Abstract
Plants are photosynthetic organisms that depend on sunlight for energy. Plants respond to light through different photoreceptors and show photomorphogenic development. Apart from Photosynthetically Active Radiation (PAR; 400–700 nm), plants are exposed to UV light, which is comprised of UV-C (below 280 nm), UV-B (280–320 nm) and UV-A (320–390 nm). The atmospheric ozone layer protects UV-C radiation from reaching earth while the UVR8 protein acts as a receptor for UV-B radiation. Low levels of UV-B exposure initiate signaling through UVR8 and induce secondary metabolite genes involved in protection against UV while higher dosages are very detrimental to plants. It has also been reported that genes involved in MAPK cascade help the plant in providing tolerance against UV radiation. The important targets of UV radiation in plant cells are DNA, lipids and proteins and also vital processes such as photosynthesis. Recent studies showed that, in response to UV radiation, mitochondria and chloroplasts produce a reactive oxygen species (ROS). Arabidopsis metacaspase-8 (AtMC8) is induced in response to oxidative stress caused by ROS, which acts downstream of the radical induced cell death (AtRCD1) gene making plants vulnerable to cell death. The studies on salicylic and jasmonic acid signaling mutants revealed that SA and JA regulate the ROS level and antagonize ROS mediated cell death. Recently, molecular studies have revealed genes involved in response to UV exposure, with respect to programmed cell death (PCD).
Highlights
Light energy from the sun and the ability of photoautotrophs to fix that energy in the presence of chlorophyll has promoted life on earth
UV radiation is broadly classified based on wavelength as UV-C radiation (200–280 nm), which is the most hazardous range of UV light but physiologically insignificant since these wavelengths are completely absorbed by the atmosphere; UV-B radiation (280–320 nm), which is filtered through the stratospheric ozone layer and, only a small proportion reaches the earth surface; and UV-A radiation (320–400 nm), which cannot be absorbed by the ozone layer and is fully transmitted to the earth’s surface
Dependant manner to activate expression of a set of genes that protects against potential damage by UV-B exposure, including genes encoding flavonoid biosynthesis enzymes, DNA repair enzymes, and proteins involved in mitigating oxidative stress as shown in Figure 1 [34]
Summary
Light energy from the sun and the ability of photoautotrophs to fix that energy in the presence of chlorophyll has promoted life on earth. UV radiation is broadly classified based on wavelength as UV-C radiation (200–280 nm), which is the most hazardous range of UV light but physiologically insignificant since these wavelengths are completely absorbed by the atmosphere; UV-B radiation (280–320 nm), which is filtered through the stratospheric ozone layer and, only a small proportion reaches the earth surface; and UV-A radiation (320–400 nm), which cannot be absorbed by the ozone layer and is fully transmitted to the earth’s surface Among these three types of UV radiation, UV-B is of prime importance despite its small proportion i.e., 1.5% of total radiation, because of its severe damaging effects on plant growth and development. The current review focuses on the detailed mechanism of PCD in response to higher UV radiation and its physiological significance
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