Small Pollen Grains Research Articles

Digest: Scarce pollen resources and asymmetric reproductive isolation.

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

PALYNOLOGICAL DIVERSITY OF POLLEN MORPHOLOGY IN ENDEMIC NORTHERN IRAQI HYPERICUM SPECIES (HYPERICACEAE)

The presented research investigated the pollen morphology of endemic Iraqi Hypericum species. The study revealed phenotypic features of pollen grains in the polar and equatorial views and their quantitative and qualitative characteristics. The results showed that the pollen grains of the genus Hypericum were radially symmetrical and isopolar, and their apertures were simple and tricolporate, except the species H. davisii, distinguished as tetracolprate. Dividing the studied species based on pollen grain sizes comprised two groups. Small pollen grains with an average length of the equatorial view ranged between 10–16 μm in H. lysimachioides and H. vermiculare. Medium-sized pollen grains with an average extent between 17–26 μm emerged in the species, i.e., H. retusum, H. triquetrifolium, H. perforatum, H. lydium, H. tetrapterum, H. asperulium, H. scabrum, and H. davisii. Pollen grains, also divided according to the P/E ratio, had two main groups. The pollen grains were subprolate and spherical, with the exine sculpturing examined by a scanning electron microscope (SEM), and isolated into four groups: 1) microreticulate reticulum, including H. asperulium, H. lydium, and H. vermiculare, 2) perforate, i.e., H. retusum, H. scabrum, H. tetrapterum, and H. triquetrifolium, 3) psilate with H. perforatum and H. davisii, 4) and reticulate exine sculpturing in H. lysimachioides, all isolated from the rest of the species. SEM images showed the thickness of exine ranged from 0.5 to 2 μm. The topical study also added H. davisii as a new species with no previous records in Iraq. This pollen study added valuable data for taxonomy and suggested that it should proceed with its first-time registration in Iraq. The pertinent research could provide a taxonomical key for Hypericum species in Iraq.

Pollen morphology of Matthiola and the related genus Dvorakia (Brassicaceae) in Iran

Our study focused on the pollen morphology of 13 species of Matthiola and the closely related genus Dvorakia. We used light and scanning electron microscopes to examine the importance of pollen characteristics in classifying these genera. Pollen grains were acetolysed, measured, photographed, and described based on qualitative and quantitative characteristics. Here, we present statistical analyses and multivariate statistics for quantitative data. Pollen in both genera are tricolpate and varies in shape from subprolate to prolate. We distinguish two pollen types based on lumen width. Matthiola pollen has both reticulate and macroreticulate ornamentation, while Dvorakia alyssifolia pollen is reticulate. The thickness of the exine and the width of the mesocolpium are important traits in addition to exine ornamentation. Iranian Dvorakia and Matthiola species’ pollen size can be divided into four types, one of which is Type I (Dvorakia alyssifolia type). Among the examined species, M. tomentosa has the smallest pollen grains, while D. alyssifolia has the largest grains. Pollen morphology confirms the transfer of D. alyssifolia from Matthiola to Dvorakia. Additionally, we propose a species key for the genera.

Systematic study in Cressa cretica L. (Convolvulaceae) species from Lake Qarun, El-Fayoum province, Egypt

Cressa cretica L. is a monotypic species belongs to the plant family Convolvulaceae, tribe Cresseae. It is an erect, small, dwarf shrub, commonly grown in coastal areas and considered as an important medicinal plant with many therapeutic effects. Individuals of this species became restricted in specific areas in Egypt in became under threat of extinction. This study dealt with careful examination of the external and leaf internal structure beside pollen grain morphology. The study aims to understand the species morphological characteristics and protect it from localization and destruction processes. The results showed that the leaf macro- and micro-morphological characters are of the halophytic ones, with long unicellular hairs as well as T-shaped hairs and sunken stomata. The leaf internal structure has mesophyll differentiated into one layer palisade and spongy layers full of ca-oxalate crystals and salt glands distributed in the mesophyll. Pollen grains productivity was few and they are small, spheroidal to subprolate with tricolporate aperture and tectate perforate with supra-tectum granules. The results obtained show that Cressa cretica has external and internal halophytic structure in addition to few small pollen grains. Germination experiments needed to test the pollen productivity of this plant under non-saline habitats for its conservation.

Taxonomic Comparison, Antioxidant and Antibacterial Activities of Three Ebenus pinnata Ait. ecotypes (Fabaceae) from Algeria

Ebenus pinnata is not known as a traditional medicinal plant, but modern research has revealed its richness in components of medicinal value. Yet, the species remains understudied. Here, we assess the climate effect on its morphology, pollen grains size, chromosome numbers, pollen fertility, and antioxidant and antibacterial activities. Plant material was collected from the humid, sub-humid, and semi-arid areas of Northeastern Algeria. Data treatment by principal component analysis and/or cluster analysis and ANOVA post hoc tests revealed three significantly discriminated ecotypes correlated with the climate stage. Significant differences were detected for whole plant morphology, pollen size, and antioxidant activity. No differences were revealed for chromosome numbers, pollen fertility, and antibacterial activity. The studied material showed a chromosome number of 2n = 14, high pollen fertility (94.04 ± 2.64–95.01 ± 2.02%), small pollen grains (polar axis: 17.95 ± 1.10–19.47 ± 1.27 µm; equatorial axis: 12.80 ± 1.18–13.03 ± 0.99 µm), high antioxidant activity (TPC: 50.79 ± 0.51–56.89 ± 0.46 mg/g; DPPH: 71.18 ± 2.24–95.67 ± 2.02 mg/g; RP: 11.09 ± 1.24–25.88 ± 0.26 mg/g), and efficient antibacterial activity (Inhibition area diameter: 9.25 ± 1.06–12.00 ± 1.41 mm). The climate seems to exert a significant impact on multiple aspects of the plant’s biology. It would be interesting to assess the genetic basis of this phenomenon in E. pinnata and other species.

Effects of sexual polyploidization on reproductive development in a full-sib poplar family

Populus is an important source of woody biomass in the Northern Hemisphere. Sexual polyploidization plays a valuable role in the genetic improvement of Populus, resulting in tremendous variation in phenotypic traits. Most studies have focused on the variations in the vegetative growth of allopolyploid Populus; however, variations in the reproductive development of different polyploid genotypes of the progeny remain unclear. In this study, catkin traits, pollen size and viability, meiotic development, and reproductive ability were analyzed based on a full-sib family including diploid and triploid hybrids of (Populus pseudo-simonii × P. nigra ‘Zheyin3#’) × (P. × beijingensis) to understand the effects of sexual polyploidization on reproductive development in Populus hybrids. Catkin traits varied among the genotypes in the full-sib family. A ploidy change resulted in significant variation in male catkin length and male flower number per catkin but not in female catkin traits, suggesting that Populus catkin development may be more sensitive to respond to a change in ploidy level in male plants than in female plants. The male diploid hybrids had significantly smaller pollen grains, but higher pollen germination rates than the triploid hybrids. Giant pollen grains with large diameters were recorded in all-male diploid and triploid hybrids, which were speculated to be unreduced gametes. Premature cytokinesis, misorientation of the spindles, and aberrant cytokinesis were observed in a cytological analysis, which explained the production of unreduced pollen. Premature cytokinesis was only detected in triploid hybrids, which might be attributed to a ploidy change. The frequencies of meiotic abnormalities, such as precocious chromosomal migration, chromosome bridges, and micronuclei in the triploid hybrids were higher than those in diploid hybrids, suggesting that the unbalanced chromosomes in the triploid hybrids caused more complex meiotic chromosome behaviors. Backcrosses with the triploid hybrids resulted in low seed sets and seed germination rates, suggesting that polyploidization reduced pollen viability. Our findings provide new insight into the effect of sexual polyploidization on reproductive development in Populus and could be used to guide a Populus polyploid breeding program.

Ancillary polymorphic floral traits between two morphs adaptive to hawkmoth pollination in distylous plant Tirpitzia sinensis (Linaceae)

BackgroundFloral morphs are characterized differentiations in reciprocal positions of sexual organs and ancillary floral traits in heterostylous plants. However, it remains unclear how differential floral morphs ensure reproductive success between morphs using the same pollinator.ResultsMeasurements of floral traits in white-flowered Tirpitzia sinensis with long corolla tubes indicated that it is typically distylous, long-styled (L-) morph producing more but smaller pollen grains per flower than short-styled (S-) morph. Both morphs secreted more nectar volume at night than in the day and the sugar composition was rich in sucrose, potentially adaptive to pollination by hawkmoths (Macroglossum spp.) which were active at dusk. A bumblebee species functioned as the nectar robber in both morphs and a honeybee as the pollen feeder in the S-morph. The L-morph secreted more nectar volume but relatively lower sucrose/hexose ratio than the S-morph. Floral visitation rate by hawkmoths was higher but its pollination efficiency was lower in the S-morph than the L-morph. Hand pollination treatments indicated self-incompatibility in T. sinensis and seed set of open-pollinated flowers did not differ between morphs.ConclusionsOur findings suggest that the two morphs differ with respect to traits relevant to pollination. The L-morph, with its exserted stigma, has more pollen grains per anther and a greater volume of nectar, which may prolong the foraging time and increase the pollination efficiency of hawkmoths. The S-morph has a higher sucrose/hexose ratio in its nectar which can be more attractive to hawkmoths and increase the visit rates. Ancillary polymorphic floral traits between two morphs are adaptive to hawkmoth and ensure reproductive success in distylous plant T. sinensis.

Pollen of Pterocarya (Juglandaceae) representatives from natural habitats and St. Petersburg environments

Background. Comparative palynomorphological studies of naturally occurring and introduced Pterocarya Kunth representatives reveal the taxonomic significance of pollen morphological features and pollen characters of cultivated plants. The quality of pollen material and the potential of the plants from the Botanical Garden of BIN RAS for introduction are characterized.Materials and methods.Pollen grains were investigated using light, confocal laser scanning and scanning electron microscopes. Fertility was assessed using the standard acetocarmine method.Results.Comparison of pollen morphology in cultivated and naturally growing plants of this genus was made for the first time. Pollen fertility of two cultivated species (Pterocarya rhoifolia Siebold et Zucc., and P. stenoptera DC.) was very high, generally over 90%. Fertility of P. fraxinifolia (Lam.) Spach grains varied from 28 to 73% in different years, which is a low or medium level of pollen quality. Morphologically, pollen grains of all 12 specimens from five taxa are flattened, medium sized, 21–45 μm in diameter, with 4–8 pores; pores are located mainly at or near the equator. The pores are round or oval, with a limbus. Exine is three-layered, thickened near the pore. The sculpture is microechinate. The low-fertile P. fraxinifolia specimen contains small pollen grains, as well as grains in tetrads and dyads. The data on the introduction of the genus in St. Petersburg are presented.Conclusion.The palynonomophological description is diagnostic for the genus Pterocarya. The Pterocarya pollen is well distinguishable from other wind-pollinated taxa; however, species identification by pollen for spore-pollen analysis is not practicable. Morphologically, the most diverse are the grains of the low fertile specimen P. fraxinifolia. The limited possibility of seed propagation of P. fraxinifolia is probably explained by low pollen fertility. The pollen quality of the introduced P. rhoifolia and P. stenoptera is high.

Mixed pollination system and floral signals of Paepalanthus (Eriocaulaceae): insects and geitonogamy ensure high reproductive success.

Eriocaulaceae exhibit a great variety of floral traits associated with insect (e.g. nectariferous structures) and wind pollination (unisexual flowers, exposed sexual organs and small pollen grains), as well as the 'selfing syndrome' (small flowers, short distance between stigma and anthers, and temporal overlap of male and female phases). Paepalanthus bifidus, P. subtilis and P. tortilis are related species that differ in form, size and colour of floral structures. We aimed to investigate the pollination and reproductive biology of these three species. We analysed the floral biology, floral visitors, pollinator behaviour, and the contribution of insects, wind and spontaneous geitonogamy to fruit set. We also evaluated the floral colour and scent of the species. Colour reflectance of capitula of each species was measured and plotted in models of insect vision. Floral scent samples were extracted and the compounds were compared to vegetative scent samples. In all species, the staminate and pistillate flowers are arranged in alternating cycles with a temporal overlap between these phases. Ants were the most frequent floral visitors and were effective pollinators in P. bifidus and P. tortilis, while flies were occasional pollinators in P. tortilis. Floral visitors were not observed in P. subtilis. In all species, fruits were produced by spontaneous geitonogamy, with no evidence of wind pollination. According to the models of insect vision, the colours of the capitula of P. bifidus and P. subtilis are the most inconspicuous for ants and flies. We found no difference between the emission of volatiles of inflorescences and vegetative structures. This study suggests that ant pollination might be more widespread in Eriocaulaceae than currently assumed. Furthermore, for small monocarpic plants, mixed mating strategies are most favourable, by ensuring reproduction either by outcrossing when pollinators are abundant or by spontaneous geitonogamy when pollinations are scarce/absent.

Pollen typification and palynotaxonomy of subfamily Salsoloideae Ulbr. (Chenopodiaceae Vent.) in the flora of South Transcaucasia

The article presents the results of a comparative palyno-morphological analysis of the representatives of the Salsoloideae subfamily (Chenopodiaceae) in South Transcaucasia. Out of 25 species belonging to 13 genera of Salsoloideae subfamily in South Transcaucasia, pollen morphology of 23 species from 12 genera was investigated, as well as an analysis of the pollen characteristics was conducted. Data on five key features of pollen (on LM level) were statistically analyzed including pollen diameter, pore number, pore diameter, exine thickness, and mesoporium width. The results indicated that within the Salsoloideae subfamily of South Transcaucasian flora the first three features may be considered diagnostic. The application of a scanning electron microscope (SEM) has revealed the fourth diagnostic feature of the pollen within the Salsoloideae subfamily, specifically, the number of spinules on the unit surface of the pollen, which enables, in several cases, to conduct intergeneric or interspecific differentiation. Based on the obtained data, typification of pollen within the Salsoloideae subfamily of South Transcaucasia was carried out for the first time. As a result, two morphological types and four subtypes combined in two palynogroups were distinguished. The subdivision into palynogroups is based on differences in the size of pollen grains. Only species Climacoptera crassa with pollen of average sizes (26–33/29 μm in diameter) is included into the monotypic Palynogroup I, all other investigated species with small pollen grains (10–25 (27)/22 μm in diameter) are joined in Palynogroup II. Allocation of species into two different Types of Palynogroup II is based on the presence of a significant difference in the size of small pollen grains of individual species. In particular, species with relatively large pollen grains (> 20 μm in diameter) are included in Type 1, while species with relatively small ones (≤ 20 μm in diameter) are joined in Type 2. And finally, the distribution of species into the subtypes and variations of Palynogroup II is based on differences in pore number and size. The identified key palyno-morphological features made it possible in some cases to specify the taxonomic boundaries, as well as the relationship between taxa within the subfamily Salsoloideae.

Studies on size, sterility and germination of pollen grains of certain members of the family Malvaceae

The present study attempted to evaluate the pollen size, percentage of sterility using acetocarmine, percentage of germination in sucrose medium among the members of the family Malvaceae like Malvaviscus arboreus Cav., Sida rhombifolia L., Urena lobata L. Hibiscus furcatus Roxb. Hibiscus rosa-sinensis L. and Gossypium arboreum L. Regarding the size pollen grains of Hibiscus rosa-sinensis showed largest pollen. The smallest pollen grains belong to Urena lobata, L. The pollen sterility using acetocarmine indicated that the pollens of Hibiscus furcatus were completely fertile, while Sida rhombifolia showed highest amount of sterility. The germination of pollen grain in sucrose medium indicated that the pollen grain of all the members studied showed poor germination.

Palynological study on selected species from Hyacinthaceae with focus on taxonomical implications in Iran

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

<p><strong>Palynological observations on the genus <em>Gundelia </em>L. (Asteraceae) growing in Turkey</strong></p>

The pollen morphology of 17 taxa of Gundelia, of which 13 taxa are endemic to Turkey, was investigated by light microscopy (LM) and scanning electron microscopy (SEM). In this study, the pollen morphology of 16 taxa except G. tournefortii was investigated for the first time. The quantitative data were analyzed by descriptive statistics and multivariate statistics. The pollen grains are oblate spheroidal and prolate spheroidal in shape with the polar diameter of 37.01–61.2 μm and the equatorial diameter of 31.2–63.4 μm. The smallest pollen grains were observed in G. anatolica, G. rosea and G. tournefortii, while the largest pollen grains were observed in G. vitekii, G. komagenensis and G. colemerikensis. Pollen ornamentation is echinate in LM and echinate-microperforate in SEM. Statistically, the relationships between pollen characters of the examined taxa were identified using Principal Component Analysis (PCA) and Clustering Analyzis. In addition, a dendrogram was constructed by applying UPGMA based on the determined 15 pollen morphological characters, and the degree of their relationship was discussed. Polar axis, equatorial diameter and colpus length were the major explanations of the pollen morphological characters’ total variation in PCA. Pair group method was used to divide the main pollen taxa into three groups based on the pollen morphology by using arithmetic averages analysis (PCA scatterplot and cluster analysis). As a result, the pollen shape, polar axis, equatorial diameter and spine length were important characters distingushing the taxa from each other. We found some matches and mismatches between pollen and morphological characters, whose significance requires further study.

Viability of black currant pollen before and after cryopreservation in liquid nitrogen, and its morphological features

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

<p><strong>Comparative assessment of pollen micromorphology of <em>Salvia assurgens</em> (Lamiaceae), an endemic sage from Mexico</strong></p>

The present study provides novel information about the pollen of Salvia assurgens. Pollen grains were collected and described based on their observed characters by light microscope and scanning electron microscopy. The species is distinguished from other Mexican salvias by having small pollen grains (14.2 × 18.2 µm), thin primary muri (0.2 µm thick), elongated primary lumina (1.03 µm long) and secondary lumina with relatively few perforations (9, range 5–14). Pollen characters are similar to those of the majority of American salvias. Regarding Mexican sages, there has been little palynological research, and only 23 species of 32 examined have been quantitatively studied. Standardization is needed in different aspects of palynological studies, especially in relation to measurement protocols and data analysis, as well as the increased use of scanning electron microscopy (SEM), since the majority of differences among species are provided by SEM microscope observation.

Supergene evolution via stepwise duplications and neofunctionalization of a floral-organ identity gene

Heterostyly represents a fascinating adaptation to promote outbreeding in plants that evolved multiple times independently. While l-morph individuals form flowers with long styles, short anthers, and small pollen grains, S-morph individuals have flowers with short styles, long anthers, and large pollen grains. The difference between the morphs is controlled by an S-locus "supergene" consisting of several distinct genes that determine different traits of the syndrome and are held together, because recombination between them is suppressed. In Primula, the S locus is a roughly 300-kb hemizygous region containing five predicted genes. However, with one exception, their roles remain unclear, as does the evolutionary buildup of the S locus. Here we demonstrate that the MADS-box GLOBOSA2 (GLO2) gene at the S locus determines anther position. In Primula forbesii S-morph plants, GLO2 promotes growth by cell expansion in the fused tube of petals and stamen filaments beneath the anther insertion point; by contrast, neither pollen size nor male incompatibility is affected by GLO2 activity. The paralogue GLO1, from which GLO2 arose by duplication, has maintained the ancestral B-class function in specifying petal and stamen identity, indicating that GLO2 underwent neofunctionalization, likely at the level of the encoded protein. Genetic mapping and phylogenetic analysis indicate that the duplications giving rise to the style-length-determining gene CYP734A50 and to GLO2 occurred sequentially, with the CYP734A50 duplication likely the first. Together these results provide the most detailed insight into the assembly of a plant supergene yet and have important implications for the evolution of heterostyly.

Pollen grain size associated with pollinator feeding strategy.

Angiosperm pollen grain diameter varies greatly from a few microns to over 100, but the selective forces driving the interspecific variation in pollen size remain unclear. Although both pre- and post-pollination hypotheses have been proposed, empirical evidence remains scarce. Here we propose that visits by pollen-foraging pollinators have selected against large pollen grains. An association between pollinator behaviour and pollen grain size was confirmed by field studies of 80 flowering species in natural communities, showing that pollinators positively collected pollen in those species with relatively smaller pollen grains but rarely did so in species with larger ones. Allowing for the confounding effects of pollinator type, flower size or style length and pollen grain number, we found a significant effect of pollen-foraging behaviour on variation in pollen grain size, particularly in bee-pollinated plants. While these results suggest that many plant species whose pollen is collected or consumed by pollinators produce small pollen grains, it remains unclear whether pollen grain size is directly affected by pollinator foraging habit or indirectly mediated by pollen number trade-offs.

Buckwheat heteromorphic self-incompatibility: genetics, genomics and application to breeding.

Common buckwheat (Fagopyrum esculentum Moench 2n = 2x = 16) is an outcrossing crop with heteromorphic self-incompatibility due to its distylous flowers, called pin and thrum. In pin plants, a long style is combined with short stamens and small pollen grains; in thrum plants, a short style is combined with long stamens and large pollen grains. Both the intra-morph self-incompatibility and flower morphology are controlled by a single genetic locus named the S locus; thrum plants are heterozygous (Ss) and pin plants are homozygous recessive (ss) at this locus. Self-incompatibility is an obstacle for establishing pure lines and fixation of agronomically useful genes. Elucidation of the molecular mechanism of heterostylous self-incompatibility of common buckwheat has continued for a quarter of a century. Recent advances in genomic and transcriptomic analyses using next-generation sequencing have made it possible to determine the genomic region harboring the buckwheat S locus and to identify novel genes at this locus. In this review, we summarize the current knowledge on buckwheat heterostyly gained from conventional and molecular genetics and genomics. We also discuss the application of these studies to breeding of common buckwheat.

Comparative palynology and seed morphology in annual pansies (Viola sect. Melanium, Violaceae): implications for species delimitation

This integrated study provides new insights into pollen and seed morphology and pollen heteromorphism of four closely related annual taxa of Viola sect. Melanium. The plant material, both fresh and dried, was collected in Italy and studied using light and scanning electron microscope. Palynological data for V. hymettia together with a detailed comparative analysis of seed morphology and micromorphology of the four species are reported for the first time. Results of this work highlight some pollen and seed features as useful diagnostic characters. The pollen size proves to be of diagnostic value to easily separate V. kitaibeliana, having the smallest pollen grains, from the others, especially from V. arvensis with the largest ones. Exine ornamentation is microreticulate, showing no relevant differences among species. We can partially confirm the diagnostic value of the prevailing pollen morph as it can be useful only for V. arvensis (five-aperturate) versus V. tricolor and V. hymettia (four-aperturate). The macro- and micromorphology of seeds provide additional useful distinguishing characters. Particularly, seed size was found to be a good delimitating character, especially to distinguish V. kitaibeliana (with the smallest seeds) from V. arvensis, and easy to be measured with no need of particular equipment.

Reproductive development response to high daytime temperature in field pea

AbstractFlowering plants are highly sensitive to heat stress during reproductive phase, which covers development from floral initiation to seed maturity. The objectives of this study were to diagnose high temperature effects on pollen production and morphology, production of reactive oxygen species (ROS) in pollen grains and ovules in pea cultivar “CDC Golden.” This study also investigated timing and duration of heat exposure at specific developmental stages of floral buds, open flowers and early set pods on flower and pod abortion, seed development and seed yield in “CDC Golden” and a second cultivar “CDC Sage.” The experiments were conducted in growth chambers with two temperature regimes (24/18°C and 35/18°C day/night temperature for 4–14 days) during reproductive development. Heat stress reduced the number of pollen grains per anther, induced smaller pollen grains and increased ROS production in pollen grains, but it did not affect ROS accumulation in ovules and ovule number per ovary. Heat exposure when young floral buds were visible at the first reproductive node was more detrimental to flower retention, seed set, pod development and seed yield compared to heat exposure started later when flowers at the second reproductive node were fully open.