Ripe pollen carbohydrate changes in Trachycarpus fortunei: the effect of relative humidity

Turtle ants harbor metabolically versatile microbiomes with conserved functions across development and phylogeny

Gut bacterial symbionts can support animal nutrition by facilitating digestion and providing valuable metabolites. However, changes in symbiotic roles between immature and adult stages are not well documented, especially in ants. Here, we explored the metabolic capabilities of microbiomes sampled from herbivorous turtle ant (Cephalotes sp.) larvae and adult workers through (meta)genomic screening and in vitro metabolic assays. We reveal that larval guts harbor bacterial symbionts with impressive metabolic capabilities, including catabolism of plant and fungal recalcitrant dietary fibers and energy-generating fermentation. Additionally, several members of the specialized adult gut microbiome, sampled downstream of an anatomical barrier that dams large food particles, show a conserved potential to depolymerize many dietary fibers. Symbionts from both life stages have the genomic capacity to recycle nitrogen and synthesize amino acids and B-vitamins. With help of their gut symbionts, including several bacteria likely acquired from the environment, turtle ant larvae may aid colony digestion and contribute to colony-wide nitrogen, B-vitamin and energy budgets. In addition, the conserved nature of the digestive capacities among adult-associated symbionts suggests that nutritional ecology of turtle ant colonies has long been shaped by specialized, behaviorally-transferred gut bacteria with over 45 million years of residency.

Light and electron microscopies reveal unknown details of the pollen grain structure and physiology from Brazilian Cerrado species

Pollen grains have a relatively simple structure and microscopic size, with two or three cells surrounded by the protective sporoderm at maturity. The viability and efficiency of pollen transport from anther to stigma depends on pollen physiological properties, especially the relative water content of the vegetative cell. Pollen transport is a crucial fate for most angiosperms that depends on biotic pollinators and studies focusing on understanding the morpho-physiological properties of pollen grains are still scarce, especially to tropical open physiognomies as the Brazilian Cerrado. Therefore, we investigate some structural and physiological aspects of pollen grains from six native species naturally growing in one Cerrado area: Campomanesia pubescens (Myrtaceae), Caryocar brasiliense (Caryocaraceae), Erythroxylum campestre (Erythroxylaceae), Lippia lupulina (Verbenaceae), Pyrostegia venusta (Bignoniaceae), and Xylopia aromatica (Annonaceae). We selected dehiscent anthers and mature pollen grains to analyze (1) the anther wall and pollen microstructure, (2) the pollen water status at the time of anther dehiscence, and (3) the pollen chemical compounds. In all analyzed species, the anther and pollen developed in a successfully way, and except for Caryocar brasiliense, all species were able to emit pollen tubes in the germination tests. As expected for a dry and open environment, most species dispersed their pollen grains in a partially dehydrated form, as indicated by our harmomegathy experiment. As indicated by our study, the pollen ability in preventing dissection, maintaining its viability in a dry and hot environment during its transport from anther to stigma, may be related to the sporoderm apertures and to the reserve compounds, mainly carbohydrates in the form of hydrolysable starch grains.

Can pollen explain the seasonality of flu-like illnesses in the Netherlands?

Current models for flu-like epidemics insufficiently explain multi-cycle seasonality. Meteorological factors alone, including the associated behavior, do not predict seasonality, given substantial climate differences between countries that are subject to flu-like epidemics or COVID-19. Pollen is documented to be allergenic, it plays a role in immuno-activation and defense against respiratory viruses, and seems to create a bio-aerosol that lowers the reproduction number of flu-like viruses. Therefore, we hypothesize that pollen may explain the seasonality of flu-like epidemics, including COVID-19, in combination with meteorological variables. We have tested the Pollen-Flu Seasonality Theory for 2016-2020 flu-like seasons, including COVID-19, in the Netherlands, with its 17.4 million inhabitants. We combined changes in flu-like incidence per 100 K/Dutch residents (code: ILI) with pollen concentrations and meteorological data. Finally, a predictive model was tested using pollen and meteorological threshold values, inversely correlated to flu-like incidence. We found a highly significant inverse correlation of r(224) = -0.41 (p < 0.001) between pollen and changes in flu-like incidence, corrected for the incubation period. The correlation was stronger after taking into account the incubation time. We found that our predictive model has the highest inverse correlation with changes in flu-like incidence of r(222) = -0.48 (p < 0.001) when average thresholds of 610 total pollen grains/m³, 120 allergenic pollen grains/m³, and a solar radiation of 510 J/cm² are passed. The passing of at least the pollen thresholds, preludes the beginning and end of flu-like seasons. Solar radiation is a co-inhibitor of flu-like incidence, while temperature makes no difference. However, higher relative humidity increases with flu-like incidence. We conclude that pollen is a predictor of the inverse seasonality of flu-like epidemics, including COVID-19, and that solar radiation is a co-inhibitor, in the Netherlands.

Pollen Developmental Arrest: Maintaining Pollen Fertility in a World With a Changing Climate

During evolution of land plants, the haploid gametophytic stage has been strongly reduced in size and the diploid sporophytic phase has become the dominant growth form. Both male and female gametophytes are parasitic to the sporophyte and reside in separate parts of the flower located either on the same plant or on different plants. For fertilization to occur, bi-cellular or tri-cellular male gametophytes (pollen grains) have to travel to the immobile female gametophyte in the ovary. To survive exposure to a hostile atmosphere, pollen grains are thought to enter a state of complete or partial developmental arrest (DA). DA in pollen is strongly associated with acquisition of desiccation tolerance (DT) to extend pollen viability during air travel, but occurrence of DA in pollen is both species-dependent and at the same time strongly dependent on the reigning environmental conditions at the time of dispersal. Several environmental stresses (heat, drought, cold, humidity) are known to affect pollen production and viability. Climate change is also posing a serious threat to plant reproductive behavior and crop productivity. It is therefore timely to gain a better understanding of how DA and pollen viability are controlled in plants and how pollen viability can be protected to secure crop yields in a changing environment. Here, we provide an overview of how DA and pollen viability are controlled and how the environment affects them. We make emphasis on what is known and areas where a deeper understanding is needed.

ZmSTK1 and ZmSTK2, encoding receptor-like cytoplasmic kinase, are involved in maize pollen development with additive effect

Pollen germination and pollen tube growth are important physiological processes of sexual reproduction of plants and also are involved in signal transduction. Our previous study reveals that ZmSTK1 and ZmSTK2 are two receptor-like cytoplasmic kinases (RLCK) homologs in Zea mays as members of receptor-like protein kinase (RLK) subfamily, sharing 86% identity at the amino acid level. Here, we report that ZmSTK1 and ZmSTK2, expressed at late stages of pollen development, regulate maize pollen development with additive effect. ZmSTK1 or ZmSTK2 mutation exhibited severe pollen transmission deficiency, which thus influenced pollen fertility. Moreover, the kinase domains of ZmSTKs were cross-interacted with C-terminus of enolases detected by co-immunoprecipitation (Co-IP) and yeast two-hybrid system (Y2H), respectively. Further, the detective ZmSTK1 or ZmSTK2 was associated with decreased activity of enolases and also reduced downstream metabolite contents, which enolases are involved in glycolytic pathway, such as phosphoenolpyruvate (PEP), pyruvate, ADP/ATP, starch, glucose, sucrose and fructose. This study reveals that ZmSTK1 and ZmSTK2 regulate maize pollen development and indirectly participate in glycolytic pathway.

It is a matter of timing: asynchrony during pollen development and its consequences on pollen performance in angiosperms-a review

Functional pollen is needed to successfully complete fertilization. Pollen is formed inside the anthers following a specific sequence of developmental stages, from microsporocyte meiosis to pollen release, that concerns microsporocytes/microspores and anther wall tissues. The processes involved may not be synchronous within a flower, an anther, and even a microsporangium. Asynchrony has been barely analyzed, and its biological consequences have not been yet assessed. In this review, different processes of pollen development and lifetime, stressing on the possible consequences of their differential timing on pollen performance, are summarized. Development is usually synchronized until microsporocyte meiosis I (occasionally until meiosis II). Afterwards, a period of mostly asynchronous events extends up to anther opening as regards: (1) meiosis II (sometimes); (2) microspore vacuolization and later reduction of vacuoles; (3) amylogenesis, amylolysis, and carbohydrate inter-conversion; (4) the first haploid mitosis; and (5) intine formation. Asynchrony would promote metabolic differences among developing microspores and therefore physiologically heterogeneous pollen grains within a single microsporangium. Asynchrony would increase the effect of competition for resources during development and pollen tube growth and also for water during (re)hydration on the stigma. The differences generated by developmental asynchronies may have an adaptive role since more efficient pollen grains would be selected with regard to homeostasis, desiccation tolerance, resilience, speed of (re)hydration, and germination. The performance of each pollen grain which landed onto the stigma will be the result of a series of selective steps determined by its development, physiological state at maturity, and successive environmental constrains.

Carbohydrates, pollinators, and cycads

Cycad biology, ecology, and horticulture decisions are not supported by adequate research, and experiments in cycad physiology in particular have been deficient. Our recent report on free sugar content in a range of cycad taxa and tissues sets the stage for developing continued carbohydrate research. Growth and development of cycad pollen, mediation of the herbivory traits of specialist pollinators, and support of expensive strobilus behavioral traits are areas of cycad pollination biology that would benefit from a greater understanding of the role of carbohydrate relations.

Water status and associated processes mark critical stages in pollen development and functioning

BACKGROUND

The male gametophyte developmental programme can be divided into five phases which differ in relation to the environment and pollen hydration state: (1) pollen develops inside the anther immersed in locular fluid, which conveys substances from the mother plant--the microsporogenesis phase; (2) locular fluid disappears by reabsorption and/or evaporation before the anther opens and the maturing pollen grains undergo dehydration--the dehydration phase; (3) the anther opens and pollen may be dispersed immediately, or be held by, for example, pollenkitt (as occurs in almost all entomophilous species) for later dispersion--the presentation phase; (4) pollen is dispersed by different agents, remaining exposed to the environment for different periods--the dispersal phase; and (5) pollen lands on a stigma and, in the case of a compatible stigma and suitable conditions, undergoes rehydration and starts germination--the pollen-stigma interaction phase.

SCOPE

This review highlights the issue of pollen water status and indicates the various mechanisms used by pollen grains during their five developmental phases to adjust to changes in water content and maintain internal stability.

CONCLUSIONS

Pollen water status is co-ordinated through structural, physiological and molecular mechanisms. The structural components participating in regulation of the pollen water level, during both dehydration and rehydration, include the exine (the outer wall of the pollen grain) and the vacuole. Recent data suggest the involvement of water channels in pollen water transport and the existence of several molecular mechanisms for pollen osmoregulation and to protect cellular components (proteins and membranes) under water stress. It is suggested that pollen grains will use these mechanisms, which have a developmental role, to cope with environmental stress conditions.

Pollen and seed desiccation tolerance in relation to degree of developmental arrest, dispersal, and survival

In most species, arrest of growth and a decrease in water content occur in seeds and pollen before they are dispersed. However, in a few cases, pollen and seeds may continue to develop (germinate). Examples are cleistogamy and vivipary. In all other cases, seeds and pollen are dispersed with a variable water content (2-70%), and consequently they respond differently to environmental relative humidity that affects dispersal and maintenance of viability in time. Seeds with low moisture content shed by the parent plant after maturation drying can generally desiccate further to moisture contents in the range of 1-5% without damage and have been termed 'orthodox'. Pollen that can withstand dehydration also was recently termed orthodox. Seeds and pollen that do not undergo maturation drying and are shed at relatively high moisture contents (30-70%) are termed 'recalcitrant'. Since recalcitrant seeds and pollen are highly susceptible to desiccation damage, they cannot be stored under conditions suitable for orthodox seeds and pollen. Hence, there are four types of plants with regard to tolerance of pollen and seeds to desiccation. Orthodoxy allows for dispersal over greater distances, longer survival, and greater resistance to low relative humidity. The advantage of recalcitrance is fast germination. Orthodoxy and recalcitrance are often related to environment rather than to systematics. It has been postulated that certain types of genes are involved during presentation and dispersal of pollen and seeds, since molecules (sucrose, polyalcohols, late embryogenic abundant proteins, antioxidants, etc.) that protect different cell compartments during biologically programmed drying have been detected in both.

The impact of plant and flower age on mating patterns

BACKGROUND

Over a season, plant condition, amount of ongoing reproduction and biotic and abiotic environmental factors vary. As flowers age, flower condition and amount of pollen donated and received also vary. These internal and external changes are significant for fitness if they result in changes in reproduction and mating.

SCOPE

Literature from several fields was reviewed to provide a picture of the changes that occur in plants and flowers that can affect mating over a season. As flowers age, both the entire flower and individual floral whorls show changes in appearance and function. Over a season, changes in mating often appear as alteration in seed production vs. pollen donation. In several species, older, unpollinated flowers are more likely to self. If flowers are receiving pollen, staying open longer may increase the number of mates. In wild radish, for which there is considerable information on seed paternity, older flowers produce fewer seeds and appear to discriminate less among pollen donors. Pollen donor performance can also be linked to maternal plant age. Different pollinators and mates are available across the season. Also in wild radish, maternal plants appear to exert the most control over paternity when they are of intermediate age.

CONCLUSIONS

Although much is known about the characters of plants and flowers that can change over a season, there is less information on the effects of age on mating. Several studies document changes in self-pollination over time, but very few, other than those on wild radish, consider more subtle aspects of differential success of pollen donors over time.

Pollen carbohydrates and water content during development, presentation, and dispersal: a short review

Pollen accumulates starch reserves during development and the final stage of ripening. Before the anther opens, starch is totally or partially converted to pectins, glucose, fructose, sucrose, and to some unknown polysaccharides. Pollen is exposed to dispersing agents in an arrested developmental state which differs according to pollen water content. Pollen is classified as partially dehydrated or partially hydrated. The final water content may be reached before or after anther opening. Especially during exposure and dispersal, partially dehydrated pollen may interconvert soluble and insoluble reserves, modifying internal turgor pressure and hindering water loss or gain. Partially hydrated pollen is commonly devoid of mechanisms to conserve viability in time but has the advantage of quickly emitting pollen tubes on reaching the stigma.