and for female catkins until late May. In 2023, male catkins started flowering from March 10 to March 14 and female catkins from March 17 to March 24, with similar flowering durations. Inflorescence diameters varied among individual trees, ranging from 4.4 mm to 7.7 mm for male catkins and 6.1 mm to 8.1 mm for female catkins across the two years. Pollen production exhibited significant variability with the highest recorded at 4,600,995,000 grains per tree and the lowest at 498,312,500 grains per tree. On average, trees produced approximately 2,164,836,667 pollen grains. Pollen viability ranged from 75% to 80%, with sizes between 16 µm and 26 µm. The pollen-ovule ratio also showed substantial differences, with the highest ratio observed at 7600:2 and the lowest at 2345:7. These findings underscore the considerable year-to-year and tree-to-tree variation in the reproductive traits of Salix alba, which may have implications for its breeding and conservation strategies.

Forage legume responses to climate change factors

AbstractIncorporating forage legumes into grasslands is a recommended climate change mitigation strategy, but accruing desired benefits from legumes is contingent upon their resilience when exposed to climate change factors (CCF). Our objective was to synthesize literature describing responses to CCF of a broad array of forage legume species, including annuals and perennials from both temperate and tropical/subtropical regions. Most‐represented species in the related literature include alfalfa (Medicago sativa L.), various Trifolium and Lotus species, rhizoma peanut (Arachis glabrata Benth.), and capitata stylo (Stylosanthes capitata Vogel). The data indicate that while CCF effects on forage legumes can be generalized, interactions among CCF, species, and site‐specific soil/climate conditions may cause variation from expected responses. In most instances, exposing forage legumes to CO2 enrichment (eCO2) increased forage accumulation (FA), but elevated temperature (eT) often reduced the magnitude of the positive response to eCO2. Photosynthetic acclimation to eCO2 occurs in non‐N‐fixing plants, but legume nodules are large C sinks and drive sustained increases in legume FA to eCO2. Legume N2 fixation and the proportion of legume N derived from N2 fixation increase with eCO2, but the magnitude of the increases lessens with eT. Legume nutritive value (NV) responses to eCO2 are less pronounced than FA responses, but decreased herbage N and greater nonstructural carbohydrate concentrations are common. Exposure to eT negatively affects NV unless intervals between defoliation events are shortened. Limited data on reproductive performance show CCF affect flower number, pollen grain morphology and viability, and behavior of pollinators, potentially influencing legume reproductive success.

Assessment of Cassava Pollen Viability and Ovule Fertilizability under Red-Light, 6-Benzyl Adenine, and Silver Thiosulphate Treatments.

Understanding pollen and ovule fertility as factors influencing fruit and seed set is important in cassava breeding. Extended daylength with red light (RL) and plant growth regulators (PGRs) have been used to induce flowering and fruit set in cassava without any reference to effects on pollen viability or ovule fertilizability. This study investigated the effects of field-applied RL and PGR on pollen viability and ovule fertilizability. Panels of cassava genotypes with early or moderate flowering responses were used. RL was administered from dusk to dawn. Two PGRs, 6-benzyl adenine (BA), a cytokinin and silver thiosulphate (STS), an anti-ethylene, were applied. Pollen viability was assessed based on pollen grain diameter, in vitro stainability, in vivo germinability, ovule fertilizability, and ploidy level. Treating flowers with RL increased the pollen diameter from 145.6 in control to 148.5 µm in RL, 78.5 to 93.0% in stainability, and 52.0 to 56.9% in ovule fertilizability in treated female flowers. The fruit set also increased from 51.5 in control to 71.8% in RL-treated female flowers. The seed set followed a similar trend. The ploidy level of pollen from RL-treated flowers increased slightly and was positively correlated with pollen diameter (R2 = 0.09 *), ovule fertilization (R2 = 0.20 *), fruit set (R2 = 0.59 *), and seed set (R2 = 0.60 *). Treating flowers with PGR did not affect pollen diameter but increased stainability from 78.5% in control to 82.1%, ovule fertilizability from 42.9 to 64.9%, and fruit set from 23.2 to 51.9% in PGR-treated female flowers. Combined BA + STS application caused the highest ovule fertilizability, fruit, and seed set efficiency. These results show that RL and PGR treatments increase pollen viability and ovule fertilizability. This is important for planning pollination strategies in cassava breeding programmes.

Potent pollen gene regulation by DNA glycosylases in maize.

Although DNA methylation primarily represses TEs, it also represses select genes that are methylated in plant body tissues but demethylated by DNA glycosylases (DNGs) in endosperm or pollen. Activity of either one of two DNGs, MDR1 or DNG102, is essential for pollen viability in maize. Using single-pollen mRNA sequencing on pollen segregating mutations in both genes, we identified 58 candidate DNG target genes that account for 11.1% of the wild-type transcriptome but are silent or barely detectable in the plant body (sporophyte). They are unusual in their tendency to lack introns but even more so in their having TE-like methylation in their CDS. The majority have predicted functions in cell wall modification, and they likely support the rapid tip growth characteristic of pollen tubes. These results suggest a critical role for DNA methylation and demethylation in regulating maize genes with potential for extremely high expression in pollen but constitutive silencing elsewhere.