5
B
Boron
10.811
Essential: plants
Beneficial:
some marine organisms
Boron
Major functions in cells: (1)
- Required in plant cell walls
- Bacterial quorum sensing
- Boron-containing siderophore
- Required for nitrogen fixation in some microbes
- Borolithochromes
Environmental and health impacts:
- Several antibiotics, like boromycin, contain boron
- B availability impacts nitrogen fixation
Learn More!
(1) Boron: Required for Plants and Some Microbes
The biological role of boron is versatile and varies greatly amongst organisms. While it is required in plants and some microorganisms, it currently has no known role in animals or fungi.
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Boron is generally considered an essential element for plants, where it is a critical constituent of cell walls (Gonzalez-Fontes, 2020; Wimmer et al., 2020). Boron is particularly adept at coordination with compounds containing vicinal hydroxyl groups (Bolaños et al., 2004), and this allows the formation of diester complexes between B and rhamnogalacturonan units in cell wall synthesis. (O'Neill et al., 2001).
Boron has several roles in microbes. B is found in a bacterial autoinducer AI-2, which allows communication between bacterial cells in a process called quorum sensing (Chen, et al., 2002). It has also been found that a siderophore in Marinobacter called vibrioferrin is capable of binding boron, although the role of boron binding by this molecule is not yet known (Amin et al., 2007). Boron is a required element for nitrogen fixation in Azotobacter, as well as heterocystous cyanobacteria and Actinomycetes (Bonilla et al., 1990). In these organisms, boron deficiency caused a decrease in growth rate. It has been suggested that a possible role for B in these cells is as a stabilizing mechanism for the glycolipid inner layer of heterocysts.
Another biological function for boron is its role in borolithochromes, which cause the pink coloring of certain red algae (Wolkenstein et al., 2010).
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(2) Germanium Substitutes for Boron
Boron is an essential element for many plant functions. In some plants, it has been found that germanium can partially substitute for the cellular functions of boron. In carrot cell cultures, germanium can substitute for boron in the cell wall (Loomis and Durst, 1992). In sunflower plants, the addition of germanium dioxide can delay the damaging effects of boron deficiency for a short time (McIlrath and Skok, 1996).
(3) Enhancing B Uptake in Plants
In many regions of the world, especially under drought conditions, B is the soil is limited, so several techniques have been developed in the agriculture industry to enhance B uptake and transport to achieve maximum production (Shireen et al., 2018). Though these techniques are man-made, unlike many of the cellular mechanisms that cells use to spare other elements, these techniques take advantage of the plants' own structure and adaptive mechanisms.
1. Modify roots so they have increased root length and hair density, which allows increased uptake of nutrients, like B. Under conditions of B limitation in the soil, the structure of the roots is significantly altered, with a larger number of lateral roots compared to primary roots, which increases B uptake.
2. Grafting is another technique to increase B uptake. This process involves connecting the scion and the rootstock, which absorbs B from the soil and transports it to upper parts of the plant.
3. Biostimulators interfere with the signaling cascade of stressed plants, reducing negative reactions so that growth is optimal. Since these plants are less stressed, they will more effectively uptake ions, like B.