Bee pollen, from the flower to the harvest, and its potential therapeutic properties

Pollen is contained in flowers, and it is the strategic element that the gymnosperms and angiosperms have implemented to carry out sexual reproduction. The pollen grain can have different shapes, from round to triangular, up to multilobed shapes typical of each species. Each pollen grain is a single cell containing two male gametes. Inside we find the cytoplasm, with the nucleus and the organelles, and externally, a coating layer that determines its resistance. Both male gametes are involved in fertilization, resulting in the formation of a zygote and an endosperm. Pollen in angiosperms is contained in the apical part of the stamens. In gymnosperms, pollen is produced in microcones. The stamens are filaments with buttons in the upper part, called anthers. The anther usually contains four paired pollen sacs responsible for producing the pollen grains. Once mature, the anther opens, and the pollen is released. The pollen, on the surface of the anthers, appears as a powder with colors ranging from white and yellow, to the different varieties of red, brown, black, or green, based on the botanical species, whose dimensions vary from 250 μm up to 5 μm. The female organ of the flower is the Pistil. This organ in the larger basal part contains the ovary, where the ovules are stored. In the apical part, we find the stigma, which, thanks to an adhesive substance, will hold the pollen, which, by opening, will allow the pollen tube to descend into the ovary and fertilize the ovule, which will become a seed. This phenomenon is called pollination. Self-pollination occurs in monecious plants when pollen grains are transferred from the anther to the stigma on the same flower or an adjacent flower on the same plant. Crosspollination occurs in diecious plants when pollen grains are carried on the stigmas of different plants. Pollination can occur thanks to the wind as for conifers or by other vectors and is defined as anemogamous, hydrogamous, or zoogamous. The first depends on the wind, the second on the water, and the third on animals; particularly, the one that occurs thanks to insects is said to be entomogamous. Evolution has ensured that this union between the vegetable and animal worlds was created, and to make it even more effective, the plants have dressed their flowers in colors, scents, and sweet nectar to attract animals and use them as vectors for the pollination. Even the choice to place the pollen on the anthers was successful as the insect to get to the nectar must obligatorily get dirty with pollen. The passage from flower to flower will carry out the pollination service. Bees play a role of primary importance. Bees retain blooms of the same type to best perform their task before moving on to another. In this way, the plants ensure the species’ survival and the bees’ nectar and pollen to be used as food for the hive. Some trees have specialized in producing flowers, fruits, and male and female genital organs so that a particular insect can only reach them. This mutualistic relationship has allowed the creation of botanical biodiversity over time. Even the morphology of the pollen changes according to the species it belongs to. Pollen transported by the wind is usually small and with smooth shapes to better allow their transport. Typically, these pollens determine allergic phenomena in humans. The pollen grains, which require entomophilous pollination, have different shapes and sizes; externally, they are covered by a layer composed of lipids and carotenoids called Pollenkit, which makes the grains sticky, whose purpose is to be recognized by the female part of the flower. They can also present hooks or protrusions to better attach to pollinators. In the outer part, the pollen grain has a layer called Sporoderma. The Sporoderma is divided into two structures, the intina in the innermost part, which surrounds the plasmalemma, the cell with its internal organs and has a structure made up of cellulose fibers, which offers mechanical protection against crushing. The outermost layer is called Esina; its function is support and resistance thanks to a conformation rich in Sporopolleine, which is highly structured and cross-linked polymer. It is divided into nexin more internally and sexin more externally. Its external morphology is typical for each species and variety. This characteristic is exploited in palynology for the identification of the botanical origin of the pollen, which also allows the distinction of the various kinds of honey, which, thanks to the pollen of origin, acquire typical flavors and aromas. Other substances are present in the granule, which makes it a perfect system to survive for a long time, maintaining its peculiarities. There may be openings on the surface, which, if circular in shape, are defined as Pores or Shots if they have an elongated shape; their task is to let the pollen tube out. They can occur on the entire surface or only in the equatorial zone. Internally there are two nuclei whose function is to develop the seed and the fruit simultaneously. As far as Propolis is concerned, it is not naturally present in the hive; rather, bees produce it after collecting resinous substances from arboreal essences and are mixed with bee enzymes, pollen, and wax. The resin plays a protective role for both floral and vegetative buds against external agents such as bacteria and fungi, as well as an attractive purpose for the bees and all pollinating insects. Resin can be found at the bark level, and it is produced mainly to protect the plants from infections and pathogens entry.