Pollen grain: definition and meaning

Pollen grain: definition and meaning

POLLIN GRAIN

The pollen grain (which together forms the pollen) is a tiny grain, invisible to the naked eye, formed by several cells and is produced by the anthers of the flowers. a flower.
Pollen grains have specific shapes for each flower and can be considered their "fingerprints". It is thanks to them, for example, that fraud in honey is discovered: if it is declared that a certain honey is, for example, only from lavender flowers (monofloral honey), then it must contain only the pollen grains of lavender.
The science that studies pollen is called Palynology.

Botanical dictionary from A to Z.


Italian dictionary

Online dictionary taken from:

Great Italian Dictionary
of GABRIELLI ALDO
Dictionary of the Italian Language

  • grainy 1
  • grainy 2
  • maize
  • Gran Turismo
  • granular 1
  • granular 2
  • granularity
  • granulated
  • granulator
  • granulation
  • granule
  • granulocyte
  • granuloma
  • granulomatous
  • granulometry
  • graininess
  • grainy
  • graphic computer
  • graphic design
  • graphic novel
  • grappa 1

From A to Z

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Attention to the environment and its interrelations with the health of patients has always been a priority interest of allergists. Therefore, the use of study tools such as Aerobiology became physiological. This fairly recent discipline studies the production and dissemination of biological material that can damage human health and, in the last twenty years, in Italy, it has also been introduced in Clinical Allergology, in order to better evaluate and control respiratory allergies induced by pollen, fungal spores and other allergenic entities, such as algae, Arthropods and their emanations, protozoa.

However, in more recent years it has been realized that it was necessary to broaden the overview of aerobiological studies, including assessments related to atmospheric pollution and in particular of particulate matter of anthropogenic origin. Indeed, some studies show an interaction between atmospheric pollutants and airborne pollen. The relevance and importance of this topic is underlined by the fact that the nascent association A.A.I.T.O. (Association of Territorial and Hospital Allergologists Immunologists) has included in its Statute the establishment of a Section of Aerobiology, Ecology and Environmental Prevention which is planning the activation of study groups and has already put into operation a Pollen and Sporological Monitoring Network. The network has been in operation since January 2002, with the participation of approx 25 Centers distributed throughout the territory and the diffusion of a Weekly bulletin which not only spreads the situation of the previous week but also the pollen forecast for the following week.

The data is available directly on this site (www.pollinieallergia.net) or on the link inserted on the AAITO website www.aaito.it.


The natural history of the pollinated patient is part of a broader and more complex story linked to the reproduction of plant species (Solomon 2002).
Pollen grains, together with fungal spores, microbes and viruses, become part of the biological aerosols that we inhale daily. The pollen grain is a complex structure whose purpose is to transmit the male gametes of seed plants, Angiosperms and Gymnosperms. Pollination is the process of transferring pollen grains from male to female reproductive structures, it can be performed by three vectors: wind, water or animals. Since this is a less efficient means of transport than in entomophilic pollination, anemophilic plants produce a copious amount of pollen to ensure effective fertilization.
Pollen, unlike all plant cells, has two walls: the external one: hexine, formed by sporopollenin, formed by polyterpenes, and the internal one, formed by polysaccharides.
Among the sculptures of the exine, on the pores and in the intestine there are, in addition to enzymes, proteins and glycoproteins that have the original function of cell recognition factors, enzymes facilitating the germination of pollen, or nutritional proteins. allergenic properties.

The presence of pollen in the air depends on the abundance of the corresponding producing plants and on release and dispersion factors.
To be able to cause allergic symptoms, a pollen grain must respond to Thommen's 5 postulates:

1 - must contain sensitizing allergens
2 - must use anemophilic pollination
3 - it must be produced in sufficiently abundant quantities
4 - it must be sufficiently aerodynamic to be able to be conveyed over considerable distances
5 - the plants that produce pollen must be distributed over the territory widely and in great abundance.

The amount of pollen produced is generally a function of the temperature absorbed by the soil in the previous year, so that it is possible, for some species, such as Cypress, to define forecast parameters (Ariano, 1994).
Humidity has the property of closing the anthers, so the pollen is retained in the plant. The pollen emission limit is located around 65% relative humidity. With humidity, pollen is heavier and flies less. Rainy days and days with high relative humidity cause pollen to fall to the ground. Pollen glides better when dehydrated, as they are more aerodynamic. A short but intense rain is more efficient in breaking down the pollen particles than a prolonged drizzle. The raising of the temperature facilitates the release of pollen from the anthers making the pollens less rich in water, with a lower specific weight and therefore lighter and more volatile. Wind increases the spread of pollen. Pollen begins to rise from wind speeds above 3 meters per second. When the wind speed exceeds 12-15 km per hour, the granules tend to fall.

Airborne allergen-carrying particles follow the same physical rules as any particle of the same aerodynamic diameter. The pollen grain will undergo the laws that regulate the movements of the air masses and transport phenomena at the microscale, mesoscale and macroscale.
Microscale transport is limited in time and space, in hours and hundreds of meters. It is believed that 80% of the pollen produced by plants follows this type of transport.
The mesoscale transport, which is linked to conditions of nocturnal and diurnal temperature excursion, concerns a period of time of a few days and a distance of a few hundred km. It affects pollen released by grasses or plants placed in elevated positions.
Long-distance transport, which occurs in particular conditions of atmospheric turbulence, can transport pollen even thousands of km.

The usefulness of a precise and timely forecast of the short-term atmospheric presences of pollen and spores is intuitive. Numerous investigators have published models designed to predict concentrations of specific allergen-carrying particles. Forecasting models are numerous and increasingly complex. They are based on historical data, on correlations with meteorological data and use statistical methodologies. In recent times, neural networks on historical total pollen concentrations have also been used. There are different types of short, medium and long term forecasts. Although predictive models continue to improve, published models fail at least 25% of the time and are available for not all pollen species. Unfortunately, the systems are still unsatisfactory and this constitutes a further field of research for the future.

Sub micronic particles

Pollen regains its full activity when it hydrates again and this happens when
meets the stigma of a flower or comes into contact with water, both in the atmosphere and on the ground and, finally, when it comes into contact with the mucous membranes of the airways.
In fact, in contact with water the pollen hydrates and releases its own proteins. Within 2-30 seconds those of the exine, after 30 seconds those of the intestine it is possible, at least for some species, the release of proteins from the cytoplasm.
By now there are numerous evidences that testify that pollen allergens can be carried not only by pollen grains but also by smaller particles measuring a few microns and which have been called paucimicronic particles. (Takahashi, 1995).
Allergens of Graminaceae (Lol p 5) have been found on particles


Medicine

Fertilization in humans can be hindered by diseases affecting the female or male genital system or by hormonal alterations that prevent the embryo from nesting and the continuation of gestation. For this reason the so-called artificial fertilization techniques have been developed, which allow to induce the meeting of male and female gametes in the laboratory and then implant the obtained embryo in the womb of the aspiring mother. The gametes are obtained from the couple themselves affected by sterility or from donors (heterologous fertilization).


Basic mechanism of the allergic reaction

Pollen contains particular substances, called antigens, capable of "sensitizing" genetically predisposed subjects. In the allergic patient, these substances are released in the respiratory mucous membranes and are able to cause an excessive reaction of the immune system, stimulated to produce particular antibodies, class E immunoglobulins (IgE).

As a consequence of the intervention of IgE, chemical mediators of inflammation are released: histamine, prostaglandins, leukotrienes, bradykinin and others. These substances act by causing an inflammatory process: they dilate the capillaries and attract particular defense cells from the blood and tissues, which participate in the reaction. The end result is the induction of the typical symptoms of pollen allergy.

Note. Not all plants release pollen capable of inducing an allergic reaction and, generally, a person is allergic to only some allergens. Furthermore, pollen allergy occurs when the concentration of pollen in the atmosphere reaches a certain threshold.


Italian dictionary

Online dictionary taken from:

Great Italian Dictionary
of GABRIELLI ALDO
Dictionary of the Italian Language

  • chicken
  • foal
  • poultry
  • inch
  • chicken farmer
  • chicken farming
  • pollicultura
  • droppings
  • pollinaro
  • pollination
  • pollen
  • pollen
  • pollinifago
  • polliniferous
  • pollinium
  • pollen 1
  • pollen 2
  • pollen 3
  • pollinosis
  • poultry seller
  • chicken

From A to Z

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