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The complex processes of pollen germination and pollen tube elongation are important events in the sexual reproduction of flowering plants and are essential to the success of seed formation. However, unfavourable environmental and climatic conditions affect pollen performance negatively. Integrating the application of various biostimulants represents one of the most innovative and promising strategies to improve crop productivity. Biostimulants are known to sustainably improve pollen viability, germination and elongation. However, there is limited information on the effects of biostimulants on pollen grains. The present review investigates the potential of biostimulants (such as seaweed extracts, smoke–water, polyamines, amino acids, melatonin, carbohydrate-based biostimulants and inorganic biostimulants) as signaling molecules that can improve crucial stages of pollen growth in a range of crops, both in optimal and suboptimal environments. Furthermore, this review investigates the stages of pollen development, including uninucleate microspores and different stages of mature pollen, following various biostimulant treatment during the flowering period. Regulation of biostimulant-induced pollen germination and elongation has also been discussed along with recent developments regarding the mechanism of action of biostimulants in various growth aspects of pollen. This review not only summarizes what is known currently, but it also lays the groundwork for future investigations to clarify the complex physiological and molecular processes involved in pollen performance as well as the regulatory systems that are impacted by biostimulants. [ABSTRACT FROM AUTHOR]

Main conclusion: Allotetraploid wheat reflects evolutionary divergence and domestication convergence in the karyotypic and phenotypic evolution, accompanied with the transformation from r- strategy to K- strategy in reproductive fitness. Allotetraploid wheat, the progenitor of hexaploidy bread wheat, has undergone 300,000 years of natural evolution and 10,000 years of domestication. The variations in karyotype and phenotype as well as fertility fitness have not been systematically linked. Here, by combining fluorescent in situ hybridization with the quantification of phenotypic and reproductive traits, we compared the karyotype, vegetative growth phenotype and reproductive fitness among synthesized, wild and domesticated accessions of allotetraploid wheat. We detected that the wild accessions showed dramatically high frequencies of homologous recombination and copy number variations of simple sequence repeats (SSR) comparing with synthetic and domesticated accessions. The phenotypic traits reflected significant differences among the populations shaped by distinct evolutionary processes. The diversity observed in wild accessions was significantly greater than that in domesticated ones, particularly in traits associated with vegetative growth and spike morphology. We found that the active pollen of domesticated accessions exhibited greater potential of germination, despite a lower rate of active pollen compared with the wild accessions, indicating a transformation in reproductive fitness strategy for pollen development in domesticated accessions compared to the wild accessions, from r-strategy to K-strategy. Our results demonstrate the condensation of karyotype and phenotype from natural wild accessions to domesticated accessions in allotetraploid wheats. Ecological strategy transformation should be seriously considered from evolution to domestication in polyploid plants, especially crops, which may provide a perspective on the adaptive evolution of polyploid plants. [ABSTRACT FROM AUTHOR]

The present study investigated the effects of five Iranian male palm pollen grains as pollen sources on the fruit quality of two cultivars, ‘Barhee’ and ‘Piyarom’ (offshoot-derived and tissue culture-derived). The biochemical and enzymatic properties of fruit dates at the Tamar stage (full maturity) enabled the evaluation of pollen source effects on fruit quality. The research location was Jahrom Research Station, Fars Province, Iran, from 2018 to 2019. The pollen sources were genotypes ‘7001’ (control), ‘7005’, ‘7013’, ‘7030’, and ‘B11’. Pollinated with 7013 pollen, Offshoot-erived (OFS) trees of the ‘Barhee’ cultivar had the highest fruit flesh pH (7.07). In contrast, the lowest pH value (5.84) occurred in fruits of Tissue Culture-Derived (TCD) trees of the ‘Piyarom’ pollinated with the 7030. In the OFS ‘Piyarom’ the pollen source 7001 caused the highest fruit TSS (68.83%). When pollinated with the B11, ‘Barhee’ had the lowest fruit TSS (44.90%). In TCD ‘Piyarom’ trees, the 7030 pollen caused the highest TSS (62.53%). By receiving pollen from B11, the ‘Barhee’ produced fruits with the lowest TSS (44.23%). Regardless of being OFS or TCD and of the pollen source, on average, ‘Barhee’ produced fruits with more moisture content than fruits of the ‘Piyarom’. In OFS ‘Piyarom’ trees, pollen from the 7030 caused the highest Fruit Dry Matter (FDM) (87.40%), whereas the ‘Barhee’ pollinated with the 7001 produced fruits with the lowest FDM (67.15%). In TCD ‘Piyarom’ palms, pollen from the 7030 caused the highest FDM (85.19%), compared to the ‘Barhee’ pollinated with the 7013, which showed the lowest FDM (67.87%). Pollen from the 7030 caused the highest total sugar content in the fruits of OFS and TCD ‘Piyarom’ trees. The fruits of OFS ‘Piyarom’ trees had more Fe and Polyphenol Oxidase (PPO) activity than TCD ‘Piyarom’ trees. [ABSTRACT FROM AUTHOR]

Self-incompatibility (SI) is a genetic mechanism that promotes out-breeding and maintains genetic diversity in plant species. The inhibition of pollen germination and pollen tube growth is one of the major characteristics of SI response. The involvement of Ca2+ signaling mediated by Ca2+ sensors in the SI response has been demonstrated to affect the germination of incompatible pollen and the normal elongation of pollen tubes. In this study, the calmodulin-like 49 (BrCML49) gene in Chinese cabbage (Brassica rapa L. ssp. pekinensis) was down-regulated expression during the SI process, indicating that BrCML49 may participate in the regulation of SI response. The transient suppression of BrCML49 gene induced the abnormal germination of pollen in vitro, which showed the putative positive roles of BrCML49 in regulating pollen germination. The inhibited germination of self- and cross-pollen in BrCML49-suppressed stigma was also observed, which revealed the activated SI response. After BrCML49 suppression, the increases in Ca2+ level in stigmatic papilla cells were consistent with the increases in ROS/H2O2 contents in the stigma, which may be essential for the occurrence of SI response. Furthermore, heterologous overexpression of BrCML49 in Arabidopsis validated the positive regulation of BrCML49 in pollen germination and pollen tube growth. In addition, BrCML49 overexpressed Arabidopsis exhibited an enhanced tolerance of pollen germination to high Ca2+ condition. These results will provide valuable information for understanding the roles of BrCML49 in regulating pollen germination and pollen tube growth during SI process in Chinese cabbage. [ABSTRACT FROM AUTHOR]

Major constituents of the plant cell walls are structural proteins that belong to the hydroxyproline-rich glycoprotein (HRGP) family. Leucine-rich repeat extensin (LRX) proteins contain a leucine-rich domain and a C-terminal domain with repetitive Ser–Pro3–5 motifs that are potentially to be O -glycosylated. It has been demonstrated that pollen-specific LRX8–LRX11 from Arabidopsis thaliana are necessary to maintain the integrity of the pollen tube cell wall during polarized growth. In HRGPs, including classical extensins (EXTs), and probably in LRXs, proline residues are converted to hydroxyproline by prolyl-4-hydroxylases (P4Hs), thus defining novel O -glycosylation sites. In this context, we aimed to determine whether hydroxylation and subsequent O -glycosylation of Arabidopsis pollen LRXs are necessary for their proper function and cell wall localization in pollen tubes. We hypothesized that pollen-expressed P4H4 and P4H6 catalyze the hydroxylation of the proline units present in Ser–Pro3–5 motifs of LRX8–LRX11. Here, we show that the p4h4-1 p4h6-1 double mutant exhibits a reduction in pollen germination rates and a slight reduction in pollen tube length. Pollen germination is also inhibited by P4H inhibitors, suggesting that prolyl hydroxylation is required for pollen tube development. Plants expressing pLRX11::LRX11-GFP in the p4h4-1 p4h6-1 background show partial re-localization of LRX11–green fluorescent protein (GFP) from the pollen tube tip apoplast to the cytoplasm. Finally, immunoprecipitation-tandem mass spectrometry analysis revealed a decrease in oxidized prolines (hydroxyprolines) in LRX11–GFP in the p4h4-1 p4h6-1 background compared with lrx11 plants expressing pLRX11::LRX11-GFP. Taken together, these results suggest that P4H4 and P4H6 are required for pollen germination and for proper hydroxylation of LRX11 necessary for its localization in the cell wall of pollen tubes. [ABSTRACT FROM AUTHOR]

SUMMARY: Low phytic acid (lpa) crop is considered as an effective strategy to improve crop nutritional quality, but a substantial decrease in phytic acid (PA) usually has negative effect on agronomic performance and its response to environment adversities. Myo‐inositol‐3‐phosphate synthase (MIPS) is the rate‐limiting enzyme in PA biosynthesis pathway, and regarded as the prime target for engineering lpa crop. In this paper, the rice MIPS gene (RINO2) knockout mutants and its wild type were performed to investigate the genotype‐dependent alteration in the heat injury‐induced spikelet fertility and its underlying mechanism for rice plants being imposed to heat stress at anthesis. Results indicated that RINO2 knockout significantly enhanced the susceptibility of rice spikelet fertility to heat injury, due to the severely exacerbated obstacles in pollen germination and pollen tube growth in pistil for RINO2 knockout under high temperature (HT) at anthesis. The loss of RINO2 function caused a marked reduction in inositol and phosphatidylinositol derivative concentrations in the HT‐stressed pollen grains, which resulted in the strikingly lower content of phosphatidylinositol 4,5‐diphosphate (PI (4,5) P2) in germinating pollen grain and pollen tube. The insufficient supply of PI (4,5) P2 in the HT‐stressed pollen grains disrupted normal Ca2+ gradient in the apical region of pollen tubes and actin filament cytoskeleton in growing pollen tubes. The severely repressed biosynthesis of PI (4,5) P2 was among the regulatory switch steps leading to the impaired pollen germination and deformed pollen tube growth for the HT‐stressed pollens of RINO2 knockout mutants. Significance Statement: For engineering lpa rice, the knockout of RINO2 significantly enhanced susceptibility of spikelet fertility to heat injury at anthesis, which was mostly ascribed to the heat injury‐induced obstacle in pollen germination and pollen tube growth. High temperature significantly reduced the concentrations of inositol and PI (4,5) P2 concentration in pollen grains, this occurrence was strongly responsible for the disorder Ca2+ gradient and actin filament cytoskeleton in growing pollen tubes. These findings provide new understanding for the regulatory mechanism by which the loss of RINO2 function negatively affects pollen germination and pollen tube growth in response to HT exposure at anthesis. [ABSTRACT FROM AUTHOR]

The European hazelnut (Corylus avellana L.) is a self-incompatible, wind-pollinated species of significant economic-productive interest, mainly cultivated between the Mediterranean basin and the Black Sea. Hazelnut breeding programs and high cropping in commercial orchards are necessarily linked to the availability of fertile pollen with wide germinability and high viability. The objective was to develop an improved method to determine the germinability of pollen, comparing the results with those found in the literature. Pollen germinability was firstly evaluated on a wild-type accession using boric acid (H3BO3), calcium nitrate (Ca(NO3)2), magnesium sulfate (MgSO4), potassium nitrate (KNO3), casein hydrolysate and different concentrations of sugars, including sucrose (10, 15 and 25%) and two monosaccharides, glucose (15%) and fructose (15%). The optimal composition included 15% sucrose in a semi-solid medium composed of 1% animal gelatin, containing collagen. This formulation was then tested on three cultivars of commercial interest, evaluating the effect of different concentrations of sucrose. The comparison between different in vitro germination methods showed that the hanging drop technique in a semi-solid medium provides a statistically higher germination index compared to the liquid and solid/agarized techniques. This study proposes an easy-to-use medium for the in vitro germination of Corylus avellana L. pollen. [ABSTRACT FROM AUTHOR]

Adaptation or acclimation to local temperature regimes has often been used as a proxy for predicting how plant populations will respond to impending novel conditions driven by human-caused climate change. To understand how plants may successfully respond to increasing air temperatures (extreme and moderate) in the future, we explored how temperature tolerance traits differ in populations of Solanum carolinense from northern (MN) and southern (TX) regions of the continental USA in a two-experiment study. In the first experiment, we compared the heat and cold tolerance in vegetative (sporophyte) and reproductive (male gametophyte) traits. In the second experiment, we studied if long-term heat influences plant development by examining how development in moderate heat affected reproductive structures and reproductive success. We found that temperature sensitivity differed between southern populations, which regularly experience extreme heat, and northern populations which do not. In contrast to our expectations, northern populations appeared more heat-tolerant than southern populations for vegetative traits such as chlorophyll stability and reproductive traits such as pollen germination. Our results are consistent with a heat-avoidance, rather than tolerance mechanism to mitigate extreme heat during pollen germination. In the second experiment, plants developing under the moderate heat treatment had significantly smaller reproductive structures and reduced seed production (27% fewer seeds on average than in the control treatment). Reproductive structures that developed in moderate heat were also reduced in size, particularly in the northern populations relative to populations from the south. We conclude that rising temperatures have the potential to incur substantial negative consequences for the reproductive success of individuals in this species and that some populations already mitigate stressful temperature conditions through phenotypic plasticity. [ABSTRACT FROM AUTHOR]

Rice straw lignin was extracted via alkaline hydrolysis and structurally characterized using FT-IR and 1H NMR spectra. Ethyl acetate extract of acid solubilized lignin was found to contain p-coumaric acid, ferulic acid and caffeic acid as major phenolic acids which were isolated and characterized using spectral data. Amides of isolated phenolic acids were synthesized by their reaction with propyl and butyl amines using microwave irradiation and analysed using spectral studies. Phenolic acids and amides were evaluated for their effect on pollen germination and tube growth in pumpkin. Pollen tube length was significantly increased with N-butyl-3-(3, 4-dihydroxyphenyl) acrylamide and N-butyl-3-(4-hydroxyphenyl) acrylamide at 5 ppm concentration than the control. These results could be utilised in increasing pollen tube length of Cucurbita pepo while making interspecific cross between C. moschata and C. pepo in order to transfer hull-less character of C. pepo to virus resistant C. moschata genotypes. [ABSTRACT FROM AUTHOR]

Abstract Background The La-related proteins (LARPs) are a superfamily of RNA-binding proteins associated with regulation of gene expression. Evidence points to an important role for post-transcriptional control of gene expression in germinating pollen tubes, which could be aided by RNA-binding proteins. Results In this study, a genome-wide investigation of the LARP proteins in eight plant species was performed. The LARP proteins were classified into three families based on a phylogenetic analysis. The gene structure, conserved motifs, cis-acting elements in the promoter, and gene expression profiles were investigated to provide a comprehensive overview of the evolutionary history and potential functions of ZmLARP genes in maize. Moreover, ZmLARP6c1 was specifically expressed in pollen and ZmLARP6c1 was localized to the nucleus and cytoplasm in maize protoplasts. Overexpression of ZmLARP6c1 enhanced the percentage pollen germination compared with that of wild-type pollen. In addition, transcriptome profiling analysis revealed that differentially expressed genes included PABP homologous genes and genes involved in jasmonic acid and abscisic acid biosynthesis, metabolism, signaling pathways and response in a Zmlarp6c1::Ds mutant and ZmLARP6c1-overexpression line compared with the corresponding wild type. Conclusions The findings provide a basis for further evolutionary and functional analyses, and provide insight into the critical regulatory function of ZmLARP6c1 in maize pollen germination.

Background: The La-related proteins (LARPs) are a superfamily of RNA-binding proteins associated with regulation of gene expression. Evidence points to an important role for post-transcriptional control of gene expression in germinating pollen tubes, which could be aided by RNA-binding proteins. Results: In this study, a genome-wide investigation of the LARP proteins in eight plant species was performed. The LARP proteins were classified into three families based on a phylogenetic analysis. The gene structure, conserved motifs, cis-acting elements in the promoter, and gene expression profiles were investigated to provide a comprehensive overview of the evolutionary history and potential functions of ZmLARP genes in maize. Moreover, ZmLARP6c1 was specifically expressed in pollen and ZmLARP6c1 was localized to the nucleus and cytoplasm in maize protoplasts. Overexpression of ZmLARP6c1 enhanced the percentage pollen germination compared with that of wild-type pollen. In addition, transcriptome profiling analysis revealed that differentially expressed genes included PABP homologous genes and genes involved in jasmonic acid and abscisic acid biosynthesis, metabolism, signaling pathways and response in a Zmlarp6c1::Ds mutant and ZmLARP6c1-overexpression line compared with the corresponding wild type. Conclusions: The findings provide a basis for further evolutionary and functional analyses, and provide insight into the critical regulatory function of ZmLARP6c1 in maize pollen germination. [ABSTRACT FROM AUTHOR]

The knowledge of pollen morphology, suitable storage condition, and species compatibility is vital for a successful grapevine improvement programme. Ten grape genotypes from three different species, viz., Vitis vinifera L., Vitis parviflora Roxb., and Vitis champini Planc., were studied for their pollen structure and pollen storage with the objective of determining their utilization in grape rootstock improvement programs. Pollen morphology was examined through the use of a scanning electron microscope (SEM). The viability of the pollen was assessed using 2,3,5-triphenyltetrazolium chloride (TTC). In vitro pollen germination was investigated using the semi-solid medium with 10 % sucrose, 100 mg/L boric acid, and 300 mg/L calcium nitrate. The results revealed variations in pollen micro-morphology in 10 genotypes, with distinct pollen dimensions, shapes, and exine ornamentation. However, species-wise, no clear difference was found for these parameters. Pollen of V. parviflora Roxb. and Dogridge was acolporated and did not germinate. The remaining eight genotypes exhibited tricolporated pollen and showed satisfactory in vitro pollen germination. Storage temperature and duration interactions showed that, at room temperature, pollen of most of the grape genotypes can be stored for up to 1 day only with an acceptable pollen germination rate (>30 %). However, storage for up to 7 days was successfully achieved at 4 °C, except for 'Pearl of Csaba'. The most effective storage conditions were found to be at -20 °C and -196 °C (in liquid N2), enabling pollen storage for a period of up to 30 days, and can be used for pollination to overcome the challenge of asynchronous flowering. Four interspecific combinations were studied for their compatibility, among which V. parviflora Roxb. × V. vinifera L. (Pusa Navrang) and V. parviflora Roxb. × V. champini Planc. (Salt Creek) showed high crosscompatibility, offering their potential use for grape rootstock breeding. However, V. parviflora Roxb. × V. vinifera L. (Male Hybrid) recorded the lowest compatibility index among studied crosses. In the case of self-pollinated flowers from V. parviflora Roxb. and V. parviflora Roxb. × V. champini Planc. (Dogridge), pollen failed to germinate on the stigma due to male sterility caused by acolporated pollen. As a result, the flowers of these genotypes functioned as females, which means they are ideal female parents for grape breeding without the need for the tedious process of emasculation. [ABSTRACT FROM AUTHOR]

Pollen allelopathy positively or negatively influences the fertilization of plants and has great significance from ecological perspectives. The release of allelochemicals from foreign pollen grains on the stigmatic surface obstructs the processes of fertilisation, seed establishment, tube formation, stigma receptivity, and pollen germination. So far, pollen allelopathy has received little attention and still a growing topic of ecological studies. Therefore, a literature review was undertaken to provide the valuable information regarding the ecological and reproductive implications of pollen allelopathy, heterospecific pollen transfer mechanisms of allelopathic anemophilous and entomophilous plants, and to shed light on the biochemistry and mode of action of allelochemicals. The majority of entomophilous plants share pollinators within communities, and heterospecific pollen transfer by both anemophilous and entomophilous plants causes a reduction in their reproductive success, like pollen germination, tube development, ovule maturation and seed set. For detailed study of pollen allelopathy, a few factors should be considered like metrological parameters, distance travelled by pollen, pollen viability, and stigma receptivity during foreign pollen deposition. A thorough understanding of the biochemical and enzymatic processes that occur after foreign pollen is deposited on the native stigma will open up new perspectives on plant reproduction. Pollen allelochemicals, which have important significance as biocontrol agents for the maintenance of agroecosystems, need to be identified and characterised. The ecological aspects of pollen allelopathy may be well understood with the help of field studies. [ABSTRACT FROM AUTHOR]

The development and germination of pollen play crucial roles in the sexual reproduction of plants, and this process holds great potential for improving grain yield in crops. In this study, we established a germination system for foxtail millet pollen and identified culture temperature and time as key factors for successful germination. Specifically, we found that a temperature of 22 °C and a duration of 30 min provided the optimal conditions for pollen germination. It is worth noting that if the culture temperature was too high, the top of the pollen tube would expand. Additionally, we discovered that sucrose and boric acid were essential for in vitro germination of foxtail millet pollen, with 15% sucrose and 0.01% boric acid being the suitable concentrations. Moreover, we observed that the time required for pollen germination in foxtail millet was significantly shorter compared to other cereals, opening up new avenues for studying the stress resistance of foxtail millet from a reproductive development perspective. This germination system holds promise for guiding the application of male sterility or cross breeding techniques.Key Message: The establishment of in vitro pollen germination and discovery of key influencing factors in C4 gramineae Foxtail Millet. [ABSTRACT FROM AUTHOR]

Stigma development and successful pollination are essential for the continuous existence of flowering plants. However, the specific mechanisms regulating these important processes are not well understood. In this study, we investigated the development of the stigma in Fraxinus mandshurica, dividing it into three stages: S1, S2, and S3. Transcriptome data were used to analyze the gene expression patterns across these developmental stages, and 6,402 genes were observed to exhibit variable expression levels. Our analysis revealed a significant enrichment of pathways related to reactive oxygen species (ROS) and flavonoids, as indicated by the Kyoto Encyclopedia of Genes and Genomes enrichment analysis of the differentially expressed genes. Further examination by cluster analysis and quantitative polymerase chain reaction revealed that 58 genes were associated with ROS synthesis and seven genes were linked to flavonoid synthesis during the S2 and S3 stages. ROS accumulated during stigma development, which decreased rapidly upon pollen germination and pollen tube elongation, as confirmed by H2DCFDA staining. Moreover, ROS levels in mature stigmas were reduced by treatment with ROS scavengers, such as copper (II) chloride, sodium salicylate, and diphenyleneiodonium, an inhibitor of NADPH oxidases, which enhanced pollen adhesion and germination. These findings suggest that the balance between ROS production and sequestration plays a critical role in regulating stigma development and pollen germination in Fraxinus mandshurica.

Abstract Pollen germination is a crucial process in the life cycle of flowering plants, signifying the transition of quiescent pollen grains into active growth. This study delves into the dynamic changes within organelles and the pivotal role of autophagy during lily pollen germination. Initially, mature pollen grains harbor undifferentiated organelles, including amyloplasts, mitochondria, and the Golgi apparatus. However, germination unveils remarkable transformations, such as the redifferentiation of amyloplasts accompanied by starch granule accumulation. We investigate the self-sustained nature of amylogenesis during germination, shedding light on its association with osmotic pressure. Employing BODIPY 493/503 staining, we tracked lipid body distribution throughout pollen germination, both with or without autophagy inhibitors (3-MA, NEM). Typically, lipid bodies undergo polarized movement from pollen grains into elongating pollen tubes, a process crucial for directional growth. Inhibiting autophagy disrupted this essential lipid body redistribution, underscoring the interaction between autophagy and lipid body dynamics. Notably, the presence of tubular endoplasmic reticulum (ER)-like structures associated with developing amyloplasts and lipid bodies implies their participation in autophagy. Starch granules, lipid bodies, and membrane remnants observed within vacuoles further reinforce the involvement of autophagic processes. Among the autophagy inhibitors, particularly BFA, significantly impede germination and growth, thereby affecting Golgi morphology. Immunogold labeling substantiates the pivotal role of the ER in forming autophagosome-like compartments and protein localization. Our proposed speculative model of pollen germination encompasses proplastid differentiation and autophagosome formation. This study advances our understanding of organelle dynamics and autophagy during pollen germination, providing valuable insights into the realm of plant reproductive physiology.

Context. Reproductive success in dioecious plant species may be limited by severe pollen limitation owing to their separate sexes and pollination barriers. Aims. Dodonaea viscosa subsp. angustifolia (Jacq.) (Sapindaceae) is a dioecious and wind-pollinated species that has a long flowering period. This study sought to determine the relationship between its reproductive behaviour and pollen availability during different flowering phases. Methods. Extra-stigmatic pollen germination and reproductive performance during different phases of flowering were investigated and correlated with pistil elongation under natural conditions. Results. The species offers whole stigmatic and stylar surfaces for pollen to land and germinate under natural conditions. During pollen-limiting conditions, the length of the pistil increases significantly to enhance pollen capture. Depending on where on the pistil pollen lands, the timing of pollen tube arrival at the ovary varies. Conclusions. Dodonaea viscosa subsp. angustifolia is the first reported wild species in the Sapindaceae where pistil elongation is regulated by pollination conditions and extra-stigmatic pollen germination ensures reproduction during phases of differing pollen availability. Our results indicated that the flexibility of female function and reproductive behaviour in Dodonaea viscosa subsp. angustifolia adds to the evolutionary possibilities to overcome pollination constraints. Implications. This unique strategy for increasing female fitness through pollen presentation in D. viscosa subsp. angustifolia could be explored in other subspecies of D. viscosa on the Australian subcontinent. [ABSTRACT FROM AUTHOR]

Pollen germination is a crucial process in the life cycle of flowering plants, signifying the transition of quiescent pollen grains into active growth. This study delves into the dynamic changes within organelles and the pivotal role of autophagy during lily pollen germination. Initially, mature pollen grains harbor undifferentiated organelles, including amyloplasts, mitochondria, and the Golgi apparatus. However, germination unveils remarkable transformations, such as the redifferentiation of amyloplasts accompanied by starch granule accumulation. We investigate the self-sustained nature of amylogenesis during germination, shedding light on its association with osmotic pressure. Employing BODIPY 493/503 staining, we tracked lipid body distribution throughout pollen germination, both with or without autophagy inhibitors (3-MA, NEM). Typically, lipid bodies undergo polarized movement from pollen grains into elongating pollen tubes, a process crucial for directional growth. Inhibiting autophagy disrupted this essential lipid body redistribution, underscoring the interaction between autophagy and lipid body dynamics. Notably, the presence of tubular endoplasmic reticulum (ER)-like structures associated with developing amyloplasts and lipid bodies implies their participation in autophagy. Starch granules, lipid bodies, and membrane remnants observed within vacuoles further reinforce the involvement of autophagic processes. Among the autophagy inhibitors, particularly BFA, significantly impede germination and growth, thereby affecting Golgi morphology. Immunogold labeling substantiates the pivotal role of the ER in forming autophagosome-like compartments and protein localization. Our proposed speculative model of pollen germination encompasses proplastid differentiation and autophagosome formation. This study advances our understanding of organelle dynamics and autophagy during pollen germination, providing valuable insights into the realm of plant reproductive physiology. [ABSTRACT FROM AUTHOR]

SUMMARY: Phosphatidylinositol 4‐phosphate 5‐kinase (PIP5K) is a key enzyme producing the signaling lipid phosphatidylinositol 4,5‐bisphosphate [PtdIns(4,5)P2] in eukaryotes. Although PIP5K genes are reported to be involved in pollen tube germination and growth, the essential roles of PIP5K in these processes remain unclear. Here, we performed a comprehensive genetic analysis of the Arabidopsis thaliana PIP5K4, PIP5K5, and PIP5K6 genes and revealed that their redundant function is essential for pollen germination. Pollen with the pip5k4pip5k5pip5k6 triple mutation was sterile, while pollen germination efficiency and pollen tube growth were reduced in the pip5k6 single mutant and further reduced in the pip5k4pip5k6 and pip5k5pip5k6 double mutants. YFP‐fusion proteins, PIP5K4‐YFP, PIP5K5‐YFP, and PIP5K6‐YFP, which could rescue the sterility of the triple mutant pollen, preferentially localized to the tricolpate aperture area and the future germination site on the plasma membrane prior to germination. Triple mutant pollen grains under the germination condition, in which spatiotemporal localization of the PtdIns(4,5)P2 fluorescent marker protein 2xmCHERRY‐2xPHPLC as seen in the wild type was abolished, exhibited swelling and rupture of the pollen wall, but neither the conspicuous protruding site nor site‐specific deposition of cell wall materials for germination. These data indicate that PIP5K4–6 and their product PtdIns(4,5)P2 are essential for pollen germination, possibly through the establishment of the germination polarity in a pollen grain. Significance Statement: Phosphatidylinositol 4‐phosphate 5‐kinase (PIP5K) and its product phosphatidylinositol 4,5‐bisphosphate [PtdIns(4,5)P2], a membrane lipid known to serve as a signal for cell polarization, dynamically localize to the future germination site on the plasma membrane of Arabidopsis pollen. Comprehensive genetic analysis reveals that Arabidopsis PIP5K4–6, which belong to a conserved clade in the molecular phylogenetic tree of angiosperm PIP5Ks, redundantly play an essential role in pollen germination, through the establishment of germination polarity. [ABSTRACT FROM AUTHOR]

Maize is a dynamic cereal of world’s agriculture community. It is grown in spring and autumn seasons in Pakistan and both pistillate and staminate flowers experience severe temperature stress during spring sowing (February sowing) at reproductive phase, which ultimately results in poor seed setting because of increased silk dryness and pollen desiccation. In-vivo haploid induction was performed by using 2nd generation tropically adapted maize haploid inducer allocated from CIMMYT. Indigenously developed maize double haploid (DH) lines using local segregating population as source were screened out against high temperature stress. DH lines were evaluated and selected by using various indicators cell membrane thermostability (CMT), leaf temperature (LT), pollen production potential (PPP), pollen germination %age (PG%), pollen tube length (PTL), grain yield per plant (GY/P), plant height (PH), ear height (EH), days to tasseling (DT), days to silking (DS), number of grains per row (NGPR) and number of rows per cob (NRPC). Significant differences were noted at allelic level among the DH lines for high temperature tolerance related indicators, which provided wide range of option for selection, opportunity to improve tolerance level against high temperature stress and usage of these DH lines in different future maize breeding programs. Correlation coefficient analysis depicted PH, NGPR, HGW, PPP, PTL, and PG as suitable selection criteria for GY/P. The most effective physiological benchmarks for evaluating germplasm resistance to high temperature stress are CMT, PG%, and PTL. According to principal component analysis (PCA) DH lines viz. 5 (PBG-5), 11 (PBG-11), 15 (PBG-15), 19 (PBG-19), 24(PBG-24), 30(PBG-30), 33(PBG-33), 39 (PBG-39), 46 (PBG-46) and 52 (PBG-52) showed high level of diversity and performed well under the normal and high temperature stress conditions and DH lines viz. 10 (PBG-10), 13 (PBG-13), 26 (PBG-26), 37 (PBG-37) and 51 (PBG-51) performed poor under the normal and high temperature stress conditions. To develop maize varieties that can thrive in high-temperature conditions, it is necessary to cultivate DH lines that exhibit strong adaptability when exposed to induced stress. These lines could serve as a valuable genetic resource, as they likely contain a diverse array of genes that contribute to high temperature tolerance. [ABSTRACT FROM AUTHOR]

Roses are known for their low pollen quality. It remains unclear how many days of pollen should be used in order not to reduce crossbreeding success. The study was conducted to determine whether short-term pollen storage is effective on the crossing success of roses comparatively in vivo and in vitro. The study was conducted in a greenhouse and a cytology laboratory at Ankara University, Turkey. The 'Avalanche' rose variety was used as the seed parent, and 'Magnum' was the pollen parent. A total of 210 crosses were made. Pollens were used immediately (day 0) and stored at +4°C for 6 days after collection. The pollen viability by IKI and the germination rates by the petri dish method, the fruit and seed set, the fruit and seed weight, and the seed germination rate were recorded. All examined traits showed a decreasing trend as the storage time increases. The pollen germination rates were recorded at 1.63% for stored pollen at six days and 15.27% for fresh pollen. The highest fruit and seed set rates were obtained from crossing with pollen stored for one day. The fruit set decreased below 10% as of the 5th day, and the seed numbers decreased 1.8 times compared to one day of storage. No germination was observed in seeds obtained from crosses with pollen stored for 5 or 6 days. A positive correlation was found between seed number and pollen germination rate. The study concluded that successful crossing could be made with pollen stored at +4°C for up to 3 days. [ABSTRACT FROM AUTHOR]

The European hazelnut (Corylus avellana L.) is a self-incompatible, wind-pollinated species of significant economic-productive interest, mainly cultivated between the Mediterranean basin and the Black Sea. Hazelnut breeding programs and high cropping in commercial orchards are necessarily linked to the availability of fertile pollen with wide germinability and high viability. The objective was to develop an improved method to determine the germinability of pollen, comparing the results with those found in the literature. Pollen germinability was firstly evaluated on a wild-type accession using boric acid (H3BO3), calcium nitrate (Ca(NO3)2), magnesium sulfate (MgSO4), potassium nitrate (KNO3), casein hydrolysate and different concentrations of sugars, including sucrose (10, 15 and 25%) and two monosaccharides, glucose (15%) and fructose (15%). The optimal composition included 15% sucrose in a semi-solid medium composed of 1% animal gelatin, containing collagen. This formulation was then tested on three cultivars of commercial interest, evaluating the effect of different concentrations of sucrose. The comparison between different in vitro germination methods showed that the hanging drop technique in a semi-solid medium provides a statistically higher germination index compared to the liquid and solid/agarized techniques. This study proposes an easy-to-use medium for the in vitro germination of Corylus avellana L. pollen.

Plants in the Gesneriaceae family are appreciated for their decorative leaves and flowers, ease of cultivation, and shade tolerance. Sexual hybridisation has long been carried out for producing novel hybrids. However, scientific knowledge is lacking on the correct timing of pollination in this family. This study was conducted to elucidate the optimal timing for pollination by screening pollen viability and stigma receptivity throughout the flowering period in eight gesneriad taxa. Pollen viability was evaluated by the in vitro germination test and stigma receptivity was based on stigma morphology and pistil length. The flowering duration varied from 10 days in Alsobia to 18 days in Streptocarpus. While the pollens of Episcia, Kohleria, Saintpaulia, Sinningia, and Smithiantha had totally lost viability 2–5 days before the flowers withered, a slightly contrasting situation was observed in the cases of Alsobia, Deinostigma, and Streptocarpus, where a small portion of pollen grains remained viable towards the end of the flowering period. The highest pollen germination rate was recorded from 1 day in Alsobia, Episcia, and Kohleria, to 9 days in Deinostigma. The reduction in pollen germination was rapid in Alsobia, Saintpaulia, and Smithiantha, and moderate in the remaining taxa. The greatest pollen tube growth occurred at 1–3 days after flower opening and decreased rapidly in all the taxa tested. The longest pistil of 2.03–3.50 cm was observed at 3–8 days of anthesis depending on the plant tested. The findings in this study suggest that higher pollination success may be achieved using pollen grains of newly opened flowers and stigmas of mature flowers in this family.

The knowledge of pollen morphology, suitable storage condition, and species compatibility is vital for a successful grapevine improvement programme. Ten grape genotypes from three different species, viz., Vitis vinifera L., Vitis parviflora Roxb., and Vitis champini Planc., were studied for their pollen structure and pollen storage with the objective of determining their utilization in grape rootstock improvement programs. Pollen morphology was examined through the use of a scanning electron microscope (SEM). The viability of the pollen was assessed using 2,3,5-triphenyltetrazolium chloride (TTC). In vitro pollen germination was investigated using the semi-solid medium with 10 % sucrose, 100 mg/L boric acid, and 300 mg/L calcium nitrate. The results revealed variations in pollen micro-morphology in 10 genotypes, with distinct pollen dimensions, shapes, and exine ornamentation. However, species-wise, no clear difference was found for these parameters. Pollen of V. parviflora Roxb. and Dogridge was acolporated and did not germinate. The remaining eight genotypes exhibited tricolporated pollen and showed satisfactory in vitro pollen germination. Storage temperature and duration interactions showed that, at room temperature, pollen of most of the grape genotypes can be stored for up to 1 day only with an acceptable pollen germination rate (>30 %). However, storage for up to 7 days was successfully achieved at 4 °C, except for ‘Pearl of Csaba’. The most effective storage conditions were found to be at −20 °C and −196 °C (in liquid N2), enabling pollen storage for a period of up to 30 days, and can be used for pollination to overcome the challenge of asynchronous flowering. Four interspecific combinations were studied for their compatibility, among which V. parviflora Roxb. × V. vinifera L. (Pusa Navrang) and V. parviflora Roxb. × V. champini Planc. (Salt Creek) showed high cross-compatibility, offering their potential use for grape rootstock breeding. However, V. parviflora Roxb. × V. vinifera L. (Male Hybrid) recorded the lowest compatibility index among studied crosses. In the case of self-pollinated flowers from V. parviflora Roxb. and V. parviflora Roxb. × V. champini Planc. (Dogridge), pollen failed to germinate on the stigma due to male sterility caused by acolporated pollen. As a result, the flowers of these genotypes functioned as females, which means they are ideal female parents for grape breeding without the need for the tedious process of emasculation.

This research was carried out in fig fields in the village of Kafar-Jales, in the north of Syria. The analyses were conducted in the laboratories of the Faculty of Agriculture at Idlib University during the 2022 farming season, to evaluate the viability and germination of three local varieties of Caprifig (Bunduqi, Azraq, Panjani). The morphological characteristics, the date of the exodus of insects (Blastophaga psenes) from male fruits, the quantity of pollen, and the percentage of germination and viability were studied on four nutritive media at a temperature of 27°C. The measurements were taken after 24 h, 48 h, and 72 h. These three pollinators were used to pollinate three varieties of edible figs (white Satehi, Safrawi, and Habashi) to study the effect of pollen source on the productive characteristics of edible fig fruits. The result showed significant superiority of the Bunduqi cultivar over the rest of the cultivars in traits of the fruit’s early ripening, pollen quantity, and date of departure of insects. The Azraq cultivar is found to be superior to Bunduqi and Panjani cultivars in the germination rate of pollen at all stages of the experiment and in all used media. The addition of stigma flower extract in culture media increased germination percentage by 35% for all studied Caprifig cultivars. The addition of 10% sucrose in the cultivation environment increased the percentage of pollen germination by 20%. The cultivars that were inoculated with the Panjani pollinator outperformed the characteristics of the length, diameter, and weight, demonstrating that the fruit’s quality characteristics are affected by the genotype of the pollinator used. The results of this research can be beneficial for both fig growers and plant breeders, as they help to select the best pollinators and contribute to the development and improvement of the quality of the cultivated fig fruits.

Morphological response of cells to environment involves concerted rearrangements of microtubules and actin microfilaments. A mutant of WAVE-DAMPENED2-LIKE5 (WDL5), which encodes an ethylene-regulated microtubule-associated protein belonging to the WVD2/WDL family in Arabidopsis thaliana, shows attenuation in the temporal root growth reduction in response to mechanical stress. We found that a T-DNA knockout of WDL6, the closest homolog of WDL5, oppositely shows an enhancement of the response. To know the functional relationship between WDL5 and WDL6, we attempted to generate the double mutant by crosses but failed in isolation. Close examination of gametophytes in plants that are homozygous for one and heterozygous for the other revealed that these plants produce pollen grains with a reduced rate of germination and tube growth. Reciprocal cross experiments of these plants with the wild type confirmed that the double mutation is not inherited paternally. These results suggest a critical and cooperative function of WDL5 and WDL6 in pollen tube growth.

Commercially, leguminous crops (Fabaceae) are the second most important group of cultivated plants, just after grasses (Poaceae). This study focuses on the analysis of pollen development and stainability in two species belonging to the Fabaceae family: Vicia faba L. and Lupinus angustifolius L. Morphological analysis of the anthers at various stages of flower development allowed us to trace the processes of microsporogenesis and microgametogenesis. Nine different cell staining protocols with diverse mechanisms of action, including acetocarmine, Alexander's dye, aniline blue in lactophenol, Calcein AM, FDA, MTT, TTC, Lugol's iodine, and aceto-orcein, were tested for their suitability in assessing the viability of microspores as well as pollen grains in both species. Among the applied dyes, four allowed for the discrimination between viable and nonviable microspores in V. faba, and six dyes allowed for this in L. angustifolius. For mature pollen grains, all dyes enabled differentiation between viable and nonviable cells in both species. The highest viability indications for V. faba microspores were obtained with acetocarmine (94.6%), while for mature pollen, aniline blue in lactophenol, MTT, and aceto-orcein yielded the highest viability indications (90.8–96.3%). In L. angustifolius, the highest percentages of viable microspores (64.9–66.5%) were obtained with the acetocarmine, aniline blue in lactophenol, and TTC dyes. For mature pollen, the highest viability indications (83.4%–92.9%) were obtained with acetocarmine, aniline blue in lactophenol, Lugol's iodine, and aceto-orcein. The viability of V. faba pollen grains in an in vitro germination test showed that the highest pollen germination (61.3%) was observed on the BK medium (rich in minerals with 10% sucrose). In L. angustifolius, the highest pollen germination was observed on the media containing boric acid and 5% sucrose (70.5%) and on the medium containing 10% sucrose only (74.2%). [ABSTRACT FROM AUTHOR]

Autophagy is an evolutionarily conserved mechanism for degrading and recycling various cellular components, functioning in both normal development and stress conditions. This process is tightly regulated by a set of autophagy-related (ATG) proteins, including ATG2 in the ATG9 cycling system and ATG5 in the ATG12 conjugation system. Our recent research demonstrated that autophagy-mediated compartmental cytoplasmic deletion is essential for pollen germination. However, the precise mechanisms through which autophagy regulates pollen germination, ensuring its fertility, remain largely unknown. Here, we applied multi-omics analyses, including transcriptomic and metabolomic approaches, to investigate the downstream pathways of autophagy in the process of pollen germination. Although ATG2 and ATG5 play similar roles in regulating pollen germination, high-throughput transcriptomic analysis reveals that silencing ATG5 has a greater impact on the transcriptome than silencing ATG2. Cross-comparisons of transcriptome and proteome analysis reveal that gene expression at the mRNA level and protein level is differentially affected by autophagy. Furthermore, high-throughput metabolomics analysis demonstrates that pathways related to amino acid metabolism and aminoacyl-tRNA biosynthesis were affected by both ATG2 and ATG5 silencing. Collectively, our multi-omics analyses reveal the central role of autophagy in cellular metabolism, which is critical for initiating pollen germination and ensuring pollen fertility. [ABSTRACT FROM AUTHOR]

This research was carried out in fig fields in the village of Kafar-Jales, in the north of Syria. The analyses were conducted in the laboratories of the Faculty of Agriculture at Idlib University during the 2022 farming season, to evaluate the viability and germination of three local varieties of Caprifig (Bunduqi, Azraq, Panjani). The morphological characteristics, the date of the exodus of insects (Blastophaga psenes) from male fruits, the quantity of pollen, and the percentage of germination and viability were studied on four nutritive media at a temperature of 27℃. The measurements were taken after 24 h, 48 h, and 72 h. These three pollinators were used to pollinate three varieties of edible figs (white Satehi, Safrawi, and Habashi) to study the effect of pollen source on the productive characteristics of edible fig fruits. The result showed significant superiority of the Bunduqi cultivar over the rest of the cultivars in traits of the fruit's early ripening, pollen quantity, and date of departure of insects. The Azraq cultivar is found to be superior to Bunduqi and Panjani cultivars in the germination rate of pollen at all stages of the experiment and in all used media. The addition of stigma flower extract in culture media increased germination percentage by 35% for all studied Caprifig cultivars. The addition of 10% sucrose in the cultivation environment increased the percentage of pollen germination by 20%. The cultivars that were inoculated with the Panjani pollinator outperformed the characteristics of the length, diameter, and weight, demonstrating that the fruit's quality characteristics are affected by the genotype of the pollinator used. The results of this research can be beneficial for both fig growers and plant breeders, as they help to select the best pollinators and contribute to the development and improvement of the quality of the cultivated fig fruits. [ABSTRACT FROM AUTHOR]

For a successful reproduction in angiosperms, pollen germination and pollen tube growth must proceed normally. The processes are regulated by transcriptional regulation and cellular activities, in which signaling proteins are the key. Ras homolog (Rho)-type GTPases (Rops), which are known as RACs, are a group of Rho small GTP-binding proteins which evolved in plants. However, the molecular mechanisms of the rice Rac family (OsRac) genes in pollen germination are not yet understood. In this investigation, the OsRac6 gene, which is only expressed only during the pollen development stage, was identified. A functional characterization of OsRac6 using gene-edited mutants exhibits male sterility due to the disruption of pollen germination. Then, to determine downstream candidate genes modulated by the OsRac6 genes during pollen development, we performed RNA-seq analysis by comparing osrac6-1 and wild-type (WT) anthers. Subsequently, we identified 652 genes with pollen-preferential expression which were upregulated compared with the WT, and 608 genes which were downregulated. Furthermore, gene ontology (GO) enrichment and MapMan analyses show that downregulated genes are closely associated with transcription, protein ubiquitination, proteolysis, cell wall modification, cell organization, cell cycle, and calcium regulation. The results of this study will help in elucidating the molecular mechanisms of pollen germination in rice mediated by OsRac6. [ABSTRACT FROM AUTHOR]

Background: In a genetic breeding program, understanding the viability of pollen germination and pollen tube growth is an essential factor for artificial hybridization. Currently, little is known about the influence of sucrose, boric acid concentrations and calcium chloride on pollen viability in alfalfa. This study is valuable for providing information about pollen germination requirements to support further improvement of artificial pollination and breeding programs in alfalfa. Methods: The single-factor experimental and an orthogonal design method (L16 [4]3) was used to compare the effectiveness of key factors (e.g., concentrations of sucrose, boric acid and calcium chloride) to determine the pollen vigor of Medicago varia Martin. 'Caoyuan No.1'and M. ruthenica L. Trautv. 'zhilixing' and to optimize the culture medium for in vitro pollen germination. Four different varieties were chosen to compare the diurnal variation of pollen vigor. Result: The four factors that influenced pollen germination in Medicago varia Martin. 'Caoyuan No.1' and M. ruthenica L. Trautv. 'zhilixing' in order of significance are as follows: sucrose > H3BO3 > CaCl2. These variables influenced pollen tube growth in the following order: sucrose > H3BO3 > CaCl2. The optimal culture medium for promoting pollen vigor of Medicago varia Martin. 'Caoyuan No.1' was 10% sucrose, 300 mon/L H3BO3 and 100 mon/L CaCl2; that of M. ruthenica L. Trautv. 'zhilixing' was 10% sucrose, 200 mon/L H3BO3 and 50 mon/L CaCl2. Among several species of alfalfa, 'Caoyuan No.1' shows the highest pollen vigor and the daily pollen activity curves of all varieties showed a single peak type. [ABSTRACT FROM AUTHOR]

Global climate changes have led to frequent and recurrent heat stress, which has seriously affected the world maize production. The experiment presented in this paper was carried out during the maize‐growing season in 2021 and 2022 at the Huang–Huai–Hai Region Maize Science and Technology Innovation Center (36°09′N, 117°09′E) in Tai'an, Shandong province, China. The test site is located in the semi‐humid warm temperate continental monsoon climate zone, soil is brown loam. We selected different heat‐sensitive maize varieties: heat‐tolerant variety Zhengdan 958 (ZD958) and heat‐sensitive variety Xianyu335 (XY335) to study the stress effects of high temperature on the development of tassel in the key stage of its differentiation (the 12‐leaf stage, V12). We found that exposure to heat stress during the V12 stage significantly reduced the tassel size and the anther dehiscence area, making it difficult to disperse pollen, thus effectively reducing pollen production. In addition, heat stress had significant negative effects on pollen development, resulting in deformed pollen and lower pollen viability and germination rate. Our results also showed that heat stress significantly increased the activities of key reactive oxygen species‐scavenging enzymes including superoxide dismutase, peroxidase and catalase, and that the malondialdehyde and H2O2 content in tassels exposed to heat stress were significantly higher than those control group, where it should be noted that for the XY335, these effects were more pronounced than for the ZD958. The endogenous hormone content of tassels exhibited a variety of responses. After heat stress, the zeatin and salicylic acid content in tassels of both maize varieties were significantly lower than those in the respective control groups, while the abscisic acid and gibberellin acid content were significantly higher. With respect to the jasmonic acid and 3‐indoleacetic acid content, the two maize varieties exhibited opposite responses: in tassels from ZD958 plants subjected to heat stress were higher than those in the respective control group, while in tassels from XY335 plants, they were lower. The observed changes in protective enzyme activities and endogenous hormone contents induced by heat stress significantly affected the development of maize tassels and significantly reduced the amount, activity and germination rate of pollen. [ABSTRACT FROM AUTHOR]

Highland papaya (Vasconcellea pubescens A.DC.) is a member of the family Caricaceae and native to Ecuador. The plant's introduction and cultivation were successful in specific highland areas of Indonesia but with limited growing areas. V. pubescens has monoecious and dioecious characteristics and allows fruit production from female dioecious and monoecious plants. This plant is valuable, and the knowledge about its sex pattern, though still limited, is crucial for its efficiency, productivity, and development. Hence, the presented study aimed to explain the patterns of plant segregation, as well as, pollen morphology and germination based on sex in V. pubescens. The investigations began by recognizing the total population of V. pubescens in its cultivated area for grouping and mapping according to sex. Observations on the pollen characteristics, such as, morphology and germination, used light microscopy and a Scanning Electron Microscope (SEM). The results revealed that the basis for plant segregation pattern depended on sex in male and female dioecious and monoecious plants of V. pubescens (1:5:1). In both sexes, the pollen morphological characteristics showed that the unit of monads, prolate spheroidal, radial, tricolporate, isopolar, reticulate, and P/E index of male dioecious pollen was 0.70, while monoecious was 0.52. Anthers and pollen grains from the male plant were round, but those of monoecious elongate more. However, no significant differences occurred among the sexes for pollens. The pollen grains from male flowers on male dioecious plants showed faster germination than monoecious individual plants, having a difference of 25.14 days. [ABSTRACT FROM AUTHOR]

Background: The plant-specific valine-glutamine (VQ) motif containing proteins tightly regulate plant growth, development, and stress responses. However, the genome-wide identification and functional analysis of Brassica oleracea (B. oleracea) VQ genes have not been reported. Objective: To identify the VQ gene family in B. oleracea and analyze the function of Bo25-1 in pollen germination. Methods: The Hidden Markov Model (HMM) of VQ family was used to query the BoVQ genes in the B. oleracea genome. The BoVQ genes preferentially expressed in anthers were screened by qRT-PCR. Subcellular localization of VQ25-1 was observed in Nicotiana benthamiana (N. benthamiana) leaves. To analysis the role of BoVQ25-1 in pollen germination, the expression of BoVQ25-1 was suppressed using antisense-oligonucleotides (AS-ODN). Results: A total of 64 BoVQ genes were identified in the B. oleracea genome. BoVQ25-1 was found to be preferentially expressed in the B. oleracea anthers. BoVQ25-1 was cloned from the anthers of the B. oleracea cultivar 'Fast Cycle'. BoVQ25-1 is localized to the nucleus. The pollen germination rate significantly decreased after AS-ODN treatment. Conclusion: Sixty-four BoVQ genes were identified in the B. oleracea genome, of which BoVQ25-1 plays an important role in pollen germination. [ABSTRACT FROM AUTHOR]

Banana (Musa spp.) is a major global economic fruit crop. However, cross-pollination from other Musa cultivars grown in nearby plantations results in seeded fruit that exceeds market demand. This study investigated pollen viability and germination and examined the expression profiles of pollen development-related genes across seven Musa genomes (AA, BB, AAA, BBB, AAB, ABB and ABBB). Twenty-three Musa cultivars were assessed for pollen viability using lacto-aceto-orcein and triphenyltetrazolium chloride staining methods. Results revealed that pollen viability obtained from both methods was significantly different among all the studied cultivars. Cultivars carrying BB (diploid) genomes had higher viability percentages than AA (diploid), AAA, BBB, AAB and ABB (triploid) and ABBB (tetraploid) genomes. Germination of the studied cultivars was also investigated on pollen culture medium, with results showing significant differences between the pollen of each cultivar. The best germinating cultivar was TKM (11.0 %), carrying BB genome. Expression profiles of pollen development-related genes by RT–qPCR indicated that both TPD1A and MYB80 genes were highly expressed in triploid Musa genomes but the PTC1 gene showed down-regulated expression, resulting in non-viable pollen. Pollen viability, pollen germination and pollen development-related genes differed across Musa cultivars. This knowledge will be useful for the selection of male parents for Musa cross-breeding programs. Pollen viability should also be considered when planning Musa production to avoid seeded fruit. [ABSTRACT FROM AUTHOR]

Background: Long-term space missions will necessarily require producing viable seeds to be used for plant cultivation over time under altered gravity conditions. Pollen is known to play a key role in determining seed and fruit production over seed-to-seed cycles, but very few studies have evaluated pollen functionality under altered gravity. Methods: We performed ground-based experiments to test how simulated microgravity can affect the directional growth of pollen tubes as a potential bottleneck in seed and fruit sets. The effect of clinorotation was assessed in the pollen of Solanum lycopersicum L. cv. 'Micro-Tom' and Brassica rapa L. var. silvestris, both eligible for cultivation in space. Pollen tube length and tortuosity were compared under 1g and simulated microgravity with a uniaxial clinostat. Results: The main results highlighted that simulated microgravity significantly increased pollen tube length and tortuosity compared to 1g conditions. Further, clinorotation prompted a differential effect on pollen germination between S. lycopersicum and B. rapa. A more in-depth analysis evaluating the effect of gravity on the directional growth of pollen tubes excluded gravitropic responses as responsible for the tube tip position reached after germination. Discussion: This research provides new insights into how altered gravity can interfere with plant reproduction and, in particular, microgametophyte functionality. Our findings represent a basis for further studies aimed at understanding the effect of real microgravity on plant reproduction and developing countermeasures to ensure seed-to-seed cultivation in long-term space missions and achieve self-sufficiency in food supplies from Earth. [ABSTRACT FROM AUTHOR]

“Autonomous fruit set” refers to self-pollination and fruit set without pollen vectors such as vibration or insects. Autonomous fruit set under high-temperature stress is an important breeding goal as climate change can reduce fruit yields in Capsicum. We screened Capsicum cultivars for autonomous fruit set ability in a greenhouse environment and investigated pollen germination, viability, pollen grains number, chlorophyll fluorescence (Fv/Fm), style length, anther cone length, and anthesis stage under high temperatures in order to identify indicator traits for screening more genotypes with autonomous fruit set ability. The fruit set of the ‘Takanotsume’ (57.7 ± 20.6%) and ‘Goshiki Kyokko’ (52.2 ± 14.2%) cultivars (both C. annuum) were higher than those of other cultivars. Correlation analysis showed that pollen germination had the highest correlation with fruit set in C. annuum cultivars (r = 0.63). These results indicate that ‘Takanotsume’ and ‘Goshiki Kyokko’ are useful cultivars for novel breeding programs focusing on autonomous fruit sets under high temperatures, and pollen germination in C. annuum was a convincing candidate for an indicator trait of autonomous fruit set ability under high temperatures.

Yield in cherimoya (Annona cherimola Mill.) is affected by various factors reducing fertilization and fruit production such as: the protogynous dichogamy of the flowers, deficient natural pollination, and low pollen quality. The objective of this study was to determine in vitro the differences in pollen quality of nine ecotypes and one cultivar of A. cherimola from pollen samples collected at the female and male phenological stages of flowering. The percentage of pollen germination and the length of pollen tubes was evaluated in vitro at 2 and 24 hours after incubation at 21°C, in two phenological stages of the flowers during bloom in 2018 and 2019 seasons. The germination medium contained: 10% sucrose, 1% agar, 0.005% boric acid, and 0.025% calcium nitrate. Fabulosa and Austro ecotypes and the Fino de Jete cultivar had the highest pollen germination in the male phenological stage, after 2 and 24 hours in both seasons. Fabulosa had the highest percentage of germination in the female stage in both seasons. The ideal phenological stage for pollen collection was at anther dehiscence. Austro and Fabulosa ecotypes had the longest pollen tubes after 2 and 24 hours, in both phenological stages for both seasons. Fabulosa and Austro ecotypes, and Fino de Jete cultivar, showed promising pollen characteristics for hand pollination of cherimoya.

Solanum melongena is susceptible to diverse diseases and parasites, in particular the wilts (bacterial, Fusarium and Verticillium), nematodes, and some insects. Solanum torvum is robust to Verticillium and some bacterial wilts and root-knot nematode. It was reported that interspecific hybrid plants originated out of the hybridization of these species were sterile. In our previous studies that have been carried out to overcome this interspecific hybridization barrier, only from Faselis F1 that was used as the female parent, many interspecific hybrid seeds were obtained and 9.07% of the seeds grew into plants in vitro. The percentage of pollen viability and germination of tetraploid interspecific hybrid (amphidiploid) genotypes that have been produced by in vitro colchicine treatment, were 6.8 and 3.4 fold of its source diploid genotype, respectively. However, the increment was not high enough to overcome the interspecific hybridization barrier between S. torvum and S. melongena. In this study, the changes in pollen fertility of diploid interspecific hybrids and tetraploid plants, which have grafted on Pala or Faselis F1, were investigated. Pollen viability and germination percentage in diploid genotypes were not affected by grafting, although they increased significantly (51.54% and 119.73%, respectively) in tetraploid genotypes by grafting. It was determined that the fertile diploid rootstock used for the tetraploid genotypes that produced by chromosome doubling from cultured eggplants could increase the number of seeds per fruit. It was concluded that some fertile diploid varieties can be used as rootstocks in order to increase pollen viability, germination rate and seed yield of tetraploid genotypes with low pollen yield obtained from cultivated eggplant by chromosome doubling. [ABSTRACT FROM AUTHOR]

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The pollen grains of Phalaenopsis orchids are clumped tightly together, packed in pollen dispersal units called pollinia. In this study, the morphology, cytology, biochemistry, and sucrose transporters in pollinia of Phalaenopsis orchids were investigated. Histochemical detection was used to characterize the distribution of sugars and callose at the different development stages of pollinia. Ultra-performance liquid chromatography-high resolution-tandem mass spectrometry data indicated that P. aphrodite accumulated abundant saccharides such as sucrose, galactinol, myo-inositol, and glucose, and trace amounts of raffinose and trehalose in mature pollinia. We found that galactinol synthase (PAXXG304680) and trehalose-6-phosphate phosphatase (PAXXG016120) genes were preferentially expressed in mature pollinia. The P. aphrodite genome was identified as having 11 sucrose transporters (SUTs). Our qRT–PCR confirmed that two SUTs (PAXXG030250 and PAXXG195390) were preferentially expressed in the pollinia. Pollinia germinated in pollen germination media (PGM) supplemented with 10% sucrose showed increased callose production and enhanced pollinia germination, but there was no callose or germination in PGM without sucrose. We show that P. aphrodite accumulates high levels of sugars in mature pollinia, providing nutrients and enhanced SUT gene expression for pollinia germination and tube growth. [ABSTRACT FROM AUTHOR]

Cysteine proteases (CPs) are vital proteolytic enzymes that play critical roles in various plant processes. However, the particular functions of CPs in maize remain largely unknown. We recently identified a pollen-specific CP (named PCP), which highly accumulated on the surface of maize pollen. Here, we reported that PCP played an important role in pollen germination and drought response in maize. Overexpression of PCP inhibited pollen germination, while mutation of PCP promoted pollen germination to some extent. Furthermore, we observed that germinal apertures of pollen grains in the PCP-overexpression transgenic lines were excessively covered, whereas this phenomenon was not observed in the wild type (WT), suggesting that PCP regulated pollen germination by affecting the germinal aperture structure. In addition, overexpression of PCP enhanced drought tolerance in maize plants, along with the increased activities of the antioxidant enzymes and the decreased numbers of the root cortical cells. Conversely, mutation of PCP significantly impaired drought tolerance. These results may aid in clarifying the precise functions of CPs in maize and contribute to the development of drought-tolerant maize materials. [ABSTRACT FROM AUTHOR]

The olive (Olea europaea L.) is an ancient crop of great importance in the Mediterranean basin due to the production of olive oil and table olives, which are important sources of fat and have benefits for human health. This crop is expanding and increasing its production worldwide and five olive genomes have recently been sequenced, representing a wild olive and important cultivars in terms of olive oil production, intensive agriculture, and adaptation to the East Asian climate. However, few bioinformatic and genomic resources are available to assist olive research and breeding, and there are no platforms to query olive gene expression data. Here, we present OliveAtlas, an interactive gene expression atlas for olive with multiple bioinformatics tools and visualization methods, enabling multiple gene comparison, replicate inspection, gene set enrichment, and data downloading. It contains 70 RNA-seq experiments, organized in 10 data sets representing the main olive plant organs, the pollen germination and pollen tube elongation process, and the response to a collection of biotic and abiotic stresses, among other experimental conditions. OliveAtlas is a web tool based on easyGDB with expression data based on the 'Picual' genome reference and gene annotation. [ABSTRACT FROM AUTHOR]

Abstract High temperature at reproductive stage causes a decrease in seed set that ultimately results in yield loss in important crops. Limited research is available regarding the effect of high temperature on viability attributes of pollen grain in sunflower. This study was planned to reveal the effects of high temperature stress on pollen grains in sunflower. An experiment was laid out in a triplicated Completely Randomized Design with split-split plot arrangements at the Oilseeds Research Institute, Ayub Agricultural Research Institute Faisalabad during spring 2021. Two temperature treatments T1 = 45° C for 10, 20 and 30 minutes, and T2 = 50° C for 3, 5 and 10 minutes were used on 10 sunflower inbred lines. Normal (untreated) pollen grains were used as control (T0). Data were collected on pollen viability, pollen germination, and pollen tube length. Recorded data were subjected to analysis of variance, Tukey’s HSD mean comparison test, and correlation. According to the results, ORI-1 showed the highest mean for pollen viability, whereas, RL-86 had highest mean for pollen germination and pollen tube length under normal conditions. RL-86 and ORI-73 revealed their ability to withstand both heat stresses as all pollen traits were least affected under high temperature stresses. It is advised to incorporate these inbred lines in future breeding programs aimed at the development of heat tolerant sunflower hybrids. Moreover, correlation studies displayed a positive, strong and highly significant relation of pollen germination with pollen tube length under normal and heat stress conditions revealing their importance in pollen study and reproduction.