A SMALL SCIENCE POPULARIZATION ON UV-B

Ultraviolet-B radiation (UV-B; 280-320 nm) is a basic component of sunlight. Most of the UV-B that reaching the earth is absorbed by the stratospheric ozone layer, therefore, the UV-B wavelength only accounts for a small part of the sunlight that reaches the earth's surface. However, UV-B has a significant impact on the biosphere because it is the most energic component in the sunlight spectrum. UV-B can damage large molecules such as DNA and proteins, and produce reactive oxygen species (ROS) and damage cellular. It is well known that the UV-B content in sunlight is sufficient to cause damage to sensitive tissues of humans and other animals, and promote certain forms of skin cancer. However, it is increasingly clear that ultraviolet B is not only the cause of damage, but also plays an important role as an information signal. In particular, the plant's perception of low levels of UV-B will actively promote survival because it stimulates responses that help protect and repair damage. In addition, the response to UV-B will change the biochemical composition of plant tissues, affect plant morphology, and help prevent pests and pathogens.

In nature, plants are inevitably exposed to UV-B because they need to capture sunlight to perform photosynthesis. The fact that plants rarely show signs of UV damage in the natural environment indicates that they have evolved very effective UV-protection and repair mechanisms. The protective mechanism includes depositing ultraviolet-absorbing phenolic compounds in the outer layer of the epidermis and producing antioxidant system. Repair involves enzymes such as DNA photolyase. UV-B exposure stimulates the expression of genes involved in UV protection and repair. Therefore, it is important to understand the cellular and molecular mechanisms of UV-B sensing and signal transduction, and determine the contribution of UV-B response to normal plant growth and development. In fact, it is impossible to fully understand the role of light in controlling plant development without understanding the regulation of UV-B.

There are many studies on the effects of UV-B on plants. This research involves various species, different developmental stages, different growth conditions and various spectral qualities, the number and duration of UV-B treatment. These studies are inevitably difficult to compare, but some general conclusions can be drawn.

It is obvious that UV-B has a wider range of effects on plants, from the effects on gene expression, cell physiology and biosynthesis to the effects on growth, morphology and development. These effects depend on the environment of UV-B treatment, that is, the interaction with other environmental variables (such as other light quality, temperature, water and nutritional status). Generally, the UV-B effect observed under field conditions is less than that of a controlled environment.

Some key points should be emphasized on the various effects of UV-B on plants. The high flux rate of UV-B can damage plant tissues and eventually lead to necrosis. In addition, high-throughput UV-B can generate ROS and trigger cellular stress response. However, the UV-B content used in some studies is much higher than the level in nature, so some observations have limited relevance to normal plant growth. The extent of damage in plants grown under high environmental levels of UV-B is unclear, because if the plants are adapted to a specific light environment, the repair mechanism is usually sufficient to prevent damage from occurring. The damage is most likely to become apparent when plants are exposed to high UV-B levels and do not adapt to the environment.

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