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Natural Plant Compounds Provide UV Protection

Plant UV Protection

Scientists at the University of Malaga have identified a group of natural molecules in plants that act as natural sunscreens to protect against UV-B radiation, which can damage DNA and hamper growth. This protection is provided by the plant cuticle and comes from a suite of natural plant chemicals called phenolics.

UVB

UVB is the medium-wavelength radiation from sunlight, with wavelengths between 280-315 nm. This type of radiation accounts for about 10% of the total solar UV radiation that reaches Earth’s surface. It is the most common form of UV radiation that affects plants.

Depending on the species and experimental set-up, UVB exposure can have different effects on plant physiology. For example, it can increase the accumulation of secondary phenolic compounds such as quercetin and cyanidin in guar beans (Cyamopsis tetragonoloba) and urad beans (Vigna mungo L). However, the use of UV blocking covering materials can reduce the accumulation of these compounds.

Exposure to UVB can also have positive effects on the plant’s defense against biotic agents. The interaction between ambient UVB and abiotic stress factors can trigger the formation of soluble proteins in the leaves that can protect the plant against pests and viral diseases. In particular, a recent study showed that high levels of ambient UVB can induce resistance to rice blast disease caused by the fungus Magnaporthe oryzae by stimulating the expression of the HY5 gene.

UVC

The shortest UVC wavelengths are also the most dangerous. They penetrate the skin and cause damage to chromosomes. Fortunately, most of the UVC that reaches Earth is absorbed by the ozone layer. However, artificial UVC can still be used to kill bacteria and viruses. This type of UV is also known as germicidal UV.

The most effective UV treatments include those that increase stomatal opening and photosynthesis. They can also stimulate the production of secondary plant compounds, such as anthocyanins and total phenolics. However, they must be delivered in a controlled manner to prevent burning of leaves and to avoid affecting the plant’s physiology.

Studies of the effects of greenhouse covering materials on the agronomic performance of crops usually have pests and viral diseases as their primary objectives, but these materials have a range of other benefits, too. For example, they can increase crop yields and improve the quality of harvested produce. One study found that strawberries had a higher color, size, and weight when exposed to UVB. Another study found that lettuce plants had better shape and biomass production when exposed to UVB.

UVA

UVA is a type of electromagnetic radiation that has a wavelength between 10-400 nanometers and is also known as UV light. It is one of the most common types of radiation that reach the Earth and can be found in sunlight, but it is less harmful than UVB and UVC.

In contrast to the detrimental effects of UV-B and UV-C on microorganisms, UVA has a positive impact on them by upregulating certain specialized metabolites. These metabolites can help plants fight off pathogens and herbivores.

Many studies have shown that UVA increases the production of plant hormones such as salicylic acid (SA) and jasmonic acid (JA). These hormones are involved in defense responses against biotrophic pathogens and herbivory. They also improve the vigor of the plant and increase its growth rate. In addition, UVA can also stimulate the production of resin in a plant, which is essential for its quality and potency. This can have a huge impact on the final product.

UVD

Plants sense UVB and respond to it by deploying antioxidant defenses, increasing photosynthesis rates, and accumulating “sunscreen” flavonoids. Mutant screens have identified several factors that participate in the UV-B response, including the HY5 gene and the UVR8 monomer. UVR8 binds to COP1 and RUP2 in plants that are acclimated to high UV-B. This binding reduces the permeability of the photosynthetic membrane and prevents oxidative stress in plant cells.

Phenylpropanoids, such as kaempferol-3,7-dirhamnoside from Achillea biebersteinii15 and Achillea millefolium16 and caffeic acid, epigallocatechin, epicatechin, and rosmarinic acid from Dalloa hebecarpa17 and Plectranthus ecklonii Benth18, also have anti-UV properties. These compounds can reduce oxidative damage and decrease penetration of UV radiation into the palisade and spongy mesophyll tissues.

Many studies have found that the use of UV blocking materials has a positive effect on crop physiology and productivity, but other factors need to be taken into account as well. For example, a study conducted in the UK showed that the use of UV-blocking films reduced the amount of phenolics and anthocyanins in red lettuce crops.

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