UV and plants

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Ultraviolet radiation (UV) is arbitrarily divided into three regions A (315 nm to 400 nm), B (280 nm to 315 nm), C (280 nm to 200 nm). UV-C radiation is not present in sunlight at ground level, while UV-B and UV-A are. The energy fraction of global solar radiation in the UV-B region is very small (< 1%) but the energy per photon is large, making UV-B photons capable of disrupting bonds between atoms. Plant responses to UV-C radiation are of interest only in especial cases when certain artificial light sources are used.

Responses to UV-C radiation are most frequently the result of direct or indirect damage to plant cells and their components, UV-C radiation is not considered to have a regulatory function. In contrast, UV-A radiation has most frequently been considered to have a regulatory role via its perception by photoreceptors such as cryptochromes and phototropins. Occasionally, strong and sudden exposures to UV-A radiation have been described as causing damage to plant cell components. The case with UV-B radiation is mid way, as could be expected from the intermediate energy content of its photons. Large and/or sudden exposure of plants to UV-B radiation can cause damage, while smaller and gradual exposure normally results in regulatory processes. Both types of responses can be easily demonstrated, however, the question is, which ones predominate in plants growing in sunlight under natural conditions. While damage can be expected to always be detrimental to plant growth and crop yield, regulatory responses can result in a wide array of different effects, both positive and negative, on growth, yield and nutritional quality of plants.

Significant new understanding of UV-B mediated processes in plants has been gained during the last decade. As a result of improved experimental design and methods the view of UV-B radiation as a damaging agent, has given way to a view where UV-B radiation is considered as a specific regulator of gene expression, metabolite profiles, and responses to climate change for plants growing in sunlight. In the last few years substantial progress has been made in identifying specific, regulatory UV-B-mediated processes in plants. Recent genetic studies have revealed the existence of UV-B specific signalling pathways in plants, and have identified several components including a photoreceptor. The discovery of these UV-B specific signalling pathways has confirmed the contention that UV-B irradiance is a specific regulatory factor in plant-environment relationships. Research on the molecular basis of UV-B mediated regulatory process in plants is now yielding novel understanding of the mechanisms underlying growth and phenotypic plasticity, and consequences thereof for plant performance in crop and natural ecosystems.

If we accept, based on the overwhelming evidence, that UV-B perception is used by plants as a sensory mechanism, we still need to discover what information plants are acquiring from their environment through the UV-B perception systems. This is the next big challenge for UV photobiology research on plants: understanding the ecological role of these responses, and learning to use these knowledge in practical plant production settings through management and breeding.

A brochure titled “All you wanted to know about UV radiation and plants” is available in PDF format at the publications page.

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