Pollen's Air Pollution: Understanding The Impact Of Pollen Grains

Pollen grains are minute bodies in the form of fine to coarse dust from the catkins of certain plant species. They contain pores through which their proteins can be distributed to human upper airways, which means humans are inhaling pollen grains almost everywhere. Pollen from birch trees and ragweed are responsible for hay fever, also known as allergic rhinitis. Air pollution can impact pollen morphology, the pollen cell wall, the pollen protein content or protein release from the pollen, as well as the pollen protein itself. Laboratory research has shown several noxious effects on pollen grains. For a large number of plant species, the viability and germination of pollen grains are modified by air pollutants, even at very low doses of exposure. The chemical composition of pollen is also modified by air pollution.

Pollen grains can cause air pollution when released from plants grown in polluted soil

Pollen grains are minute bodies in the form of fine to coarse dust from the catkins of certain plant species. They contain pores through which their proteins can be distributed to human upper airways. When inhaled, pollen grains can cause severe allergic reactions and several medical conditions.

The impact of air pollution on pollen includes changes in pollen morphology, the pollen cell wall, the pollen protein content or protein release from the pollen, and the pollen protein itself. The pollen coat, a complex mixture of pigments, waxes, lipids, aromatics, and proteins, might be impaired due to air pollution. Pollen-derived lipids, also called pollen-derived lipid mediators (PALMs), interact with the human immune system and can modify the allergenic reaction.

Air pollution can also cause pollen grains to shrink, thin, and become fragile. The adverse effects of some MTE (e.g., Pb, Zn, Ca, and Cu) on the plants and then on the airborne pollen grains may be delayed by several days, months, or years. In addition, injury to floral organs, especially anthers, can cause pollen abnormality and sterility, consequently resulting in the malfunction of fertilization.

Air pollution can cause pollen grains to release proteins that trigger allergies

Air pollution can have a significant impact on pollen grains, altering their structure, chemical composition, and allergenicity. This, in turn, can lead to the release of proteins that trigger allergies in susceptible individuals.

Several studies have shown that air pollutants can interact with pollen grains, causing changes in their physiology, ontogeny, and morphology. For example, research on the pollen grains of Thuja orientalis L. (Cupressaceae) revealed that air pollution caused shrinkage, thinning, and fragility of the pollen grains. Similarly, studies on Lagerestroemia indica showed a decrease in total protein content and staining intensity of protein bands under air pollution.

The chemical composition of pollen grains is also affected by air pollution. Pollen proteins can undergo nitration due to high NO2 content in polluted areas, and the interaction between pollen and air pollutants can result in the formation of degraded components. These changes in the chemical composition of pollen grains can lead to the release of pollen proteins that act as allergens.

In addition, air pollution can influence the production of pollen and its allergenicity. For example, elevated ozone concentrations can significantly increase the symptoms of allergic rhinitis during the pollen flight seasons of birch, grass, and ragweed. The continuous burning of fossil fuels and the resulting increase in temperature can also lead to longer pollen seasons, exposing allergy sufferers to relevant amounts of pollen allergens for up to 10 months a year.

Furthermore, certain air pollutants can act as adjuvants by binding to allergens and stimulating IgE synthesis, exacerbating asthma symptoms. Diesel exhaust particles (DEPs) are considered one of the most important adjuvants in the environment, aggravating allergic reactions and even causing sensitization to new allergens.

While the exact mechanisms are still being studied, it is clear that air pollution can cause pollen grains to release proteins that trigger allergies, impacting the health of individuals with pollen allergies.

Pollen grains can be damaged by air pollutants, causing them to spontaneously release subparticles

One of the key findings from these studies is that air pollutants can modify the viability and germination of pollen grains, even at very low doses of exposure. For example, high levels of nitrogen dioxide (NO2) in polluted areas can lead to the nitration of pollen proteins, causing pollen grains to release inner subparticles spontaneously. This process can be visualized using immunogold labeling techniques, as demonstrated by Knox et al. in their research on grass pollen allergens.

In addition to NO2, other traffic-related air pollutants such as ozone (O3) can also damage pollen grains and increase the release of inner subparticles. The interaction between air pollutants and pollen grains can have significant implications for human health, particularly for individuals with respiratory allergies. Plant pollen is recognized as the primary aeroallergen responsible for allergic reactions, and urban residents experience more respiratory allergies than rural residents due to the interplay between chemical air pollutants and pollen grains.

The effects of air pollution on pollen grains can be direct or indirect. Direct effects include morphological changes in the pollen grains, such as shrinkage, thinning, and fragility. Indirect effects can occur when plants grow in polluted soil, altering their physiologic functions and affecting the developing pollen grains. For example, injury to floral organs, especially anthers, can lead to pollen abnormality and sterility, impacting fertilization.

Furthermore, air pollutants can bind to pollen-derived particles, exacerbating allergic disorders. Pollen grains release biologically active lipids that activate immune cells, and the presence of air pollutants can enhance the allergenic potential of these particles. While the impact of air pollution on pollen grains is well-studied, there are still knowledge gaps and areas that require further investigation, such as the potential effects of herbicides, pesticides, and weed-killers on pollen and allergic individuals.

Air pollution can alter the chemical composition of pollen grains, including their protein content

Laboratory research on artificial pollution of pollen and studies on pollen sampled in polluted zones have shown several adverse effects on pollen grains. The viability and germination of pollen grains are modified by air pollutants, even at very low doses of exposure.

Air pollution can also alter the chemical composition of pollen grains, including their protein content. Changes in inorganic ions composition are the most abundantly studied and documented chemical effect. Because of the high NO2 content in polluted areas, results have shown that pollen proteins can be nitrated by urban or industrial pollution. However, the ratio of nitrated pollen proteins in atmospheric conditions, whether polluted or unpolluted, remains unknown.

In addition, the presence of elevated CO2 levels affects the chemical composition of pollen and seed development. Studies have shown that CO2 increases the carbohydrate, lipids, and proteins content in seeds, which may enhance pollen germination. On the other hand, high O3 levels reduce the stored carbohydrates, lipids, and proteins in seeds, which are fundamental for pollen germination, elongation of the pollen tube, and growth rate.

Pollutants can also play a role in the variation of protein amounts in pollen. For example, studies have found a decrease in total protein amounts in polluted sites' pollen, as well as a net decrease in Cup a 1. In a study on rural versus urban pollen, researchers observed differences in protein profiles, with certain protein bands disappearing in the pollen collected from more polluted areas.

Furthermore, air pollution can cause pollen grains to release allergens or sub-pollen particles containing allergens into the environment. The oxidative properties of air pollutants may modify the composition and chemical properties of proteins, affecting the germination and elongation of the pollen tube.

Air pollution can cause pollen grains to shrink, thin, and become more fragile

Pollen grains are affected by air pollution in several ways. Firstly, the viability and germination of pollen grains are modified by air pollutants, even at very low doses of exposure. The chemical composition of pollen is altered, with changes in inorganic ions composition being the most abundantly studied and documented chemical effect. For instance, due to high NO2 content in polluted areas, nitration occurs, and results have shown that pollen proteins can be nitrated by urban or industrial pollution.

Secondly, air pollution affects the structure, proteins, and flavonoids in pollen grains. Studies have shown that air pollutants interact with pollen, causing alterations in the physiology, ontogeny, and morphology of pollen grains, both at the surface and within the pollen protoplasm. This can lead to changes in the cell wall structure, such as shrinkage, thinning, rupture of exine, and dilatation of the intine wall. Pollen grains with thinner exine may be more susceptible to deformation, fragility, or rupture.

Thirdly, air pollution can have indirect effects on pollen grains via the soil. If a plant grows in polluted soil, its physiologic functions may change, which can, in turn, affect the properties of the developing pollen grains. Additionally, injury to floral organs, especially anthers, can cause pollen abnormality and sterility, impacting the fertilization process.

Lastly, air pollution can affect the allergenicity of pollen grains, exacerbating symptoms in vulnerable individuals. The presence of elevated CO2 levels, for example, can enhance the germination rate, favoring pollen production. This increased pollen production, combined with changes in pollen structure and composition due to air pollution, can have significant impacts on allergic individuals.

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