Pollen, anther, stamen, and androecium mimicry.

Floral colours represent a highly diverse communication signal mainly involved in flower visitors' attraction and guidance, but also flower discrimination, filtering non-pollinators and discouraging floral antagonists. The divergent visual systems and colour preferences of flower visitors, as well as the necessity of cues for flower detection and discrimination, foster the diversity of floral colours and colour patterns. Despite the bewildering diversity of floral colour patterns, a recurrent component is a yellow UV-absorbing floral centre, and it is still not clear why this pattern is so frequent in angiosperms. The pollen, anther, stamen, and androecium mimicry (PASAM) hypothesis suggests that the system composed of the flowers possessing such yellow UV-absorbing floral reproductive structures, the flowers displaying central yellow UV-absorbing structures as floral guides, and the pollen-collecting, as well as pollen-eating, flower visitors responding to such signals constitute the world's most speciose mimicry system. In this review, we call the attention of researchers to some hypothetical PASAM systems around the globe, presenting some fascinating examples that illustrate their huge diversity. We will also present new and published data on pollen-eating and pollen-collecting pollinators' responses to PASAM structures supporting the PASAM hypothesis and will discuss how widespread these systems are around the globe. Ultimately, our goal is to promote the idea that PASAM is a plausible first approach to understanding floral colour patterns in angiosperms.

Pollen-stigma incompatibility within and between species: Tread lightly, sedate the dogs, and don't wake the guards!

In a recent issue of Nature, Huang et al. identify and show how to overcome the barriers to successful pollen germination after interspecific crosses.1 Their findings answer a long-standing question about reproductive barriers in flowering plants and open the door to harnessing genetic diversity of distant relatives for crop improvement.

Global analysis of floral longevity reveals latitudinal gradients and biotic and abiotic correlates.

The length of time a flower remains open and functional - floral longevity - governs important reproductive processes influencing pollination and mating and varies considerably among angiosperm species. However, little is known about large-scale biogeographic patterns and the correlates of floral longevity. Using published data on floral longevity from 818 angiosperm species in 134 families and 472 locations world-wide, we present the first global quantification of the latitudinal pattern of floral longevity and the relationships between floral longevity and a range of biotic and abiotic factors. Floral longevity exhibited a significant phylogenetic signal and was longer at higher latitudes in both northern and southern hemispheres, even after accounting for elevation. This latitudinal variation was associated with several biotic and abiotic variables. The mean temperature of the flowering season had the highest predictive power for floral longevity, followed by pollen number per flower. Surprisingly, compatibility status, flower size, pollination mode, and growth form had no significant effects on flower longevity. Our results suggest that physiological processes associated with floral maintenance play a key role in explaining latitudinal variation in floral longevity across global ecosystems, with potential implications for floral longevity under global climate change and species distributions.

Plant biodiversity assessment through pollen DNA metabarcoding in Natura 2000 habitats (Italian Alps).

Monitoring biodiversity is of increasing importance in natural ecosystems. Metabarcoding can be used as a powerful molecular tool to complement traditional biodiversity monitoring, as total environmental DNA can be analyzed from complex samples containing DNA of different origin. The aim of this research was to demonstrate the potential of pollen DNA metabarcoding using the chloroplast trnL partial gene sequencing to characterize plant biodiversity. Collecting airborne biological particles with gravimetric Tauber traps in four Natura 2000 habitats within the Natural Park of Paneveggio Pale di San Martino (Italian Alps), at three-time intervals in 1 year, metabarcoding identified 68 taxa belonging to 32 local plant families. Metabarcoding could identify with finer taxonomic resolution almost all non-rare families found by conventional light microscopy concurrently applied. However, compared to microscopy quantitative results, Poaceae, Betulaceae, and Oleaceae were found to contribute to a lesser extent to the plant biodiversity and Pinaceae were more represented. Temporal changes detected by metabarcoding matched the features of each pollen season, as defined by aerobiological studies running in parallel, and spatial heterogeneity was revealed between sites. Our results showcase that pollen metabarcoding is a promising approach in detecting plant species composition which could provide support to continuous monitoring required in Natura 2000 habitats for biodiversity conservation.

Turgor regulation defect 1 proteins play a conserved role in pollen tube reproductive innovation of the angiosperms.

Sexual reproduction in angiosperms is siphonogamous, and the interaction between pollen tube and pistil is critical for successful fertilization. Our previous study demonstrated that mutation of the Arabidopsis turgor regulation defect 1 (TOD1) gene leads to reduced male fertility, a result of retarded pollen tube growth in the pistil. TOD1 encodes a Golgi-localized alkaline ceramidase, a key enzyme for the production of sphingosine-1-phosphate (S1P), which is involved in the regulation of turgor pressure in plant cells. However, whether TOD1s play a conserved role in the innovation of siphonogamy is largely unknown. In this study, we provide evidence that OsTOD1, which is similar to AtTOD1, is also preferentially expressed in rice pollen grains and pollen tubes. OsTOD1 knockout results in reduced pollen tube growth potential in rice pistil. Both the OsTOD1 genomic sequence with its own promoter and the coding sequence under the AtTOD1 promoter can partially rescue the attod1 mutant phenotype. Furthermore, TOD1s from other angiosperm species can partially rescue the attod1 mutant phenotype, while TOD1s from gymnosperm species are not able to complement the attod1 mutant phenotype. Our data suggest that TOD1 acts conservatively in angiosperms, and this opens up an opportunity to dissect the role of sphingolipids in pollen tube growth in angiosperms.

Epicormic bud protection traits vary along a latitudinal gradient in a neotropical savanna.

Regrowth via production of epicormic shoots is an important strategy for many woody plants after environmental disturbances such as fire, drought, and herbivory. Populations spreading across a broad latitudinal gradient offer opportunities to investigate if essential traits vary with heterogenous environmental conditions, such as in savanna ecosystems. This information can help us predict plant responses to climate change. Here, we evaluated if epicormic bud protection traits varied among populations of three focal savanna species (Miconia albicans, Solanum lycocarpum, and Zeyheria montana) that have a wide distribution and grow under variable climatic conditions. We randomly sampled 225 individuals over five spatially independent sites (7°, 10°, 15°, 18°, and 24° S) in Brazil, totaling 15 individuals per species per area. We analyzed anatomical transverse sections of five buds per species per area to assess the relative area occupied by crystal and phenolic idioblasts, the thickness of the trichome boundary layer, and to test if these traits were associated with climatic conditions. The buds were protected by cataphylls and composed of a variable number of undeveloped leaves enveloping the shoot apex. For M. albicans, we found an association between maximum temperature and both phenolic idioblasts and trichome boundary layer, but no association with crystal idioblasts. In S. lycocarpum, only the trichome boundary layer was associated with maximum temperature plus high radiation. Z. montana showed no variation. Combination of two or more traits can lead to the development of adaptative strategies to different climatic conditions. We present for the first time an analysis of epicormic bud traits in plant populations occurring in an extensive latitudinal gradient and shed light on how maximum temperature is associated with these traits, contributing to a better understanding of plant resprouting capabilities in widespread savanna plant species.

North American Prairie Is a Source of Pollen for Managed Honey Bees (Hymenoptera: Apidae).

Prairie was a dominant habitat within large portions of North America before European settlement. Conversion of prairies to farmland resulted in the loss of a large proportion of native floral resources, contributing to the decline of native pollinator populations. Efforts to reconstruct prairie could provide honey bees (Apis mellifera) a source of much-needed forage, especially in regions dominated by crop production. To what extent honey bees, which were introduced to North America by European settlers, use plants native to prairies is unclear. We placed colonies with pollen traps within reconstructed prairies in central Iowa to determine which and how much pollen is collected from prairie plants. Honey bee colonies collected more pollen from nonnative than native plants during June and July. During August and September, honey bee colonies collected more pollen from plants native to prairies. Our results suggest that honey bees' use of native prairie plants may depend upon the seasonality of both native and nonnative plants present in the landscape. This finding may be useful for addressing the nutritional health of honey bees, as colonies in this region frequently suffer from a dearth of forage contributing to colony declines during August and September when crops and weedy plants cease blooming. These results suggest that prairie can be a significant source of forage for honey bees in the later part of the growing season in the Midwestern United States; we discuss this insight in the context of honey bee health and biodiversity conservation.

Biosynthesis and characterization of silver nanoparticles using Ochradenus arabicus and their physiological effect on Maerua oblongifolia raised in vitro.

Silver nanoparticles (AgNPs) are presently the most commonly generated engineered nanomaterials and are found in a wide range of agro-commercial products. The present study was designed to synthesize AgNPs biologically using Ochradenus arabicus leaves and investigate their effect on the morphophysiological properties of Maerua oblongifolia raised in vitro. Physicochemical methods (ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy were performed for characterization and for obtaining microphotographs of the AgNPs. Shoots of M. oblongifolia (2-3 cm) grown in Murashige and Skoog medium supplemented with different concentrations of AgNPs (0, 10, 20, 30, 40, or 50 mg L-1) were used. Following 6 weeks of in vitro shoot regeneration, the shoot number, shoot length, leaf number, fresh weight, dry weight, chlorophyll content, total protein, proline level, and antioxidant enzyme activities of the plants were quantified. We found that 20 mg L-1 AgNPs increased the shoot number, shoot length, fresh weight, dry weight, and chlorophyll content of the plants. The maximum total protein was recorded in plants that were administered the lowest dose of AgNPs (10 mg L-1), while high concentrations of AgNPs (40 and 50 mg L-1) increased the levels of proline and the enzymes superoxide dismutase and catalase. Our results indicate that green-synthesized AgNPs may be of agricultural and medicinal interest owing to their effects on plants in vitro.

Dimorphic flowers modify the visitation order of pollinators from male to female flowers.

Sexual dimorphism is a pervasive form of variation within species. Understanding how and why sexual dimorphism evolves would contribute to elucidating the mechanisms underlying the diversification of traits. In flowering plants, pollinators are considered a driver of sexual dimorphism when they affect female and male plant fitness in distinct ways. Here, we found that flowers appear to manipulate the behavior of pollinators using sexually dimorphic traits in the dioecious tree Eurya japonica. In this plant, female flowers present a higher-quality reward for pollinators, whereas male flowers have a more conspicuous appearance. Plants benefit by inducing pollinators to carry pollen from male to female flowers, and their sexual dimorphism might thus facilitate pollen movement through pollinator behavior. In two-choice experiments, pollinators frequently moved from male to female flowers, whereas computer simulation suggested that sexually dimorphic traits would evolve if pollinators changed behavior depending on the traits of the flowers they had just visited. These results suggest that the floral traits affecting the visiting order of pollinators have evolved in plants. Using E. japonica, we theoretically show that the induction of sequential behavior in pollinators might be crucial to the evolution of sexual dimorphism in flowers, and our experiments support these findings.

The maleness of larger angiosperm flowers.

Flower biomass varies widely across the angiosperms. Each plant species invests a given amount of biomass to construct its sex organs. A comparative understanding of how this limited resource is partitioned among primary (male and female structures) and secondary (petals and sepals) sexual organs on hermaphrodite species can shed light on general evolutionary processes behind flower evolution. Here, we use allometries relating different flower biomass components across species to test the existence of broad allocation patterns across the angiosperms. Based on a global dataset with flower biomass spanning five orders of magnitude, we show that heavier angiosperm flowers tend to be male-biased and invest strongly in petals to promote pollen export, while lighter flowers tend to be female-biased and invest more in sepals to insure their own seed set. This result demonstrates that larger flowers are not simple carbon copies of small ones, indicating that sexual selection via male-male competition is an important driver of flower biomass evolution and sex allocation strategies across angiosperms.

Fertilization in flowering plants: an odyssey of sperm cell delivery.

KEY MESSAGE: In light of the available discoveries in the field, this review manuscript discusses on plant reproduction mechanism and molecular players involved in the process. Sperm cells in angiosperms are immotile and are physically distant to the female gametophytes (FG). To secure the production of the next generation, plants have devised a clever approach by which the two sperm cells in each pollen are safely delivered to the female gametophyte where two fertilization events occur (by each sperm cell fertilizing an egg cell and central cell) to give rise to embryo and endosperm. Each of the successfully fertilized ovules later develops into a seed. Sets of macromolecules play roles in pollen tube (PT) guidance, from the stigma, through the transmitting tract and funiculus to the micropylar end of the ovule. Other sets of genetic players are involved in PT reception and in its rupture after it enters the ovule, and yet other sets of genes function in gametic fusion. Angiosperms have come long way from primitive reproductive structure development to today's sophisticated, diverse, and in most cases flamboyant organ. In this review, we will be discussing on the intricate yet complex molecular mechanism of double fertilization and how it might have been shaped by the evolutionary forces focusing particularly on the model plant Arabidopsis.

Greenhouse gas emissions and wastewater treatment performance by three plant species in subsurface flow constructed wetland mesocosms.

Greenhouse gas (GHG) emissions from constructed wetlands (CWs) have raised environmental concern and thus offset their environmental and ecological benefits. This study evaluated the influence of plant species, i.e., Canna indica (C. indica), Cyperus alternifolius (C. alternifolius), Phragmites australis (P. australis) and unplanted control, on GHG emissions, pollutant removal and associated microbial abundance in subsurface flow constructed wetland (SSFCW) mesocosms. C. indica outperformed the other tested plant species in pollutant removal, and the presence of plants irrespective of species enhanced the removal efficiencies of nitrogen, phosphorus and organics in SSFCW mesocosms compared to unplanted control. The greatest carbon dioxide (CO2) flux (582.01 ±â€¯89.25 mg/m2/h), methane (CH4) flux (21.88 ±â€¯2.51 µg/m2/h) and nitrous oxide (N2O) flux (37.27 ±â€¯15.82 µg/m2/h) were observed in mesocosms planted with C. indica, P. australis and C.alternifolius, respectively. Unexpectedly, the mcrA and pmoA genes were not detected in any mesocosms. For denitrifiers, the N2O fluxes showed a significantly (p < 0.05) positive correlation with nirS and nirK genes abundance. The abundance of nosZ gene (ranged from 0.18 × 104 to 0.75 × 104 copies/mg gravel) and nosZ/(nirS + nirK) (ranged from 1.29 × 10-4 to 2.12 × 10-4 copies/mg gravel) in this study was lower than that in most reported studies. Regarding the global warming potential (GWP), the lowest value was observed in mesocosms planted with C. indica. In conclusion, C. indica is selected as the optimal plant species in this study due to its lower GWP and excellent pollutant removal performance.

Deterioration of ovary plays a key role in heat stress-induced spikelet sterility in sorghum.

In sorghum (Sorghum bicolor [L.] Moench), the impact of heat stress during flowering on seed set is known, but mechanisms that lead to tolerance are not known. A diverse set of sorghum genotypes was tested under controlled environment and field conditions to ascertain the impact of heat stress on time-of-day of flowering, pollen viability, and ovarian tissue. A highly conserved early morning flowering was observed, wherein >90% of spikelets completed flowering within 30 min after dawn, both in inbreds and hybrids. A strong quantitative impact of heat stress was recorded before pollination (reduced pollen viability) and post pollination (reduced pollen tube growth and linear decline in fertility). Although viable pollen tube did reach the micropylar region, 100% spikelet sterility was recorded under 40/22°C (day/night temperatures), even in the tolerant genotype Macia. Heat stress induced significant damage to the ovarian tissue near the micropylar region, leading to highly condensed cytoplasmic contents and disintegrated nucleolus and nucleus in the susceptible genotype RTx430. Whereas, relatively less damages to ovarian cell organelles were observed in the tolerant genotype Macia under heat stress. Integrating higher tolerance in female reproductive organ will help in effective utilization of the early morning flowering mechanism to enhance sorghum productivity under current and future hotter climate.

Pollination of Cretaceous flowers.

Insect pollination of flowering plants (angiosperms) is responsible for the majority of the world's flowering plant diversity and is key to the Cretaceous radiation of angiosperms. Although both insects and angiosperms were common by the mid-Cretaceous, direct fossil evidence of insect pollination is lacking. Direct evidence of Cretaceous insect pollination is associated with insect-gymnosperm pollination. Here, we report a specialized beetle-angiosperm pollination mode from mid-Cretaceous Burmese amber (99 mega-annum [Ma]) in which a tumbling flower beetle (Mordellidae), Angimordella burmitina gen. et sp. nov., has many tricolpate pollen grains attached. A. burmitina exhibits several specialized body structures for flower-visiting behavior including its body shape and pollen-feeding mouthparts revealed by X-ray microcomputed tomography (micro-CT). The tricolpate pollen in the amber belongs to the eudicots that comprise the majority of extant angiosperm species. These pollen grains exhibit zoophilous pollination attributes including their ornamentation, size, and clumping characteristics. Tricolpate pollen grains attached to the beetle's hairs are revealed by confocal laser scanning microscopy, which is a powerful tool for investigating pollen in amber. Our findings provide direct evidence of insect pollination of Cretaceous angiosperms, extending the range insect-angiosperm pollination association by at least 50 million years. Our results support the hypothesis that specialized insect pollination modes were present in eudicots 99 million years ago.

TOR and SnRK1 signaling pathways in plant response to abiotic stresses: Do they always act according to the "yin-yang" model?

Plants are sessile photo-autotrophic organisms continuously exposed to a variety of environmental stresses. Monitoring the sugar level and energy status is essential, since this knowledge allows the integration of external and internal cues required for plant physiological and developmental plasticity. Most abiotic stresses induce severe metabolic alterations and entail a great energy cost, restricting plant growth and producing important crop losses. Therefore, balancing energy requirements with supplies is a major challenge for plants under unfavorable conditions. The conserved kinases target of rapamycin (TOR) and sucrose-non-fermenting-related protein kinase-1 (SnRK1) play central roles during plant growth and development, and in response to environmental stresses; these kinases affect cellular processes and metabolic reprogramming, which has physiological and phenotypic consequences. The "yin-yang" model postulates that TOR and SnRK1 act in opposite ways in the regulation of metabolic-driven processes. In this review, we describe and discuss the current knowledge about the complex and intricate regulation of TOR and SnRK1 under abiotic stresses. We especially focus on the physiological perspective that, under certain circumstances during the plant stress response, the TOR and SnRK1 kinases could be modulated differently from what is postulated by the "yin-yang" concept.

Risk versus reward: host dependent parasite mortality rates and phenotypes in the facultative generalist Triphysaria versicolor.

BACKGROUND: Parasitic plants engage in a complex molecular dialog with potential host plants to identify a host and overcome host defenses to initiate development of the parasitic feeding organ, the haustorium, invade host tissues, and withdraw water and nutrients. While one of two critical signaling events in the parasitic plant life cycle (germination via stimulant chemicals) has been relatively well-studied, the signaling event that triggers haustorium formation remains elusive. Elucidation of this poorly understood molecular dialogue will shed light on plant-plant communication, parasitic plant physiology, and the evolution of parasitism in plants. RESULTS: Here we present an experimental framework that develops easily quantifiable contrasts for the facultative generalist parasitic plant, Triphysaria, as it feeds across a broad range of diverse flowering plants. The contrasts, including variable parasite growth form and mortality when grown with different hosts, suggest a dynamic and host-dependent molecular dialogue between the parasite and host. Finally, by comparing transcriptome datasets from attached versus unattached parasites we gain insight into some of the physiological processes that are altered during parasitic behavior including shifts in photosynthesis-related and stress response genes. CONCLUSIONS: This work sheds light on Triphysaria's parasitic life habit and is an important step towards understanding the mechanisms of haustorium initiation factor perception, a unique form of plant-plant communication.

Flowers anticipate revisits of pollinators by learning from previously experienced visitation intervals.

Plants - and their pollinating counterparts - display complex and sophisticated mechanisms to achieve successful pollination. It probably was only a matter of time for proof of plant intelligence in the context of floral ecology to surface, i.e. the memorization of previous events and a corresponding adjustment of flower behavior. In a recent study we presented a large experimental dataset on the evolution of stamen movement patterns observed in Loasaceae and the apparent role of plant behavior in the diversification of this plant group. The findings at species level suggest that individual plants may be able to adjust the timing of their pollen presentation to the actual pollination scenario they experience. Here we provide first evidence for a pre-emptive stamen presentation in Nasa poissoniana (Loasaceae), based on previously experienced pollinator visitation intervals. Using the unique ability of fast and precise stamen movements in response to a previous stimulus of the nectar scales, the plants should be able to reduce pollen loss and increase outbreeding success via optimizing the timing of male function. We discuss this behavior and its implications in the light of the recent literature and propose questions for future investigations.

When flowering plants ruled Antarctica: evidence from Cretaceous pollen grains.

The replacement of seed-free plants and gymnosperms by flowering plants during the Cretaceous is one of the most important biotic events in the evolution of life. However, the magnitude of this global turnover remains largely unknown. Here we present sampling-standardized diversity estimates from a high resolution palynological record of the Late Cretaceous (85-66 Ma) from Antarctica, in the context of the past climatic events. Our fossil evidence reveals the occurrence of a rich Campanian flora peaking at c. 80 Ma, with angiosperms as the most diverse group of plants for the first time in Antarctica. This peak of diversity was followed by a period of a stepwise deterioration; 60% of ferns and 40% of gymnosperms became locally extinct from the early/mid-Campanian to the late Maastrichtian. Although angiosperms also faced several extinctions - 25% became extinct - they were far less affected than nonangiosperms. The onset of deterioration of the greenhouse conditions at the end of the Cretaceous - low CO2 and global cooling trends - would have led to our observed pattern of change. Overall, our study reveals the beginning of a profound floristic turnover in the highest southern latitudes that pre-dates the major extinction event of the end of the Cretaceous by 15 Myr.

Floral plasticity: Herbivore-species-specific-induced changes in flower traits with contrasting effects on pollinator visitation.

Plant phenotypic plasticity in response to antagonists can affect other community members such as mutualists, conferring potential ecological costs associated with inducible plant defence. For flowering plants, induction of defences to deal with herbivores can lead to disruption of plant-pollinator interactions. Current knowledge on the full extent of herbivore-induced changes in flower traits is limited, and we know little about specificity of induction of flower traits and specificity of effect on flower visitors. We exposed flowering Brassica nigra plants to six insect herbivore species and recorded changes in flower traits (flower abundance, morphology, colour, volatile emission, nectar quantity, and pollen quantity and size) and the behaviour of two pollinating insects. Our results show that herbivory can affect multiple flower traits and pollinator behaviour. Most plastic floral traits were flower morphology, colour, the composition of the volatile blend, and nectar production. Herbivore-induced changes in flower traits resulted in positive, negative, or neutral effects on pollinator behaviour. Effects on flower traits and pollinator behaviour were herbivore species-specific. Flowers show extensive plasticity in response to antagonist herbivores, with contrasting effects on mutualist pollinators. Antagonists can potentially act as agents of selection on flower traits and plant reproduction via plant-mediated interactions with mutualists.

Correlated evolution of self and interspecific incompatibility across the range of a Texas wildflower.

Selection to prevent interspecific mating can cause an increase or a decrease in self-pollination in sympatric populations. Characterizing the geographical variation in self and interspecific incompatibilities within a species can reveal if and how the evolution of self and interspecific mate choice are linked. We used controlled pollinations to characterize the variation in self and interspecific incompatibility across 29 populations of Phlox drummondii. We evaluated seed set from these pollinations and described the developmental timing of variation in pollen-pistil compatibility. There is extensive quantitative variation in self-incompatibility and interspecific-incompatibility with its close congener P. cuspidata. Phlox drummondii populations that co-occur and hybridize with P. cuspidata have significantly higher interspecific incompatibility and self-incompatibility than geographically isolated P. drummondii populations. The strength of self and interspecific incompatibility is significantly correlated among individuals and the strength of both incompatibilities is explained by the success of pollen adhesion to the stigma. The correlated strength of self and interspecific incompatibility across the range of P. drummondii and the concurrent developmental timing of the pollen-pistil interaction, suggests these incompatibilities have an overlapping molecular mechanism. The geographical distribution of variation in incompatibilities indicates that this mechanistic link between incompatibilities may affect the evolution of mate choice in plants.